impact of mining on evrnmt

8/9/2019 Impact of Mining on Evrnmt

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How Ore Mineral Deposits Forms

One useful way to classify mineral deposits is todistinguish deposits that were formed at the time as the

host rocks from those that were formed afterward.Syngenetic mineral deposits are those which form fromigneous bodies or by way of sedimentary processes.Epigenetic mineral deposits form in rocks that alreadyexist. For example, solid rock may fracture and veins maybe deposited in the fractures.Ores can be formed by the processes that produce rocks

there are mineral deposits that appear to have been createdby the crystallization of magma of from erosion and re-deposition of mineral that compromises sedimentary rocks.But mineral deposits also form by another process, calledhydrothermal activity, which is the action of heated fluidsin the earth. Many mineral deposits are chemicalprecipitates from hydrothermal solutions that is, theyhave come out of solution as solids. In a hydrothermalprocess, hot water, circulating through rocks by way offractures and pore spaces, can leach minerals out of therocks through which it passes and transports the mineralsin solution. The minerals remain dissolved in the wateruntil something makes them precipitate. A number of

things can happed to do this. Sometimes the temperaturefalls or the confining pressure of the rock suddenlydecreases. Other times the water encounters another rocktype that reacts chemically with the dissolved metal,forming new minerals. Sometimes one fluid meets anotherwith different chemical species in solution, and thedissolved species from each fluid react.
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A mineral deposit is made up of ore minerals, which carrythe metal, and gangue minerals, which are formed alongwith the ore minerals but contribute nothing to the value

deposit. For example, gold veins often are made up oflarge amounts of quartz and carbonate gangue, with somepyrite and a little gold. Only the gold is there in a form andamount that is worth extracting.Wherever the hot water goes, it reacts chemically with therock, causing alteration. Alteration is the chemicaldestruction of some or all the existing minerals in a rock

and the creation of new ones. Mafic minerals like pyroxene can be converted to chlorite; feldspars areconverted to micas and clays; carbonate and sulphideminerals and quartz are left behind in the rock.Hydrothermal alteration is a sign that fluids have passedthrough a rock, and is one of natures clearest messagesthat there may be a mineral deposit nearby.


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Drilling and Sampling

SamplingThe process of taking a small representative portion of a

biggermass is called sampling. The potential value of thebigger mass has the possibility of being determined byanalyzing the sample to determine the the metalconcentration that it contains.Grab samples is the name of the first samples taken from amineral showing. Geological field crews and prospectorsgrab samples from the outcrops, river beds, road cuts or

trenches. These rocks are specifically selected due to thefact that they appear to contain a significant quantity ofmetal, so they are not considered to be a representative ofthe road cut or outcrop which the come from.Grab samples are gathered from the field, the originallocation of the samples is recorded, labels are placed oneach rock and the ones which appear to be more promisingare sent to a laboratory for a metal analysis.Channel sampling may be warranted if significant orworthwhile quantities ofmetals are present in such grabsamples. In this technique of sampling, the badrock fromwhere the sample was taken is exposed as completely aspossible, by using some type of earth-moving equipment, a

typical equipment which is used for this is the backhoe.What is done afterwards is that the outcrop is hosed downwith water, if by any chance, an area of mineralization isrevealed, representative surface samples are taken atregular intervals across the zone which is exposed. Thesesamples are most of the time cut with a portable circularsaw which is equipped with a diamond-studded blade, this

leaves a linear channel across the outcrop.
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The most desirable kind of sample is the surface channel.Most of the time it is cut about 4 inches (10cm) wide and inch (2 cm) deep across the predicted ore area. The

chips of rock removed from it are carefully collected,marked and bagged for further analysis.The samples of chips are at times taken by the engineerorgeologist for a quick approximation of the containedvalue. A hammer and a chisel are what quickly knock offthe random pieces out of the outcrop, an effort is made totake representative amounts of those pieces. The samples

of chips should not be completely relied on, so they mostof the time do not enter final mathematical calculations ofpossible reserves.To space surface channels at regular intervals along themineralized area is extremely desirable but often it is notpractical. This makes one mathematical calculation in theinterpretation process obvious.In some circumstances, particularly when samplingkimberlite rock for diamonds, to collect a bulk sample isvery useful, this has the possibility of ranging from acouple hundred kilograms to several tonnes in weight. Fora bulk sample, it is important for it to be a representative ofthe area since this material can be used in the future for

definitive metallurgical grades and test work.TESTS

From what will be said later in regard to the limitedapplicability of these methods, it will be evident thatanyone undertaking the study for the first time of eitherthe application of the processes to a particular ore, or a

study of the theory of the processes themselves, should
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begin with an ore that is easily treated by flotation. What isneeded is an ore that presents the fewest special problems.An ideal mixture for the experimental work of a beginner

would be one composed of 60% quartz and 40% brown blende, or say, 70% quartz and 30% of pyrite orchalcopyrite. These mixtures are not common in nature, but approximations thereto occur frequently. With theabove proportions in mind as ideal ores for the beginner, itis well to ascertain that the ore chosen does not containmore than 2.5% of calcium carbonate or other carbonates.

