25012121 Education Under Ground Mining E Book 06

8/8/2019 25012121 Education Under Ground Mining E Book 06

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Second edition 2007www.atlascopco.com

Mining Methodsin Underground Mining


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Atlas Copco Rock Drills AB

www.atlascopco.com

Committed to your superior productivity.

When safety comes first

Add a solid body hydraulic breaker to a proven folding boomon the worlds most tested underground carrier, and you havethe Scaletec MC a scaling rig for tunnelling and miningapplications. Scaletec MC will give you higher producti-

vity, less accidents, and take you a giant step along the routetowards full mechanization.


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underground mining methods 1

Fo o

2 Foreword by Hans Fernberg M ScMining Engineering, Senior Adviser,Atlas Copco Rock Drills AB

T T ch c3 Trends in underground mining7 Geology for underground mining

13 Mineral prospecting and exploration17 Finding the right balance in exploration drilling

21 Underground mining infrastructure 25 Principles of raise boring

29 Mechanized bolting and screening 33 Mining in steep orebodies

39 Mining in flat orebodies43 Backfilling for safety and profit46 Atlas Copco rock bolts for mining

C s St s 47 Innovative mining at Garpenberg

53 Changing systems at Zinkgruvan59 Increasing outputs at LKAB iron ore mines63 From surface to underground at Kemi

69 Mining magnesite at Jelava73 All change for Asikoy copper mine

77 Mining challenge at El Soldado83 Pioneering mass caving at El Teniente91 Boxhole boring at El Teniente97 Modernization at Sierra Miranda99 Mount Isa mines continues to expand

105 High speed haulage at Stawell109 Sublevel stoping at Olympic Dam115 Improved results at Meishan iron ore mine119 Mechanized mining in low headroom at Waterval121 Large scale copper mining adapted to lower seams

125 Underground mining of limestone and gypsum129 Sub level caving for chromite133 Getting the best for Peoles137 Keeping a low profile at Panasqueira

F o t cov : Headframe at Australias Golden Grove mine.

All product names such as Boomer, Boltec, Simba, COP, Scooptram and Swellex are registered Atlas Copco trademarks. For machine specifications contact your local Atlas Copco Customer Center or refer to www.a la c pc .c / ck

Co t ts

Produced by tunnelbuilder ltd for Atlas Copco Rock Drills AB, SE-701 91 rebro, Sweden, tel +46 19 670 -7000, fax - 7393.Publisher Ulf Linder [email protected] Editor Mike Smith [email protected] Senior Adviser Hans [email protected] Picture Editor Patrik Johansson [email protected] Marcus Eklind, Patrik Ericsson, Jan Jnsson, Mathias Lewn, Gunnar Nord, Bjrn Samuelsson,all [email protected], Adriana Potts [email protected], Kyran Casteel [email protected],Magnus Ericsson [email protected]. The editor gratefully acknowledges extracts from Underground Mining Methods engineering fundamentals and international case studies by William A Hustrulid and Richard L Bullock, published by SME,details from www.smenet.org

Designed and typeset by ahrt, rebro, SwedenPrinted by Welins Tryckeri AB, rebro, Sweden

Copyright 2007 Atlas Copco Rock Drills AB.

Digital copies of all Atlas Copco reference editions can be ordered from thepublisher, address above, or online at www.atlascopco.com/rock. Reproduction

of individual articles only by agreement with the publisher.


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2 underground mining methods

H s F b

M Sc Mining Engineering Senior Adviser Atlas Copco Rock Drills AB

[email protected]

In history, before miners had access to productive equipmentand blasting agents, mining was hard and hazardous manual

work. The idea of excavating large volumes of rock to accesseven the richest mineral zones was not feasible, and, as a re-sult, ore veins were selectively followed, predominantly closeto the surface, or inside mountains. During the past century,introduction of diesel power and electricity, combined withnew methods of mineral dressing, paved the way for largescale open pit mining, and later for mechanized undergroundmining. Nevertheless, the largest quantities of ore are stillexcavated from surface deposits.

Atlas Copco, as an equipment supplier with a truly globalpresence, has been at the forefront of technical and innova-tive development. From pneumatic to hydraulic power, fromrailbound to trackless haulage, from handheld to rig mountedrock drills, and lately, from manual to computerized opera-tion, Atlas Copco expertise is making mining safer and moreefficient.

Today, the mining industry, in its continuous battle for profit-ability, is getting more and more capital intensive. Technicaldevelopment, especially in underground mining, has beenextremely rapid during the past decade. Less labour is re-quired, and safety and environmental aspects are of primeimportance.

Growing demand for metals has resulted in todays world wideexploration and mining boom. However, mining companieshave experienced increasing difficulties in recruiting skilledlabour to work in remote mining communities. This has ledto a stronger involvement from contractors now car rying outtasks beyond the more traditional shaft sinking operations.Today, contractors get engaged in all kinds of mine infra-structure works such as drifting, both inside and outsidethe orebodies, and might also be involved in production andmine planning, as well as scheduling. The miners, tradition-ally focusing on maximizing the utilization of their equipment

mine-wide, are benefiting from experience gained by tunnelcontractors, who frequently have to concentrate their focus

on a single tunnel face. This makes the latter more suited forhigh-speed ramp and drift development, and is one reasonwhy contractors are increasingly being employed by mineowners on this type of work. Also, contractors bring withthem a range of skills developed under various conditions inmultiple locations, and frequently have the latest and mostsophisticated equipment immediately available. Gone are thedays when contractors got only the jobs that the mine manage-ment could not do, or simply didnt want to do. Nowadays, itis normal for a contractor to bring specialist skills and equip-ment to the project, and for the mine to get its developmentwork completed faster and cheaper than by doing it itself.After all, when bringing mines to production, time and costare crucial factors in their viability.

When designing, manufacturing, selling and servicing AtlasCopco equipment, we commit ourselves to achieving the high-est productivity, and the best return on customer investment.Only by being close to customers, by sharing their problemsand understanding their methods and applications, do we earnthe opportunity to be the leading manufacturer, and the natu-ral first choice.

Our main ambition with this book is to stimulate technicalinterchange between all people with a special interest in thisfascinating business. These include, in particular, undergroundminers, managers and consultants, universities, and our ownsales and marketing organization.

The various cases from leading mines around the world illus-trate how geological and geotechnical conditions, never beingidentical, give birth to new and more successful variants of mining methods. We hope that some of this material willresult in expanded contacts between mining companies intheir battle to be more competitive and profitable.

Fo o


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Mining TrendS


St b owthInvestments into new mines have in-creased dramatically and all indicatorspoint to a continued high level of proj-ect activities during the next couple of years, see figure 1.

Whatever the investment act ivitiesor metal prices, the amount of metalproduced every year in global miningis fairly stable and increasing slowly butsteadily. Total volumes of rock and orehandled in the global mining industryamount to approximately 30,000 Mt/y.This figure includes ore and barren rockand covers metals, industrial mineralsand coal. Roughly 50% are metals, coal

about 45%, and industrial minera lsaccount for the remainder.

Dynamic growth in China.

T s o m

Boom t m mThe mining boom continuesunabated. After a difficult endingto the 20th century, with metalpr ices t rending downwardsfor almost 30 years, the globalmining industry recovered inthe early 2000s. Some observersclaim that the industry will see along period of increasing metalprices and, although develop-ments will continue to be cyclical,there are predictions of a supercycle. Already it is obvious thatthe present boom is somethingextraordinary in that it has lastedlonger than previous booms inthe late 1970s and the early 1950s.An almost insatiable demand formetals has been created by theunprecedented economic growthin several emerging economiesled by China, with India andRussia trailing not far behind. Thedistribution of the value of metalproduction at the mine stage isshown in figure 2 on page 4 page.China and Australia are competingfor first place with roughly 10 per-cent each. Some economic theo-retitians, active during the late1980s, who claimed that econo-mic growth could take place with-out metals have been proved ut-terly wrong.

5 000

2001 2002 2003 2004 2005 2006

10 000

15 000

20 000

25 000

30 000

M USD

Figure 1: Mining projects under construction. (Raw Materials Data 2007)

T r e n d s

T r e n d s


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Mining TrendS


M t oGlobal metal ore production is around5,000 Mt/y. Open pit mining accountsfor some 83% of this, with undergroundmethods producing the remaining 17%.Barren rock production from under-ground operations is small, not exceed-ing 10% of total ore production, but thebarren rock production from open pitoperations is significant.

Open pits typically have a strip ratio,the amount of overburden that has to beremoved for every tonne of ore, of 2.5.Based on this assumption, the amount

of barren rock produced can be calcu-lated as some 10,000 Mt/y. In total, theamount of rock moved in the metals mi-ning business globally is hence around15,000 Mt/y. The dominance of open pitoperations stems in terms of the amountsof rock handled, to a large extent, fromthe necessary removal of overburden,which is often drilled and blasted.

By necessity, the open pit operationsare larger than the underground ones.The map below shows the distributionof metal ore production around theworld, and also the split between openpit and underground tonnages.

