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llic ores is expressed as a percentage or as grams per ton which is equal to ppm parts per million the minimum grade in an ore needed to become a profitable extraction is called cut off grade or simply cutoff see 7 chap 4 this concept is essential in all mining projects a prospect is a term mainly used in mining exploration it can be broadly defined as a limited area of ground with a possibility to include a mineral deposit it commonly receives the name of a geographical location finally there are some terms that are also frequently used in mining but they are combining words such as mineral occurrence ore deposit more or less similar to mineral deposit ore reserves mineral prospect etc a mineral resource classification is used to organize information about raw materials or commodities of economic value the classification systems can be grouped into three main categories which are the most accepted by the industry resource companies the financial community and the regulatory bodies a classifications developed by government agencies e g geological surveys these classifications use a combination of both enterprise data and geological studies human societies need natural resources for their existence including wood water and minerals which are essential in the growth and prosperity of the modern way of life it is necessary to construct roads with aggregates and bituminous materials to build houses with concrete formed principally by aggregates and cement both obtained from minerals or to manufacture cars with aluminum and steel in the day to day minerals are present everywhere since the carpet for our feet very early in the morning made with calcium carbonate among others or the coffee pot made of either glass or ceramics until the medicine or pharmaceuticals many excipients are minerals the communications equipment incorporates numerous minerals for example quartz or silica for the silicon chips in pc or coltan used in many digital products including the cell phones finally high level technological products can incorporate more than 70 different metals therefore exploitation of minerals provides the necessary raw materials for manufacturing construction and chemical industries to obtain mineral raw materials the mining companies have to develop a complex time consuming and high risk process however the consumption generates sometimes harmful consequences being an example the everyday violence in congo this is because the control of coltan production essential when making the new generation of cell phones since demand of coltan is growing exponentially in the last years the so called three t s tin tungsten and tantalum which can be found in coltan are the best known conflict resources produced in the congo in this sense the oecd promoted at 2011 a due diligence guidance the guidance aims to help companies respect human rights observe applicable rules of interna

tional humanitarian law in situations of armed conflict avoid contributing to conflict and cultivate transparent mineral supply chains and sustainable corporate engagement in the mineral sector the distinct phases in successful mine development and production involves finding outlining and evaluating a mineral prospect mine construction and exploitation processing of runof mine material obtained in the mine and post mining closure and reclamation all these activities jointly form what is called the mining cycle or mining life sequence fig 1 9 each step in the sequence is unique and most mining projects proceed progressively from one step to the next it is important to bear in mind that the timescale from discovery of a mineral deposit to mine production is generally a very long one fig 1 10 for example small mining projects may pass from exploration to mine production within a few years followed by closure of the mine 10 years after the start of operation on the contrary large and complex mining projects may spend 20 years for exploration and several decades for mining regarding expenditures of the mining projects overall expenditures can range from usd 100 million for small projects to several usd billions for large projects the search for mineral resources usually called exploration or prospection is the first step in the mine cycle and includes a complete sequence of multidisciplinary activities mineral resources are rare and they are buried beneath the surface of the earth economic mineral resources are even rarer since mineral deposits are rare finding one is challenging and the odds of success of any exploration program are relatively low even where a mineral deposit has been defined the probability of it becoming an operating mine is at best one in a thousand at a preliminary exploration stage large areas of possible economic interest prospects are evaluated by airborne or ground based geophysical methods from the obtained maps and existing data specific areas are singled out for more detailed studies a second stage involves specific surveys including additional mapping sampling take a small representative portion of a larger mass and drilling preliminary understanding of the deposit type facilitates the design of appropriate and effective exploration program in this regard mineral deposit models play an active role because these models provide a framework for research in economic geology as well as background for mineral exploration prior to geological mapping satellite imagery science of acquiring processing and interpreting images obtained mainly from satellites and aerial photography have proven to be important tools to define mineral exploration projects providing reflection data and absorption properties of soils rocks and vegetation this makes it easier to map terrain elevation large scale geological structures like faults or geological contacts and also to plan

regional mapping or soil stream sampling campaigns in some regions such as deserts color changes may denote variations in rock type or show places of rock alteration used extensively for exploration for more than 100 years geological mapping provides many types of information essential in exploration for new mineral resources the map scales can range from 1 100 000 to 1 25 000 or even 1 10 000 depending on the stage of exploration from regional scale geological mapping to district scale exploration targeting geological mapping of outcrops is also utilized to describe the lithology and morphology of rock bodies as well as age relationships between rock units and improves the utility of geophysical data for refinement of subsurface targets traditional paper recorded geological mapping data are now commonly converted to digital format in the office and analyzed with gis software geochemical exploration also known as geochemical prospecting and exploration geochemistry as defined by hawkes 1957 includes any method of mineral exploration based on systematic measurement of one or more chemical properties of a naturally occurring material the purpose of the measurements is the discovery of a geochemical anomaly or area where the chemical pattern indicates the presence of ore in the vicinity the database obtained in geochemical prospecting the sets of data often contain thousands of observations with as many as 50 or more elements provides an opportunity to discover a wide range of geochemical processes that are associated with underlying geology alteration or weathering and mineralization the interpretation of database obtained in geochemical prospecting commonly including thousands of data requires special handling using univariate analysis combined to bivariate and multivariate analysis another classic method used in mineral prospecting is geophysical exploration working on principles of physics to study earth interpretation highlights signal of mineral related features under investigation or nongeological the geophysical anomalies must be explained geologically and can indicate possible occurrences of mineral resources first airborne geophysical surveys fig 1 11 provide the quickest and often the most cost effective ways of obtaining geological information about large and unexplored areas a more detailed ground survey is carried out once a target area is identified using techniques such as seismic surveys direct sampling and drilling finally exploration drilling is performed mainly from the surface with holes laid out on a prescribed grid or pattern there are two main methods of drilling in mineral resources exploration core drilling and reverse circulation drilling core drilling is the most commonly used method of getting information about the subsurface presence of minerals this technique yields solid cylinder shaped samples of the ground at an exact depth the other method is reverse circulatio

n drilling which produces samples called chips formed by small particles of sediment or rock in reverse circulation drilling the cuttings from the hole are transported to the surface where they are collected in plastic bags this method offers higher productivity than diamond core drilling but the quality of the samples is obviously lower for this reason diamond core drilling has long been the preferred choice of many exploration companies nevertheless a combination of these two methods can often provide the optimum solution offering the most cost effective way of working on the other hand underground drilling often drilling the holes at any angle is essential to explore and define new mineral resources to mine in the future the mineral resource evaluation process commonly involves a technical and an economic stage plus a socioeconomic one technical evaluation fig 1 12 leads to the estimation of tonnage quantity and mineral or metal content quality from analytical data calculated in samples assays either globally or for parts of the deposit the estimation is obtained through classical or geoestatistical methods the first methods are old style but easy to understand methods some of them were developed before the twentieth century and examples of these methods are panel section polygons inverse distance weighted triangulation and contour methods the selection of the specific classical method can be modified based on the type and form of the material contained annels 1991 the uncertainties in determining the level of significance and confidence of traditional estimations with classical methods are overcome by application of geostatistical procedures matheron 1962 being this modeling method paramount in modern mineral resource estimation the most important step in geostatistical procedure is the spatial correlation among samples regionalized variables it is expressed by the semivariogram and the kriging technique using the obtained semivariogram let to interpolates the needed values e g grades for mineral resource estimation after technical evaluation the selection of the most adequate economic evaluation method is of crucial importance to carry out this economic evaluation many other variables of the project such as production cost capital cost royalties taxes among many others are also needed it must be taken into account that mining industry presents different characteristics than other industries for instance mining industry needs many years of production before a positive cash flow and requires longer project life moreover the overall process is extremely capital intensive the most significant feature which sets mining projects apart from other commercial activities lies in the nature of the main asset the mineral deposit this asset is imperfectly defined it is not possible to move it is depleted and exhausted in several years and it cannot be replaced the predominant e

conomic evaluation technique for a mineral project is the discounted cash flow method using net present value npv internal rate of return irr and payback period pp calculations this methodology is easy to understand and accepted by the industry and the financial community for this reason all the mining project evaluation processes for investment decision worldwide are based on these indexes because many of the items included in the calculation of npv irr and pp are almost impossible to be predicted the process must be adjusted to risk from a financial viewpoint the risk is the possibility that shareholders will lose money where they invest in a company there are quite a number of methods to evaluate the risk being the monte carlo method probably the most used and well known especially since the introduction of the computing equipment the monte carlo method is based on the simulation of the various sources of uncertainty affecting the studied value and subsequent determination of the average value over the range of resultant outcomes if the economic evaluation of a mining project offers positive results pointing to high probability that the exploitation of the mineral deposit will produce benefits mining will be the next step exploitation or mining is the process of excavation and recovery of ore and associated waste rock from earth s crust mine method selection criteria is based on rock competency distance to surface characteristics of the mineral and economics conditioned by the distance to surface the mining methods are broadly grouped into surface fig 1 13 and underground fig 1 14 about 85 of the global tonnage is produced in open pit mines including placer operations while the rest 15 from underground mines ericsson 2012 operating mines range from small size underground operations to large open pit some of them moving tens of thousands of rock per day surface mining is a form of operation led to extract minerals lying near the surface in the last decades surface production spreads out since openpit mining is less expensive than underground mining due to the higher cost of underground extraction methods the depletion of richer mineral bodies combined with the development of new technologies makes necessary to work in open pit mines with lower mineral contents the present day tendency is large scale surface mining using the economy of scale that is the saving in cost of production that is due to mass production in mining language a big mine will produce significantly more output per unit of input than will a small mine thus large scale equipment are used to make operations efficient and economical for example today trucks are huge carrying up to 500 tons per load if the depth of an ore deposit is such that removal of overburden makes surface mining unprofitable underground methods must be considered underground mining refers to extraction of raw materials from below the surfac

e of the ground one logical procedure to categorize underground mining methods is to divide them into the following three groups a methods producing openings naturally supporting or requiring minimum artificial support e g room and pillar b methods requiring substantial artificial support e g cut and fill and c caving methods where collapse of the rock is integral to the extraction process e g block caving for instance in the room and pillar method very common in underground mining the minerals are obtained from large voids rooms and pillars are left between the rooms to support the overlying rocks in general the mineral body included in the pillars remains upon completion of mining and is not recovered if the mineral body extends from surface to great depth mining sometimes starts near the surface from an open pit and later continues the exploitation with underground mining for the deeper parts of the mineral body this method is usually called combined mining the use of explosives is often indispensable in mineral resources exploitation therefore blasting is usually a part of the mining cycle blasting is the process of fracturing material by the utilization of an amount of explosive loaded in special holes there are many different types of explosives used today such as anfo ammonium nitrate plus fuel oil slurries and emulsions the holes drilled for blasting are loaded so that each one is fired in a designed sequence to obtain the desired break of the rocks the explosives are then detonated in the drill holes after exploitation mineral processing separates useful minerals from waste rock or gangue producing a more concentrated material for further processing the concentration of valuable minerals in the run on mine material is also known as beneficiation or concentration process the objective is to reduce the bulk of the material using cheap and low energy physical methods to sort out the valuable minerals from the waste rock in general the heavier the material the more costly it is to transport therefore metal ores become much lighter once upgraded to concentrates or processed into semi finished products making them more economical to transport long distances thus metal ores are commonly processed at least partly close to their extraction site the material obtained in the mine is concentrated using particle size reduction fig 1 16 liberation and concentration with mainly physical methods to begin the rock is crushed grinded and classified utilizing a very broad variety of equipment the primary crushing can be carried out during the mining especially where an underground method is selected regarding concentration or beneficiation methods there are many types since metal content and physicochemical properties of minerals are quite different it is necessary to produce concentrates of every category with maximum efficiency the three main groups of concentration systems me

thods are magnetic gravity and froth flotation methods the last one being the most used to concentrate metallic minerals magnetic methods use the difference in magnetic properties of the mineral particles they are implemented in four different ways being the devices distinguished firstly on the basis of dry or wet material and secondly on the basis of magnetic field intensity high or low gravity concentration separates grains of minerals depending on their density the separation process is also determined by the size of the particles minerals with value can be removed along with the material despite differences in density if the particle sizes change for this reason particle sizes must be uniform and the use of as screens and hydrocyclones is essential however most of profitably minerals e g sulfides of cu zn or pb pge minerals and many others are best suited to froth flotation method this concentration method is a technique where particles in a mineral water slurry are adhered to air bubbles using chemical reagents which preferentially react with the desired mineral then the particles are carried to the surface and removed in general it is very useful for processing fine grained ores and can be applied to many types of mineral separations e g separating sulfide minerals from silica gangue removing coal from ash forming minerals or separating different industrial minerals among others the nonvalue minerals obtained in froth flotation or any concentration process are disposed to tailing pond or void filling stabilization of underground mines since water is usually involved in the concentration process the last stage in mineral processing is to remove water in the slurry this process is called dewatering and commonly starts with thickening utilized if the liquid to solids ratio is high the mechanism employed is based on sedimentation where the solids are allowed to settle through the liquid phase resulting in a liquid essentially solid free and a thickened slurry afterwards vacuum or pressure filtration is applied to remove water from the slurry using a porous filter medium which prevents the passage of the solid particles the product obtained usually named cake can be already sent to metallurgy process two different types of equipment are commonly used in vacuum filtration drum and disk filters on the other hand pressure filtration is carried out with plate filter mine closure is the last phase in the mining cycle since mining is a temporary activity with the operating life ranging from some years to several decades closure starts when the mineral resource is exhausted or operations are no longer profitable mine closure plans are required by most regulatory agencies worldwide before a mining permit is granted financial assurance is required in many countries as a guarantee that the funds needed for mine closure will be available if the responsible company is unable to complete the proc

ess as it was planned reclamation which occurs at all stages of the mine life environmental analysis begins at the earliest stages of the exploration of the mineral resource involves earthwork and site restoration including revegetation of disposal areas fig 1 17 the aim of reclamation must always be to return the site to a condition that match the premining condition other possibilities include to use the mine sites recreational areas gardens parks etc previously an environmental impact assessment eia is requested and presented an eia can easily be defined as a study of the effects of a proposed mining project on the environment the environmental impact assessment process is an interdisciplinary and multistep procedure to ensure that environmental aspects are included in decisions regarding mining projects potential environmental impacts linked to mining activities include impacts such as hazardous materials land use biodiversity visual impacts and air and water quality among others in general underground mines are much less apparent than surface mines and they disturb a relatively small area of the land surface close to the principal shaft where underground mining activities finish the shafts can be sealed and the area returns to previous condition especially in which respects to visual impact in relation to the impact of waste disposal tailings dam which usually incorporate small amounts of harmful elements it can contaminate surface and groundwaters occasionally tailings dam failures cause huge environmental disasters as occurred in alnazc llar spain in 1998 where los frailes mine tailings dam failed and released five million cubic meters of acidic tailings the fine grained material contained dangerous levels of several heavy metals that travelled about 40 km before it stopped just near a unesco world heritage site do ana national park which is one of the largest national parks in europe although the definition and classification of mineral resources and reserves shown in 7 sect 1 2 are widely accepted and used in many countries the main guidelines to apply these terms are undoubtedly the international reporting standards also known as mineral reporting codes they are essential nowadays to any project evaluation process of mineral resources especially if the financial world is involved it is important to note that mineral resources and reserves are the most important economic asset for a mining company since the financial strength of the enterprise depends mainly on the size and quality of its resources and reserves however reported mineral reserve data for mining projects include numerous types of uncertainty such as geological estimation and difficulties to predict the future commodity price dimitrakopoulos and abdel sabour 2007 since a reserve is only a small portion of the total ore body variations in price obviously alter reserve estimations for this reason regulatory guide

lines for reserve estimation must take in consideration the potential economic variability in the complete lifetime of the mining project evatt et al 2012 mining is historically important in many regions around the world being the major mining centers countries such as australia south africa the usa and canada thus these countries together with europe especially the united kingdom are the main sources of capital for mining projects for this reason these countries have promoted the reporting standards most used worldwide after its initiation in the usa australia got ahead in providing codes and guidelines for reporting and classifying mineral resources and reserves omitting the mckelvey box really the precursor to mining codes the first international reporting code was the jorc code australia it was published in 1989 and later updated afterwards a rapid increase in the creation of these codes and standards in other countries was produced this process of creating new standards began in the late 1990s and continues today these standards codes derived from the globalization of the mining industry and their objectives are to give a certain level of comfort to investors and other stakeholders regarding quality and usefulness of valuation of mineral deposits see bre x affair in box 1 4 the increasing investment by foreign countries in developing countries of asia africa and south america among other reasons needs to an international method to define the assets of mining companies and also the mineral wealth of the countries major mining companies commonly finance new projects internally and develop many times their own systems of control although these are usually similar to common codes and standards a relevant exception is that the responsibility for determining and certifying ore reserves lies on a qualified team of professionals rather than an individual expert broadly international reporting codes can be classified into two groups a international systems crirsco and unfc and b national codes e g 43 101 jorc or sma there are differences between them but certainly many terms and definitions are similar in all documents mineral resources are present in the earth s crust a thin outer shell about 10 100 km thick which comprises no more than 0 4 of the earth s mass being assigned the rest of the mass to the core and mantle the oceans are underlain by a thin 10 km homogeneous crust that covers approximately 70 of the surface and the continents have a much thicker crust 30 100 km covering the remaining 30 the continental crust is quite more inhomogeneous since magmatic sedimentary and metamorphic processes have led to segregation and local concentration of elements it represents the main focus of exploration and exploitation of mineral resources the average concentration of elements in the earth s crust controls the occurrence of mineral deposits nine elements called major elemen

ts make up over 99 5 of the continental crust while the rest of the elements called minor and trace elements account for less than 0 5 table 1 2 major elements are abundant enough to form the most usual minerals and rocks but minor and trace elements including most of the metals need to be enriched under exceptional geological conditions to form exploitable mineral deposits usually combined with other elements like oxygen oxide sulfur sulfide and sulfate and carbon carbonate thus although any piece of rock in the earth s crust contains small amounts of metallic and nonmetallic elements a specific natural process is necessary to produce sufficient enrichment of the element to form an exploitable mineral deposit fig 1 20 an additional point is that processes forming mineral deposits operate at geological time scales so that most economic mineral resources are basically nonrenewable in other words new deposits are impossible to be generated in human timescales the distribution of mineral resources in the earth s crust is irregular from not only a commodities point of view but also considering the geographical position of the mineral deposits across the different continents the major reserves of metal ores are geographically concentrated in a handful of countries even the distribution of the valuable mineral in each deposit is varied according to the grade and the tonnage of the mineralization geographically the global distribution of mineral resources depends on the type of mineral or metal thus gold deposits are present in more than 100 countries but the largest reserves are concentrated in south africa 27 28 of world s reserves on the contrary platinum metal group deposits are known only in 16 countries and the share of two largest countries south africa and russia covers 97 of world s reserves in general the global distribution of mineral resources is very conservative and it was not changed over a long time for instance today world s reserves of tin are distributed in the same countries and regions as they were 30 years ago although the contribution of each country or region has changed these variations of the contribution are related to the world economic development and the situation of the raw material markets for every substance it is possible to calculate a value called concentration or enrichment factor dividing the economical concentration that is the necessary concentration in a mineral deposit for profitable mining by the average crustal abundance for that substance concentration factors and average crustal abundances for some of the most important metals are listed in for example aluminum average crustal abundance of about 8 has a concentration factor of 3 4 because a mineral deposit of aluminum e g gibbsite mineral can contain between three and four times the average crustal abundance to be economical between 24 and 32 aluminum obviously this enrichment o

r concentration factor is very different for each element ranging from low values 3 4 for aluminum to very high values 4000 5000 for gold it is essential to estimate the amount of a given mineral resource in the world from its abundance in the earth s crust the reason is that strategic planning for future supply of a mineral or a metal is controlled by the estimates of prognostic resources although the predictions of undiscovered resources quantifications are obviously very difficult the methods proposed are usually based on extrapolation of resources in well known regions to less known but geologically similar parts of the earth e g singer and menzie 2010 however the topic of mineral resource assessment is quite complex assessment methods considered were time rate crustal abundance cumulative tonnage versus grade geometric probability and discriminant analysis among many others the selection of the method to be employed in an assessment must be based on different factors such as adequacy of the material to the problem constraints in resources e g information or time forthcoming for the assessing the level of uncertainty and acceptance of errors in the evaluation and finally the requirement for checking outcomes and approval of the technique singer and mosier 1981 mckelvey 1960 was one of the first authors to analyze the distribution of mineral resources in the earth he pointed out that the tonnage of mineable reserves in short tons r for many elements in the united states was equal to crustal abundance in percent a times 109 to 1010 and that the linear relation that appears to prevail between reserves and abundance is useful in forecasting reserves in large segments of the earth s crust or over the world at large even for purposes of estimating world reserves of unexplored elements mckelvey affirmed that a figure of a 1010 to 1011 probably will give the right order of magnitude in other words reserves for some elements exhibit a constant ratio to their average crustal abundance and for less explored commodities the reserves can be estimated from well explored ones with regard to the question as to whether or not the usa is a representative sample of the earth s crust it does have all the major kinds of geological terranes found anywhere and may be accepted as a reasonably representative sample of the earth s crust the total amount of different metals in the earth s crust can be calculated combining crustal abundance data and the mckelvey reserveabundance relationship thus the potential recoverable resource in metric tons for most elements should approach 2 45a 106 where a is abundance expressed in parts per million erickson 1973 if the abundance reserve relationship is accepted the amount expressed is a minimum total resource estimate because the relationship is based upon currently recoverable resources and does not include resources whose feasibility of economic recovery is not e

stablished the abundance reserve relation should become more closely defined as analytical techniques progress as the understanding of geochemical processes enhances and as exploration techniques advance and it was possible to explore and examine the crust until a reasonable depth estimating contemporary reserves is very useful but it is only a starting point because the focus of the question is not on the short term but on long sighted availability e g graedel et al 2011 these authors tried to estimate the extractable global resource egr that is the quantity of a given resource that is judged to be worthy of extraction over the long term given anticipated improvements in exploration and technology for most metals considering that information available on the potentially extractable geological resources of metals is negligible the main conclusion of this study was that it is not possible at the moment reliably to estimate the extractable global resource egr for any metal the aforementioned aspects deal with the distribution of mineral resources in big areas or regions even in the earth as a whole however a crucial point is to know how the resources reserves grades and tonnage are distributed in a mineral deposit with a gradation from relatively rich to relatively poor mineralization that is to say the relation between grades and tonnages in an ore deposit lasky 1950 was the pioneer in applying mathematical laws to predict reserves of ore deposits and to study how the recoverable reserves of porphyry copper deposits a copper deposit type see 7 chap 2 varied as a function of the usual selection criterion the grade in cu percentage box 1 5 lasky s law the relationship between ore grade and tonnage in a mineral deposit can be analyzed in terms of fractals turcotte 1986 because grade relations and tonnage for economic ore deposits show a fractal behavior if the tonnage of ore with a specific mean grade is proportional to this mean grade raised to a power if it is assumed that the concentration of elements in ores is statistically scale invariant the renormalization group approach can be used to derive a fractal relationship between mean grade and tonnage moreover the obtained results are independent of the mechanism of mineral concentration as long as the concentration mechanism is scale invariant this approach would not be expected to be valid if different concentration mechanisms are operative at different scales thus in terms of fractals the relationship between ore grade and tonnage in a mineral deposit can be defined by using the following equation turcotte 1997 c c m m d ore ore min min 3 where core is the average grade of the tonnage more cmin is the minimal grade included of the mass mmin and d is the fractal dimension mmin may be the mass of ore exploited at the lowest grade mine or even source rock from which the ore in a district is thought to be derived based on thi

s correlation undiscovered resources can be estimated tonnage versus cut off and average grade versus cut off models can be outlined according to the fractal distribution of element concentrations considering that the cut off grade has great influence on the reserve and resource calculation in a single deposit wang et al 2010 another possibility is to combine the fractal modeling and geostatistics for mineral resource classification to look for a clear separation identification and assessment of high grade ore zones from low grade ones in a deposit which are extremely important in mining of metalliferous deposits e g sadeghi et al 2014 compared to existing methods of mineral resource classification the technique that combines geostatistics and fractal modeling can address the complexity of the data for different parts of a mineral deposit natural resources provide essential inputs to production world population is growing faster than at any time in history meanwhile mineral consumption is increasing more quickly than population as new consumers enter the market for minerals and as global standard of living rises according to gl ser et al 2015 the rapid economic development of emerging countries in combination with an accelerating spread of new technologies has led to a strongly increasing demand for industrial metals and minerals regarding both the total material requirement and the diversity of elements used for the production of specific high tech applications therefore minerals and metals are consumed in greater quantities than ever before since 1900 the mine production of the main metals has increased by several orders of magnitude graedel and erdmann 2012 fig 1 21 increased world demand for minerals will be affected by three factors kesler 2007 applications for mineral commodities the level of population that consumes these raw materials and the standard of living that will establish how much each person consumes as new materials and applications are found markets for mineral commodities can expand considerably in this sense present technologies utilize almost the entire periodic table the best way to mitigate the problem of mineral resources depletion is to use them in a sustainable way the definition of sustainable development that is most commonly used today was presented by the united nations in 1987 the brundtland report in this report sustainable development is defined as development that meets the needs of the present without compromising the ability of future generations to meet their own needs this has become the most accepted definition of sustainable development internationally this report stressed the need for the world to progress toward economic development that could be sustained without permanently harming the environment in this sense the discovery of new reserves may be viewed as only a temporary possible solution to mineral resource sustainability other potential