A series of experiments for the beginner who has had noprevious knowledge of the processes can easily be madewithout special apparatus, and such experiments will serveto illustrate some of the phenomena of concentration byfloating part of an ore at the surface of a liquid. At the veryoutset a standard test should be selected for trying eachnew ore studied or each new oil investigated. The behaviour of the new material under these standardconditions can then be compared with previous results,thus giving the investigator a point of departure in hisexplorations. A good standard experiment is 1,000 parts ofore crushed to 6o-mesh, 3,000 parts of water, 10 parts ofsulphuric acid, and i part of oil, all by weight and at a

temperature of 70 C. Variations can then be made fromthese proportions in conformity with the specialcharacteristics of each ore under examination, or thespecial nature of the oil used, or of any other variable thatmay be under examination. In beginning the investigationof any ore, the above is a good combination with which tostart the first experiment, and then the proportions may be


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varied by gradual steps until the combination giving themaximum result is reached.In the following experiments the ore can be weighed in an

ordinary balance ; the water can be measured in cubiccentimetres, calling I cc. a gramme ; the acid can bemeasured from a burette, but the oil should be measured bycounting drops from a glass tube drawn to a medium finepoint, previously having determined by trial how manydrops of a given oil go to make up one-tenth and one-hundredth of a gramme, because the preliminary

experiments will be with small amounts of materials.EXPERIMENT

Take 10 grammes of ore.30 grammes of water.o.1 grammes of acid.

o.o1 grammes of oleic acid.Temperature 75 C.

Place these in a test-tube of 75 to 100 cc. capacity ; warmcontents to about 75 C ; close the tube with the thumb, andshake energetically for about a quarter of a minute. Theonly measure that can be cited for the amount of shakingnecessary is to shake the tube until the arm aches. Uponallowing the tube to stand a few seconds there should be

decided indications of a separation into layers. At thebottom should be a layer of quartz or gangue much lighterin colour than the original ore ; then a layer of graduallysettling gangue-slime ; then a small layer, graduallyincreasing, of sulphides dropping through the liquid ; thena considerable layer of dirty water ; and finally, on top ofall, a layer of froth composed of bubbles of air and

sulphide particles. By varying the amounts of oil or other


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ingredient of the mixture a series can be secured forcomparative inspection. Some of the froths made withcertain oils are of wonderful persistence, and if

undisturbed will stand without alteration for months.The next step is to take a larger vessel, say, a wide-mouthed bottle holding 200 cc., one that can be graspedcomfortably by both hands and held in front of theoperator with the thumbs over the cork. The shaking mustalso proceed to the aching point by the energetic use of thearms and shoulders. The charge in a series of tests of this

kind will be :Ore (6o-mesh) 30 grammes.

Water 90 grammes.Acid 0.3 grammes.Oil 0.03 grammes.Temperature 75C

Shake and allow to settle. By carefully preparing a set olbottles for comparison, or by familiarity with a long rangeof similar tests, the operator can make a rough estimate asto the result. In both the case of the test-tube and the bottleit is difficult, if not impossible, to get quantitative results.The question of securing, on a small scale, quantitativeresults that would bear some known relation to actual

milling operations, and at the same time be under readycontrol as to the various factors, has occupied considerableattention. Small machines built exactly like large machinesdo not always duplicate the large-scale operations. Perhapsthe best all-round apparatus for a study of ores and theinfluence of oils, acids, temperatures, etc., on surface-tension results is a small machine,* suggested originally by

the author to H. L. Sulman and John Ballot, first made by


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H. F. K. Picard. and improved to its present form by JamesM. Hyde and others of the Minerals Separation, Ltd., Staff,as illustrated in the accompanying photograph. The driving

mechanism to the left of the picture does not require anydescription, and can with advantage be discarded in favourof a small motor. The motor also has the advantage thatexact speeds can be duplicated, as well as exact lengths oftime of agitation. The portion of the apparatus on the rightcan be better described by reference to Fig. 10, which is asection drawn through the apparatus parallel to the plane of

the photograph. Fig. n is a transverse section, and Fig. 12 aplan of the machine.This machine is made in two parts, an upper one A, and alower one C, both sliding easily on a rubber cushion Bbetween the two parts, or, better still, having the bearingsurfaces highly polished. The rectangular section of theinterior is 4^ inches. The upper part A has a tail D, thepurpose of this being to prevent leakage of the froth whenthe upper part is slid to the right for the purpose ofremoving the froth. Windows of glass in each of the twoparts enable the operator to watch the progress of the test.At E there is a simple agitator with four arms at rightangles. The shaft driving this agitator goes through the

bottom G of the lower part C and is packed with a smallstuffing-gland to prevent leakage. At F is a holecommunicating with the interior at the bottom, closed witha valve. This hole is for the withdrawal of tailing. Theagitator-arms are 2 inches long from the centre of the shaft,thus describing a circle of 4 ins. when revolving, and soleaving a clear space of J in. wide between the ends of the

arms and the sides of the interior. The normal speed of this


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agitator is about 1,500 r.p.m. The machine should be madeof some metal that gives a clear casting. The lower surfaceof A, which rests on the rubber cushion B, and the upper

surface of C, upon which the rubber cushion rests, shouldbe planed and polished smooth. The cushion is a piece ofrubber insertion about one-sixteenth of an inch thick, andjust wide enough to fill the space between the edges H andJ of the tray-like top of C. The cushion can be discarded ifthe surfaces are accurately planed and polished.The equipment necessary for the tests will also include a

