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ver its importance in mineral exploration is becoming more relevant as more experimental data and its interpretation are published geometallurgy geometallurgy is a relatively recent technique in mineral exploration it is based on precise quantitative mineralogical and chemical measurements using electron microprobes or similar instruments followed by statistical analyses to determine variabilities in physical mineralogical and geochemical characteristics of a mineral prospect the information obtained is used in all stages of exploration as well as in the development of an ore deposit reserve and resource evaluation and metallurgical processing geometallurgy may be applied to stream sediment samples mineralized outcrops drill cores or even in productive mine stopes ore deposit models can be proposed and strategies for further exploration may then be designed it is also very useful in ore body modeling predicting possible extensions and determining the quality of mineral accumulations geophysics prospecting is defined as making and interpreting measurements of physical properties to determine subsurface conditions usually with an economic objective for example discovery of fuel or mineral deposits measurements include seismic travel times and wave shape changes electrical potential differences magnetic and gravitational field strengths and radiometrics sheriff 2002 geophysicists have developed methods for estimating physical properties from surface measurements it is a difficult problem to solve because there is often much ambiguity in the solution this problem is overcome to some extent by constraining the problem with factual information from surface geological mapping measured physical properties or drill hole information therefore it is critical to understand the ranges or errors in data acquisition those introduced through processing and those introduced through the assumptions made while interpreting the data the answer is never exact nevertheless some geophysical tools have major technical and financial impacts on mine planning often with significant influence on the costs of development outline of methods and techniques applied geophysical methods are classified according to the transmitting energy source table 3 3 1 detection of the resulting signals is achieved by contact with the ground or remote sensing platforms in near mine or on mine exploration this is usually done through physical contact with the ground greenfield exploration projects mostly tend to use airborne methods natural sources include the following potential fields such as magnetic and gravity fields electromagnetic energy due to sun flares and sunspots radiometric methods based on the radioactive emissions from thorium potassium and uranium seismic energy from earthquakes and tremors as well as rockfalls passive seismic active human made sources include the following grounded current electrodes and

inductive loops powered by batteries and or generators seismic energy from surface excitation hammers vehicles dynamite vibrators core drilling etc the application of a geophysical technique in the mining environment is usually constrained by the mining infrastructure geophysics is usually most effective in mining at the prefeasibility stage for instance conducting a three dimensional 3 d seismic survey at the prefeasibility stage establishes a base case for future mine planning to undertake such a survey after the mine has been developed is disruptive to mining and production schedules and it increases the cost while producing inferior signal quality due to infrastructure noise natural sources the earth s magnetic gravitational and natural electromagnetic fields are included in the potential fields category magnetic and gravitational fields are important contributors to geophysical prospecting accuracy is a function of position vertical and horizontal and the sensitivity of the instrument the application of potential fields in prospecting is summarized in table 3 3 2 by exploration objective table 3 3 2 can assist the engineer in selecting the most appropriate geophysical tools for an exploration objective the output and products required column is intended as a guideline for discussion with the contracting geophysicist when writing the scope of the work all costs in this chapter are in u s dollars potential fields magnetics magnetic surveys should be designed for the target objective see table 3 3 2 for example for targets 100 m deep airborne systems are the most cost effective way to collect the data shallow target objectives require high spatial resolution surveys 100 m target objective on the ground with relatively high sample density per unit area two sets of internationally accepted units can be used to denote the magnetic field h the international system of units is the tesla t and the centimeter gram second cgs unit is the oersted oe one nanotesla nt equals 10 5 oe the earth s magnetic field is about 0 1 oe the earth s magnetic field originates within the earth and acts like a giant bar magnet located near the center of the earth s core buffeting of the earth s magnetosphere by solar wind is the primary cause for the diurnal field field reversals i e the north pole and the south pole swap positions have been common throughout geologic history a magnetic pole is located where the inclination of the magnetic field is vertical at the north pole the field enters the earth and at the south pole the field leaves the earth by convention at the magnetic equator the inclination of the field is horizontal susceptibility k is the ratio of the magnetic moment per unit volume m to the magnetic field strength h or k m h the quantity has no units values are positive for paramagnetic materials and negative for diamagnetic materials this is the fundamental property expl

oited by the magnetic method this can be rewritten as m k h normally the earth s magnetic field magnetizes earth materials proportional to the magnetic susceptibility of the material types of magnetism all matter reacts to a magnetic field but only two classes of matter actually exhibit strong interactions ferromagnetic and ferrimagnetic clark et al 2003 1 ferromagnetic refers to materials that one normally thinks of as magnetic such as fe ni co such as primary ore for iron nickel sulfides and volcanogenic sulfides they exhibit parallel alignment of moments resulting in large net magnetization even in the absence of a magnetic field 2 ferrimagnetic materials exhibit a more complex alignment of atomic moments but they exhibit the same general magnetic character as ferromagnetic material magnetite maghemite pyrrhotite mostly in ore bodies derived from alteration processes such as iron oxide copper gold iocg deposits and ni laterites the most common magnetic material within the earth s crust is magnetite fe3o4 which is mostly found in iron ores banded iron formations metamorphic and igneous rocks and in small concentrations in some sedimentary rocks magnetite is often associated with metallic sulfide ores such as pyrrhotite fe1 xs ilmenite fetio3 is the next most common magnetic mineral but to a much lesser extent than magnetite the following list describes the types of magnetization remanent magnetization remanent magnetization is the magnetization remaining in the absence of an induced magnetic field such as in a common iron bar magnet it is important because interpretations of magnetic data are highly complicated by remanent magnetization and this can result in serious and costly errors if disregarded normal remanent magnetization nrm nrm is the residual magnetization retained by rock and other material in situ unless otherwise qualified this is the implied meaning thermo remanent magnetization trm trm remains after a sample has been cooled to a temperature below the curie point in a magnetic field chemical remanent magnetization crm crm is acquired when a magnetic substance is chemically formed or crystallized in a magnetic field at a temperature below the curie point depositional or detritus remanent magnetization drm drm is acquired in sediments when magnetic mineral particles are preferentially aligned by the ambient magnetic field during deposition usually by settling through water isothermal remanent magnetization irm irm is remanent magnetization in the ordinary sense that is it is the magnetization after application and subsequent removal of a magnetic field irm is not involved in palaeomagnetism except for the effect of lightning currents in exposed surface rocks pressure or piezo remanent magnetization prm prm is remanent magnetization acquired under the application of stress the effects generally become more pronounced as the strain proceed

s from elastic to plastic deformation the magnetic properties in rocks are affected by many geological and physical processes that all contribute to the complexity of the final magnetic vector direction and this is the reason why the magnetic surveys are so useful magnetic surveys are useful for mapping geological structure lineaments and intrusive volcanic rocks from the earlier explanation of remanence in rocks the practice of assuming a uniform induced magnetic direction inclination and declination of the induced field is simplistic and an unreliable approach recent developments in 3 d inversion will produce block models of the vector magnetic components that are useful in discriminating different lithologies recent work shows that it may discriminate alteration zones in mineralized sequences magnetometers a magnetometer is an instrument that measures magnetic field strength the most common magnetometer used today is the proton precession magnetometer also known as a proton magnetometer it measures the resonance frequency of protons hydrogen nuclei in the magnetic field due to nuclear magnetic resonance because the precession frequency depends only on atomic constants and the strength of the ambient magnetic field the accuracy of this type of magnetometer is very good a direct current flowing in an inductor creates a strong magnetic field around a hydrogen rich fluid causing some of the protons to align themselves with that field the current is then interrupted and as protons realign themselves with ambient magnetic field they precess at a frequency that is directly proportional to the magnetic field this produces a weak alternating magnetic field that is picked up by an inductor amplified electronically and fed to a digital frequency counter whose output is typically scaled and displayed directly as field strength or output as digital data the relationship between the frequency of the induced current and the strength of the magnetic field is called the proton gyromagnetic ratio and is equal to 0 042576 hz nt hertz per nanotesla cesium vapor magnetometers are commonly used in airborne systems optically pumped cesium vapor magnetometers are highly sensitive 0 004 nt hz and are well suited to higher resolution surveys superconducting quantum interference devices squids measure extremely small magnetic fields they are very sensitive vector magnetometers with noise levels as low as 3 ft hz 0 5 in commercial instruments and 0 4 ft hz 0 5 in experimental devices ft stands for femtotesla 1 ft 10 15 tesla magnetic surveys and survey design magnetic data are obtained using a magnetometer transported over land water or in the air referred to as ground marine and airborne surveys respectively normally a stationary reference magnetometer base magnetometer measures the diurnal magnetic field during data acquisition a global positioning system gps is used on most airborne and marine surveys and is st

andard practice in ground surveys data are normally obtained along parallel lines perpendicular to geological strike tie line data are collected at right angles to survey lines but at a much wider spacing usually 10 tie lines help correct for magnetic instrument drift and diurnal variation in the earth s magnetic field data collected along a line is referred to as a magnetic profile the resolution of a survey is dependent on the sensor height and line and station spacing table 3 3 3 can help prevent oversampling of the field and therefore unnecessary acquisition costs depending on the depth of the target table 3 3 3 summarizes the maximum line spacing used in various types of surveys to avoid misleading results if the target is 100 m below the magnetic sensor h it makes little sense to collect data at a line spacing dx of less than 200 m to produce a useful contour map however if one needs to resolve lineaments and dykes then one should fly 100 m flight line spacings so that gradient maps can be calculated the maximum height of the sensor should be 50 m if single anomalies need to be modeled at a 100 m line spacing line bearings should parallel magnetic north south when the geological strike varies considerably otherwise one should choose lines at right angles to geological strike common practice is to fly tie lines at right angles with intervals approximately 10 the flight line spacing with a modern gps or flight line photographic tracking is no longer required for positioning and drift leveling of the magnetic map compilation survey costs for airborne surveys vary from 10 to 120 km depending on the access and remoteness the wide variance is due to a number of factors which will be discussed later guidelines for scope of work for magnetic surveys general specifications for a scope of work should include the following project scope the area outline and number of line kilometers to be surveyed needs to be clear time the time period of the contract needs to be specified authorities in some countries there is a no flyover policy over areas licensed to another explorer s properties permission is required to traverse across such tenements one may be required to access private property to map geological structures effectively so permission must be sought deliveries it is important to ensure that the contractor has performance criteria for the project including health and safety environment and cultural standards and criteria for work schedules and the delivery of data and reports legalities property access and aboriginal rights are the primary legal concerns payment the basis of payment needs to be specified excluded costs the contractor should indicate if accommodation transport and fuel access are excluded and should indicate whether goods and services taxes are included or excluded missing or substandard data noise specifications should be realistic the issue of drop out

s i e when the magnetometer is not properly orientated and data are lost needs to be addressed and an agreement on possible reflights is required contract price a price quote needs to be submitted survey equipment specifications should include the following instrument or survey type minimum data accuracy and frequency of measurement data acquisition system minimum navigational accuracy and navigation systems ground monitoring requirements digital recording medium for delivery survey flying specifications need to include the following traverse line spacing and when necessary control line spacing base station for diurnal variations in the magnetic field recorded in close proximity to the survey area and the variation envelope defined and magnetic storms from sun flares monitored flight altitude tolerances rugged terrain becomes a major consideration for airborne surveys because the data sensitivity is compromised instrument calibration requirements navigation and flight path tolerances base map source and coordinate systems to be selected data compilation and interpretation include the following flight path recovery method and accuracy data corrections required leveling procedure for magnetic data final compilation products required including map and chart scales titles and legends interpretation if required and presentation products and procedures survey costs depend on the following survey type number of parameters measured number of required products delivered type of platform required ground helicopter or fixed wing acceptable measurement and navigation tolerances time constraints of the survey location of the survey current fuel costs and or fuel adjustments mobilization time required for contractor to arrive at the survey area usually quoted at cost other required products e g interpretation products survey size potential fields gravity gravity instruments measure the acceleration due to gravity g the average value of g at the earth s surface is 9 80 ms 2 gravitational attraction depends on the density of the underlying rocks so the value of g varies across the surface of the earth a simple gravity meter figure 3 3 1 can be thought of as a mass on a spring the spring exerts an upward and opposite force to exactly oppose the downward component gd of gravity acceleration the extension of the spring is proportional to the force exerted the meter requires a stable and level platform for operation airborne gravity and gradiometer systems have been developed for petroleum and minerals exploration the airborne gravity systems are commonly used for petroleum exploration basin analysis whereas the gravity gradiometer systems are used in minerals exploration where the detectability requirements are for small compact ore bodies figure 3 3 2 costs range from 150 km for gravity gradiometer surveys 0 1 mgal at 200 m half wavelength and range f

rom 75 km to more than 1 000 km for petroleum gravity surveys accuracy 2 0 mgal at 3 km half wavelength note gal is the cgs unit of acceleration one gal is an acceleration of 1 cm s2 in minerals exploration the gravity anomalies over structures are very small so they are measured in thousandths of a gal or mgal the detection of ore bodies is highly variable but in general iron rich ore bodies are most readily detected as seen in figure 3 3 2 the size of the anomaly is proportional to the total mass or density volume variations of g due to density differences in rocks near the surface of the earth are very small compared to the g due to earth s overall mass many corrections to the data are needed so that density variations can be observed and recorded there are two types of gravity measurements absolute gravity and relative gravity 1 absolute gravity to determine absolute gravity an object is dropped inside a vacuum chamber and gravity is measured at reference points 2 relative gravity relative gravity is a change in gravity from one place to another in exploration it is necessary to measure small changes in gravity accurately gravity surveying is carried out with a portable gravimeter that determines the variation of gravity relative to one or more reference locations several corrections are required to transform gravity accelerations into useful exploration information gravity instruments ground gravity meters have accuracies between 5 and 15 mgal the primary application of ground gravity is in engineering geophysics in minerals prospecting gravity often is used to verify airborne gravity survey anomalies prior to drilling the cost of ground gravity surveys range from 20 to 50 per point depending on terrain and size of surveys gravity survey design is similar to magnetic survey design for both airborne and ground surveys gravity meters are usually calibrated at a national gravity grid base station point information on the locality of national gravity grid points is available at all government geological departments for example for australia one can obtain information from geosciences australia wellman et al 1985 gravity measurements are the vertical component of the gravity field the potential field due to the density of rocks does not have the vector complications that the magnetic field has such as the remanent magnetic field superimposed on the earth s magnetic field interpretation of the gravity potential field is similar to magnetic interpretation and 3 d inversions are common practice in interpretation electromagnetic fields from natural passive sources natural electromagnetic em sources come from a variety of processes from within the earth s core and from distant galaxies frequencies for minerals and mining exploration are in the range 0 001 to 10 000 hz the only two sources that qualify are from the atmosphere and the magnetosphere electric storms in the lower atmosphere genera

te em frequencies ranging from 1 hz to 10 khz frequencies lower than 1 hz originate mainly from hydromagnetic waves in the magnetosphere the concept of skin depth d estimates the depth of exploration as given by zonge and hughes 1991 as approximately d 503 r f meters where r is resistivity of a half space uniform earth and f is the frequency in hertz figure 3 3 3 illustrates the skin depth graphically showing the increase in depth with increased resistivity passive em methods include magnetotellurics and natural source audio frequency magnetotellurics nsamt as seen in figure 3 3 3 a broadband frequency system can explore from near surface to great depths using natural em energy making the use of artificial sources superfluous when using the appropriate measuring equipment and software the em fields generated by lightning activity are seasonal and one needs to make sure the surveys are conducted during the times of maximum em activity goodman 1995 the trend in brownfields exploration is toward deeper depths of exploration which makes high powered artificial current sources unacceptable in busy mine site environments nsamt is a viable alternative that minimizes the risk of electrical accidents active sources in electromagnetic methods principle of induction faraday s law states that if the magnetic flux perpendicular to the plane of the loop changes with time then an electromotive force emf of the same magnitude as the rate of change of flux db t will be induced in the loop the induced emf causes current to flow in the loop so that the magnetic field of the current opposes the change of flux lenz s law so if the applied b field is increasing then current will flow in the loop in a direction so as to reduce the rate of increase figure 3 3 4 active source methods active source methods employ an artificially generated inducing field configurations used in minerals exploration using inductive loop sources include the following fixed transmitter methods moving transmitter methods downhole electromagnetics dhem airborne electromagnetics aem controlled source audio frequency magnetotellurics csamt very low frequency vlf methods time domain electromanetic tdem systems figure 3 3 5 are popular because the data are recorded during the off time which eliminates the need for the high precision geometry required by the frequency domain system frequency domain systems are very sensitive to geometry of the receiver and transmitter orientation however tdem systems are sensitive to telluric noise which seriously affects the late time information frequency domain noise can readily be filtered using fourier analysis galvanic resistivity and induced polarization ip can be thought of as special cases of em the lower the frequency of the signal the greater will be the depth of em penetration within a conductive earth airborne electromagnetic methods the use of aem methods has become mandatory

in many exploration strategies because of their ability to map conductivity contrasts to relatively large depths the broadband nature allows for depth sounding that when stitched together can be converted to conductivity depth images cdis these data integrated with magnetic and gravity inversion images effectively reduce ambiguity in the interpretation aem methods produce good quality cdis because of the excellent electronic technologies available one can expect improvements in both functionality and miniaturization in the future aem technologies are fast approaching the resolution achieved by ground em methods so that the cost benefit of ground em surveys is rapidly diminishing aem surveys are orders of magnitude more cost effective than groundwork except when small areas and or mine infrastructure surveys are required mine infrastructure is always an issue when working with em methods because of the electrical interference i e noise generated by mining activity the high electrical currents deployed are seen as a safety risk figure 3 3 6 shows a typical helicopter tdem system in flight the transmitter loop is at an altitude of about 30 m the receiver is at the center of the loop and a magnetometer is halfway between the helicopter and the transmitter loop many publications describe the theory of em prospecting figure 3 3 7 reviews and recommends em methods by commodity and although not exhaustive it is a convenient and quick guide to most common exploration situations galvanic methods galvanic em methods involve grounded electrode current sources which cycle below a frequency of 1 hz the convention is to refer to conductivity in relation to em methods and to resistivity in galvanic resistivity induced polarization methods the units of resistivity are ohm meters and the units of conductivity the inverse of the resistivity are siemens per meter electrical conduction in rocks occurs in the following ways electronic motion of electrons electrolytic movement of ions dielectric displacement of electrons and positively charged atomic nuclei most rocks are electronic conductors semiconductors the conductivity of rock matrices is generally poor because there are usually only a few unbound electrons the bulk conductivity of rocks in the upper few kilometers of the crust is due mainly to electrolytic conduction i e through the movement of ions contained in pore fluids major factors affecting electrolytic conductivity of rocks include the following porosity conductivity increases as porosity increases this includes macro and microscale porosity e g fracturing jointing intergranular porosity and vugs vesicles water saturation conductivity increases with increased saturation water salinity conductivity increases with increased salinity connectivity of pore spaces permeability pore tortuosity conductivity is higher in permeable rocks clay content conductivity increases wi

th increasing amounts of clay other factors affecting electrolytic conductivity of rocks include the following fresh crystalline rocks typically have low conductivity because of their low porosity however they can be relatively conductive if extensively fractured jointed unconsolidated materials weathered layers are generally conductive due to high porosity and clay content and the presence of saline groundwater alteration of rocks into clay increases the conductivity of unmineralized rocks geological processes that decrease porosity e g silicification will decrease conductivity processes that increase porosity e g fracturing weathering also increase conductivity electrode arrays used for galvanic resistivity surveys the exploration objective usually defines which electrode array is most suitable and cost effective to image the target the selection also depends on whether the survey is required to map a large two dimensional 2 d area e g for detecting gravel channels for groundwater or for porphyry copper targets or whether the survey is for preparing a drilling campaign where finer resolution is required using a 2 or 3 d approach several arrays illustrated in figure 3 3 7 were developed and include the following regional mapping arrays gradient grounded current electrodes are fixed throughout the survey data are collected on a grid within an area approximately one third of the current electrode separation this method produces a resistivity map of the area vector this array is designed for rapid mapping of resistivity and induced polarization of large 2 d areas current electrodes separations are 2 to 5 km and potential fields are measured parallel and at right angles to the azimuth of the current electrodes tensor this array has the same setup as for vector array except current electrodes are deployed at right angles requiring measurements from each of the current orientations for calculating tensor fields this array is useful when there is no reliable geological map for an area where geological strike directions which could control current channeling are uncertain targeting for drill hole positioning arrays dipole dipole the electrode array is symmetrical which simplifies the interpretation the array is sensitive to steeply dipping structures pole dipole this array is more labor efficient than the dipole dipole array because only one current electrode needs to be moved the asymmetrical array is difficult to interpret unless 2 d inversion software is used to create a cdi pole pole this array has only two moving electrodes making it even more labor efficient interpretation is effective when using 2 d inversion software schlumberger expansion and profiling this is the most popular method for groundwater and sedimentary basin mapping it is sensitive to flat lying sedimentary layers for coal and oil exploration a symmetrical array makes interpretation rel

atively easy wenner expansion and profiling this is much the same as schlumberger soundings but it is more sensitive to lateral effects such as dykes and faults three dimensional similar to seismic 3 d surveys the current field is active in three dimensions so that all 3 d geological effects are mapped this is becoming an important prefeasibility mapping tool for resource estimation marine recently developed for oil exploration hydrocarbons are imaged as resistive layers in the sedimentary sequence interpretation is relatively simple using inversion software drill hole resistivity arrays in hole current and potential field electrodes are built into a flexible tube allowing similar survey methods as for surface mapping this method is essential for reviewing ip targets mise a la masse this method maps the surface image of an ore body at depth current electrodes are positioned in two drill holes at the sulfide intersection and potential fields are measured on a grid at the surface the method is based on the premise that current is channeled along the conductor downhole radial this is similar to the mise a lamasse method but with only one current electrode in the drill hole potentials are measured along radial lines starting from the drill collar used for detecting extensions when only one drill hole has intersected ore induced polarization the arrays described previously are all used to measure ip on an exploration play the method is used for detecting the presence of sulfide at depth unfortunately ip effects are also produced by other minerals such graphite clay and some shales ip is a measure of the earth s storage capacity for electrical energy when current ceases to flow in the presence of an ip but no em coupling the voltage will drop instantaneously figure 3 3 8 to a secondary voltage value and then decay toward zero the ratio of the secondary voltage vs to the steady state or primary voltage vp is the true chargeability m which is a dimensionless parameter where m vs vp by transmitting current into the ground through two grounded electrodes and measuring the electrical potential between two other electrodes ip and resistivity are measured transmitted currents will range from 0 1 to 15 a larger currents improve the signal to noise ratio an ip transmitter will put out up to 1 000 v if the transmitting circuit has a resistance of 100 the transmitted current will be 10 a ohm s law i v r except for the contact resistance between the electrodes and the ground all parts of the circuit including the earth itself have negligible resistance so contact resistance is the only important parameter therefore special attention is given to the position of electrodes to lower the contact resistance during a survey ip costs are represented in table 3 3 4 which shows the relative costs based on a dipole dipole coverage equal to one of arrays previously discussed vector ip

would be about onetenth the cost of dipole dipole surveys similarly a 3 d array would cost about three times that of a dipole dipole survey electromagnetic methods em methods are an important geophysical technique in the exploration for most ore bodies table 3 3 5 is a guide for selecting the appropriate em method by exploration objective seismic methods seismic methods are discussed to assist the engineer in understanding the scope and benefits to mining table 3 3 6 shows the seismic methods deployed using natural passive sources as well as those more generally used in exploration geophysics natural sources are primarily used for crustal and mantle studies earthquake prediction and mine seismicity monitoring are used for safety management and are mandatory applications in all underground mining ventures these are outside the scope of this chapter but nevertheless are very important applications of geophysics active source seismic methods are employed as either refraction or reflection surveys the seismic method ranks as a high resolution technique because of its ability to map relatively thin beds and local discontinuities it is the only effective method to map geological unconformities snell s law figure 3 3 9 is the guiding principle of seismic exploration the law of reflection states that the angle of incidence of a ray is equal to the angle of reflection the law of refraction states that a ray will refract at an interface where its velocity changes exploration geochemistry or geochemical prospecting includes any method of mineral exploration based on the systematic measurement of one or more chemical or chemically influenced properties of a naturally occurring material the property measured is most commonly the trace concentration of some chemical element or group of elements the naturally occurring material may be rock soil stream sediment glacial sediment surface water groundwater vegetation microorganisms animal tissues particulates or gases history of geochemical prospecting it is clear from historical records that the principles of geochemical exploration have been applied in prospecting over several thousand years the prospector who panned for gold and traced the colors upstream to a bedrock source used mineralogical observations in a similar way to the modern geochemist who utilizes sensitive chemical analyses to outline patterns of dispersion in the surficial environment geobotanical indicators were recognized as early as the eighth and ninth centuries the mid 16th century work by agricola 1556 describes the analysis of natural waters springs and their residues modern methods of exploration geochemistry were first used in the early 1930s in the soviet union shortly thereafter the methods were applied in the scandinavian countries particularly sweden in north america the earliest geochemical surveys were carried out between 1938 and 1940 by h lundberg in newfoundland and in 1944 by h wa