solutions to sustainability of mineral resources include the following wellmer and becker platen 2007 1 improvement removal from the deposit 2 finding new material to replace 3 enhancing recycling processes 4 decreasing consumption by more efficient use and 5 looking for new possibilities on the other hand the concept of sustainable production and consumption was implemented at the beginning of the 1990s its main goal is the correct production and use of natural resources the minimization of wastes and the optimization of services and products sustainable production and consumption intends to provide the utilization of goods and services over the life cycle so as not to jeopardize the needs of future generations sustainable consumption symposium in oslo norway 1994 regarding substitution of mineral resources to promote sustainable development the importance of the hierarchy of relative mineral resource values must be emphasized according to this model wellmer and becker platen 2007 the most valuable resources energy resources occupy the top of the hierarchy the next lower value category consists of those mineral resources whose deposits are created by natural enrichment for example metalliferous deposits and some nonmetallic deposits like phosphate and barite the next lower level consists of bulk raw materials such as those used in construction and those whose availability from a geological viewpoint is unlimited in the earth s crust finally waste products and residues from beneficiation or burning of higher value resources occupy the lowermost part of the hierarchy obviously if possible the main goal of any policy leading to mineral sustainable development is to utilize low value resources at the base of the mineral resources hierarchy thus the high value resources at the top are conserved another relevant tool for comparing materials consumption is eco efficiency which combines the notions maximum environmental and economic benefit and minimum environmental and economic cost eco efficiency also decreases raw materials consumption throughout the life cycle to a limit more or less in line with the earth s calculated capability this concept focuses heavily on effective resource consumption and the reduction of waste fleury and davies 2012 the role of developed countries in sustainable development is crucial since these countries are mostly involved in mineral resource consumption and depletion for instance europe environmental footprint is one of the largest on the planet if the rest of the world lived like europeans it would require the resources of more than two earths to support them for this reason some developed countries such as eu countries have elaborated extensive programs trying to resolve the dualism rich countries poor countries as an example of these programs the european union eu is developing the named sustainable consumption and production and sustainable indus

trial policy action plan this plan includes different actions of which 11 are devoted to natural resources europe 2020 strategy has as its flagship initiative a resource efficient europe to help decouple economic growth from the use of resources being the resource efficiency the key political priority previously the eu raw materials initiative of 2008 included an integrated strategy based on the following three pillars 1 ensure access to raw materials from international markets under the same conditions as other industrial competitors 2 set the right framework conditions within the eu to foster sustainable supply of raw materials from european sources and 3 boost overall resource efficiency and promote recycling to reduce the eu s consumption of primary raw materials and decrease the relative import dependence there is a growing awareness that the construction structures building and other products in the economy today could be the urban mines of the future oecd 2015 thus anthropogenic stocks have been less studied than geological stocks they represent a growing area of interest particularly in industrialized economies the global market of mineral raw materials is characterized by a increasing demand for minerals from both industrial and developing countries b dramatic changes in where minerals are sourced c volatile markets and pricing and d increased vulnerabilities in the mineral supply chain in this framework modern society is increasingly dependent on mineral resources which differ in their availability the way of use the cost of production and their geographical distribution raw materials are essential for the development of the economy of industrialized regions sectors such as construction chemicals automotive aerospace and machinery are completely dependent on access to certain raw materials european extraction covers only 29 of the demand for concentrates necessary to meet the requirements for production in metallurgical plants therefore the potential effects of mineral supply disruption are essential for maintaining and improving the quality of life moreover a type of scarcity referred to as technical scarcity or structural scarcity presents a particular challenge and may be difficult and expensive to alleviate technical scarcity applies chiefly graedel et al 2014 to a range of rare metals used mostly in high tech applications where geological stocks are limited but manmade stocks are believed to be large much of the study of anthropogenic stocks focuses on metals because they can be infinitely recycled and unlike minerals which dissipate with consumption e g fossil fuels salt for deicing metals retain their chemical and physical properties over time many of the potential negative environmental impacts associated with the production and consumption of metals can be reduced using these anthropogenic stocks with recycling simultaneously pressure on virgin sto

cks could be diminished many of these are not mined on their own rather they are by products of the mining of the ores of the more common and widely used metals e g aluminum copper lead and zinc these byproducts are present as trace constituents in the ores of the host metals and under favorable economic conditions they can be extracted from these ores which means that there is a little economic incentive to increase production at times of shortage demand for a variety of mineral resources such as rare earth elements rees platinum group elements pges beryllium and lithium among others has increased with continued consumption in developed economies and the emergence of other developing countries such elements are crucial to a variety of manufacturing high tech and military applications in this framework many governments consider that a stable supply of some mineral resources is essential for economic prosperity it is important to note that the production of minerals that supply many of these elements is concentrated in a few countries thus china produces more than 95 of the global rare earth elements supply and almost 80 of global platinum production is from south africa table 1 4 european commission 2014 indicates the primary supply in percentage of some critical raw materials from most important producing countries in this scenario the concept of critical mineral or raw material must be introduced the term criticality was first used in 1939 the american administration decided in those days to build up a stock for 42 raw materials with military relevance this was enforced by the socalled critical material stock piling act the geopolitical situation after the end of the cold war relaxed but the stock piling of military relevant raw materials is continued until today achzet and helbig 2013 the national research council in the book entitled minerals critical minerals and the u s economy 2008 mentions the difference between strategic and critical commenting that the terms critical and strategic as mineral or material descriptors have been closely associated but commonly not definitely differentiated a mineral can be regarded as critical only if it performs an essential function for which few or no satisfactory substitutes exist thus the dimension of criticality is therefore related to the demand for a mineral that meets very precise specifications required in certain key applications but it is not simply related to overall demand for all applications furthermore a mineral can be regarded as critical if an assessment indicates a high probability that its supply may become restricted leading either to physical unavailability or to significantly higher prices for that mineral in key applications consequently the two main dimensions of criticality are importance in use and availability obviously the criticality of a specific mineral can change overtime as production techno

logies evolve and new products are developed a more recent definition in the american mineral security act of 2015 us congress says that a critical mineral means any mineral element substance or material designated as critical pursuant to 1 subject to potential supply restrictions including restrictions associated with foreign political risk abrupt demand growth military conflict violent unrest anti competitive or protectionist behaviors and other risks throughout the supply chain and 2 important in use including energy technology defense currency agriculture consumer electronics and health care related applications the term does not include here fuel minerals water ice or snow with regard to the european union the last report on critical raw materials for the eu 2014 establishes that non energy raw materials are intrinsically linked to all industries across all supply chain stages and consequently they are essential for eu way of life sectors may rely on these materials as direct inputs for instance metals refining relies on metallic ores as well as on industrial minerals this primary industry underpins downstream sectors which utilize processed materials in their products and services thus the healthcare sector uses equipment containing high performance magnets made from rare earth elements electricity distribution relies on pylons and cables constructed of aluminium and copper respectively and most vehicles are equipped with tyres that are comprised of natural rubber the eu is in a particularly vulnerable position on imports for many raw materials e g eu produced only 3 of the world metal production which are increasingly affected by growing demand pressure moreover the production of many materials is concentrated in a small number of countries supply risks may arise as a result of political economic instability of the producing countries and export or environmental restrictions imposed by these countries to assess criticality the methodology utilized in the eu is a combination of two components economic importance and supply risk the result is a relative ranking of the materials across the assessment components with a material classified as critical if it exceeds both the threshold for economic importance and the supply risk sievers et al 2012 fig 1 22 for a country economy the importance of a raw material is difficult to determine as it presents not only data but also conceptual and methodological difficulties the analysis is carried out by evaluating the proportion of each raw material associated with industrial megasectors at an eu level and then scaled to define the overall economic importance for a material on the other hand the overall supply risks are a combination of factors such as substitutability high concentration of producing countries with poor governance and end of life recycling rates the last updated list of critical and noncritical raw materials

both metals or metallic ores and industrial minerals from the european commission 2014 includes 20 critical raw materials fig 1 23 the main characteristics that make them critical for eu are a the import dependence of the eu generally more than 70 in most cases 100 b their use is fundamental in emerging technologies c they are produced as by products of other main metals treatment or coupled elements d their recycling rate is quite low and e the substitution options are limited china is the major producer of the eu critical raw materials and it is the most influential in terms of global supply other countries such as the usa for beryllium and brazil for niobium provide specific raw materials the list of critical raw materials is being used to help prioritize needs and actions it serves as a supporting element when negotiating trade agreements challenging trade distortion measures or promoting research and innovation the list not only includes the name of the raw material but also some data about main producers main sources of imports substitutability index and end of life recycling input rate these two last indexes are essential for the supply of critical raw materials according the european list the substitutability index is a measure of the difficulty in substituting the material scored and weighted across all applications the end of life recycling input rate measures the proportion of metal and metal products that are produced from end of life scrap and other metal bearing low grade residues in end of life scrap worldwide the european commission adopted a strategy document as a result of previous considerations the aim of this document is to secure and improve access to raw materials for the eu countries materials security and materials criticality have also been of growing interest for other international forums leading to a number of studies and initiatives related to raw material supply and criticality e g resourcing future generations iugs waste management priorities are organized according to the named the three r s reduce reuse and recycling box 1 7 the three r s in a broad sense there are three main groups of mineral resources that can be reused or recycled construction and demolition waste industrial minerals and metals each of them has its own characteristics dealing with source and capability to be recycled recycling will never be 100 efficient and varies greatly among different mineral commodities due to the use and functionality in their respective applications construction and demolition waste cdw is one of the most significant waste streams in the world it comprises very many materials such as metals glass concrete gypsum bricks wood plastic solvents and excavated soil among others many of which can be recycled cdw has high potential for recycling because many of the components have high resource value in particular there is a market f

or aggregates derived from cdw waste in roads drainage and other construction projects for instance recycled and secondary materials account for 30 of the aggregates market in great britain they include construction and demolition waste asphalt planings used railway ballast etc in the european union cdw has been identified as a priority waste stream since it accounts for approximately 25 to 30 of all the waste generated in the eu approximately 900 million tons per year two tons per capita the quantitative target set by the waste framework directive of the eu at 2008 is the following by 2020 the preparing for reuse recycling and other material recovery including backfilling operations using waste to substitute other materials of non hazardous construction and demolition waste shall be increased to a minimum of 70 by weight concrete is the most important fraction in the cdw it presents many treatment options e g landfill recycling into aggregates for road construction or backfilling among others but barriers to recycling the waste are numerous among them the misconception about the quality of recycled products compared to new materials is the most important since ignorance of the good results of these materials in some applications probably will continue for years the valuable physical properties of many minerals used in industrial and manufacturing processes are either destroyed in use or the minerals are dispersed and they cannot be recoverable in their original form thus plasticity of ceramic clays is lost during firing in the kiln some industrial minerals that are valued for their chemical properties are impossible to reuse or recycle the most classical example is salt utilized to treat roads in the winter and potassium or phosphorous minerals that are the basis of numerous agricultural fertilizers however many industrial minerals can be recovered and recycled in their manufactured form for example ceramic materials can be recycled as construction fills or as aggregates glass is an outstanding case of material with high recycling capacity fig 1 25 it is a manufactured product that may simply be melted and reformed in a similar way than metals according to ima europe 2013 in general recovering these minerals from their end applications would be technically complicated time consuming and ultimately environmentally unsound however although the minerals themselves may not be recyclable per se many of them lead second third fourth or even an infinite number of lives the industrial minerals sector in europe estimates that a total 40 50 of all the minerals consumed in europe are recycled which is the case for about 73 of all silica used in europe markets for this recycled silica are varied construction and soil container and flat glass foundry ceramics etc other data about recycling rates for industrial minerals in europe are 50 of bentonite 58 of calcium carbonate

67 of feldspar 49 of kaolin or 60 of talc despite the vast reserves of several industrially important metals the growing world population cannot keep consuming metals at current standard for the western industrialized society this is no doubt beyond what is likely to be sustainable altogether metal production today represents about 8 of total global energy consumption and a similar percentage of fossil fuel related co2 emissions obviously recycling will help in decreasing this footprint as it usually requires less energy than primary manufacture unep 2013 when recycling metals energy use is diminished because scrap metals commonly require less energy to convert back into high grade materials than mining and refining processes for this reason carbon emissions from recycling are substantially lower than those derived from mining as a rule the main benefits from recycling metals are a lowering energy consumption by 60 95 compared to primary production b reducing co2 emissions and environmental impact on water and air c preserving primary geological resources and d decreasing the dependency on raw material imports depending on the metal and the form of scrap recycling can save as much as an indicator of ten or twenty in power consumption reck and graedel 2012 in the metals industry the term recycling is commonly used to include two fundamentally different kinds of scrap 1 new scrap or process scrap the material generated during processing and manufacturing and 2 old scrap fig 1 26 or obsolete scrap also post consumer scrap or end of life scrap the material recovered after being built into a construction or a manufactured article that has been used and eventually discarded thus scrap is generally categorized as new scrap or old scrap a broad range of terms such as external scrap home scrap internal scrap mill scrap prompt scrap and purchased scrap have been developed to design scrap originated by different industry operations papp 2014 hagel ken 2014 affirmed that recycling possibilities or recyclability of a product is based on various technical economic structural and organizational factors a the intrinsic metal value of the base material depending on its absolute metal content and the metal price and determines the economic attractiveness of recycling b the material composition beyond the chemical composition to include physical characteristics such as shape size and the type of connection between materials and components and c the application field of a product and how it is used referring to the area of use while the latter deals with new or reuse products user behavior risk of dissipation etc few metals are used in pure form and most are components of alloys or other mixtures in cases where these materials undergo reprocessing some elements will be reprocessed to their elemental form e g copper but many will be reprocessed in alloy form e g nick

el or tin reck and graedel 2012 tercero 2012 suggests that a main obstacle to recycling is the complexity of the products themselves there are many difficulties such as the energy and labor required to separate the materials of interest so that they can be recycled sometimes an adequate large scale technology is not available locally or worldwide to recover the desired materials in a useful quality this is the case for phosphors in energy saving lamps which are to date not recycled on a large scale there is also an important difficulty yet recycling might be possible but too expensive given current technology and prices forcing downcycling or preventing recycling altogether an example of downcycling is lithium from discarded lithium ion batteries it is currently possible but too expensive to produce technical grade lithium carbonate out of recycled lithium compared to primary production in spite of the resulting benefits from an environmental economic and social perspective current recycling rates are still rather low for most metals table 1 5 the world s most recycled material is steel the metal used in 8 9 times greater quantity than all other metals combined of the three r s recycling is probably the most recognized attribute of steel more than 475 million tons of steel scrap was removed in 2008 from the waste stream into the recycling stream this is more than the combined reported totals for other recyclable materials including paper plastic glass copper lead and aluminum in 2012 the united states recycled 69 million metric tons mt of selected metals an amount equivalent to 59 of the apparent supply of those metals and more than 91 of recycled metal was steel papp 2014 obviously steel recycling has an enormous impact on the reduction of co2 emissions however the greatest request for logistical and technological advance in steel recycling is in recovery and processing of scrap covering enhancement in contaminant removal and recovery bowyer et al 2015 one of the most promising recycling sources is waste electronic and electrical equipment weee which contains many of the metals of rising demand much of weee is typically metal not only the 60 metals slice but also the metal and metallic compounds found in printed circuit boards lcd screens cables and metal plastic mixes etc table 1 6 bakas et al 2014 shows the critical metals included in eee and hence in weee with increasing gross domestic product gdp world consumption of these products accelerates and the size of their waste streams increases weee volumes are already enormous estimated between 20 and 50 million tons per annum or 3 7 kg person each year assuming seven billion people unep 2013 in summary recycling represents a major way to mitigate negative impacts on increasing metals demand and to ensure the potential of economic growth for instance the largest recycling park in china is able to recover

one million tons of copper per year it is important to bear in mind that the largest copper mine in this country generates less than half of that amount of copper this urban mining anthropogenic stock is important in producing recycled raw materials hence reinforcing the recycling of metals is a clear strategy for a sustainable future unep 2011 according to graedel et al 2014 expenditures included in creating a new mine and to put it into production nowadays commonly amount to hundreds of millions of usd or more than a billion of usd for a big mine on a greenfield place in this sense a metal mine commonly operates for a decade as the minimum period although depending mainly on economic circumstances it can go ahead for more than 100 years e g reoc n mine a lead zinc deposit in northern spain operated continuously from 1856 to 2003 fig 1 28 the mining industry is a very large one with a market capitalization of hundreds of billions dollars in ftse100 index this index includes the 100 companies listed on the lse with the highest market capitalization london lies as the heart of the industry and hosts the headquarters of some of the largest and more important mining companies in the world the structure of the global mining industry is composed by three main types of mining companies the largest companies are the socalled majors and they operate across many geographies and minerals e g bhp billiton rio tinto or anglo american a second type is formed of companies more focused to a commodity or a country examples are freeport mc moran or antofagasta focused on copper barrick gold or newmont mining focused on gold de beers focused on diamonds or norilsk nickel and kazakhmys both operating in the ancient soviet union finally a third type is constituted by small companies ranging from companies with two or three mines to small family companies some of these companies produce for international markets but others just supply local markets they often operate in markets where demand is small or where mineral deposits can be mined at small scale such as mining of precious metals on the other hand the major mining companies can be subdivided in two groups according the property of the company the first one formed by the companies mentioned above quotes in stock markets from which their capitalizations are derived the second group is formed of companies that are either wholly or predominantly owned by the states classical examples are codelco owned by the state of chile which is the world s largest copper producer and several chinese companies e g china shenhua yanzhou coal chinalco etc the other essential actors in the mineral market are the exploration companies since exploration is an extremely high risk activity and the majority of exploration ends in failure with investors losing their money the exploration companies use to have their own sources of funding mainly stock markets

examples of these markets for exploration companies are the toronto stock exchange tsx or the australian stock exchange asx however the global economy is formed not only of companies and consumers but also of nations thus nations have strategic interests and they view the mineral products in terms of the contribution that they can make to national projects here is basic vocabulary dealing with formation of mineral deposits which is not used in other disciplines of mineral resources such as evaluation exploitation or environmental impact some terms are genetic others are related to the geometry of the ore and most of the following definitions are similar to those included in the glossary of geology bates and jackson 1987 since metallogeny is the synthesis of scientific endeavors to understand ore formation pohl 2011 expressions such as metallogenic maps fig 2 2 metallogenic provinces and metallogenic epochs are usually found in the literature related to mineral deposits a metallogenic province may be defined as a mineralized area or region containing mineral deposits of a specific type or a group of deposits that possess features e g morphology style of mineralization or composition suggesting a genetic relationship a metallogenic epoch is a geological time interval of pronounced formation of one or more kinds of mineral deposits turneaure 1955 the size of a metallogenic province can be as large as the superior province canadian shield and a metallogenic epoch can be as broad as the entire proterozoic a detailed way to define metallogenic epoch and metallogenic province is as those time intervals of earth history and regions of earth respectively which contain a significantly greater number of deposits or larger tonnage of a specific deposit type than would have resulted from average rates of mineralization that have occurred over phanerozoic time wilkinson and kesler 2009 another relevant term is metallotect a geological tectonic lithological or geochemical feature that is believed to have played a role in the concentration of one or more elements and hence is thought to have contributed to the formation of ore deposits the use of genetic terms is also very varied thus syngenetic denotes that ore or minerals have formed at the same time as their host rock a rock serving as a host for a mineral or ore it is commonly but not only used for sedimentary rocks by contrast epigenetic means that the ore or minerals have emplaced in pre existing rocks of any origin e g veins both terms are essential and commonly used in genetic descriptions of mineral deposits although they have caused intense controversies through time other used terms are hypogene and supergene the former refers to ores formed by ascending solutions whereas the latter deals with ore formation by descending solutions classically meteoric waters interacting with rocks during surficial weathering endogenetic indicat

es concentrations caused by processes in the earth s interior e g magmatism whereas exogenetic points to concentration caused by processes in the earth s surface e g sedimentation stratiform and stratabound are also essential terms in mineral deposits formed by sedimentary processes thus a stratiform deposit means a mineral deposit related to a concrete stratigraphic bedding while a stratabound deposit is limited to a determined part of the stratigraphic column many terms are used in relation to the shape of a mineral deposit since it is very variable from concordant tabular and stratiform to discordant veins and breccia bodies veins are sheetlike zone of minerals that fill a fracture they are formed from hydrothermal solutions and commonly composed of quartz and or carbonates with minor sulfide minerals a breccia is a fragmented rock in which the clasts are cemented together by minerals it is a good host for hydrothermal mineral deposits other terms are disseminated ore minerals dispersed through the host rock stockwork an interlacing network of small and narrow close spaced ore bearing veinlets traversing the host rock fig 2 3 massive mineralization comprising more than 50 of the host rock tabular an ore zone that is extensive in two dimensions but has restricted development in its third dimension vein type mineralization in veins commonly discordant to the host rock layering misra 2000 pipe shaped the mineralization body has the form of a carrot and is typical of diamond deposits and lens shaped the mineralization body is much thicker in the center than around the edges and it may be flat lying dipping or vertical the use of terms associated with formation temperature of ore deposits is common examples are epithermal formed at less than 1500 m and temperatures between 50 and 200 c mesothermal originated at intermediate depths 1500 4500 m and temperatures between 200 and 400 c and hypothermal formed at greater than 4500 m and temperatures between 400 and 600 c mineral deposits can be named according to different criteria sometimes the name of a place region or city is used e g alpine type sudbury type cyprus type mississippi valley type other times the deposits are known using their acronyms e g bif means banded iron formation ores mvt means mississippi valley type lead zinc ores or sedex means sedimentary exhalative ore in addition the deposits may be called according to the rock type like pegmatite large crystals porphyry copper disseminated stockwork linked to plutonic intrusives and skarn calc silicate rock finally deposits can be known by their shape being the most representative example a type of uranium deposits namely roll front uranium deposit plate tectonics is a theory of kinematic character showing that the lithosphere is divided into a finite number of plates that migrate across the surface of the earth box 2 2 plate tectonics

it has revolutionized the theories about formation of mineral deposits since plate tectonics determine the origin and distribution of many ore deposits thus plate tectonics plays an essential role in the detection of geological environments with different characteristics consequently the classification of mineral deposits based on plate tectonics is intensively used particularly when discussing the broad scale distribution of ore deposits tectonic setting controls factors favorable for the formation of mineral deposits such as the form and composition of igneous bodies the formation of sedimentary basins and the characteristics of sediments that infill the basins and the development of faults and shear zones that provide conduits for mineralizing fluids or places for ore location thus it is not surprising that many authors have attempted to relate the distribution of mineral deposits to plate tectonics tectonics not only controls the architecture of a basin but also facilitates the interaction between fluid and rock the study of relationships between mineral deposits and plate tectonics has been particularly successful for many kinds of deposits e g porphyry copper deposits volcanic hosted massive sulfide deposits and much more fig 2 5 but others e g precambrian massive sulfide and ni sulfide deposits cannot yet be easily assigned to specific plate tectonic processes some plate tectonic settings especially during the precambrian are still highly controversial it is important to keep in mind the overall influence of plate tectonics in each group of mineral deposits since mineral deposits can be commonly separated into those originated by endogenous processes and those formed by surficial ones sawkins 1984 proposed that the deposits formed by endogenous processes are invariably associated with thermal processes and in general can be related more readily to magmatic and tectonic events instigated by plate activity while deposits formed by surficial processes such as weathering or shallow marine sedimentation will show relationships to their tectonic environment that are more tenuous moreover since most mineral deposits are concentrated by subsurface chemical processes related to magmas and hot waters as well as by near surface chemical and physical processes such as erosion and evaporation these processes are much more common on the continental crust and their products are better preserved there because the continents are floating on the mantle in contrast ocean crust sinks back into the mantle at subduction zones thus the oldest known ocean crust is only about 200 million years whereas the oldest rocks on the continents are about 4 billion years old kesler 1994 consequently the continental crust is the archive of earth history cawood et al 2013 the list of captions in ore forming processes is much larger than the list of geological processes found in any geology text explaining the origin

of rocks thus some mineral deposits are formed by magmatic processes while other mineral deposits are produced by sedimentation or surface weathering probably the main difference between both lists is the secondary importance of metamorphism in the enumeration of substantial ore forming process compared to its fundamental role in generating rocks another major difference is the essential function of hydrothermal fluids hot aqueous fluids in the genesis of ore deposits the circulation of this kind of fluids in the crust is usually cited as a factor that modifies locally the composition and texture of previous rocks ore forming processes can be classified into four main categories evans 1993 internal hydrothermal metamorphic and surficial processes the former three processes are related to subsurface phenomena while the last one covers those processes occurring at the earth s surface hydrothermal should be further subdivided into magmatic metamorphic diagenetic and surface to refine the nature of the hydrothermal process therefore the first approach to ore forming processes can be outlined according to the next four types described below magmatic metamorphic sedimentary and hydrothermal processes whatever the ore forming process because of chemical and geological factors some minerals metals tend to occur together in mineral deposits while others may be found associated with a particular rock type examples of the former are galena with sphalerite copper sulfides with molybdenite gold with arsenopyrite or pyrite and silver with galena regarding the association of mineralization host rock examples are lead zinc in carbonates copper or copper lead zinc with volcanic rocks tin and tungsten with granite intrusions chromite in large ultramafic intrusions and uranium in sandstone and shales ore deposits in metamorphosed rocks can be formed before during or after metamorphic processes the first category is of premetamorphic origin independent from later metamorphic overprinting and it is the class of metamorphosed ore deposits pohl 2011 metamorphic deposits owe their origin to contact or regional metamorphism and involve recrystallization commonly accompanied by mobilization of disseminated ore constituents by metamorphic fluids misra 2000 metamorphic rocks host many ore deposits and metamorphic fluids are thought to be a source for various mineral deposits thus this type of fluids usually carries important metal content although for chloride complexed metals maximum concentrations are commonly lower for magmatic fluids for instance gold ore is the type of mineralization usually linked to metamorphic fluids therefore based on chemistry it is possible to argue that in some circumstances metamorphic fluids can contain high concentrations of metals and may therefore be potential ore fluids banks et al 1994 according to yardley and cleverley 2014 there are three situations in which ore depo