tin boiler, with the proper connections to make steam at alow pressure, the steam being introduced by a tubehanging from the top of the machine almost to the agitatorinside. An assortment of agateware dishes, burettes,pipettes, etc., is an obvious necessity. Having arrangedeverything in order, the method of making a test is asfollows . Measure 1,500 cc. water and place in themachine. This will fill it to about J inch above the bottomof the upper window. There will be no leak at the plane ofjunction between the upper part A and the lower part C, because the planed surfaces adhere to the rubbersufficiently to prevent leakage under the slight head. Startthe agitator at half-speed, and then admit the steam. While

the agitator is running, steam in large volume can beadmitted without any ' bumping.'* Weigh 500 grammes ofproperly crushed ore, and put it into the agitating water ;test the temperature, and when it is at 75 C add the oil andacid in such quantity as the test requires. Turn on themotor to full speed, and let it run, say, five minutes. Stopthe motor and agitator, and let the whole experiment set for

one half-minute to allow time for the froth to collect on the


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surface of the water and for the gangue to settle. If theexperiment is a success, the gangue will be much lighter incolour than was the original ore, and will mostly settle to

the bottom of the machine, where it can be seen throughthe lower window. Immediately above the heaviest sandygangue will be seen the finer gangue and slime rapidlysettling. At the bottom of the upper window will be agradually increasing layer of nearly clean water, and on thesurface of the water will be from J to 1 1 inches of a densesulphide froth, the amount of froth depending on the

proportion of sulphides in the ore and the success withwhich the experiment is conducted.The purpose of the peculiar construction of the apparatuswill then be apparent, for the upper part A can be slidalong the cushion B, carrying with it the froth and thatportion of the clean waterabove the plane of junction ofthe two parts. When the upper part has been slid to a position where the screws in the righthand side of theupper window are directly over the lip K, the froth andclear water will run out into a dish placed under K. Thetailing, slime, and remaining water can be given a furtheragitation, but enough water should be added to bring thewater up to a line above the bottom of the upper window.

After the second period of agitation, a further amount offroth will be formed ; this can be removed in a similarmanner, and a third and fourth also, if desired. After all thefroth has been secured, the tailing, slime, and remainingwater can be removed at F, and the two products,concentrate and residue, examined for weight, size, orcomposition. In this machine an average of 20 tests per day
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can be made, and the following series is suggested asinstructive :Take 100 Ib. of ore crushed to 6o-mesh, such as described

above as being suitable ; mix thoroughly and put in a dryplace for use in the whole series of experiments.A useful series of observations can be secured by simplyobserving the weights of concentrate produced. Moreinteresting data, however, can be obtained by sizing boththe tailing and the concentrate on a standard series ofscreens and then assaying the sizes. When the results are

plotted from the weights of the various concentratessecured in this series, the curve will be of the nature of Fig.13. This curve shows that for this ore under theseconditions the maximum effect is secured with 0.8 grammeof oil. More than that amount is detrimental, which factwould be proved by still further increasing the amount.According to the amount of carbonate in the ore, the curveof the plotted results will be something like Fig. 14. Thisore needs but little acid, the maximum result being securedwith 3 grammes. It will probably be ascertained that if theacid is increased sufficiently the recovery is less, because apoint is reached where H2S gas begins to be evolved, andthis gas is generally fatal to flotation.

Other series can be built upon the two illustrations alreadygiven by varying at regular intervals the temperature, theproportions of ore and water, the nature of the oil, thelength of time of agitation, and the speed of agitation.Then having exhausted-trieThe above series of tests, it will be observed, is by meansof a process that includes the use of oil and acid and the

addition of air by violent agitation. The general principles


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are the same as in any other combination, and as they areeasily applied and approach working conditions, and theresults are comparable with those secured in large plants,

they are of considerable value. Over a period of four years,when thousands of small tests were made on an ore thatwas being treated in two plants of 1,000 tons per day, theresults from the small tests averaged 5% less recovery and3% lower-grade zinc in the various concentrates than weresecured in the large plant.This machine is a useful addition to the ore-testing

laboratory, whether flotation processes are in view or not,because, by the use of it and the expenditure of sufficientacid and agitation, the sulphide contents of almost any orecan be determined accurately.Another machine of simpler design and cheaperconstruction is shown in section in Fig. 19, and in plan inFig. 20. It is made of easily procurable materials, and canbe constructed in the laboratory. It has the disadvantage,however, that it requires some skill in removing froth afterthe agitation. The froth can be removed by carefulskimming with a spoon. Some froth will unavoidably besunk during the skimming operation, but the agitator canbe started again, followed by a second skimming. If there

appears to be still further chance of a useful result, a thirdand fourth period of agitation and skimming can be tried.If this machine is made 4^ inches square, insidemeasurement, and 10 inches deep, it will be the right sizefor tests on 500 grammes of ore. The equipment necessaryfor making tests will also include a tin boiler, with thenecessary connections for introducing steam into the

apparatus. The agitator should be so belted to the motor


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that it will run about 1,500 r.p.m. The agitator should beabout 4 inches in diameter, thus leaving J inch clear allround its path of rotation. The method of conducting a test

