UniversityUniversity ofof SaskatchewanSaskatchewan

GeologicalGeological EngineeringEngineering GEOEGEOE 498.3498.3

IntroductionIntroduction toto MineralMineral EngineeringEngineering LectureLecture 22

•• UndergroundUnderground MiningMining MethodsMethods – Bulk vs. Selective – Reasons for Selection (Geotechnical, Geometry, Value, Grade, Dilution Control, Skill of work force, health and safety, etc) – Mining Equipment (mobile) – Tunneling Methods UndergroundUnderground MiningMining MethodsMethods

• MINING METHOD Is defined as the manner of extraction of an ore deposit underground and depends on many factors. • Different Methods are used for Hardrock and Softrock as well as Bulk and Selective Mining FactorsFactors toto ConsiderConsider

•• GeologicalGeological andand GeotechnicalGeotechnical ConsiderationsConsiderations –– StrengthStrength ofof OreOre –– StrengthStrength ofof hosthost rockrock –– StressStress fieldfield –– StructuralStructural GeologyGeology (faults,(faults, contacts,contacts, joints,joints, folds,folds, etc.)etc.) –– DimensionsDimensions ofof orebodyorebody (thickness,(thickness, strikestrike length,length, height)height) –– OrientationOrientation (dip,(dip, plunge)plunge) –– DepthDepth FactorsFactors toto ConsiderConsider

•• EconomicEconomic andand LogisticalLogistical – Availability of Skilled Labour – Availability of Equipment – Availability of backfill – Legacy issues – Health and Safety factors – Economics • Production Requirements • Value of ore • Operating Cost • Capital cost • Processing cost CommonCommon RequirementsRequirements forfor allall MiningMining MethodsMethods •• AccessAccess forfor equipment,equipment, personnel,personnel, servicesservices (electricity,(electricity, water,water, compressedcompressed air,air, ventilation).ventilation). •• ArteriesArteries forfor thethe transporttransport ofof oreore && wastewaste outout ofof thethe minemine andand possiblypossibly backfillbackfill intointo thethe mine.mine. •• DrainageDrainage •• safesafe workingworking conditionsconditions ClassificationClassification ofof MiningMining MethodsMethods

7 Choice of Mining Method will impact • Orebody recovery and Dilution • Amount of development needed • Capital requirement and operating costs • Type of equipments required • Cycle time and sequence of operations • Production (tonnes per year) • Risk Classification of Underground Mining Methods • Two main Classes of Underground Mining Methods: –Bulk Mining (Caving, Open Stoping, VCR) –Selective Mining (Cut and Fill, Room and Pillar, Shrinkage) Sub-Classifications

•• OverhandOverhand StopingStoping –– BottomBottom UpUp MethodMethod •• UnderhandUnderhand StopingStoping –– TopTop DownDown MethodMethod

•• LongitudinalLongitudinal StopingStoping –– LongLong axisaxis ofof stopestope isis parallelparallel toto orebodyorebody strikestrike •• TransverseTransverse StopingStoping –– LongLong axisaxis ofof stopestope isis perpendicularperpendicular toto orebodyorebody strikestrike Sub-Classifications

•• UnderhandUnderhand StopingStoping – Stability of the Orebody is very poor or there is no access to the lower part of the orebody – Examples: Underhand Cut and Fill used in narrow veins at depth or underhand Blast hole open stoping used for bulk mining. – Workers are always standing on solid ore and below supported or filled back. •• OverhandOverhand StopingStoping – Stoping operation start a the bottom of the orebody and proceeds to upward – Most popular method of stoping. Example: Shrinkage stoping, Cut and Fill stopes, Room and Pillar, Caving Methods, VCR Method of Mining, Sub Level Stoping HardHard RockRock SelectiveSelective MiningMining MethodsMethods •• RoomRoom andand PillarPillar •• CutCut andand FillFill •• ShrinkageShrinkage •• AlimakAlimak MiningMining •• RaiseRaise borebore andand BoxBox holehole MiningMining RoomRoom andand PillarPillar

• Applicable to relatively flat orebodies and employ natural support (rock pillars). The orebody is excavated as completely as possible leaving ore/waste as pillars to support the hanging wall (back). Dimensions of the stopes and pillars depend upon factors such as the stability of the back, stability of the ore, thickness of the deposit and rock stresses.