rren in british columbia the first comprehensive geochemical exploration studies commenced at the u s geological survey under the leadership of h e hawkes in 1947 and at the geological survey of canada with r w boyle in the early 1950s the applied geochemical research group was established at the imperial college of science and technology in london in 1954 under the direction of j s webb and in france research related to exploration geochemistry began in 1955 the successful application and adaptation of geochemical exploration techniques in all parts of the world the rapid development of analytical and computer technology and improvements in field transportation have made geochemistry one of the more effective and widely applied exploration disciplines analytical capability is such that relatively rapid sensitive analysis can be achieved for virtually all metals of economic interest new technological advances are expanding our established capability to cost effectively detect and interpret dispersion patterns related to mineral deposits in a wide variety of environments recent geochemical research has focused on detecting ore bodies hidden beneath transported overburden and development of geochemical dispersion models to aid in the interpretation of anomalies developed in these environments cameron et al 2004 through multielement analysis geochemical data can reveal signatures related to distinct geological units and geochemical processes this capability when applied to rock samples permits geological correlation as well as the more precise delineation of otherwise invisible alteration features related to mineralization when applied to soil and other types of samples multielement data can help outline major geological units and the extent of alteration systems and identify the presence of mineralization buried under extensive cover geochemical prospecting methods the various components of a geochemical exploration program include sampling design choice of sample media sample collection sample analysis quality control of analyses data visualization and evaluation and interpretation these components of a geochemical survey are interdependent and should be focused on the geologic objective to be achieved good design and planning including orientation and wellconducted sampling programs constitute the foundation of all sound geochemical exploration work closs and nichol 1989 inappropriate sample preparation prior to analysis can destroy the integrity of the well chosen sample it follows that no matter how accurate and precise the techniques used for analysis or how advanced the statistical treatments and computer programs used for data handling and interpretation they cannot resurrect the lost quality and representativity and restore the decreased probability of exploration success caused by poor planning improper field sampling faulty sample preparation or mismatch between sample media and digestion metho

d geochemical program planning experience has confirmed that the success of a geochemical survey depends largely on the correct assessment of all the natural factors that influence the mobility and dispersion of the metallic elements of interest these natural factors which are described more fully in textbooks by rose et al 1979 and levinson 1974 1980 are physical and chemical properties of the elements or parameters of interest nature of the geology and mineralization geomorphological history of the field area vegetation and topographic and climatic conditions these factors are completely interrelated and any change in one condition such as a geologic change from an acidic to a basic environment a local climatic change caused by elevation or a topographic change from rolling to mountainous terrain can significantly influence element mobilities and the lateral extent of the dispersion from any mineralization type consequently procedures for sampling sample preparation and analysis that prove to be satisfactory in one field area may be inadequate and unreliable in an adjacent region the processes of oxidation weathering erosion transportation sedimentation and diagenesis that characterize the surficial environment are too complex to describe in detail in this summary the physiochemical conditions determine whether the weathering products of mineralization disperse either in solution in a hydromorphic form or in a solid or clastic form the low ph high eh conditions of the acidweathering environment e g oxidizing massive sulfides promotes the solubilization of many base metal and other elements and their more widespread hydromorphic dispersion in surface and groundwaters alkaline conditions developed over a weathering limestone or in a semiarid climatic condition prohibit or arrest this hydromorphic dispersion under these conditions the insoluble metal particles disperse mechanically to form clastic patterns a series of publications sponsored by the association of exploration geochemists develops conceptual models based on conditions in canada bradshaw 1975 scandinavia kauranne 1976 the basin and range province of the western united states lovering and mccarthy 1978 australia butt and smith 1980 tropical and subtropical terrains butt and zeegers 1992 and arctic and temperate terrains kauranne et al 1992 these conceptual models describe the principles and mechanisms of formation and configuration of anomalies and dispersion patterns revealed through geochemical exploration surveys in these regions this format has been expanded in the handbook of exploration and environmental geochemistry published by elsevier currently with 11 volumes covering many aspects of geochemical exploration geochemical orientation surveys when contemplating a geochemical survey in a new region the most reliable method of determining the extent and nature of dispersion patterns is to conduct an orientatio

n survey the objective of orientation sampling is to determine and outline the existence and characteristics of dispersion patterns or anomalies associated with mineralization and also background levels in similar environmental conditions the specific sample media used are dependent on a knowledge of the field area the prospecting problem and if available previous experience but may include any of the following rocks soils stream sediments surface waters groundwater glacial sediment lake sediment vegetation soil gases and microorganisms the orientation survey commonly involves the collection of a number of relatively closely spaced samples over and in the vicinity of known but preferably undisturbed mineralization with the express purpose of outlining the dispersion patterns in the available sampling media this information can then be used to select the most reliable sampling method sample preparation and analytical techniques capable of detecting similar anomalies under similar environmental conditions the detailed examination of the nature and shape of the dispersion patterns invariably yields information on the principal natural factors responsible for the observed distribution of anomalies this is a significant aid in the development of interpretation procedures table 3 4 1 is a synthesis of the important parameters that can be derived from a properly planned and executed orientation survey based on this information the optimum physical parameters sample depth sample interval analytical technique etc for routine surveying can be chosen that necessarily take into account the defined dispersion characteristics as well as the physical logistical and economic conditions pertaining to the project large samples should be taken to provide sufficient material for the full evaluation of the parameters listed in table 3 4 1 and representative samples should be collected from nonmineralized areas to adequately define background conditions and contrast of anomalies where contrast is defined as the ratio between background and threshold value of anomalous samples a survey conducted over gold silver vein mineralization at mount nansen in the yukon territory of canada coope 1966 illustrates the application of the orientation approach detailed profile sampling of soil and overburden exposed in a trench across virgin mineralization produced patterns of lead antimony and zinc as illustrated in figure 3 4 1 it is apparent from these patterns that the dispersion behavior of lead and antimony is similar but quite contrasting with the patterns for zinc all metals have been influenced by downslope movement in the overburden but the zinc pattern is compatible with dispersion in solution along the bedrock surface examination of the patterns also indicates that near surface sampling 0 to 300 mm or 0 to 12 in would not reliably indicate the mineralized vein it was concluded that a sample depth of 460 to 610 mm 18 to

24 in and a sample interval of one third the anomaly width at this depth 5 m or 15 ft were the optimum parameters necessary for routine surveying figure 3 4 2 observation of these sampling criteria led to the discovery of several previously unknown veins the soil profile interval in an orientation survey over more extensive types of mineralization will be proportionately larger than the intervals chosen for narrow vein type mineralization the sample intervals employed in orientation surveys will vary according to the anticipated size of the target mineralization and the dispersion characteristics of the metals of interest in areas where no previous experience exists a short interval is recommended so that three or more samples are collected within the distance spanning the zone of mineralization this interval should then be progressively expanded with distance from the metal source to the limits of the known or anticipated dispersion pattern samples must also be collected from nonmineralized areas to establish the background range and sufficient material should be collected at each site to allow for the determination of optimum size fractions analytical techniques and other factors listed in table 3 4 1 sample collection and handling effective sampling of all surficial media requires well trained personnel capable of recognizing and describing the correct sample material and the sample site characteristics samplers should be able to recognize and if possible avoid situations where contamination from human activity or changes in the natural physiochemical conditions can produce spurious or unusual results in most situations these sampling duties can be undertaken by trained technical personnel with geochemical exploration experience for some specialized types of surveys where identification of the correct sample material is critical as in biogeochemical or glacial till sampling programs it is prudent to employ qualified specialists e g botanists and quaternary geologists to conduct orientation surveys and instruct and supervise the sampling teams sampling tools vary according to the medium and the field situation non contaminating equipment is essential and care should be exercised in not only choosing noncontaminating steels for shovels trowels augers and so forth but in ensuring that lubricants and adhesives weldings and solders are metal free too this awareness of geochemical cleanliness extends to the dress of the sampler who should avoid wearing metal buckles gold rings and so forth and avoid handling coins which might lead to contamination by chipping or transfer of metal on fingers the same caution is necessary in the choice of sample containers kraft paper with noncontaminating waterproof glue and closures olefin and plastic bag containers of appropriate size are frequently used kraft and olefin allow samples to be dried without transfer while plastic bags are commonly used for larger

samples more rigid polypropylene bottles can be utilized in water sampling and a variety of sampling devices are available for the sampling of gases and particulates collecting different sample media soil soils vary considerably in composition and appearance according to their genetic climatic and geographic environment classified into residual and transported types according to their relationship to their substrate soils are mixtures of mineral and biologic matter and may be distinctively differentiated into a series of soil horizons residual soils characteristically contain detectable dispersion patterns developed during the weathering of mineralization in the underlying bedrock and these patterns are revealed by careful sampling of appropriate soil horizons transported soils present more difficult sampling problems but meaningful sampling is possible in many areas after the genetic origins of the transported cover are understood with all but a few exceptions soils are sampled along traverses or grids in the follow up or detailed prospecting stage of a geochemical program orientation programs define criteria such as sample depth or soil horizon to be sampled sample interval and the size fraction for analysis it is essential that these criteria be applied consistently through the survey hoffman and thomson 1987 stream sediments and surface water stream sediment is one of the more commonly used media for geochemical reconnaissance surveys the sediment at any point in a stream is a natural composite sample of erosional materials from upstream in the drainage basin and will include clastically hydromorphically and biogenically derived products from weathering mineralization the length of anomalous dispersion trains will vary with the nature of the mineralization source and physiochemical environment of the field area or drainage basin in humid actively oxidizing environments dispersion trains from sulfide rich base metal deposits may extend downstream for several kilometers active stream sediment material constantly or most frequently washed by stream waters is collected from the center of a drainage avoiding sites that may be contaminated or influenced by bank collapse in most survey programs approximately 500 to 1 000 g 1 1 to 2 2 lb of fine grained material are collected from the upper few tens of millimeters of the sediment if heavy minerals are to be examined larger samples from deeper in the streambed are collected from carefully selected sites in all surveys in new areas the critical parameters of sample interval sediment size fraction appropriate analytical procedures significant anomaly contrasts and background levels are determined through orientation surveys hale and plant 1994 in the regional reconnaissance prospecting mode stream sediment surveys can be designed to systematically cover areas up to several hundred square kilometers to pinpoint source areas in more detail anomalous indica

tions of mineralization can be followed up with more detailed sediment sampling follow up sampling of seepage areas is particularly effective in delimiting anomalous groundwater sources containing metal derived from oxidizing mineralization if appropriate soil sampling can be used to define suboutcropping mineralization in the anomalous source areas defined by the sediment survey regional reconnaissance can also be achieved by sampling the waters of actively flowing streams where metal is dispersing in solution a prospecting approach similar to the sampling of stream sediments is necessary collecting waters in clean 250 ml 0 07 gal polypropylene or glass bottles sampling of groundwater seepage sites is an integral part of stream water surveys to keep the dissolved metals from adhering to the bottle walls a few milliliters of acid is routinely added to the water samples after collection temperature ph total dissolved solids conductivity and certain other measurements are commonly made at the sample site lake sediments and lake water lake sediments and lake water sampling have been developed into effective geochemical reconnaissance techniques in areas of canada and scandinavia where lakes are common conditions are swampy and or where stream drainages are inaccessible or poorly developed in low relief regions the lake sediment medium is dependent on the hydromorphic dispersion of metals into the lake environment through groundwaters and the adsorption of this metal onto hydrous oxides and the organic rich muds deposited on the lake bottoms the sampling focuses on the collection of these organic muds using specially designed sampling devices in more mountainous areas fine grained clastic dispersion into the lake sediment becomes a more important factor in all areas satisfactory sample locations are found well away from lake shores and are reached using boats float planes or helicopters lake waters are commonly collected at the same sites as the lake sediments coker et al 1979 glacial deposits extensive quaternary glacial deposits occurring over most of canada and the northern united states northern europe and northern asia have presented major challenges to exploration as a better understanding of the origin and formation of these glacial sediments has grown their blanketing presence has become progressively less formidable and effective exploration techniques have been developed mineralized boulder tracing in glaciated regions is an established technique of the traditional prospector in scandinavia and parts of canada methods were developed for sampling tills in the 1950s and this technique is now the preferred sampling method in modern geochemical exploration programs approximately 70 of lodgment till is locally derived and most of the early success with till sampling was in areas of shallow till cover 10 m 30 ft where the sample medium is reasonably accessible in the 1960s lightweight percussion

drills such as the pionjar and cobra models were adapted to collect small samples of till from immediately above the suboutcropping bedrock to geochemically categorize anomalous geophysical features at depths of up to 21 24 m 70 80 ft overburden drilling technology particularly reverse circulation and sonic drilling advanced rapidly with the utilization of larger drills in programs for uranium and gold deposits in glaciated areas because most types of gold deposits are not detectable by conventional geophysical methods lodgment till sampling using overburden drills to depths of 100 m 330 ft has been used routinely in prospecting for gold in the canadian shield through the 1980s large samples of till 10 kg 20 lb are recovered in these programs from which the heavy mineral fraction is separated and examined both visually and chemically for gold and other metals averill 2001 the correct interpretation of these data is dependent on an understanding of the till stratigraphy and provenance of the transported material the technique is expensive with combined drilling sample treatment and analytical costs ranging from 20 to 50 m 60 to 100 ft but it is cost effective in this deep overburden covered environment where other methods in gold exploration have not been as successful in contrast with the heavy mineral sampling of tills practiced in canadian exploration scandinavian explorers place a greater reliance on the 63 m 240 mesh fraction of till this fraction has successfully indicated the presence of several types of mineralization including gold rocks rock sampling or lithogeochemical surveys comprise systematic sampling of outcrops trenches drill cores or drill cuttings as with other types of geochemical surveys the sampling procedures and the sample material collected in lithogeochemical work should be standardized as much as possible lithogeochemical sampling necessarily must take into account the geological environment and the type of mineral deposit of interest to the explorer very briefly syngenetic lithogeochemical patterns which developed at the same time as the rocks that enclose them can develop for example in 1 intrusives genetically associated with specific mineral deposit types 2 volcanic stratigraphy where exhalative activity has dispersed detectable quantities of metals during the formation of volcanogenic massive sulfide deposits or 3 the vicinity of sedimentary deposits the scale of sampling necessary for detection of these and other types of patterns will be determined by orientation surveys but may include the regional sampling of individual plutons or more detailed sampling of specific parts of an exposed stratigraphic section epigenetic lithogeochemical patterns those developed long after the rocks that enclose them can develop as diffusion aureoles in the rocks hosting epigenetic mineral deposits or as leakage aureoles along fractures and other structures that mark

the pathways followed by hydrothermal or groundwater fluids prior to and subsequent to the deposition of the significant mineral deposits both these processes introduce the concept of mineral zoning of geochemical aureoles the ratios of the different elements introduced during the mineralization period varies with distance from the principal deposit according to the properties of these elements and the host rocks and the physiochemical conditions at the time of deposition leakage anomalies can extend for hundreds of meters or feet from a deposit whereas diffusion anomalies rarely exceed 30 m 100 ft the scale of dispersion the presence of zoning patterns and the sampling parameters for epigenetic geochemical patterns are determined by appropriate lithogeochemical orientation surveys it is clear that surveys designed to detect leakage anomalies will focus on a standardized collection of fault or fracture zones and possibly bedding structures in contrast the preferred lithogeochemical sample material for the detection of syngenetic haloes is likely to be unfractured and the scale of sampling much more detailed in all instances geochemical analysis of lithogeochemical material has the potential of delimiting dispersion patterns associated with mineralization beyond visible alteration vegetation and humus early scientific observers dating from the eighth and ninth centuries recorded that the morphology and distribution of certain plants were affected by the presence of metals in the soils such visible variations in a plant species are referred to as geobotanical indicators many other plants while not showing any visible variations are capable of concentrating metals in their tissues and the presence of anomalous metals in the soils or groundwater is often reflected in the metal content of leaves twigs or other plant organs these invisible metal concentrations are known as biogeochemical indicators brooks 1983 the seasonal fall of leaves and needles transfers some of the accumulated metals to the surface soil where they are incorporated in the humus layer sampling of this humus alternatively known as mull ao or ah material by scandinavians in the 1930s revealed its potential for geochemical prospecting this is especially true in areas of transported material where the root penetration of the plant exceeds the thickness of this cover and obtains nutrients from the underlying mineralized bedrock and groundwater in addition to the direct recognition of geobotanical indicators the most attractive feature of vegetation sampling is the ability of biogeochemical and mull prospecting to see through thicknesses of barren transported overburden plants are complex organisms and so is their metabolism different species respond differently to the same conditions and consequently some species are more effective biogeochemical indicators than others deep rooted plants e g the mesquite are much more effective prospectors o

f the deeper groundwater than the shallow rooted flora of the southwestern u s deserts and are therefore preferred species in biogeochemical work evapotranspiration has been suggested as a mechanism for movement of metals into the nutrient depth of these plants some species preferentially concentrate metals in specific tissues such as leaves twigs bark or wood it is therefore important to establish the most favorable tissues for sampling after a useful species has been identified dunn 2007 this complexity is accentuated by the fact that metal uptake may vary with aspect and degree of uptake commonly varies with the seasons in temperate forest regions accelerated uptake and higher concentration commonly occur during the spring growth following a dormant winter season in hot desert regions following the exhaustion of available near surface water during the dry season deep rooted plants will tap the deeper more metal rich groundwater these variables make biogeochemical sampling a specialized exercise the expertise of an experienced geochemist or botanist is essential during orientation studies and the supervision of vegetation surveys because of the seasonal variations biogeochemical surveys must be completed quickly and sampling in the spring and fall is generally avoided the same complexities do not affect the humus or mull medium dead tissues are not subject to seasonal variations and annual accumulation has an integrating effect weathering leaching and bacterial decomposition will work to diminish the metal contents but signatures in mull are generally preserved soil gas under certain conditions weathering mineral deposits produce gaseous emanations that can be detected by specialized measurements radon for example is produced during the radioactive decay of uranium and radium survey techniques measuring the alpha particle emissions during radon decay have been used extensively in the search for uranium helium is another gas produced during radiogenic decay and is considered by many to be also of deep seated origin mercury bearing minerals which can include sphalerite and other sulfides often release mercury vapor during oxidation the oxidation of sulfides leads to the generation of sulfur dioxide dihydrogen sulfide h2s and carbon dioxide co2 because of the consumption of oxygen in the oxidation process the atmospheric proportions of carbon dioxide and oxygen change in the vicinity of oxidizing sulfides and these imbalances can be measured in the soil gas to detect buried mineralization more recently organic gases have been used to define mineralized and alteration zones located beneath transported cover organic gas species are zoned relative to mineralization with heavier reduced compounds occurring over ore and lighter more oxidized gas species occurring at the boundaries of mineralization klusman 1994 sample preparation inappropriate sample preparation can completely nullify the caref

ul work of the sampler who has invested time and expertise in the selection and collection of representative material furthermore it is impossible to restore the integrity of the poorly prepared sample by enterprising analytical treatments and interpretational procedures drying prior to mechanical treatment surficial and rock geochemical samples have to be dried in some climates this can be achieved by exposure to the sun but most samples are dried in drying ovens heating these ovens to temperatures in excess of 70 c 160 f can lead to the loss of volatile elements hg as sb that may be of value to the exploration program organic samples including humus may be dried in a conventional drying oven or in a microwave oven at temperatures not to exceed 70 c 160 f sieving and crushing after drying surficial samples should be agitated and disaggregated to achieve complete separation of component particles without crushing this can be done with a pestle and mortar or other suitable non contaminating mechanical device that can be thoroughly cleaned between samples in earlier geochemical prospecting work orientation studies on soils stream sediments and other surficial materials revealed that the separation of 80 mesh material for analysis was appropriate in many surveys with some elements such as those commonly concentrated in residual minerals w sn and other elements dispersed in weathering products in arid semi arid environments fractions coarser than 80 mesh give superior geochemical patterns with better contrasts surveys in glacial till environments benefit from the analysis of the 240 mesh 63 m or even finer fractions careful size fraction analysis during orientation will not only indicate the most appropriate fraction for routine work but the metal distribution throughout the sample reveals invaluable information on metal behavior for interpretation purposes sieves must have a non contaminating composition those most frequently used are made from stainless steel heavy mineral separations heavy mineral separations from stream sediment glacial till and rock samples commonly utilize the liquids tetrabromoethane specific gravity sp gr 2 9 and methylene iodide sp gr 3 3 more recently solutions of sodium polytungstate with specific gravity ranging from 1 0 to 3 1 according to dilution can also be used to avoid the disposal issues associated with tetrabromoethane and methlyene iodide usually these liquid separations are carried out on coarser sample size fractions e g 30 80 mesh but separations can be made on material down to 200 mesh if the metal of interest is present in the finer size fractions if necessary heavy mineral concentrates can be further subdivided by electromagnetic separation into magnetic paramagnetic and nonmagnetic fractions and analyzed separately vegetation samples ideally vegetation and humus samples should contain no clastic material dust on leaves and twigs can be

removed by rinsing with demineralized water but humus material is rarely 100 organic the presence of excessive clastic material may dilute or contaminate the metal content of the organic material and adversely interfere with lower detection limits possible on organic material using the neutron activation analytical technique after drying at temperatures of less than 70 c 160 f in a standard drying or microwave oven vegetation samples are macerated in a wiley mill to a 2 mm mesh size this material is compressed into either 8 0 or 30 0 g pellets for direct analysis by neutron activation or can be ashed in a muffle furnace at 450 to 470 c 842 to 878 f for approximately 15 hours the plant ash is then analyzed in a similar manner to clastic sample material rock samples some surveys call for the analysis of specific minerals in rock samples such minerals may include magnetite biotites feldspars and sulfides that may be concentrated by magnetic separation or with heavy liquids from the most suitable size fraction after appropriate sample treatment govett 1983 most rock samples collected in geochemical programs are analyzed for their whole rock or trace element contents this requires crushing and pulverizing and if the contained metals of interest are heterogeneously distributed e g as with coarse gold the principles of sampling theory must be observed pitard 1993 the pulverized whole rock product that is commonly analyzed has a grain size of less than 150 to 200 mesh the sample is rarely reduced to this fine grain size in its entirety but as a general rule the finer the sample can be crushed or ground prior to sample splitting the more representative the split is likely to be the emphasis on gold exploration in recent years has focused attention on sample heterogeneity this has stimulated some significant developments in the design and adaptation of crushing and grinding equipment for improved sample preparation in addition to sample representativity the geochemist must be concerned with sources of contamination in the sample preparation equipment grinding plates and blades of different composition are available so that the obvious contamination from chrome steel tungsten carbide and other materials can be avoided similarly loss of sample representivity through smearing of native copper native gold molybdenite or other soft material on pulverizer plates can be avoided in many instances by the selection of alternative equipment with a different comminuting action because sample weights analyzed in geochemical work are small 0 1 to 50 g 0 0002 to 0 1 lb compared with the original sample size sample homogeneity is important improved mixing can be achieved when necessary by careful blending and the pulverization of coarser fractions to the 200 mesh size analytical techniques analytical methods a prime requirement for cost effective geochemical exploration surveys is the availability of analytica

l procedures capable of high productivity low detection limits high precision and acceptable accuracy these criteria were met in the 1950s by a series of colorimetric analytical techniques with productivities ranging from 20 to 100 samples per day technological developments have subsequently led to the introduction of atomic absorption spectrophotometry aas inductively coupled plasma icp spectrometry x ray fluorescence xrf and instrumental neutron activation analysis inaa with far greater analytical sensitivity and vastly increased productivity these analytical techniques provide accurate precise determinations with detection limits of less than 5 ppb to 1 ppm for many of the elements commonly measured in exploration geochemical surveys the icp mass spectrometer instrument is capable of even greater sensitivity comparison of some of these analytical methods is shown in table 3 4 2 in the minds of the inexperienced the spectacular analytical capabilities of these instruments often overshadow the critical importance of the sample preparation and sample decomposition stages of sample treatment it was emphasized in the preceding section on sample preparation that the most informative fraction of a geochemical sample may be the heavy mineral fraction a relatively coarse fraction 30 80 mesh a fine fraction 80 mesh or a very fine fraction 250 mesh depending on the material being analyzed or the particular property of interest in a sample if an improperly chosen solid sample material is correctly analyzed the results can be no better than mediocre in the context of the exploration program and may even be misleading digestion methods sample decomposition presents even greater complexities the newer analytical methods require that elements of interest be introduced to the instruments in solution the choice of method to take elements into solution requires careful consideration of the mineralogy of the material figure 3 4 3 strong decompositions of a geochemical sample can be achieved through treatment with hot concentrated acids or by fusion some resistant minerals e g chromite may not be soluble in hot concentrated acids but are broken down by fusion the amount of metal extracted by the strong decompositions achieved with nitric hydrochloric or perchloric acids or their mixtures is not total and will vary with the mineralogy of the sample hydrofluoric acid is the only acid decomposition medium that will dissolve silicate minerals in the typical clastic or lithogeochemical sample even with acid mixtures extraction efficiency will vary with the acid sample to acid ratio and the duration and temperature of extraction fletcher 1981 of the fusion techniques lithium metaborate can be effective in attacking resistant minerals and extracting specific elements comparison of the quantities of metals extracted by techniques capable of different degrees of decomposition can be informative metals in sil