will be just the same with this machine as with the other,except in the matter of removing the froth, and in thisinstance it will have to be removed by an ingenious hand.Carefully dip as much as possible of this froth off thesurface of the water with a large spoon. The design andmaterial of this spoon can be left to the ingenuity of theexperimenter, as each man will fancy one of his own

invention. Some froth, as said before, will be sunk duringthe skimming operation, but the agitator can be started andrun for one minute previous to another skimming. A thirdand a fourth, if necessary, will give a fair recovery, provided good mineral-frothing conditions have beenestablished. This machine will yield much instruction, butis not as direct in its results as the one in Fig. 6.An interesting series of experiments can also be conductedin an ordinary soda-water syphon. The cap of the bottleshould be altered so that the pressure can be raised in thebottle with a bicycle pump. The necessary alterations arequite easily done, and can be effected in the laboratory.The charge will be 100 grammes of ore, 300 gm. water,

with acid and oil to suit. The air-pump should be one witha pressure-gauge attached, so that pressures can be noted.After pumping to 30 Ib. pressure, the bottle with thecharge should be shaken a few times, so that the air willdissolve. Then the lever being depressed, most of thecharge can be drawn into a beaker, and the froth andtailing examined at will. It is worth noting in this


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connection that excellent mineral froths can be made atnormal atmospheric temperature.


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Before Mining BeginsEnvironmental protection starts at the earliest stages of mine exploration, long before the firstore is extracted. During this stage, companies make every effort to minimize the impact of

prospecting, drilling, trenching, road building and other related activities. Exploration

activities usually affect the environment only temporarily and, work can be carried out withminimal disturbance to land, vegetation and wildlife habitats with proper planning. Eventhen, companies have learned that it is important to keep local communities informed abouttheir activities. This consultation process sets the stage for good community relations oncemine planning has begun.To keep public support, mining companies must demonstrate respect for the ecosystem inwhich they are working and adopt a extense range of protective measures. The drilling fluidsand lubricants used in diamond drilling can seep into the water used to bring cuttings tosurface. This water must be appropriately contained and disposed of so that it does notcontaminate the groundwater. Drill holes often have to be sealed with impermeable concreteor bentonite which is a clay material to ensure that the drill hole cannot act as a channelway

for contaminants to reach the groundwater from the surface.Another consideration in the exploration of minerals is the safe handling of camp wastes.This means much more than just being careful not to litter, as isolated exploration campsmust make sure that they handle fuels and dispose of human wastes in ways that do notcontaminate the natural environment.It is common for governments to demand that exploration crews have permits to work, settingdown limits on what the crew can do in very sensitive areas, such as tundra regions. Respectforwildlife must be shown at all times. With proper planning, forethought and goodhousekeeping, all of the impacts of an exploration campaign can be minimized.Once a deposit of economic interest has been outlined, studies and sampling programs arecarried out to provide data that are used to shape the design of a project.

Specialists researchall aspects of the environment to establish basic data, against whichfuture test results will be evaluated and compared. A few of the various areas investigatedare: soil composition; the concentrations of metals in water-courses which are nearby; the

populations of animal and plant species that live nearby; climate and air quality; cultural andhistorical sites; and a variety of other pieces of data that permit regulators to determine if themine, once in operation, is causing adverse changes to the environment.
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A Mining Project Feasibility StudyWinners and Losers: Mining is a large, vital and lucrative business. Its rewards are spreadacross a wide cross-section of our population. But not all mining ventures are successful.Risks are high and they take many forms.The process of discovering and developing any mineral deposit involves dozens of varied

people with a variety of skills, and the expenditure of many millions ofdollars. But thequestion to ask when evaluating a deposit is always the same one: Does it hold enoughrecoverable and marketable metal or gems to be dug out of the ground, transported to themarket and sold at aprofit? Obviously, there are risks which are involved in each of the steps,and one calculation wrongly made can be disastrous.The most serious risks in any mining project are those associated with geology (the actualsize and grade of the mineable portion of the orebody), metallurgy (the amount of the metalwhich can be recovered) and economics (metal markets, interest rates, transportation costs).But there are many others, such as problems arising from unforeseen political developments,new restrictive regulations or the availability of workers, to mention a few.

Feasibility StudiesOne of the features which distinguishes a mining enterprise from many other businesses isthat during production, the company's asset (for example, the ore) is progressively consumed.Some day, the assets of the mine will be gone; hence, a mine is referred to as a wasting asset.This has important implications for the justification of allocating capital to any new mining

project.The time value ofmoney plays an important role here. To put it simply, the annual profitsgenerated by a mine must be sufficient to pay back (within a reasonable time) the moneyinvested in the mine. It is the job of mining engineers to estimate the "payback period" inwhat is called a study of feasibility.One of the important elements in a feasibility study is the estimate of costs of mine operating.