– Horizontal Mining is the most commonly used room and pillar method. It is applicable to horizontal or near horizontal deposits (< 5° dip) and to inclined deposits of greater thickness, with the floor arranged for a moderate slope that allows for use of mobile equipment.

– Inclined Mining is for inclined orebodies (20° - 30° dip). Stoping proceeds upwards along the dip direction. The steep slope precludes use of mobile equipment.

– Step Mining adapts horizontal stoping to an inclined orebody (20° - 45° dip). This is a recent development in the industry for mining orebodies that would otherwise be precluded by their steep dip. It requires a special layout of stopes and a sequence of extraction resulting in the use of mobile equipment. HorizontalHorizontal RoomRoom andand PillarPillar InclinedInclined RoomRoom andand PillarPillar StepStep RoomRoom andand PillarPillar RoomRoom andand PillarPillar RoomRoom andand PillarPillar RoomRoom andand PillarPillar FeaturesFeatures

• Summary of Applications – relatively flat orebodies – limited thickness – competent hanging wall and ore

• Advantages ... – good productivity – moderate cost – flexible method, amenable to mechanization – Selective – minimal early development – No backfill required

• Disadvantages ... – possible ground control problems – Medium to low recovery, ore lost in pillars

CutCut andand FillFill • Cut and fill stoping methods excavate ore in horizontal slices or lifts, starting at the bottom of a stope and advancing upwards. • The broken ore is removed from the stope after each lift is blasted. • After a slice is mucked out, the void is filled with backfill. The fill supports the walls and provides a working platform for mining the next lift. • Fill material can consist of waste rock however, it is more common to use tailings from the mill transported to mine in slurry form. • When water in the fill is drained off a competent fill with a smooth surface is produced. In some cases the material is mixed with cement to provide a harder and more durable surface with improved support characteristics. • Suited to steeply dipping, irregular orebodies, weak host rock or large tabular steeply dipping irregular orebodies for multiple lifts or cuts CutCut andand FillFill CutCut andand FillFill CutCut andand FillFill CutCut andand FillFill LongitudinalLongitudinal MCFMCF LongitudinalLongitudinal MCFMCF TransverseTransverse MCFMCF CutCut andand FillFill CutCut andand FillFill

• Summary of application – orebody width 2m - 30m – tabular shape ... good for irregular orebodies – orebody dip 35o -90o – good for low strength / high stress regions – requires safe, stable back for man entry – Expensive, generally high grade ore required for this method to be economic – good selectivity minimum dilution CutCut andand FillFill

• Advantage… – moderate production and scale – good selectivity – low development cost – adaptable to mechanization – flexible method – excellent recovery with low dilution – tailings can be disposed of as fill • Disadvantage… – high production cost – fill complicates cycle – requires stope access for mechanized equipment – labour intensive – ground settlement/instability risk

CutCut andand FillFill VariationsVariations

• Underhand Cut and Fill or Undercut and Fill – Developed to recover pillars or to mine low strength ore bodies – Mining top down and placing a cemented/reinforced mat over the working area ... enabling mining below.