icate lattices of rock forming minerals commonly constitute the background or threshold level of the geochemical sample material the mineralization component of an anomalous sample is generally contained in sulfides iron or manganese oxides or in adsorbed positions on clay minerals the metal on the clays and that contained in the sulfides and hydroxides is more easily extractable than the background threshold component contained in the rockforming minerals stronger decompositions which break down the rock forming minerals will effectively dilute the anomalous metal components by releasing the lower concentrations of metal in the background threshold component partial decomposition techniques utilizing cold or weaker acids and other reagents that do not break down the rockforming silicates enhance the more readily extractable mineralization component resulting in a much greater contrast between the anomalous and background values in the survey in numerous geochemical surveys therefore the data from partial decompositions when ratioed against total decompositions can be much more definitive in target delineation than data from strong or total decompositions examples of different decomposition techniques and the corresponding mineral phases digested into solution are shown in figure 3 4 3 sequential extractions are series of digestions of progressively increasing strength which can be used to selectively remove mineral phases in succession within a sample this protocol has been used to successfully delineate copper mineral phases in copper deposits and delineate ore types for mineral processing parkison and bhappu 1995 gold analyses gold can be analyzed using geochemical or assay methods for reconnaissance and follow up programs gold can be analyzed using geochemical methods including aqua regia digestion with an inductively coupled plasma optical emission spectrometry icp oes finish for resource evaluations gold should be analyzed using traditional assay methods including 30 g fire assay digestion followed by an icp oes or aas finish if the grades are below 2 ppm and by gravimetric finish if grades exceed 2 ppm this would be true for any element of ore grade concentrations if the samples are to be analyzed and incorporated into a resource evaluation the assay methods are the preferred method to determine concentrations for the element s of choice in the resource determination if a nugget effect exists metallics assays should be used to establish grades quality control in addition to observing the basic principles of orientation sampling sample preparation and analysis adequate assurance of analytical quality representativity accuracy and precision are essential when all data are evaluated the term qa qc is used in discussing quality control programs qa indicates quality assurance which is the plan for implementing a quality control program quality control is the analysis and evaluation of the results

of the analytical control program quality controls should be introduced at all stages in the geochemical program specially prepared certified reference samples standards with known metal contents provide essential material for checking the accuracy of an analytical laboratory on a batch basis and also for monitoring analytical drift with time when numerous batches are forwarded to the same laboratory over the life of a project it is important to know that analytical data from all stages of a project are comparable without any significant bias between analytical batches the reference materials should be prepared from a similar matrix as the project samples using a vendor accustomed to preparing certified reference materials failing that personnel responsible for monitoring qc programs should acquire certified reference materials standards from a reputable source duplicate sampling can be used at every level where the sample volume is reduced and then subsampled to measure sample sample preparation and analytical reproducibility duplicate sampling of the designated material at the same sample site produces two samples sample duplicates that will give a measure of the sample reproducibility splitting of a subsample after the appropriate sample preparation preparation or crush duplicates and pulp or analytical duplicates will provide information on sample preparation reproducibility and analytical variance the accepted practice is to include a suite of standard reference samples as well as sample preparation and analytical duplicates to provide a 10 qc volume within every analytical batch for each batch the client should include a higher grade standard a lower grade standard a coarse blank that needs to undergo sample preparation a sample duplicate and an analytical duplicate as a minimum where samples are being submitted to determine ore reserves the frequency of standard insertion should be greater routine scanning of results from these standards and duplicates will give an immediate indication of unsatisfactory accuracy and precision and sample inhomogeneity a set of pass fail criteria should be established for the project acceptable industry practice recommends that standards should report within 2 standard deviations of the mean using the mean and standard deviations determined from the reference material standard certification process figure 3 4 4 illustrates a qc chart for presenting standard analyses samples can be arranged by analytical sequence number or date in this illustration by sequence number to display accuracy lines indicating the certificate value solid line and 2 standard deviations dashed lines are also plotted those analyses that exceed the 2 standard deviation pass fail criteria are considered failures which need to be investigated generally sample duplicates should be reproducible to within 20 preparation duplicates to within 15 and analytical duplicates to within 10

figure 3 4 5 illustrates a qc chart used for presenting results of duplicate analyses in this case for analytical duplicates with a precision envelope of 10 any control samples exceeding the pass fail criteria should be reanalyzed and reevaluated because it is the objective of the geochemical laboratory to produce good and reliable data and maintain an ongoing profitable customer relationship quality control is of concern to both the laboratory and the exploration client if irregularities are noted the laboratory should be contacted immediately and the discrepancies discussed every reputable laboratory will have its own standard reference samples and other controls and should rerun samples if the quality of its output is questioned if erratic analytical results are experienced with the duplicate and batch samples but not with the standard reference materials sample inhomogeneity nugget effect is indicated experienced commercial laboratory personnel can assist with these problems by utilizing special preparation techniques designed to overcome sample inhomogeneity interpretation principles geochemical interpretation does not begin only after all samples have been collected prepared and analyzed interpretive methodologies develop progressively throughout a geochemical project the patterns observed during the orientation program are directly related to the dispersion characteristics of the metallic elements the nature of the overburden and the overall general geochemical environment such recognition contributes to the formulation of interpretation procedures and this understanding directly affects the sampling sample preparation and analytical procedures that are selected for the geochemical program the cumulative experience of geochemical behavior gained from orientation surveys and case histories in a broad spectrum of environments has enabled geochemists to compile models that represent dispersion behavior in a wide variety of landscape configurations the simplified example in figure 3 4 6 illustrates the formation of geochemical anomaly as patterns related to natural factors within the landscape all dispersion models have certain common features hoffman and thomson 1987 a body of mineralization or another source that may mimic mineralization the relative distribution of bedrock overburden soil groundwater surface water vegetation and other factors highlighted dispersion pathways related to mineralization and anomaly formation preferential sites or geochemical barriers where metals concentrate to form anomalies portrayal by each model of dispersion as a series of patterns related to and controlled by a variety of identifiable natural factors fundamentally geochemical interpretation involves the recognition of these patterns the identification of the factors causing them and the extrapolation of the patterns back to a mineralized or other source the importance of the preferred emphasis on patte

rns of dispersion rather than the magnitude of the geochemical values in units of parts per million or parts per billion can be illustrated by reference to figure 3 4 7 precipitation and accumulation of hydromorphically transported metal in the seepage anomaly area adjacent to the stream channel can invariably result in concentrations markedly higher than in the surface horizons of a residual soil anomaly on a well drained slope in such a situation reference only to the magnitude of values would result in first priority for follow up being assigned to the seepage anomaly whereas recognition of the location and shape of the seepage anomaly would immediately indicate its origin and direct the interpretation to the source areas upslope in parallel with pattern recognition geochemical interpretation requires a knowledge of the anomalous threshold and background values of the elements of interest in the survey the fundamental observations leading to the identification of these values come from the orientation survey in the simplest orientation scenario background values are not influenced by the presence of mineralization and in figure 3 4 7 are represented by the relatively homogeneous areas of low values at the extremities of the hypothetical soil traverse anomalous values are in this example the higher values peaking a short distance downslope of the suboutcropping vein zone weaker mineralization disseminated in the rocks on either side of the vein zone also gives rise to anomalous but less spectacular values which are also influenced by the topographic slope the upper limit of the background population is referred to as the threshold and it is clear that contouring this data at the threshold level will outline an anomalous pattern related to the mineralization in the bedrock it is common for background levels to shift with changes in lithology or alteration systems which also need to be determined during interpretation of the data such as the lower and the elevated background of the volcanic rocks illustrated in figure 3 4 7 introduction of geological and geomorphological complexities such as those shown in figure 3 4 7 can also produce spurious anomalies which need to be considered during interpretation conversely during mineralization processes some elements may be leached from the host rocks by the mineralizing fluids in such a situation a depletion in values below the regional background for the element will cause an anomalous low that is geochemically and economically significant the interpretation of geochemical data and the correct identification of significant anomalies therefore require a fundamental awareness of the geochemical environment as presented in the geochemical model figure 3 4 6 a knowledge of the geology structure and other characteristics of the type of deposit sought and an underlying understanding of the geochemical behavior of the elements of interest this procedure is clearly describ

ed and illustrated with numerous actual examples in a workbook format by levinson et al 1987 during the past several decades geochemists have adapted statistical methods of evaluation to assist in geochemical interpretation effective application of statistical methods whether univariate or multivariate requires not only the same full appreciation of the geochemical environment the geology and the chemistry of the elements as described in the preceding paragraphs but also an understanding of the statistical technique employed in addition this effectiveness is also dependent on correct design representativity and quality of the sampling and analytical phases of the program given these essential understandings statistical techniques provide useful and often powerful tools for geochemical data analysis they can assist in explaining previously unrecognized characteristics in a data set and making significant anomalous patterns more easily recognizable a basic assumption applied in the statistical treatment of geochemical data is that the data are unbiased and continuous most geochemical data are discrete but fortunately in practice these discrete values commonly are sufficiently abundant exploration geology focuses on activities that lead to the discovery of a potentially valuable mineral deposit recognizing that the deposit may develop into a mine project geology following discovery focuses on the more detailed evaluation of the mineral deposit up to and including feasibility studies and evolves into mining geology which is directed toward the planning and operation of the mine methods employed for project and mining geology require an engineering discipline to ensure that the data and information provided are appropriate for use in project evaluation and mine production the most important aspect of the geologist s work is to discover and delineate the mineral deposit and to prepare a detailed definition that describes the deposit s location size shape variability and grade continuity this detailed definition ensures accurate and reliable mineral resource and reserve estimates every mineral project or mine is based on a geologic entity an ore mineral deposit a well defined mineral deposit and its geologic characteristics are the only aspects of a project that cannot be altered mine plans can be modified to exploit the deposit using alternative approaches that often yield similar results varied processing methods also are typically available for producing comparable results major modifications can be made to other aspects of a project without substantially changing project economics regardless of the approach taken however all engineering and metallurgical aspects of a mine must be accommodated to the specific location and unique geologic characteristics of the deposit being evaluated geologic data and interpretations form the foundation for both mine evaluation and mine production providing essential info

rmation for estimating resources and reserves and for mine planning and process design or control proper geologic work requires a keen awareness of and an ability to anticipate the technical requirements of mining engineers metallurgists geotechnical engineers hydrologists and other technical specialists who all rely on the geologic data geologists are integral members of the project evaluation or production team presentation of pertinent data in a usable format and frequent communication of new geologic knowledge to the other technical specialists are integral components of the geological program thus excellence in written and oral communications of geologic information is essential to guide the evaluation process and to achieve production goals the ultimate objective of the exploration geologist is to find ore that of the project geologist is to define the ore that of the mine geologist is to keep the mine in ore project geology sequentially follows exploration after a discovery of potentially economic mineralization has taken place and evaluation and development proceed mining geology begins on commencement of production though sometimes it has been defined to include project geology by comparison project geology combines many elements of both exploration and mining geology through the delineation of mineralization and the estimation of resources and reserves with the large number of mineral deposits that have been developed in recent decades project geology has become recognized as a separate discipline requiring special knowledge distinct from either exploration or mining geology feasibility studies and development decisions involving large capital outlays require great accuracy in mineral deposit definition and resource and reserve estimation the greatest single cause of mine failure worldwide is unreliable reserve estimates in addition to involvement with these aspects of the work the project or mine geologist is expected to identify various metallurgical ore types as well as potential ground stability and hydrological problems ore reserves are the basic wealth of mining and minerals companies and the principal source of future earnings a mining company s existence growth and survival depend on its ore reserves it is necessary to periodically review and update resource and reserve estimates to account for changes related to additional ore discovery mine ore depletion upgrading or downgrading of resource categories or fluctuations in economic conditions during the 1990s the international mining industry established standardized definitions for the terms resources and reserves that are generally accepted throughout the world in 2005 the society for mining metallurgy and exploration sme established guidelines in the sme guide for reporting exploration results mineral resources and mineral reserves which it revised to accommodate requirements of the u s securities and exchange commission sme 2007

the canadian institute of mining metallurgy and petroleum cim also adopted its rules in the estimation of mineral resources and mineral reserves best practice guidelines which uses the standard international definitions cim 2003 the cim guidelines were subsequently codified and are generally accepted throughout north america and in many countries elsewhere in the world where north american mining companies are established to ensure best practices project management and to comply with national instrument ni 43 101 standards of disclosure for mineral projects 2005 additional support provided by geologists to other specialists in mine evaluation and production includes gathering and assessing geologic data and samples for geotechnical analysis collecting groundwater data for hydrological investigations defining the ore body and distinguishing ore grades and types for mine planning and production exploring for additional ore bodies and other materials in the district collecting samples for metallurgical testing evaluating geology and ore potential of sites designated for waste dumps a mill leach pads shops offices and associated facilities and assisting with land legal environmental and permitting studies geologic data collection and recording mining is a physical endeavor that extracts some valuable resource from the earth for a mining company to do this effectively it is essential that company management has as accurate as possible a characterization of resource zone geometry a good understanding and clear representation of the shape size quality variability and limits the geologic characteristics of the resource zone are needed at the evaluation development and productive stages of a project this characterization requires a high quality geologic database so the geologist can provide management with the information needed for critical project decisions the financial success of the mining venture is directly related to the accuracy and completeness of the geologic database and the quality and understanding of the characterization that describes a resource zone the geologist who fails to provide the best geologic characterization based on data available at the time is delinquent in his or her responsibility for providing management with the best possible information for intelligent decision making barnes 1980 this chapter deals with basic geologic data collection principles and the need to improve the accuracy of this deposit characterization and modeling by collecting more and betterquality geologic data general comments are provided first followed by a review of the type of data needed also presented are common symbols and abbreviations typically used in geologic data collection mapping and core or cutting logging general comments geologic data vary greatly within a deposit and from deposit to deposit this applies if we are concerned with metallic coal or nonmetallic commodities s

pecific geologic features differ considerably and likewise the importance of any specific feature varies from deposit to deposit geologists are faced with the task of collecting many types of geologic data and seldom know in advance which features are critical therefore they must collect detailed data on all features of potential importance data may be collected via surface or underground mapping drilling geophysical or geochemical surveys or specific studies examining such features as structure rock mechanics properties specific gravity alteration effect and distribution or mineralogy the data may be collected using the long established pencil and paper based method of mapping posting and compiling data collected via this conventional method can be converted to digital electronic form through the use of computer aided design cad systems computer spreadsheets a geographic information system and other software in computer facilitated systems alternatively the development and evolution of computer based systems and software has enabled collection of data by direct digital means through the use of portable or pen and tablet computers hosting the appropriate software in the latter method data are recorded electronically on computer screens that host digital base maps probably topographic maps or alternatively propertyspecific simple grid sheets that are stored in the computer and commonly linked to global positioning system gps methodologies this allows the user to create electronic geologic maps or drill logs for direct use on computer screens or to provide hard copy printouts as desired collecting adequate geologic data requires a great deal of time effort and expense and with either data collection methodology similar geologic skills are required it is essential that data collection systems be planned in advance so that all data and descriptions are systematically gathered to ensure high quality and completeness data collection should employ some standardized system or format to ensure consistency accuracy neatness legibility objectivity quantification and timely completeness fact must be discernible from inference personnel should be trained in the requirements imposed by either the conventional or computed assisted or computerbased recording system it does little good to have two people biased by personal experience making data recordings on the same outcrop or sample the ultimate records suggesting two entirely different geologic units quantification of the geologic variable should be done wherever possible this requires estimation which although imprecise is far superior to vague generalizations such as much or strong amounts of some particular mineral species accuracy is a recurring theme in the foregoing discussions of any of the numerous types of geologic data normally collected this accuracy requirement implies that an appropriate qa qc quality assurance quality control system o

r algorithms of some type are in place to ensure that the data collected are checked for accuracy and correctly entered into databases and that automatic backup is available not uncommonly these algorithms are present in data entry programs that check to ensure that drill hole data are entered sequentially from top to bottom and that transposition errors are minimized some data entry programs contain algorithms that identify and flag for review or reduction assay values that appear high or out of normal for the type of deposit under study numerous other checks and balances of this nature exist adequate security and restrictions against database access should be in place to prevent corruption of data by inappropriate access or improper data handling or updating geologic data the facts must remain available and in an unaltered and periodically updated and secure form to ensure that as interpretations are developed they do not inadvertently become part of the facts geologic data are extremely important and costly to obtain and they are essential for proper interpretation evaluation and ultimately mining and processing ores from a deposit the data collection may be a one chance occurrence due to constraints imposed by mining or distance a second observation of a critical area may be impossible as the drift or bench may be mined out or the core crushed for assay if data are collected in the manner just described they will provide a useful record that is timeless in character ultimately it is essential that geologic data be converted to some digital format this conversion will enable their incorporation into the database to support interpretations control resource and reserve estimation characterize mineralogical and metallurgical conditions or clarify other mining related issues further observations on these topics are made by mckinstry 1948 and malone 1995 malone discusses the roles of the geologist and the mine geologist the importance of comprehensive standardized mapping and core logging areas where geologic input is essential in operational support and positive and less desirable aspects of computer based logging and mapping systems he points out that while computer systems do not reduce the geologic effort and skill required for accurate mapping and logging they do however provide much greater flexibility and speed in manipulating and using the data malone also suggests that it is never good for management to try to save money by reducing the quality of geologic mapping attempts to constrain mapping to fit an artificially simplified geologic model are always counterproductive in the long run accurate geologic mapping faithfully recording the exposed geology the geology that is revealed not what is expected is the best insurance a mine can have against unexpected disasters the practice of geology is not easy and requires a great deal of patience diligence discipline and simply hard work adequa

te training and a high level of professionalism are required required data every effort must be made to observe objectively record and describe all geologic features that may be of importance in characterizing the size shape and variability of the resource and its associated environment under study broad categories of data to be collected routinely are location information and data on lithology mineralogy assay samples alteration and structural and rock competency as experience is gained in specific areas deposits or suites of rocks the capability to subdivide various units into key subunits typically will be developed this will enable the geologist to improve description correlation projection and understanding of the genesis of the deposit more importantly it will allow for superior resource estimation and will improve recommendations needed for management decision making geologic data collection key features for the following categories of data collection the keys are careful observation and clear description location data sample map mine or drill location should be recorded on each sheet this may include geographic data such as state county section township range latitude longitude coordinates elevation mining district mine pit bench level working claim claim corner or any and all information that will clearly identify the unique location of the geologic data points data cannot be used if the geologist does not know where they came from lithologic data typical data to describe rock sample or unit should include color texture mineralogical characteristics lithology and rock type appropriate descriptive modifiers stratigraphic information if known top and bottom data age relationships and general gross features such as hardness competency and bedding characteristics should be included subjective generic terms should be avoided unless well established or qualified to distinguish inference from observable facts primary sedimentary structure and sedimentologic features e g bedding laminations casts soft sediment deformation graded bedding burrows bioturbation and fossil content as well as banding foliation and lineation with appropriate attitudes should be noted where possible structural data secondary structural features that postdate rock formation should be described data should include a clear description and attitudes of joints fractures and faults breccias with quantitative description of selvages gouge zones and fragment size and healed or re cemented character of breccias information related to rock competency such as rock quality designation rqd and natural fracture frequency is important these data are best if collected at the drill site prior to boxing of core although useful data are frequently accumulated after the core has been boxed folds drag folds crenulations lineations and foliation should be noted age relationships mineralization ass

ociation and overall effect on rock mass are important weathering and oxidation intensity data are usually critical and commonly structure related but may be included with lithologic data quantification of structural data where possible is extremely important as it may play a key role in determining mineability of a deposit alteration data alteration data include nature mineralogy intensity and distribution of features this should include color texture mineralogy intensity fracture or vein veinlet relationship control stages mineralization association and pervasiveness with respect to the overall effect on rock mass weathering and oxidation intensity are important but may be included with lithologic data quantification where possible is extremely useful as is description of age relationships of various alteration features mineralization data this category includes nature intensity mineralogy and distribution of the desired resource it should include primary and secondary classification estimates of specific and total quantity of various minerals intensity character of veinlets vein or disseminations supergene features weathering and oxidation intensity and associated gangue mineralogy as an example estimates of total sulfide content mineral and metal ratios and gangue mineralogy are of use in deposit description in support of metallurgical studies and testing and in waste characterization vein age relationships tied to mineralogy alteration or lithology provide important data in understanding both zoning and grade estimates and overall deposit genesis assay work should include desired ore elements deleterious elements arsenic etc and iron or sulfur or both to calculate total sulfide content for the previously mentioned waste characterization geologists must clearly understand the methods and the significance of sampling sample preparation sampling procedure and sampling protocol individual ore deposits typically host multiple metallurgical ore types based on mineralogy alteration or oxidation most of which are based in geology and therefore require careful geologic description and metallurgical testing to determine distributions possible process modification or varying mining sequences to ensure optimum recoveries coal data in addition to standard lithologic and structural data it is important to map or log any and all features that aid in correlation understanding the distribution of sedimentary facies and constructing a depositional model of the coal bed s and coal bearing sequence detailed descriptions of horizons immediately above and below the roof and floor are critical as are accurate measurements of depths and thickness of all units associated with the coal some key features include abundance and type of marine or freshwater fossils slickenside in roof or floor rocks the presence of roots representing old soil horizons pyrite bands nodules or streaks siderite or ironst

one nodules and plant debris description of individual coal beds either the banded or nonbanded groups requires careful measurement or estimates of the banded lithotypes vitrain clarain durain and fusain content ward 1984 a more practical system schopf 1960 describes the thickness and amount or concentration of vitrain and fusain bands in a matrix of atrital coal the latter is described by five luster levels that range from bright to dull description of nonbanded sapropelic coals and boghead and cannel end members relies on identification of these massive faintly banded fine grained accumulations of algae or spores and usually requires a microscope for adequate description the nature of cleats partings bone and shale layers needs description and careful thickness measurements to separate net from gross coal bed thicknesses coal bed description while straightforward requires some supervised training to ensure adequate data recording other features other features that may supply extremely important information with direct bearings on mining and or metallurgy should be recorded this may be reasonably objective fracture frequency rock quality determination measurements longest and shortest unbroken core recovered in a run or more subjective an overall estimate of rock strength friability or competency total sulfide content or assay is extremely important for waste characterization as well as metallurgical process development metallurgically significant features such as hardness which affects grindability grain size which controls grinding for particle liberation or oxidation intensity should be noted as well as mineral species and alteration mineralogy which affects flotation recoveries as an example supergene copper mineralization coatings on sphalerite provides a challenging metallurgical problem as does activated pyrite due to similar chalcocite coatings on pyrite beneath more thorough supergene copper enrichment zones metallurgical personnel need to be made aware of the presence of these features numerous other examples could be cited added testing is almost always needed here however geologic data collections should indicate these and other potential problem areas requiring specialized study surface or underground mapping requires uniformity and standardization as well as systematic unbiased and objective data collection and recording note taking abbreviation and symbology are best if they employ a company wide established methodology that reflects common initial training of personnel involved in addition to being consistent with logging to be discussed in the following section mapping data must be accurately located and tied to known locations that preferably have been surveyed conventionally or using survey quality gps in general regardless of the resource type geologic mapping is for the purpose of providing data on lithology alteration mineralization structure and ground condi

tions as well as analytical data i e assays or coal quality for resource evaluation the following eight item list summarizes the typical requirements considerations and steps in the mapping process the list illustrates how one might proceed in what is essentially an exercise in detailed mineral and rock identification characterization and record keeping which will be discussed in more detail later in this chapter these steps assume a basic knowledge and understanding of the symbols and abbreviations generally used in geologic data collection 1 conduct a pre mapping review based on general geologic knowledge of the area and deposit type under investigation this is to determine the purpose of the mapping to identify geologic parameters of probable importance identified according to guidance in the geologic data collection key features section in this chapter to consider the scale s to be used and to determine the local physical geography of the area under investigation 2 secure base maps air photos grid sheets survey information claim locations and ownership survey points and geographic information system gis data secure approval for property access as appropriate 3 secure typical items useful during the mapping process such as mapping vest compass tapes hand lens and so on the core cutting logging process section lists other items for conventional work or in support of observation entry into portable laptop computers 4 select recording bases as available such as air photos or topographic maps data may be recorded directly on the base map or on acetate overlays attached to the base if no base maps are available notes on observations of geologic data can be taken on simple grid sheets and locations can be determined through the use of compass and tape or gis data cut selected recording base maps air photos or grid sheets to the size that is appropriate for the aluminum sheet holder to be used 5 make one or more visit s to the field location i e deposit exploration evaluation area or mine site to make observations and collect and record geologic data with appropriate symbols and abbreviations on selected base maps air photos or grid sheet alternatively use laptop computers to record geologic data directly and construct maps using mapping software as mapping proceeds it is important to carefully note and record the location of important cultural features such as roads buildings key topographic features or survey points for later data compilation and development of the geologic map if surface or underground mine workings are involved secure ground outlines as available annotated with known survey point locations if possible 7 unless the geologist is extremely experienced it is inadvisable to enter old mine workings alone 8 compile note sheet data on larger sheets to build the geologic map of the project historically compass and tape s commonly have been used to construct