It is impossible to suggest what the costs might be for a particular mine without looking at allthe details of the planned operation, and reasonable estimates can only be made when preciseinformation is available. The final estimate will only be as dependable as the informationused to arrive at the individual cost estimates from which it is derived.all factors that influence the capital cost of a miningproject are the prices the miningcompany will have to pay for labor, electrical power, supplies and shipping out of itsconcentrate.Each country has its cost-related advantages and disadvantages. For example, mining in thevast, undeveloped regions of Canada makes the construction of roads, railways and airstripsmuch more expensive than in developing countries. Also, miners in both Canada and theUnited States demand higher wages than their counterparts which are in countries that are in

development.On the other hand, mining companies working in many developing countries can encounter

problems such as high taxand tariff costs, and the corruption of civil servants such as customsofficials, without whose help they would have difficulty getting theirproject off the ground.The overall political instability of some countries can be a great deterrent to the developmentof mines.However, somewhat perversely, the existence of any combination of negative factors leads toless exploration in that region or country, which, in turn, can increase one's chances ofdiscovering an economic orebody. In mineral exploration, something is always better thannothing.
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The Mining TeamMine Finders

As a result of advances in technology, mineral exploration has changed dramatically from thedays when the lone prospector packed a pick and a rabbit's foot into a canoe and headed into

the bush for a season's work. Mineral exploration and mining is presently a business that callsfor highly skilled professionals to work as a team, using powerful, often computerized,mining and exploratory equipment. The exploration team can have prospectors, geologists,

geophysicists and geochemists (and their assistants) included, whose skills complement eachother as they look for new mines.

Prospectors even now play an important part in generating showings (evidence of localmineralization), which are later optioned and explored by mining companies. To find theseshowings, prospectors depend on geological maps,government reports, evaluation files and

aerial photographs.Government geologists lay the foundation for future discoveries by conducting regional-

scaleprograms and by preparing reports and maps from the data gathered. The release of new

information by government geological surveys is, therefore, eagerly anticipated by dedicatedprospectors. Exploration is a competitive business, so having the jump on the competition canmake the difference between making a discovery and missing out on one.

Prospectors test potential areas by early-stage field work, which might include following atrain of mineralized boulders to their source or collecting samples from soils and rocks to

identify and test anomalies. Old-fashioned "boot-and-hammer" prospecting is still animportant tool in mineral exploration and has led to many spectacular discoveries, includingthe Voisey's Bay nickel-copper-cobalt deposit in Labrador. Because prospectors play such an

important role in discovering new showings, some governments offer small grants toencourage their continued efforts.

Prospectors often sell theirproperties to mining companies, which will after send out a team

of geologists to carry out more detailed sampling programs. A geophysicist searches foralterations in the physical characteristics of the earth that may be caused by the presence ofminerals. A geochemist analyzes the metal content in rocks, soils, surface waters or plants,looking for anomalous values that are different from background metal levels in the region.

Most of the time, more than one technique is used to check any anomalies which areidentified. Trenching or pits may give some early samples of mineralized rock for testing.

Advancedproperties see the arrival of diamond drillers. These men and women spend a lot oftheir time in field camps and are used to moving from job to job since diamond drill contracts

rarely last that long.In all but the smallest field camps, one of the most important members is the camp cook,

whose offerings play an important part in sustaining the morale of the crew.
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Mining and the Environment

Safeguarding the EnvironmentMining companies give us the metals and minerals that humanity uses for shelter, survival,

work and pleasure, as well as the expansion into space and interplanetary endeavors. At thesame time, they want to conduct this business in an environmentally responsible inanner. Yetmining by its very nature requires that land, air and water systems be disturbed. While l heeconomic benefits of the industry are as important today as they ever were, the public hasliecome increasingly concerned about the impact that mining is having on the naturalenvironment.The metals and industrial minerals that mining produces can find their way into theenvironment and become pollutants. The byproducts that occur with the metals, such assulphur and arsenic, can be dangerous to the environment if they are released. The fuelsandchemicalsthe industry uses to do its job are potential pollutants too. Mining creates andemploys hazardous substances that must be handled with a lot of care.

Other pollutants produced by the mining industry are of more concern to the workers in theindustry than to the public which are at large. Dusts, for example, which are most of the timehazardous hygienically, are produced by a lot of mining activities. Noise, too, is a formofpollution of concern for those in the environment of work. In uranium mines, the productsof radioactive decay are a principal concern.The challenge for industries is to find, extract and process mineral resources with the least

possible environmental disruption. To be able to meet this challenge, they adopt an expandedrange of protective measures, including: sensitive treatment of the land during exploration;environmental and aesthetic management of land under development; environmentallysustainable production procedures during the mining and metallurgical processes; anddecommissioning and reclamation practices aimed at restoring the land.

Accountability and environmental performance are important issues for the miningcompanies, their share-holders and the public. Most companies now include a discussion ofenvironmental topics in their yearly reports so as to keep shareholders and the publicinformed about the measures they are taking to protect the land, water and air quality at theiroperations.
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Environmental effectsEnvironmental issues can include erosion, formation of sinkholes, loss of biodiversity, andcontamination of soil, groundwater and surface water by chemicals from mining processes. Insome cases, additional forest logging is done in the vicinity of mines to increase the available

room for the storage of the created debris and soil.[26] Contamination resulting from leakageof chemicals can also affect the health of the local population if not properly controlled.[27]Mining companies in most countries are required to follow stringent environmental andrehabilitation codes in order to minimize environmental impact and avoid impacts on humanhealth. These codes and regulations all require the common steps of Environmental impactassessment, development of Environmental management plans, Mine closure planning(which must be done before the start of mining operations), and Environmental monitoringduring operation and after closure. However, in some areas, particularly in the developingworld, regulation may not be well enforced by governments. For major mining companies,and any company seeking international financing, there are however a number of othermechanisms to enforce good environmental standards. These generally relate to financing