• Drift and Fill – Used to mine wide, flat, thin (<6m) orebodies with poor hanging wall conditions. Mining involves a series of parallel drifts with an access heading driven along the hanging wall contact. Each mined drift is filled with cemented sand fill ... providing back support for the next drift. • Post Pillar – Hybrid between room and pillar and cut and fill – moderately thick, flat, tabular ore bodies – moderate to low strength back UnderhandUnderhand CutCut andand FillFill Underhand cut-and-fill

•Weak, narrow vein orebodies •Cemented backfill required PostPost PillarPillar CutCut andand FillFill ShrinkageShrinkage

•• OreOre isis brokenbroken inin horizontalhorizontal slicesslices workingworking upwards.upwards. •• SufficientSufficient oreore withdrawnwithdrawn atat thethe bottombottom afterafter eacheach sliceslice toto accommodateaccommodate swellswell (30%(30% -- 40%)40%) •• RemainderRemainder staysstays inin thethe stopestope toto provideprovide aa workingworking platformplatform ...... removedremoved atat thethe end.end. •• StopesStopes separatedseparated byby intermediateintermediate (recoverable)(recoverable) pillarspillars ShrinkageShrinkage

•• orebodyorebody widthwidth 1.2m1.2m -- 30m30m •• tabulartabular orebodyorebody;; regularregular boundariesboundaries •• dipdip >50>50°° •• stablestable hanginghanging wallwall andand footwallfootwall •• uniformuniform drawdraw downdown importantimportant •• dilutiondilution generallygenerally lowlow •• OreOre mustmust bebe unaffectedunaffected byby storagestorage inin stopestope •• LabourLabour intensiveintensive method,method, limitedlimited scopescope forfor mechanizationmechanization ShrinkageShrinkage ShrinkageShrinkage ShrinkageShrinkage • Summary of Application… – Shrinkage not a common method ... too labour intensive – Employed only where mechanization not possible. – Maintaining stope full of muck increases possible stope spans and minimizes dilution .. support and development costs reduced. – Limited production capacity and bulk of ore tied up for a long time.

• Advantages… – moderate production rate. – draw down by gravity – conceptually simple (small mine usage) – low capital investment – minimal support in stope – moderate development – good recovery, low dilution

• Disadvantages… – low productivity – moderate to high mining cost. – labor-intensive – dangerous working conditions – ore tied up in stope – ore subject to oxidation, packing in stope ShrinkageShrinkage VariationVariation -- RaiseRaise oror AlimakAlimak MiningMining •• AA variationvariation ofof shrinkageshrinkage miningmining •• LongLong holehole drilldrill isis mountedmounted onon anan alimakalimak raiseraise climberclimber •• Mechanized,Mechanized, costcost effectiveeffective methodmethod AlimakAlimak MiningMining AlimakAlimak MiningMining RaiseRaise oror AlimakAlimak MiningMining AlimakAlimak MiningMining AlimakAlimak MiningMining AlimakAlimak MiningMining AlimakAlimak MiningMining AlimakAlimak MiningMining AlimakAlimak MiningMining RaiseRaise borebore andand BoxBox holehole MiningMining

• Summary of application – Raise bore holes are excavated and filled. – Can be used to mine tabular narrow steeply dipping deposits or moderately thick flat deposits. – Low to high strength ore – None entry – Requires very high grade ore as method is very expensive • Advantages… – Very safe – Low dilution – High recovery – Miners not exposed to environmental hazzards • Disadvantages… – Very expensive – Low production rates RaiseRaise BoreBore MiningMining RaiseRaise BoreBore MiningMining Raise Bore Chamber

Extraction Chamber BoxBox holehole MiningMining RaiseRaise BoreBore MiningMining HardHard RockRock BulkBulk MiningMining MethodsMethods

•• SublevelSublevel // BlastholeBlasthole // LongLong HoleHole •• VerticalVertical CraterCrater RetreatRetreat (VCR)(VCR) •• AvocaAvoca •• SublevelSublevel CavingCaving •• BlockBlock CavingCaving SublevelSublevel StopingStoping MethodsMethods