Op p t vs oThere was a slow trend in the late 20thcentury towards open pit production.Two of the most important reasons forthis were as follows:

Lower ore gradesDue to depletion of the richer orebodies, the higher-cost undergroundextraction methods are not economic.See the figure below.

New technologiesThe more efficient exploitation of lower-grade deposits using new equipment andnew processes, such as the hydrometal-lurgical SX-EW methods for copperextraction, has enabled companies towork with lower ore grades than withtraditional methods.

F tDevelopment of new mining technolo-gies is driven by a range of underlyingfactors, which affect all stakeholders.Mines are getting deeper and hotter, andare now more often located in harsh en-vironments.

Legislation, particularly concerningemissions, and increased demands on

Metal shares of total value gold copper iron ore nickel lead zinc PGMs diamonds other

i

Value of metal production at mines. (Raw Materials Data 2007)

open pit underground

898/77 Mt

1319/117 Mt

750/185 Mt

401/188 Mt

244/175 Mt

455/85 Mt

Total 5 000 Mt

Europe + Russia

Metal ore production from open pits (green), underground (red). (Raw Materials Data 2005)


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Mining TrendS


noise and vibration, affect the minersand equipment operators. Safety de-mands have already completely changedsome unit operations, such as rock bolt-ing and scaling. Similar developmentswill continue.

Customers demand higher productiv-ity, and there is an increasing focus onmachine availability and simpler serviceprocedures in order to reduce down-time. Reduction of internal developmentand production costs by the equipment

manufacturer promotes new technolo-gies, as does competition from othersuppliers. In the early years of the 21stcentury, new efficient underground me-thods and equipment have made itpossible to turn open pit mines that hadbecome uneconomical because of theirdepth into profitable underground ope-rations. The orebody in these mines isusually steep dipping, and can be minedwith the most efficient block caving meth-ods. The competition for land in some

densely populated countries has furthermeant that underground mining is theonly viable alternative. Such developmentshave halted the growth of open pit mi-ning and it is projected that the pre-sent ratio 1:6 underground to open pitmining will continue in the mediumterm.

M s e csso Raw Materials Group

Rock production (2005)

Ore(Mt)

Waste(Mt)

Total(Mt) %

Metals

Underground 850 85 935 3Open pit 4 130 10 325 14 500 47

Total 4 980 10 410 15 400 50

Industrial minerals

Underground 65 5 70 0

Open pit 535 965 1 500 5

Total 600 970 1 570 5

Sub total 5 600 11 400 17 000 55

Coal

Underground 2 950 575 3 500 12

Open pit 2 900 7 250 10 000 33Total 5 850 7 825 13 500 45

Overall total 11 450 19 225 30 700 100

Assumptions: 10% waste in underground metal and industrial mineral operations. Strip ratio (overburden/ore) in openpit metal operations is 2.5. The strip ratio in industrial minerals is 1.8. For coal, underground barren rock is set at 20%, and the stripratio in open-pit mines is 2.5. Industrial minerals includes limestone, kaolin, etc. but excludes crushed rock and other constructionmaterials. Salt, dimensional stones, precious stones are not included. Diamonds are included in metals.

2500

2000

1500

1000

1930 1945 1960 1975 1988 1991 1994 1997 2000

O r e g r a

d e

( % )

500

0

21.81.61.41.210.80.60.40.20

C o p p e r / o r e m e

t a l

p r o

d u c t

i o n

( m t )

Copper production Ore production Copper ore grade


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Mining TrendS


Bingham Canyon copper mine near Salt Lake City, Utah, USA.


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geOlOgy FOr Mining


to mine or tunnel through them, or both.Some of these important characteris-tics, which are also important for cor-rect mineral identification in the fieldbefore chemical analysis, are hardness,density, colour, streak, lustre, fracture,cleavage and crystalline form.

The particle size, and the extent towhich the mineral is hydrated or other-wise mixed with water, can be very im-portant to the behaviour of the rockstructure when excavated. Mineral hard-ness is commonly graded according tothe Moh 10-point scale

The density of light-coloured miner-als is usually below 3. Exceptions arebarite or heavy spar (barium sulphate

BaSO 4 density 4.5), scheelite (cal-cium tungstate CaWO 4 density 6.0)

and cerussite (lead carbonate PbCO 4 density 6.5). Dark coloured miner-als with some iron and silicate havedensities between 3 and 4. Metallic ore

minerals have densities over 4 Gold hasa very high density of 19.3. Mineralswith tungsten, osmium and iridium arenormally even denser.

Streak is the colour of the mineralpowder produced when a mineral isscratched or rubbed against unglazedwhite porcelain, and may be differentfrom the colour of the mineral mass.

Fracture is the surface characteristicproduced by breaking of a piece of the

mineral, but not following a crystal-lographically defined plane. Fractureis usually uneven in one direction oranother.

Cleavage denotes the properties of a crystal whereby it allows itself to besplit along flat surfaces parallel withcertain formed, or otherwise crystal-lographically defined, surfaces. Bothfracture and cleavage can be importantto the structure of rocks containing sub-stantial amounts of the minerals con-cerned.

P op t s

Rocks, normally comprising a mixtureof minerals, not only combine the prop-erties of these minerals, but also exhibit

properties resulting from the way inwhich the rocks have been formed, orperhaps subsequently altered by heat,pressure and other forces in the earths

crust. It is comparatively rare to findrocks forming a homogeneous mass,and they can exhibit hard-to-predictdiscontinuities such as faults, perhapsfilled with crushed material, and major

jointing and bedding unconformities.These discontinuities can be importantin mining, not only for the structuralsecurity of the mine and gaining access

to mineral deposits, but also as pathsfor fluids in the earths crust which

cause mineral concentrations. In orderfor mining to be economic, the requiredminerals have to be present in sufficient

concentration to be worth extracting,and within rock structures that can beexcavated safely and economically. Asregards mine development and produc-tion employing drilling, there must be acorrect appraisal of the rock concerned.This will affect forecast drill penetra-tion rate, hole quality, and drill steelcosts, as examples.

One must distinguish between micro-scopic and macroscopic properties, todetermine overall rock characteristics.As a rock is composed of grains of vari-ous minerals, the microscopic proper-ties include mineral composition, grainsize, the form and distribution of thegrain, and whether the grains are looseor cemented together. Collectively, thesefactors develop important properties of the rock, such as hardness, abrasiveness,compressive strength and density. Inturn, these rock properties determine thepenetration rate that can be achieved,and how heavy the tool wear will be.

In some circumstances, certain min-

eral characteristics will be particularlyimportant to the means of excavation.

Mohs hardness Typical mineral Identification of hardnessscale1 Talc Easily scratched with a fingernail

2 Gypsum Barely scratched with a fingernail

3 Calcite Very easily scratched with a knife

4 Fluorite Easily scratched with a knife

5 Apatite Can be scratched with a knife

6 Orthoclase Difficult to scratch with a knife, butcan be scratched with quartz

7 Quartz Scratches glass and can bescratched with a hardened steel file

8 Topaz Scratches glass and can bescratched with emery board/paper(carbide)

9 Corundum Scratches glass. Can be scratchedwith a diamond

10 Diamond Scratches glass and can only bemarked by itself

Amphibolite.

Samples of common rock types

Dolomitic limestone.


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geOlOgy FOr Mining


Many salts, for example, are particu-larly elastic, and can absorb the shocksof blasting without a second free facebeing cut, thereby directly influencingmining method.

The drillability of a rock depends on,among other things, the hardness of itsconstituent minerals, and on the grainsize and crystal form, if any.

Quartz is one of the commonest mi-nerals in rocks. Since quartz is a veryhard material, high quartz content inrock can make it very hard to drill, andwill certainly cause heavy wear, par-ticularly on drill bits. This is known asabrasion. Conversely, a rock with a highcontent of calcite can be comparativelyeasy to drill, and cause little wear ondrill bits. As regards crystal form, min-erals with high symmetry, such as cubicgalena, are easier to drill than mineralswith low symmetry, such as amphibolesand pyroxenes.

A coarse-grained structure is easierto drill, and causes less wear of the drillstring than a fine-grained structure. Con-sequently, rocks with essentially thesame mineral content may be very dif-

ferent in terms of drillability. Forexample, quartzite can be fine-grained

(0.5-1.0 mm) or dense (grain size 0.05mm). A granite may be coarse-grained(size >5 mm), medium-grained (1-5mm) or fine-grained (0.5-1.0 mm).

A rock can also be classified in termsof its structure. If the mineral grains aremixed in a homogeneous mass, the rockis termed massive, as with most granite.In mixed rocks, the grains tend to besegregated in layers, whether due tosedimentary formation or metamorphicaction from heat and/or pressure. Thus,the origin of a rock is also important,although rocks of different origin mayhave similar structural properties suchas layering. The three classes of rockorigin are:

Igneous or magmatic: formed fromsolidified lava at or near the surface, or

magma underground.Sedimentary: formed by the deposi-

tion of reduced material from otherrocks and organic remains, or by chemi-cal precipitation from salts, or similar.