standards such as Equator Principles, IFC environmental standards, and criteria for Sociallyresponsible investing. Mining companies have used this financial industry oversight to arguefor some level of self-policing.[28] In 1992 a Draft Code of Conduct for TransnationalCorporations was proposed at the Rio Earth Summit by the UN Centre for TransnationalCorporations (UNCTC), but the Business Council for Sustainable Development (BCSD)together with the International Chamber of Commerce (ICC) argued successfully for self-regulation instead.[29] This was followed up by the Global Mining Initiative which wasinitiated by nine of the largest metals and mining companies, and led to the formation of theInternational Council on Mining and Metals to "act as a catalyst" for social andenvironmental performance improvement in the mining and metals industry internationally.[28] The mining industry has provided funding to various conservation groups, some of

which have been working with conservation agendas that are at odds with emergingacceptance of the rights of indigenous people - particularly rights to make land-use decisions.[30]Ore mills generate large amounts of waste, called tailings. For example, 99 tons of waste aregenerated per ton of copper, with even higher ratios in gold mining[citation needed]. Thesetailings can be toxic. Tailings, which are usually produced as a slurry, are most commonlydumped into ponds made from naturally existing valleys.[31] These ponds are secured byimpoundments (dams or embankment dams).[31] In 2000 it was estimated that 3,500 tailingsimpoundments existed, and that every year, 2 to 5 major failures and 35 minor failuresoccurred (citation needed); for example, in the Marcopper mining disaster at least 2 milliontons of tailings were released into a local river.[32] Subaqueous tailings disposal is another

option.[31] The mining industry has argued that submarine tailings disposal (STD), whichdisposes of tailings in the sea, is ideal because it avoids the risks of tailings ponds; althoughthe practice is illegal in the United States and Canada, it is used in the developing world.[33]Certification of mines with good practices occurs through the International Organization forStandardization (ISO) such as ISO 9000 and ISO 14001, which certifies an 'auditableenvironmental management system'; this certification involves short inspections, although ithas been accused of lacking rigor.[28]:183-4 Certification is also available through Ceres'Global Reporting Initiative, but these reports are voluntary and unverified. Miscellaneousother certification programs exist for various projects, typically through nonprofit groups.[28]:185-6[edit]Regulations and World Bank relationship


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The World Bank has been involved in mining since 1955, mainly through grants from itsInternational Bank for Reconstruction and Development, with the Bank's MultilateralInvestment Guarantee Agency offering political risk insurance.[34] Between 1955 and 1990it provided about $2 billion to fifty mining projects, broadly categorized as reform andrehabilitation, greenfield mine construction, mineral processing, technical assistance, and

engineering. These projects have been criticized, particularly the Ferro Carajas project ofBrazil, begun in 1981.[35] The bank established mining codes intended to increase foreigninvestment, in 1988 solicited feedback from 45 mining companies on how to increase theirinvolvement.[28]:20In 1992 the bank began to push for privatization of government-owned mining companieswith a new set of codes, beginning with its report The Strategy for African Mining. In 1997,Latin America's largest miner Companhia Vale do Rio Doce (CVRD) was privatized. Theseand other movements such as the Philippines 1995 Mining Act led the World Bank to publisha third report (Assistance for Minerals Sector Development and Reform in MemberCountries) which endorsed mandatory environment impact assessments and attention to thelocals. The codes based on this report are influential in the legislation of developing nations.

The new codes are intended to encourage development through tax holidays, zero customduties, reduced income taxes, and related measures.[28]:22 The results of these codes wereanalyzed by a group from the University of Quebec, which concluded that the codes promoteforeign investment but "fall very short of permitting sustainable development".[36] Theobserved negative correlation between natural resources and economic development is knownas the resource curse.

Safety

Danger sign at an old Arizona mine.

Abandoned mine entrance in Yorkshire, England, United KingdomSafety has long been a controversial issue in the mining business especially with sub-surfacemining. While mining today is substantially safer than it was in the previous decades, miningaccidents are often very high profile, such as the Quecreek Mine Rescue saving 9 trappedPennsylvania coal miners in 2002. Mining ventilation is a significant safety concern for manyminers. Poor ventilation of the mines causes exposure to harmful gases, heat and dust inside

sub-surface mines. These can cause harmful physiological effects, including death. Theconcentration of methane and other airborne contaminants underground can generally becontrolled by dilution (ventilation), capture before entering the host air stream (methanedrainage), or isolation (seals and stoppings).[41] Ignited methane gas is a common source ofexplosions in coal mines, or, the more violent coal dust explosions. Gases in mines can also

poison the workers or displace the oxygen in the mine, causing asphixiation.[41] For thisreason, the MHSA requires that workers have gas detection equipment in groups of miners. Itmust be able to detect common gases, such as CO, O2, H2S, and % Lower Explosive Limit.Additionally, further regulation is being requested for more gas detection as newertechnology such as nanotechnology is introduced. High temperatures and humidity may resultin heat-related illnesses, including heat stroke which can be fatal. Dusts can cause lung

problems, including silicosis, asbestosis and pneumoconiosis (also known as miners lung or


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black lung disease). A ventilation system is set up to force a stream of air through theworking areas of the mine. The air circulation necessary for the effective ventilation of amine is generated by one or more large mine fans, usually located above ground. Air flows inone direction only, making circuits through the mine such that each main work areaconstantly receives a supply of fresh air.