sits are formed from metamorphic fluid processes a where relatively metal rich metamorphic fluids provide a medium for segregation b where decarbonation reactions lead to focused fluid flow and skarn formation and c where rapid uplift drives dehydration reactions despite falling temperature so that the rate of fluid production is not limited by heat flow since magmatic activity is common in certain metamorphic settings it is reasonable to consider that some mineral deposits in metamorphic rocks were formed by combined metamorphic and magmatic processes skarn and contact metamorphism ore deposits are intimately related to thermal aureoles of magmatic intrusions they can be envisaged as products of contact metamorphism but the causal agent is the interaction with magmatic fluids and not simply change by heating pohl 2011 because of the complications of describing skarns based on alteration minerals which are a combined function of wall rock chemistry and the superimposed system mineralized skarns are best classified in terms of component of interest seven major types are recognized iron gold tungsten copper zinc molybdenum and tin herrington 2011 the different metals found in skarn deposits are a product of the differing compositions oxidation state and metallogenic affinities of the igneous intrusion for instance fe and au skarn deposits are usually associated with intrusions of more mafic to intermediate compositions most of the large and economically viable skarn deposits are associated with calcic exoskarns a limestone calcic being the host rock and the metasomatic assemblage external to the intruding pluton exo prefix thus tungsten skarns produce the bulk of the world production of tungsten fig 2 9 and are typically associated with calco alkaline intrusions emplaced relatively deep in the crust low temperature surface processes can be responsible for the formation of economic ore deposits at or very near the earth s surface under favorable conditions sediments and sedimentary rocks become selectively enriched in some elements of potential economic value two main types of sedimentary processes can be outlined sedimentation and weathering sedimentation may lead to the formation of mineral deposits through clastic accumulation e g gold or diamond placer deposits and chemical and or biochemical precipitation of economically important constituents in lakes coastal settings or shallow to deep oceans including evaporation processes in clastic accumulation physical processes such as physical erosion transportation and deposition lead directly to the redistribution and accumulation of specific minerals thus these deposits are formed as a result of the differing physical and chemical behavior of the minerals forming the original rock either hydraulic water or aeolian wind being the physical processes examples of these deposits are the already mentioned diamond placer deposits

fig 2 10 in river sediments and deposits of heavy minerals in beach sands regarding chemical and or biochemical precipitation metals and other valuable minerals are soluble in surface waters they precipitate where they meet saturation levels evaporation or where the composition or physical conditions on the water shift examples of the latter are sediments enriched in iron or manganese resulting from mixing of waters with different composition or redox states evaporation is a surface phenomenon where dissolved salts precipitate as water is lost in an evaporating basin or by the evaporation of water from the ground s surface due to heat energy from the sun sedimentation is limited to the surface of the earth which is also the realm of life and its biochemical cycles therefore sedimentary ore formation will almost always show biogenic components southam and saunders 2005 it is very obvious in phosphate deposits made of bones and coprolites and in lignite seams composed of fallen trees bacteria can enhance dissolution of rocks and minerals containing metals aid in metal transport affect porosity and permeability of rocks and cause the precipitation of biogenic sulfur sulfides and carbonates in particular iron reducing bacteria and sulfate reducing bacteria may play important roles in low temperature ore genesis thus iron reducing bacteria can cause reductive dissolution of fe oxyhydroxides such that it occurs in red beds causing adsorbed and coprecipitated metals to be released to solution organic compounds produced by bacterial degradation of a more complex organic matter could enhance metal transport by formation of metal organic complexes similarly biogenic h2s could form stable aqueous metal sulfide complexes leading to transport of certain metals such as ag at low temperature kyle and saunders 1996 weathering may also lead to residual concentration of weathering resistant minerals of the parent rock or of relatively insoluble elements reconstituted into stable minerals misra 2000 in this regard weathering is a very important ore forming process resulting in chemical change and redistribution of components in surface rocks by migrating solutions the differential chemical properties of minerals at the earth s surface and in the surface crustal interface can lead to residual upgrades or chemical dissolution and reprecipitation mechanisms to concentrate the metal mineral of interest under these conditions ore formation is driven by the circulation of largely meteorically derived water at the earth s surface although similar analogous processes can take place on the seafloor these subsurface waters can dissolve and reprecipitate components at favorable mineral sites or surface interfaces herrington 2011 supergene processes usually originate different types of raw materials such as iron manganese or aluminum ores in supergene process two basically different process types may lead to concentration 1 th

e valued component is enriched in a residuum while much of the rock mass is dissolved and carried away an example are laterite deposits in which iron or aluminum is enriched in the clayey sandy soils of the tropics and subtropics and 2 the valued component is dissolved transported and concentrated on reprecipitation in this case the transport distance is commonly very short meters to ten of meters pohl 2011 a special case of weathering would be the so called supergene enrichment process which involves the leaching of ore forming elements e g copper from surficial parts of a low grade sulfide deposit and reprecipitation below the water table the process involves the release of ore metals from unstable sulfide minerals to downward percolating meteoric water and precipitation of more stable secondary oxide and sulfide mineral assemblages in the subsurface environment these deposits are usually called gossan fig 2 11 in the nineteenth and twentieth centuries gossans were important guides used by prospectors in their quest for buried ore deposits a big problem dealing with the word hydrothermal is its meaning hydrothermal means hot water which is an extremely lax sense of the word because hot water can range from 70 to 200 c or even 400 c the former temperature can be attained in the sedimentary realm during diagenesis and the others are characteristic temperatures of endogenous conditions hydrothermal fluids generally travel along temperature or pressure gradients from hot areas to cool areas or from high pressure to low pressure they migrate until they reach a suitable site for metal deposition for this deposition the following is necessary a rapid decrease in temperature such as where hot fluids exit at the seafloor a rapid decrease in pressure such as where fluids enter a fault cavity and or a change in the chemical composition of the fluid such as where fluids react with a rock stevens 2010 hydrothermal processes can develop in almost all geological environments the application of new technologies in geosciences in the last 50 years e g fluid inclusions trace element analysis isotope geochemistry among many others has changed many of the geological concepts including metallogenic thinking for instance expelled fluids in sedimentary basins during diagenesis can produce numerous metallic concentrations excluding the participation of endogenous processes in the past decades many efforts are carried out toward a better understanding of the complexity of hydrothermal processes although there are several natural processes that concentrate elements within the earth s crust and form mineral deposits the most important of which is the hydrothermal process hydrothermal ore forming processes are ubiquitous and many mineral deposits on earth have been originated straightly from hot aqueous solutions flowing through the crust direct evidence for the presence of hydrothermal fluids in the earth

s crust is surface manifestations such as hot springs and fumaroles in this sense the concept of hydrothermal mineralization can be extended to deposits related to fluids derived from sources other than magmatic solutions such fluids include those formed from metamorphic dehydration reactions from the expulsion of pore fluids during compaction of sediment the release of trapped water from sedimentary basins undergoing diagenetic change and from meteoric waters it also considers seawater as a hydrothermal fluid with specific reference to the formation of base metal deposits on the ocean floor robb 2005 magmatic hydrothermal fluids form as a body of magma cools and then crystallizes in some circumstances the magmatic system can be a passive source of heat that drives the circulation of fluids exotic to the magma through adjacent fractured crust into which the magma is intruding in other situations the magmas particularly felsic magmas that form granitic rocks include very significant amounts of miscible water which is carried in the magma itself as the magma cools and crystallizes it becomes more concentrated and eventually forms an immiscible fluid phase which in the process collects other components that prefer to partition from a silicate melt into a hydrous fluid phase williams jones et al 2002 suggest that these metal rich fluid phases can then migrate away from the magma and interact with minerals and fluids in previously crystallized magma or outside rocks which cause these to become altered by chemical reaction and lead to precipitation of new mineral phases including the ore minerals surface or seafloor hydrothermal fluids are generated as deeply penetrating meteoric or seawater derived waters descend and become heated deeper in the crust this process is particularly apparent in regions where there is elevated crustal heat flow often where the earth s crust is being thinned in the case of seafloor this phenomenon is common where a new ocean is formed by the seafloor spreading through the formation of submarine volcanoes on land such hydrothermal fluids can be generated in zones of crustal attenuation often associated with subaerial volcanism surface manifestations of this process are the presence of hot springs on land fig 2 12 or seafloor hydrothermal vents the various stages of diagenesis that result in the transformation from uncompacted particles of sediment to lithified sedimentary rock produce aqueous solutions that evolve with time and depth such type of fluids are often involved in the formation of ore deposits robb 2005 this process may develop on a large scale in a sedimentary basin undergoing burial and lithification and is a related process to hydrocarbon generation the released water can pick up dissolved salts becoming a brine table 2 2 which then has a greater ability to transport many cations and ligands to a point of deposition to form an ore deposit brimhall and crera

r 1987 in sedimentary basins evaporite beds may be a specific source of salts that can be dissolved by the basinal water basins undergoing diagenesis become heated and thus the basinal brine may be a highly effective solvent for dissolving large quantities of metals these basinal brines can then migrate via crustal faults and permeable horizons to depositional environments diagenetic process evolves to metamorphism as rocks are gradually buried and temperatures overcome approximately 200 c thus metamorphic hydrothermal fluids form as metamorphism results in mineral chemical processes that may release volatiles often dominated by water but which may include gases such as co2 metamorphism is induced in rocks by external heat or pressure or by a combination of both heat may be provided by the deep burial of a rock mass through time or alternatively by the intrusion of a magma body nearby pressure to cause metamorphism may be provided again during deep burial or else by tectonic processes mineral deposits can be classified according to the valuable raw material being extracted this classification finds some application in a purely economic context and gives raise to three main groups a energy commodities this group is formed by petroleum natural gas tar sands bituminous shales coal and uranium b metallic commodities a very large group that includes many metal types related to their uses density monetary value etc and c nonmetallic commodities in turn the latter can be subdivided into two essential categories industrial minerals and industrial rocks the minerals used by their specific chemical and physical properties e g sodium sulfate utilized as laundry detergent fit in the first category the second one developed after the second world war and of growing commercial interest includes a wide variety of raw materials mainly rocks that are used preferably in construction e g buildings roads or bridges typical examples are natural aggregates and building stone energy commodities include mainly fossil energy raw materials and uranium to produce nuclear energy coal was the first fossil energy raw material used by man at the beginning of the industrial revolution and this predominant role spanned until early in the twentieth century since then oil has displaced coal to a second rank here the terms oil and petroleum are used interchangeably although some differences exist in 2014 the world s primary energy supply was provided by 32 9 from oil 23 7 natural gas 23 8 coal 6 8 hydroelectricity 4 4 nuclear power and 2 8 renewables bp statistical review of world energy 2016 altogether they form the so called primary energy in the future the energy outlook 2035 establishes that economic expansion in asia will produce a continued growth in the world s demand for energy rising by 37 from 2013 to 2035 or by an average of 1 4 a year petroleum fig 2 13 is derived from ancient fossiliz

ed organic materials such as zooplankton and algae box 2 3 petroleum formation it is formed by hydrocarbons with the addition of some other substances thus the main hydrocarbons commonly present in petroleum are the following paraffins 15 60 naphthenes 30 60 and aromatics 3 30 with asphaltics making up the remainder the percentages for these hydrocarbons can vary greatly depending upon the geographic region regarding the chemical composition the basic components are carbon 93 97 hydrogen 10 14 nitrogen up to 2 oxygen up to 1 5 and sulfur 0 5 6 with a few trace metals making up a very small percentage of the petroleum composition the properties of each different petroleum source are defined by the percentage of the four main hydrocarbons found within petroleum as part of the petroleum composition petroleum is generally measured in volume a barrel is equal to 159 liters the petroleum industry classifies the different oil types by the location where the petroleum is produced west texas intermediate or brent the density in api gravity if the api gravity of a crude oil is greater than 10 it floats on water if less than 10 it sinks and its sulfur content the major oil producing regions around the world are located in kuwait and saudi arabia although other countries in the middle east region also make up a significant part of world production e g iran and iraq fig 2 15 the north sea crude oil fields are the second most influential oil field in economic terms the main application of petroleum is for power combustion engines gasoline or petrol other applications include manufacturing of plastics and synthetics paving road and roofing in general a lighter raw petroleum composition is more useful as a fuel source while denser petroleum composition is more suitable for plastic manufacturing and other uses broadly a barrel of crude oil produce the following components 43 gasoline 21 diesel 10 jet fuel 4 fuel oil 4 liquefied petroleum gases and 18 other products petroleum also known as crude oil or simply oil is a fossil fuel that was formed from the remains of ancient marine organisms coal natural gas and petroleum are all fossil fuels that formed under similar conditions in fact petroleum is frequently found in reservoirs along with natural gas in the past natural gas was either burned or allowed to escape into the atmosphere now technology has been developed to capture the natural gas and either reinject it into the well or compress it into liquefied natural gas lng which is easily transportable and has versatile uses formation of naturally occurring raw petroleum takes millions of years large amount of the organisms sourcing the petroleum remains settled to sea or lake bottom mixed with sediments and buried under anoxic conditions as the microscopic algae and phytoplankton died they sank to the bottom and accumulated in large quantities in the o

xygen free sediments over time they were buried deeper and subjected to a long process of chemical conversion by bacterial decomposition followed by the effects of high temperatures this caused the formation of liquid and gaseous hydrocarbons in the source rock hydrocarbons are simply chemicals made up of hydrogen and carbon petroleum source beds are fine grained clay rich siliciclastic rocks mudstones shales or dark colored carbonate rocks limestones marlstones which have generated and effectively expelled hydrocarbons most of the economically useful petroleum deposits were deposited during the phanerozoic this is thought to reflect the lower rate of organic carbon production and burial in the earlier eons increasing heat and pressure cause the organic matter to change first into kerogen one of the products of anaerobic decomposition of organic matter it is found in various oil shales around the world and then into liquid and gaseous hydrocarbons in a process called catagenesis thus catagenesis comprises all processes that act on rock matrix and organic matter after considerable burial and that result in petroleum generation higher pressure and temperature are essential factors of change the main result of catagenesis is the generation of oil and wet gas while kerogen matures at about 60 c oil begins to form in the source rock due to the thermogenic breakdown cracking of organic matter kerogen there is a temperature range in which oil forms it is called the oil window often found in the 60 120 c interval approx 2 4 km in depth below the minimum temperature oil remains trapped in the form of kerogen while above the maximum temperature is converted to natural gas through thermal cracking about 160 c the gas produced in this way is often separated from the petroleum if temperature reaches high value 250 c the original biomass will be destroyed and no gas or petroleum is formed typically lower temperatures during petroleum formation will result in thicker darker raw petroleum deposits the most solid of which being a bitumen substance after expulsion from the source rock fig 2 14 both oil and gas lighter than water migrate upward through permeable rocks e g sandstones or fractures until they are stopped by a non permeable layer of rock e g shale the production of petroleum increases pressure within the rock because oils and gases are less dense than solids and hence take up more volume the overpressure fractures the source bed enabling migration of the gas and oil into adjacent permeable rocks migration occurs vertically and laterally through the fractures and faults until an impermeable barrier is reached oil and gas migration takes thousands or millions of years and may extend over tens of kilometers gravity forces the oil to move out of the source rock and upward toward the surface looking for a reservoir reservoir is a rock that has the ability to store fluid such

as sandstone where oil or gas can be between grains of sandstone porous limestone is also a good reservoir rock since many cavities can be connected with each other thus reservoir rocks are porous and always saturated with water oil and gas in various combinations petroleum reservoirs can be found beneath the land or the ocean floor in addition impermeable rock has to be present to stop petroleum escaping from reservoir rock impermeable rock that forms a seal over reservoir rocks is called cap rock cap rocks of most petroleum fields are fine grained clay rich sediments like shales or mudstones due to their low permeabilities and very small diameter pores capillary entry pressures are so high that they cannot be overcome by the buoyancy of a high oil or gas column the most ideal and best sealing cap rocks are however evaporite strata like anhydrite or rock salt such good quality cap rocks hold many of the large petroleum accumulations in the middle east in place if there is a suitable combination of source rock reservoir rock and cap rock and a trap in an area recoverable oil and gas deposits may be discovered there if there is no cap rock the oil and gas will slowly continue to migrate toward the surface in certain geological locations as the oil migrated and came closer to the earth s surface microorganisms slowly consumed the hydrocarbons beginning with the lightest the heavy oil and bitumen now being produced are the remnants of that migration heavy oil deposits e g tar sands are the world s largest known liquid hydrocarbon resources and comprise about 65 of all the liquid petroleum in the world very large deposits of tar sands occur in northern canada athabasca tar sands and eastern venezuela natural gas plays a vital role in the world s supply of energy in its pure form natural gas is colorless shapeless and odorless compared to other fossil fuels natural gas is cleaner and emits lower values of harmful components to the air although it is a blend of different hydrocarbon gases natural gas is formed mainly of methane 70 90 ethane propane butane all three together up to 20 and other components e g pentane carbon dioxide oxygen nitrogen or hydrogen sulfide temperature and pressure determine the composition of the gas phase because several higher hydrocarbons are gaseous in the reservoir but condense if the pressure is lowered natural gas is called dry if it is almost pure methane and wet if other hydrocarbons are present the dryness of gas can be characterized by the percent methane percent ethane ratio other denominations are sour gas if it has elevated fractions of sulfur and co2 and sweet gas if it contains less than 2 of co2 and no h2s only sweet gas can be directly used and the rest must be first refined natural gas is found in reservoirs often associated with oil deposits since gas is dissolved in oil a free gas cap forms on top of the oil pool where sa

turation is reached when natural gas is formed it rises toward the surface because it has a low density some of this methane will dissipate into the air but it will also rise up into geological formations that trap the gas under the ground these formations are mainly composed of layers of porous sedimentary rocks with an impermeable layer of sediment on top to prevent the migration of the natural gas until the surface the obtained natural gas is then refined to remove impurities e g water other gases or sand after refining the natural gas is usually transmitted through a network of pipelines to its point of use natural gas can be measured in cubic feet or like other forms of energy in british thermal units btu the definition of a btu is the following 1 btu is the quantity of natural gas that will generate sufficient energy to heat 1 pound of water by 1 degree at normal pressure regarding the production and reserves of natural gas fig 2 16 shows the reserves to production ratios in 2015 by region tar sands fig 2 17 sometimes referred to as oil sands are a combination of bitumen water clay and sand the bitumen being a heavy black viscous oil tar is a term for heavy and extra heavy oils 6 12 api that are highly viscous and sulfur rich it is the residuum of a degradation or normal petroleum degradation is essentially the loss of light hydrocarbons and an increase of n s o compounds deposits of tar sands may be mined to obtain the oil rich bitumen which is later refined to produce oil because the bitumen in tar sands cannot be pumped in its natural state tar sand deposits are commonly mined using open pit mining in other cases the oil is extracted by underground heating with additional upgrading this process involves injecting steam into the ground to melt the bitumen from the sands and pumping the bitumen up to the surface during many decades the oil industry clearly ignored tar sands oil since the exploitation of this energy source is much more expensive difficult and more important from an environmental view point dirty than conventional oil theoretically much of the world s oil reserves e g 2 trillion barrels are in tar sands form although obviously it is not all mineable the largest deposits in the world of tar sands are found in canada athabasca deposit and venezuela although various countries in the middle east and russia have also important reserves in this sense only canada has a large scale commercial tar sands industry exploitation of tar sands produces actually a strong dispute in canada essentially for the environmental impacts of this kind of mining oil shale or bituminous shale is a sedimentary rock that contains up to 50 of organic matter in fact it represents certainly an old petroleum parent rock once extracted from the ground the rock can either be used directly as fuel for a power plant or be processed to produce shale oil and other chemicals and materials

with a few exceptions e g fracking these deposits are yet little exploited because environmental considerations and other factors make extraction of these raw materials relatively unattractive the strategical character of oil shales as a resource of oil and gas depends on a number of criteria such as the ultimate destination of the raw material the basic cost of extraction and processing and the environmental costs among many others the heating value of bituminous shale is low and similar for example to that of brown coal or average forest residues and less than half of that of the average bituminous coal this is drastically changing with the introduction of fracking or hydraulic fracture techniques box 2 4 hydraulic fracking natural gas produced from shale is often referred to as unconventional gas by contrast to conventional gas produced from other kinds of rock usually sandstones or limestones conventional gas is found in reservoirs in sandstone or limestone where gas has migrated up from source rocks in these rocks organic matter becomes gas or oil through the action of heat and pressure over time according to the international energy agency iea the volume of unconventional gas resources including shale gas tight gas and coalbed methane is currently estimated at 340 trillion cubic meters equivalent to about 40 of global gas resources in this statistics shale gas accounts for the biggest share of these resources thus the emergence of shale gas and shale oil has quickly changed the landscape of opportunities for energy provision and security in different regions of the world as the reserves of conventional natural gas and oil falling inexorably and could be nearly exhausted the extraction of unconventional oil and gas trapped in shale appears to be an attractive alternative for several countries especially the usa because shale is a fine grained sedimentary rock the gas and oil it contains do not easily flow and therefore must be released before it can be pumped from the ground the technique used to extract shale gas is called hydraulic fracturing or colloquially fracking it consists of injecting water proppant e g granules of sand and chemicals at high pressure into a shale or sandstone formation the buildup in pressure causes the formation to fracture and the proppant fills the fractures to keep them from resealing this allows the natural gas impounded in the formation to rush into the well for extraction a combination of factors including technological advance desire to decrease dependence from foreign energy new geopolitical realities and high oil prices have made unconventional gas and subsequently hydraulic fracturing particularly attractive hydraulic fracturing is most often performed in horizontally drilled wells fig 2 18 a typical horizontal well has an average lateral extension of 1400 m maximum of 3000 m after a period of vertical drilling in order to reach sha

le deposits most of unconventional gas is trapped deep inside of shale formations at depths between 1500 and 3000 m a lateral extension of up to 2000 m is drilled parallel to the rock layer containing the shale in the next step fracking fluids are injected into the recently bored hole in order to release the hydrocarbons that are trapped the fluid is injected under high pressure with the intent of fracturing the soft shale the rock is hydraulically fractured multiple times every 100 m along this horizontal extent occasionally other substances such as gels foams compressed gases and even air are injected chemical mixtures are usually included in the injection and their objectives are to increase the permeability of the rock by dissolving various components regarding the fracking fluid it can be injected at various pressures and reach up to 100 mpa 1000 bar with flow rates of up to 265 liters second the cracks being produced typically less than 1 mm wide the fracking fluid contains around 20 percent of sand and this helps to open and keep open the tiny cracks allowing gas to flow into the well fracturing fluid consists of about 98 99 5 water and proppant the rest 0 5 2 by volume is composed of a blend of chemicals often proprietary that enhance the fluid s properties the concentration varies depending on the geology and other water characteristics these chemicals typically include acids to clean the shale to improve gas flow biocides to prevent organisms from growing and clogging the shale fractures corrosion and scale inhibitors to protect the integrity of the well gels or gums that add viscosity to the fluid and suspend the proppant and friction reducers that enhance flow and improve the ability of the fluid to infiltrate and carry the proppant into small fractures in the shale coal is a solid black mineral made up of carbon hydrogen oxygen and nitrogen in varying proportions in addition it contains impurities such as ash and sulfur in the industrial revolution coal was a major fuel competing with charcoal and wood coal is an essential fuel for steel and cement production and other industrial activities as well as to provide electricity coal commonly contains altered remains of prehistoric vegetation because it is of vegetable origin with components growing in swamps and lagoons and going through a peat stage all with the combined effect of pressure and heat over millions of years to form coal seams the change from plant debris to coal involves biochemical action preservation of the material from further decay and pressure under accumulated plant materials and other later sediments this caused physical and chemical changes in the organic remains transforming them into peat and then into coal coal formation began during the carboniferous period called the first coal age which spanned 360 290 million years ago however coal occurs in all post devonian periods for instance cenozoic yields

most of the lignite of the world the types of vegetation depth of burial temperature and pressure and this depth and length of the time forming the deposits are factors to define the quality of a coal deposit the degree of change undergone by a coal deposit as it matures from peat to anthracite is known as coalification coalification has an important bearing on coal s physical and chemical properties and is referred to as the rank of the coal ranking is determined by the degree of transformation of the original plant material to carbon the ranks of coals according to the carbon content are lignite subbituminous bituminous and anthracite fig 2 19 the use of carbon as an energy source causes bad effects on both humans and the environment examples of these issues are acid rain waste products high levels of carbon dioxide contaminated water poisonous emissions and increased risks of lung cancer for coal plant workers despite this fact nearly 70 of china s electricity comes from coal and around 40 of the world s electricity is produced after this energy source coal seam extraction can be carried out by surficial or underground mining depending on the depth and quality of the seams and the geological and environmental factors in addition lignite can be broken down chemically through a process called coal gasification to create synthetic natural gas coal reserves in 1995 2005 and 2015 by region are shown in fig 2 20 uranium is the raw material for nuclear power a radioactive metal being present on the crust of the earth it is important to bear in mind that nuclear power actually originates about 16 of electricity of the world uranium can come from mining directly uranium rich ore bodies or as a by product from mining other minerals such as copper phosphate or gold in this sense the uranium concentration in the mineralization can range from 0 03 up to 20 the most important uranium rich ore producers in the world are kazakhstan canada and australia there are three methods to obtain uranium in the mine classical open pit and or underground methods and in situ leaching in the latter uranium is leached directly from the ore it is the leading method to produce uranium today in a process called in situ leaching isl the wna world nuclear association reports that isl mining accounted for approximately 49 of world production in 2014 isl processing implies that mining solution is passed through the underground ore body using several bores or wells the uranium then is brought to the surface in a dissolved state for further purification after the chemical treatment to separate uranium the product is the so called yellow cake which is a yellow powder of uranium oxide u3o8 where the uranium concentration is reaching more than 80 natural uranium includes mainly two isotopes u 238 99 3 and u 235 0 7 the fission process in the nuclear reactor is carried out using preferably u 235 fig 2 21