ground outlines for data recording to locate outcrops and to tie in culture or survey control and if used carefully they will provide sufficient accuracy this is a fairly straightforward procedure and consists of stretching a cloth measuring tape or tapes from or between known points and determining the bearing of the tape with a compass this tape line is then plotted to scale in its proper orientation on the field note sheet and tick marks are posted and identified each 3 m 10 ft along the bearing of the tape line following this offset measurements are taken at right angles to the cloth tape from the tape to the edge of the drift or pit bench a small pocket tape is used to take these offset measurements at 3 m 10 ft intervals along the cloth tape points corresponding to these offsets are then plotted on the field note sheet and connected and an outline of the drift or edge of the pit bench is thus created for geologic note taking figure 4 1 1 illustrates the methodology of developing a ground outline and shows some simple geologic notes location scale date geologist and orientation are clearly indicated on each example in typical mine related work geologic field note taking is commonly done on a relatively large scale such as 1 240 or 1 600 1 in 20 ft or 1 in 50 ft smaller scales 1 1 200 and 1 2 400 1 in 100 ft and 1 in 200 ft are also used generally to collect data on overall resource setting or to simplify more detailed work in the mine itself for regional work scales of 1 12 000 or 1 24 000 1 in 1 000 ft or 1 in 2 000 ft may be appropriate some variability is necessary and the actual mapping scale used depends on needs of specific projects advance planning here is useful although detailed 1 240 1 in 20 ft mapping in a vein or massive sulfide deposit is desirable attempting to get the same detail in a 13 5 mt a 15 million tons yr open cut coal mine or a 1 8 mt a 2 million tons yr underground coal operation would be inappropriate mapping techniques are described in a number of good references which vary somewhat in perspective proper supervised training is desirable peters 1987 provides considerable detail in a good description of general surface surface open pit and underground work he describes an outcrop mapping system in which three acetate overlays shown in modified form in figure 4 1 2a are superimposed over a base map or air photo and used to take notes describing geology mineralization and alteration for each outcrop the field manual by compton 1985 provides good coverage of geologic mapping techniques as do earlier textbooks by mckinstry 1948 or forrester 1946 both of which remain excellent sources on techniques in mine mapping the geologic data may be collected conventionally using the long established pencil and paper based mapping and compilation system or methodology this system can be augmented with the use of digitizers or other computer f

acilitated electronic databases to prepare maps sections or other displays for use alternatively because of the rapid development of computers enlarged electronic storage capacity and software the data may be collected by direct digital means using portable or pen and tablet computers with these devices it is possible to record data directly on computer screens in the form of spreadsheets commercially available digital base maps visible on the screen or perhaps property or company specific custom grid sheets the geologic data contacts attitudes mineralogy structure and so on are posted directly on the screen and captured digitally xyz coordinates through the software and saved in the storage medium of the computer the stored data are available for later use as desired in plan map or cross section construction three dimensional 3 d manipulation and study geologic or resource model development resource estimation or other needs walker and black 2000 review the development of a computer based field mapping program at a midwestern university they note that computer use is increasing in most aspects of geologic work that the location dependent nature of geologic data corresponds to both the importance and the limitations of digital information that direct digital recording may save time and that digital topographic data are generally readily available additionally they supply some key references identify hardware and software issues and some products and conclude that in addition to teaching conventional field skills they will continue to use computers in field courses at the university another technological development is the portable x ray analyzer which can provide useful analytical data to incorporate into geologic mapping brimhall et al 2006 provide a thoughtful review of the fundamental importance of geologic mapping and some history of the development and modification of the anaconda system of geologic mapping the system was initially developed in the early 1900s at butte montana and underwent subsequent modifications and expansion to 10 colors and the use of specific symbols and plotting positions on the field sheets in chile in south america nevada in the united states and elsewhere einaudi 1997 discusses this mapping technique in an excellent well illustrated unpublished stanford university paper geologists interested in ore deposit mapping may wish to secure a copy of this paper additionally an excellent paper by proffett 2003 demonstrates and documents the results that can be expected through the use of careful detailed field mapping and core logging or relogging discussed and referenced in chapter 4 2 of this handbook techniques that serve as the basis for the geologic evaluation of the bajo de la alumbrera copper gold deposit in argentina in addition to fully describing and illustrating the use of this paper based mapping system brimhall et al 2006 also discuss digital ma

pping based on pen and tablet portable computers as well as the gis revolution in mapping and data manipulation with cad systems importantly both conventional and computer based digital methodologies require the same basic geologic skills and both have their advantages and disadvantages malone 1995 adequate training is needed for either methodology geologic mapping in underground coal mines can greatly increase the geologic understanding productivity and ultimately the profitability of a mine krausse et al 1979a 1979b provide excellent examples of underground mine mapping methodology and the effect of lithology and structural features on mining their work and that of ledvina 1986 further describe the increasing use of geologic mapping in underground coal mines and stress the importance of roof rock characterization moebs and stateham 1984 summarize contract studies investigating the relationship between geologic factors and roof stability in coal mines the work is well referenced and clearly identifies mine and core mappable geologic features that control roof stability the coal mine roof rating cmrr system developed by the national institute for occupational safety and health niosh anon 2008 incorporates rock composition structural defects and thickness into a rating index that ranges from 1 to 100 the system is increasingly being used as a basis previous discussion in this chapter has introduced the concept of geologic characterization the interpretative model and has emphasized the importance of developing a good model for accurate resource evaluation the discussion now turns to guidelines on how best to construct a geologic model of a resource emphasis is on an empirical model one that accurately records the factual geologic observations the same principles apply whether developing a conventional or computer based geologic model the typical steps in constructing and interpreting a geologic model are summarized in the following list these steps are generally time consuming because of the dependence on data collection through mapping and logging they vary somewhat depending on the resource being evaluated 1 begin with fundamental knowledge and understanding of various deposit types and their models 2 accurately and precisely locate surface and drill hole data points accurately collect the appropriate geologic data accuracy is essential 3 carefully plot drill hole locations and the data on drillhole traces on a set of cross sections 4 identify correlatable contacts geologic units mineralization or other features on the drill hole traces 5 correlate the interpreted limits of geologic features on a drill hole to drill hole basis on individual cross sections 6 carefully plot data transfer information and correlate interpreted limits of the geologic features on a drill holeto drill hole basis on a second set of cross sections at right angles to the first 7 construct a set of plan maps at des

ired elevations using drill hole intersections on the plan maps and interpreted limits of units as developed on sets of cross sections 8 construct simple illustrations the geologic model for discussion and comparison the geologist usually starts with surface outcrop data and drill hole logs that as reviewed in chapter 4 1 are of high quality and have been collected using rigorous standardized methodology and appropriate quality assurance quality control qa qc measures this will provide unbiased factual data for compilation and analysis the geologist builds a geologic outcrop map from surface work that contains all geologic observations this map hard copy or on a computer screen must clearly differentiate factual outcrop data from geologic interpretation and inference between outcrops a common graphic methodology uses bold solid lines and patterns or dark colors for outcrops and dashed or dotted lines of similar colors but applied in a paler or lighter fashion for interpretations herness 1977 emphasizes that there must be no screening of data to eliminate unimportant facts because frequently the importance of insignificant data is realized 20 or 50 years later when mine workings or core may not be available for remapping with respect to core availability the deliberate disposal of core from known ore deposits or established mining districts is unconscionable stored core is simply one of many items in the geologist s files that will be constantly examined and reviewed as new ideas or data become available e klohn manager of the geology department of compa a minera disputada comments core is our record we must always go back to it personal communication numerous ore discoveries have been made because core was available for reexamination re sampling and reinterpretation braun 1991 and personal communication emphasizes the importance of the availability of old drill core for relogging and re sampling that may lead to the discovery of a new gold ore body the sample preparation and assaying procedures discussed in this chapter apply equally to in house facilities as well as commercial laboratories they are applicable to samples derived from reconnaissance exploration through development drilling to mine operations and mineral processing these procedures assume that the samples submitted were collected properly and a representative portion of the original samples is submitted for preparation and analysis the character of the material being sampled influences the size of the sample that should be collected and the manner in which it should be prepared for analysis ingamells and pitard 1986 present a good review of the necessity for the collection of appropriate samples as well as techniques for establishing proper sample sizes abbott 2007 emphasizes the importance of quality assurance and quality control procedures throughout the life of a project the focus herein is on operations in metal mines in

deed much worldwide mining activity at this writing is concerned with exploration for and development of gold deposits the requirements for the preparation of samples of many goldbearing materials are more stringent than those for many other metallic deposits thus the practices described here generally fulfill the requirements for most metallic mineral deposits as well as many nonmetallics the preparation and testing of coal samples is a specialized field and these procedures are summarized later in this chapter as is true for coal the preparation and testing of samples of industrial minerals raw materials is highly specialized for many products the preparation and testing procedures are end product sensitive that is the preparation and testing procedures to be used are controlled by the properties desired in the final product one must attempt to select sample preparation and testing procedures that will produce a product comparable to one produced by the actual process procedures to be used industrial minerals and rocks kogel et al 2006 presents perhaps the best overall background on a wide variety of industrial minerals products although little specifically on sample preparation and testing few additional general publications exist and no specific guidelines can be given here other than to suggest that sample preparation and testing procedures be established for individual deposits through frequent and close communication among the exploration and mining staff laboratory personnel mill managers marketing staff and end users sample preparation sample preparation is the process of converting samples of geologic materials from the larger sample collected in the field or mine into finely divided homogeneous powders suitable for chemical analysis or other testing this is accomplished by the screening of soil or sediment samples or the mechanical reduction of pieces of rock to a smaller particle size in a stepwise sequence alternating with the reduction of sample volume or mass by an unbiased splitting process error can be introduced in many ways during sample preparation as a consequence attention to detail and thorough cleaning of equipment between samples is necessary the desired end result of sample preparation is a powder or pulp that contains the elements to be analyzed in the same concentrations and proportions as in the original sample received the reduction in particle size will be affected by many factors including particle shape hardness specific gravity lubricity malleability residual moisture and the quantity of clay minerals or organic matter present selecting a sample preparation procedure virtually every mineral deposit has its own characteristics and an individual sample preparation procedure should be developed for each unless the deposit is known to be finegrained and relatively homogeneous soil and sediment samples typically are dried sieved through 10 mesh and 80 mesh screens and in

some cases pulverized before analysis rock samples routinely are dried if necessary crushed in stages if necessary to 10 mesh riffle split and a 250 g to 1 kg portion pulverized to a nominal 150 or 200 mesh a safe sample preparation procedure is given by royle 1988 based on a method originally developed by gy 1977 similarly pitard 1993 presents sampling nomographs that enable one graphically to analyze an existing sample preparation process and to develop an optimum protocol pitard markets programs for personal computers that describe tests to perform on gold ores of unknown characteristics and enable one to plot sampling nomographs from which an appropriate sampling protocol can be developed in their chapter 1 titled sampling ingamells and pitard 1986 present a good review of the necessity for intelligent sampling both before and during the sample preparation and analytical stages sample preparation equipment the equipment required to adequately prepare mineral samples for analysis depends to some extent on the nature and quantity of the samples and even on the climatic environment in hot desert environments samples can be adequately air dried under the sun and a laboratory with only a handful of small rock samples to crush and pulverize per day could do an adequate job with a manual bucking board and muller dryers electric or gas fired ovens are used to remove moisture from samples before crushing and pulverizing an airflow is maintained through the oven to remove water vapor released from the samples for routine assay purposes oven temperatures are usually maintained from 104 to 140 c 220 to 285 f the higher temperatures being used on clays although the temperature should not exceed 37 c 100 f if mercury is to be determined the submission of larger and excessively wet drill cutting samples to high volume minerals laboratories has started a trend toward drying rooms or even buildings equipped to dry large quantities of samples screens soil and sediment samples should be screened through screens with both frame and screen as well as a pan made of stainless steel the screen pressed or welded in not soldered screen sizes typically are 10 mesh to remove coarse fragments and 80 mesh for the final product crushers jaw crusher the first stage of crushing normally is accomplished in a laboratory sized jaw crusher some of these can be choke fed through a hopper with feed up to 100 mm 4 in across and they will produce a 2 4 mm 8 mesh product in one pass while the operator is attending to other duties a newer double acting jaw crusher with one jaw top driven and one bottom driven has a 25 1 reduction ratio and will produce a 10 mesh product jaw crushers have a relatively high productivity and reduction ratio and are generally easy to clean between samples cone crusher normally used in a second stage of crushing cone crushers produce a uniform sized product with a smaller percentage of fines

considered better for metallurgical testing and most can crush to 2 mm 10 mesh cone crushers are not effective on clays but work best on hard siliceous materials they have a relatively low productivity and are difficult to clean especially after clayey samples roll crusher as an alternative to cone crushers for second stage crushing roll crushers have a higher productivity and can produce a 2 mm 10 mesh product however they produce a poorly sorted product with a higher percentage of fines and are noisy dusty and difficult to clean the feed to roll crushers must be sized to 10 or 12 mm 3 8 or in and the feed rate must be controlled to prevent choking hammer mill hammer mills have a high productivity rate and the potential to produce a product suitable for splitting and pulverizing in one pass from feed as large as 100 mm 4 in however they are extremely noisy dusty hard to clean and subject to excessive wear when processing tough siliceous materials their product is not well sorted typically consisting of a large percentage of fines with a small percentage of very coarse fragments hammer mills are more often used to crush clays limestone coal and similar softer materials splitters at some point in the sample size reduction process it becomes impractical and unnecessary to further reduce the particle size of the entire sample the sample volume is then reduced by half or more depending on the procedure selected for the material at hand by using a sample splitter riffle splitter the riffle splitter or jones splitter is most commonly used for sample size reduction the technique of splitting must be carefully monitored to ensure that statistically valid splits are taken splitter chutes should be at least three times as wide as the diameter of the largest particles in the sample and the delivery pan should be no longer than the distance across all of the chutes the sample should be evenly distributed along the length of the delivery pan and should be poured along the center line of the splitter not against one side or the other the rate of pouring must be slow enough to avoid choking the chutes the splitter must be cleaned between samples rotating sectorial splitter the most effective splitter in terms of sampling error is the rotating sectorial splitter allen and khan 1970 shop made laboratory sized versions of the rotating sectorial splitter are in use in some sample preparation facilities one design consists of a rotating circular table driven by a variable speed motor at about 10 rpm four plastic cartons of 1 or 2 l 1 pt or 1 qt capacity rest on the rotating table the gaps between the cartons are covered by pieces of angle iron the sample is fed from a feed hopper by a vibratory feeder professionally manufactured rotating sectorial splitters are available that will produce a split of any proportion from 2 to 50 of the original sample pulverizers after the sample is reduced t

o an appropriate weight typically 100 to 500 g or to 1 lb it is then pulverized to a nominal 150 to 75 m 100 to 200 mesh two basic types of pulverizers have been in common use for many years plate pulverizers and vibratory ring mills or swing mills although plate pulverizers are being phased out plate pulverizers plate pulverizers reduce the particle size of samples through a shearing action as the samples pass between a fixed and a rotating plate plates are made of steel or ceramic if metallic contamination is to be avoided controlling the spacing between the plates and thus the product size has been a problem and has required almost constant attention by the operator but newer models of plate pulverizers have better mechanical or even pneumatic controls that maintain a constant plate separation they can pulverize a large sample and are easily cleaned but they are dusty and their product is inhomogeneous requiring thorough blending before assaying mikli 1986 does not recommend plate pulverizers for the final pulverizing of nuggety gold ores as the plate pulverizer does not significantly reduce the particle size of gold nuggets plate wear is high requiring frequent changing and refinishing or replacing of plates vibratory ring or swing mills two basic versions of vibratory mills are made the ring mill consists of a steel bowl with lid the bowl containing a cylindrical steel puck plus one or two steel rings that surround the puck the crushed sample is placed in the open space between the wall of the bowl the rings and the puck the bowl is clamped in a housing which is made to oscillate around a vertical axis by an electric motor carrying an eccentric weight on its shaft the oscillatory motion causes the puck and rings to revolve in a planetary motion inside the bowl thus grinding the sample the second version of this mill also consists of a bowl with lid but only a single grinding element a discus or flying saucer shaped oblate spheroid of steel with a flat rim the center of gravity of this steel element is off center so that when the bowl oscillates the grinding element revolves in a planetary pattern within the bowl bowls of this style have a capacity of 800 g to 5 kg 1 8 to 11 lb of sample whereas the puck and ring bowls range from 50 to 450 g 0 1 to 1 lb in capacity an alternative to the single grinding element is a split discus consisting of two elements with matching concave or convex upper and lower surfaces that oscillate independently in a planetary pattern vibratory mills exhibit the following advantages they require no operator adjustment produce a relatively homogeneous product that requires no further blending create little dust are available in a variety of materials to avoid sample contamination have a low noise level because of a supplied noise suppressant cabinet and have a moderate productivity of some 10 to 20 samples per hour the productivity depends on the character of

the samples with the lower productivity being achieved on high clay samples which require just a few minutes to pulverize but several minutes cleanup time between samples vibratory mills have been described by mikli 1986 as the only type of pulverizer that can actually reduce the particle size of gold nuggets however to reduce the particle size of coarse nuggety gold or to pulverize a 2 kg 4 5 lb or larger sample thoroughly to 150 m 100 mesh or finer can require 10 or more minutes and result in excessive bowl wear coarse nuggety gold is best screened out weighed and assayed separately from the fine fraction of the sample blenders and pulp splitters pulps prepared on plate pulverizers or pulps that have been extensively vibrated during transport require blending the most common approach although not the most effective is to roll the pulp on a rubberized cloth taggart 1945 gives instructions for proper rolling rolling is accomplished by drawing the corners of the cloth horizontally toward diagonally opposite corners causing the sample to roll over and over on itself if the corner is lifted instead of drawn horizontally the sample merely slides along the surface of the cloth and no mixing occurs plastic sheeting should not be used for blending because of the static charges that build up causing retention of some particles and difficulty in cleaning a superior alternative to rolling is the use of a mechanical blender however small sizes suitable for blending assay pulps are not common individual sample blenders are slow a multisample mechanical wheel blender that meets the productivity requirements of a high volume minerals laboratory has been described by gilbert 1987 a simple approach to splitting a pulp is to roll it on a rolling cloth into a sausage flatten the sausage to the height of the scoop being used and then cut several increments from the sausage using a flat bottomed verticalsided scoop until the required weight has been withdrawn mechanical rotating sectorial splitters appropriate for splitting pulps are available and are used in some automated sample preparation systems automated sample preparation systems mine laboratories that process large numbers of samples of similar materials on a routine basis have invested in automated sample preparation systems designed individually for each operation the systems range from simply crushing and splitting to complex systems involving two stages of crushing rotary splitting two stages of pulverizing in continuous flow ring mills rotary splitting of the resulting pulp and even weighing into test tubes or beakers for analysis automated sample preparation systems cost from several tens of thousands to a few millions of dollars but their cost is offset by high productivity and dramatically lower labor costs assay methods two basic classes of assay methods historically have been available geochemical and quantitative but current instrumental

methods of measurement and standardized dissolution techniques have tended to merge the two classes of analysis geochemical procedures typically are used in prospecting and the early stages of exploration when results of high accuracy and precision are not as necessary but low levels of detection are required quantitative procedures are used during exploration drilling sampling and analysis for ore reserve estimation and subsequent stages of mine development and operation geochemical methods of analysis in the past have been considered semiquantitative but most of these now approach quantitative methods in accuracy and precision and they offer the advantage of considerably lower levels of detection the following procedures are not applicable to all materials encountered in the mineral industry for example placer samples should be processed by gravity methods panning sluicing jigging to produce results comparable to the recoveries to be expected from gravity production techniques nuggety gold bearing rock samples are best analyzed either by screen fire assays or by bottle roll cyanide leach tests of large samples in preference to routine fire assays or wet chemical analyses of smaller samples whether one is establishing an in house laboratory or selecting a commercial laboratory there is no substitute for a chemist with experience in the analysis of earth materials the wide variety of materials to be analyzed constituents to be determined and matrix compositions to be encountered pose a myriad of challenges to the minerals analyst constructive comments on the art of geochemical analysis are given by ingamells and pitard 1986 many methods of analysis of earth materials are given in publications of the u s geological survey the geological survey of canada and several australian organizations wet chemistry most analytical procedures today involve wet chemical digestion of the sample followed by instrumental measurement of the elements of interest digestion techniques the most common digestion techniques in current use are aqua regia four acids hydrofluoric hydrochloric nitric and perchloric and fusions using either lithium borate lithium metaborate or sodium peroxide followed by acid digestion of the fusion product aqua regia digestions may not liberate all elements quantitatively especially from more resistive minerals but the acid leachable results are considered by some to be valuable in geochemical exploration fusions followed by acid dissolution produce the most quantitative liberation of a wide suite of elements but are somewhat slower and more expensive than simple acid digestions purposely weak selective leaches are used in some geochemical exploration programs they include demineralized water ammonium acetate hydroxylamine hydrochloride and sodium pyrophosphate as well as the proprietary procedures known as enzyme leach mobile metal ion leach and terrasol leach instrumental measurement ins

trumental methods of measurement follow the wet chemical dissolution of the sample and have dominated minerals laboratories since the development of the atomic absorption spectrophotometer aas in australia in the 1950s and the inductively coupled plasma emission spectrometer icp es in the 1970s aass are used when results for only a few specific elements are desired whereas icp ess measure a large number of elements either sequentially or simultaneously the simultaneous instrument is faster for routine work on similar materials whereas the sequential instrument is more versatile as it can be tuned for specific elements the aas enables the analyst to measure the concentration of some cations down to a fraction of a part per million and with specialized attachments down to a part per billion the aas instrument generally is specific for the element selected although there are various interferences and operational nuances that the analyst must be aware of and either avoid or compensate for icp es instruments utilize the high energy of an argon plasma to excite atoms of various elements in a sample solution that is aspirated into the plasma the excited atoms emit light that is passed through a spectrometer wherein the energy of light at various wavelengths is measured electronically and converted into the concentration of each element in the sample solution a more sensitive version of the icp es couples plasma excitation of the sample with a mass spectrometer to measure isotopes of many elements enabling the reporting of more than 60 elements in some cases at detection limits of a few parts per billion icp ess have a linear response over some five to seven orders of magnitude of concentration of the element in question a much broader operating range than the aas several other instruments are used for specific determinations in minerals laboratories specific ion electrodes for example are used to measure the concentration of cyanide in dilute solutions as well as the content of fluorine chlorine and several other constituents in earth materials fire assay a fire assay is a chemical fusion method for separating concentrating and measuring the content of gold and silver in exploration samples ores and concentrates the pulverized sample is weighed mixed with a lead oxide alkali carbonate flux and a small amount of a reducing agent such as flour and fused in a fire clay crucible the reduced lead collects the precious metals as it settles down through the melt the molten charge is then poured into a mold to cool the lead sinks to the bottom of the mold and is broken from the glassy slag when cool the precious metals are separated from the lead by cupellation the lead button containing the precious metals is placed in a cupel of bone ash or magnesia which is heated in the furnace under oxidizing conditions the cupel acts as a semipermeable membrane allowing the lead oxide formed from the button to be absorbed into the

cupel leaving the precious metals in a tiny bead on the surface of the cupel the bead is weighed the silver is chemically separated from the gold and the resulting gold bead is either weighed or dissolved and measured instrumentally fire assay is the standard method of the industry details theory and variations of the method are described in references such as bugbee 1940 haffty et al 1977 and heady and broadhead 1976 nondestructive analysis x ray the x ray diffractometer is used in some well equipped minerals laboratories to determine the mineral species present in a sample by recording their characteristic crystallographic patterns the instruments are not extensively used in mine and project assay work x ray fluorescence spectrometry xrf is used for the rapid analysis of silicate rocks and the routine determination of the concentration of selected elements in exploration samples ores concentrates and mill products xrf analysis is most satisfactory when applied to a continuing series of samples of similar matrix the method is subject to matrix effects and interelement interferences most of which can be corrected for in the comprehensive computer software that accompanies all modern instruments xrf instruments require for calibration previously analyzed standards similar in bulk composition to the unknowns the instruments are capable of excellent precision but without proper calibration and intelligent operation they can be rather inaccurate neutron activation analysis neutron activation analysis naa is available principally through commercial laboratories with access to nuclear reactors most of the laboratories offering commercial neutron activation analyses of earth materials at a reasonable cost are canadian based naa is indicated when 1 a conventional technique does not have acceptable limits of detection for the element of interest 2 the sample is unique and cannot be consumed in analysis 3 only a small quantity of sample material is available or 4 conventional methods of analysis are unacceptable because of interferences or inherent instrumental errors the sample typically is pulverized loaded into a capsule rabbit and introduced to a reactor in which it is bombarded by neutrons after recovery of the capsule from the reactor the radioactivity induced in the sample is measured and analyzed thus giving a measure of the concentration of each element present in the sample naa currently has much application in the analysis of vegetation or mull for trace amounts of gold and in the analysis of the platinum group elements the rare earth elements and uranium coal preparation and analysis the procedures used in the preparation of coal and coke samples for analysis are similar to those of rock samples the astm international standard method of preparing coal samples is astm d 2013 07 standard practice for preparing coal samples for analysis astm international 2009 the principal diffe