Metamorphic: formed by the trans-formation of igneous or sedimentaryrocks, in most cases by an increase inpressure and heat.

i o s oc s

Igneous rocks are formed when mag-ma solidifies, whether plutonic rock,deep in the ear ths crust as it rises tothe surface in dykes cutting across otherrock or sills following bedding planes,or volcanic, as lava or ash on the sur-face. The most important mineral con-stituents are quartz and silicates of vari-ous types, but mainly feldspars. Plutonicrocks solidify slowly, and are thereforecoarse-grained, whilst volcanic rockssolidify comparatively quickly and

become fine-grained, sometimes evenforming glass.

Depending on where the magma soli-difies, the rock is given different names,even if its chemical composition is thesame, as shown in the table of mainigneous rock types. A further subdivi-sion of rock types depends on the silicacontent, with rocks of high silica con-tent being termed acidic, and those withlower amounts of silica termed basic.The proportion of silica content candetermine the behaviour of the magmaand lava, and hence the structures it canproduce.

S m t oc sSedimentary rocks are formed by the

deposition of material, by mechanicalor chemical action, and its consolidationunder the pressure of overburden. Thisgenerally increases the hardness of therock with age, depending on its mineralcomposition. Most commonly, sedimen-tary rocks are formed by mechanicalaction such as weathering or abrasionon a rock mass, its transportation by amedium such as flowing water or air,and subsequent deposition, usually instill water. Thus, the original rock will

partially determine the characteristicsof the sedimentary rock. Weathering orerosion may proceed at different rates,as will the transportation, affected bythe climate at the time and the natureof the original rock. These will alsoaffect the nature of the rock eventuallyformed, as will the conditions of deposi-tion. Special cases of sedimentary rockinclude those formed by chemical depo-sition, such as salts and limestones, andorganic material such as coral and shell

Table of main igneous rock types

Silica (SiO 2) Plutonic rocks Dykes and Sills Volcanic (mainlycontent lava)

Basic 65% Quartz diorite Quartz porphyrite DaciteSiO2

Granodiorite Granodiorite Rhyodaciteporphyry

Granite Quartz porphyry Rhyolite

Sandstone.

Gneiss.


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limestones and coals, while others willbe a combination, such as tar sands andoil shales.

Another set of special cases is gla-cial deposits, in which deposition isgenerally haphazard, depending on icemovements.

Several distinct layers can often beobserved in a sedimentary formation,although these may be uneven, accord-ing to the conditions of deposition. Thelayers can be tilted and folded by subse-quent ground movements. Sedimentaryrocks make up a very heterogeneousfamily, with widely varying character-

istics, as shown in the table of sedimen-tary rock types.

M t mo ph c oc sThe effects of chemical action, increasedpressure due to ground movement, and/or temperature of a rock formation cansometimes be sufficiently great to causea transformation in the internal struc-ture and/or mineral composition of the original rock. This is called meta-morphism. For example, pressure andtemperature may increase under theinfluence of up-welling magma, or be-cause the strata have sunk deeper intothe earths crust. This will result inthe recrystallization of the minerals,or the formation of new minerals. Acharacteristic of metamorphic rocks isthat they are formed without completeremelting, or else they would be termedigneous. The metamorphic action oftenmakes the rocks harder and denser, andmore difficult to drill. However, many

metamorphic zones, particularly formedin the contact zones adjacent to igneous

intrusions, are important sources of valuable minerals, such as those con-centrated by deposition from hydrother-mal solutions in veins.

As metamorphism is a secondary pro-cess, it may not be clear whether a sedi-mentary rock has, for example, becomemetamorphic, depending on the degreeof extra pressure and temperature towhich it has been subjected. The min-eral composition and structure wouldprobably give the best clue.

Due to the nature of their formation,metamorphic zones will probably beassociated with increased faulting and

structural disorder, making the plan-ning of mine development, and efficientdrilling, more difficult.

roc st ct s mm thoMacroscopic rock properties includeslatiness, fissuring, contact zones, lay-ering, veining and inclination. Thesefactors are often of great significance in

drilling. For example, cracks or inclinedand layered formations can cause holedeviation, particularly in long holes, andhave a tendency to cause drilling toolsto get stuck, although modern drillingcontrol methods can greatly reduce thisproblem. Soft or crumbly rocks make itdifficult to achieve good hole quality,since the walls can cave in. In extremecases, flushing air or fluid will disap-pear into cracks in the rock, withoutremoving cuttings from the hole. Insome rocks there may be substantialcavities, such as with solution passagesin limestones, or gas bubbles in igne-ous rock. These may necessitate priorgrouting to achieve reasonable drillingproperties.

On a larger scale, the rock structure

may determine the mining method, ba-sed on factors such as the shape of themineral deposit, and qualities such asfriability, blockiness, in-situ stress, andplasticity. The shape of the mineraldeposit will decide how it should bedeveloped, as shown in the chapters onmining flat and steep orebodies later inthis issue. The remaining rock qualitiescan all be major factors in determiningthe feasibility of exploiting a mineraldeposit, mainly because of their effect

on the degree of support required, forboth production level drives and fordevelopment tunnels.

M pos tp o t o

There will be a delicate economic ba-lance between an investment in devel-opment drives in stable ground, perhapswithout useful mineralization, and

Some sedimentary rock types

Rock Original materialConglomerate Gravel, stones and boulders, generally with

limestone or quartzitic cementGreywacke Clay and gravelSandstone SandClay Fine-grained argillaceous material and

precipitated aluminatesLimestone Precipitated calcium carbonate, corals,

shellfishCoals Vegetation in swamp conditionsRock salt, potash, gypsum, etc Chemicals in solution precipitated out by

heatLoess Wind-blown clay and sand

Typical metamorphic rocks

Rock type Original rock Degree of metamorphismAmphibolite Basalt, diabase, gabbro HighMica schist Mudstone, greywacke, etc Medium to highGneiss Various igneous rocks HighGreen-schist Basalt, diabase, gabbro LowQuartzite Sandstone Medium to highLeptite Dacite MediumSlate Shale LowVeined gneiss Silicic-acid-rich silicate rocks HighMarble Limestone Low


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drives within the mineral deposit, per-haps of shorter life, but requiring moresupport measures. Setting aside sup-port requirements, in general terms itwould seem beneficial to carry out asmuch of the development work as pos-sible within the mineral deposit, ma-king development drives in non-pro-ductive gangue rocks as short as pos-sible. However, it may be decided that amajor development asset, such as a shaftor transport level, should be in as stablea ground area that can be found, withfurther drives or levels made from it.

In extreme cases, it may be foundthat the mineral deposit cannot supportdevelopment workings without consid-erable expense. In these circumstances,it might be better to make development

drives near and below the mineral de-posit, and exploit it with little direct en-try, such as by longhole drilling andblasting, with the ore being drawn off from below.

Depending on the amount of distur-bance that the mineral-bearing stratahas been subjected to, the mineral de-posit can vary in shape from stratifiedrock at various inclinations, to highlycontorted and irregular vein formationsrequiring a very irregular development

pattern.The latter may require small drivesto exploit valuable minerals, althoughthe productivity of modern miningequipment makes larger section drivesmore economic, despite the excavationof more waste rock.

The tendency of a rock to fracture,sometimes unpredictably, is also im-portant to determine drivage factors,such as support requirements, and thecharging of peripheral holes to preventoverbreak. Although overbreak may notbe so important in mining as in civiltunnelling, it can still be a safety con-sideration to prevent the excavation of too much gangue material, and to pre-serve the structure of a drive.

i v st t o p o t o

It is clear that rock structures, and theminerals they contain, can result in awide variety of possible mining strate-

gies. Obviously, the more informationthat is gained, the better should be the

chances of mining success. There areplenty of potential risks in undergroundmining, and it is best to minimize these.

Using modern mining equipment,there is the potential to turn the mineinto a mineral factory. However, if un-certainties manifest themselves in un-foreseen ground conditions, disap-pearing orebodies, and factors such asexcessive water infiltration, then theadvantage of productive mining equip-ment will be lost, as it is forced to standidle.

The only way to avoid these situa-

tions is to carry out as much explorationwork as possible, not only to investigate

the existence and location of worthwhileminerals, but also to check on rock qua-lities in and around the deposit. In un-derground mining, information fromsurface borehole and geophysical me-thods of investigation can be supple-mented by probe or core drilling under-ground. The resulting vast amount of data may be too much to be assessedmanually, but computer software pro-grams are available to deduce the beststrategies for mineral deposit exploi-tation. In addition, the mining exper-tise of Atlas Copco is available to helpmining engineers decide, not only onthe best equipment to use for investi-gation, development and production, butalso how these can be used to maximumeffect.

The value of the mineral to be minedwill obviously be a determinant on howmuch investigation work is desirable,but there will be a minimum level foreach type of mine, in order to give someassurance of success.