• Sublevel stoping is also known as "blasthole stoping" or "longhole stoping". • vertical or steeply dipping ore bodies with regular boundaries • mined from levels at predetermined vertical intervals • drilling/blasting from sublevels (overcut or undercut), mucking from undercut • ore pillars between stopes for support, may be recovered later • The orebody is divided into sections up to 100 m high and further divided laterally into alternating stopes and pillars. A main haulage drive is created in the footwall at the bottom, with cut-outs for draw-points connected to the stopes. • Long hole blasthole and stoping uses longer and larger diameter blastholes than sublevel stoping, thus requiring less drilling than sublevel stoping. Greater drilling accuracy is required SublevelSublevel StopingStoping MethodsMethods • minimum orebody width 2m • tabular or massive shape • Can be mined transverse or longitudinal • dip >50° • large stopes (non-entry) • limited selectivity, orebody should be regular • No Backfill – pillar size considerations similar to room and pillar – competent footwall, ore zone and hanging wall – dilution a potential problem • With Backfill – pillar size must be suitable for recovery – stress on pillars should be low – fill material must allow recovery of pillars with minimum dilution SublevelSublevel StopingStoping MethodsMethods SublevelSublevel StopingStoping MethodsMethods SublevelSublevel StopingStoping MethodsMethods SublevelSublevel StopingStoping MethodsMethods SublevelSublevel StopingStoping MethodsMethods SublevelSublevel StopingStoping MethodsMethods SublevelSublevel StopingStoping MethodsMethods SublevelSublevel StopingStoping MethodsMethods SLOSSLOS Primary/SecondaryPrimary/Secondary withwith TransverseTransverse DrillingDrilling andand ExtractionExtraction

67 SublevelSublevel StopingStoping MethodsMethods SublevelSublevel StopingStoping MethodsMethods SublevelSublevel StopingStoping MethodsMethods BlockBlock PlanPlan

SublevelSublevel StopingStoping MethodsMethods

• Summary of Application… – method became popular after development of large diesel LHD’s in the last 40 years – efficient in drilling, blasting and loading – high utilization of mechanized equipment – limited selectivity with irregular orebodies • Advantages – good productivity – moderate cost – amenable to mechanization – safe operating conditions – good recovery; moderate dilution • Disadvantages… – Expensive initial development – inflexible / non-selective

AvocaAvoca

• Allows mining of narrow ore zones with high recovery. • Requires stope development with upper and lower drill drifts, similar to longhole mining. • Stope is backfilled with waste rock from the upper drill horizon ... no pillars required.

Advantages… – Flexibility – no requirement for pillars – waste storage with short haulage

• Disadvantages – higher dilution – advance limited by backfill availability must have two accesses AvocaAvoca

76 AvocaAvoca AvocaAvoca

78 VerticalVertical CraterCrater RetreatRetreat // VCRVCR

• Very similar to Sub level stoping. • Employs a unique blasting technique called the crater blasting • Also resembles Shrinkage stoping as ore is extracted in horizontal slices. • The ore is recovered from an undercut drawpoint system resembling that used in sublevel open stoping • Can be used in steeply dipping ore bodies under the same conditions as sub level stoping and shrinkage stoping • Blasted ore remains in the stope and is used to support the hanging wall VerticalVertical CraterCrater RetreatRetreat // VCRVCR VerticalVertical CraterCrater RetreatRetreat // VCRVCR

• Advantages – VCR is a bulk, high-capacity mining method with good recoveries; – It is an efficient stoping method that is very susceptible to mechanization and can have productivities in excess of 32 tonnes/employee-shift; – It offers good wall support during the stoping phase by using shrinkage techniques; – It is a safe method with miners working under a fully supported back that can be adequately ventilated. • Disadvantages – VCR requires extensive diamond drilling, pre-stope planning, and development lead-time for maximum effectiveness; – Ore is tied up in the stope until final drawdown ... representing lost income; – Some ores are mineralogically unstable and may be subject to breakdown, causing problems with benefaction, drawing, etc.. – High concentration of explosive and hole deviation may damage walls and may increase dilution problems SublevelSublevel CavingCaving • The orebody is divided into closely spaced vertical sublevels. From each sublevel the orebody is developed by a series of drifts from hangingwall to footwall to lateral extremity on strike • From the sublevel drifts the ore immediately above is drilled with longholes in a fan shape pattern • size should be large enough to allow for sufficient vertical sub-levels for lateral and vertical interaction • massive and/or tabular and steep, uniform shape • steeply dipping >50 degrees unless massive • competent ore with a waste hangingwall that can cave. Stable footwall for development access. • high dilution, very sensitive to poor fragmentation • limited selectivity • surface conditions must allow for subsidence Sublevel caving is usually carried out underneath an open pit when it becomes uneconomic to mine from the pit SublevelSublevel CavingCaving SublevelSublevel CavingCaving SublevelSublevel CaveCave • Summary of ApplicationSublevelSublevel… CavingCaving – Longhole drilling is performed in a fan shaped pattern that radiates upwards from sublevel drift. – Ore is mucked from the sublevel drift, transported and dumped into orepasses by LHD's. – Production drilling and loading are carried out on separate levels and are independent of each other – many work faces result due to the large number of drift faces – ore is blasted against a caved face therefore explosive consumption is high