rence in coal sample preparation is the use of lower temperatures and indeed even air drying to preclude oxidation as much as possible crushing and pulverizing is accomplished with much the same equipment as used on rocks however samples are pulverized only to 250 m 60 mesh and only 50 g 0 1 lb is retained for analysis a variety of tests are available for coal samples some of these include sieve analyses washability hardgrove grindability moisture sulfur ash content carbon and hydrogen content and calorific value two of the most common determinations are proximate and ultimate analyses a proximate analysis as described in astm standard method d 3172 07 standard practice for proximate analysis of coal and coke covers the determination of moisture volatile matter and ash as well as the calculation of fixed carbon astm 2009 according to astm the results of a proximate analysis are used to establish the rank of coals to show the ratio of combustible to incombustible constituents to evaluate the coal for beneficiation and other purposes and to provide a basis for buying and selling an ultimate analysis according to astm standard method d 3176 89 reapproved 2002 standard practice for ultimate analysis of coal and coke when tabulated along with a proximate analysis provides the data for a cursory valuation of coal for use as fuel and coke for metallurgical purposes astm 2009 an ultimate analysis includes the determination of carbon and hydrogen as well as sulfur nitrogen ash and the calculation of oxygen by difference typically moisture is reported as well the procedures for an ultimate analysis are also specified by astm international in addition to the analytical procedures described previously data on the major minor and trace elements in coal and coke ash often are of use in the evaluation of coal quality accordingly methods for these determinations are presented in astm d 3682 01 reapproved 2006 standard test method for major and minor elements in combustion residues from coal utilization processes astm d 4326 04 standard test method for major and minor elements in coal and coke ash by x ray fluorescence and astm d 6357 04 standard test method for determination of trace elements in coal coke and combustion residues from coal utilization processes by inductively coupled plasma atomic emission inductively coupled plasma mass and graphite furnace atomic absorption spectrometry astm 2009 quality control the necessity of establishing a quality control program for every project is presented by abbott 2007 most laboratories have an adequate quality control program covering their analytical work and many commercial laboratories currently are certified under the international organization for standardization quality control standard iso 9001 2000 currently being supplanted by iso 9001 2008 how intensively the quality of sample preparation is controlled is unknown yet it

is just as important as the chemistry for as a g royle 1989 personal communication has commented wait until you see the numbers that show all the horrible things that happen in sample preparation of gold samples during sample preparation maximum particle size can be readily monitored by screening at various stages as the material is crushed and pulverized other parameters are more easily checked by actually analyzing the material analysis of several pulps prepared from different splits of the crushed bulk sample will provide data on reproducibility of splitting analogously the homogeneity of a pulp can be checked by taking a number of replicate portions for analysis from the same pulp and calculating the precision of replication a simple procedure to evaluate the effectiveness of sampling drill cuttings is presented by schwarz 1989 analytical precision and accuracy are best established and maintained through the use of reference standard samples and analytical control samples hill 1975 certified standard samples of mineral materials are available from mineral industry suppliers and some governmental agencies and professional or trade groups in several countries but such standard materials are expensive and limited in quantity the elements present and concentration ranges in certified standards may not adequately cover the character of materials that the laboratory is engaged with nevertheless such standard materials may help to provide initial calibration matrix matched control samples to provide batch to batch and day to day calibration and quality control in the laboratory can be prepared and blended from the reject samples from the project the analytical development of these in house control samples can be calibrated to the certified standards ideally every set of analyses produced by the laboratory should have one or more control samples and duplicates included for quality control and assurance some governmental agencies that contract out a large quantity of sample preparation and analytical work arrange for 3 of each 20 samples to be controls or replicates astm gives guidelines for evaluating laboratories performing analysis of coal and coke method d 4182 97 reapproved 2004 standard practice for evaluation of laboratories using astm procedures in the sampling and analysis of coal and coke the evaluation and development of an ore body requires the input of many disciplines including geology and related subjects mining engineering process engineering and environmental sciences as well as marketing and financial modeling work commences during the exploration phase with extensive sampling programs designed primarily to evaluate the grades and tonnages of mineralization present in a feasibility study a deposit s ore reserve grades and tonnages are quoted according to strict accounting procedures such as those of the australasian joint ore reserves committee jorc its variants in the west and the sta

te commission on mineral reserves of russia gkz in the former commonwealth of independent states countries however methods for evaluating exactly what is recoverable from an ore body are not well defined and it is usually up to the process engineer with assistance from geologists and mining engineers to develop a metallurgical test program quality monitoring in chemical analysis the general quality standards not specific to laboratories of the iso 9000 series developed by the international organization for standardization iso are guidelines to ensure that a quality system exists and is followed but they do not assess actual quality or competence iso 17025 2005 specifies general requirements for the competence of laboratories to carry out tests and calibrations including sampling it covers testing and calibrations performed using standard nonstandard and laboratory developed methods it is applicable to all laboratories regardless of the number of personnel or scope of testing activities it requires a laboratory to state its quality policies and procedures provide building facilities and equipment appropriate to the tests performed use suitable methods recruit and train competent staff maintain good document control and keep thorough records laboratories seeking accreditation must prepare a list of the tests they perform and describe the quality control qc procedures associated with these tests an independent national or private organization then assesses the laboratory for accreditation if the laboratory is accepted it receives a registration document showing the tests for which it is accredited follow up visits usually annually are made to maintain accreditation under iso 17025 prospective clients must confirm that any laboratory that they are considering using is registered to perform their required tests in addition to having overall iso accreditation although iso 17025 is achieving international acceptance some countries still maintain their own national systems with the drive toward stricter reporting conditions for mineral exploration and the requirement for so called competent person reports the need for laboratories to be accredited is of increasing importance this applies not only to assay laboratories but also to laboratories providing services such as mineral processing test work and mineralogy assay laboratories should have written procedures under the following main headings sample handling sample preparation sample analysis quality control in house qc procedures for both sample preparation and assay external control by assay of samples with other accepted laboratories and by participation in round robin analytical programs such as those organized by geostats and canmet sample documentation accreditation is not the same as certification the latter requires an independent third party to give written assurance that a service conforms to specified requirements in the context of mi

neral exploration and mining where companies may have varying requirements it is probably better that certification of a laboratory whether external or in house be carried out as part of a company s own qc program overall a comprehensive qc program should increase the number of individual analyses by about 40 compared with the original number of samples being analyzed the laboratory should maintain tables of its qc performance on all of the above factors with charts as appropriate and make these available to current and prospective clients for in house mine and process plant laboratories qc data should form part of monthly reports and be open for discussion at management meetings laboratory clients should not rely on only laboratoryproduced data as part of their own qc programs they may wish to insert duplicates blanks and standards as part of their sample batches the following terms are used in the analysis of samples accuracy closeness of agreement between a measured value and the true value lack of accuracy can be measured and quantified in terms of bias or systematic error bias statistically significant difference between a measured value and the true value precision magnitude of randomly distributed variations in the measurement procedure geostatistics geostatistics is a branch of statistics concerned with analysis of not only data values but also the positions of data samples and time related data variations although originally developed in the mining industry it is now widely applied in a range of disciplines basic principles the basic principles of geostatistics involve summary statistics variance variograms and kriging summary statistics normal analysis of any geological data usually starts with the production of summary statistics to provide an initial view of the data ranges and distributions summary statistics include not only the mean standard deviation variance median and mode but also the coefficient of variation standard deviation mean and log estimates of the mean graphical analysis usually includes histograms log histograms and log probability plots that enable analysis of whether different populations are present and whether some sort of domaining is necessary a decile analysis can also be helpful in assessing outlier grades the data set is ordered by grade then the metal content contained in each 1 10th of the data set is calculated and 1 100th parts for the top most decile are analyzed variance for the purposes of estimation the variance of grade distributions is as useful if not more than the mean variance is a fundamental measure of variability and precision variance between pairs of samples a specific distance apart is a measure of the interdependence of grades for points separated by this distance points closer together are normally more closely related have lower variance than are points farther apart for pairs of samples formed by for example checksamplin

g from different laboratories specific techniques exist for the analysis of variance anova variance also depends on the size of a sample so composites usually have a lower variance than do raw samples as many geostatistical processes are involved in anova irregularly sized samples must usually be composited to a regular length greater than the majority of raw sample lengths so that the composites have the same approximate size support for subsequent analysis variograms in comparisons of a large number of sample pairs some differences are positive and some are negative squaring these differences gives a new set of all positive values differences measured between samples separated by similar distances can then be averaged giving a variance a graph called a variogram can be developed of variance versus distance of separation lag between points figure 4 4 1 shows a sample variogram strictly it should be called semivariogram as it is the variance 2 fitted with a spherical model variogram the distance at which the variogram levels off is called the range of influence samples separated by more than this distance are uncorrelated different variograms can be created and modeled in different directions enabling measurement of the anisotropy of mineralization the position where the variogram cuts the y axis gives a measure of the so called nugget effect designated co which describes how well the sampling results can be reproduced by repeated sampling at the same location this measure incorporates the natural inherent variability of the deposit plus the variability due to sample size preparation and analysis a very high nugget effect relative to sill height may therefore indicate poor data quality as might result when sample data stems from a mix of different laboratories over many years a low or near zero nugget effect indicates very homogeneous mineralization kriging an important use of variogram parameters in grade estimation is the so called kriging method of estimation kriging involves the following steps 1 perform a structural study of the sample data to determine the variogram 2 select samples to be used for evaluation of a particular block 3 calculate variogram values between all selected samples as well as between each sample and the block itself to set up a kriging system of equations 4 solve the kriging system of equations to obtain weighting coefficients for each sample 5 estimate the block grade from the weighted average in mining and geostatistical software systems model variogram parameters and search parameters are user defined the search parameters themselves particularly the distances involved also largely stem from the variography analysis the model software uses the parameters to complete the previous kriging steps and produce a separate kriged grade for each block of a supplied block model drilling and sampling during a geostatistical study variogram ranges and other derived mod

el parameters can be helpful in determining the minimum spacings required for future drilling or sampling if different ranges exist in different directions anisotropy this information can be used to guide different drilling spacings in the corresponding directions ore body modeling computer based resource estimations usually involve the generation of block models each cuboid block represents a volume of ground and has a number of numeric typically grades densities or metallurgical parameters or alphanumeric rocktype attributes assigned to it a parent block size is usually assigned the size is established when the model is initially generated although some mining software systems also allow sub blocks to be generated within the same framework so that more complicated geological or topographical features can be accurately represented volumetric modeling the first stage in resource modeling is generally to build a volumetric block model that uses topographical and geological surfaces and envelopes to split and code blocks this process often involves modeling mineralized zones into which grade values are subsequently interpolated mineralized zone boundaries can stem from drill hole or other sample data and can take into account cutoff grades lithological differences and extrapolation of other geological features some mining software offers advanced facilities for extrapolating geological and ore body features grade estimation the next stage is generally to use grades stemming from the sample data in order to estimate grades in the mineralizedzone blocks often the boundaries used to define mineralized zones have also been used to set corresponding codes onto the sample data these data can then also be composited either into regular lengths for large ore bodies or cross intersection composites for veins or seams search parameters need to be defined to control which composites or samples are used for each block estimate generally geostatistical analysis helps set these search parameters an estimation method is then applied to assign weights to each selected composite sample during a block s estimate the block value is derived from a weighted average the following are commonly applied estimation methods indicator methods instead of grade values being weighted directly composites are first set to either 0 or 1 depending on whether they are above or below a specified cutoff grade a series of different indicator 0 1 values for a range of cutoffs is estimated for the block model possibly by means of kriging these interpolated indicator values decimal numbers between 0 and 1 are reconstituted into a block model grade value a number of indicator methods and variants are available including multiple indicator kriging inverse distance weighting weights are assigned that are inversely proportional to the distance between the sample and block the distance can optionally be raised to a power typically 2 or 3

before weights are assigned the method is easy to apply but does consider clustering of sample data and generally performs poorly beyond the edge of the available sample data kriging parameters defined by the model variogram are used and the resultant weights are dependent on the sample pattern and spacing clustered samples automatically have their individual weightings reduced many variants of kriging are available the commonest of which is probably ordinary kriging nearest neighbor polygonal weighting the block grade is set to the grade of the nearest available sample composite results are similar to those produced by sectional evaluation where polygons are assigned sample composite grades simulation methods in a derivative of kriging called conditional simulation a number of alternative block models are generated which are smaller than those used for conventional estimation methods grades differ for each block but can be thought of as equally likely outcomes for the same input sample composite data the types of grade pattern produced by this method are generally more realistic on a smaller scale than are those produced by conventional methods having a series of block model outcomes enables good probabilistic assessment of results that can be used for resource classification mine design and prediction of production tonnages and grades model validation regardless of the estimation method used it is recommended practice to complete a number of validation steps before performing final resource calculations as a check on the modelgeneration procedures validation steps can include the following visual examination superimpose the sample or composite data onto sectional views of the block model and coloring and or annotating grade data global average comparisons determine the average grade of samples and composites within principal divisions of the mineralized zones and compare these with corresponding average grade values from the block model local average comparisons depending on the geometry of the ore body capture sample and model data onto regular parallel slices e g vertical sections or benches then produce graphs depicting the variation in grade by slice position e g easting variations in average grade from samples composites and models can be compared in the form of model grade profiles swath plots that can include principal grade fields estimated for example by kriging and also alternatively derived grades estimated perhaps by inverse distance or nearest neighbor weighting historical comparisons when older estimates are available compare these with newer revised estimates to help understand differences in the updated procedures and or data test block analysis isolate particular blocks in the block model and study the associated grade estimates in more detail retrieve the sample composite data used for estimation and plot it along with the weightings that the esti

mation method applied if kriging was used determine other parameters associated with the estimation process along with the resultant block grade and from these assess how well informed that particular block may be analysis parameters can include kriging variance which is the expected value of the squared error between the actual and estimated grades and is a useful indication of the geostatistical confidence in a given block with respect to the sample data configuration analysis can also include comparison with reconciliation data planned and produced tonnages and grades when available resource evaluation the following terms are used in ore body assessment average grade average quantity of an ore s valuable constituents the average relative quantity or percentage of ore mineral or metal content in an ore body bulk density dry or wet dry or wet weight of an object or material divided by its volume including pore spaces often expressed in metric tons per cubic meter or t m3 for dry bulk density the sample must have been oven dried to a constant weight at 105 c contained metal weight of a given metal contained within a unit amount of ore or mineral bearing material density ratio of the mass of a substance to its volume specific gravity ratio of the weight of a unit volume of a substance to that of water based on the volume of solid material excluding pore spaces stripping ratio unit amount of spoil overburden or waste that must be removed to gain access to a unit amount of ore or mineral bearing material generally expressed in cubic meters of overburden to raw metric tons of mineral material m3 t resource classification along with estimated grades some assignment of resource categories is necessary so that results can be reported according to normal resource estimation practice in most international systems resource categories are measured indicated and inferred reflecting decreasing levels of confidence only measured and indicated resources should be used as the basis for mine design and resultant ore reserve calculation these class categories can be set as attributes directly in the block model alternatively separate physical limits can be constructed again so that block model evaluation can be subdivided into classes criteria involved in assigning classes should include the following drilling sampling and assay integrity sample spacing and patterns mineralization continuity often described by means of model variogram parameters estimation method and block size samples composites encountered during estimation for each block the number found and proximity to the nearest and general coverage are important sample types in some instances older less reliable data sets might have been used for inferred resources only other modeling parameters such as maximum distance of extrapolation reliability of other supporting measurements such as density likely mining dimensio

ns as resources must be reported to a realistic degree of selectivity other more sophisticated procedures relevant to resource classification might include use of results from kriging operations such as maps of kriging variance or other forms of risk assessment such as use of conditional simulation for producing mines the ore production rate may also be used such that the confidence associated with measured indicated and inferred resource categories corresponds to the confidence associated with tonnage grade predictions in short term medium term and long term mine planning evaluation methods for ongoing or future mine development the resource block model usually becomes the main tonnage and grade reference source for mine planning all embedded attributes grades resource classes and resource properties are useful for open pit mines the model is useful for pit optimization and determination of future exploration drilling requirements for underground mines the model is useful for stope optimization mining software provides a variety of planning tools for interactive design work using the block model as a threedimensional backdrop after a resource block model has been set up with some means of resource classification it can be evaluated in various ways resource evaluation can be subdivided by rock or ore type resource classification cutoff grade interval or model increment such as benches the model can be evaluated as a whole or by retrieval within defined bounds physical bounds in the case of a mine design or a particular zone or range defined by coordinates evaluation results are commonly displayed by means of grade tonnage curves that show the available tonnage and average grade of that tonnage for a range of different cutoff grades figure 4 4 2 shows a sample curve according to the figure for a zn cutoff grade of 4 11 500 t are available with an average grade of 7 6 zn in these curves the x axis represents the cutoff grades applied generally the left hand y axis represents the tonnage above cutoff and the right hand y axis represents the average grade above cutoff it is important to be aware of the selectivity associated with a grade tonnage curve if the curve is produced directly from a block model selectivity is a function of the block size and the grade estimation parameters used curves produced from mining blocks defined by polygons or three dimensional shapes may differ in shape and selectivity thus different curves can exist for the same deposit at different levels of selectivity this equation can be expanded for more than two mineral phases objectives of a metallurgical test program the main objectives of a metallurgical test program are to define the recoveries of the metals or minerals to a salable product determine the grade or quality of the products conduct a liberation analysis process develop one or more flow sheets for ore processing if reserves are to be declared demons

trate the economic viability of the process specify and size process equipment estimate capital and operating costs and evaluate the characteristics of tailings or waste products the stage of the study determines the level of detail and degree of accuracy required for a metallurgical test program for example a conceptual study typically has relatively little measured ore resources and only conceptual mining and process plant flow sheets and therefore capital and operating cost estimates might be accurate to within only 30 in contrast a detailed feasibility study typically has detailed design criteria including balanced process flow sheets and completed equipment designs based on firm supply quotations and estimates might be accurate to within 10 the detailed study then provides the formal basis for the final contractual design of the process and the selection and sizing of plant equipment and other associated facilities it also includes all operating criteria including throughputs operating schedules design capacities feed characteristics and mass balances types of samples used for metallurgical testing samples for metallurgical studies can be obtained from a variety of sources including drill cores of diameters up to 200 mm trenches small pits and channel samples residual samples from initial exploration programs or from dedicated metallurgical sampling exercises can also be used field sampling methodologies the prime objective of field sampling is to create a sample that is suitable for laboratory processing and representative of its source this is the most critical step in the development of a sampling flow sheet errors incurred at this point are usually large have great variance and cannot be rectified by subsequent treatment major types of error include splitting in the field loss of sample and contamination assay pulps the ore body at this point has been subjected to a sampling program to determine the grades of metals or minerals present and a considerable amount of sample material often remains from this exercise such material can be in the form of a dry solid called an assay pulp either moderately crushed 12 mm finely crushed 1 mm or pulverized 75 m the latter is of little use in a metallurgical test program but the crushed materials have some value an advantage of using assay pulp is that it is usually plentiful and reasonably representative of the deposit a disadvantage is that minerals may have deteriorated during storage and testing based on wholerock response e g crushability is precluded split core in an exploration program diamond drill core samples are generally cut in half one half is sent for chemical analysis the other half is then generally quartered and one quarter subjected to metallurgical testing and the other quarter kept for reference trenching and pitting near surface ore bodies can be sampled by means of pitting or trenching both are relativel

y inexpensive means for obtaining bulk samples for testing a disadvantage is that the samples taken may not represent the mineralization below the level of pitting particularly where the ore body has been subjected to weathering near the surface channel sampling where there is access to the ore body the mineralized face can be channel sampled this involves cutting a channel over the mining width without preferential recovery of highly mineralized or softer minerals the width of the sample can be extended into the footwall or hanging wall so as to include mining dilution the formula considers particle size mineral content degree of liberation of the minerals and particle shape the sampling constant c depends on the material being sampled and takes into account the mineral content and its degree of liberation it may vary with d and often must be experimentally calibrated for the material being sampled the term s can be used to measure the confidence in the results of the sampling exercise applications of the formula involve the introduction of sampling constants shape factors size range factors liberation factors and mineralogical factors and the concept of fundamental error the formula is also widely used in the sampling of alluvial material alluvial deposits generally contain very low levels of economic minerals and the formula can determine the size of sample that must be taken to achieve a given degree of sampling accuracy the required size is often such that a small scale or pilot gravity processing plant must be constructed on site sample selection for metallurgical testing if the style of mineralization is the same throughout an ore body with the same minerals present in the same proportions with no significant degree of alteration then a single composite sample can be taken for testing if the style of mineralization is not the same or if some doubt exists regarding ore consistency then several samples should be taken and subjected to a range of basic mineralogy and scoping beneficiation tests if all samples yield the same test results the samples can be combined into a single composite sample for testing however it is more likely that mineralization is variable with different styles and processing characteristics the most common examples of this are gold and base metal ores that have both primary and oxide ore zones often separated by a transition zone mineralization within these zones is clearly different and each zone must be tested separately other examples of ore body variability include mineralization hosted within different lithologies spatial variation in grade either with depth or laterally mineral alteration and variation in the ratios of economic minerals where more than one is present the distribution of deleterious elements can also affect the selection of test samples classical related pitfalls of sample selection include the following the sample is not representative of the minera

lization being sampled the mineralization being sampled is not representative of the rest of the deposit the sample represents the average characteristics of the deposit but does not consider factors such as range of head grades mineralogy and physical characteristics laboratory test programs laboratory test programs are undertaken in a number of phases each of increasing detail complexity and cost scoping test program the first level of testing scoping testing identifies the processing characteristics of the ore and any potential factors that may hinder realization of its perceived economic value the aim at this point is to identify minerals of economic interest and broadly define the processing characteristics of the ore while minimizing testing costs if test results are favorable and the ore body is deemed potentially viable more detailed test programs are then undertaken the scale of testing increases as knowledge of the deposit and confidence in the ore reserves increase scoping tests can be undertaken on samples weighing as little as a few kilograms in particular basic optical mineralogy can reveal the limits of recoverability of certain mineral phases or the grade of mineral concentrate that can be produced mineral phases or elements that are deleterious to final product quality can also be identified and quantified at an early stage preliminary test program the second level of testing preliminary testing defines more clearly the processing characteristics of the ore and provides basic test data needed to size crushers primary grinding mills beneficiation plants and thickeners preliminary testing involves more detailed analytical mineralogical and beneficiation tests often on a range of samples taken from different areas of the deposit preliminary tests investigate the ore s response to processing at a range of grind sizes determined from the mineralogical analysis beneficiation tests are performed using a range of techniques appropriate to the minerals to be recovered for gravity and flotation testing initial batch tests can take the form of so called rougher tests where the sample is processed in a single stage to produce a number of products of varying grades depending on the beneficiation method used concentrates from a rougher test can then be subjected to cleaning tests to determine final product quality a batch test does not give a final measurement of either quality or recovery as some mineral values are lost with material rejected during cleaning in a continual process these cleaner tailings are normally recirculated to some degree which increases product recovery but may well reduce the final product grade physical tests performed at this stage are normally limited to the bond ball mill work index test detailed test program the third level of testing detailed testing is normally undertaken as part of a full feasibility study at this stage the grade of ore to be processed should be

known to a high degree of confidence a mining plan should also have been established although it is in the nature of feasibility studies that mine plan optimization is normally run concurrently with the final stages of metallurgical testing and plant design it is important that dialogue be maintained among geologists mining engineers and process engineers as mine plans can often change rapidly when computer mine modeling systems are used mining engineers determine the optimum ore extraction rate and convert the geological resources into mining reserves by applying mining recovery and dilution factors as well as conceptual mine design and commodity price considerations samples of the products from the test program may be sent for vendor testing particularly if performance guarantees are to be sought and such tests are often undertaken for dewatering of tailings or concentrates laboratory settling tests using measuring cylinders can readily be undertaken on relatively small samples similarly vacuum filtration tests can be undertaken using standard laboratory filter leaf tests although tests for pressure filtration require considerably larger samples than are normally generated in a laboratory bench scale test program bulk samples of concentrates or tailings for such testing specific test methodologies the following tests are related to minerals processing test work physical testing physical tests evaluate the resistance of ore to breakage and determine the crushing and grinding power required during comminution abrasion tests determine the consumption of grinding media and liners during grinding the following tests are available bond abrasion index ai test each test requires at least 1 600 g of 19 13 mm 0 75 0 50 in material the test provides an index from which the wear rates of grinding media and liner wear rates can be determined bond ball mill work index test each test requires 10 kg of sample stage crushed to pass 3 36 mm the test uses a closing screen size of 100 m and a range of factors to determine the grinding power required to achieve a given product d80 80 passing size bond low energy crushing work index wic test each test requires at least 20 pieces sized between 51 and 76 mm bond rod mill work index test each test requires 15 kg of sample stage crushed to pass 12 mm autogenous grinding ag and semiautogenous grinding sag milling tests can also be performed several types of tests can be undertaken to evaluate how an ore will respond to milling advanced media competency test a suite of tests covers impact crushing rod and ball mill work indices abrasion index and uniaxial compressive strength tests to determine whether a material is suitable for autogenous or semiautogenous milling an advantage of this test suite is that it can be used on pq core material 85 mm autogenous media competency test each test requires 200 kg of material in discrete size ranges from 1