For example, lowvalue stratified de-posits, which are known to be fairlyuniform in thickness and have regulardips, may not necessitate many bore-holes, although there could still besurprises from sedimentary washouts

or faults. On the other hand, gold de-posits in contorted rock formations willrequire frequent boreholes from under-ground, as well as from the surface, togive assurance of the location of thedeposit and to sample the minerals itcontains.

roc c ss f c t o fo

Having determined the value and shapeof a mineral deposit, the nature andstructure of the rocks that surround it,and the likely strategy for the mine deve-lopment, it should be possible to deter-mine the suitability of various excava-tion methods for the rocks likely to beencountered.

It will also be necessary to deter-mine which ancillary equipment maybe required, and how best to fit this intothe excavation cycle.

With dri ll-and-blast developmentdrivages, for example, the rock types

and structure may determine that sub-stantial support is required. This, in

Diabase.

Granite.


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geOlOgy FOr Mining


turn, may require a rockbolting facilityon the drill rig, perhaps with an accessbasket suitable for erecting arch crownsand charging blastholes. It may be de-cided that an additional rockbolting rigis required, for secondary support.

In order to systematically determinethe likely excavation and support re-quirements, the amount of consumablesrequired, and whether a particular me-thod is suitable, a number of rock clas-sification systems have been developed.These are generally oriented to a par-ticular purpose, such as the level of sup-port required or the rocks drillability.

The methods developed to assess dril-lability are aimed at predicting produc-tivity and tool wear. Factors of drillabil-ity include the likely tool penetration

rate commensurate with tool wear, thestand-up qualities of the hole, its straight-ness, and any tendency to tool jamming.Tool wear is often proportional to drill-ability, although the rocks abrasivenessis important.

Rock drillability is determined by se-veral factors, led by mineral composi-tion, grain size and brittleness. In crudeterms, rock compressive strength orhardness can be related to drillabilityfor rough calculations, but the matter is

usually more complicated.The Norwegian Technical Universityhas determined more sophisticatedmethods: the Drilling Rate Index (DRI)and the Bit Wear Index (BWI).

The DRI describes how fast a par-ticular drill steel can penetrate. It alsoincludes measurements of brittlenessand drilling with a small, standard ro-tating bit into a sample of the rock. Thehigher the DRI, the higher the penetra-tion rate, and this can vary greatly fromone rock type to another, as shown inthe bar chart.

It should be noted that modern drillbits greatly improve the possible pene-tration rates in the same rock types.Also, there are d ifferent types of bitsavailable to suit certain types of rock.For example, Secoroc special bits forsoft formations, bits with larger gaugebuttons for abrasive formations, andguide bits or retrac bits for formationswhere hole deviation is a problem.

The BWI gives an indication of

how fast the bit wears down, as deter-mined by an abrasion test. The higher

the BWI, the faster will be the wear.In most cases, the DWI and BWI areinversely proportional to one another.

However, the presence of hard min-erals may produce heavy wear on the bit,despite relatively good drillability. Thisis particularly the case with quartz,which has been shown to increase wearrates greatly. Certain sulphides inorebodies are also comparatively hard,impairing drillability.

Other means of commonly used rockclassification include the Q-system(Barton et al, through the NorwegianGeotechnical I nstitute), Rock Mass

Rating RMR (Bieniawski), and theGeological Strength Index GSI (Hoek

et al). Bieniawskis RMR incorporatesthe earlier Rock Quality Designation(RQD Deere et al), with some impor-tant improvements taking into accountadditional rock properties.

All give valuable guidance on therocks ease of excavation, and its self-supporting properties. In most cases,engineers will employ more than onemeans of rock classification to give abetter understanding of its behaviour,and to compare results.

Bj S m sso

Relationship between drilling rate index and various rock types.

Marble Limestone


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Mineral PrOSPeCTing and exPlOraTiOn

P osp ctProspecting involves searching a districtfor minerals with a view to further ope-ration. Exploration, while it sounds si-milar to prospecting, is the term usedfor systematic examination of a deposit.It is not easy to define the point whereprospecting turns into exploration.

A geologist prospecting a district islooking for surface exposure of miner-als, by observing irregularities in co-lour, shape or rock composition. He uses

a hammer, a magnifying glass and someother simple instruments to examinewhatever seems to be of interest. Hisexperience tells him where to look, tohave the greatest chances of success.Sometimes he will stumble across an-cient, shallow mine workings, whichmay be what led him to prospect thatparticular area in the first place.

Soil-covered ground is inaccessibleto the prospector, whose first checkwould be to look for an outcrop of the

mineralization. Where the ground covercomprises a shallow layer of alluviums,

trenches can be dug across the miner-alized area to expose the bedrock. Aprospector will identify the discovery,measure both width and length, andcalculate the mineralized area. Rocksamples from trenches are sent to thelaboratory for analysis. Even when mi-nerals show on surface, determining anyextension in depth is a matter of quali-fied guesswork. If the prospector'sfindings, and his theorizing about the

probable existence of an orebody aresolid, the next step would be to explore

the surrounding ground. Explorationis a term embracing geophysics, geo-chemistry, and also drilling into theground for obtaining samples from anydepth.

g oph s c xp o t oFrom surface, different geophysical me-thods are used to explore subsurface for-mations, based on the physical proper-

ties of rock and metal bearing mineralssuch as magnetism, gravity, electrical

Gold panning in the wind.

M p osp ct p o t o

F o bo sFor a geologist in the mining busi-ness, exploiting an orebody is theeasy part of the job. The hardestpart is to find the orebody and de-fine it. But how do you find theseaccumulations of metallic miner-als in the earth's crust? The miningcompany has to ensure that an ore-body is economically viable, andneeds a guarantee of ore produc-

tion over a very long period of time,before it will engage in the heavyinvestment required to set up amining operation. Even after pro-duction starts, it is necessary tolocate and delineate any exten-sions to the mineralization, andto look for new prospects thatmay replace the reserves beingmined. Investigating extensions,and searching for new orebodies,are vital activities for the miningcompany.


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conductivity, radioact ivity, and soundvelocity. Two or more geophysical meth-ods are often combined in one survey,to acquire more reliable data. Resultsfrom the surveys are compiled, andmatched with geological informationfrom surface and records from any coredrilling, to decide if it is worth proceed-ing with further exploration.

S v sMagnetic surveys measure variationsin the Earth's magnetic field caused bymagnetic properties of subsurface rockformations. In prospecting for metallicminerals, these techniques are parti-cularly useful for locating magnetite,pyrrhotite and ilmenite. Electromagneticsurveys are based on variations of elec-tric conductivity in the rock mass. Anelectric conductor is used to create aprimary alternating electromagneticfield. Induced currents produce a sec-ondary field in the rock mass. The res-

ultant field can be traced and measu-red, thus revealing the conductivity

of the underground masses. Electromag-netic surveys are mainly used to mapgeological structures, and to discovermineral deposits such as sulphidescontaining copper or lead, magnetite,pyrite, graphite, and certain manganeseminerals.

Electric surveys measure either thenatural flow of electricity in the gro-und, or "galvanic" currents led into theground and accurately controlled.Electrical surveys are used to locatemineral deposits at shallow depth andmap geological structures to determinethe depth of overburden to bedrock, orto locate the groundwater table.

Gravimetric surveys measure smallvariations in the gravitational field cau-sed by the pull of underlying rock mas-ses. The variation in gravity may becaused by faults, anticlines, and saltdomes that are often associated withoil-bearing formations.

Gravimetric surveys are also usedto detect high-density minerals, like

iron ore, pyrites and lead-zinc miner-alizations.

In regions where rock formations con-tain radioactive minerals, the intensityof radiation will be considerably higherthan the normal background level. Mea-suring radiation levels helps locate de-posits containing uranium, thorium andother minerals associated with radioac-tive substances.

The seismic survey is based on varia-tions of sound velocity experienced indifferent geological strata. The time ismeasured for sound to travel from asource on surface, through the underly-ing layers, and up again to one or moredetectors placed at some distance onsurface. The source of sound might bethe blow of a sledgehammer, a heavyfalling weight, a mechanical vibrator,or an explosive charge. Seismic surveys

determine the quality of bedrock, andcan locate the contact surface of geo-logical layers, or of a compact mineraldeposit deep in the ground. Seismic sur-veys are also used to locate oil-bearingstrata.

Geochemical surveying is another ex-ploration technology featuring several

Two computer generated views of Agnico Eagle's Suurikuusiko gold mining project showing both surface and underground mining.

Is there gold in the trench? International Gold Exploration AB, IGE conducts exploration works in Kenya.


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specialities, the main one being to de-tect the presence of metals in the top-soil cover. By taking a large number of samples over an extended area andanalyzing the minute contents of eachmetal, regions of interest are identi-fied. The area is then selected for moredetailed studies.

exp o to For a driller, all other exploration me-thods are like beating about the bush.Drilling penetrates deep into the ground,and brings up samples of whatever itfinds on its way. If there is any miner-alization at given points far beneath thesurface, drilling can give a straight-forward answer, and can quantify itspresence at that particular point.