therefore because nuclear power plants need fuel with u 235 enriched to a level of 3 5 the material must be enriched to achieve this concentration since enrichment process is produced in gaseous form the yellow cake is turn to uranium hexafluoride gas uf6 enriched uranium uf6 cannot be directly used in reactors so that it must be converted into uranium oxide uo2 fuel pellets are formed by pressing uo2 which is sintered baked at temperatures of over 1400 c to achieve high density and stability the pellets are packed in long metal tubes to form fuel rods which are grouped in fuel assemblies for introduction into a reactor as the spent fuel assemblies are very hot and radioactive they must be removed from the reactor and are stored under water which provides both cooling and radiation shielding after a few years spent fuel can be transferred to an interim storage facility after 40 years in storage the fuel s radioactivity will be about a thousand times lower than where it was removed from the reactor some countries chemically reprocess usable uranium and plutonium to separate them from unusable waste despite some limitations such as their low specific strength or corrosion processes metals are still one of the most important components of our way of life this situation will continue in the future thanks to unique properties that make them irreplaceable according to lu 2010 metals possess much higher fracture toughness than other materials steels are the toughest known materials secondly the properties of metals are uniform in all directions their strength is the same in tension and compression and it is usually predictable being these features critically important for predicting fracture in engineering structures third most metals are more conductive than ceramics and polymers and fourth they have the best overall mechanical properties at temperatures up to a few hundred degrees moreover most metals are recyclable making them more competitive for quantity applications in order to separate the metals in groups there is a general consensus that five clusters can be outlined 1 iron and steel metals 2 base metals copper lead zinc and tin 3 precious metals gold silver and pgm 4 light metals aluminum and magnesium and 5 minor and specialty metals this group is formed by numerous metals e g mercury fig 2 22 antimony arsenic bismuth titanium cobalt tungsten molybdenum and many others iron ore is destined to the production of pig iron in the blast furnace high iron concentration in ore low content of sio2 and alumina and coarse grain size are favorable properties the basic materials for pig iron production are iron ore coal and coke also used as energy input to the process and alternative reducing agents such as limestone and dolomite the main application of this raw material is to produce steel the toughest of all construction materials which is an a

lloy made of low carbon iron steel production requires iron steel scrap and lime non metallurgical uses of iron ore such as chemical applications pigments and abrasives consume a very small share of total iron ore production steel is obtained by blowing oxygen through molten iron thereby reducing its carbon content up to 2 the properties of steel can be adapted by alloying it with other metals such as manganese chromium nickel cobalt molybdenum tungsten and vanadium the so called steel metals the most famous and used alloy steel is stainless steel iron and the most common iron alloy steel are relatively poor materials from a corrosion viewpoint in spite of this there is a group of iron base alloys the iron chromium fe cr alloys often with nickel ni additions known as stainless steels which do not rust in seawater which are resistant to concentrated acids and which do not scale at temperatures up to 1100 c the combined effect of the alloying elements heat treatment and to some extent the impurities establishes the property profile of a certain steel type outokumpu 2013 applications of stainless steel include food handling processing medical instruments and structural architectural uses among many others fig 2 23 base metals such as copper and zinc are widely used in communication and information technology copper and its alloys exhibit many desirable properties it is ductile malleable hard tough strong wear and corrosion resistant it also has high tensile strength fatigue strength and thermal and electrical conductivity the production of copper is mainly utilized by the wire and cable markets taking advantage of properties such as the electrical conductivity corrosion resistance and thermal conductivity excellent malleability ductility and resistance against atmospheric attack distinguish copper metal and its alloys e g tin or zinc copper shows also strong antibacterial properties other applications include structural and aesthetic uses with regard to zinc and lead there are few ore deposits that contain only lead or zinc and most mines produced both metals zinc is used predominantly in galvanizing and alloys steel coated with zinc galvanized steel exhibits high levels of corrosion resistance this application is responsible for around 50 of total demand zinc based alloys are also used in die casting ranging from automotive components to toys and models lead is a heavy metal soft and malleable lead is commonly utilized in alloyed form which increases its low tensile strength when added to metal alloy lead improves their machinability regarding tin it is a soft weak malleable and ductile metal and has many important uses as an alloy it can be alloyed with lead and with copper to produce bronze the most important properties of tin based alloys are their high resistance to corrosion low fatigue strength and compressive strength for its part nic

kel also a base metal is hard and ductile fig 2 24 and the main application is in steel alloys apart from copper gold is one of the earliest metals intentionally looked for by humans gold was always a metal valued for wealth adornment and strong currency there is little difference today and only 10 are consumed by industry e g electronics and dental applications for the future an increasing role of nano sized gold particles as catalysts in chemical production in pollution control and in medical applications is predicted pohl 2011 in respect of silver it is obtained mainly as a by product from copper lead zinc and gold ores in fact the economic viability of many base metal and gold deposits relies on by product silver the use of silver is basically in industrial applications but nearly 40 is consumed in jewelry coins and silverware the platinum group metals pgm are used in several industrial applications as well as in jewelry the six chemical elements normally referred to as the platinum group elements pge are ruthenium ru rhodium rh palladium pd osmium os iridium ir and platinum pt platinum and palladium are actually the most commercially important of the pgm with largest utilization in the automotive industry where they are applied to decrease harmful emissions from vehicle systems gunn 2014 rhodium is the third more important pgm it is also used in autocatalysts although its consumption is an order of magnitude less than platinum and palladium aluminum is the most important of the non iron metals and it is commonly produced from bauxite which is a loose soil or a hard rock with 30 65 al2o3 about 95 of bauxite produced is processed into aluminum metal the remaining 5 serves as an industrial raw material for numerous special products such as abrasives portland cement technical ceramics glass chemicals paints and refractories favorable attributes of aluminum metal such as lightweight strength and excellent corrosion resistance lu 2010 allow its use in many applications from building air frames to food packaging the other light metal is magnesium very diverse raw materials natural and industrial brines and seawater are used for the production of magnesium and magnesium compounds for instance harvesting salts on the shores of the great salt lake is a source of magnesium applications of the extremely light magnesium metal density 1 74 g cm3 employ the pure metal or aluminum alloys magnesium aluminum alloys are mainly consumed for beverage container making about 40 of magnesium is used for die casting in the car industry in order to reduce weight and fuel consumption other sectors include the space aircraft and chemical industry magnesium is mainly utilized as magnesium oxide in applications such as refractory material e g furnace linings for the production of iron and steel glass and cement the term minor metals encompasses a vast array of m

etals including tungsten titanium cobalt and molybdenum to name just a few these metals are crucial to the global economy and many of them are by products of the major exchange metals only the precious metals are more valuable than many of the minor and specialty metals minor metals show relatively low annual production volume compared to base metals and they have commonly high technology applications uses include filaments in lightbulbs electronic pastes components in mobile phones and tablet pc s agriculture and flat panel screens as well as alloying agents in specialist steels for the automotive and aerospace sectors among many others as technology progresses new applications are found which will create new supply and demand patterns as demonstrated by the growth in renewables technology minor metals trade association mmta nowadays one of the most important groups of these metals is rare earth elements ree because their chemical properties make them indispensable and non replaceable in many high technology applications for this reason ree consumption is growing due to their daily contribution to our lives in products like hybrid cars catalytic converters wind power generators household appliances industrial motors mri machines ipods and computer hard drives and green energy technology the use of the term industrial minerals and rocks is very common in the literature e g kuzvart 1984 carr and herz 1989 jeffrey 2006 and it cover both types of raw materials in this section industrial minerals are described separately from industrial rocks because the characteristics of the materials and applications are wholly different the economically usable minerals automatically classify themselves into four broad groups based on the stages of processing required for conversion to finally usable products chatterjee 2009 1 those that are mainly used directly in consumer product industries 2 those that are not used without first extracting metals from them 3 those that are used in both ways but mainly valued for their metal content and 4 those that are used in both ways but their direct uses are of importance and their metal values are of minor significance it has become a convention to refer to the first and fourth groups as industrial minerals earlier called nonmetallic minerals while the second and third groups are considered as metallic minerals industrial minerals are valuable economic raw materials that are not used in the production of metals or energy compared with metals and other nonmetallic resources they are mainly processed by physical methods both definitions however are not without exceptions and some attributions to the group are rather by tradition pohl 2011 typical examples of industrial minerals are talc fig 2 25 mica and fluorite several ore minerals such as chromite bauxite and rutile also have industrial applications but the bulk of production f

eeds metallurgy because of multiple and even changing uses and a wide genetic variety the most common classification of industrial minerals is based in the alphabetical order occasionally final applications of the industrial minerals are used as a basis for their classification although the industrial mineral deposits are generally exploited for single minerals a significant number are worked together as by products such as fluorite and barite from mississippi valley type lead zinc deposits or quartz feldspar and mica from pegmatites most industrial minerals and rock commodities also have multiple uses for instance a pure limestone deposit could supply material for lime aggregate and cement production in granular form for flue gas desulfurization and in a range of powders for fillers soil stabilization and agricultural uses each of these applications can command very different prices per ton so evaluating the overall value of the deposit is difficult and involves assessing for multiple quality requirements and variable product splits in many cases the evaluation process for an industrial mineral resource is considerably more technically complex than that for metal deposits jeffrey 2006 globalization is an important economic driver in the industrial mineral sector large international corporations e g sibelco in belgium have formed by consolidation and acquisition of smaller companies in some cases this process has led to one or two corporations having dominant control over individual mineral commodities such as borates nepheline syenite garnet and talc as the technical demands on specific minerals increase or supplies are restricted companies explore the possibilities of making synthetic mineral products this is especially true for gemstones but major industries are making synthetic zeolites for use in washing powders as intermediates such as synthetic rutile for tio2 manufacture and in pigments and as bulk materials such as magnesite gypsum and soda ash jeffrey 2006 in some applications the boundaries with material science become blurred such as in industries making synthetic corundum and silica for laser military and electronic applications here the mineral structure has been perfected to a point not found in nature some of these synthetic minerals are also produced as by products of upgrading other mineral products but all affect the demand for primary industrial minerals from new or existing deposits more often a shortage of suitable mineral supplies or the possibility of cost savings leads to substitution by function other minerals that can perform the same role in a product are then used instead the increased use of fine ground or precipitated calcium carbonate at the expense of kaolin in paper coating is a good example as a tool to assist in teaching about industrial minerals a classification that defined seven groups of commodities based on the relative importance of physical and che

mical applications or a combination of the two can be established smith 1999 the classification is constructed using a matrix of commodities and uses that are grouped according to applications clustering of commodities reveals the following groupings 1 principal abrasives diamond alumina garnet and pumice 2 principal refractories pyrophyllite sillimanite group magnesite and graphite 3 principal fillers wollastonite titanium minerals mica barite and iron oxide 4 principal physical and chemical minerals feldspar and zeolite 5 mixed application physical minerals silica perlite clay fig 2 26 and talc 6 principal chemical minerals phosphate salt and sulfur and 7 mixed application physical and chemical minerals olivine chromite fluorspar gypsum and limestone regarding the trade value of industrial minerals most of them are essentially high volume low value commodities while metals are the opposite mainly precious metals beyond the difference in scale of value between the two groups of commodities a key issue is the fact that industrial minerals do not have markets whose prices are set by an exchange system e g london metal exchange in metals some attempts have been made by various organizations in recent years especially with the advent of the internet and e commerce for the reasons outlined here it is unlikely that any kind of industrial mineral pricing exchange will be created in the foreseeable future the industries in which industrial minerals are utilized are cover paint electronic metal casting paper plastic glass ceramic detergent pharmaceutical and cosmetic environmental engineering and construction ima europe for instance glass in buildings is manufactured with industrial minerals mainly silica the following descriptions are a brief resume of the application of industrial minerals in these sectors the glazes that cover ceramics are largely composed of minerals mainly borates silicates and metallic pigments ceramics and refractory articles are indispensable in buildings pipes tiles and refractory bricks are all 100 industrial minerals even if some ceramics are being replaced by resins these also contain important amounts of industrial minerals technological developments in the ceramic sector represent an area in which industrial minerals are at the forefront of progress for instance ceramic tiles protect space shuttles in order to support the high temperatures of the earth s atmosphere industrial minerals such as clays sand feldspar kaolin and other minerals are basic to all construction materials from bricks to tiles and from cement to limes and plastics apart from the basic structure industrial minerals are also present in all parts of the building as a constituent or during their manufacturing for instance all ceramic compounds of a house e g tiles tubing etc include industrial minerals even the wallpaper paints and

carpet lining contain important amounts of industrial minerals detergents such as the powder ones utilized for laundry and dishwashers include a bleaching system two systems are currently in use perborate and percarbonate both rely on industrial minerals borates or calcium carbonate respectively which are chemically processed up to the required properties detergents are a major consumer of silica which makes a whole family of detergents based on sodium silicate other industrial minerals e g bentonite and sepiolite are also used in detergent applications because of their adsorption properties in this sense sepiolite is the main component in making cat litter fig 2 27 the nervous system of a computer is made of silicon this component being extracted from silica sand or massive quartz rocks this quartz crystals also pace actually the functioning of most of clocks after extraction the silicon is delivered to the electronic manufacturers in the form of wafers a few centimeters wide industrial minerals are crucial in water management whether considering drinking water preparation or wastewater treatment thus silica sands are used as filters perlite zeolites or talc as flocculants or adsorbents bentonite as a degreasing agent and calcium carbonate as a neutralizing agent to mention but a few industrial mineral based liners and geosynthetic liners either basal or superficial are increasingly used to avoid escape of leachate from landfill sites air treatment of industrial effluents also largely relies on minerals activated carbon is the best known technique but other minerals are used as well for instance flue gas desulfurization of power station fumes is achieved with calcium carbonate the glass industry is one of the primary consuming markets for industrial minerals with the highest demand in terms of volume for silica sand limestone feldspar and soda ash fiberglass and glass wool are also members of this group the mineral blend is a determinant to the glass properties during manufacture and use historically fillers and extenders were used to furnish low cost bulk to paint solid content today the range of extenders available is extremely wide and determines many of the paint s properties gloss opacity flow film toughness permeability rheology resistance etc waterborne systems low solvent paints powder coatings high solid coatings and industrial minerals are crucial to all the environment friendly developments of paint technology the paper industry particularly printing and writing paper is by far the largest volume user of industrial minerals box 2 5 papermaking additives the role of industrial minerals in pharmaceuticals falls into one of two main categories excipient or active substances the excipients have no intrinsic health benefit on their own they are used solely as carriers allowing the intake of minute amount of active substances ph regulation or adsorbents

are the kind of applications for which some minerals are used as active ingredients thus antacid pills are composed mainly of calcium carbonate lithium used in antidepressants is derived from industrial minerals and many excipients are minerals such as talc magnesium carbonate or silica many cosmetics incorporate important amount of industrial minerals such as talc although others like mica silica or borates are utilized for their abrasive visual or stabilizing properties it is necessary to remember that earliest civilizations e g the romans already made use of earth pigments for body painting finally polymeric resins such as pvc and pp are generally filled and or reinforced with industrial minerals e g talc and calcium carbonate they are also used in polyamide unsaturated polyesters hdpe high density polyethylene and ldpe low density polyethylene small amounts of minerals particularly talc and silica are used in the compounding and manufacturing of rubber goods thus the new generation car tire relies its energy saving on the silica content of the polymer 2 7 box 2 5 2 7 papermaking additives papermaking starts with the production of the most important raw material wood the pulping process then converts the wood into the most appropriate type of pulp pulping of wood can be done in two ways mechanically or chemically in the case of mechanical pulp the wood is processed into fiber form by grinding it against a quickly rotating stone under addition of water in chemical pulp the pure fiber has to be set free the wood chips being cooked in a chemical solution the next step is pulp bleaching it is a complex process consisting of several chemical process steps with washing taking place between the various chemical treatments the paper machine then converts the pulp into a thin base paper which at the end of the production process is coated to give it a superb flat surface and bright shade coating a paper enhances its optical and tactile characteristics whiteness and shade gloss and smoothness but it also improves its printing behavior allowing the use of very fine screens yielding more color in thinner ink layers and producing more contrast in printed images in all the previous processes many types of additives fillers binders and many others are used to improve the efficiency and quality of the final product in papermaking minerals are used either as fillers or as a coating on paper some minerals like talc are also used in pitch control absorption of wood resins that tend to obstruct the machines the use of minerals in paper production increases the speed of the machine performance and fluidity the final characteristics of the paper strength whiteness gloss ink retention etc are largely determined by the blend of minerals used high quality glossy paper is obtained by applying a thin layer of industrial minerals on the surface of the paper as for fillers the final

characteristics of the coating and its fitness for use are governed by the nature of the mineral blend the list of minerals used as additives in papermaking is impressive soda ash dissolves out the noncellulose parts without weakening the finished paper titanium dioxide is a strong white pigment which makes paper whiter and more opaque acting as a filler and giving a smoother surface to the paper the filling effect is much stronger than with calcium carbonate but it does not have the ability to neutralize paper acids titanium dioxide is also used to tint colored pulps china clay is a fine white powder also known as opal gamma kaolin which is used to make paper more opaque and smooth and reduce shrinkage it is especially useful in paper casting and will appeal to papermakers and model makers alike calcium carbonate provides an alkaline reserve in paper which promotes acid free archival qualities being also used as filler and in coating it retards shrinkage in paper castings and makes a smoother surface in paper sheets it improves opacity and whiteness talc gives paper a greasy or soapy feel and enables it to take a high finish kaolin is one of the most used filler lime is used in alkaline pulping process magnesite is a common component of cigarette paper as filler being also considered as an excellent ingredient for harmless smoking hydromagnesite and huntite are used to control the burning rate of cigarette papers sodium silicate is utilized in waste paper deinking for wetting ink dispersion and peroxide stabilization finally many pigments and dyes used in papermaking come from industrial minerals such as iron oxide titanium oxide zinc compounds e g zinc sulfide or zinc oxide lead compounds cadmium sulfide etc a type of mixture containing coprecipitates of titanium and mica or other minerals is used to make a pearlescent which is transparent and highly light refractive imparting to the ink film the luster characteristic of mother of pearl 2 7 4 industrial rocks this term encompass a group of rocks single mineral species are excluded of this group whose main application is addressed to construction market industrial rocks typically comprise of multi mineral hard and unconsolidated rocks and sediments aggregates sand and gravel for road construction limestone for cement and dimensional stone granite marble or slate for building material are all well known examples of industrial rocks the main characteristics of industrial rocks can be outlined as follows firstly the price of the raw material is low to very low and sometimes the price of the finished product is low as well one of the principal industrial rocks namely aggregates displays the lowest price for a raw material in the industry e g 7 dollars per ton of concrete sand for this reason exploration exploitation and mineral processing costs must be very low secondly the very high prices of transport resulted in a proximit

y to consumption center consequently the markets for the product are commonly local markets especially in aggregate industry finally resources and reserves of industrial rocks are almost infinite moreover one particular type can be substituted by another one for example if the price of the product suddenly increases and even a finished product can also be replaced by another one of similar specifications according to the main markets of construction industrial rocks can be grouped in to five main types 1 aggregates 2 ornamental rocks 3 limestone for cement and lime 4 gypsum and 5 clay for bricks and tiles 2 7 4 1 aggregates aggregates are granular materials used in construction formed of natural or crushed hard sound and durable particles of nonreactive minerals sand gravel and crushed rock are typically the most common natural aggregates in the market while aggregate is used primarily in asphalt and concrete asphalt pavement includes 94 aggregate and concrete is formed by 80 aggregate all construction worldwide involves the use of this raw material in fact aggregates are the second natural resource more used by the humankind after water aggregates are mainly obtained by mining quarries and gravel pits and in some countries from sea dredged materials marine aggregates recycled aggregates see chap 1 are derived from reprocessing materials previously used in construction such as demolition debris the production and consumption of this raw material are impressive according to the union europ enne des producteurs de granulats uepg european aggregates association the european aggregate consumption is 2 8 billion tons per year the average aggregate consumption being 5 2 tons per person per year about 90 of all aggregate produced are from quarries and pits 25 000 quarries and pits in europe and the remaining 10 from recycled aggregates 6 and marine and manufactured aggregates 2 each us aggregate consumption includes approximately 1 billion tons of sand and gravel in 2016 and similar amount of crushed rock usgs aggregates are indeed the main component in all homes offices social buildings and infrastructures for instance the construction of a common new home uses up to 400 tons of aggregates from the foundations through to the roof tiles other examples are roads or railways the construction of 1 km of motorway consumes up to 25 000 tons of aggregates and the construction of 1 m of railway for a high speed train tgv uses up to 10 tons of aggregates drainage dams and breakwaters fig 2 28 are a few more of other important construction items involving aggregate specifications for the most important applications of aggregates such as concrete and ballast are closely regulated and subject to industrial standards e g astm in the usa en in europe iso worldwide and concern petrographical composition geometrical properties such as particle size and grain shape

mechanical and physical properties e g resistance to wear or resistance to fragmentation thermal and weathering properties e g boiling test for sonnenbrand basalt and chemical properties e g determination of acid soluble chloride salts 2 7 4 2 ornamental rocks for centuries natural stone has been used by nearly all civilizations being applied mainly in architecture ornamental rocks are the main economic component of the natural stone industry the market is shaped by three rock types granites fig 2 29 marbles and shales fig 2 30 although they do not always represent the same typology of geological rock thus limestone is a marble in natural stone industry although obviously the limestones need a metamorphism to become a marble other example is basalt which is defined as granite in natural stone industry although the former is a volcanic rock and the latter a plutonic one ornamental rock blocks are exploited in quarries currently the most common method to extract the blocks is by using diamond wire diamond wires are cutting tools for rocks marble granite or slates the wires are composed of a stainless steel cable over which are assembled diamond sintered pearls 10 12 mm in diameter and spaced 25 mm along the wire the utilization of this slabbing technology has expanded all over the world due to its advantages facing other techniques such as explosives or thermal lance after extraction in quarries the blocks are manufactured using different techniques which depend on the size of the products and the type of rock marble or granite is commonly polished to perform products for interior paving granite is also processed to obtain flamed granite most used in pavements 2 7 4 3 carbonate rocks for cement and lime carbonate rocks are extremely important raw materials for industry construction agriculture forestry and environmental engineering the most representative application of these rocks is in cement and lime industry cement is a fine powder that sets after a few hours when mixed with water it then hardens in a few days into a solid and strong material the so called portland cement is the most classical type of cement although there are many types of common cement this product is manufactured in a controlled chemical combination of mainly calcium silicon aluminum and iron box 2 6 manufacture of cement the main use of cement is to make concrete the most important construction material in the last century regarding the other main product obtained from carbonate rocks lime is a term specifically used to refer high quality products such as quicklime cao and calcium hydroxide also known as hydrated lime ca oh 2 the raw material for all this type of products is limestone commonly formed by almost exclusively calcium carbonate caco3 limestone is processed to form lime being heated in a specially designed kiln to over 900 c in this process called calcination a chemica

l reaction occurs and creates calcium oxide the applications of lime are huge but those in environmental engineering are the most widely consumed e g soil conditioning or to neutralize the acidic effluents 2 7 4 box 2 6 2 7 4 manufacture of cement cement is a fine gray powder that when reacted with water hardens to form a rigid chemical mineral structure that gives concrete its high strengths the credit for its discovery is given to the romans who mixed lime caco3 with volcanic ash producing a cement mortar that was used during construction of such impressive structures as the colosseum when the roman empire fell information on how to make cement was lost and not rediscovered until many centuries later roman cement was not improved upon until 1758 when smeaton noticed that using a limestone that was 20 25 clay and heating the mixture resulted in a cement that could harden under water portland cement the most common type of cement in common use today is manufactured in a four step process a quarrying b raw material preparation c clinkering and d cement milling and mixing the name portland was given owing to the resemblance of this hardened cement paste to the natural stone available at a place called portland in england most common way to manufacture portland cement is through the so called dry method the raw material for cement manufacture is a rock mixture of about 80 limestone which is rich in caco3 and 20 clay or shale a source of sio2 al2o3 and fe2o3 lime and silica provide the main strength of the cement while iron reduces the reaction temperature and gives the cement its characteristic gray color raw material preparation includes a variety of blending and sizing operations that are designed to provide a feed with appropriate chemical and physical properties thus quarried clay and limestone are crushed separately and samples of both rocks are then sent off to the laboratory for mineral analysis if necessary minerals are then added to either the clay or the limestone to ensure that the correct amounts of aluminum iron etc are present since the four basic oxides must be present in exact proportions calcium oxide 65 silicon oxide 20 alumina oxide 10 and iron oxide 5 limestone and clay are mixed together with many other raw materials such as slate marl blast furnace slag silica sand iron ore and much more these are called correctors because they must define the final proportions of all oxides the clay and limestone and correctors are then fed together into a mill where the rock is ground until the material is less than 100 200 m in diameter in the third step of manufacturing the fine grained raw materials are then dried heated and fed into a rotating kiln fig 2 31 here the raw materials react at very high temperatures to form 3cao sio2 tricalcium silicate 2cao sio2 dicalcium silicate 3cao al2o3 tricalcium aluminate and 4cao al2o3 fe2o3 tetracal

cium aluminoferrite minor compounds such as mgo tio2 mn2o3 k2o p2o5 and na2o are also present in clinker the cement kiln heats all the raw materials to about 1500 c in huge cylindrical steel rotary kilns 60 m long the materials are continuously and slowly moved to the lower end by rotation of the kiln a burner is located at one end of the kiln and the ground raw materials are introduced at the other end as the material moves through the kiln some elements are driven off in the form of gases the remaining elements are joined to form a new substance called clinker and formed by gray balls they are discharged red hot from the lower end of the kiln and commonly are brought down to handling temperature in various types of coolers the final step includes clinker milling and mixing with other components to obtain the so called portland cement thus after the clinker is cooled cement plants grind it in large ball mills to obtain a very fine powder e g 20 m finally it is then mixed with small amount of either gypsum or anhydrite both of which are forms of calcium sulfate as setting retardant and other materials it is essential to note that cement manufacture is an energy intensive process one of the most significant challenges facing the industry into the twenty first century is a requirement to reduce co2 emissions co2 is produced during the calcination phase of the manufacturing process and also as a result of burning fossil fuels opportunity to reduce emissions through increased energy efficiency is only possible on the latter of the co2 emissions in this sense due to the characteristics of the production process the cement industry is capable of coprocessing a alternative fuels which have significant calorific value e g waste oils b alternative raw materials the mineral components of which mean they are suitable for the production of clinker or cement e g contaminated soil and c materials that have both a calorific value and provide mineral components e g paper sludge used tires without coprocessing the wastes and by products that make up these materials would have to be incinerated or landfilled with corresponding greenhouse gas emissions 2 7 4 4 clays for bricks and tiles clay rocks are cohesive unconsolidated or indurated clastic sedimentary rocks where size fraction lower than 0 002 mm is dominant they vary considerably in physical properties color and mineralogical content clay rocks mainly consist of clay minerals such as kaolinite illite montmorillonite chlorite and mixed layer clay minerals besides clay minerals clay and claystone contain fine grained clastic silicates quartz mica and feldspar biogenic matter carbonate microfossils kerogen and coaly particles and diagenetic minerals marcasite pyrite carbonate and phosphate these clays are mainly used for the production of bricks roof tiles ceramic tiles and other fired and sintered products ceramic m