Since mining entails removing dirt and rock from its natural location creating large emptypits, rooms and tunnels, cave-ins are a major concern within mines. Modern techniques fortimbering and bracing walls and ceilings within sub-surface mines have reduced the numberof fatalities due to cave-ins, but accidents still occur.[citation needed] The presence of heavyequipment in confined spaces also poses a risk to miners, and despite modern improvementsto safety practices, mining remains dangerous throughout the world.[edit]Abandoned mines

Abandoned mine in Nevada.

Warning sign near Jerome, ArizonaThere are upwards of 560,000 abandoned mines on public and privately owned lands in theUnited States alone.[42][43] Abandoned mines pose a threat to anyone who may attempt toexplore them without proper knowledge and safety training. Old mines are often dangerousand can contain deadly gases. Standing water in mines from seepage or infiltration poses asignificant hazard as the water can hide deep pits and trap gases below the water.Additionally, since weather may have eroded the earth and rock surrounding it, the entranceto an old mine in particular can be very dangerous. Old mine workings, caves, etc. arecommonly hazardous simply due to the lack of oxygen in the air, a condition in mines known

as blackdamp.[edit]Hearing lossMiners utilize equipment strong enough to break through extremely hard layers of the Earth'scrust. This equipment, combined with the closed workspace that underground miners workin, can cause hearing loss.[44] For example, a roof bolter (commonly used by mine roof

bolter operators) can reach sound power levels of up to 115 dB.[44] Combined with thereverberant effects of underground mines, a miner without proper hearing protection is notonly at a high risk for hearing loss,[44] but is also going against OSHA standards[45].


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Hardrock Mining: Environmental Impacts

Overview

Hardrock mining is a large-scale industrial activity that takes place in the naturalenvironment, potentially disturbing large amounts of material and land area. Hardrock mininggenerates large volumes of mining waste because of the high waste-to-product ratiosassociated with producing most ores. This page describes some of the potentialenvironmental effects of hardrock mining.

EPA recognizes that some of the discussion on this page may not accurately reflect theenvironmental conditions at modern hardrock mining operations that are well-designed, well-operated, and well-regulated. The intent of this discussion is to highlight environmental

problems at (predominantly historic) mining sites and to indicate the potential problems thatcould occur at existing and future sites.

Acid Mine Drainage

Definition

Acid mine drainage is the drainage that results from sulfide oxidation in rocks exposed to airand water. Metal sulfide minerals are common constituents in the rocks associated with metalmining activity. Before mining, oxidation of these minerals and the formation of sulfuric acidis a slow function of natual weathering processes. Natural discharges from such deposits poselittle threat to aquatic ecosystems except in rare instances. Mining and benefication

operations greatly increase the rate of these same chemical reactions by removing sulfiderock material and exposing the material to air and water.

Characteristics

Acid generation primarily results from the oxidation of metallic sulfides. The major metallicsulfide of concern is iron sulfide (FeS2) or pyrite. Other metal sulfides that contribute to acidgeneration include lead sulfide (galena), zinc sulfide (sphalerite), and iron copper sulfide(chalcopyrite).

Both water and oxygen are necessary to generate acid drainage. Water serves as both areactant and a medium for the bacteria to catalyze the oxidation process and transports the

oxidation products. Oxygen is particularly important to maintain bacterially-catalyzedoxidation at pH values below 3.5

During acid generation, the pH values of the associated waters typically decrease to valuesnear 2.5. These conditions result in the dissolution of the minerals associated with themetallic sulfides and release of toxic metal cations (e.g., lead, copper, silver, manganese,cadmium, iron, and zinc). In addition, the concentration of dissolved anions (e.g., sulfate)also increases.


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Potential Impacts

Acid generation and drainage affect both surface water and groundwater. The sources ofsurface water contamination are leachate from mine openings, seepage and discharges from

waste rock, tailings, ground water seepage, and surface water runoff from waste rock andtailings piles. Mined materials such as waste rock or tailings used for construction or other

purposes (e.g., road beds, rock drains, and fill material) can also develop acid mine drainage.

The receptors of contaminated surface water include birds, fish, and other aquatic organisims.Humans can also be affected by direct ingestion of contaminated surface water or directcontact through outdoor activities such as swimming.

Control

There are no easy or inexpensive solutions to the problem of acid mine drainage. Twoprimary approaches to addressing acid generation are:

1. Avoiding mining deposits with high acid generating potential2. Isolating or otherwise special-handling wastes with acid generating potential

In practice, avoiding mining in areas with acid generating potential may be difficult becauseof widespread distribution of sulfide minerals. Isolation of materials with the potential togenerate acids is now being tried as a means of reducing the perpetual effects of mining wasteon surface water and groundwater. Control of the material can be implemented by preventingor minimizing its contact with oxygen, preventng its contact with water, and/or ensuring thatan adequate amount of natural or introduced material is available to neutralize any acid

produced. Techniques used to isolate acid generating materials include subaqueous disposal,covers, waste blending, hydrologic controls, bacterial controls, and treatment.