There are two main methods of ex-ploratory drilling. The most common,core drilling, yields a solid cylindershaped sample of the ground at anexact depth. Percussion drilling yields

a crushed sample, comprising cuttingsfrom a fairly well-determined depth

in the hole. Beyond that, the drillholeitself can provide a complementaryamount of information, particularly bylogging using devices to detect physicalanomalies, similar to the geophysicalsurveys mentioned above.

Core drilling is also used to definethe size and the exact borders of minera-lization during the lifetime of the mine.This is important for determining oregrades being handled, and vital for cal-culating the mineral reserves that willkeep the mine running in the future. Astrategically-placed underground coredrill may also probe for new ore bodiesin the neighbourhood.

Co In 1863, the Swiss engineer M Lescotdesigned a tube with a diamond set face,for drilling in the Mount Cenis tunnel,where the rock was too hard for conven-tional tools. The intention was to explorerock quality ahead of the tunnel face,

and warn miners of possible rock falls.

This was the accidental birth of coredrilling, a technique now very widelyused within the mining industry. Coredrilling is carried out with special drillrigs, using a hollow drill string with animpregnated diamond cutting bit to re-sist wear while drilling hard rock. Thecrown-shaped diamond bit cuts acylindrical core of the rock, which iscaught and retained in a double tubecore-barrel.

A core-catcher is embedded in, or just above, the diamond bit, to makesure that the core does not fall out of thetube. In order to retrieve the core, thecore-barrel is taken to surface, either bypulling up the complete drill string or,if the appropriate equipment is beingused, by pulling up only the inner tubeof the core-barrel with a special fishingdevice run inside the drill string at theend of a thin steel wire.

The core is an intact sample of the un-derground geology, which can be exam-ined thoroughly by the geologist to

determine the exact nature of the rockand any mineralization. Samples of

Atlas Copco underground core drilling rig Diamec U4.


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special interest are sent to a laboratoryfor analysis to reveal any metal con-tents. Cores from exploration drillingare stored in special boxes and kept inarchives for a long period of time. Boxesare marked to identify from which hole,and at what depth, the sample was ta-ken. The information gathered by coredrilling is important, and represents sub-

stantial capital investment.Traditionally, core drilling was a veryarduous job, and developing new techni-ques and more operator-friendly equip-ment was very slow, and the cost perdrilled metre was often prohibitive. AtlasCopco Geotechnical Drilling and Explo-ration pioneered several techniques toreduce manual work, increase efficiencyand cut the cost per dr illed metre.

Over the years, the company developedthin walled core barrels, diamond impreg-nated bits, aluminium drill rods, fastrotating hydraulic rigs, mechanical rodhandling, and, more recently, partly ortotally computer-controlled rigs. Coredrilling has always been the most power-ful tool in mineral exploration. Now thatit has become much cheaper, faster andeasier, it is being used more widely.

r v s c c t o

To obtain information from large ore-

bodies where minerals are not concen-trated in narrow veins, reverse circulation

drilling is used. Reverse circulation dril-ling is a fast, but inaccurate, explora-tion method, which uses near-standardpercussion drill ing equipment. Theflushing media is introduced at thehole collar in the annular space of adouble-tubed drill string, and pusheddown to the bottom of the hole to flushthe cuttings up through the inner tube.

The drill cuttings discharged on sur-face are sampled to identify variationsin the mineralization of the rock mass.Reverse circulation drilling uses muchheavier equipment than core drilling,and has thus a limited scope in depth.

F om p osp ct tomEvery orebody has its own story, butthere is often a sequence of findings.After a certain area catches the interestof the geologists, because of ancientmine works, mineral outcrops or geo-logical similarities, a decision is takento prospect the area. If prospecting con-firms the initial interest, some geophy-sical work might be carried out. If inter-est still persists, the next step would beto core drill a few holes to find out if there is any mineralization.

To quantify the mineralization, andto define the shape and size of the orebody, then entails large investment to

drill exploratory holes in the requiredpatterns.

At every step of the procedure, thegeologists examine the information athand, to recommend continuing the ex-ploration effort. The objective is to befairly certain that the orebody is eco-nomically viable by providing a detailedknowledge of the geology for a clearfinancial picture. Ore is an economicconcept, defined as a concentration of minerals, which can be economicallyexploited and turned into a saleableproduct.

Before a mineral prospect can belabelled as an orebody, full knowledgeis required about the mineralization,proposed mining technology and pro-cessing. At this stage a comprehensivefeasibility studied is undertaken cover-ing capital requirements, returns on

investment, payback period and otheressentials, in order for the board of di-rectors of the company to make t hefinal decision on developing the pros-pect into a mine.

When probabilities come close tocertainties, a decision might be taken toproceed with underground exploration.This is an expensive and time-consum-ing operation, involving sinking a shaftor an incline, and pilot mining drifts andgalleries. Further drilling from under-

ground positions and other studies willfurther establish the viability of theorebody.

After the mineralization has beendefined in terms of quantity and quality,the design of mine infrastructure starts.The pictures on page 14 show recentplans at the Suurikuusikko gold mineproject in Finland where the optimummining methods combine both open pitand un-derground mining. Productioncan start in the open pit while preparingfor the underground operation.

With an increasing level of geologi-cal information the mineral resourcesget better confirmed. The feasibilitystudy will take into consideration alleconomical aspects, as well as the ef-fects of the selected mining method.Depending on the mining method, therecould be essential differences betweenmineral resources and ore reserves, bothin terms of quantity and grade.

H s F b

Exploration Results

Mineral Resources Ore Reserves

Increasing levelof geologicalknowledge andconfidence

Indicated

Inferred

Measured Proved

Probable

Consideration of mining, metallurgical, economic, marketing,legal, environmental, social and governmental factors

(the modifying factors)

The 2004 Australasian code for reporting exploration results, mineral resources and ore reserves.


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rigHT BalanCe


Co v t o co The technique which produces cores of subsurface material, core drilling, is themost commonly used method of obtain-ing information about the presence of minerals or precious metals, as well asrock formations. However, reverse cir-culation drilling (RC), which producessamples as chips, is gaining ground.

The reason is easy to see. RC drillingis a faster and more economical way of

pre-collaring a deep hole in order to getdown to where the orebody is located.Once there, the driller can then decideto continue with RC drilling to extractchips for evaluation, or switch to dia-mond core drilling to extract cores. Inthis way, RC drilling becomes the per-fect complement to conventional coredrilling. Selecting which method touse for actual sampling work dependslargely on the preference of the geo-logists, and their confidence in the

quality of the samples. Today, RC dr il-ling has become so advanced that more

F th ht b c p o t o

Ch ps o co s?The question often faced by geolo-gists and contractors is decidingwhich method of exploration dril-ling will get the most effective andeconomical results. These days, theanswer is quite likely to be a com-bination of chip sampling and co-ring. Three key factors have proveddecisive in the successful searchfor minerals and precious metals:

time, cost and confidence. In otherwords, the time required, the costof getting the job done, and con-fidence in the quality of the sam-ples brought to the surface foranalysis. This is more a questionof basic technology and logic thanone of science. But it is interest-ing to see these three factors ex-pressed as a mathematical for-mula: confidence over time multi-plied by cost, equals profit. Withprofit, as always, as the drivingforce.

There are pros and cons with both RC drilling and core drilling.

Substantial savings can be made by pre-collaring holes using RC drilling, once the general location of the mineralized zone has been established.

P -co

Fast andeconomicalRC drillingwithout takingsamples

Mineralized zone: Chipsamples from RC and/orcores for evaluation


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rigHT BalanCe


and more geologists believe that chipsare perfectly sufficient as a means of determining ore content. The commer-cialization of RC drilling started in the1980s but the technique has certainly

been around for much longer.

As early as 1887, Atlas Copco Craelius

had developed a rig that could retrievecores from depths of 125 m. Confidencein these samples among geologists washigh, allowing them to evaluate a pieceof solid rock. In those days, time wasnot necessarily of any great importanceand neither was cost, with inexpensivemanpower readily available.

However, the demand for such pro-ducts quickly increased, and availabilityhad to keep pace. This is very much thecase today with sharp market fluctu-

ations, and so technology innovatorshave to find ways to optimize profit inall situations.

T m f ctoDTH hammers were invented in 1936and became popular dur ing the 1970s,mainly for water well drilling applica-tions. However, the method provedvery useful for prospecting, affordingan initial evaluation on the spot of thecuttings emanating from the borehole.

DTH drill ing offers a considerablyhigher drilling speed compared to coredrilling, and the method was further developed to increase its performance.Higher air pressures combined with highavailability of the hammer are two fac-tors that make it possible to drill faster.Durability of the bit inserts is also muchimproved, allowing more metres to bedrilled without having to pull up thedrillstring, further improving efficiencyand utilization of the hammer.

The logistics surrounding the dr il-ling programme concerning availability

of parts, fuel, casing, water, and con-sumables also have a direct inf luenceon the number of metres drilled per shift.