• Advantages… – high productivity rate – many work faces and efficient – highly mechanized – safe method as non-entry

• Disadvantages… – high dilution – surface subsidence results – potential for high ore losses - low recovery – explosive consumption high (choke blasting) – high development costs – hi intensity of drill and blast required in order to generate a mobile granular ore within a cave medium

BlockBlock CavingCaving

•• BlockBlock cavingcaving isis applicableapplicable toto large,large, deep,deep, lowlow-- gradegrade deposits.deposits. •• ItIt isis oftenoften donedone toto continuecontinue miningmining afterafter openopen pitpit miningmining becomesbecomes uneconomicuneconomic oror impossible.impossible. However,However, somesome minesmines startstart asas blockblock cavecave operations.operations. •• AA gridgrid ofof tunnelstunnels isis drivendriven underunder thethe orebodyorebody.. TheThe rockrock massmass isis thenthen undercutundercut byby blasting.blasting. IdeallyIdeally thethe rockrock willwill breakbreak underunder itsits ownown weight.weight. •• BrokenBroken oreore isis thenthen takentaken fromfrom drawdraw points.points. ThereThere maymay bebe hundredshundreds ofof drawdraw pointspoints inin aa largelarge blockblock cavecave operationoperation (Figure(Figure 3).3). BlockBlock CavingCaving

• orebody and hangingwall must cave therefore the ore must have sufficient plan area to initiate cave through the undercut (>1000m2). Vertical dimension generally greater . • massive and/or tabular and steep, uniform shape • steeply dipping >50 degrees unless massive which then requires a high vertical dimension • orebody and hangingwall must be weak and cavable. Otherwise the undercut area must be large and consequently fragmentation is large. • high dilution, very sensitive to poor fragmentation • no selectivity • surface conditions must allow for subsidence BlockBlock CavingCaving BlockBlock CavingCaving BlockBlock CavingCaving BlockBlock CavingCaving BlockBlock CavingCaving • Summary of application… – upon completion of the undercut the ore falls down finger raises or cones and is a continuous process as material is removed at the draw level – theoretically no production drilling is required. In practise, long holes are drilled widely spaced to induce fracturing, secondary drilling of oversize rock is a frequent operation. – ore handling in track mining utilizes gravity forces to deliver material to rail cars. However, chutes require small fine fragmentation and grizzly is very labour intensive and is generally a bottleneck in the production cycle. – Ore handling in trackless mining is through drawpoint mucking and the development work required is substantially reduced since no grizzly level or raises. – Rule of thumb: for an orebody to be cavable approximately 50% of the ore fragments should break to 1.5m or less in maximum dimension. One can't have large arches formed since will result in an air blast/or high stresses in the abutments. BlockBlock CavingCaving • Advantages… – highest production rate of any underground mining method – lowest operating cost of any underground mining method – production (not development) is entirely by caving ie. No drill or blast other than secondary blasting – ability to be highly mechanized

