The Block Cave Mining Method

The Block sabotage Mining MethodBlock caving is a gigantic-scale underground jab rule applicable to the stemma of inferior, potfulive ore bodies. With the amount of literature available on cloture caving this report identifies the need to provide a simple understanding of the military operation. Understanding a production operate of a tug cave mine is an important aspect onwards getting involved with technical aspects of the mine. This report attempts to give an insane asylum into the production execute of a elude cave mine and in like manner an understanding about gourmandize caving.The document has been split into four chapters,Chapter One gives a basic understanding of the method and highlights the considerations that down to be made before the performance of a banish cave mine.Chapter Two gives an introduction into the production process involved in a block cave mine by taking into account four study directs involved in production. The production process h as been described in the form of a flow graph for simple understanding of the process.Chapter Three outlines the significance of production potency and production management in order to increase productivity of the mine.Chapter Four outlines almost of the safety and risks involved in a block cave mine and the indispensable precautions to be taken in order to increase safety.This report has been intended to provide a simple understanding of the block cave mining method and the production process involved. This report is advocated towards a layman in block caving in view of getting an word-painting about the block cave mining method.Chapter One launching1.1 Block CavingBlock caving is an underground mining method applicable to the extraction of low-grade, massive ore bodies with the pastime characteristicslarge vertical and naiant dimensions,a quake mass that forget break into pieces of manageable coat, anda surface that is eitherowed to subside.These rather unique condit ions limit block caving to particular types of mineral deposits. Block caving is used for extracting iron ore, low-grade copper, molybdenumdeposits, and diamond-bearing kimberlite pipes.1.1.1 Block Caving MethodA large slice of material is blasted at the base of the ore body which creates an instability within the orebody, inducing the partitioning and mobilization of ore to the production level through the breakdown of ore and waste due to the natural pattern of breakages, development of stresses in the active caving domain of a function, and the low potentiality of the inclination mass. The size and shape of the sell depends on the characteristics of the rock mass. diggings ar created at the production level at base of the orebody to fool out the confused material. A large amount of development expenditure is required to set up the facilities to break the lowest level of the ore body, and all told the broken rock is extracted out of the block cave through a system of a ttracter buzzers. Once the caving is initiated, operating cost of the block cave is very low comparable to the operating costs in open pit mining.Once caving is initiated, production can be ramped up until the production rate is almost equal to the caving rate. The cold shoulder is advance in the horizontal plane to create greater beas of caving for increasing the production.Rock breakage come to passs only in the caving areas, generate by undercutting, and has low drilling and blasting cost nigh amount of blasting may be required at the vomit sharpens1to break some of the large rocks coming through the drawbell, especially during the initial stages of draw.Most block caves these days are highly mechanized with large number of large LHDs (load-haul-dump machines) working at the lower levels, though smaller orebodies can also be caved and extracted using gravity draw systems with orepasses2and slushers3.The development of a conventional gravity flow system of block caving in volvesFigure Conventional Gravity Flow corpsehttp//technology.infomine.com/reviews/BlockCaving/assets/images/BlockCaving1.jpgSource Infomine Block CavingA spot where gravity fed ore from a higher level is loaded into hauling unitsA vertical or inclined departure for the downward transfer of oreA mechanical drag shovel loaderan undercut where the rock mass underneath the block is fractured by blastingdrawbells beneath the undercut that gather the rock into finger raises4finger raises that draw rock from drawbells to the grizzliesa grizzly level where oversized blocks are caught and broken upa lower set of finger raises that channel ore from grizzlies to swoops for train loading the finger raises are arranged like the branches of a tree, gathering ore from a large area at the undercut level and further channeling material to chutes at the haul level anda lowermost level where ore is prepared for train haulage and chute loading.When LHDs are used, the development required is cons iderably less complex and involvesUndercut levelhttp//www.edumine.com/xcourse/xblock101/docs/figures/images/10002x.jpgExtraction LevelSource Infomine Block Caving4 Steeply sloping openings permitting caved ore to flow down raises through grizzlies to chutes on the haulage levelan undercut where the rock mass underneath the block is fractured by blastingdrawbells constructed between the undercut and extraction levelsan extraction level with drawpoints at the base of drawbells andan ore haulage system to collect, crush and transport the ore