Significant time savings can be achie-ved by using RC and core drilling ina balanced combination (see table 1).Here we can see that one RC rig can beused to drill enough pre-collars to keepthree core drilling rigs running for 24h/day. The time factors show obvious

benefits using a combination of the twomethods. In this scenario, a minimumof 25% of the total metres drilled werespecified as core drilling.

Cost f ctoThe cost perspe ctive does not have

any negative surprises in store as thecosts are mostly related to the time fac-tor. The investment in RC rigs and equip-ment is higher compared to those of core drilling, but as shown in table 2,the costs are reduced when a combina-tion of the two methods is used.

In this example, it is shown that bothtime and costs favour RC drilling. Thefigures are easy to evaluate. They varydepending on the location and the localconditions, but the relativity remainsthe same, and is strongly reflected inthe development of the explorationdrilling process.

To further shorten time and cost, im-mediate results from on-site evaluationcan be used, for which a scanning pro-cess is already available.

However, in the future it may not benecessary to drill to obtain sufficientinformation about the orebodies, andmanufacturers such as Atlas CopcoCraelius are already taking up the chal-lenge to develop equipment and tech-nologies with no limits and low envi-ronmental impact.

Co f c f ctoThe third variable in the equation isthe confidence factor, because investorsand geologists place strict demands oncontractors to deliver the highest qual-ity geological information. Investorsalways require a fast return on their in-vestments, and the geologists need solid

results for the mine planners. However,whenever a gold nugget is found, the

Sc o 1girgnillirderoc1h tiwsruoh42 /erocm07gnillirderoc%001

457 days

Sc o 250% RC (pre-collars only), 50% core drill ing 70m core / 24 hours with 1 core drill ing rig301 days

Sc o 375% RC (pre-collars & full holes), 25% core drilling 70m core / 24 hours with 1 core drilling rig223 days

In case three core drilling rigs would have been available in scenario 1, expected time is152 days compared with 457 days.In case three core drilling rigs would have been available in scenario 2, expected time is149 days compared with 301 days.A rough conclusion gives that the RC rig is somewhat faster than 3 core drilling rigs together.

457 days 2,580,000 USD301 day223 day

Principles for RC drilling showing flow of compressed air and chips. The sampling collection box is integrated into the cyclone.

Table 1.

Table 2.

740,000 USD320,000 USD

Approx. cost of RC drilling 30 USD / metreApprox. cost of core drilling 80 USD / metre


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rigHT BalanCe


exploration drilling will not be carriedout by the same people, so reliability of

information is critical. There are manyreasons why geologists should choosetheir drilling method carefully.

If there is no need for continuous in-formation about the geological forma-tion on the way down, there is no needfor samples. It is just a matter of mini-mizing the drilling time. The geometryof the orebody is already known, and

just a reconfirmation of the boundariesis necessary. In this case, RC drilling isan efficient method to use.

A first scanning of virgin territoryis being done where the goal is just toobtain a preliminary indication of pos-sible content. In this case, the geologistis not relying on any mineralized struc-ture or geometry. With an evaluationgiving positive results, a programme of core drilling is the logical way to con-tinue in order to bring the project to aresource/reserve status.If the minera-lized structure is identified but thegeometry and rate of content varies,RC drilling is used as an indicator for ensuring continued grade control.

The geologist wants dry and repre-sentative samples in order to make opti-mal evaluations. RC drilling below thegroundwater table was previously be-lieved to undermine sample quality.Core drilling therefore remained theonly viable method for these depthsToday, the availability of high pressurecompressors and hammer tools makesit possible for RC drilling to reducecosts even for these depths.

These days, professional contractorsdeliver dry sampling down to depths

of 500 m. By sealing off the bit fromthe rest of the hole it can be kept dry.

A correct selection of shroud vs bit tol-erance maintains a pressurized zonearound the bit. Boosted ai r pressure isneeded to meet the higher water pres-sure on its way down the hole. In addi-tion, a dry bit drills faster.

It must be remembered that infor-mation from a core is crucial in esti-mating the per iod of mineralized struc-tures. The core helps the geologist tocalculate the cost of extracting themineral from the ore. Large volumes of

rock have to be excavated to obtain justa few grammes of a valuable mineral.Cores also yield geotechnical data.

Data about slope stability can be of thehighest importance. Ground conditionsare naturally also of great importanceand may produce questionable sam-

ples if some of the information fromfissured zones is left behind in thehole and not collected. In such circum-stances, core drilling could be the onlyalternative.

i c s s ofrC RC drilling is on the increase, and maywell account for 55% of all metresdrilled in 2008. The diagram aboveshows some estimated ratios betweencore and RC drilling in different partsof the world in 2002. In terms of metresdrilled, RC accounts for 50% and coredrilling for 50%. Tradition and environ-mental impact play large roles. RC rigs

are heavy, and are mounted on trucksor track carriers. This fact tends to

favour core drilling rigs, which are muchlighter and more adaptable in order

to be flown into remote and sensitiveenvironments.

In areas with extremely cold climatesand where permafrost is present, RCdrilling may have its limitations. Anti-freeze rock drill oil can help to keepthe hammer and bottom of the hole freefrom ice. Other purely practical issuesdetermine the choice of one or the other drilling method.

An intelligent, balanced choice be-tween the two methods is the key to

optimal results. The geologist plays anextremely important role in finding this balance, as do the manufacturers suchas Atlas Copco Geotechnical Drillingand Exploration, who continue to pro-vide the right tools for the job.

J J sso

Ratios between core and RC drilling. The figures reflect total exploration expenditures from national statistics for surface and underground.

0

20

40

60

80

100

C n d l tinam ic

r ssiChin

a st i Se asi uSa af ic

rC d i ingCo d i ing

%

Explorac 220RC.


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Superior Productivityin Exploration Drilling


www.atlascopco.com

In these busy times for exploration drillers, the focus is onsuperior productivity at lower cost.

Through innovative products, local presence and technicalsupport, Atlas Copco delivers the most competitive solutionsfor diamond core drilling and reverse circulation.

On surface or underground, from Arctic regions to sunburntdeserts - you can count on the most comprehensive range ofexploration drilling equipment wherever you are.


23/144

Mine inFraSTruCTure


u o f st ctMining methods used underground areadapted to the rock conditions, and theshape, dimensions, strength and stabil-ity of the orebody. In order to work theunderground rock mass, infrastructureis required for access to work places, oreproduction, power supply, transport of ore, ventilation, drainage and pumpingas well as maintenance of equipment.

Traditionally, the most common me-thod to transport men, material, ore andwaste is via vertical shafts. The shaftforms the access to the various main un-derground levels, and is the mines main

artery for anything going up or down.Shaft stations, drifts and ramps connect

stopes with orepasses, tramming levels,and workshops for movement of minersand equipment.

Efficient ore handling is important.The blasted ore is loaded from produc-tion stopes, via orepasses to a main hau-lage level, commonly railbound, andthence to the crusher at the hoistingshaft.

The crushed ore is then stored in asilo before transfer by conveyor to themeasuring pocket at the skip station,from where it is hoisted to the surfacestockpile. To decide on the shaft bottomand main haulage level elevations arecrucial, as these are permanent instal-lations offering little or no flexibility in

the event that mining progresses belowthese levels. Consequently extensive

exploration drilling has to be conductedto identify sufficient ore reserves abovethe main haulage level before final de-sign of the permanent installations canprogress.

There is currently a strong tendency toavoid shaft sinking by extending rampsfrom the surface successively deeper, todepths exceeding 1,000 m. There are anumber of locations where the deeperore is hauled by trucks up ramps to anexisting railbound haulage system tothe main crusher, from where it can behoisted to the surface.

S v c s

Electric power is distributed throughoutthe mine, and is used to illuminate work

Ramp access for transport and haulage.

u o m f st ct

M mcovThe underground mine aims formaximum economic recovery ofminerals contained in the bed-rock. The orebody is the recove-red volume containing valuableminerals, taking ore losses anddilution into account. The amountof ore losses in pillars and rem-nants, and the effects of wastedilution, will largely depend onthe mining method to be applied.Waste dilutes the ore, so minerstry to leave it in place, whereverpossible, especially when expen-sive mineral dressing methodsare applied. Flotation of sulphideore is more expensive than mag-netic separation of iron ore. Oreclose to the surface is mined byopen pit techniques, in which thewaste rock can be separated byselective blasting and loading,and trucked to the waste dumpinstead of entering and diluting

the ore flow into the concentra-tor. Subsurface orebodies are ex-ploited by underground mining,for which techniques are morecomplex. A combination of openpit mining and preparation forfuture underground mining iscommonly used.


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Mine inFraSTruCTure


places and to power drill rigs, pumpsand other machines. A compressor plantsupplies air to pneumatic rock drills andother tools, through a network of pipes.

Water reticulation is necessary in themine, wherever drilling, blasting andmucking takes place, for dust suppres-sion and hole flushing. Both groundwater and flushing water are collectedin drains, which gravitate to settlingdams and a pump station equipped withhigh-lift pumps to surface.