aterials are one of the most important components of the construction industries and they are primarily utilized as building materials these include two big groups a bricks and roof tiles and b ceramic tiles clay for bricks and roof tiles is used in a wide range of buildings from housing to factories as well as in the construction of tunnels bridges etc in brick and roof tile making terms clay includes a range of naturally occurring raw materials in manufacturing process clay must possess some specific properties and characteristics it usually shows the most important property to obtain these products plasticity this property permits clay to be shaped and molded when mixed with water all types of clays used for bricks and roof tiles contain some percentage of silica and alumina sand silt and clay with varying amount of metallic oxides metallic oxides act as fluxes promoting fusion of the particles at lower temperatures 950 c in geological terms the key in the manufacturing process is the mineral content of the raw material due to variances in the age of the deposits depositional conditions and impurities involved there are variations between different clay types even in the same deposit these variations may affect the brickmaking process and the properties of the finished product regarding the second group ceramic wall and floor tiles fig 2 32 they are made from clay and other inorganic raw materials that are ground and or mixed and then molded before drying and firing at sufficiently high temperatures 1400 c to acquire the necessary stable properties the raw materials that make up the ceramic tile are essentially clays feldspars sand carbonates and kaolin from a glazed point of view ceramic tiles can be unglazed or glazed the former is fired only once whereas glazed tiles include a vitrified coating between the firing the manufacturing of glaze and frit is a complex process involving many different raw materials such as carbonates silicates borates and many others according to the main ore forming processes a simple genetic classification of mineral deposits encompasses four main groups 1 magmatic 2 hydrothermal 3 sedimentary and 4 metamorphic metamorphosed the following is a description of the main classes included in these groups however it is not obviously an exhaustive overview of all types of mineral deposits existing in the earth s crust 2 8 1 magmatic ore deposits a magmatic ore deposit is formed by an accumulation of magmatic minerals some of them are extremely rare and almost never encountered in common rocks e g alloys of the platinum metals however other minerals such as magnetite are common a very large and diverse group of ore deposits originates by magmatic processes according to ardnt and ganino 2012 many magmatic ore deposits are hosted by granites but the ore results from precipitation of ore minerals from aqueous fluids and not from the

granitic magma itself the type of ore mineral in magmatic deposits is directly linked to the composition of the host rock for instance deposits of nickel chromium and platinum group elements are founded in mafic ultramafic hosts by contrast felsic rocks generate ores from the elements confined that concentrate in evolved magmatic liquids some of these elements are present in late crystallizing phases such as ilmenite which contains ti and cassiterite the ore of sn and others enter the water rich fluid that separates from the silicate liquid to be redeposited in pegmatites or in hydrothermal ore bodies pegmatites are also an important source of rare but increasingly important metals such as lithium and beryllium crystallization of economic minerals normally occurs from mafic to ultramafic magmas that are low in viscosity and have important content of nickel copper and platinum group elements magmatic ore deposits associated with ultramafic and mafic rocks span most of the history of the earth being well represented in all continents currently these deposits are estimated to account for approximately 7 of the total value of annual global metal and mineral mining and they include the world s greatest concentration of metals the bushveld complex which has an estimated total metal endowment value representing past production and current reserves and resources of us 3 6 trillion peck y huminicki 2016 the description of magmatic deposits can be carried out according to the host rock association or related to the commodity the latter is easier and allows to summarize the main groups of deposits present in the earth s crust from a magmatic viewpoint on this basis four types of magmatic ore deposits can be defined 1 chromite deposits 2 nickel copper sulfide deposits 3 platinum group element pge deposits and 4 diamond deposits since the four types can be considered as orthomagmatic deposits a fifth type related to granitic pegmatites can be added 2 8 1 1 chromite deposits chromite mg fe2 cr3 al fe3 2o4 is the only commercial source of chromium the source to obtain this metal comes mainly from four different mineral deposit types podiform deposits stratiform deposits placer deposits and laterites the latter are derived from weathering of ultramafic rocks that contain chromite in particular most of the world s resources are located in stratiform chromite deposits such as the bushveld complex south africa fig 2 33 and the great dyke zimbabwe the bushveld complex contains the main type examples of ore deposits in a large layered intrusion important podiform chromite deposits are located in kazakhstan turkey the philippines new caledonia and russia known resources of alluvial and eluvial placer deposits derived by erosion of such rocks are low in grade and of very minor importance misra 2000 the major stratiform chromite deposits also contain important contents of platinum

palladium rhodium osmium iridium and ruthenium regarding the genesis of the deposits little consensus has been reached about the magma chamber processes responsible for chromite segregation and crystallization although extensive studies have been carried out in general the most widely accepted explanation involves the mixing of primitive and fractionated magmas thus the commonly cited hypotheses include 1 mixing of a parent magma with a more primitive magma during magma chamber recharge and 2 contamination of the parent magma by localized assimilation of country rock at the roof of the magma chamber the mixing of magmas would produce a partially differentiated magma which could then be forced into the chromite stability field and result in the massive chromitite layers found in stratiform complexes schulte et al 2012 in this sense chromitite is a term used for massive chromite containing 50 to more than 95 of cumulus chromite the sequences of massive chromitite layers 90 chromite or seams of disseminated chromite 60 chromite are commonly found in the lower ultramafic parts of the layered intrusions these intrusions were emplaced in stable cratonic settings or during rift related events throughout the archean or early proterozoic although a few younger deposits exist the intrusions extend anywhere from 2 to 180 km in diameter and can reach thicknesses of as much as 15 km as a rule the individual seams included in the intrusions range from less than 1 cm to 5 8 m thick the mineral occurs in layers that reach a meter or more in thickness alternating with layers composed of other magmatic minerals arndt and ganino 2012 in some cases the chromite deposit is not economic due to the low grade of the mineralization or the low tonnage of chromite available for mining podiform chromite deposits another important source for chromite are small magmatic chromite mineralization originated in the ultramafic part of an ophiolite complex in the oceanic crust most podiform chromite deposits are located in dunite or peridotite close to the contact of the cumulate and tectonite zones in ophiolites mosier et al 2012 accordingly chromite that occurs in podiform deposits has a geotectonic environment distinctly different from the model in stratiform chromite deposits in podiform deposits chromite shows different textures such as massive aggregates and banded nodular net or graded layers which indicate relict cumulate features nodular texture is probably the most important feature to distinguish podiform chromite deposits from stratiform deposits 2 8 1 2 nickel copper deposits these deposits are referred as magmatic sulfide rich ni cu pge deposits related to mafic and or ultramafic dyke sill complexes the name of the deposits emphasizes the relation of these ni cu sulfide rich deposits to mafic and ultramafic rocks and to mostly small to medium sized dykes and sills as opposed to the generally muc

h larger layered mafic ultramafic intrusive complexes that typically host sulfide poor pge enriched deposits such as stillwater complex in montana usa nickel sulfide deposits can be classified into two principal classes based on the petrology of the host rocks peridotite dunite class komatiitic association and gabbroid class tholeiitic association fig 2 34 according to schulz et al 2014 sulfide deposits containing nickel and copper with or without platinum group elements pge account for approximately 60 of the world s nickel production and they form where mantle derived sulfur undersaturated picrite or tholeiitic basalt magma becomes sulfide saturated commonly following interaction with continental crustal rocks sulfur saturation results in formation of an immiscible sulfide liquid which tends to segregate into physical depressions in the lower parts of dike and or sill like intrusions because of changes in the magma flow dynamics such dynamic systems appear to promote the interaction of sulfide liquid with a sufficiently large amount of silicate magma to concentrate chalcophile elements to economic levels the ore metals nickel copper and the pge are all chalcophile and show a tendency to partition more or less strongly into the sulfide nickel is lithophile as well as chalcophile and in normal ultramafic rocks it is distributed between olivine and sulfide copper is moderately chalcophile but the pges are enormously chalcophile this means that any droplet of sulfide will extract most of the copper and nickel and effectively all of the pge from the surrounding silicate liquid in this sense if the sulfide droplets can then be concentrated effectively for instance by gravitational processes then an ore deposit is formed arndt and ganino 2012 deposits of magmatic ni cu sulfides occur with mafic and or ultramafic bodies emplaced in diverse geological settings they generally are found in penetrating faults which permit the efficient transport of magma undersaturated in sulfur from the mantle to relatively shallow crustal depths for this explanation sulfur bearing crustal rocks such as black shales evaporites or paragneisses are near to many deposits and a potential source of sulfur these deposits range in age from archean to cenozoic but the largest number of deposits are archean and paleoproterozoic although the deposits occur in most continents the biggest ones are located in russia china australia canada and southern africa the major ni cu sulfide mineralogy typically consists of an intergrowth of pyrrhotite pentlandite and chalcopyrite in most cases the massive and matrix ore is zoned with copper rich zones relatively enriched in gold palladium and platinum those zones as footwall dykes and veins either overlie or are separated from cu poor zones relatively enriched in osmium iridium ruthenium and rhodium the compositional zonation is attributed to fractionation of monosu

lfide solid solution from a sulfide liquid cobalt pge and gold are extracted from most magmatic ni cu ores as by products although such elements can have a significant impact on the economics in some deposits the noril sk talnakh deposits being a good example which produce much of the world s palladium in addition these deposits may contain between 1 and 15 magnetite associated with the sulfides schulz et al 2014 the sulfide rich ni cu pge deposits contain ore grades of between 0 5 and 3 of nickel and between 0 2 and 2 of copper tonnages of individual deposits range from a few tens of thousands to tens of millions of tons bulk ore two giant ni cu districts with 10 mt nickel dominate world nickel sulfide resources and production these are the sudbury district in ontario canada where sulfide ore deposits are at the lower margins of a meteorite impact generated igneous complex and contain 19 8 mt of nickel and the noril sk talnakh district in siberia russia where the ore deposits are in subvolcanic mafic intrusions and contain 23 1 mt of nickel three other ni cu sulfide deposits in the world are also important voisey s bay in newfoundland kambalda in australia and jinchuan in china 2 8 1 3 pge deposits the concentration of pge in terrestrial environments ranges from sub ppb level in rocks of felsic and intermediate composition to generally 1 100 ppb in mafic and ultramafic rocks economic deposits typically contain 5 10 ppm pge and involve concentration factors in the order of 1000 similar to those for gold deposits anomalous concentrations of pge are known from high temperature magmatic to low temperature hydrothermal and sedimentary environments but significant concentrations of pge are virtually restricted to ultramafic rocks two types of deposits both intimately associated with ni cu sulfides account for about 98 of the world s identified pge resources a stratabound deposits in large layered complexes e g bushveld stillwater and great dyke mined primarily for pge and b ni cu sulfide deposits mined primarily for ni cu sulfides but containing recoverable amounts of pge as by products e g sudbury noril sk talnakh jinchuan and karnbalda deposits misra 2000 the large layered intrusions contain about 90 of the world s pge resources with the bushveld complex accounting for about 80 in general the deposits generally occur as sparsely dispersed sulfide minerals in basal units or stratabound layers or reefs in very large to medium sized typically layered mafic and or ultramafic intrusions in the bushveld complex there are in the lower part important deposits of the platinum group elements mainly at two specific horizons the upper layer is the merensky reef a thin 1 10 m layer of pegmatoid pyroxenite the second principal mineralized layer termed ug2 is a group of thick chromite reefs that in addition to high pge concentration are also extracted for their chromium contents

arndt and ganino 2012 there is no consensus regarding the origin of these types of pge deposits one line of thinking argues that these deposits formed through magmatic processes whereas the opposing view ascribes an important role to the migration of volatile rich fluids arndt and ganino 2012 also said that in the first case a plume of primitive magmatic liquid was injected into the base of the chamber and then mixed with evolved liquid to produce a hybrid magma that became saturated in sulfide the other view propose that volatile rich fluids migrated up through the cumulus pile leaching out the pge from the cumulus minerals then redepositing them at favorable horizons 2 8 1 4 diamond deposits diamonds form under extreme high pressures and temperatures at depths greater than 150 km below the surface predominantly though not exclusively in the earth s lithospheric upper mantle they are transported into the crust either rapidly in explosively emplaced volatile rich kimberlite lamproite or related magmas or more slowly by tectonic processes in rocks that have undergone ultrahigh pressure metamorphism fig 2 35 diamond ore deposits are confined to a minority of the volcanic sources and to secondary deposits derived from them gurney et al 2010 since diamonds only form beneath old stable and thick parts of the earth s crust this greatly restricts the global distribution of primary deposits although diamond deposits are often very low grade the value of the individual diamonds makes the overall deposit highly valuable thus diamond deposits represent some of the highest value mines globally grade values in diamond deposits commonly range from 0 25 to 1 5 carats t carat being the measurement of weight in diamonds 1 carat equals 0 2 g the value of the diamonds can be very variable depending on its size shape color and quality large equidimensional colorless and clear diamonds without defects are most highly valued therefore the common measure used to assess the economic potential of a deposit is a combination of the grade of the deposit carats per ton and the dollar value per carat of the diamonds in the deposit stevens 2010 diamond in kimberlite is probably the best known type of magmatic mineral deposit box 2 7 diamond in kimberlite the famous diamond deposits at india and borneo were the only diamond producers until the eighteenth century some big and famous diamonds such as koh i noor or the great mogul diamond were obtained from these countries several decades ago almost all diamond mines were located in southern africa but large and important deposits have been found and mined in russia australia and canada examples of these deposits are the mir pipe in yakutia russia perhaps the most diamond bearing kimberlite pipe in the world which contains only one part of diamond per every one and half million parts of kimberlite the diamond bearing kimberlites of africa angola botswana

lesotho sierra leone south africa swaziland tanzania the diamond deposits in australia western australia and the kimberlite pipes in canada nwt secondary diamond deposits such as placer deposits are formed from these primary source kimberlite rocks by weathering and transportation the resulting deposits are commonly very rich in high quality diamonds examples include those of the ural mountains the marine deposits of namibia and the alluvial deposits of west africa brazil and venezuela these deposits have supplied about 90 of the world s diamond output diamond is one of the most sought after gemstones on earth they are formed mainly in the earth s lithosphere where pressure conditions are appropriate for carbon to crystallize as diamond and they are brought to the surface mostly through the eruption of alkaline igneous rocks following the discovery of diamonds in river deposits in central south africa in the mid nineteenth century it was at kimberley where the volcanic origin of diamonds was first recognized these volcanic rocks that were named kimberlite were to become the cornerstone of the economic and industrial development of southern africa thus the name of the rock comes from the town of kimberley in south africa where the discovery of a diamond called the star of south africa in 1869 spawned a diamond rush and creating the big hole fig 2 36 it is claimed to be the largest hole excavated by hand early mining of the kimberlites around kimberley was a chaotic business with many claim holders digging small individual claims of 10 by 10 m later as mining reached deeper levels and became more difficult claims were consolidated into numerous companies in 1888 de beers consolidated mining company was created and this company consolidated all mining operations under the one company thereby creating the leading diamond producer in the world for the next 90 years a variety of mantle derived igneous rocks comprise the primary sources of diamond with the principal hosts being kimberlite and lamproite kimberlite is a special type of ultramafic magma and derived from the earth s mantle at more than 140 km depth lamproite a rock type similar to kimberlite can also contain commercial diamond deposits all kimberlite hosted diamond mines which exist in the world like in south central and southern africa western africa canada china russia and the usa are located in archean continental blocks they are virtually restricted to ancient 2 4 ga cratons and the younger 1 0 ga accreted belts of cratonized regions that are underlain by cratons the ages of kimberlites range from proterozoic to tertiary diamonds in economic deposits are estimated to be mainly 99 derived from subcontinental lithospheric mantle gurney et al 2010 in both kimberlites and lamproites diamonds range in size from microcrystals smaller than 50 microns to macrocrystals occasionally over l cm in size it is importan

t to remember that most kimberlites and lamproites contain no diamonds in fact diamonds are a very minor xenocryst component 5 ppm in even the richest ore bodies of the approximately 1000 individual kimberlite intrusions known in south africa only about 50 carry significant quantities of diamonds of these many are considered subeconomic either because the quantity or quality of the diamonds or the quantity of ore is insufficient the presence and quality of diamonds in a kimberlite can only be determined with confidence by the collection and processing of a large and representative sample the typical diamond deposit is pipe or carrot shaped with a circular surface diameter of 50 500 m and a depth extent of several hundred to one thousand meters or more the distribution of the diamond xenocrysts is variable in the whole host rocks and the concentration has a level of less than 0 01 2 0 ppm strictly speaking diamonds in kimberlites are not truly magmatic kimberlite magma is merely a vehicle that transports the diamonds rapidly to the surface under conditions that prevent them from reverting to graphite their unattractive low pressure polymorph diamonds remain hidden unless they are picked up by younger kimberlites lamproites or other magmatic rocks originated either within or below the mantle source region and intruding fast enough for the diamonds to survive transport to the surface or near surface emplacement site probably kimberlites move to the surface through the mantle at velocities of 10 30 km h by crack propagation processes 2 8 1 5 pegmatite deposits another type of magmatic ore deposit is found in pegmatites in these rocks metals like lithium beryllium boron tin niobium thallium and the rare earth elements are mined pegmatites are formed by the crystallization of melts expelled from granitic magmas pegmatitic rocks are very coarse grained basement rocks abundant in quartz feldspar and or mica in places endowed either with megacrystals of the aforementioned rock forming minerals or rare element minerals apart from the size of their crystals it is the varied spectrum of rare elements and the significant number of extraordinary minerals resultant from these elements which renders these crystalline rocks so different from granitic rocks dill 2015 most pegmatites show a paragenesis of orthoclase microcline albite mica quartz and common minor minerals including topaz tourmaline cassiterite beryl and lithium granite pegmatites occur in the form of dikes oval and lenticular bodies being homogeneous without a change of mineralogy or texture from wall to wall and isotropic or strikingly inhomogeneous and anisotropic zoned or complex pegmatites most pegmatite bodies are relatively small with a thickness that rarely surpass tens of meters and a length of a few hundred meters pohl 2011 but with increasing industrial request for high technology metals such as lithium and the rare ea

rth elements arndt and ganino 2012 pegmatites may host many useful raw materials ores of be li fig 2 37 rb cs ta nb u th ree mo bi sn and w the industrial minerals muscovite feldspar kaolin quartz spodumene fluorite and gemstones as well as rare mineral specimens emerald topaz tourmaline ruby etc linnen et al 2012 the complex type pegmatites of the lithium cesium thallium lct family being an important class of rare element pegmatites the nyf pegmatites are a different family of pegmatites and are enriched in niobium yttrium and fluoride their current economic importance is much less than that of the lct family but these pegmatites could be a source in the future for rare earth elements and other strategic metals pegmatites of the lct family were emplaced in orogenic hinterlands intruding metasedimentary rocks typically at low pressure amphibolite to upper greenschist facies the largest deposits being archean in age giant deposits of these pegmatites include tanco in canada 2 1 mt at 0 215 ta2o5 greenbushes in australia 70 4 mt at 2 6 li2o and bikita in zimbabwe 12 mt at 1 4 li2o bradley and mccauley 2013 on the other hand nyf pegmatites are also sometimes ree enriched pegmatites traditionally the vast majority of this kind of pegmatites has been exploited for their major mineral content feldspar quartz and muscovite studies of ree enriched granitic pegmatites as a whole lag severely behind those of lct pegmatites in terms of classification numbers and detail of field descriptions and mineral compositional data ercit 2005 2 8 2 hydrothermal ore deposits they represent an essential group of ore deposits because they are the source for most of the metal production of the world hydrothermal deposits provide almost 100 of lead zinc molybdenum and silver and 60 90 of copper gold and uranium as well as gemstones and industrial materials such as clay minerals and quartz hydrothermal deposits are quite different being located in a broad rank of geological and tectonic settings some of them are closely linked with granitic rocks others form on the ocean floor and still others are in sedimentary basins all the deposits have common origin via the precipitation of metals or ore minerals from hot aqueous fluids arndt and ganino 2012 the main examples of hydrothermal ore deposits include 1 porphyry deposits 2 volcanogenic massive sulfide vms deposits 3 sedimentary exhalative sedex deposits 4 iron oxide copper gold deposits and 5 gold deposits 2 8 2 1 porphyry deposits porphyry copper deposits pcd are large low to medium grade cu au mo hydrothermal deposits related to igneous intrusions being the largest source of the world in copper and a major source of molybdenum gold and silver despite relatively low grades pcds have significant economic impact due to their large size commonly hundreds of millions to billions of metric tons lon

g mine lives decades and high production rates billions of kilograms of copper per year with incrementing molybdenum copper ratio these deposits are transitional to low fluorine quartz monzonite type porphyry molybdenum deposits with incrementing gold copper ratio they are transitional to porphyry gold deposits john et al 2010 thus it is common to describe several subtypes of porphyry deposits according to the dominant metal porphyry cu porphyry cu au and porphyry cu mo porphyry copper deposits are constituted by disseminated copper minerals in veins and breccias and form high tonnage greater than 100 million tons and low to moderate grade 0 3 2 0 copper mineral deposits in contrast to vms deposits see next section which normally are small 1 5 mt but of high grade 3 10 ore metals porphyry deposits are enormous but of low grade these deposits were the first group of metallic mineral deposits mined by large scale open pit methods in the early twentieth century the best known deposits are in the cordilleras of north and south america the bingham mine in the usa 2 7 billion tons of ore grading 0 7 cu and 0 05 mo and the chuquicamata mine in chile 11 billion tons of 0 56 cu and 0 06 mo arndt and ganino 2012 box 2 8 chuquicamata copper mine chile the mineralization in the porphyry deposits consists of disseminated small concentrations of sulfide minerals in the highly altered upper portions of the intrusion and in surrounding rocks closely associated with the mineralization is a moderate to intense alteration that shows a zoning concentric about the intrusion this alteration also span outside the zone of mineralization and it is commonly utilized as a guide during the exploration of this type of deposits most pcd deposits are located within felsic to intermediate igneous intrusions and in the country rocks that surround the intrusion original sulfide minerals are pyrite chalcopyrite bornite chalcocite and molybdenite gold is often in native form and is found as tiny blobs along borders of sulfide crystals or it occurs in sulfosalts like tetrahedrite molybdenite distribution is variable and radial fracture zones outside the pyrite halo may contain lead zinc veins with significant gold and silver contents in deposits with an extensive supergene enrichment zone developed in the upper parts of the deposit copper oxide minerals and native copper may be present in many districts plutons and batholiths that host the mineralization are older and not related to the ore forming system although they can be part of long lived magmatic successions in other districts they are only slightly older and range from multiple large stocks to composite batholiths john et al 2010 the regional deposit scale and local scale environments of porphyry copper can be very varied they are widespread but mostly localized in time and space through the evolution of magmatic arcs along convergent p

late margins where subduction of oceanic crust and arc type magmatism generates hydrous oxidized upper crustal granitoids genetically related to ores it is possible that many porphyry copper deposits are formed during unusual periods of subduction deposits have formed throughout most of earth s history but because they generally form in the upper crust less than 5 10 km depth in tectonically unstable convergent plate margins and are prone to erosion more than 90 of known deposits are cenozoic or mesozoic in age pcds are thought to derive from hydrothermal fluids generated near the top of a cooling magma body at depths between 1 and 5 km stevens 2010 the close spatial and temporal association between the ore bodies and granitic intrusions is clearly indicative that magmas are directly linked to the ore forming process porphyry copper systems are mainly formed by magmatic fluids that were released during shallow emplacement of porphyritic granitoid stocks the fluids create a fracture network in the rocks as they travel thereby producing the characteristic stockwork texture of this type of deposits the ore minerals crystallize out of the hydrothermal fluids as a result of cooling of the fluid as it moves away from the magma body thus formation of porphyry copper deposits as john et al published in 2010 involves a complex series of processes including magma generation differentiation emplacement crystallization and degassing high temperature reactions between degassed fluids and meteoric and other non magmatic waters and near surface reactions between low temperature meteoric water and earlier formed high temperature minerals external saline waters such as sedimentary brines were probably involved in the earlier stages of evolution of some porphyry copper systems resulting in sodic and sodic calcic alteration 2 8 2 box 2 8 2 8 2 chuquicamata copper mine chile chile is known worldwide as the site of one of the largest copper concentrations on earth thus chuquicamata mine fig 2 38 property of codelco is one of the largest open pit copper mines and the second deepest open pit mine in the world popularly known as chuqui the name comes from indigenous communities chuquis who lived in the area and obtained native copper the open pit measures are 5 km large 3 km width and 1 km deep forming an ellipse chuquicamata mine began open pit mining in the year 1915 although its mining properties had been known for centuries by the pre hispanic cultures in 1971 the mine was nationalized and management and operation were taken over by the corporaci n nacional del cobre chile codelco at the end of the year 2005 it had mined out about 2 6 billion tons of copper ore with a mean grade of 1 53 reaching a pit depth of 850 m the chuquicamata mine complex is located 1650 km north of the chilean capital city santiago at 2870 m above sea level chuquicamata produces electrorefined and electrowon cathodes havi