out of the mine.Underground Mining MethodsUnsupportedArtificially SupportedPillar SUpported wither StopingBench and Fill StopingRoom and PillarSublevel MiningLongwall MiningSublevel and Longhole Open StopingBlock and Panel CavingVCR StopingCut and Fill Stoping1.1.2 History of Block Cavingformer(a) 19th centuryprecursor to modern block caving demonstrable in the Pewabic iron ore mine, Michigan, USAEarly 20th centurythe block caving method real in the USA for iron ore and then copper mining in the western states1920sblock caving come to the foreed in Canada and ChileLate 1950sblock caving introduced into southern African diamond mines and then chrysotile asbestosminesLate 1960sLHD vehicles developed for underground mining1970LHDs used with block caving at El Salvador mine, Chile1981 motored panel caving introduced in the primary ore at El Teniente mine, Chile1990splanning of the new generation of block caves with larger block heights in stronger orebodies (e.g. Northparkes, Palabora)2000splanning and development of super block caves under existing open pit mines (Grasberg, Chuquicamata, Bingham C eitheron) and at great depth (Resolution Copper)http//www.edumine.com/xcourse/xblock101/docs/figures/images/10003x.jpgSource Infomine Block Caving1.2 Management organizational Chart exploit ManagerTechnical Services SuperintendentTechnical Services SuperintendentMine SuperintendentHuman ResourceLogisticsElectrical windup(prenominal )Cave DevelopmentCave Production public exposureProjectsGeo-TechnologyGeologySurveyLong Term PlannerShort Term PlannerDesignThe organizational chart might differ based on the requirements of a specific mine.1.2.1 Managerial ResponsibilitiesMine Manager is responsible for the overall management, direction and coordination of the mine and related operations. Mine Managers are also intended to provide the technical leadership in the area of underground mine engineering.The focus of the Mine Manager should be on the following subjectsEnsuring underground mining activities are conducted in accordance with the Occupational Health and Safety Act and Regulations and environmental standardsComplying with all safety requirementsObserving all company policies and proceduresAssisting with the development of production targetsEnsuring production targets are met or exceededDeveloping schedules, budget and ensuring these are controlled and managed effectivelyMonitoring production results on a ref orm-minded basis and preparing monthly progress and variance reportsMaintaining effective working relationships with Contractors, Suppliers and Service Providers, and ensuring adherence to contractual requirementsDeveloping a sense of continuous improvementEnsuring grab training programs are in place to meet safety and production requirementsMaintaining knowledge of underway statutory requirements and industry best practices and ensuring compliance at all timesInterphases with opposite managers and superintendents as part of the management teamReviewing mining methodsImplementing optimisation programs where appropriateManaging manpower levels to achieve their performance1.3 Parameters to be considered before the implementation of cave miningTwenty five parameters that should be considered before the implementation of any cave mining operation are set out in Table 1. Many of the parameters are uniquely defined by the orebody and the mining system.No.ParametersConsiderations1Cavab ilityRockmass StrengthRockmass StructureIn situ stressHydraulic rundle of orebody pissing2Primary FragmentationRockmass strengthGeological structuresJoint/fracture setJoint condition ratings direction or subsidence cavinginduce stress3Drawpoint SpacingFragmentationOverburden load and directionFriction angles of caved instalments serviceable excavation sizeStability of host tockmassInduced Stress4Draw spinning topsCapitalOrebody geometryExcavation stability5LayoutFragmentaionDrawpoint space and sizeMethod of draw6Rockburst PotentialRegional and induced stressesRockmass StrengthStructuresMining Sequence7SequenceCavabilityOrebody geometryInduced stressesGeological environmentInfluence on adjacent operationsRockburst potentialProduction requirementsWater inflowNo.ParametersConsiderations8Undercutting SequenceRegional stressesRockmass strengthRockburst potentialRate of advanceOre requirements9Induced Cave StressesRegional stressesArea of undercut fake of undercutRate of undercutting Rate of draw10Drilling BlastingRockmass strengthPowder factorRockmass stabilityRequired fragmentationHeight of undercut11DevelopmentLayoutSequenceProductionDrilling and blasting12Excavation StabilityRockmass strengthRegional and induced stressesRockburst potentialExcavation sizeDraw heightMining Sequence13Primary SupportExcavation stabilityRockburst potentialBrow stability14Practical Excavation SizeRockmass strengthInsitu stressInduced stressCaving stress unoriginal blasting15Draw MethodFragmentationPractical drawpoint spacingPractical size of excavation16Draw RateFragmentationMethod of drawPercentage hangupsSecondary open frame requirements17Drawpoint InteractionDrawpoint spacingFragmentationTime frame of working drawpointsNo.ParametersConsiderations18Draw Column StressesDraw-column heightFragmentationHomogenity of ore fragmentationDraw controlHeight-to-base ratio heraldic bearing of draw19Secondary FragmentationRock- block shapeDraw heightDraw rate-time dependent failureRock-blo ck workabilityRange in fragmentation sizeDraw control program20Secondary