Air quality in mine workings must

be maintained at an acceptable healthstandard. The mine needs a ventilation

system, to remove smoke from blastingand exhaust gases from diesel-poweredmachines, and to provide fresh air forthe workers. This is normally providedvia downcast fresh-air shafts. High-pressure fans on surface extract exhaustair through the upcast shafts. Ventilationdoors control the underground airflow,passing fresh air th rough active workareas. Polluted air is collected in a sy-stem of exhaust airways for channellingback to the upcast shafts. As most of theinfrastructure is located on the footwall

side of the orebody, the fresh air isnormally channelled via the footwall

towards the hangingwall, from wherethe exhaust air is routed to the surface.

T spo t f st ctEach mining method requires a differ-ent underground infrastructure, suchas access drifts to sublevels, drifts forlonghole drilling, loading drawpoints,and orepasses. Together, they form anintricate network of openings, drifts,ramps, shafts and raises, each with itsdesignated function.

The shaft is a long-lived installation,and may be more than 50 years old. Thehoist and cage provide access to the shaftstation, which connects with a main levelalong which trains or conveyors mayrun. The skip is the most efficient way to

hoist ore from underground to surface.Materials handling may be by utility

vehicles or locomotive-hauled trains.The co-ordination of train haulage withshaft hoisting, from level to level, makesthe logistics of rail transport complex.Workers in a rail-track mine are requi-red to wait for cage riding until shi ftchanges, or scheduled hours, with ma-terial transport only permitted at certainperiods. Ore hoisting takes priority overmanriding and material transport.

The Load Haul Dump (LHD) loaderintroduced mines to diesel power andrubber-tyred equipment in the 1970s.This was the birth of trackless mining,a new era in which labour was replacedby mobile equipment throughout themine. Maintenance workshops are nowlocated underground at convenientpoints, usually on main levels betweenramp positions.

The shaft remains the mines mainartery, and downward development is byramps to allow access for the machines.On newer mines, as mentioned above, adecline ramp from surface may facili-tate machine movements and transportof men and materials, and may alsobe used for ore transportation by truckor conveyor, eliminating the need forhoisting shafts.

r mps sh ftsMine development involves rock excava-tion of vertical shafts, horizontal drifts,

inclined ramps, steep raises, crusher sta-tions, explosives magazines, fuel stores,

Settlingpond

HeadframeProductionplant

Tailings

Skip

SkipWater basin

Pump station

Conveyor belt

Orebin

Skip fillingstation

SumpMeasuringpocket

Ventilationshaft

Decline

Open pit(mined out)

Producingstopes

Developmentof stopes

Mined outandbackfilled

Abandoned

level

Sublevel

Internalramp

Haulage level

Future reserves?

Exploration

Drilling

Main level

Orepass

Ore

Cage

Crusher

Atlas Cop co Ro ck Drills AB, 2000

Workshop,fuelling,storage

Basic infrastructure required for a typical underground mine.


25/144

Mine inFraSTruCTure


pumphouses and workshops. Drill/blastis the standard excavation method fordrifting. Firing sequence for a typicalparallel hole pattern is shown to theright. Note that the contour holes arefired simultaneously with light explo-sives, and that the bottom holes, or lift-ers, are fired last to shake up the muckpile for faster mucking.

A deep shaft may secure many years of production, until ore reserves above theskip station are exhausted. The shaft canbe rectangular, circular or elliptical inprofile. Extending the shaft in an ope-rating mine is costly and difficult, re-quiring both expert labour and special-ized equipment.

Drifts and ramps are dimensioned toaccommodate machines passing through,

or operating inside. Space must includea reasonable margin for clearance, walk-ways, ventilation ducts, and other facili-ties. Cross-sections vary from 2.2 m x2.5 m in mines with a low degree of mechanization to 5.5 m x 6.0 m whereheavy equipment is used. Only 5.0 sq msection is sufficient to operate a rail-bound rocker shovel, whereas 25.0 sq mmay be needed for a loaded mine truck,including ventilation duct.

Normal ramp grades vary between

1:10 and 1:7, with the steepest grade to1:5. The common curve radius is 15.0m. A typical ramp runs in loops, withgrade 1:7 on straight sections, reducedto 1:10 on curves.

r s wRaises are steeply inclined openings,connecting the mines sub levels at dif-ferent vertical elevations, used for lad-derways, orepasses, or ventilation. In-clination varies from 55 degrees, whichis the lowest angle for gravity transportof blasted rock, to vertical, with cross-sections from 0.5 to 30 sq m. When theexcavation of raises is progressing down-wards they are called winzes.

Manual excavation of raises is atough and dangerous job, where theminer climbs the raise by extending theladderway, installs the temporary plat-form, and drills and charges the roundabove his head. As such, manual raisesare limited to 50 m-high. However, the

efficiency can be greatly improved byusing a raise climber up to 300 m.

The drop raise technique is used forslot raises and short orepasses, usinglonghole dril ling and retreat blastingfrom bottom to top, see figure below.Inverted drop raising is performed theother way around.

r s boThe raise boring machine (RBM) may beused for boring ventilation raises, ore-passes, rock fill passes, and slot raises.

It provides safer and more efficient me-chanized excavation of circular raises,up to 6 m-diameter.

In conventional raise boring, a down-ward pilot hole is drilled to the targetlevel, where the bit is removed and re-placed by a reaming head. The RBMthen reams back the hole to final dia-meter, rotating and pulling the reaming

head upward. The cuttings fall to thelower level, and are removed by anyconvenient method. An RBM can also

1

1

2 2

3

3

3

44

44

3

Firing sequence of a typical hole pattern (*contour holes).

Long hole drilling alternative to raise boring.


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Mine inFraSTruCTure


be used to excavate raises where thereis limited, or no, access to the upper le-vel. In this boxhole boring method, themachine is set up on the lower level, anda full diameter raise is bored upward.This method is used for slot hole drill-ing in sub level caving and block caving

methods. The cuttings are carried bygravity down the raise, and are deflected

from the machine by the use of a muckcollector and a muck chute.

An alternative method to excavatebox holes is to use longhole drilling withextremely accurate holes to enable bla-sting in one shot. The Simba MC 6-ITHshown below is modif ied for slot dri l-

ling so that the holes will closely fol-low each other, providing sufficient open

space for consecutive blasting. The dril-ling and blasting results are shown below.Hole opening, or downreaming, usinga small-diameter reamer to enlarge anexisting pilot hole, can also be carriedout by an RBM.

The capital cost of an RBM is high,but, if used methodically and consis-tently, the return on investment is veryworthwhile. Not only will raises beconstructed safer and faster, they willbe longer, smoother, less disruptive thanblasting, and yield less overbreak. Therock chips produced by an RBM are con-sistent in size and easy to load.

The BorPak is a small, track-mountedmachine for upward boring of inclinedraises. It starts boring upwards througha launching tube. Once into rock, grip-

pers hold the body, while the head ro-tates and bores the rock fullface. BorPakcan bore blind raises with diameters from1.2 m to 1.5 m, up to 300 m-long.

g no

Atlas Copco Robbins 53RH-EX raise boring machine.

Simba MC 6-ITH with slot hammer.

Sufficient expansion space is created for production blast holes to follow.

Holes at breakthrough after 32 m.


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raiSe BOring


r s bo co c pt

The raise boring machine (RBM) is setup at the surface or upper level of thetwo levels to be connected, and a small-diameter pilot hole is drilled down tothe lower level using a string of dr illpipes and a tricone bit. A reamer is thenattached to the drill string at the lowerlevel, and the RBM provides the rota-tional torque and pulling power to reamback to the upper level. The cuttingsfrom the reamer fall to the lower levelfor removal. Raise bore holes of over 6m-diameter have been bored in mediumto soft rock, and single passes in hardrock can be up to 1 km in length.

Advantages of raise boring are thatminers are not required to enter the ex-cavation while it is underway, no explo-sives are used, a smooth profile is ob-tained, and manpower requirements arereduced. Above all, an operation thatpreviously was classified as very dan-gerous can now be routinely undertakenas a safe and controlled activity.

Specific applications of bored raises

in mining are: transfer of material;ventilation; personnel access; and ore

Robbins 73RH C derrick assembly layout.

P c p s of s bo

eff c c s f tRaise boring is the process of me-chanically boring, drilling or ream-ing a vertical or inclined shaft orraise between two or more levels.Some 40 years ago, the worlds firstmodern raise boring machine wasintroduced by the Robbins Com-pany. It launched a revolution inunderground mining and construc-tion, and the technique is now ac-cepted as the world standard formechanical raise excavation. Newproducts from Atlas Copco, suchas the BorPak, concepts such asautomatic operation and comput-erization, and techniques such ashorizontal reaming, are creatingexciting new opportunities in theunderground environment. AtlasCopco Robbins supplies the com-plete raise boring package for allsituations, together with technicaland spares backup.

Raise boring process.


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raiSe BOring


production. Standard RBMs are capableof boring at angles between 45 degreesand 90 degrees from horizontal, and withminor adjustment can actually bore atangles between 45 degrees and hori-zontal.