52 140 mm down to 114 102 mm the sample is loaded into a drum 1 83 0 3 m and rotated for 500 revolutions while power draw is measured a range of bond crushing rod and ball mill tests are performed on the mill product and on fresh ore jk tech drop weight test each test requires 100 kg of crushed ore in the size range 75 to 12 mm if diamond drill core is used the core diameter should be at least 50 mm the test measures impact breakage and abrasionbreakage parameters the former is determined by a tumbling test the latter by a high energy impact device called a jk drop weight tester these parameters are then used in a computer model jksimmet to predict ag and sag mill performance macpherson autogenous work index test each test requires 250 kg of material stage crushed to pass 32 mm the test is performed in a mill of diameter 46 cm or 18 in as a dry grinding process with cyclone classification it does not evaluate the competence of the ore at the coarse sizes used in autogenous or semiautogenous milling but gives a preliminary indication of whether the ore is better suited to autogenous or semiautogenous milling the number and type of samples submitted for testing depend on the complexity of the ore body and the associated host rocks it is important that the samples include mining dilution for an underground mine it is also important to consider the expected proportions of hanging wall and footwall dilution when designing comminution circuits for a concentrator it is important to know not only the average value of the ore s hardness resistance to breakage but also the range of values that will be experienced throughout the life of the mine it is therefore important to test a range of samples to determine how energy requirements and plant throughput will vary the choice of these samples should generally be made based on the lithology of the rock types present rather than the ore mineralogy particularly if the economic mineral is a relatively minor component of the ore the final value of the work index used for plant design purposes depends on the nature of the ore body and the mine plan for example in an open pit mine if the ore body has a work index that is lower at the top and higher at the bottom of the pit then it is clearly necessary to design the comminution circuits to treat the harder ore at the bottom in an underground mine ore may vary in hardness but in practice it is likely to be produced from several stopes in different parts of the ore body in which case it may be adequate to design not for the hardest ore type but rather for a calculated blend based on the predictions of the mine plan comminution circuits are normally designed based on a stated average value of work index as well as the range of values with which the plant is expected to cope gravity testing high density minerals can be recovered by means of gravity processing the following test methods may be appropriate heavy m

edia separation test some ores are amenable to preconcentration using heavy media separation hms hms can be used to reject a significant portion of ore at a relatively coarse crush size with low loss of mineral value tests are performed with heavy liquids typically with densities in the range 2 6 3 3 g cc crushed ore is screened into size ranges and each size fraction is subjected to sink float separations within closely sized density ranges heavy liquid test results are usually sufficient to evaluate the efficiency of most hms processes it is not necessary to perform pilot plant testing unless bulk samples of hms product are required for subsequent processing spiral test gravity separations can be performed using spirals on material in the size range 1 5 0 05 mm a full size spiral requires a minimum of 30 kg of material although smaller units can be used tests are normally performed in a closed circuit with products periodically removed and fresh material added table test shaking table tests are usually performed in an open circuit the feed material should be reasonably closely sized products can be subjected to further cleaning and computer models can determine the effect of recycling these products gravity recoverable gold test the use of centrifugal concentrators such as those made by falcon and knelson is a well established method for treating gold ore concentrators are often installed within a grinding circuit for treating a portion of the circulating load cyclone underflow a standard gravity recoverable gold test involves stagegrinding a sample 10 kg and performing a gravity separation after each grinding stage the gravity concentrate is generally cleaned using a mozley table or other laboratory panning device and the gravity tailings are combined and ground to liberate further values this method simulates gold recovery in a grinding circuit and recovers gold as soon as it is liberated so as to prevent overgrinding gravity concentrate should be cleaned to the point that it is either salable or readily processed by smelting or further processing methods such as intense cyanidation flotation testing froth flotation is a widely used beneficiation method the response of an ore to froth flotation can be readily tested in the laboratory using bench scale flotation machines samples typically 1 kg are ground in a laboratory rod or ball mill and subjected to batch tests in which samples of concentrate are collected for timed periods a flotation test program generally involves the following stages 1 determining the relationship between mineral recovery and grind size 2 collector screening 3 testing the effect of ph 4 testing modifiers to reduce or increase the floatability of minerals 5 regrinding rougher or scavenger concentrates 6 performing cleaning tests a test program often culminates in a series of locked cycle tests this laborious procedure involves a series of identical tests or cycles in which inte

rmediate cleaner tailings products are added at the appropriate point in the subsequent cycle to simulate closed circuit cleaning the tests predict how mineral values that report to the cleaner tailings during the cleaning stages will be redistributed between the final products and tailings during continual processing the locked cycle test generates a final metallurgical balance for the process and determines the final product concentrate grades and recoveries undertaking such tests requires experience and it is essential that the test be kept in balance or equilibrium such that the weight of metal in the final products of each cycle matches the input of new material gold ore testing the testing of gold ores is often complicated by the low levels of gold present sampling errors increase as the grade of gold decreases and the gold particle size increases cyanidation remains by far the most common method of processing gold and is used increasingly in conjunction with gravity processing the following cyanidation tests are available diagnostic leach test the diagnostic leach test determines the gold mineralogy or gold associations within an ore the test is actually a series of tests in which the gold in the sample is progressively recovered test stages might include the following 1 gravity testing and amalgamation to determine free gold 2 an initial cyanidation test to determine cyanide recoverable gold 3 treatment of the cyanide tailings with warm nitric acid to break down sulfide minerals followed by filtering thoroughly washing of the residue and a further cyanidation test to determine gold associated with sulfides 4 fire assay analysis of the residue to determine gold encapsulated within silicate minerals there are no standard test methods rather tests are usually tailored for a particular ore type based on the basic mineralogy of the sample bottle rolls test preliminary cyanidation tests often involve bottle rolling a sample is ground wet often without measuring particle size and placed in a bottle with lime and cyanide the bottle is then rolled typically for 24 or 48 hours and the amount of soluble gold is determined analysis of the solid residue determines the gold recovery the test is often undertaken by assay laboratories to give an initial indication of the feasibility of using cyanidation for gold recovery however the test is generally not sophisticated and the levels of cyanide and oxygen present both of which are essential for leaching to proceed are sometimes not measured agitated leach test laboratory cyanidation tests can also be performed in a stirred vessel where the pulp is agitated by a mechanical stirrer the test is akin to industrial methods of processing it enables air or oxygen to be sparged through the pulp and it is easy to monitor pulp conditions throughout the test the main process variables are grind size pulp density cyanide concentration ph and air requirement the test determi

nes whether it is advantageous to add carbon during the leaching process carbon in leach to minimize the effect of preg robbing in which soluble gold is adsorbed onto organic carbon that may be present in the ore the test can be performed with impellers and reaction vessels that give known scale up factors the dimensions and speed of the impellers should be carefully controlled and the reaction vessel fitted with baffles to improve mixing carbon adsorption test carbon adsorption tests determine the gold and silver loadings that will be achieved during continuous processing using carbon in pulp technology the test involves adding varying amounts of carbon to samples of leached pulp and determining how the levels of precious metal decrease with time test results can predict the number of carbon adsorption stages required column leach test column least tests determine the feasibility of using heap leach technology to recover gold the static tests are performed in vertical columns typically ranging from 0 15 to 0 30 m in diameter although pilot plant tests may be performed in vessels several meters in diameter the ore sample is crushed and placed in the column often on top of a filter medium consisting of crushed rock and hessian if the sample contains clay it may be necessary to agglomerate the ore using cement in the laboratory agglomeration is normally performed by rolling the sample in a cement mixer adding measured amounts of cement and water and curing for 24 to 48 hours before testing cyanide solutions are pumped into the top of the column by peristaltic pumps the solutions percolate down through the bed of material leaching gold and silver minerals they are collected and measured daily and assayed for metal content ph and cyanide concentration then passed through carbon columns to recover the precious metals the barren solutions are pumped back through the column environmental testing tightening requirements for obtaining environmental permits for mining projects are resulting in similarly increased requirements for testing of tailings low grade ore and other waste products test objectives are generally to determine the nature of the products arising from long term degradation of mineral species tailings characterization tests tailings characterization tests can involve the following analyses chemical analysis major and trace element analysis mineralogical analysis using optical methods and xrd particle size analysis chemical and mineralogical tests and particle size analysis were discussed previously the goal of these tests is to gain a basic understanding of the nature of the tailings chemical analysis should identify the presence of elements that are potentially toxic and have the potential to enter the environment acid base accounting analysis acid base accounting aba seeks to determine the acidproducing potential of tailings material the method involves determining the total sulfur and sulfa

te sulfur contents of a sample and calculating the sulfide sulfur content by difference the levels of sulfide sulfur indicate the acid generating potential of the material it being assumed that all sulfide sulfur present converts to sulfuric acid some methods involve only total sulfur analysis and assume that all sulfur present converts to sulfuric acid over time the acid neutralizing potential of a material is determined in a separate test that involves reacting a known weight of sample with hydrochloric acid and determining the amount of acid consumed by titration the net generating potential is the difference between acid generating potential and acid neutralizing potential and is normally quoted in metric tons of calcium carbonate per 1 000 t of material an alternative aba method is the net acid generating test which uses hydrogen peroxide to oxidize sulfide minerals the ph at the end of the test is regarded as a measure of the sample s ability to generate acid there are several variations of aba procedures and the methodologies are continually being refined leachate analysis two types of leachate analysis are appropriate 1 synthetic precipitation leaching procedure splp test the test determines the mobility of toxic organic and inorganic materials into groundwater it involves shaking a sample 100 g with a very dilute acid that represents rainwater and analyzing the filtered leachate for a range of determinands the strength of the acid used in the test should match the perceived levels of pollution 2 toxicity characteristic leaching procedure tclp test the test determines the mobility of the organic and inorganic phases in a material it involves shaking a sample 100 g with an acid buffer for a prescribed period of time the ph of the buffer depends on the ph of the sample the pulp is filtered and the leachate analyzed for a specified suite of 40 determinands although this can be modified depending on the material being tested humidity cell test the humidity cell test is an accelerated weathering test in which a sample 1 kg is placed in a cell and subjected to the following cycle 3 days of dry air permeation followed by 3 days of humid air permeation and 1 day of washing with a fixed volume of water the water samples are collected carefully stored and analyzed for a range of determinands the test period can range from 20 weeks to 2 years mineral resource estimation is the process of estimating the tonnage grade size shape and location of mineral deposits the ore reserve estimate follows the resource estimate and generally requires at least a prefeasibility study to establish quantity and grade of a mineral that may be profitably and legally extracted from the deposit estimation of ore reserves involves not only evaluation of the tonnage and grade of a deposit but also consideration of the technical and legal aspects of mining the deposit beneficiating the ores and selling the product estimatio

n of the mineral resource generally involves only the geologist and a resource estimator who may be a geologist geostatistician or mining engineer that specializes in resource estimation this team works together to define a resource model that defines the in situ characteristics of the mineral deposit the mineral resource model does not generally require consideration of mining costs or mining method but it may be convenient to incorporate some mining features such as bench height in a deposit that will be mined by open pit or minimum mining width for an underground vein mine reporting of the mineral resource is a different matter however and at least minimal consideration of project economics will be required to determine a cutoff grade above which resources are reported the standards for reporting resources and reserves are different for the various countries and the resource estimator must be careful to follow the appropriate regulations some examples of reporting requirements and standards include the securities and exchange commission industry guide 7 for the united states ni 43 101 for canada the jorc code for australia and new zealand and the samrec code for south africa sec 2007 national instrument 43 101 2005 ausimm 2004 samrec 2007 resource estimation methodology a resource estimate is based on prediction of the physical characteristics of a mineral deposit through collection of data analysis of the data and modeling the size shape and grade of the deposit important physical characteristics of the ore body that must be predicted include the size shape and continuity of ore zones the frequency distribution of mineral grade and the spatial variability of mineral grade these physical characteristics of the mineral deposit are never completely known but are projected from sample data the sample data consist of one or more of the following physical samples taken by drilling trenching test pitting and channel sampling measurement of the mineral quantity in the samples through assaying or other procedures surveys to determine the location of the samples in threedimensional 3 d space measurement of in situ rock density direct observations such as geologic mapping and drill core logging metallurgical testing to define the amenability of the minerals for upgrading and extraction estimation of the resource requires analysis and synthesis of these data to develop a resource model methods used to develop the resource model may include compilation of the geologic and assay data into maps reports and computer databases delineation of the physical limits of the deposit based on geologic interpretation of the mineralization controls compositing of samples into larger units such as mining bench height seam thickness or mineable vein width modeling of the grade distribution based on histograms and cumulative frequency plots of grades evaluation of the spatial variability of grade using e

xperimental variograms and selection of a resource estimation method and estimation of quantity and grade of the mineral resource the estimation procedure must be made with at least minimal knowledge of the proposed mining method because different mining methods may affect the size shape and or grade of the potentially mineable ore reserve the most important mining factors for consideration in generating an ore reserve estimate from a mineral resource estimate are the range of likely cutoff grades the degree of selectivity and the size of the selective mining unit for likely mining methods and variations in the deposit that affect the ability to mine and or process the ore these mining factors often determine the degree of detail that is required for the resource model for example a disseminated gold deposit may be continuous and regular in shape if mined by bulk open pit methods the same deposit may be discontinuous and difficult to estimate however if mined by more selective underground methods at a higher cutoff grade such large differences in deposit shape due to variations in cutoff grade and mining method may require different ore reserve estimation methods for different mining methods data collection and verification data that must be collected and compiled for the resource estimate are as follows reliable assays from an adequate number of representative samples coordinate locations for the sample data consistently recorded geologic data that describe the mineralization controls cross sections or plan maps with the geologic interpretation of the mineralization controls the geologic interpretation may be developed interactively on the computer using 3 d modeling methods in which case paper plans and sections may not be required tonnage factors or specific gravities for the various ore and waste rock categories a surface topographic map especially for deposits to be surface mined metallurgical testing for samples representative of the various types of mineralization in the deposit although small deposits may be evaluated manually using data on maps and in reports manual methods of resource estimation are nearly obsolete resource estimations are primarily done using computer methods with the resource data entered into a computer database computer programs can then be used to retrieve the data for printing reports plotting on digital plotters statistical analysis and resource estimation the minimum information that should be included in a drill hole database are drill hole name number or other unique identification hole length collar coordinates and down hole surveys sample intervals and assay data geologic data such as lithology alteration oxidation etc and geotechnical data such as rock quality designation entry of data into a computer database is a process that is subject to a high degree of error if not carefully controlled and checked some procedures that may be use

d to ensure that the data have been entered correctly are as follows verification of the data using independent entry by two persons this may also include importing of the data by two persons methods and electronically comparing the results manual comparison of a random sample of hard copy data sheets with data in the database scanning the data for outlier values for example drill locations outside the project limits high and low assays and sample intervals that overlap or are not continuous comparison of computer plotted data with manually plotted maps of the same data collar location maps and cross sections are especially useful to rapidly locate inconsistent collar locations and downhole surveys an independent audit of the data as part of statutory requirements which may be required by some regulatory bodies assay data are generally transferred from the analytical laboratory to the client using electronic means such as e mail to transfer the data in electronic format although this dramatically reduces data entry errors compared to manual keyboard entry it creates a new set of problems a particular issue is that the laboratory may change the reporting units for instance from parts per million au to ounces au t or parts per million to parts per billion from one report to the next or even within the same report the recent practice of surveying collar coordinates using global positioning system gps methods is also a frequent source of errors particular problems include reporting using different datum improper units incorrect conversion from gps units to a local survey and use of a low resolution inaccurate consumer handheld gps units the geologist or resource estimator should always ensure that the survey method survey datum data postprocessing methods datum conversions and the type of instrument are reported with the survey data additional care and attention to the detail and accuracy of the resource database are essential a database with a large number of errors may result in a resource estimate that is inaccurate and requires a complete revision to provide defensible results geologic interpretation the sample database represents a large 3 d array of point locations in a deposit the sample data are quantitative and have been subjected to minimal reinterpretation after the original measurements there is another body of geologic knowledge however that does not fit this description this is the interpretation resulting from the geologist s assimilation of the geologic data these interpretative data are often represented on plan maps or cross sections that show outlines of the geologic features or iso grade contours that define mineral zones the current industry practice is to create a 3 d model of a geologic interpretation known as a wireframe model the wireframe model is created by displaying a slice through the deposit on the computer screen and interactively digitizing the outlines of t

he geologic feature the digitized line is frequently attached or snapped to points on drill holes such as contacts and grade zone boundaries to provide a more precise location of the line relative to the locations established by the drilling the interpretation process is continued on an adjacent slice through the deposit to extend the interpretation adjacent lines are then connected using a mesh of triangles to form a continuous 3 d ribbon of triangles that links the two lines after this process has been completed across the extent of the deposit the interpretation is a series of adjacent connected ribbons that are built from a mesh of triangles the visual appearance of the resulting object the wireframe model is that of a triangular network of wires connecting an irregular set of points a significant body of mathematical tools has been developed by computer software developers to provide for manipulation and analysis of wireframe models as solid objects for use in resource estimation these interpretations provide an interpretative geologic model that is one of the most critical factors in the resource estimation failure to develop an appropriate geologic orebody model is the most common reason for large errors in the resource estimates as shown in figure 4 5 1 an inappropriate geologic model may lead to errors greater than an order of magnitude the geologist s interpretation of the ore body should be used as much as possible in developing the resource estimate there are however practical limits to the amount of complexity that can be included in the resource model and the geologic interpretation will be limited to critical inputs that define the shape and trends of the mineral zones at different cutoff grades and the character of the mineral zone contacts examples of geologic features that are often modeled include receptive versus nonreceptive host rocks alteration types that accompany mineralization or create problems in beneficiation faulting folding and other structural modifications multiple phases of mineralization and post mineral features such as oxidation and leaching changes in lithology are often important variables in resource estimation as mineralization can vary because of physical or chemical attributes of the host rocks the differences may be distinct such as the sharp contact between a skarn ore body and an unmineralized hornfels country rock they also may be gradational such as the gradual decrease in grade that is often observed between a favorable and slightly less favorable host in a porphyry copper deposit other important lithologic controls include barren post mineral intrusive rocks nonreceptive shale beds and other unmineralized materials that are contained within the mineralized zone the effects of faulting will vary according to whether the faulting occurred before or after the mineralization and what processes accompanied the faulting a simple post ore displacement

may create a discontinuity in the mineralization trends preventing simple interpolation across the fault the same type of fault occurring prior to mineralization may have little or no effect on the mineralization on either side of the fault or may localize high grade vein type mineralization that must be modeled independently of a more uniformly disseminated ore body it is also important to determine whether the fault is a thin well defined structure or many smaller structures in a complex wide shear zone in the first case the fault is modeled as a simple surface with zero thickness in the second the fault zone must be defined and modeled as a volumetric unit distinct from the adjoining rock units folding is particularly significant in sedimentary and stratabound deposits modeling of folding depends on whether folding happened before or after ore deposition on the tendency of the mineral zoning to follow the stratigraphy on any remobilization that occurred with the folding and on the creation of mineral traps or other favorable structures in addition to defining the shape of the folds it is important to determine whether the mineralization follows the contours of the folds or is independent of the fold geometry multiple phases of mineralization must be defined individually particularly where they complicate the mineral zoning pattern through overlapping discordant trends and through post mineral oxidation or leaching secondary enrichment and oxidation will almost always require delineation of these enrichment features as modified ore zones the character of the ore zone contact must be determined and input into the resource model a sharp contact will be handled as a discontinuity a hard boundary and the data used independently on either side of the contact a transitional contact however is a broad gradational boundary a soft boundary that may require data selection from zones of 5 m to more than 30 m to achieve true differentiation between the different grade zones as a transitional zone becomes thinner it will eventually approach a sharp contact for practical purposes any transitional boundary thinner than the smallest selective mining unit will be modeled as a discontinuity in addition to definition of these physical ore controls and post mineral modifications a clear understanding of ore genesis will always be beneficial in creating a resource model in the simplest case the ore genesis will give clues to the behavior of the grade distributions and variograms in other cases the genetic structure is so dominant that it can be used as a direct control in the estimation of mineral resources grade zoning is another common method for adding geologic control to the resource model grade zones are usually created by manually drawing grade contours on plans or sections through the mineral deposit correctly drawn grade zones will synthesize all of the known geologic controls and the assay grade distribution to

define a shape for the deposit that is much more informative than just the grades themselves the grade zone contours may then be wireframed to form 3 d grade shells for use in coding the block model and selecting assay data for estimation some general rules for grade zoning are as follows grade zones should be fairly smooth continuous lines if it is necessary to draw very irregular lines to contour the sample data grade zoning is generally not appropriate unless the grade zone boundary is coincident with a natural break in a grade distribution the grade zone boundaries should not be treated as strict hard boundaries for grade estimation mineralization is usually gradational across a grade zone boundary and it is generally appropriate to treat adjacent grade zones as soft boundaries and nonadjacent grade zones as hard boundaries defining a grade zone based on the anticipated mining cutoff grade and using that grade zone as a hard boundary is incorrect unless the mining cutoff grade is coincident with a natural break in the grade distribution the use of the grade zone as a hard boundary in this fashion will create an estimate that is a polygonal estimate along the boundary and additional dilution is usually required to create an unbiased estimate of the resource grade compositing compositing is a procedure used in developing resource estimates in which sample assay data are combined by computing a weighted average over longer intervals to provide a smaller number of data with greater length compositing is usually a length weighted average if density is extremely variable e g massive sulfides however compositing must be weighted by length times density or specific gravity some of the reasons for and benefits of compositing include the following irregular length assay samples must be composited to provide equal sized data for geostatistical analysis compositing incorporates dilution such as that from mining constant height benches in an open pit mine or from mining a minimum height width in an underground mine compositing reduces wild variations caused by erratic high grade values the nugget effect several methods for compositing may be used depending on the nature of the mineralization and the type of mining common compositing methods are 1 bench compositing 2 constant length downhole compositing and 3 ore zone compositing bench compositing is a method often used for resource modeling for open pit mining and is most useful for large uniform deposits composite intervals for bench compositing are usually chosen at the crest and toe of the mining benches bench compositing has the advantage of providing constant elevation data that are simple to plot and interpret on plan maps in addition the dilution from mining a constantheight constant elevation bench is approximated by the bench composite downhole composites are computed using constant length intervals that generally start from the collar

of the drill hole or the top of the first assayed interval downhole composites are used when the holes are drilled at oblique angles 45 or less to the mining benches and bench composites would be excessively long downhole composites should also be used where the sample interval is long compared to the composite interval for example if the composite interval is 10 m and the sample interval is also 10 m it is possible for a bench composite to straddle two sample intervals in the worst case the composite will be composed of two 5 m sections of the 10 m sample intervals and the resulting composite will have exactly the same grade as a 20 m composite and will contain significant excess dilution where the drill holes are drilled in many directions with respect to the ore zone the composite length may need to be varied based on the orientation of the drill relative to the ore zone for example when mineralization in a tabular structure has much better continuity along the structure than across the structure drill holes oriented perpendicular to the structure should be composited to a short interval while drill holes oriented parallel to the mineralization should be composited to a longer interval the ratio of the length of the composites should respect the relative continuity of mineralization in each direction ore zone compositing is a method of compositing that is used to prevent dilution of the composite when the width of the contact between waste and ore or low grade and high grade mineralization is less than the length of a composite use of bench compositing or downhole compositing in this case may distort the grade distributions by adding low grade mineralization to the ore population and highgrade mineralization to the waste population resulting in underestimation of ore grade and overestimation of waste grades ore zone composites are computed by first identifying the interval containing each ore zone in the drill hole each ore zone is then composited individually as follows 1 the length of the ore zone is divided by the desired length of the composite to estimate the number of composites that will be created 2 the number of composites is rounded up or down to provide the composite interval that is closest to the desired composite length and 3 the ore zone is composited using length composites starting at the beginning of the ore zone and length as determined in the previous step geologic codes are usually assigned to composites according to the rock type ore zone or other geologic feature this is often a simple procedure since most composites will be computed from samples taken from a single geologic unit assignment of geologic codes to composites that cross geologic contacts is more complex since the composite will be computed using data from multiple geologic units in most cases the geologic code for the composite is assigned according to the dominant code within the composite a special case of ore zone c