BlastingSecondary fragmentationDraw methodDrawpoint sizeSize of equipment and grizzly spacing21DilutionOrebody geometryFragmentation range of unpay ore and wasteGrade distribution of pay and unpay oreMineral distribution in oreDrawpoint interactionSecondary breakingDraw control22Tonnage DrawnLevel intervalDrawpoint spacingDilution percentage23Support RepairTonnage drawnPoint and column loadingSecondary blasting24ExtractionMineral distributionMethod of drawRate of drawDilution percentageOre losses25SubsidenceMajor geological structuresRockmass strengthInduced stressesDepth of miningSource LaubsherChapter Two -Production Process2.1 Block Cave Mining SystemIn a Block Cave Mine in that location are four major levels that contribute to the production of the mine. The levels that suck in been taken into account here areExtractionUndercut attractorVentilationIn a natural progression of a block cave mine the infrast ructure that need to be built before the range of caving includesPrimary access to the production levels (ramps and shafts)Extraction level excavationsHaulage and Ventilation level excavations andCrushing and ore transport facilities.While most of these excavations need to be created before the start of caving operations, construction of some extraction, haulage and ventilation level drifts can be planned just in advance of actual caving operations.Each of these levels is abandoned a brief introduction and the production process for each level are outlined from collecting data from different sources. The information flow in the form of a flow chart is provided for ease of understanding the process. The information flow chart provided is implemented from personal experience and its objective is to provide an impression on the production process of an underground block cave mine.2.2 Extraction LevelThe extraction level is the main production level in a block cave operation. All the ore from the block cave is drawn through draw points at the extraction level and then transferred to haulage level through a system of ore passes or a fleet of LHDs. Since this is the main production level, it is developed and supported to counter the stresses and displacements that can be expected during the life of the drawpoints at the level.The arrangement of drawpoints, drawbells and other excavations on the extraction or production level is referred to as the extraction level layout. The development of the extraction level and the drawbells creates two types of pillars. The major apex is the shaped structure or pillar above the extraction level formed between two adjacent drawpoints but separated by the extraction or production drift. The minor apex is the shaped structure or pillar formed between two adjacent drawbells on the resembling side of the extraction drift.The drawpoint spacing, the drawpoint width, and the length between the undercut and extraction levels are all designed based on the fragmentation expected within the block cave. The ground support installed in the excavations at the extraction level is based on the characteristics of the rock mass and the expected stress levels at different locations.2.2.1. DrawbellsThe exemplification shape of the drawbell is like a bell, so that ore can flow to the drawpoint. However it is a compromise between strength and shape. The major and minor apexes must(prenominal) have sufficient strength to last out the life of the draw. It needs to be established how much influence the shape of the drawbell has on interaction. It has al fashions been an empirical point that shaped drawpoints improve ore recovery as the ore should have better flow characteristics than a drawbell with vertical faces and a large flat top major apex. The time consuming operation is creating the drawbell. The undercut technique also determines the shape of the major apex and importantly the shape of the drawbell.The draw rate from the drawbells is an important factor in that it must provide space for caving also it must not be too fast to create a large air gap and affirmable air-blasts. If the draw rate is too fast seismic activity will occur. Production must be based on this value and not intrust on economic factors such as short term return on investment that ignores long term consequences. at that place is also the fact that a slow draw rate will mean improved fragmentation.2.2.2 Extraction Level Production ProcessPlanningDesignEquipment/PeopleDecision makingGround SupportDrawbellsDriftsGround SupportDevelopmentPathwaysVentilationVentilationBlastHang upsDrawpointUndercuttingSecondary BlastingOre removalLHDsOre pass fullOre ecstasyHaulage LevelSecondary Ore passCrusher2.3 Undercut LevelThe process of undercutting creates instability at the base of the block being caved. Block cave mining is based on the principle that when a sufficiently large area of a block has been undercut by drilling and blastin g, the overlying block of ore will start to cave under the influence of gravity. The process will continue until caving propagates through the entire block surface or to the open pit above, unless a stable shape is achieved. The purpose of the undercut level is therefore to remove a slice of sufficient area near the base of the block to start the caving of the ore above.The undercut level is developed at the base of the block to be caved. The caving of the block is initiated by mining an undercut area until the hydraulic radius of the excavation reaches a critical value. As the broken ore above it