ng a purity of 99 99 copper it also produces fine molybdenum as well as other by products such as anode slimes and sulfuric acid the chilean cordillera contains 9 of the 16 giant porphyries along the circum pacific belt chuquicamata lies in the precordillera of northern chile which is parallel and west of the volcanoes that form the modern continental arc of the andean cordillera the chuquicamata mine lies on the chuqui porphyry complex a north northeast trending elongated tabular intrusive complex that measures 14 km 1 5 km virtually the entire ore deposit at chuquicamata is hosted by and related to this 36 33 ma porphyry complex that comprises a number of phases many of which do not have well defined contacts the porphyry copper ore body is rectangular in plan and dips vertically being the zone s porphyries largely affected by potassic alteration the great majority of the mineralization at chuquicamata occurs in veins and veinlets the earliest of which are quartz and k feldspar veinlets with little or no sulfides these are cut by more continuous quartz veins ranging up to 5 cm in width with molybdenite and traces of chalcopyrite the next generation is the pyritic main stage veins which carry pyrite chalcopyrite bornite and digenite the final phase of mineralization is represented by a partly preserved leached cap and extensive oxide ore that replaces an upper chalcocite blanket which overlies a high grade supergene blanket that persists to nearly 800 m below surface in the zone of fault brecciation and pervasive pyritic main stage quartz sericite alteration finally chuquicamata underground mine is a structural and strategic project that represents an important part of codelco s future and which considers transforming the world s largest open pit mine into a gigantic underground operation this new underground mine is being developed to access the ore body situated beneath the present open pit mine because currently the mine is producing 400 000 tons of waste rock and since it increases the cost and distance that must be reached to find mineralization it generates higher costs the geological data from drillholes indicate that below the final pit bottom there are about 2 3 billion tons of ore with a mean copper grade of 0 81 the project involves ore extraction by macro blocks and block caving in an underground mine at depths of 1300 1800 m the underground mine scheduled to begin operations in 2020 will comprise four production levels a 7 5 km main access tunnel five clean air injection ramps and two air extraction shafts 2 8 2 2 volcanogenic massive sulfide vms deposits this type of deposits is referred to as volcanogenic massive sulfide vms although similar terms have been used volcanic massive sulfide submarine exhalative massive sulfide and volcanic hosted massive sulfide among many others more recently the term polymetallic massive sulfide deposit has been also applied by many authors to v

ms mineralization on the modern seafloor that contains significant quantities of base metals volcanic massive sulfide deposits are small to medium sized moderate to high grade cu zn pb au ag hydrothermal deposits hosted in volcanic and or sedimentary rocks they are significant sources of copper and zinc and to a lesser extent lead silver gold cadmium selenium tin bismuth and minor amount of other metals the polymetallic and sometimes high grade character of the deposits make them a preferential target for exploration as in the case of the porphyry deposits there are several subtypes of vms deposits depending on the dominant metal and host rocks vmss are among the best understood of all ore deposits due to the ore bodies that are relatively simple both in their structure and their composition and mineralogy and they have been studied intensively over the last decades they are one of very few deposits whose formation by way of precipitation of sulfides at or just below the ocean floor can be observed directly black smokers vms deposits were among the first ever to be mined because this mineralization was mined in cyprus and in spain more than 2000 years ago providing much of the copper utilized in the weapons of roman centurions the old rio tinto mine in southwestern spain has one of the world s longest known mining histories with copper having been mined there even before roman times box 2 9 rio tinto copper mine spain this mine was the foundation stone for the mega mining company that still bears its name rio tinto has subsequently gone on to become one of the world s biggest diversified mining companies volcanogenic massive sulfide deposits are stratabound concentrations of sulfide minerals precipitated from hydrothermal fluids in extensional seafloor environments the term volcanogenic implies a genetic link between mineralization and volcanic activity but siliciclastic rocks dominate the stratigraphic assemblage in some settings relation to volcanoes ranges from proximity to quite tenuous connections to volcanism as in parts of the southern iberian pyrite belt pohl 2011 vms deposits are hosted in volcanic rocks dominated by basalt there are usually important felsic volcanic and sedimentary rock layers closely associated with the deposit and small intrusive igneous rock bodies are often located beneath the deposits stevens 2010 the deposits are formed by two parts a concordant massive sulfide lens 60 sulfide minerals and discordant vein type sulfide mineralization commonly called the stringer or stockwork zone individual lenses are 2 20 m thick and extend for tens to hundreds of meters laterally large lenses can reach more than 100 m thick and extent for more than 1000 m laterally they show different mineralization textures such as breccias layering and laminations the deposits are characterized by abundant fe sulfides pyrite or pyrrhotite normally comprises more than 80

of the minerals in the massive sulfide bodies vms deposits are derived from hydrothermal fluids that circulate through a sequence of volcanic rocks and exit on the seafloor as a plume of metal rich fluids they encompass a wide variety of geodynamic and more local genetic settings thus the main tectonic settings include mid oceanic ridges volcanic arcs intraoceanic and continental margin back arc basins rifted continental margins and pull apart basins the composition of volcanic rocks hosting individual sulfide deposits range from felsic to mafic but bimodal mixtures are not uncommon and the volcanic strata consist of massive and pillow lavas sheet flows hyaloclastites lava breccias pyroclastic deposits and volcaniclastic sediments a zonation of metals within the massive sulfide body from fe cu at the base to zn fe pb ba at the top and margins characterizes many deposits koski and mosier 2012 deposits range in age from early archean 3 55 ga to the present and significant occurrences of vms mineralization are found in greenstone belts of almost all precambrian shield areas of particular importance are the archean and early proterozoic greenstone belts of the canadian shield the lower paleozoic volcanic belts of the caledonides in scandinavia and the northern appalachians of newfoundland canada the upper paleozoic iberian pyrite belt extending from southern portugal to southern spain and the miocene green tuff belt of japan e g kuroko sulfide deposits misra 2000 2 8 2 box 2 9 2 8 2 rio tinto copper mine spain the iberian pyrite belt is located in the sw of the iberian peninsula comprising part of portugal and of the provinces of huelva and sevilla in spain being one of the most important volcanogenic massive sulfide districts in the world r o tinto mine is located at the eastern end of the iberian pyrite belt within the pyrite belt there are eight major mining areas each thought to contain more than 100 million tons or ore these are from east to the west aznalc llar los frailes r o tinto sotiel migollas la zarza tharsis masa valverde neves corvo and aljustrel r o tinto mining area is the largest of these and includes two big open pit mines cerro colorado fig 2 39 and corta atalaya the high geological interest of this mining district is because it is most probably the biggest sulfur anomaly on the earth s crust with original tonnages around the 2500 million tons of mineralized rock in different degrees in fact the cerro colorado deposit contained one of the largest known concentrations of sulfides in the world the name of r o tinto mines comes from r o tinto river in turn it takes the name from its red color trace amounts of gold are present in a wide variety of mineral deposits ranging from 0 01 ppm au in mississippi valley type deposits to concentrations in some sulfide deposits high enough to be recoverable as a by product main types of ores that routinely produce

by product gold are ni cu sulfide ores associated with mafic and ultramafic rocks vms ores and cu ores of porphyry copper deposits however most of the important gold deposits belong to one of the following seven types a young placer deposits b deposits hosted by quartz pebble conglomerates witwatersrand type c volcanic associated epithermal deposits d sediment hosted disseminated deposits carlin type e deposits hosted by banded iron formations f intrusion related deposits and g lode deposits misra 2000 type c is possibly the most important gold type deposit of hydrothermal affiliation other essential types for gold extraction e g witwatersrand type are also described below volcanic associated epithermal gold deposits got the name epithermal according to the classification of lindgren 1913 who coined this term for deposits that form from hydrothermal fluids at shallow crustal levels occurring in a variety of structural settings they are commonly associated with subduction related calc alkaline to alkaline arc magmatism as well as back arc continental rift magmatism because of their relatively higher grades and amenability to cheaper open pit mining and heap leach extraction of gold epithermal deposits have been a favored target of exploration since the early 1970s the main distinguishing characteristics of epithermal gold deposits are the following 1 andesitic volcanic and pyroclastic rocks are the more common host to ore early to late tertiary 2 the deposits formed in extensional tectonic settings in zones with well developed tension fracture systems and in normal faults that could channel hydrothermal fluids and localize mineralization 3 c the mineralization is epigenetic and occurs commonly in the form of quartz veins 4 ore and associated minerals occur dominantly as open space fillings producing characteristic banded and crustiform textures 5 gold and silver are the principal economic metals main ore minerals in the veins are native gold and silver electrum argentite ag bearing as sb sulfosalts and au bearing pyrite associated base metal sulfides which are generally concentrated below the precious metal horizon include sphalerite galena and chalcopyrite 6 quartz and calcite are the most abundant gangue minerals in the veins 7 hydrothermal alteration of wall rock is a characteristic feature of all epithermal precious metal deposits misra 2000 2 8 2 6 vein deposits the most convincing examples of hydrothermal deposits are vein systems discordant to stratification or lithologic boundaries in host rocks box 2 10 panasqueira tungsten mine portugal they represent dominantly open space filling of structurally controlled fractures and faults some vein type deposits are believed to be genetically related to exposed or buried igneous especially felsic intrusions because fluid inclusion and isotopic data provide evidence for a major contribution of m

agmatic water in the ore forming fluids ore fluids for other types of vein deposits may have been dominated by magmatic water meteoric water or basinal brines many veins in this type of deposit are developed upward into a fan of thinner veins and veinlets which resemble a branching tree thickness vertical extent and horizontal length of veins vary widely less than 0 5 m in thickness may allow profitable mining of high grade gold and silver ore veins fig 2 42 whereas tin and tungsten require a width of 1 m and barite and fluorite a minimum of 2 m width the distribution of veins in space ranges from horizontal to vertical although steeply dipping veins are the majority from a tectonic viewpoint many veins are associated with large scale tensional tectonics including rifting and late orogenic relaxation of orogens however veins may also originate during convergent tectonics pohl 2011 the most important control on vein formation is related to the mechanical properties of the host rocks fractures form more readily in competent rocks than in ductile materials very brittle rocks such as dolomite or quartzite use to create a network of short fractures instead of spatially separated longer ones in that case hydrothermal activity may result in stockwork ore stockwork ore bodies consist of numerous short veins of three dimensional orientation which are so closely spaced e g 30 veins m that the whole rock mass can be mined the distribution of ore in veins is usually inhomogeneous and only a small part of the total vein fill is exploitable veins commonly consist of quartz sometimes of several varieties e g chalcedony this quartz commonly occurs as interlocking crystals with a great variety of sizes or as finely laminated bands parallel to the walls of the vein minor amount of sulfide and other gangue minerals such as calcite and various clay minerals occur typical mineral associations in vein deposits are gold with pyrrhotite gold with arsenopyrite gold with pyrite gold with chalcopyrite gold with minor sulfides free gold silver with galena and galena sphalerite silver with tetrahedrite or antimony or copper arsenic sulfides sedimentary mineral deposits are those that form by sedimentary processes they include placers originated by erosion transportation and sedimentation processes as well as deposits related to water infiltration supergene alteration and diagenetic processes the boundary between sedimentation and diagenesis is subtle moreover diagenetic ore deposits can be many times considered as diagenetic hydrothermal mineral deposits 2 8 3 1 supergene enrichment deposits if the sulfide mineralizations are exposed at the surface of the earth it is very common that these minerals become oxidized the ore metals being leached downward and usually concentrated at the top of the water table thus supergene enrichment is a consequence of near surface oxidation caused by meteoric water seeping d

ownward through the unsaturated zone this oxidation process can be very useful if the previous mineralization has a low grade character in some cases the copper grade can increase from 0 8 cu in the primary ore to 2 3 in the thick layer of supergene enrichment consequently these layers of supergene enrichment contain two to five times more ore metals than the primary ore and they are conveniently located close to the surface where they can be recovered at the start of the mining operation for sulfide copper and silver ores iron oxides and some uranium ore deposits this process is of economic significance pohl 2011 the best known examples of supergene enrichment zones are perhaps those overlying porphyry copper deposits other example of supergene enrichment deposits is lateritic nickel ore deposits nickel cobalt laterites fig 2 43 an important source of nickel are supergene deposits of ni co formed from pervasive chemical and mechanical tropical weathering of ultramafic rocks which contain as much as 0 3 percent nickel marsh and anderson 2011 suggest that the extreme weathering removes all elements except the least soluble ones from the protolith and the residual material can average as much as 5 nickel and 0 06 cobalt thus the enrichment of nickel in the weathering profile is controlled by several interplaying factors that include parent rock climate chemistry rates of chemical weathering drainage and tectonics in some cases these deposits can be later subsequently weathered redeposited reconcentrated and probably covered by new sediments in this type of deposits the economically interesting component is concentrated in situ while weathering removes diluting parts of the rock examples are residual and eluvial placers bauxite lateritic gold platinum iron and nickel ores residual enrichment of subeconomic iron and manganese ores and industrial minerals such as phosphate magnesite and kaolin pohl 2011 the fundamental geochemical principle of the enrichment is the steady activity of a reaction front in soil while the land surface is lowered by weathering and erosion at the reaction front the valuable component is immobilized and the enrichment is due to retention and accumulation of the component of interest contained in the removed rock and soil volume an example of this process is eluvial enrichment of phosphate from carbonatites by leaching of carbonate whereas apatite remains in place probably one of the most characteristic ores of this group is bauxite fig 2 44 the purest bauxites form through a combination of processes 1 the presence of al rich and fe poor parent rocks such as alkali granite syenite tuff or clay rich sediment and their metamorphosed equivalents 2 an appropriate balance of temperature and rainfall high temperatures favor fe rich laterites and 3 a pronounced alternation of wet and dry seasons arndt and ganino 2012 as a result of these re

strictions the most important bauxite deposits in the world are located mainly in equatorial countries with tropical climates such as guinea australia brazil and jamaica in parts of africa south and central america and australia the concentration of al2o3 increases from about 15 in the source rock to close to 60 the level in rich al ore ardnt and ganino 2012 infiltration mineral deposits are formed where meteoric water takes up a substance that is dissolved by weathering and it is concentrated after considerable transport by infiltration in a different geological setting the so called roll front uranium deposits are the most typical example of this type of deposits in this deposit uranium is quickly dissolved from rocks such as granite gneiss and felsic tuff and then transported during hundreds of kilometers by rivers until infiltrating into an aquifer where reduced conditions produce the precipitation and concentration of uranium minerals uraninite uo2 or pitchblende uo3 u2o5 the critical aspect to the formation of uranium deposits is the great different solubility of uranium in oxidized and reduced fluids uranium occurs in two valence states the reduced form u4 and the oxidized form u6 the latter is highly soluble in oxidized fluids where it forms stable complexes with fluoride phosphate or carbonate ligands under these conditions uranium is readily transported in the fluids that circulate along sedimentary basins some deposits of metal such as copper iron vanadium silver and pb z ba f could have a similar genesis pohl 2011 from a geological viewpoint roll front uranium deposits host in coarse grained permeable sandstones which at depth contain a reduced array of pyrite calcite and organic matter the age of this host sediment ranges from upper paleozoic to cenozoic in many cases the sandstone bed is confined above and below by shale or other impermeable rocks fig 2 45 this forces the groundwater to flow through the sandstone and provides a better opportunity to form an economic deposit the colorado plateau region in the usa is the most famous place showing this type of uranium deposit 2 8 3 4 placer deposits a placer ore body is a deposit of sand gravel or soil containing eroded particles of valuable minerals due to the chemical and physical properties of the minerals they can resist and become concentrated in the surface environment classical minerals in placer deposits are platinum metals gold present in the native or metallic form many heavy minerals such as rutile ilmenite zircon and monazite they are sources of titanium zirconium niobium and other high technology metals and gemstones such as diamond garnet or ruby moreover in this type of deposit the valuable minerals are clearly denser than other minerals that are transported at the earth s surface this allows minerals to be separated from detrital minerals or rock fragments that constitute the overall se

diment load and finally to become concentrated in ore bodies therefore a simple washing in a gold pan easily separates light minerals of valuable ones there are many classifications of placer deposits of economic importance but the most useful separate them as residual eluvial colluvial fluviatile and coastal marine and beach placers are also terms used for coastal placer deposits other types include aeolian placers and placers in glacial sediments but they commonly have no economic significance placer gold deposits have produced two thirds of the gold mined over time the fluvial placers of california australia and elsewhere were mined out very rapidly in the gold rushes usually over periods of only a few years at present production continues in the witwatersrand ore bodies of south africa a hydrothermally reworked conglomeratic paleoplacer deposit that is the largest gold deposit in the world an example of placer exploitation in the past is las m dulas in spain mined by the romans see box 3 the processes that form coastal deposits of heavy mineral sands usually begin inland and can be described in the following sequence van gosen et al 2014 high grade metamorphic and igneous rocks that contain heavy minerals are weathered and eroded contributing detritus composed of sand silt clay and heavy minerals to fluvial systems streams and rivers carry the detritus to the coast where they are deposited in a variety of coastal environments such as deltas the beach face foreshore the nearshore the barrier islands or dunes and the tidal lagoons as well as the channels and floodplains of streams and rivers in the coastal plain fig 2 46 the sediments are later reworked by waves tides longshore currents and wind which are effective mechanisms for sorting the mineral grains on the basis of differences in their size and density regarding the age most economic deposits of heavy mineral sands are paleogene neogene and quaternary in age famous placer deposits also include diamond placers which are the source of about 34 of global diamond production the first diamonds discovered in south africa were in gravels of the orange river and its tributaries and tracing these rivers back to their sources led first to the discovery of the primary diamond sources in kimberlites around the town of kimberley in the center of south africa and then to huge beach placers at the western coast of the continent in countries such as south africa and namibia fig 2 47 other interesting examples of placer deposits are those related to tin platinum and thorium uranium metals regarding the tin placer deposits malaysia is the world s greatest producer of cassiterite and about half of the deposits are located in placers in rivers beach sands and offshore deposits the other half is related to granites the same pattern can be applied to the platinum group elements this type of deposits includes a large number of sedime

ntary ore deposits of varied characteristics sulfide deposits mainly in black shales conform the first group deposits focused in two metals iron and manganese form the second group and phosphate and different types of salt deposits shape the third group autochthonous sulfide deposits are the second most important sources of copper in the world behind porphyry copper deposits and the most important sources of cobalt hayes et al 2015 stratiform sediment hosted copper deposits are hosted in black gray green or white reduced sedimentary strata within or above a thick section of red oxidized beds mineralization consists of fine grained copper and copper iron sulfide minerals that occur as stratabound to stratiform disseminations in siliciclastic or dolomitic sedimentary rocks regarding their tectonic setting they are found in intracontinental rift related sedimentary sequences and vary considerably in size grade and metal association these deposits are characterized by zoning of ore minerals laterally along and across bedding from pyrite and chalcopyrite to bornite and chalcocite most famous deposits of this type are the kupferschiefer in central europe and the central african copperbelt the models proposed for the formation of these deposits fall under two main groups synsedimentary syngenetic and diagenetic syndiagenetic according to the syngenetic model sulfides precipitated in an anoxic water column containing h2s from bacterial sulfate reduction as in the present black sea in the diagenetic model the ore emplacement occurred during early diagenesis or late diagenesis of the host sediments which is a difficult question to answer especially for deposits that have been subjected to metamorphism and deformation misra 2000 taylor et al 2013 and hayes et al 2015 suggested that sediment hosted stratabound copper mineralization is derived from hydrothermal fluids generated during diagenesis and lithification in sedimentary basins with regard to iron and manganese autochthonous ores are chemical partly biogenic marine sediments although manganese nodules and crusts of the deep oceans may become an essential source of these metals actually the most important raw materials of this group are enriched parts of marine banded iron formations and manganese formations predominantly formed in the paleoproterozoic and ooidal or massive iron and manganese ore beds that are of phanerozoic in age the so called banded iron formations bif constitute by far the most abundant and economically the most important iron rich sediments the term bif means bedded chemical sediments which comprise alternating layers of iron minerals commonly oxides or hydroxides and fine grained quartz e g chert the banding is manifested at different scales not only centimeter thick beds but also millimeter or submillimeter lamellae in the major iron formations the bedding has an impressive continuity a single 2 5 cm thick

band has been traced over an area of 50 000 km2 and varves at a microscopic scale are continuous for 300 km banded iron formations were deposited at three different time periods all in the precambrian receiving different names for each type algoman superior and rapitan respectively algoman type deposits are usually small and are found in archean greenstone belts in association with volcanic rocks superior type deposits were the first iron rich deposits mined being located in marine shelf sediments finally the rapitan type deposits are a relatively minor type occurring in association with neoproterozoic glacial deposits oxides such as hematite or magnetite are the main phase in most banded iron formations although carbonate silicates or sulfide are the main minerals in other bifs primary iron formations contain 20 30 fe but the ores mined in most countries contain grades ranging from 55 to 65 fe this is because enrichment processes act on the iron formations as they are exposed at or near the surface exposure under hot humid climate conditions to circulating groundwater leaches silica from the rock and replaces it by iron oxides more autochthonous sedimentary deposits include manganese deposits fig 2 48 phosphate deposits and sodium and potassium nitrates and sulfates fig 2 49 regarding bedded manganese deposits they are formed in a similar manner to iron formations and the mineralogy assemblage is formed by pyrolusite mno2 and rhodochrosite mnco3 which precipitate from seawater as bedded sedimentary rocks manganese deposits occur in rocks of all ages the largest deposits occurring in proterozoic ore bodies of the kalahari in south africa phosphorites which are mined to be used as fertilizers form on shallow continent shelves either through direct precipitation from seawater or by diagenetic replacement of limestone although current global production and resources of potash are dominated by stratabound potash bearing salt deposits in some areas of the world closed basin potash bearing brines are the main source for production of potash and potash bearing brine resources these brines may be alkaline or enriched in chloride sulfate or calcium depending on the geological features of the drainage basin and the resultant chemistry of the inflows into the basin potash bearing brines form in salt lakes and salars or playas in closed basins in arid environments where high rates of near surface evaporation concentrated the brine the duration of this process is very variable but it can range from hundreds of years to tens of thousands of years even over a million years from acidic to intermediate volcanic rocks and sometimes saline and continental sedimentary rocks are the main source rocks for this type of deposit orris 2011 the evaporation of brines fig 2 50 produces chemical precipitates that are extracted to obtain common salt sylvite kcl gypsum and anhydrite evaporites incl

uding halite or gypsum can also form from seawater evaporation in broad inland seas where there are extensive water evaporations sodium and potassium nitrates and sodium sulfates are also evaporation deposits in this sense one of the driest regions in the world the atacama desert of chile includes the world s largest natural deposits of sodium nitrate on the other hand the process of evaporation can be induced artificially as occurs in some lithium brine deposits these deposits account for about three fourths of the world s lithium production lithium brine deposits are accumulations of saline groundwater enriched in dissolved lithium all producing lithium brine deposits share a number of first order characteristics such as arid climate closed basin including a playa or salar tectonically driven subsidence associated igneous or geothermal activity adequate lithium source rocks one or more suitable aquifers and enough time to concentrate a brine bradley et al 2013 all closed basin lithium brine deposits that are of present economic interest are of quaternary age e g atacama salar fig 2 51 brine typically carrying 200 1400 milligrams per liter mg l of lithium is pumped to the surface and concentrated by evaporation in a succession of artificial ponds each one in the chain having a greater lithium concentration after a few months to about a year a concentrate of 1 2 lithium is further processed in a chemical plant to yield various end products such as lithium carbonate and lithium metal s aforementioned diagenetic deposits form a complex group of mineral deposits where the qualification of the ore forming fluid as diagenetic or hydrothermal is almost impossible since both are sometimes the same the previous described stratiform sediment hosted copper deposits are a good example of this controversy the mississippi valley type pb zn f ba deposits hosted in marine carbonates are probably the most representative mineral deposit type of this group box 2 11 reoc n pb zn mine spain mississippi valley type mvt deposits are a large and heterogeneous group that contains a substantial amount of the reserves of zinc and lead in the world they are the main source of these metals in the usa and contribute significantly to the production of lead and zinc in canada and europe usually occurring in districts clusters that may extend over hundreds of square kilometers and contain up to 500 million tons of ore these deposits constituted a wide group of lead zinc mineral deposits that occur mainly in carbonates of any age from the proterozoic to the cretaceous no mvt deposits have been reported from the archean in spite of the abundance of appropriate carbonate rocks the proterozoic contains only a few mvt deposits mvt deposits display their maximum presence from devonian to carboniferous by that time vast and permeable carbonate platforms and abundant evaporites are formed according to leach et al 2010

the intense orogenic activity during the assembly of pangea in relatively low latitudes created abundant opportunities for the migration of sedimentary brines into the interior carbonate platforms and within extensional domains landward of the orogenic belts to form mvt deposits this type of deposit is typically stratabound and takes place in dolostones although limestone or sandstone can also include this mineralization and always at shallow depths along the flanks of sedimentary basins the most common depositional setting is represented by platform carbonate sequences commonly reef facies located in fairly undeformed foredeeps or in foreland thrust belts mvt deposits are mineralogically simple although considerable variation exists among districts in terms of the total ore gangue assemblage thus the most typical mineralogy includes sphalerite and galena as dominant minerals and lesser amount of pyrite marcasite dolomite calcite and quartz the textures of the sulfide minerals are very varied and examples are coarse and crystalline to fine grained textures and or massive to disseminated ones one of the most characteristic structures in this type of deposit is banded and colloform structure which is common as a result of deposition in open spaces other recognizable processes consist mainly of dolomitization brecciation mineralization in breccias is one of the most characteristic features of mississippi valley type deposits and host rock dissolution fluid inclusion studies invoke low mineralization deposition temperatures ranging from 50 to 200 c however these temperatures are higher than those attributable to normal thermal gradients within the sedimentary pile regarding the composition of the ore fluids they were dense basinal brines commonly containing 10 30 wt dissolved salts classical examples of this type of deposit are viburnum trend southeast missouri usa and pine point canada regarding the origin the general framework of genetic models for typical mvt deposits is constrained by two important common factors the ore fluids were moderately hot highly saline brines and the mineralization was epigenetic controversies are centered in the origin and migration of ore fluids the source s of the mineralization constituents and the mechanisms of mineral precipitation as commented previously mineral deposits in metamorphosed rocks can have been originated before during or after metamorphic processes the first category which is of premetamorphic origin independent from later metamorphic overprinting is the class of metamorphosed ore deposits some authors consider that the skarn type deposits can be included in the magmatic domain but here are considered as metamorphic ore deposits because they are a product of contact metamorphism on the other hand the formation of ore deposits by regional metamorphism is now generally accepted pohl 2011 and examples of these deposits are orogenic gold gr