ompositing is encountered in a vein or bedded deposit in that the width of the ore zone is determined by a combination of minimum mining thickness height and assay limits in these situations composites must be computed for each combination of assay cutoff grade and minimum mining thickness that is used for the resource model if the geologic contact is transitional and does not separate contrasting grade distributions it is appropriate to assign the geologic codes according to the majority rule if the composite crosses a sharp boundary between contrasting grade distributions it is best to use geologic unit compositing or to assign the composite to the geologic unit with the most similar grade if some sample intervals in the data are missing assays it is important to determine the reason for the missing data and account for it appropriately typical examples follow the missing zone was not assayed because it was low grade or barren by visual inspection or the sample was missing because of poor core recovery in a barren zone action composite using the average of the barren unit or zero grade for the grade of the missing assay the sample was missing because of poor core recovery in a narrow post mineral fault action ignore the missing interval when computing composites the volume of the fault zone is small and the grade will be similar to the grades in the country rock the sample was missing because of poor core recovery in a vein that is higher grade and less competent than the surrounding country rock action ignore the missing interval when computing composites but retain the length of the interval for use in estimating the width of the vein computation of basic statistics and evaluation of grade distributions are the first quantitative analyses of the grade data and are basic tools to provide both feedback to the geologic analysis and input to the resource modeling important factors in these basic studies include detection of high grade or low grade outlier values evaluation of different lithologies to determine which are favorable and which are unfavorable host rocks for mineralization differentiation of complex grade distributions into simple populations for resource modeling and identification of highly skewed and or highly variable grade distributions that will be difficult to estimate basic statistics should be computed for sample and or composite grades in each geologic domain that is suspected to have different characteristics this may include different lithologies alteration types structural domains grade zones or other grouping of data that has been recognized or suspected to have different grade distributions statistics that should be compiled include number of data samples or composites average grade thickness etc mean standard deviation std dev and or variance coefficient of variation cov the standard deviation divided by average grade histogram of grades an

d cumulative frequency distribution probability plot the first item reviewed is the number of data generally at least 25 data points are required to make comparisons between different geologic domains if sufficient data are available average grades and covs will be compared among the various geologic domains general rules for evaluating differences in average grade and guidelines for analyzing covs are shown in tables 4 5 1 and 4 5 2 respectively distributions with covs greater than 25 often have a lognormal grade distribution and the basic statistics will also be compiled for the natural logarithms of grades for a perfectly lognormal distribution the lognormal statistics are the grade histogram and cumulative frequency distribution are also used to study the relationship between the statistical grade distribution and geologic parameters the analysis is usually begun with a histogram of sample or composite grades if the histogram is bell shaped and symmetrical a normal distribution is indicated and the cumulative frequency will be plotted as a normal probability graph normal distributions are not usually found in mineral deposits except for those that are very continuous and have low variability methods for resource estimation or modeling are generally divided into the traditional geometric methods that are done manually on plans or sections and interpolation methods such as inverse distance weighting and kriging that require the use of a computer geometric methods manual resource estimations are usually done on plan maps or cross sectional maps that cut the deposit into sets of parallel slices data plotted on the maps include drill hole locations assay values and the geologic interpretation of the mineralization controls true manual estimates on paper are seldom done anymore because of the widespread availability of computer software for resource estimation frequently the computer performs the same calculations as were used for the original manual methods and the results are comparable the two basic geometric methods are area averaging and polygonal cross sectional estimation area averaging the area averaging method is among the simplest of all reserve estimation methods involving only a geologic interpretation of the shape of the ore and averaging of the grades within that shape the tonnage is estimated by multiplying the density of the mineral and the volume of the zone volume is estimated by multiplying the thickness of the plan section and the area defined within the interpreted line the method may also be implemented in three dimensions using a wireframed volume in which case the average grade is estimated based on the samples inside the wireframe and the wireframe volume is calculated directly by the software despite its simplicity the area averaging method provides excellent estimates where the drilling pattern is uniform grades are continuous and ore boundaries are distinct and sharp problems may a

rise however when the drill pattern is not uniform with a nonuniform drill pattern a cluster of holes in a high grade zone will cause overestimation of grade area averaging methods also may be difficult to implement on deposits with discontinuous or spotty ore zones especially if the ore contacts are gradational and multiple cutoff grades are desired polygonal methods polygonal methods involve drawing a polygonal area of influence around each sample intersection measuring the area of the each polygon and then calculating the average grade by weighting each sample grade by the corresponding polygonal area tonnage is then computed using the same procedure as was used for the area averaging method except that the areas used to compute tonnage are the area of each individual polygon the classical manual polygonal estimate was done by drawing polygons on plan maps based on the perpendicular bisectors of the line between each drill hole as shown in figure 4 5 10 the current computer based approximation of the polygonal method is the nearest neighbor estimation this method requires superposition of a rectangular grid of blocks over the drilled area as shown in figure 4 5 11 the grade of the nearest sample is then assigned to each block this method will closely approximate the polygonal method if the block size is no more than 25 of the average drill hole spacing the polygonal nearest neighbor method has the advantage of simplicity and ease of implementation it is also independent of interpretation bias and provides an unbiased estimate of the average grade of a deposit at a zero cutoff grade this unbiased estimate of the average grade of the deposit is very useful for validation of an inverse distance power kriged or other advanced estimate the most common problem with geometric methods is that they may imply more selective mining than may be achieved by the mining method this results from estimating the resource from samples the size of a drill hole but mining larger less selective volumes high grade blocks usually include lower grade material when they are mined and low grade blocks usually include some higher grade material the resulting mined grades are different from the predicted distribution for cutoff grades below the average grade of the deposit the mined grade will be lower and the tonnage will be higher if the cutoff grade is significantly higher than the average grade of the deposit however both the mined grade and tonnage can be lower resulting in a severe overestimation of contained metasample selection criteria the purpose of the sample selection step is to provide a subset of the data that is representative of the region around the block weighted moving average methods may be very sensitive to sample selection the following rules can assist in defining a sample selection search 1 samples must be selected from geologic domains similar to that of the block 2 the maximum radius should be at least e

qual to the distance between samples to prevent discontinuities in the weighted average as samples drop in and out for a square grid the maximum radius is the diagonal 3 the maximum number of samples is usually on the order of 8 to 12 more than 12 samples rarely improves the estimate fewer than 8 samples may cause discontinuities in the estimated grades 4 a minimum distance to the nearest sample may be used to prevent excessive extrapolation 5 a search ellipse or other anisotropic pattern may be used to align the search with trends in the ore as shown in figure 4 5 13 the axes of the search ellipse should be oriented parallel to grade trends the length of the ellipse axes should be proportional to the range of continuity in the respective directions the variogram ranges and visual appraisal of the grade zones on plans and sections are both used as guides to determining the orientation and length of the search axes 6 three composites are usually the maximum required from a single drill hole more than three provides redundant data and may cause strange kriging weights for example the outermost composites in a group of five from the same hole may have larger weights than the inner points 7 search patterns may be modified to select data with quadrants or other geometric limits dilution and ore losses are a key factor in the conversion of mineral resources to ore reserves in general dilution and ore losses are related to either volume variance effects or geometric effects volume variance effects relate to the decrease in the variance of mining blocks or smus as the size of blocks becomes larger the general relationship between the variance of smus and samples was shown previously by krige s relationship equation 4 5 11 some general rules regarding volume variance effects on resource estimates are as follows 1 where the deposit grade distribution is entirely above the mining cutoff grade volume variance effects do not need to be considered 2 where the estimated variance is higher than the smu variance such as with a polygonal estimate cutoff grades below the median grade tend to underestimate tonnage and overestimate grade this is corrected by adding dilution tonnage with a grade that is lower than the cutoff grade the amount of dilution and grade of the dilution is difficult to estimate without production experience with the particular deposit or similar deposits at cutoff grades higher than the median grade of the deposit the average grade and tonnage may both be overestimated and the resource may need to be adjusted with both a dilution and tonnage reduction factor 3 where the estimated variance is lower than the smu variance such as with a kriged estimate cutoff grades below the median grade tend to overestimate tonnage and underestimate grade where the cutoff is above the median grade both tonnage and grade may be underestimated kriged distributions are difficult to correct for oversmoothing of t

he grade distribution which has been the driving force for development of the advanced kriging methods such as multiple indicator kriging and uniform conditioning geometric dilution and ore losses are due to the inability of the mining method to follow accurately and to segregate small isolated pods and small irregular offshoots from the main ore body geometric dilution is most significant in deposits with sharp contacts between high grade ore and barren waste and least significant in deposits with gradational contacts between ore and waste dilution tonnage is estimated according to the quantity of waste mined with the ore based on the mismatch between ore body and mining geometry overbreak in blasting or lack of accurate location of the ore waste contact as shown in figure 4 5 15 care must be taken in estimating dilution that the actual ore waste contact is not more irregular than the model given that dilution will be underestimated as shown in figure 4 5 16 dilution grade is estimated as the grade of the waste at the ore waste contact mining losses and grades are estimated according to similar procedures selection of resource estimation methods selection of an appropriate resource estimation method depends on the geometry of the deposit the variability of the grade distribution the character of the ore boundaries and the amount of time and money available to make the estimate deposit geometry determines the amount of detail that must be interpreted and input to the reserve estimation the variability of the grade distribution determines the amount of smoothing required to estimate mineable blocks the character of the ore boundaries determines how grade will be estimated at the borders between different grade zones and the available time and money determine the detail and effort that will be expended on the estimate considerations for selection of a resource estimation method are summarized in table 4 5 3 cost simple manual methods such as polygonal and crosssectional estimations are the least expensive and quickest methods for the estimation of resources when the quantity of data is small this is usually the case for preliminary evaluations at the exploration stage as the amount of data increases and a more detailed estimate is desired computer assisted methods should be used in order to save time and money the least expensive computer assisted methods are automated polygonal or nearest neighbor methods and the most expensive methods involve extensive definition of geologic controls in conjunction with the more complex geostatistical methods ore boundaries the appropriate reserve and dilution estimation method is determined by the character of the ore waste contacts sharp simple boundaries are modeled with linear outlines defining discrete mineral zones individual estimations are made for each mineral zone dilution is estimated based on the intersection between the shape of the mineral zones and the shape defined

by the geometry of a mining method a sharp irregular boundary is also described with linear boundaries defining mineral zones the actual ore waste contact will be much more irregular than the interpreted boundary and dilution must be increased accordingly geometric methods are usually appropriate for ore bodies with sharp contacts although kriging or inverse distance methods may be used within the zones if supported by sufficient data gradational boundaries are handled as transitional between different mineral zones kriging or inverse distance methods are most appropriate to model ore bodies with gradational contacts sufficient dilution for a gradational contact is usually incorporated in the modeling method extremely erratic irregular boundaries are difficult to define accurately and are most appropriately estimated using methods such as indicator kriging deposit geometry simple geometry is often found in tabular stratabound deposits veins and structural zones the geometry of these deposits is easily described using two dimensional 2 d methods such as contouring of thickness and elevation few additional controls are required other than boundaries to limit the lateral extent of the mineral zones deposits with moderately complex geometry include both deposits with simple geometry that have been moderately folded or faulted and deposits with large simple massive shapes such as porphyry copper and molybdenum definition of deposit geometry will include definition of fold axes fault boundaries and zoning of trends within the deposit although these controls are not usually difficult to define their definition is necessary to provide accurate resource estimates deposits with very complex geometry are usually associated with structural deformation and are folded faulted stretched and twisted to form extremely discontinuous shapes that are difficult to describe and model multiple ore controls such as a combination of stratigraphic and structural controls or multiple overlapping pulses of mineralization also commonly form very complex shapes definition of deposit geometry requires detailed examination of structural geology and ore controls to provide cross sections or plan maps that define the shape and location of mineral zones these sections or maps may then be used directly for manual resource estimation or may be digitized to provide control for a computer block model or 3 d wireframe model deposits with complex geometry are prone to large estimation errors because of misinterpretation of deposit geometry and ore controls order ofmagnitude errors are not infrequent grade variability deposits with low variability may be estimated with many methods common methods include automatic contouring and polygonal methods with cross sectional estimation or area averaging techniques for more complex geometry weighted averaging methods kriging and inversedistance are most commonly used for estimation of deposits with mode

rate variability although polygonal or cross sectional methods are also used weighted averaging methods may require recovery functions and polygonal methods may require dilution to compensate for volume variance effects although in most cases the adjustments are small on the order of 5 to 15 weighted averaging methods are most commonly used for estimation of deposits with high variability other appropriate methods may include indicator kriging polygonal and cross sectional methods volume variance effects are often large with these deposits and must be compensated for with recovery functions for weighted averaging methods and large dilution of polygonal and cross sectional reserves for covs above 2 0 or 3 0 local grade estimates are extremely difficult and must be tempered with judgment and caution the valuation of mineral properties or mining companies involves the integration of geology mining processing mineral markets society and the environment accordingly it is common for a multi disciplinary team to work on valuation efforts and their findings to be incorporated into the valuation it is essential however that any effort be led by an experienced valuator who assumes responsibility for the valuation report what is a valuation how does a valuation differ from an evaluation an evaluation simply focuses on the technical aspects of an asset or assets whereas a valuation focuses on the worth of the asset two major factors are considered 1 highest and best use although all mineral containing properties have an inherent value which in itself does not indicate that a valuation of the minerals is required the valuation performed must be based on the highest and best use of a property an example would be a mineral deposit suddenly discovered on an undeveloped property in the middle of an area with developed residential or commercial real estate it is possible that the value of the real estate would exceed the value of the minerals the highest use or if it did not that real estate development was the only possible use of the property because of zoning or environmental factors the best use therefore unless the valuation was for a condemnation proceeding specifically to value the mineral interest the highest and best use would be deemed to be real estate development 2 fair market value fmv the valuation should always be based on the fmv of the asset which is the price an asset would be exchanged for with the parties being a willing buyer and seller with both parties having access to the same information about the asset and with neither party being under compulsion to buy or sell the asset types of properties valuation methods vary in type and effectiveness for both undeveloped properties and properties already in operation properties warranting or requiring a valuation can range from raw land where the presence of minerals is only suspected to large developed properties that have been mined for many

years the commodities can include metallic minerals nonmetallic minerals energy minerals and gemstones valuation assumptions before a valuation is undertaken certain basic assumptions must be satisfied mineral development is the highest and best use of the property unless the valuation is for condemnation purposes a fair market value is attainable all lands have an inherent value for minerals that might occur on them a market exists for the mineral or minerals that may be on or under the land economic realism must be employed e g a granite deposit under an ice cap would have no value whereas one adjacent to a major city could be developed for aggregates or dimension stone existing mineral valuation codes although valuations of assets have many things in common it is recognized that the valuation of mineral deposits properties or mining companies requires expertise beyond that offered by the typical appraiser in recognition of these differences specific codes governing the valuation of mineral deposits and properties have been developed by professional mining associations in countries where mineral resources significantly contribute to the economy valmin code australasian institute of mining and metallurgy this code is statutory in australia cimval code canadian institute of mining metallurgy and petroleum this code is due to become statutory in canada samval code south african mining associations this code is statutory in south africa the mining and metallurgical society of america is in the process of developing recommended standards for mineral property valuation in the united states the international valuation standards council is also developing guidelines for the valuation of mineral properties these are anticipated to focus on market factors and will potentially be in conflict with the above three codes unless specifically requested otherwise mineral property valuations should be carried out in accordance with one of the valmin cimval or samval codes standards the choice of code will depend primarily on the reporting location of the company as well as the property the party requesting the valuation and the party carrying out the valuation types of valuation methods there are three primary methods of valuations 1 the income cash flow approach whereby the cash flow resulting from a financial model is discounted at an appropriate rate to yield a net present value npv 2 market related approaches which develop a value based on recent related transactions and the market multiples approach for publicly traded companies or from recent transactions 3 the replacement cost approach in which the cost required to duplicate the asset being valued is assessed secondary methods include option real option pricing valuations and monte carlo simulations table 4 6 1 lists the six valuation methods together with the types of properties to which they are applicable the methods themselves a

re described later in more detail in contrast to the other methods listed in table 4 6 1 the income approach should yield a true or long term value over the life of the asset provided that the inputs to the cash flow model are realistic the market related transaction or market multiples approach on the other hand provides a snapshot value at the time of the valuation the derived value will likely be higher than the income approach value in prosperous times and lower in difficult times the market multiples approach differs from the marketrelated transaction method in that rather than comparing the asset against one that was recently sold it is based on the value ascribed by public markets to units of production of specific commodities an example would be to base the valuation solely on the pounds of copper or ounces of gold recoverable from the property when market valuation methods are used it is essential that they be adjusted to reflect the realities and characteristics of the asset or company being valued failure to allow for these differences will result in incorrect valuations thus a property containing 1 million ounces of recoverable gold with the capability of achieving full cash plus capital production costs of 200 per ounce is clearly worth much more than another million ounce property whose full production costs are forecast to be 400 per ounce similarly an underground gold property with a refractory ore would be negatively viewed when compared with an underground gold property with an ore that would only require simple flotation and concentration the replacement cost approach can be used as a check on one of the other methods or alone if none of the other methods is particularly applicable this method puts a value on finding another similar mineral property and replacing similar infrastructure that previously existed this method is most commonly used for valuing early stage exploration properties or properties that have ceased operations but still have resources or reserves when using this approach it is essential to consider improvements in technology the option real option pricing valuation approach should be used only to value a company with multiple operations rather than an individual property this method is described later in this chapter the monte carlo simulation approach is a method of analysis based on the use of random numbers and probability statistics to investigate problems with variable potential outcomes in financial analysis and valuation there is a fair amount of uncertainty and risk involved with estimating the future value of financial numbers or quantity amounts because of the wide variety of potential outcomes i e grade of deposit reserve tonnage commodity price operating costs capital costs etc the use of monte carlo simulation is one technique that can be applied to evaluate the uncertainty in estimating future outcomes and allows for the development of plans to mitiga

te or cope with risk typically with conventional spreadsheet models the engineer geologist or analyst creates models with the bestcase worst case and average case scenarios only to find later that the actual outcome was very different with monte carlo simulation the analyst explores thousands of combinations of the what if factors analyzing the full range of possible outcomes an iterative process yielding much more accurate results with only a small amount of extra work thanks to the numerous choices of monte carlo simulation software that are available the monte carlo simulation cannot eliminate uncertainty and risk but it does make them easier to understand by ascribing probabilistic characteristics to the inputs and outputs of a model the determination of the different risks and factors affecting forecasted variables can lead to more accurate predictions the desire of all mining managers reviewing table 4 6 1 one can observe the four stages in the life of a mineral property and the likely applicable valuation methods for each one early stage exploration properties are the hardest to value whereas operating stage properties are usually the easiest in between those two stages more than one method can usually be employed with a weighted average value based on the strength of each method used or range of values developed from which a preferred value can be derived it is also possible for a given property to be in more than one stage at any given time one such example is a property with undeveloped resources undergoing exploration very near an operating mine valuation methods for developed or operating properties properties that are developed i e ready to operate or are operating and have a financial history are usually valued by the income approach this approach employs the life of mine production schedule forecast or actual operating costs forecast sustaining and replacement capital costs and reclamation closure costs on the assumption that these have been correctly forecast and projected the only parameters that would be subject to dispute in this method are the commodity prices and the discount rate used in the valuation some other valuation methods used for developed or operating properties include liquidation value market related values replacement value and the value of a royalty stream if the property is being valued for a lessor income cash flow approach the income or cash flow method involves constructing a financial model of the cash flow covering the expected life of the mine generally up to the first 20 years of production the financial model should be based on constant dollars where product selling prices cash operating costs and future capital requirements are not inflated varied it is appropriate to change future operating costs over time by reflecting changing physical conditions such as longer haul truck cycles reduced metallurgical recoveries because of a change in th

e character of the ore body and similar measures that the mining professional can predict to perform an accurate valuation using this method the following inputs are required ore reserves over the life of mine resources can be included if factored for their probability of conversion to reserves however the valuator should be cognizant of regulatory requirements such as those of the tsx venture exchange a canadian stock exchange that precludes the inclusion of resources in a cash flow model production rates operating costs including on site general and administrative g a costs ongoing development costs and nonincome taxes capital costs preproduction and sustaining replacement environmental and reclamation costs commodity prices discount rate the commodity prices and discount rate utilized in the cashflow valuation are two critical items that are based on the valuator s experience and judgment because of the critical impact these two inputs have on the income approach valuation they should be developed by the valuator from first principles commodity price selection while valuations are forward looking income approach valuations should normally incorporate a constant commodity price based on longterm historical data commodity prices should reflect the up and down cycles which are common to the mineral industry it is the authors experience that a 10 year period would normally incorporate both cycles when valuing an operating property or one near operating status however it is acceptable and appropriate to include consensus pricing for the first 2 or 3 years of operation prior to returning to the long term price as an example when an examiner values an operating copper property if the copper price for the last 10 years has averaged 1 75 per pound but the current price is 3 50 per pound the consensus view might be to use 3 50 per pound for year 1 of the cash flow model 3 00 per pound for year 2 2 25 per pound for year 3 and then level off at the 10 year average price of 1 75 per pound for the remainder of the mine life discount rate determination the discount rate essentially reflects the risks present in an investment and is the rate at which the cash flow from a mining property or of a mining company will be discounted it is never appropriate when conducting a valuation to arbitrarily assign a discount rate rather the discount rate should be derived from first principles three methods are employed for deriving a suitable discount rate the method selected is based on the nature of the asset being valued 1 weighted average cost of capital wacc method 2 capital asset pricing model capm 3 risk buildup method weighted average cost of capital discount rate derivation the wacc method is based on the proportional cost of equity and debt for a particular corporation at a specific time it should be used as a discount rate only for companies it is not appropriate for valuing single project

s the key strength of the wacc method is that it incorporates the global risks of all of a company s operations and projects into a single rate which should reflect the melded risks of the company s assets capital asset pricing model the capm was developed as a valuation tool for shares of publicly traded stocks it incorporates various elements of an investment including the riskfree rate of return offered by u s treasury bills and notes the greater risks inherent in stocks versus other investments and the volatility of the shares of a company compared to the average company s shares as measured by its beta note beta is a measure of a stock s price volatility in relation to the rest of the market in other words it is a guide on how a stock s price is likely to move relative to the overall market beta is calculated using regression analysis the whole market which for this purpose is considered to be the standard and poor s 500 s p 500 is assigned a beta of 1 stocks that have a beta greater than 1 have greater price volatility than the overall market and are more risky conversely a beta lower than 1 denotes less volatility than the market and therefore less risk for example if the market with a beta of 1 is expected toreturn 8 annually a stock with a beta of 1 5 should return 12 young technology stocks will always carry high betas many utility stocks on the other hand carry betas below 1 the capm method is appropriate only for valuing companies it is not appropriate for establishing the discount rate for individual mining projects or properties importantly the discount rate derived is after tax for a seller of the shares and pretax for a buyer of the shares risk buildup discount rate derivation the risk buildup method is preferred by the authors of this chapter as it reflects the values relevant to the specific properties in form it is similar to the capm method however it is differentiated by its inclusion of the technical and other risks associated with the typical mining project essentially it adds the components of risk at the project to arrive at an overall risk rate for a given specific property or group of properties the usual components incorporated are the real risk free rate of return the risk premium expected by an investor who would invest in mining projects which can be assumed to be the same as that for a publicly traded company there would be additional premium if the project being valued would have a market capitalization of a small cap i e less than 200 million mining industry specific risk and site specific risk for individual properties with a public company risk premium investors clearly require a greater return on their investment than that provided by risk free u s treasury notes they are willing to accept additional risk for the expectation of a greater return if the company involved is a large one s p500 the risk premium for such shares can be found at t

he ibbotson associates web site the risk in 2007 was about 7 if the company has a market capitalization of less than 200 million i e small cap an additional risk premium is warranted in 2007 this was an additional 3 for a total public company risk premium of 10 with mining industry risk based on historic company and industry returns on equity there is an above average risk premium for certain industries these include the aggregate mining and petroleum industries all of which are dependent on the vagaries of natural resources in 2007 the industry risk premium for the mining industry was 2 5 with site specific project risk multiple risk factors exist at mining properties ranging from reserve risk through processing environmental political and geotechnical risk following are some of the factors that need to be considered project status this involves exploration development or in operation as a project advances through these stages the risk factor will normally decrease for a mature operating property that is performing up to forecasts the risk will be lowest quality of analytical data if the quality of the data derived from the drilling sampling and assaying of the ore body is suspect the project risk must reflect this uncertainty processing related risk this risk can be high if adequate metallurgical test work has not been performed on samples truly representative of the whole ore body or if new unproven technology is being employed infrastructure related factors risks can occur if there are unusual circumstances that might cause interruption to the power and water supply or cause access to the property to be lost environmental considerations in contrast to projects 20 or more years ago a project located in a sensitive environmental setting must be given a risk rating higher than one that is isolated and insulated from likely environmental damage government regulatory and permitting risks are thus assessed operating and capital costs and working capital poorly predicted figures for these three items introduce substantial risk the most common of these is an underestimation of total project capital prices and markets price projections on which the project economics are based must be realistic and there must be a market for the product produced labor management issues the availability education and trainability of the required labor force in less developed countries is an issue union activism poses a risk to some projects the quality and experiences of the company s management must be considered political and social issues and the social license to operate the lack of perceived support from the local inhabitants and government bodies is a major risk it is not always possible to secure good information on all of these factors affecting site specific project risk if possible a matrix should be constructed with a ranking from 1 to 10 assigned to each factor from this an