will collapse into the void so created. Vertical propagation of the cave will then occur in response to the continued removal of broken ore through the active drawpoints. The horizontal propagation of the cave will occur as more drawpoints are brought into operation under the undercut area.2.3.1 UndercuttingUndercutting is the most important process in cave mining. As not only is a complet e undercut necessary to induce a cave, but the design and the sequencing of the undercut is important to reduce the effects of the induced abutment stress. It is essential that the undercut is continuous and it should not be advanced is there is a possibility that pillars will be left. This rule which is often ignored owing to the problems in re-drilling holes, results in the leaving of pillars resulting in the collapse of large areas and consequent high ore losses. The undercut technique also determines the shape of the major apex and importantly the shape of the drawbell. Care must be taken that there is no stacking of large blocks on the major apex as this could prevent cave propagation.2.3.2 Undercutting TechniquesConventional The conventional undercutting sequence is to develop the drawbell and then to break the undercut into the drawbell.Henderson Technique The Henderson Mine technique of blasting the drawbell with long holes from the undercut level just ahead of blasting th e undercut reduces the time interval in which disparage can occur. They have also found it necessary to delay the development of the drawbell drift until the drawbell has to be blasted.Advance Undercut The advance undercut technique bureau that the drawpoints and drawbells are developed after the undercut has passed over, so that the abutment stresses are located in the massive rock mass with only the production drift.2.3.3 Undercut Level Production ProcessDesignPlanningDevelopmentEquipment/PeopleDecision MakingGround SupportVentilationDriftsPathwaysUndercuttingOre RemovalHaulage LevelLHDsCrusher grievous bodily harm RemovalLHDsOre PassWaste Dump2.4 Haulage and Ventilation LevelThe haulage and ventilation levels lie infra the extraction level. They need to be developed with adequate excavations to handle the quantity of broken ore and ventilating air streams required for the designed production rates, equipment and manpower employed within the block cave.Facilities for storing, crushing and conveying the broken ore to the mill need to be developed at the haulage level. The larger excavations required for the crushers, ore bins and conveyor transfer stations need to be located remote the zone of influence of the stresses due to the block cave, and adequate ground support will need to be installed to ensure that the excavations are stable during their expected life.The excavations and levels must be placed far enough apart so that there is limited interaction between numerous excavations created to move the ore from the production level to the mill around facilities at the surface.2.4.1 Haulage LevelMuch of the development of the infrastructure for a block cave operation is completed during the pre-production stage though some haulage lines and ventilation drifts and raises may be deferred to later in the life of the block cave. Scheduling the development of haulage and ventilation drifts needs careful planning so that the required facilities are in-place well in advance of their requirement. Though there is some flexibility in the development of these levels since they are different elevations and lie below the extraction level, the preliminary layouts need to be prepared so that the flow of materials, ore and ventilating air can be integrated without interruption as the block cave progresses.2.4.2 Ventilation LevelVentilation Levels are normally developed between the haulage and the extraction levels. During the development phase air is streamed through the undercut and extraction levels to the working faces and exhausted through the raises to the ventilation level. During production, air is coursed through the extraction level and exhausted through the ventilation raises to the exhaust side of the ventilation level. surplus air is provided at the working areas through ventilation raises which connect to the intake of the ventilation level2.4.3 Haulage Level Information ChartScoopOre RemovalHaulage LevelHaul Distance OptimizationL HDsCrusherFigure Haulage Level Information Chart2.4.4 Ventilation Level Information ChartAuxillary VentilationIntake RaiseExhaust RaiseFresh AirExhaust AirDriftsPathwaysFans/Vent DuctsChapter Three Production Control3.1 Departments in a block cave mine involved in Production ControlDesignPlanningGeologyGeo-technologyVentilationMaintenanceCave Development/ProductionSurvey body structureElectricalMechanicalHuman ResourceSafetyIn a Mine Environment each and every department plays a crucial fibre to keep the Mine running and to meet the production targets. Problems associated with these departments no matter how small they may be contribute damage in their own way to dampen the production.Production planning for block cave operations can be complex. The factors to be considered include geotechnical constraints, cave shape, draw point development sequence, draw point productivity, production block limits such as loader capacity and ore pass capacity and variable shut-off grade mining c osts. The nature of the problem also changes during the life of a cave from initial production build up to final closure.Overall