Erosion and Sedimentation

Definition

Erosion is the process by which soil particles are detached, suspended, and transported fromtheir source of origin. Erosion can be caused by water, primarily through direct impact withraindrops and precipitation run-off, or by wind in arid environments. Sedimentation occurswhen eroded particles are deposited at a different location than the source of origin.

Source

The extent of erosion and sedimentation depends on various factors, including the degree atwhich the surface has been disturbed, the prevalence of a vegetative cover, the type of soil,the slope length, and the degree of slope. Disturbed areas with little or no vegetative cover,soil high in silt, or a steep slope are the areas most likely to erode.

Potential Impacts

Erosion and sedimentation affect surface water and wetlands more than any other media.Erosion can also adversely affect soil organisms, vegetation, and revegetation efforts becauseit results in the movement of soil, including topsoil and nutrients, from one location to

another.


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Cyanide and Other Chemical Releases

Definition

The mining industry has a long history of cyanide use. For decades, cyanide has been used asa pyrite depressant in base metal flotation. It has also been used for over a century for gold

extraction. After cyanide leaching of gold heaps proved feasible in the 1970s, the relativelyhigh price of gold has made cyanide leaching of relatively low-grade ores economicallyfeasible. Figure 2 illustrates cyanide.

Characteristics

Cyanide exists in many forms, depending on the starting compound and environmentalconditions. The most common cyanide compound used in mining is sodium cyanide(NaCN).

Potential Impacts

Cyanide released into the environment can adversely impact water, soil, aquatic organisms,

wildlife, waterfowl, and humans. Cyanide-contaminated solution in tailing ponds andsolution retention basins has proven to be attractive to unsuspecting waterfowl and wildlife.These organisms have suffered both acute and chronic poisoning as a result of direct contactwith and ingestion of cyanide-contaminated solution. Leakage from linear failure at heapscan allow the release of cyanide and other toxic constituents directly into the environment.

Other Chemicals

Other chemicals used during the beneficiation process, stored on-site for use, or used invehicles and equipment can impact human health and the environment if released. Thesechemicals include oil, petroleum products, solvents, acids, and reagents.

Control and Remediation

Proper storage of chemicals, including secondary containment, protectingchemicals from the elements, and regular inspections to identify deteriorationand/or leaks, can reduce the potential for releases.

Methods such as covering ponds with nets can discourage wildlife from beingattracted to cyanide-contaminated solution retention basins.

Using liners and/or constructing well-built dams can prevent the release ofchemicals into the environment.


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Health and Safety Are the Key

The men and women who are employed in mining must be in good health. Even thoughmechanization has reduced the amount of physical work required, the individual must stillhave reasonable strength and good hearing and eyesight. A physical examination is required

by law upon starting employment in the mining industry and medical check-ups are carriedout on a regular basis.For mining companies the development of safe job procedures, combined with commonsense, has always been a high priority. Accident prevention is the responsibility of everyonewho is involved - management, workers, unions and governments.Each mine also has a rescue team. These usually consist of six to eight miners speciallytrained to find and assist miners who are trapped in the event of cave-in, fire or some otheraccident.Powerful modern ventilation systems have considerably reduced the risks which were onceassociated with mining, but mining companies, unions and governments continue to work

with research organizations in order to certify that working conditions are always gettingbetter.Skill Level Increasing

While many workers who are not skilled and who have little formal education still work inthe mines of North America, the increasing complexity of mines today demands that thosewho wish to advance to the highly skilled and better-payingjobs should have a minimum ofsecondary school education. Technical training from a technical high school orcommunity collegeis an advantage and, ofcourse, higher education like anengineering degree or any other university degree, gives a young miner many more

probabilities for better positions in the future.Mining companies provide the inexperienced worker with a time period of initial training

which is common to all employees. This common core training (or stope school, as it issometimes called) includes an introduction to the basics of mining and mining safetyprocedures, classroom study on surface and underground, followed by on-the-job training ashelper to a miner with experience. Specialized training is afterward a necessity to becomequalified to operate individual machines.Office Staff

There are the professional and technical staff whose duties encompass such things assampling, surveying, drafting and planning besides the miners and various supervisory

personnel. Directing their activities are the mining engineers and geologists who map theprogress of the mining operations, design the mining methods, and direct the search for newore.

Uppermanagementmost of the time includes a mine manager and a mine superintendent.Naturally, there are also secretarial and personnel accounting at each mine.Mill and Smelter Worker

The treatment of ore requires another set of skills, and thus, another group of specializedoperators are on thejobto watch over the ball mills, flotation tanks and other machinery.Assayers and chemists are also on hand to perform the analysis of samples for the control ofthe mining and milling operations.When the metal concentrates are shipped out for refining, still another team of workers comeson the scene - furnace men, smelting equipment operators and refinery operators, onlynaming a few.Computerized "programmable logic controllers" are common in most mills and smelters, sooperators are demanded to monitor an entire sequence of operations from a control consolethat keeps tabs on what is happening in many parts of the plant.
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