overall risk factor can be assigned for an exceptionally low risk project a factor of 1 or 2 may be chosen for one with many uncertainties the factor is likely to be 5 or higher summary of risk buildup discount rate table 4 6 2 is an example of a risk buildup discount rate showing both pretax and after tax figures since the discount rate developed is pretax it must be converted to an after tax basis other factors to be considered in the income approach valuation method two other factors should be taken into account in an income approach valuation of a property or properties the first and more important of the two comes into play if an acquisition is involved and if the acquirer will end up being in control of the property properties or company given that the acquirer will be in charge of his or her own destiny he or she is not subject to the bad decisions of a senior owner if he acquirer is in charge a control premium should be added to the total valuation obtained from the income approach method the amount of this premium cannot be standardized and depends on the type of company and its position in the development operating chain during 2007 the control premium for acquisitions of large properties and companies frequently exceeded 30 the second factor to be considered is a terminal value of the free cash flow for operations that have a life exceeding that of the financial model a terminal value is commonly arrived at using the assumption that ongoing operations will mirror the conditions that applied to the last 5 years of the cash flow valuation unless there is good reason to expect an ore grade change or a metallurgical recovery change and so forth to occur market related transaction on the surface the market related transactions or comparable sales approach valuation method should be the simplest to understand and the easiest not to fault one can simply find several recent transactions with their documented purchase prices and then compare the price paid per pound or ounce at that property with the one requiring the valuation unfortunately it is not that simple no two mining properties are even remotely identical due to differences in all the parameters that were itemized in the site specific project risk discourse previously discussed even parts of the same mineral deposit can be different nevertheless because of the perceived simplicity of the method this is a frequently used valuation method and is a preferred technique by the international valuation standards council to achieve even relative comparability all transactions considered must be adjusted in relation to the property being valued for example if both are narrow vein underground gold properties and one has a grade of 0 6 ounces per ton and the subject property has 0 3 ounces per ton the value of an ounce at the subject property will obviously be lower than the property it is being compared with similar adjustments need to be made

for mining costs processing costs political factors geography and so on market related transactions as applied to exploration properties generally little information is available about exploration properties due to the early stage of the property in the mine development cycle assuming that results are positive the value of exploration properties increases with the level of work performed frequently a prospectivity factor is added or deducted to the value based on known results regional settings and history by the time that a property has either been fully explored reached the development stage or started production there are likely to be other transactions that can be used for developing a market related transaction valuation provided that the individual differences between the properties are taken into account market related transactions as applied to development or operating properties when a property is either in development or operating there will be much credible information available for it and unless the commodity is an unusual one there are likely to be several fairly recent comparable transactions to reference for the valuation even so care must be taken in two areas 1 the transaction prices for the comparables must be adjusted to present day conditions when either or both metals prices and costs of production may have changed and 2 the transaction prices must be adjusted to reflect the different variables that will have affected the price paid for each property including the relative size of the mineral deposit differences in ore grade mining method and processing recoveries and methods and the amount and cost of required infrastructure operating and capital costs environmental and social issues tax regimes and political risk market multiples valuation the market multiples valuation method has similarities to the market related transactions valuation method and has some of the same drawbacks principally property or corporate differences it also has the advantage wherein other transactions comparable existing properties do not have to be identified and evaluated market capitalization which is the quoted share price multiplied by the number of issued shares can be divided by many factors to derive a value per ounce or pound of proven and probable ore reserves or resources the value per pound or ounce of annual production the multiplier given to earnings and so forth these different metrics constitute a market multiples valuation and these can then be used to develop a generic value for the company such figures are available for many mineral companies enabling an average valuation per unit of the metric to be established a market multiples valuation can also be based on a multiple of average annual cash flow and a multiple of earnings before interest taxes depreciation and amortization again adjustments must be made to ensure that the value developed is truly based on com

parable factors for example a market capitalization value for a major mining company with several producing mines should not be used to develop a market multiples value for a junior company with only one producing mine replacement cost valuation replacement cost valuations are simply the expenditure that would be required in current dollars or other currency units to duplicate a prior effort replacement cost valuations are most commonly used for exploration properties at various stages and operations that have been shut down with remaining resources or reserves for exploration properties the costs of land acquisition duplicating any geological geochemical or geophysical work duplicating the prior drilling and assaying performed and so forth are determined as the basis of the property s value any negative results must be considered and using the appraiser s judgment they may be subtracted entirely or included in a factored manner when being applied to operations that have been dormant for a period of time but which still have facilities in place the replacement cost valuation focuses on the current cost required to replicate the facilities a factor that must be considered is whether new technology has made the original equipment obsolete if such is the case the cost of the new technology must be included although it is possible that this would overvalue the property another factor that should be considered is whether there has been any change in the markets for the commodity that was previously produced if the property is being valued by the replacement cost method and resources and or reserves are still present the value could be based on the cost of replacing those ounces pounds or tons present option real option pricing valuation although used less frequently than the methods already described the option real option pricing valuation method is one that can be used for valuing mining companies with multiple operating properties the philosophy behind options is based on the formula developed in 1973 by black and scholes to be used in the valuation of equities as currently applied to mineral properties option valuations are based on the following premises the income approach valuation method may undervalue both producing and nonproducing mining assets this is generally true in boom times but incorrect in difficult times mining properties offer the opportunity to be shut down when economics are negatively affecting cash flow and reopened when economic factors are positive although this is true in concept in practice closing and reopening mines based on volatile economic changes is impractical and would potentially be financially ruinous if attempted by mining companies the cost of shutting down maintaining the property on a standby basis and the time it would take to reopen and ramp up production is not considered in option theory mining properties offer a call option on increases in metals

prices if the gold price is for instance 300 per ounce then a property requiring a price of 350 per ounce to generate a positive cash flow has a finite value note for readers not familiar with the concept of options reference is made to puts and calls on 100 shares of a stock on a major stock exchange simply each call gives the call owner the right to purchase 100 shares of the stock in question at a fixed price for a fixed period of time the lower the fixed price and the longer the period of time the higher is the price of buying the call for example if party a owns 100 shares of a stock currently selling at 100 per share and the calls on a price of 110 per share expiring 2 months in the future are trading at 3 per share then party a can sell a call on his or her stock and immediately pocket a check for 300 if the stock does not reach the call price of 110 per share in the next 2 months party a will have made 300 and will still have the stock in the meantime party b has bought party a s call for 300 but if the stock does not reach 110 a share within the 2 month time period party b will have lost their 300 however should the price of the stock rise to for instance 116 per share before the 2 months are up party b will have doubled their initial investment of 300 party b s call gives them the right to buy the stock at 110 per share and they can turn around and immediately sell it for 116 per share thus realizing a net profit of 300 when considering the use of option valuations it is also important to recognize that the longer the option period the higher the value will be the greater the volatility of the commodity price the higher the value will be this valuation method will always produce the highest and probably unrealistic value and this method is applicable to valuations of companies not single properties monte carlo simulation the monte carlo simulation method can be used for any properties that are at least at the advanced exploration phase monte carlo simulations allow for multiple variables to be changed simultaneously while a specific operation is mathematically performed literally thousands of times the probabilistic value results from a range of probabilities assigned to each variable in the analysis i e capital and operating costs and commodity prices to arrive at a most likely value or range of values as based on iterations of cases that sample the distributions of each variable alternative valuation methods for undeveloped properties undeveloped properties include those with blocked out resources or properties with drill holes that have ore grade intercepts although the lack of concrete information makes the valuation of such properties more difficult a probability approach such as the risk adjusted income approach can be used the approach entails the construction of a financial model of the property using likely production rates ore grades minin

g and processing methods and capital and operating costs a justifiable commodity price is chosen the real risk free rate of return is used for the discount rate and the discounted cash flow is calculated the valuation for an example property then becomes the calculated npv say 100 million as adjusted for the percentage probability that the items incorporated in the financial model such as ore reserves costs and environmental risks have been correctly estimated if the risks for the stated items are respectively 80 90 and 50 the valuation would be 36 million 100 million 0 8 0 9 0 5 alternative valuation methods for exploration properties exploration properties include those where no work has been performed and those where some work has been performed for properties where no work has been performed two methods are commonly used 1 the valuation is a percentage of the surface value of the property for no work of any kind in a mineralized or unmineralized area the percentage is 5 for raw property but where initial reconnaissance has indicated favorable potential the percentage is 10 2 the valuation is the money that has been spent in staking leasing and maintaining the property for properties where some exploration work has been performed the following methods are commonly used modified cost of work performed with prospectivity factors included geoscience matrix valuation in the modified cost of work valuation method the direct costs of work performed are added to valid g a costs to arrive at a base value if there have been some highly favorable exploration results some enhancement of the base valuation is appropriate similarly if results on or at nearby similar properties have been negative a negative prospectivity factor is applied the geoscience matrix valuation method was developed by lionel kilburn for the british columbia securities commission to assist them in validating the values being assigned to exploration properties by junior mining companies five major criteria are considered which are divided into nineteen possibilities 1 the location of the property with respect to off property mineralization 2 the presence of any on property mineralization 3 the location of the property with respect to off property geochemical geophysical geological targets 4 the presence of any on property geophysical geochemical targets and 5 geological patterns on the property associated with known commercial deposits the starting point or base value for the valuation is the per acre or per hectare cost of acquiring the right to a mineral property usually the cost of staking and maintaining a claim for 1 year the property is then rated on the basis of its score from the matrix and this rating is then used to adjust the base value the value from the matrix is arrived at by assigning points in the five categories based on whether the property is above or below average table 4 6 3 illus

trates how the matrix rating is derived in the rules of thumb valuation method the valuation is based on a percentage of the commodity s price with the percentage dependent on the state of advancement of the particular property table 4 6 4 based on more than 500 transactions analyzed by frank ludeman in his publication a decade of deals gives the range of percentages for the different stages of properties ludeman 2000 the rules of thumb values provided in table 4 6 4 should be considered as generic and the actual percentage a property will value varies with the tenor of the mining industry the 500 properties studied provided an average value and the percentage of the commodity price assigned to a property should be based on its characteristics versus that of the average property required qualifications for a valuator the required qualifications for a valuator will depend to some extent on the complexity of the property to be valued as well as on the type and number of the methods to be employed in the rules of thumb valuation method the valuation is based on a percentage of the commodity s price with the percentage dependent on the state of advancement of the particular property table 4 6 4 based on more than 500 transactions analyzed by frank ludeman in his publication a decade of deals gives the range of percentages for the different stages of properties ludeman 2000 the rules of thumb values provided in table 4 6 4 should be considered as generic and the actual percentage a property will value varies with the tenor of the mining industry the 500 properties studied provided an average value and the percentage of the commodity price assigned to a property should be based on its characteristics versus that of the average property required qualifications for a valuator the required qualifications for a valuator will depend to some extent on the complexity of the property to be valued as well as on the type and number of the methods to be employed the greater the complexity and the number of methods to be this is the single most important principle that must be faithfully followed by any company doing property evaluations likewise it would help investment houses if all of their potential clients had projects that had equivalent feasibility studies that were more or less comparable at least with respect to completeness one of the primary purposes of this chapter is to instill in each reader the concept that there must be a strictly regimented method of complete property evaluations leading to feasibility reports what must be considered for a proper feasibility study for a properly documented property evaluation quite simply everything must be considered however that does not really help much in knowing how to start and what to look for more specifically there must be an examination of the potential mineral operation such as determining the mineral resource and reserve estimate if there is one det

ermining a mining method based on the measured and indicated resource reviewing the mineral extraction flow sheet performing a market analysis determining infrastructure needs quantifying the environmental and socioeconomic impacts and mitigation required estimating the costs of these factors and then performing an economic analysis of the assumed revenues versus the costs to determine if the project meets the company s objectives objectives of mineral property feasibility study it is often assumed that the feasibility study s objective is to demonstrate that the project is economically viable if it is developed and exploited in the manner laid out by the study but this assumes that every mineral deposit evaluated can be profitable of course this is not true development of most of the earth s mineral deposits is not currently viable so what should be the objective of mineral property feasibility study it should be to maximize the value of the property to the company by determining either to exploit it sell it wait for a technology or market change or do nothing it should also be the objective to reach that decision as early as possible with the least amount of money spent but how can this be done how does a person know when they have studied each of the hundreds of items of information enough so that they have confidence in the feasibility study and the economic analysis based on that study one learns to perform a feasibility study by a phased approach to mine evaluation several authors hustrulid and kuchta 1995 gentry and o neil 1992 stone 1997 taylor 1977 and in fact most mineral companies take a similar approach to mineral property evaluation industry approach to feasibility studies on rare occasions the activities required in a feasibility study are often described as a single continuous process from the time the resource is identified until a decision can be made to develop the property this one step approach in which single feasibility leads directly to development may sometimes be correct for extremely high grade ore bodies or if the company requires development for some reason in a specific time frame but the one step approach is risky from a technical and an economic point of view such methods will usually develop an operation that is in fact suboptimal even though it still may meet the company s needs furthermore it may cost the company far too much money to find out that the project economics prove inadequate most companies and books on the subject recommend a phased approach to mineral property evaluation content of classic three phased approach lee 1984 describes a classic three phased approach as follows stage 1 conceptual scoping study a conceptual or preliminary valuation study represents the transformation of a project idea into a broad investment proposition by using comparative methods of scope definition and cost estimating techniques to identify a potential inve

stment opportunity capital and operating costs are usually approximate ratio estimates using historical data it is intended primarily to highlight the principal investment aspects of a possible mining proposition the preparation of such a study is normally the work of one or two engineers the findings are reported as a preliminary valuation stage 2 preliminary or prefeasibility study a preliminary study is an intermediate level exercise normally not suitable for an investment decision it has the objectives of determining whether the project concept justifies a detailed analysis by a feasibility study and whether any aspects of the project are critical to its viability and necessitate in depth investigation through functional or support studies a preliminary study should be viewed as an intermediate stage between a relatively inexpensive conceptual study and a relatively expensive feasibility study some are done by a two or three man team which has access to consultants in various fields others may be multi group efforts stage 3 feasibility study the feasibility study provides a definitive technical environmental and commercial base for an investment decision it uses iterative processes to optimize all critical elements of the project it identifies the production capacity technology investment and production costs sales revenues and return on investment normally it defines the scope of work unequivocally and serves as a base line document for advancement of the project through subsequent phases frequent problems in classic three phased approach however some pitfalls are associated with using the classic approach as used by much of industry this approach is a nonuniform nonsystematic nonstandarized approach to feasibility conceptual scoping study a conceptual or scoping study can be extremely misleading nearly every exploration project that is even slightly submarginal can be shown to be worthy of further development based on casual educated guesses and optimistic simplified or even biased evaluations back of the envelope approaches to a mine feasibility study need to stay on the backs of envelopes and out of formal official looking reports at its worst this type of report can be performed by the exploration firm or project sponsor to try to sell the project to someone else however when an independent third party does the conceptual scoping study it can be employed as a useful tool for the potential investing company to determine if it wishes to proceed to the next phase of feasibility study or to calculate what the project might be worth on the open market also this approach might be appropriate when looking for commodity targets for the exploration group but not for further in house decisions to move the project to the next level based on the exploration group s mining and milling judgments this is not to say that conceptual unclassified screening studies do not have their place in justifying other

types of work but care and caution are needed so the conceptual study is not dignified beyond its engineering basis in fact some countries security exchange agencies such as the canadian securities administrators csa allow and specify such a preliminary study which they call a preliminary assessment as identified by the csa such a report includes a statement that this assessment is preliminary in nature that it includes inferred mineral resources that are considered too speculative geologically to have the economic considerations applied to them that would enable them to be categorized as mineral reserves and there is no certainty that the preliminary assessment will be realized and states the basis for the preliminary assessment and any qualifications and assumptions made by the qualified person it is completed without substantial engineering studies in a conceptual or scoping study the accuracy of the cost estimates are most often assumed in fact the accuracy of all levels of feasibility studies depends on how much good engineering has been performed on the specific project if none then the project s related cost and economics are not likely to be accurate and the study is likely to be misleading typically at this stage one might do 1 or 2 of the total engineering on the project bear in mind that for a small project this may amount to 1 800 to 2 400 hours of engineering work but for a large project this percentage may amount to 9 000 to 18 000 hours of engineering then using good engineering judgment experience and cost on similar projects the accuracy of the scoping study feasibility may be in the 45 range other authors claim that an accuracy of 30 is achievable for a conceptual scoping study white 1997 however this accuracy will likely not be achieved unless the project is being developed in an old district where a mine or plant has recently been built and the new installation is similar to the existing one the 30 accuracy will only be attained after 10 to 12 of the engineering has been completed prefeasibility study the problems that have been found with many prefeasibility studies that followed conceptual or scoping studies as outlined is that often this phase simply follows the path set by the conceptual study there is a reluctance to spend the time and money for a feasibility team to go back and justify the concepts chosen for the mining method processing method necessary infrastructure waste disposal method and overall size of the operation likewise there is a reluctance to spend the time to optimize any of the functional operations at a time when the project team is small another observed problem is that some of the elements or activities of the prefeasibility study will be taken too far in application and the project s proponents will invariably proclaim to others in management and the investors that the study is really more than a preliminary feasibility study although t

his is probably not so it will give members of management and possible financiers some unjustified overconfidence in the project another critical failure that often occurs in this system of feasibility progression is that the preliminary study is the chance to find the fatal flaws of the project if it has any sometimes this does not happen or the flaws may be found in the scoping study one definitely does not want fatal flaw discovery after a large engineering group has been assembled to work on the final feasibility study because by this time the project s momentum is huge and it will cost a lot to stop the project if the project is being undertaken by a company listed on the canadian or u s stock exchange then inferred mineral resources may not be used for mine planning purposes except if a small zone of interburden exists between measured or indicated resource material that must also be mined final feasibility study when using the classic approach by the time one gets to the final feasibility study the project direction of each element has usually been set for all aspects of the project to proceed at the same pace from this point there is little opportunity to stop and examine the many interrelated operating variables that should have been examined at an earlier stage of the study thus it is likely that a nonoptimized design will emerge from this type of study as a result the mining industry is full of nonoptimized mines and plants that have been built because those optimization studies did not take place at the proper time which in this case was during a prefeasibility study sometimes toward the end of a final study the operating management realizes that certain aspects have not been optimized and subsequently major last minute adjustments are implemented in an attempt to mitigate these errors usually such actions are based on less than the amount of engineering analysis that went into the original planning and the accuracy of such last minute changes and the ripple effect to all other aspects of the project particularly the environmental and regulatory engineering damage the credibility of the entire project recommended approach because of the problems outlined previously regarding industry abuses to the nonuniform ill defined classical threephased approach a more rigid uniform engineered and systematic three phased approach to mineral property feasibility is recommended in a more general way this has been suggested by hustrulid and kuchta 1995 and by gentry and o neil 1992 using the work of gocht et al 1988 and taylor 1977 but what is considerably different as defined here than what has been suggested by others is the sheer magnitude of details enumerated by engineered task rigorously following the details a description of which is contained in the iteration of each phase makes this method unique and bankable nowhere else has this amount of detail of the tasks required in a mineral prope

rty feasibility study been documented and published in publicly available literature many of the larger mineral groups such as bhp billiton rio tinto and anglo gold probably have equally as well documented activity lists for each step of the feasibility studies but they have not been publicly published the need for such an approach was imperative because many companies have eight to twelve mineral project feasibility studies to manage at one time it would not be unusual for such studies to address four or five different mineral commodities located in four or five different countries all having different starting dates and mine life and being studied at one time by several different project teams it is only by formalizing the feasibility study process that management can be assured that items will not be left out or that some activities would not be studied in too much depth although some companies may not have a dozen projects going at one time under the conditions described the established procedure will serve any user of the system well and yield project results that are comparable for financial decisions this chapter examines the engineered systematic threephased approach to a mine feasibility study although not the only system available many believe it is the safest and most prudent method as different situations arise on different commodities the project manager may believe that some steps can and should be omitted however one must also be aware of the potential consequences when taking shortcuts particularly if the company s experience is weak in this type of new project while looking at the details of the long lists of items that need to be studied in the different phases described in the next section the reader may believe there are far too many activities and the time and expense required to accomplish them is too great some may choose to combine many of the activities of the preliminary study with the intermediate study this may be possible and is discussed later however one must be careful that this combination does not dilute the preliminary intermediate study such that a financial decision can t be made with confidence some may believe that items can be eliminated or that the study of certain items is not applicable but a great amount of caution should be used in eliminating any study aspect unless the company has so much experience and data on that particular aspect that the study is simply not necessary the three steps of feasibility studies recommended here are 1 preliminary or conceptual feasibility 2 intermediate prefeasibility feasibility and 3 final feasibility although these appear similar to some of the systems previously mentioned they are not the same learning the content of these three studies and how to apply the work from one level of effort to the next are important parts of this chapter what will be covered is a brief description of the activities at each level of study an

d how to move a project from exploration through the feasibility phase and then to engineering design or to the back burner or for sale work breakdown structure another important aspect is to apply controls to portions of the study to do this one must first organize a list of work categories and assign numbers to them this is known as a work breakdown structure wbs no two people will develop identical wbss the important thing is to get the work organized so that it can be tracked both from an accounting and scheduling point of view and to track it on a computer within each of the three levels of the feasibility study are 50 to 150 major activities for each major activity there are 10 to 20 elements or work types a large mining company trying to grow or even holding on to its depleting asset may have as many as eight to twelve projects going at any one time at various levels of study because of the complexity of accounting for everyone s time and charging expenses to ongoing work a numbering system to keep track is essential in addition to the billing and accounting a robust wbs ensures that all activities can be handled and scheduled on a computer this is no small task because many of the activities feed information to other activities before they can begin all major projects use such a system and all u s government projects require a wbs as defined by the american association of cost engineers a wbs is a product oriented family tree division of hardware software facilities and other items that organizes defines and displays all of the work to be performed in accomplishing the project objectives an additional advantage is that if the wbs is written in a generic way all of the projects within a single company can follow the same structure thus ensuring comparable completeness for any future level of study the wbs method outlined in table 4 7 1 is a generic wbs that could be used on any number of mineral projects it also uses the project phase as part of the identification writing a wbs for each project is possible but the comparison between all of the projects would be more difficult and possibly less accurate the wbs number system carries through the six steps from the preliminary study through the project design construction and into operations the wbs illustrated here is in two parts 1 in table 4 7 1 where the first number of each line signifies the phase or step that the project is in when the activity occurred and 2 in table 4 7 2 where the numbers on each line refer to the various types of chargeable activities that occur in all of the phases thus for a market investigation and planning activity in the mine plant operation phase the wbs number would be 61300 but if the market investment and planning study occurred in the final feasibility study the wbs number would be 31300 it can be seen that a screening project is not included because it only officially becomes a project when it passes

a screening activity within each project phase a further breakdown of the numbering sequence identifies major areas of work an example of how this might be broken down is shown in table 4 7 2 the feasibility study definitions of each activity serve as a checklist and with time elements applied to each activity and subactivity form the basis for building a project schedule each project will have unique characteristics that will require changes to the activities listed but the general logic and activity identifications should apply to most mineral projects to be evaluated the more consistent the approach the more accurate the comparison in choosing between the various mineral projects using this numbering system and applying time elements to each activity by number allow a schedule network to be built on the computer breakdown of the engineered systematic three phased approach this section and appendices 4 7a d provide a detailed description of the activities and sequences that are recommended to properly perform a mineral property feasibility study with the expectation that the property if developed will perform at the levels predicted by the feasibility study in the appendices some numbers in the sequence appear to be missing to allow for future additions to the wbs system phase i preliminary feasibility study although the objective of each phase of every mineral property feasibility study should be to maximize the value of the property to the company by determining how to proceed with it more specific to the preliminary feasibility study is to consider those logical mining and processing methods and other project elements in just enough detail such that one can determine that they will work together to meet the company s objectives which are usually financial and estimate the capital and operating cost commensurate with the engineering that has been expended depending on the country where the study is to be governed the product must meet the standards of the u s securities and exchange commission industry guide 7 sec 2007 the australasian code for reporting of exploration results mineral resources and ore reserves the jorc code prepared by the joint ore reserves committee ausimm 2004 or canada s national instruments 43 101 and 43 101cp the preliminary study is based primarily on information supplied through exploration the company management should tell the exploration group that its report must contain the following information with appropriate maps and cross sections property location and access description of surface features description of regional local and mineral deposit geology review of exploration activities tabulation of geologic resource material explanation of resource calculation method including information on geostatistics applied description of the company s land and water position status of ownership and royalty conditions history of the property rock qualit