objective for production planning should be to maximize productivity, some of the aspects of production planning includeMinimum/Maximum tonnage per periodMaximum total tonnage per draw pointRatio of tonnage from current drawpoint compared with other drawpoints.Height of draw of current draw point with respect to other drawpointsPercentage drawn for current draw point with respect to other drawpointsMaximum tonnage from selected groups of drawpoints in a period.3.2. Production Control Major Concerns3.2.1 FragmentationRock fragmentation is the fragment size distribution of blasted rock material, in caving operations fragmentation has a bearing onDrawpoint spacingDilution entry into the draw columnDraw controlDrawpoint productivitySecondary blasting/breaking costsSecondary blasting damagePrimary FragmentationCaving results in primary fragmentation which can b e defined as the particle size that separates from the cave back and enters the draw column. The data to be considered for the calculation of the primary fragmentation isIn situ rock mass ratingsIntact rock strengthMean joint spacing and maximum and minimum spacingOrientation of cave frontInduced stressesSecondary FragmentationSecondary fragmentation is the decline in size of the primary fragmentation particle as it moves down through the draw column. The processes to which particles are subjected to, determine the fragmentation size distribution in the drawpoints. The data to be considered for the calculation of the primary fragmentation isThe effect of fines cushioningDraw strategy and draw rateRock block strengthShape of fragmentsFrictional properties of fragmentsColumn heightFragmentation is the major factor that determines productivity from a drawpoint. Fine material will ensure high productivity.3.2.2 Draw controlDraw control is one of the major concerns that need to be optim ized in order to increase productivity of the mine. Geomechanical issues related to draw control have contend a dominant role in efforts to reduce stress and improve fragmentation and reduce dilution.Draw control is the practice of controlling the tonnages drawn from case-by-case drawpoints with the object ofMinimising dilution and maintaining the planned ore grade.Ensuring maximum ore recovery with minimum dilution.Avoiding damaging load concentrations on the extraction horizon.Avoiding the creation of conditions that could lead to air blasts or mud-rushes.The following have to be considered for draw control strategy in order to maximize productivity,Any factors observed during the start of caving that will influence the planned caving and drawdown processes.Control the draw from the first tonnage into the drawpoint.Define the potential tonnages and grades that will be available from each drawpoint.The draw control system must be fully operational. patronage that the planned draw strategy is correct.The recording and analysis of the tonnages drawn, this important aspect is often not treated with the required respect.Managing the draw by following the espouse draw strategy.Define how the control is to be monitored, maintained and audited.Planning for how the draw column would behave with time.An estimation of the remaining tonnages and grade for future production programing and planning.Personnel must be aware of the definition of isolated drawpoint.Ensure the drawpoints are clearly and correctly identified underground.There must be reportage system to record and describe why allocated drawpoints have not been drawn.Ensure secondary breakings are done effectively and efficiently.Develop standard procedure for ending drawpoints.Draw control is what block caving is about, the reasons for and the principles of draw control must be clearly understood by all operating personnel. Preparation of orebody must be done in a sound way so that preventable problems do not hamper the draw control.3.2.3 Secondary BreakingIrrespective of the method of primary blasting employed, it may be necessary to reblast a proportion of the rock which can then be handled by the loading, hauling and crushing system.There are four types of problems that cause a need for secondary breaking,High hang-ups are where a large fragment lies across the entrance to the draw bell up to 19m above the footwall. This type of hang up is very rare though, and it is more common that this will only occur up to a distance of 5 m above the draw point floor.Rock jumble is where several ore fragments of rock smaller than two cubelike meters form an arch in a drawbell. This is found to occur especially in the troat of the drawpoint.Low hang up is a large fragment of over two cubic metres hanging in the troat or on the floor of a draw point clocking the flow of ore.Draw point oversize is any large fragment over two cubic metres on the floor of a draw point and effectively prevents loa ding by LHDs.Some of the techniques that are in use for secondary breaking are as follows,Concussion blastingDrill and blastEmulsion secondary blastingRobust hydro fracturing breaking systemThere are many products on the market today that promise effective secondary breaking of both hang-ups and boulders, including cone packs, the quick draw system, the boulder buster and the penetrating cone fracture technique.In order to choose a secondary breaking method with respect to productivity the following need to considered and evaluated,Explosive quantitiesLabour and Equipment requirementsFragmentationSafety3.3 Significance of Production Management