aphite veins and several large talc deposits among others the most important ore deposit type is undoubtedly the skarn deposits they represent a very diverse class in terms of geological setting and ore metals which range from precambrian to late cenozoic in age and constitute the world s premier source of tungsten and important sources of copper iron molybdenum and zinc a continuum exists between the porphyry type and the skarn type ore deposits and at least some skarn deposits appear to be mineralized in carbonate wall rocks within porphyry systems nevertheless skarn deposits do possess enough special characteristics to be treated as a distinct class misra 2000 the term skarn an old swedish mining term encompasses a large variety of generally coarse grained calc silicate rocks enriched in calcium iron magnesium aluminum and manganese regardless of their association with minerals of potential economic value they were formed by replacement of originally carbonate rich rocks by metasomatic processes einaudi et al 1981 carbonate rocks such as limestone and dolostone are by far the most common protoliths of skarns although occurrences of skarns in shales quartzite and igneous rocks have been reported a diagnostic feature of typical skarns is their mineral assemblages the primary assemblage varies with the compositions of the skarn forming fluids and the invaded rocks but is characterized by anhydrous ca fe mg silicates and pyroxenes including pyroxenoids and garnets are of special importance skarn deposits can be classified on the basis of the dominant economic metal s iron copper molybdenum gold tungsten tin and zinc lead the main ore minerals of these skarn types are respectively magnetite fig 2 53 chalcopyrite bornite molybdenite electrum scheelite cassiterite and sphalerite galena e g misra 2000 in addition to distinctive metal associations the skarn deposits exhibit a systematic variation in skarn mineralogy especially in terms of pyroxene and garnet compositions for instance a decrease in diopside component of pyroxenes through the sequence cu fe w zn pb skarn deposits from an economic point of view seven major skarn types can be distinguished iron calcic iron magnesian copper calcic molybdenum calcic tungsten calcic tin calcic and zinc lead calcic skarn ore bodies are also a major source of many industrial minerals including wollastonite graphite asbestos magnesite talc boron and fluorite as an example of this type of deposits skarn gold deposits consist of disseminated to massive sulfide lenses and crosscutting veins in carbonate platform sequences superimposed by volcanic and or plutonic arcs mineralization is associated with al rich garnet pyroxene skarn assemblages replacing limestone calcareous siltstone and carbonatized volcanic rocks adjacent to diorite or granodiorite stocks dykes or sills robert et al 1997 sometim

es the deposits occur in districts along with porphyry cu mo mineralization tending to be linked with more mafic hotter intrusions mineralogy includes the following minerals pyrrhotite pyrite arsenopyrite and lesser amount of telluride minerals presenting also wide variations in their gold to silver ratios au ag 1 10 to 10 1 mineral exploration can be defined as the process of analyzing an area of land to find mineral deposits fig 3 1 therefore mineral exploration covers all the processes that reflect information about the presence of ore deposits the information collected during exploration is utilized to evaluate the size and quality of an ore deposit and to establish there is an option for it to be mined metal prices mainly define exploration expenditures and in the long run by demand of metals where metal s demand peaks so does exploration expenditure most mineral exploration is carried out by companies with a capital base produced either from existing mineral production or from investors the company size can vary from small venture capital companies the so called juniors with one or two geologists to great multinational mining companies such as glencore bhp billiton rio tinto anglo american or de beers with operations on several continents the so called majors a junior exploration company can be defined as a company that focuses solely on the exploration and discovery of mineral deposits and does not operate a mine stevens 2010 although the mining industry includes about 6000 companies the majority are the 4000 5000 junior exploration companies that do not have a mine in operation the main features of the mineral exploration process can be summarized as follows 1 it is a time consuming process ranging from 2 years up to 5 years or more 2 it is also expensive 2 or 3 millions of dollars per year and high risk investment unlike ordinary businesses investments 3 it is undertaken in various stages of investigation each phase conditioned by the results of the previous step 4 it starts at the broad scale and narrows down the work area to settle on a target or a set of targets 5 the methods used vary in the different phases of the process and this variation is defined by the size of the prospect as well as the type density of information needed 6 rarely results in a mine are being developed the rate for finding new profitable mining operations commonly ranges from a high of 4 to less than 1 and even sometimes as low as 1 exploration field activities take place as part of strategies to locate and define a particular economically mineable mineral commodity in a mineral province in this sense the prospect could be an ancient mine an outcrop including mineralization an area elected based on geological items or simply some anomalous feature of the environment such as a geophysical or geochemical result that can be interpreted as showing close spatial relation to a mineralization

thus mineral exploration companies usually classify exploration programs into two categories greenfield or brownfield a terminology originally used in construction and development greenfield exploration means unknown territories where ore deposits are not already known to be present fig 3 2 on the contrary brownfield exploration refers to prospecting in areas where mineral deposits were previously discovered obviously the risk in brownfield exploration is considerably lower than in greenfield exploration because of the lack of geological information available in the latter the mineral deposits to explore now for the mining companies are mainly hidden by leached and weathered outcrops with soil or other cover for this reason very sophisticated exploration techniques are actually needed to find them since most mineral deposits located at or near the earth s surface have probably been discovered as a general rule the first stage of prospection exploration involves locating prospective deposits using knowledge of ore genesis and occurrence models thus geological environments associated with the wanted type of mineral deposit are target of investigation methods such as geological mapping and sampling geophysical surveys and geochemical analysis are commonly used at an early stage of exploration to define potential ore deposits thus the goal of geophysical geochemical exploration is to find an anomaly something different from the normal or expected anomalies can indicate the presence of minerals and could be a target for drilling an anomaly is a geological incongruity that has the possibility of being an ore deposit obviously an anomaly does not necessarily imply a mineral deposit but every mineral deposit was first an anomaly that is something out of the ordinary hartman and mutmansky 2002 where a mineral deposit has been identified the next step is to map it more extensively to obtain a first evaluation of the grade and tonnage of the mineral deposit the target is later drilled to study the mineralization in depth drilling is undertaken only in advanced mineral exploration in increasing order of cost per km2 the main methods used in mineral exploration are remote sensing geological mapping geophysical surveys geochemical surveys and drilling regarding the exploration trends in the world mining companies reacted to the poor market conditions of the last years with a strong decrease in their exploration expenditures the result was a 19 decline in worldwide nonferrous metal exploration budgets in 2015 compared with the previous year with final investment of about usd 9 2 billion snl metals mining figure 3 3 shows the main destinations for nonferrous exploration in 2015 nonferrous exploration means to look for precious and base metals uranium diamonds and several industrial minerals it particularly precludes exploration for commodities such as iron ore coal aluminum or oil and gas regardi

ng allocation of exploration latin america has been considered the leading region for mineral exploration by many companies for the past decade owing to its promising geology its long history of world class discoveries the perception of its mineral policies and its successful historical record of mineral production and development wilburn and karl 2016 is quite difficult to define exactly the number of stages in mineral exploration processes since it depends of several factors such as the commodity to investigate the region to explore the overall costs of the different steps and others up to five stages in mineral exploration the so called mineral exploration cycle are usually found in literature program design reconnaissance exploration detailed exploration prospect evaluation and preproduction however there is consensus that two main phases can be broadly outlined reconnaissance exploration and detailed exploration or prospecting and exploration commonly prospecting is the very first stage in the search for mineral deposits and permits tend to cover large areas in an attempt to see if mineral deposits are present whereas exploration involves more detailed data gathering over smaller and specific areas the complete sequence of mineral activity is carried out for only a very low number of mineral projects being the initial stages abbreviated if the information acquired in those stages is already accessible to the mining company thus a project can be quickly abandoned at any phase if the results obtained are not clearly hopeful in other words as commented above very few discovered mineral deposits become producing mines the time required for exploration of a mining project depends on its size and location the following time requirements can provide a broad approximation 1 small deposits from 2 to 4 years 2 medium sized deposits from 4 to 6 years and 3 large deposits from 6 to 10 years of exploration actually the process of mineral discovery and its development to production mine can take up to 25 years because of the large size of the modern mines 3 2 1 program design at the program design step generative stage or project generation or simply planning stage the management staff of the company with considerable experience of exploration defines the economic parameters for mineral targets technicians usually geologists and or geophysicists design the exploration program that promises the best results in the search for such target according to sillitoe 2000 the keystone to prospecting organization is to have the best forthcoming staff and appropriate finance in order to generate confidence throughout the organization the economic parameters vary widely depending on the expected exploration and development of the type of mineral deposit sought and on the economic factors and mine life the conduct of a good prospecting program is aimed at the discovery of a maximum number of minera

l deposits at minimum cost in this searching process geologists decide the types of deposits to explore and which geological and exploration models should be applied previously the management staff chooses the commodity or commodities the intensive use of mineral deposit models is a defining feature at this stage this is because the first step in a new program is to acquire information about the study areas to be investigated thus favorable regions are selected either on the basis of known potential as expressed by existing mines or mineral occurrences or on the basis of general knowledge of their geological characteristics in summary the area to be explored is identified based on literature search looking at history reports and maps and thesis works among many others these are called desktop studies at the end of this stage exploration procedures are recommended to the management by the geological staff and a time schedule and general budget are established regarding the exploration costs the exploration manager commonly considers them as an expenditure within an organization while it is as a geologist on a specific exploration project that one becomes involved in the exploration costs within the context of the project moon and whateley 2006 prospection can be commodity or site specific in other words the search can be limited to a particular mineral or metal or to a particular geographic area 3 2 2 reconnaissance exploration since a prospect has been identified a progressive series of definable exploration stages can be carried out as a rule positive results in any stage of exploration will originate an advance to the next stage and an increase of the exploration effort on the contrary negative results reveal that the prospect will be commonly abandoned although further follow up is possible if the economic conditions have changed the first stage of mineral exploration is the reconnaissance exploration although it can be named also in a variety of ways simply prospection target identification early and extended reconnaissance and many others in turn it typically includes two steps regional appraisal and reconnaissance of region the main goal of the process is to identify an ore deposit that can be the target for subsequent exploration the quantities estimated for the deposits are with a low level of confidence and these estimates are inferred that is based on interpretation of geological geophysical and geochemical results reconnaissance exploration aims at rapid and low cost sorting out of prospective parts of an area regions ranging from 2000 to 200 000 km2 are evaluated with an analysis of accessible information and parts of a region that cover 100 5000 km2 are studied through field examination spaced geochemical sampling with wide grids and geophysical exploration in this sense an invaluable information to surface regional geology is that obtained with regional geophysics airborne

magnetic radiometric and regional gravity data are available in a great part of the developed world fig 3 4 and these techniques lead to refining geological interpretation regional geochemical surveys also provide much information in areas of poor outcrop he results are brought together on maps on 1 50 000 to 1 25 000 or smaller scale they are geologically analyzed in view of the characteristics of known occurrences of the type of ore deposit being explored the next step deals with selection of smaller target areas for detailed investigation in general the targets are not clearly defined until the first stage has been accomplished in fact target identification is the main goal of reconnaissance exploration it can cost from several thousand to one million or more usd commonly spending from a several months to 2 or 3 years to complete once field studies such as rock and soil sampling have been carried out the results will be collected and models for the mineralization will be created using specialized computer software in the first phase of reconnaissance exploration regional appraisal the following procedures are usually performed 1 review of all information on the target such as government geological information as well as geophysical and geochemical surveys in the area the results of previous exploration data and the known occurrence of minerals and other previous bibliographies 2 photogeological study of available air photographs 3 study of accessible remote sensing information 4 air and ground field inspection 5 petrographic and mineralogical studies to determine main rock types mineral assemblages and identification of minerals of interest in the second phase of reconnaissance exploration reconnaissance of region techniques are 1 geological mapping and sampling 2 geochemical surveys and indicator mineral studies 3 geophysical surveys airborne or ground 4 shallow pattern drilling for regolith or bedrock geochemistry including geophysical borehole logging and drilling aimed at increasing geological knowledge 5 field inspection of outcrops and anomalous areas 6 petrographic and mineralogical studies including study of host rock of the deposits and alteration zone mineralogical studies ore microscopy x ray diffraction among others identification of oxidized and primary zones etc 3 2 3 detailed exploration if the goal of the previous stage is to locate anomalies due to the presence of a mineral deposit the objective of detailed exploration is to define and evaluate this deposit in detail the exploration will focus to determine the geological setting depth geometry grade tonnage extent and worth of the ore deposit identified similar techniques than those applied in reconnaissance exploration will be used though in a more comprehensively manner over a much smaller area exploration culminates in preparation of a pre feasibility study that either accepts or rejects the de

posit for further consideration detailed exploration is restricted to relatively small areas and is intensive and expensive especially where drilling is carried out for this reason it is essential to protect the investment and potential revenue from the prospect by obtaining exclusive exploration or mining rights and to enter in negotiations with owners of surface property in preparation for later mine development gocht et al 1988 in the final stage of exploration the target that ranges initially from 2 to 25 or more km2 is investigated through detailed field inspections geochemical sampling and ground and airborne geophysical surveys it generally begins with establishing a regular grid on interesting areas serving as a base for more detailed geochemical and geophysical studies as well as geological mapping generally undertaken at 1 10 000 to 1 2500 scales in this step it is common to carry out limited trenching drilling and systematic sampling as a guideline to developing geological conceptions in this way the target is later reduced to a smaller one ranging from 1 to several km2 for further drilling to establish if the hypothetical valuable mineral deposit really is present it is clear that investigating if a discovery displays a sufficient size and quality inevitably includes a subsurface investigation in this case the geologist usually faces the task of generating a target for drilling this stage can cost from several tens of thousands to tens of millions of usd and they will usually take 1 to several years to complete assuming that there are not disrupts once the existence of a valuable ore deposit is determined perhaps 1 or 2 years after the initial discovery of economic ore the exploration is considered finished and at that moment the development process of the mine begins classical techniques for this stage are comprehensive geological mapping and sampling detailed geochemical surveys with an elaborated grid pattern sampling and analysis detailed geophysical surveys usually on the ground drilling logging trenching and geophysical survey in the holes and bulk sampling drilling involves various types initially with a relatively wide spacing of holes in areas of poor outcropping trenching or pitting is essential fig 3 5 to verify the bedrock source of a geological geochemical or geophysical anomaly once the samples have been obtained they must be sent to a laboratory for their analysis fig 3 6 cost should not be the main factor to select the laboratory for this decision accuracy precision and an effective proceeding are also requested moon and whateley 2006 before samples are submitted to the laboratory it must be ensured that all the elements that can be associated with the explored ore deposit are incorporated in the analysis and very important that this analysis comprises possible pathfinder elements the further decision to carry out a feasibility study can be obtained fro

m the information provided by detailed exploration since resource reserve estimations for the deposits are with a high level of confidence this is probably the most critical stage of exploration because decisions involving high costs and potential costs have to be made in view of the results if a decision is taken that a potential ore deposit has been delineated the costs of subsequent exploration will drastically increase usually at the expense of other prospects at this stage it is essential to consider that if it is decided to make the decision to close prospection of a mineral deposit after this stage there is always the option that an ore body has been lost marjoribanks 2010 3 2 4 pre feasibility feasibility study the final step in mineral exploration process is the preliminary feasibility study that analyzes all components geological mining environmental sociopolitical and economical relevant to the determination to develop a mine in very large projects the costs involved in evaluation are high so that a pre feasibility study is almost always carried out during the previous step thus the main goal of this type of study is to assess the various possibilities and possible combinations of technical and business issues to evaluate the project sensitivity to changes in the individual parameters and to rank various scenarios prior to selecting the most likely for further and more accurate study upon completion of a pre feasibility study geological confidence is such that it should be possible to publicly declare ore reserves from measured and indicated resources table 3 1 and any other mineral resources that can become mineable in the future with further study scott and whateley 2006 the results of the pre feasibility study determine whether the increasingly large expense derived from full geological technical and economic evaluation of a prospect is justified in other words this study will detect if the costs involved in exploration are suitable for the earnings that logically can be expected the feasibility study is the final evaluation of the profitability of a mining venture in light of the results of exhaustive geological exploration assessment of mining and processing cost environmental factors including mine reclamation and market analysis this study usually forms the basis for the go no go decision on developing a mine gocht et al 1988 that is it is the basis for an investment decision or decision to proceed to the next stage of development obviously feasibility studies are of higher level of rigor than pre feasibility studies thus in feasibility studies social environmental and governmental approvals permits and agreements commenced during the pre feasibility study will be in place or will be approaching finalization a feasibility study incorporates all types of detailed information obtained in previous stages of mineral exploration such as geology mining environmental

infrastructure and service financial data marketing economic viability and many other factors moreover sufficient sample collection and test work have taken place during a feasibility study for more of the resource estimate to be reported in the measured category several million dollars are commonly spent in large projects to bring the project to feasibility study level and sensitivity analyses they will have been established to analyze the main factors that can have a definitive impact upon the reserve estimation this will help to calculate the risk associated with the reserve data which at this stage will enter within the acceptable risk category of the company it is very common that financial institutes utilize independent consultants to audit the resource and reserve estimations 3 3 mineral deposit models to predict and have a better knowledge of how and where an ore deposits can be present scientists developed mineral deposit models fig 3 7 a working definition of model in the context of mineral deposits is the systematically arranged information describing the essential attributes properties of a class of mineral deposits cox and singer 1986 models are very useful to organize the information about a mineral deposit because they are simplifications and abstractions based on a large number of individual observations as such they need refinement as new data are acquired and have to be set as exploration is carried out in fact it is very difficult to find a paper in the contemporary literature on economic geology of a mineral deposit that does not utilize the expression mineral deposit model mote sensing is the characterization of the surface of the earth based on measurements of its reflected or emitted electromagnetic radiation in wavelengths from 0 3 to 3 m being satellites the main observation platforms these wavelengths cover the range from the ultraviolet to the microwave radar spectrum although a great number of measurements are made in the visible range by passive methods in which the reflected natural radiation is estimated remote sensing lead to the recognition of major regional topographic features and geologic relationships and helping in the discovering of regions with mineral potential since remote sensing was forthcoming since the late 1970s the data from land observation satellites have supplied a powerful tool for the exploration of mineral resources moreover satellite imagery fig 3 11 investigates the geological characteristics of remote areas of the surface of the earth without the requirement to access the region on the ground thus remote sensing is providing information on mineral deposit exploration targets without being in contact with the objects remote sensing can highlight ore bodies and their respective mineralization or alteration signatures as well as associated other features such as lineaments and faults for instance this method originates strong signals where go

ssans associated with hydrothermal alteration and oxidation of porphyry deposits are present another example would be the discovery of fractures and faults in volcanic regions with veins of precious metals on the other hand the interpretation of satellite imagery can originate very useful models before the start of geophysical investigations in turn geological and geophysical data can gage models obtained from this technique the resolution of remote sensing is restricted by the resolution of the imagery according to this factor satellites can be classified into three main categories 1 vhr very high resolution submeter pixels 2 hr high resolution 2 5 10 m pixels and 3 mr mid resolution greater than 10 m pixels an image with 50 m resolution would start to pixelate at scales larger more detailed than 1 100 000 by contrast a very high resolution vhr satellite scene with a 50 cm resolution could be viewed at scales to 1 2500 before pixelation became apparent mid resolution data can be used for the initial broad scale study to derive locate and designate smaller areas of interest while higher resolution data are utilized for subsequent analyses in contrast to electrical magnetic and gravity methods that compute force fields remote sensing technique is usually referred to methods that use the electromagnetic energy as radio waves light and heat as the means of finding and measuring target features in the context of geological mapping electromagnetic methods can be classified as 1 passive optical methods utilize the sunlight as the source and estimate the reflectance of the surface of the earth in the visible and infrared spectral bands e g landsat 7 etm and the aster instrument from the terra satellite and 2 active microwave radar methods use a microwave source onboard of the satellite and calculate the backscatter from the earth e g radarsat 1 and the radar sensor from the shuttle radar tomographic mission srtm for its part infrared imagery is divided into three classes 1 very near infrared which detects particularly vegetation 2 short wave infrared the best possibility to discriminate sedimentary rocks and 3 thermal infrared utilized to discriminate dark materials such as non sedimentary rocks laake 2011 the most famous satellite used in geological studies is landsat box 3 2 landsat program because different rock types reflect radiation to different degrees and in different spectral ranges remote sensing allows preliminary geological interpretations of an area thus some of the geological features intimately associated with ore deposits provide strong signals that can be detected by this technique these features are often clearly recognizable even through soil cover or vegetation different surface materials such as water vegetation or clay alteration generate different signals of radiation in varying wavelength bands this pattern of reflectance is chara

cteristic for each type of land surface and is known as its reflectance signature in mineral exploration this can be especially meaningful in looking for surface alteration systems where argillic alteration can be present sabbins and oliver 2004 finally the full potential of remote sensing data can only be obtained by combining all forthcoming spectral bands in digital processing this is because the combination enables improving the interpretation of linear structures gossans hydrothermal alterations and so on geological mapping has been used extensively for mineral exploration for more than 100 years beyond the use of traditional paper based mapping tools recent technological advances incorporate global positioning systems pen tablet computers and laser ranging devices that all support direct paperless field based digital geological mapping in this sense geographic information systems gis revolutionized exploration practices box 3 3 geographic information systems there are two main reasons that mapping remains an essential part of mineral exploration first mapping creates the geometric patterns that represent the geological attributes of an exploration target second there are scientific engineering and financial implications of mapping because subsequent geophysical modeling ore reserve estimation financial forecasting and economic evaluation are based on the interpretation of such work brimhall et al 2006 the quality and scale of the geological map will vary with the importance of the program and the finance available scales of geological maps range from reconnaissance 1 24 000 or smaller to detailed project scale 1 100 to 1 12 000 geological mapping is widely used in planning exploration strategies such as the selection of regions to explore for certain types of ore deposits prior to mapping campaigns existing geological maps are examined and can be compiled to emphasize key geological features to assess exploration potential exploration geologists commonly use existing maps as the basis for preliminary examinations to assess mineral potential frequently in conjunction with geochemical geophysical or remote sensing surveys or compilation of mine and prospect data however geological maps available today either published by government surveys or in many scientific journals are generally not well suited for special needs of mineral exploration and development and require exploration geologists to undertake specialized mapping whereas published maps of general geology do outline information essential to exploration including rock units stratigraphy ages of rocks and general structure they are in most cases not sufficiently detailed to help delineate mineral deposits that are typically 1 2 km2 in outcrop area even for world class deposits consequently the geological mapping at this stage generally is done at a more detailed and larger scale than published mapping and key lithologic

units and features of mineralization or hydrothermal alteration are mapped using the reconnaissance techniques since geological information is commonly recorded on maps and cross sections at a scale appropriate to the aims property geology must be defined at a scale of 1 5000 while mineral deposit geology must be mapped to a scale of 1 1000 or even more detailed information displayed in this type of map includes faulting folding rock types fracture vein density and orientation evidence of primary porosity permeability and phases of mineralization among many others regarding geological mapping in underground mines it can play an essential role in mineral exploration abandoned mine workings are the most direct guides of the mineralization in a region and provide the immediate information on ore occurrences if the workings are active they provide a series of fresh geological exposures with each meter of advance and they supply well located sites for underground drilling and sampling a geographic information system gis is a computer system hardware software and netware and associated database designed to efficiently capture store update manipulate analyze retrieve and display all forms of geographically referenced information the first known use of the term geographic information system was in 1968 in 1986 mapping display and analysis system midas the first desktop gis product emerged for the dos operating system then this was renamed in 1990 to mapinfo for windows when it was ported to the windows platform recently a growing number of free open source gis packages run on a range of operating systems and can be customized to perform specific tasks modern gis technologies use digital information for which various digitized data creation methods are used the most common method of data creation is digitization where a hard copy map or survey plan is transferred into a digital medium through the use of a cad program and geo referencing capabilities geographic data can be stored in a vector or a raster format using a vector format two dimensional data is stored in terms of x and y coordinates for instance a road or a river can be described as a series of x and y coordinate points thus the vector system is good for describing well delineated features a raster data format expresses data as a continuously changing set of grid cells the raster model is better for portraying subtle changes such as soil type patterns over an area most geographic information systems make use of both kinds of data once all of the desired data have been entered into a gis system they can be combined to produce a wide variety of individual maps depending on which data layers are included in mineral exploration the data are usually organized in layers of different types such as topography remote sensing geophysical and geochemical results etc some gis applications for instance using arcgis are specifically developed

to represent and process particular types of geological geochemical and geophysical information raster images such as satellite or geophysical imagery can be integrated and overlain with vector data such as geology faults and sample information thus gis is essential in customizing and integrating a broad range of mineral exploration data consisting of information on drillholes with summary stratigraphic logs rock sample and drillhole sample geochemistry mineral occurrences magnetic and gravity images digital geology current and historic exploration details and much more fig 3 15 the ultimate objective of using a gis during mineral exploration is to predict the approximate positions of new mineral deposits for doing this the data to be integrated should be indicative of the mineral deposits searched according to an exploration model customized for the area under analysis in this sense remote sensing data often constitutes an important part of the database introduced in a gis because of its intrinsic digital nature and because it can be used as the base over which to overlap other data by combining gis technology with the enormous progress in recent years in remote sensing it has been possible to extend the mineral exploration all over the world moreover recent integration of exploration data with gis supported by intelligent systems has greatly enhanced the acquisition analysis and interpretation of complex problems of probabilities and decisions involved in mineral projects mapping of mineral potential using gis is conducted to delineate areas with different probabilities of hosting certain types of mineralization the main steps in generating mineral potential maps are a establishing the exploration conceptual model b building a spatial database c spatial data analysis extraction of evidence maps and assigning of weights and d combination of evidence maps to predict mineral potential mineral exploration is increasingly being addressed to searching for buried and deep targets since there are few large ore bodies to be found at the surface unlike geochemistry and other remote sensing techniques geophysics helps to look at into the subsurface and to provide information about the concealed geology thus geophysics is an integral part of most mineral exploration programs geophysical techniques have been used in mineral prospecting for the past 300 years beginning in sweden around 1640 with the use of magnetic compasses in exploring for iron ore these techniques are essential in areas where outcrop is poor or has been subject to intense mineral search over a long period in some cases geophysical techniques also enable for quick regional appraisal of areas where ground access is almost impossible for instance rain forest terrain or developing countries with insufficient infrastructure marjoribanks 2010 for a geophysical technique to be useful in mineral exploration there must be a clear co