• Disadvantages… – caving and subsidence occur on large scale – high dilution – draw control is critical to success of method – slow and extensive development requirements – high support costs – caving and fragmentation is extremely difficult to predict or control – inflexible method- no selectivity – possible ore oxidation if caving/drawing is slow

MiningMining EquipmentEquipment DrillingDrilling DrillingDrilling DrillingDrilling EquipmentEquipment -- JacklegJackleg DrillDrill –– DevelopmentDevelopment JumboJumbo DrillDrill –– DevelopmentDevelopment JumboJumbo DrillDrill –– DevelopmentDevelopment JumboJumbo DrillDrill –– longholelonghole –– ITHITH DrillDrill –– LongholeLonghole -- ITHITH DrillDrill –– LongholeLonghole -- TophammerTophammer DrillDrill –– LongholeLonghole -- TophammerTophammer DrillDrill –– LongholeLonghole -- TophammerTophammer DrillDrill –– RaiseRaise borebore rotaryrotary drilldrill DrillDrill –– RaiseRaise borebore rotaryrotary drilldrill Raisebore Station and Reamer Bit MuckingMucking EquipmentEquipment -- CavoCavo MuckingMucking EquipmentEquipment -- CavoCavo MuckingMucking EquipmentEquipment –– LHDLHD withwith 1111 mm33 bucketbucket MuchingMuching EquipmentEquipment –– RemoteRemote ControlControl ScoopScoop MuckingMucking EquipmentEquipment –– 1515 tonnetonne TruckTruck MuckingMucking EquipmentEquipment –– 5050 tonnetonne TruckTruck MuckingMucking EquipmentEquipment –– LHDLHD loadingloading TruckTruck MuckingMucking EquipmentEquipment –– 5050 tonnetonne TruckTruck MuckingMucking EquipmentEquipment –– 5050 tonnetonne TruckTruck MuckingMucking EquipmentEquipment –– U/GU/G oreore traintrain Hardrock Mining Method Selection

ƒNicolas Method ƒ Identify key factors that determine mining method ƒ Rank each of the factors for different methods ƒ Apply all factors to an orebody ƒ Orebody with the highest rating is the optimum mining method Hardrock Mining Method Selection Hardrock Mining Method Selection Hardrock Mining Method Selection Hardrock Mining Method Selection Hardrock Mining Method Selection Hardrock Mining Method Selection Hardrock Mining Method Selection Hardrock Mining Method Selection Hardrock Mining Method Selection Hardrock Mining Method Selection Hardrock Mining Method Selection •• SOFTROCKSOFTROCK MININGMINING –– PotashPotash –– CoalCoal PotashPotash MiningMining

• Long room-and-pillar mining method. Ore is mined from rooms in three passes, separated by pillars supporting the overlying strata. • Automated Marietta continuous miners are capable of extracting up to 650t/h of ore. • The run-of-mine ore is loaded on to extensible conveyors attached to the continuous miners. These connect to the main haulage conveyors, which move the ore to skip-loading pockets at the shafts, where it is hoisted to surface.

LongLong WallWall MiningMining • Highly mechanized underground mining system for mining coal. • A layer of coal is selected and blocked out into an area known as a panel. • A typical panel might be 3000 m long by 250 m wide. • Passageways areexcavated along the length of the panel to provide access and to place a conveying system to transport material out of the mine. • Entry tunnels are constructed from the passageways along the width of the panel. The longwall system mines between entry tunnels. • Extraction is an almost continuous operation involving the use of self-advancing hydraulic roof supports sometimes called shields, a shearing machine, and a conveyor which runs parallel to the face being mined. LongwallLongwall MiningMining LongLong WallWall MiningMining LongLong WallWall MiningMining LongLong WallWall MiningMining LongLong WallWall MiningMining SoftSoft RockRock RoomRoom andand PillarPillar EquipmentEquipment SoftSoft RockRock RoomRoom andand PillarPillar EquipmentEquipment SoftSoft RockRock RoomRoom andand PillarPillar EquipmentEquipment Underground Softrock Mining