A whole host of methods of mechani-cal raise and shaft excavation have beendeveloped around the use of the RBM.These include boxhole boring, blindshaft boring, rotary drilling, down rea-ming, pilot up/ream down, pilot down/ream down, hole opening, and BorPak.

a t t v bom tho sBoxhole boring is used to excavate raises

where there is limited access, or no accessat all, to the upper level. The machine is

set up at the lower level, and a full dia-meter raise is bored upward. Stabilizersare periodically added to the drill stringto reduce oscillation and bending stress-es. Cuttings gravitate down the hole andare deflected away from the RBM at thelower level.

Blind shaft boring is used where accessto the lower level is limited, or impos-sible. A down reaming system is used,in which weights are attached to thereamer mandrel. Stabilizers are locatedabove and below the weight stack toensure verticality of the hole. Cuttingsare removed using a vacuum or reversecirculation system.

Rotary drilling is used for holes upto 250 mm-diameter, and is similar inconcept to pilot hole drilling in that a bitis attached to the drill string to excavatethe required hole size.

Down reaming involves drilling aconventional pilot hole and enlarging itto the final raise diameter by reamingfrom the upper level. Larger diameterraises are achieved by reaming the pilothole conventionally, and then enlargingit by down reaming. The down reameris fitted with a non-rotating gripper andthrust system, and a torque-multiply-ing gearbox driven by the drill string.Upper and lower stabilizers are installedto ensure correct kerf cutting and to re-duce oscillation.

Pilot up/ream down was a predeces-sor of modern raise boring techniquesusing standard drilling rigs. Pilot down/

ream down, or hole opening, employsa small diameter reamer to follow the

pilot hole. Stabilizers in the drill stringprevent bending.

The BorPak is a relatively new ma-chine for blind hole boring which climbsup the raise as it bores. It comprises aguided boring machine, power unit,launch tube and transporter assembly,conveyor and operator console. Cuttingspass through the centre of the machine,down the raise and launch tube, and ontothe conveyor. The BorPak has the poten-tial to bore holes from 1.2 m to 2.0 m-diameter at angles as low as 30 degreesfrom horizontal. It eliminates the needfor a drill string and provides the steer-ing flexibility of a raise climber.

r s bo m chThe raise boring machine (RBM) pro-vides the thrust and rotational forces ne-cessary for boring, as well as the equip-ment and instruments needed to controland monitor the process. It is composedof five major assemblies: the derrick;the hydraulic, lubrication, and electricalsystems; and the control console.

The derrick assembly supplies the ro-tational and thrust forces necessary toturn the pilot bit and reamer, as well asto raise and lower the drill string. Base-plates, mainframe, columns and head-frame provide the mounting structurefor the boring assembly. Hydraulic cy-linders provide the thrust required forlowering and lifting the drillstring, andfor drilling and reaming. The drive train

assembly, comprising crosshead, maindrive motor, and gearbox, supplies the

Typical raise boring underground site showing overhead clearance.

Boxhole boring.

Clearance for derrickerection from thetransporter system

Overheadclearancefor completederrickextension


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raiSe BOring


rotational power to the drill string andcutting components.

Four types of main drive motorsystems are available:AC, DC, hydraulic and VF. The gearboxmounts directly to the main drive motors,

employing a planetary reduction for itscompactness. The hydraulic power unitis skid-mounted, and comprises the ne-cessary reservoir, motors, pumps, valves,filters and manifolds.

The lubrication system ensuresproper delivery of lubricating oil to the

high-speed bearings and other selectedcomponents of the drive train assemblygearbox, and comprises pump, motor,filter, heat exchanger, flow meter, andreservoir with level gauge, thermometerand breather.

The electrical system assembly con-sists of an enclosed cabinet containingthe power and control distribution hard-ware and circuitry for the entire raiseboring operation.

The control console provides for bothelectrical and hydraulic functions, offe-ring meter readouts for main operatingparameters.

Computerization of the raise boringfunctions is also offered, using AtlasCopcos well-tried PC base d RCSsystem.

ac ow m tsThis article has been prepared usingThe Raise Boring Handbook, Second

Edition, researched and compiled byScott Antonich, as its main reference.

Typical operating installation of the BorPak machine.

Robbins 73RM-VF set up in a workshop.


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Robbins Raise Drills... keep on raising


Atlas Copco Rock Drills ABFax: +46 19 670 7393

www.raiseboring.com

Ever since the frst Robbins raise drill was built in 1962, ithas been a constant success. By meeting customer needsthrough innovation, reliability and an unrivalled productrange, we have gained the lions share of the global market

and we intend to keep it that way!

Robbins Raise Drill Systems produce shafts and raises from0.6 m to 6.0 m in diameter, and up to 1000 m in length.


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MeCHanized BOlTing


Sp c fo s f tThere was a time when undergroundmining and safety were terms not com-monly referred to in the same sentence.However, times have changed, and todaysafety is given a place of prominence inthe operational priorities of the miningindustry.

Freshly blasted openings leave con-siderable areas of loose rock, which mustbe removed to prevent fall-of-groundinjuries. Improvements in dril ling andblasting techniques have helped to signi-ficantly reduce the amount of this looserock. Scaling, which is the most hazard-ous part of the work cycle, is used toremove loose rock.

Subsequent blasting might result inadditional rock falls, especially in frac-tured ground conditions. Screening orshotcreting, as a means of retention of this loose rock, is often used in com-bination with rockbolting. Screening,which is a time-consuming operation,is common practice in Canada and

Australia. Since the 1960s and 1970s,considerable effort has been spent on

mechanizing underground operationalactivities, including the rock excavationcycle. Within the drill-blast-muckingcycle repeated for each round, the drill-ing phase has become fully mechanized,with the advent of high productivity hy-draulic drill jumbos.

Similarly, blasting has become an ef-ficient process, thanks to the develop-ment of bulk charging trucks and easilyconfigured detonation systems. Afteronly a short delay to provide for ade-quate removal of dust and smoke by highcapacity ventilation systems, the mo-dern LHD rapidly cleans out the muckpile.

These phases of the work cycle havebeen successfully mechanized, and mo-dern equipment provides a safe operatorenvironment.

By contrast, the most hazardous ope-rations, such as scaling, bolting andscreening, have only enjoyed lim itedprogress in terms of productivity im-provements and degree of mechaniza-tion. The development of mechanizedscaling and bolting rigs has been slower,mainly due to variations in safety rulesand works procedure in specific rockconditions.

To summarize, equipment manufac-

turers have had difficulty in providingglobally accepted solutions. Nevertheless,

there is equipment available from AtlasCopco to meet most of the current de-mands of miners and tunnellers.

M ch t o st sVarious methods of mechanized boltingare available, and these can be listedunder the following three headings.

Manual drilling and boltingThis method employs light hand heldrock drills, scaling bars and bolt instal-lation equipment, and was in wide-spread use until the advent of hydraulicdrilling in the 1970s. Manual methodsare still used in small drifts and tun-nels, where drilling is performed withhandheld pneumatic rock drills. Thebolt holes are drilled with the sameequipment, or with stopers. Bolts, withor without grouting, are installed manu-ally with impact wrenches. To facilitateaccess to high roofs, service trucks orcars with elevated platforms are com-monly used.

Semi-mechanized drilling andboltingThe drilling is mechanized, using a hy-draulic drill jumbo, followed by manual

installation of the bolts by operators wor-king from a platform mounted on the

M ch bo t sc

ut t o s thIn tunnelling operations, it is quitecommon to use the same equip-ment for all drilling requirements.These days, a single drill rig canaccommodate drilling for faceblasting, bolt holes, protectionumbrellas, and drainage. As thereare normally only one or two facesavailable for work before blast-ing and mucking, it is difficult toobtain high utilization for special-ized equipment such as mecha-nized bolting rigs. By contrast, inunderground mining, especiallywhere a number of working areasare accessible using methods suchas room and pillar, high utilizationof specialized equipment can beexpected. This is where mecha-nized bolting and screening is rap-idly taking root, for speed, safetyand consistency.

Mechanized scaling with hydraulic hammer.


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MeCHanized BOlTing


drill rig, or on a separate vehicle. Theman-basket, as a working platform,limits both the practical working spaceand the retreat capability in the event of falling rock. In larger tunnels, the boltholes are drilled with the face drilling

jumbo.

Fully mechanized work cycleA special truck, equipped with boommounted hydraulic breakers, performsthe hazardous scaling job with the ope-rator remotely located away from rockfalls. Blast holes are drilled in the faceusing a drill jumbo, and all functions inthe rock support process are performedat a safe distance from the rock to besupported. The operator controls every-thing from a platform or cabin, equippedwith a protective roof.

Where installation of steel mesh isundertaken, some manual jobs may stillbe required. Mesh is tricky to handle,because of its shape and weight, andthis has hampered development of fullyautomated erection.

Q t of bo t

In 1992, it was reported that independ-ent studies were indicating that as many

as 20-40% of cement and resin groutedbolts in cu

25012121 Education Under Ground Mining E Book 06

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