ntrast in the physical characteristics of the minerals rocks and ores related to the existence of valuable minerals geophysical anomalies defined as differences from a constant or slowly varying background can be recorded ideally the actual economic minerals will produce them but even the presence of a clear physical contrast between mineralization and surrounding rocks does not imply a significant anomaly milson 2006 geophysical measurements in the natural environment will be contaminated with unwanted information this is called noise which is a source of error while the information being sought in the measurement is known as signal signal amplitude should be as high as possible whereas noise signal should be as low as possible in order to obtain an accurate measurement of the parameter of interest in any case suppression of noise is of outmost importance and must be considered at every stage of the geophysical program from data acquisition to presentation of the data for interpretation dentith and mudge 2014 geophysical methods can be classified as passive magnetism specific gravity and radioactivity and active methods electric conductivity electromagnetic properties and seismicity passive methods use natural sources of energy of which the earth s gravity and magnetic fields are two examples to investigate the ground the geophysical measurement is made with a detector sensor or receiver which measures the response of the local geology to the natural energy in turn active geophysical methods involve the deliberate introduction of some form of energy into the ground for example seismic waves or electric currents again the response of the ground to the introduced energy is measured with some form of detector fig 3 16 these methods are more complicated and expensive to work with the geophysical signal can be directly related to mineral deposits for example a magnetic anomaly caused by magnetite ore in an iron deposit more commonly geophysical methods provide indirect evidence that leads to interpretations of the subsurface geological distribution of rocks but it does not directly or necessarily reflect the presence of a mineral deposit these types of methods are applied to both mineral discovery and geological mapping they are useful because geophysical responses of materials can be measured through vegetation soil cover and extraneous overburden in many cases geophysical measurements provide the only means of interpreting the geological characteristics of the subsurface short of drilling which is much more expensive gocht et al 1988 over the area of interest geophysical instruments are deployed in the field to measure variations in a physical parameter associated with variations in a physical property of the subsurface and the measurements are used to infer the geology of the survey area of particular significance is the ability of geophysical methods to make these inferences

from a distance and for some methods without contact with the ground a considerable number of geophysical exploration methods are available for mineral exploration and each method exists in several variants the specific choice is a function of the geological and exploration model of the targeted deposits of general conditions such as remoteness climate and human land use and of the costs shen et al 2008 through either ground airborne or in ground downhole methods geophysical studies employ the types of surveys cited above to detect anomalous signals related to the presence of minerals the chief advantages of airborne surveying relative to ground surveying are the greater speed of data acquisition and the completeness of the survey coverage after their introduction in the 1950s airborne geophysical surveys became commonly used as a first step in geophysical exploration they provide the quickest and often the most cost effective ways of obtaining geological information about large areas two or more methods are commonly combined in one survey to obtain data that are more accurate in surface geophysics geophysical work on the ground is normally rather slow results from airborne and surface surveys are matched with surface geological data to decide if it is worth proceeding with further exploration geophysical techniques are routinely used in exploration programs to help the project geologist delineate areas favorable for the type of target being pursued they can be used to directly detect some minerals indirectly detect others and map geological and structural features in exploration programs direct detection includes using induced polarization ip to find disseminated sulfides magnetics to delineate magnetite hosting rocks and gravity and electrical techniques for massive sulfides for instance indirect detection of targets includes using ip to detect pyrite in association with sphalerite and gold both non responders to ip geophysical techniques and copper and molybdenum in porphyry systems magnetics are routinely used to search for hydrothermal alteration in association with porphyry systems and can be used to map buried stream channels e g magnetite sands that might host placer gold mukherjee 2011 seismic surveys are highly effective for investigating layered stratigraphy so they are the mainstay of the petroleum industry but are comparatively rarely used in the minerals industry regarding costs of geophysical surveys the seismic method is the most expensive while airborne magnetic and radiometrics are the less expensive it is very important to note that most important advances in geophysical exploration for ore deposits in the last 25 years dealt with advances in theory or practice of the different methods but also with the development of more sophisticated instrumentation and especially more powerful data processing these advances together with the use of gps for survey positioning cont

rol have greatly reduced the cost and time involved in all geophysical surveys and have increased their resolution in the detection of anomalous signals in the data traditionally most geophysical data has been presented for interpretation in the form of contoured or raster plans and sections that can be interpreted in terms of the geology and ore mineralization that they represent however new methods of analyzing and presenting geophysical data have been introduced in the last two decades to revolutionize the interpretation process these methods are generally referred to as data inversion mcgauchy 2007 oldenburg and pratt 2007 box 3 4 data inversion in geophysical exploration rock drillability is defined as the penetration rate of a drill bit into the rock it is a feature that cannot be exactly defined by a single mechanical property of the rock for this reason drillability is a function of numerous rock properties such as mineral composition grain size texture and weathering degree quartz is one of the commonest minerals in rocks since quartz is a very hard material high quartz content in rock can make it very hard to drill and will certainly cause heavy wear particularly on drill bits on the other hand a coarse grained structure is easier to drill and causes less wear of the drill string than a fine grained structure drillability is not only decisive for the wear of tools and equipment but is along with the drilling velocity a standard factor for the progress of drilling works hoseinie et al 2008 suggest that the most important rock mass parameters that affect the drilling are the following the origin of the rock s formation the mohs hardness the texture of the rock shape and size of grains porosity density abrasiveness rigidity p wave velocity elasticity and plasticity ucs point load index and schmidt hammer tensile strength structural parameters of the rock mass joints cracks and bedding and rqd the factors that concern the drillability of rocks are numerous and can be classified into two main groups controllable and uncontrollable parameters regarding the controllable parameters these are bit type and diameter rotational speed thrust blow frequency and flushing rock properties and geological conditions are uncontrollable parameters yarali and kahraman 2011 the drillability of rocks depends on not only their physical properties but also on the type of drill being used and drilling parameters such as rotation speed feed rate etc the physical properties of rocks which have some effect on drillability are 1 crushing strength defined as the pressure a rock sustains before breaking and related to grain hardness and strength grain bond strength porosity and weakness planes 2 toughness a measure of how difficult it is to pull a rock apart and related to grain shape and bond fissibility and tenacity 3 chip separation this is how readily the cuttings are cleared

from the face and it is related to pore pressure and permeability 4 abrasiveness the ability to wear downhole tools and related to grain hardness and shape hartley 1994 the norwegian technical university has defined two methods to evaluate the rock drillability the drilling rate index dri and the bit wear index bwi the dri describes how fast a particular drill steel can penetrate it includes measurements of brittleness and drilling with a small standard rotating bit into a sample of the rock the higher the dri the higher the penetration rate and this can vary greatly from one rock type to another fig 3 49 it should be noted that modern drill bits greatly improve the penetration rates in the same rock types the bwi gives an indication of how fast the bit wears down as determined by an abrasion test the higher the bwi the faster will be the wear thus in most cases the dri and bwi are inversely proportional to one another however the presence of hard minerals can produce heavy wear on the bit despite relatively good drillability this is particularly the case of quartz which has been shown to increase wear rates greatly certain sulfides in ore bodies are comparatively hard impairing drillability samuelsson 2007 other means of commonly used rock classification include the q system rock mass rating rmr of bieniawski incorporating the earlier rock quality designation rqd and the geological strength index gsi selecting the right technique or combination of techniques depends on many factors speed cost actual conditions surface or underground depths of the drillholes type of rocks required sample volume and quality logistics environmental considerations and finally the preference of the geologist moreover each of these factors depends in turn on many parameters for example drilling velocity is dependent on a lot of geological parameters such as jointing of rock mass rock anisotropy e g orientation of schistosity degree of interlocking of microstructures porosity and quality of cementation in clastic rock degree of hydrothermal decomposition and weathering of a rock mass among others thuro 1997 modern core drilling rigs carry out fast and efficient core sampling of different diameters to very large length there are many items to select the appropriate method of drilling target host rock water presence sample required access and politics hartley 1994 from a sampling viewpoint there are two types of drilling methods in mineral exploration drilling methods that originate rock chips and those that generate core samples fig 3 50 a three key factor selection process can be established the time needed the cost of getting the job done and confidence in the quality of the samples brought to the surface gustaffson 2010 for any exploration drilling the sample is the most important goal result rc drilling generates continuous drilling with high penetration rate and

can offer three times the productivity of core drilling thus significant timesaving can be obtained using rc when the ore body is located driller can decide to continue with rc drilling or switch to diamond core drilling to extract cores in so doing rc drilling and classical core drilling are perfectly combinable the logistics of the drilling program have clear influence on the number of meters drilled per shift and thereof it is a time factor 3 4 6 3 2 cost factor costs are mainly related to the time factor except that investment in rc rigs and equipment is higher compared to core drilling for shallow exploration applications time and costs are in favor of rc drilling for deeper exploration applications shallow subsoil water and rocky terrain core drilling is still the only practical alternative technical developments in drilling tools and rig technology have resulted in lower drilling costs 3 4 6 3 3 confidence factor the third variable in the equation is the confidence factor in an evaluation with positive results a program of core drilling is the common way to drill for the purpose of bringing the project to a resource reserve status because geologists need dry and representative samples to carry out optimum evaluations therefore core drilling remains the only viable method in these situations the core helps the geologist to calculate the cost of extracting the mineral from the ore moreover cores also yield geotechnical data for instance data about slope stability can be of the highest significance finally the geologist plays an extremely important role in finding an intelligent and balanced choice between the two methods considering the high costs of drilling a maximum of information must be extracted thus intense geological logging of core and drill cuttings is a common practice drillhole information is produced from many sources such as core chips down the hole geophysical measurements e g caliper natural gamma radiation gamma gamma density magnetic susceptibility or resistivity data from instruments inside the hole such as mdw measurements while drilling e g pressure at the bit face temperature or rate of water flow and performance of the drilling machinery all information related to each drillhole including topography drillhole deviation estimations mapped geological features and a copy of the data returned should be available with a single folder for each drillhole rossi and deutsch 2014 routine studies of drill cores consist of fracture spacing and orientation core recovery including the location of excessive core loss 5 lithological description e g color texture mineralogy rock alteration and rock name photographic documentation description of the geological structures visible in the core preliminary geological profile rock properties for calculating geotechnical parameters e g rqd and content and distribution of mineral and ore components inclu

ding as possible in situ assaying of ore depending upon the objective of the site investigation a secondary processing can include many other aspects such as the presence and content of clay minerals total carbonate content organic components grain size distribution sediment matrix and cement porosity pore size distribution and many others the description must be quantitative and systematic avoiding as much as possible qualitative descriptions since structural features must be captured before split the core the most useful way is to take photographs of the wet core previous the logging process with the objective of producing a permanent photographic record in noncore drilling descriptions must be again systematic and quantitative the data from core and noncore observation are plotted on graphical core logs and utilized to help in interpreting the geology of the present and next holes to be drilled regarding rqd it is used as a standard parameter in drill core logging and forms a basic element value of the major mass classification systems such as rock mass rating rmr system and q system in rock quality designation rqd the lengths of all sound rock core pieces that are greater than 100 mm in length are summed and divided by the length of the core run to obtain the final value in percentage this parameter is commonly estimated where the rock has been altered and or weakened by weathering this procedure obviously penalizes if the recovery is poor being useful since poor recovery commonly means poor quality rock since geological logging is commonly a subjective process this results in inconsistencies in the application of the logging codes to solve the problem it is desirable to use methods to objectively classify how mineralized is a sample for instance using portable xrf technology gazley et al 2014 thus a clear accurate and standardized logging procedure is essential to promote uniformity of data through what is commonly a long data gathering period it is important to note that as geological information and concepts evolve with time the context is likely to request the core be relogged sinclair and blackwell 2002 although a great number of different logging methods are utilized in the industry there are three main logging forms for recording observations on drill core and cuttings prose logging graphical scale logging and analytical spread sheet logging marjoribanks 2010 an interval is selected in prose logging being identified by its downhole depth limits and described in words it is recommended that this type of logging must be only utilized in a special column e g comments graphical scale log forms can include several mapping columns along with extra columns for recording digital data sketches verbal comments etc fig 3 65 the important feature about all such logs is that they assemble many different types of geological observations on one form linked by a single down pag

e scale finally the use of spreadsheet logging is indicated in second phase drilling programs e g resource evaluation and definition where the main geological problems associated with the ore body have been solved and the aim of the logging is the routine recording of masses of reproducible data regarding the graphical scale logging form it is usually separated into columns the columns will be referred to in numbered order from left to right for example column 1 hole depth column 2 core recovery column 3 sample no column 5 assay results it will be commonly necessary to devote several columns to insert all assay results and so on on any deposit delimitation program sampling is an essential step to establish the limits volume mass and grade of the mineral deposit thus the main goal of sampling is to generate values about the mineralization e g assays of metal grades that are the fundamental information to be utilized in carrying out resource and or reserve estimations therefore sampling of an ore deposit is a process of approximation and the objective is to arrive at an average sample value that closely depicts the true average value for the ore body readdy et al 1982 sampling is also important to study several geotechnical properties of the overburden and the host rock of the mineralization during the prospecting stage of the mining project these include properties strength or degree of weathering among others that are essential in designing a mine e g size of the underground chambers or different pit slopes sampling determines the day to day of any operation in the mine since inappropriate sampling procedure can originate incorrect estimation of present production and future potential the mine department commissioned of resource reserve estimations and mine sampling should be monitored by qualified and experienced professionals with technical backgrounds qualifying them to obtain precise data tapp 1998 in sampling an ore body to estimate grade the geologist is mainly concerned with the reliability of his estimate as measured by its accuracy and precision accuracy the close correspondence of an estimate to the true value is achieved by obtaining unbiased results through appropriate sampling sample preparation assaying and data analysis fig 4 1 to avoid bias the geologist must control issues such as salting e g bre x affaire box 1 4 or nonrepresentative samples on the other hand precision is the closeness of a single estimate obtained by sampling and ore body or other geologic entity to the estimates that would be obtained by repeated sampling of the ore body the sampling of metalliferous and industrial mineral deposits is undertaken for a variety of reasons and at various stages in their evaluation and exploitation during the exploration phase the sampling is largely confined to the analysis of drill cuttings or cores and is aimed at the evaluation of individual

often well spaced intersections of the deposit during the exploitation phase sampling is also used to define assay hanging walls and footwalls together with the grade over mineable thicknesses sampling is much more intense in this situation and is undertaken to allow the assignment of overall weighted grades to individual ore blocks or stopes also at this stage sampling will be used to extend existing reserves and attempt to prove new ore zones accessible from existing developments annels 1991 perhaps one of the most important applications of sampling during the exploitation phase is in grade control fig 4 2 e g bench grades in an open pit mine since it determines the boundaries of mineralization and waste see chap 5 it is important to remember that to take a sample means that the information obtained from the analytical data of the sample will be finally utilized to someone who will use the information contained in the analytical result to make a decision these decisions can involve immense capital engagements to open or close a mine or marginal process costs that include the decision if a batch of mineralized rock must be sent to the beneficiation plant or to the tailings dump minnitt 2007 for this reasons the process of sampling is among the most essential activities in mining operations because the possibility always exists for large occult costs to accumulate in mineral development due to sampling errors these hidden costs arise due to misunderstanding of the principal factors that affect the size of sampling errors e g amount of the sample the consequences of dividing a sample to reduce the amount or the notorious impact of the particle size in the mineralization items such as sample procedure sample reduction assaying methods and obviously geological data collecting and modeling are critical for a high quality estimation of the resources and or reserves this is because many times data collection techniques are not of adequate quality to correctly define a mineral deposit all the processes involved in sampling must be checked continuous and appropriately obviously there will constantly be a difference among the content of the lot the sample obtained and the sample for assay since the comparatively large amount of a sample is reduced to a small subsample of some grams that are needed for the final chemical analysis this discrepancy is termed the sample error attention to the matters cited above reduces the errors and improves the quality which is essential for interpretation of geological data and modeling and consequently the quality of resources reserve estimation the so called sampling due diligence which carries out an authentic geological resource evaluation requires a validation process of many components including among others a adequacy of samples b sample representation c accuracy of laboratory assays d insertion of blank and standards and e quality assurance and

quality control protocols these are the currently famous qa qc box 4 1 qa qc in coringa gold project qa qc includes duplicate analysis and standard analysis the precision of sampling and analytical data are estimated by analyzing twice the same sample utilizing the same methodology duplicates being the variance between the two data an estimation of their precision precision is affected as aforementioned by mineralogical factors such as grain size and distribution but also by errors in the sample preparation and analysis processes regarding standard samples or reference materials they are samples with a known grade and variability these are commonly used to assess analytical accuracy and bias by comparing the assay results against the expected grade of the standard in these sense managers and consultants always insist that standard and duplicate samples are invaluable items to measure the accuracy and precision of commercial analytical laboratories moreover they can ensure there can be a realistic confidence in the data by correctly utilizing these measurements of data quality to quantify the future risk of the mining project from a practical viewpoint it is impossible to gather all the components of a population for study unless the population itself is very small for this reason it is essential to resort what is commonly known as sample there are many definitions of sampling but the concept is quite elementary for example a sample is a representative part or a single item from a larger whole being drawn for the purpose of inspection or shown as evidence of quality and it is part of a statistical population whose properties e g physical and chemical are studied to gain information about the whole barnes 1980 another definition of sampling is the operation of removing a part convenient in size for testing from a whole which is of much greater bulk in such a way that the proportion and distribution of the quality to be tested e g specific gravity metal content recoverability are the same in both the whole and the part removed sample taggart 1945 both definitions are very similar being essential that the sample be representative fig 4 4 it is the key to a successful process of sampling if the samples are not representative of the deposit the rest of the evaluation is useless there is no point in geological interpretation and modeling is carried out correctly if the initial data are wrong thus the accuracy of a mineral resource or reserve calculation depends on the quality of the data gathering and handling processes used erickson and padgett 2011 large amount of sampling is carried out in the mineral industry but little attention is given to ensure representative sampling the responsibility for sampling is often tasked to people who do not take into account the significance of sampling with cost being the main factor rather than the representative of the sample the quality

of the subsequent analysis is undermined and mineral companies are exposed to enormous potential financial losses the successive steps of sampling must be therefore tested continuously although it is important to bear in mind that the condition of representativeness for the sample obtained from a whole is never fulfilled where heterogeneous materials are sampled unless the sample includes all the mineralization thus an orebody is a mixture of minerals in proportions that vary in different parts of the mass as a consequence the proportion of contained metals also varies from place to place therefore a single sample taken in any particular place would not contain the same proportion of metals as does the orebody as a whole except by a highly improbable coincidence the probable error which would be very large if only one sample were taken decreases with the number of samples but it never disappears completely unless the samples are so numerous and so large that their aggregate is equal to the orebody itself in which case the orebody would be completely used up in the process of sampling mckinstry 1948 random and systematic errors involved in the collection preparation analysis and evaluation of samples must be recognized and accounted for in fact this is not a problem but rather an incentive in this sense sarma 2009 affirmed that a good sample design must 1 result in a really representative unit 2 lead to exclusively a small error 3 be cost efficient 4 be one that monitors systematic bias and 5 the results of the sample study can be utilized for the population with a fair degree of confidence the samples must also be representative from a spatial viewpoint which means that the spatial coverage of the deposit is adequate thus the samples can be taken roughly in a regular or quasi regular sampling grid fig 4 5 representing each sample a similar volume of mass in the valuable mineralization furthermore the most important norm for an accurate sampling is that all components of the mineralization or other raw material must have the same probability of being sampled and constituting part of the final sample for the assay the logic of sampling is to collect a minimal mass grams kilograms or tons that equals a certain parameter e g gold content of a much larger mass hundreds or thousands of tons pohl 2011 it is necessary to take into account that finally only a tiny portion of the mineral deposit is collected and that often less than one millionth of the total mass of a deposit is being drilled it is quite easy to obtain this datum estimating the volume of drillholes the volume of an entire deposit and dividing both data the type and number of samples collected depend on a range of factors which include 1 the type of mineral deposit and the distribution and grain size of the valuable phase 2 the stage of the evaluation procedure 3 whether direct accessibility exists to the min

eralization 4 the ease of collection which is related to the nature and condition of the host rock and 5 the cost of collection funds available and the value of the ore annels 1991 it is clearly incorrect to take over that many samples remove any errors in the sampling procedure to obtain unbiased samples the location of the sample in relation to the mineralization and waste is just as important in fact the accuracy of a sampling procedure is only known where all the mineralization is mined and later milled and processed obviously the cost of intense sampling of a low grade or low value deposit e g aggregates for construction can be prohibitive for instance the mode of occurrence and morphology of a mineral deposit has considerable impact on the type and density of sampling and on the amount of material required indeed sampling of vein deposits where many veins are narrow is quite different than sampling of stratiform deposits where mineralization tends to be thick e g up to 30 m thus a mineral deposit classification with sampling as one of the main goals has been proposed taking into account the geometry the grade distribution and the coefficient of variation table 4 2 carras 1987 to acquire accurate analytical data for resource estimation it is indispensable to carry out a correct process of collecting samples methodology sampling pattern and sample size including a study of the ore with particular attention to the particle size distribution and the composition of the particles in each size class samples of several kilograms or even some tons are later cut to several grams the so called assay portion which are further assayed for valuable elements theoretically this final aliquot must still replicate targeted properties of the original large mass the reduction in weight is around 1 000 times with a kilogram sample and 1 000 000 with a sample mass of one ton this process obviously involves errors and gy 1992 established a relationship between sample particle size mass and sampling error analytical errors are ascribed to laboratories and commonly take place from the selection of the portion for analysis as aforementioned these errors must be considered with and external control by submitting to the laboratory duplicate samples and reference materials of similar composition of the unknown samples to reduce errors in sampling one solution is to divide the mineral deposit and the mineralization into distinct parts a previous step in the sampling process thus to take samples of the previously defined different types as separate units instead of as only one large sample can minimize natural variation and maintain the sample weight in a minimum this method is the so called stratified sampling and it is very important if the separate types of mineralization need different mineral beneficiation techniques regarding the different steps in the sampling process sampling sample prepar

ation analysis and interpretation in the final stages of exploration and mining are planned and carried out by a staff of geologists chemists statisticians and engineers who contribute their expertise to the interpretation of the sampling data the importance of thorough joint planning and interpretation is obvious because they form the basis for an economic and technical evaluation of the mineral prospect and because of the large financial commitment that the development of a potential ore deposit requires gocht et al 1988 4 2 4 sampling methods sampling methods are as different as the mines in which they can be utilized the most suitable type of sampling and the combination of methods used depend to some extent on the type of deposit being evaluated for instance to conduct an unbiased sampling in vein gold deposits presents particular challenges because the features of the mineralization and host rocks are extremely complex variance however can be diminished by carrying out a well planned procedures of sampling as well as careful collection of samples as possible the mine geologist or engineer devoted to sampling process must select a method of sampling test in a specific area and later critically evaluate the results obtained if these outcomes are sufficiently accurate within the economic limits determined by the mining company then the methodology can be embraced as a general rule in the project and or mine in general there are three hand sampling methods channel chip and grab sampling other sampling techniques include pitting and trenching or drill based sampling diamond drilling and in some cases rotary percussive drilling are the main sampling techniques available to the geologist in the exploration of a mineral deposit in fact the most satisfactory method should ensure that the sample properly represents the deposit at the smallest cost it is very important to bear in mind that whether the samples are collected on surface or underground is not in itself a significant factor that is the same process must be assigned to sampling a core drill in surface drilling and in underground drilling 4 2 4 1 channel sampling channel samples fig 4 6 are suited particularly to outcrops trenches and underground workings the method consists of cutting a relatively precise narrow channel of constant depth and width across the exposed width of the mineralization typically a vein ore the cut can be either horizontal vertical or perpendicular to the dip of the ore in the case of strongly preferred orientations e g bedding channels must be guided across the layering the samples are collected across the full width of the vein or at some uniform fixed length in wide in complex veins any identifiable subdivisions should be sampled separately in theory if the channels were continuous and uniform the channel sample would be similar to a drill core as far as possible the channel is kept at a uniform wi

dth e g 3 10 cm and depth e g 5 cm although the spacing and length depend on the inhomogeneity in the distribution of the ore or the amount of material needed for analysis the channel is best cut at a right angle to the ore zone but if this is too difficult the channel can be taken horizontally or vertically as an example of the procedure in the cornish tin mines a standard practice was to collect channel samples at 8 10 m intervals at the face on every other bench up the dip of the stope approximately 2 kg of material was collected to represent a length of channel not exceeding 50 cm annels 1991 samples are usually collected by hand and can be cut with a hammer and chisel fig 4 7 or an air hammer the chips are set out on a plastic sheet laid out the floor of the working area from which it is collected and bagged accessibility and rock hardness determine the applicable sampling tools if the quantity is large it can be quartered before being placed in the sample bag in hard rock it is quite difficult to achieve the ideal channel unless a special mechanical diamond impregnated disk cutter is used so that a reasonable approximation is generally accepted to be satisfactory the working area to be sampled must be cleaned thoroughly employing a wire brush or water among others this is done to reduce the potential for contamination of the sample by loose fragments on the face being sampled the main problem of channel sampling is related to the presence of soft minerals since they can commonly be broken preferentially thus soft mineralization can be overrepresented in a sample which imposes a high bias on the grade results on the opposite soft gangue minerals can be overrepresented and produce an undervaluation of grades this problem may be partially resolved by taking large samples or taking separate samples from soft and hard zones if possible channel has commonly a maximum length of 1 5 m and the samples must be divided into smaller parts in longer samples this subdivision is carried out based on the structures in the mineralization changes in rock types or differences in rock hardness although channel sampling possibly originates the best method of delimiting and extracting a sample the process is expensive laborious and time consuming 4 2 4 2 chip sampling chip sampling fig 4 8 is a modification of channel sampling utilized where the rock is too hard to channel sample economically or where little variation in the mineral content shows that this type of sampling method will provide results comparable to those originated by channel sampling chip sampling sometimes is applied as an inexpensive method with the objective to control if the ore is really valuable and allows the implementation of the more expensive channel sampling technique it is the most common method used for underground grade control sampling since the advantage of chip sampling is its high productivity the method is rapid a