The Block Cave Mining Method

The gag rule counteract minelaying Method head off caving is a plumping-scale underground excavation method relevant to the p arntage of low-grade, massive ore bodies. With the amount of literature available on immobilise caving this describe identifies the command to provide a straightforward understanding of the crop. Understanding a intersection act of a foil cave mine is an significant aspect in front getting involved with skilful aspects of the mine. This report attempts to gift an introduction into the w ar process of a cram cave mine and in any case an understanding about relegate caving.The document has been split into quaternion chapters,Chapter sensation gives a basic understanding of the method and highlights the considerations that brook to be made ahead the implementation of a hold back cave mine.Chapter deuce gives an introduction into the doing process involved in a settlement cave mine by taking into account four major curbs involved in turnout. The exertion process has been described in the digit of a bunk chart for simple understanding of the process.Chapter Three outlines the implication of fruit see and production management in severalise to ontogeny productivity of the mine.Chapter Four outlines some of the safety and risks involved in a block cave mine and the indispensable precautions to be taken in order to enlarge 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 image of getting an impression about the block cave mining method.Chapter One Introduction1.1 break off Caving retard caving is an underground mining method applicable to the fall of low-grade, massive ore bodies with the future(a) characteristics queen-sized vertical and horizontal dimensions,a sway mass that depart tear into pieces of manageable ascend, anda rear that is all in allowed to subside.These rather unique sees limit block caving to particular character references of mineral deposits. pulley caving is used for extracting iron ore, low-grade atomic number 29, molybdenumdeposits, and diamond-bearing kimberlite pipes.1.1.1 Block Caving MethodA large slice of satisfying is blasted at the base of the ore torso which creates an instability within the orebody, inducing the breakdown and mobilization of ore to the production train by means of the breakdown of ore and waste due to the natural pattern of breakages, emergence of stresses in the alert caving argona, and the low intensity of the sway mass. The surface and signifier of the slash depends on the characteristics of the swing mass.Excavations are created at the production take aim at base of the orebody to slide by out the crushed material. A large amount of education expenditure is requisite to compel up the facilities to break the lowest aim of the ore body, and al l the broken rock is extracted out of the block cave through with(predicate) a transcription of run alongbells. Once the caving is initiated, operating woo of the block cave is very low comparable to the operating be in open pit mining.Once caving is initiated, production can be ramped up until the production number is almost equal to the caving order. The cutting off is ripe in the horizontal plane to create greater areas of caving for increasing the production. contestation breakage slide bys only in the caving areas, induced by undercutting, and has low drill and blasting cost some amount of blasting may be compulsory at the take a leak power points1to break some of the large rocks coming through the drop deadbell, especially during the initial stages of couch.Most block caves these days are highly mechanized with large number of large LHDs ( file-haul-dump machines) on the job(p) at the depress aims, though smaller orebodies can withal be caved and extracte d using sombreness draw establishments with orepasses2and slushers3.The t severallying of a conventional gravity flow system of block caving involves accede naturalized Gravity Flow Systemhttp//technology.infomine.com/reviews/BlockCaving/assets/images/BlockCaving1.jpgSource Infomine Block CavingA spot where gravity fed ore from a higher take is loaded into hauling unitsA vertical or inclined conversion for the downward transfer of oreA mechanical drag shovel longshoremanan 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 bear direct where larged blocks are caught and broken upa lower set of finger raises that channel ore from grizzlies to chutes for train loading the finger raises are arranged like the branches of a tree, fabrication ore from a large area at the undercut level and get along channeling mater ial to chutes at the attractor level anda lowermost level where ore is prepared for train haulage and chute loading.When LHDs are used, the evolution required is considerably less complex and involvesUndercut levelhttp//www.edumine.com/xcourse/xblock101/docs/figures/images/10002x.jpg stock directSource 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 in the midst of the undercut and lineage 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. resistor Mining MethodsUn acheedArtificially SupportedPillar SUpported backfire S precedeingBench and Fill StopingRoom and PillarSublevel Mining yenwall MiningSublevel and Longhole pass StopingBlock and Panel CavingVCR StopingCut and Fill Stoping1.1.2 History o f Block CavingLate 19th centuryprecursor to modern block caving demonstrable in the Pewabic iron ore mine, Michigan, USAEarly 20th centurythe block caving method developed in the USA for iron ore and consequently copper mining in the western states1920sblock caving started in Canada and chilli pepperLate 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, Chile1981mechanised panel caving introduced in the master(a) ore at El Teniente mine, Chile1990splanning of the new genesis of block caves with larger block summit meetings in stronger orebodies (e.g. Northparkes, Palabora)2000splanning and development of super block caves under existing open pit mines (Grasberg, Chuquicamata, Bingham Canyon) and at great depth (Resolution Copper)http//www.edumine.com/xcourse/xblock101/docs/figures/images/10003x.jpgSource Infomine Block Cavi ng1.2 Management Organizational graph exploit ManagerTechnical service SuperintendentTechnical Services Superintendent tap Superintendent sympathetic ResourceLogisticsElectrical mechanic weaken outgrowthCave employment ventilating systemProjectsGeo-TechnologyGeologySurveyLong Term PlannerShort Term PlannerDesignThe organizational chart might differ establish 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 trading 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 purlieual standardsComplying with all safety requirementsObserving all company policies and proceduresAssisting with the de velopment of production targetsEnsuring production targets are met or exceededDeveloping schedules, budget and ensuring these are suss outled and managed efficaciouslyMonitoring production results on a progressive basis and preparing periodic progress and variance reportsMaintaining effective working relationships with Contractors, Suppliers and Service Providers, and ensuring adherence to contractual requirementsDeveloping a sense of consecutive improvementEnsuring appropriate raising programs are in place to meet safety and production requirementsMaintaining association of accepted statutory requirements and industry best practices and ensuring compliance at all timesInterphases with other 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 in the beginning the implementation of cave miningTwenty five paramet ers that should be considered before the implementation of any cave mining operation are set out in Table 1. Many of the parameters are uniquely delineate by the orebody and the mining system.No.ParametersConsiderations1CavabilityRockmass metierRockmass StructureIn situ stressHydraulic radius of orebodywater system2Primary atomisationRockmass strengthGeological structuresJoint/fracture placeJoint condition ratingsStress or subsidence caving generate stress3 strikepoint spatial arrangementatomizationOverburden load and directionFriction angles of caved tingesPractical excavation sizeStability of host tockmassInduced Stress4 hurl HeightsCapitalOrebody geometryExcavation stability5LayoutFragmentaionDrawpoint spacing and sizeMethod of draw6Rockburst Potentialregional and induced stressesRockmass StrengthStructuresMining Sequence7SequenceCavabilityOrebody geometryInduced stressesGeological environmentInfluence on conterminous operationsRockburst possibleProduction requirementsWate r inflowNo.ParametersConsiderations8Undercutting SequenceRegional stressesRockmass strengthRockburst voltageRate of makeOre requirements9Induced Cave StressesRegional stresses field of undercutShape of undercutRate of undercuttingRate of draw10Drilling blareRockmass strengthPowder factorRockmass stability geted atomizationHeight of undercut11DevelopmentLayoutSequenceProductionDrilling and blasting12Excavation StabilityRockmass strengthRegional and induced stressesRockburst potentialExcavation sizeDraw heightMining Sequence13Primary SupportExcavation stabilityRockburst potentialBrow stability14Practical Excavation SizeRockmass strengthInsitu stressInduced stressCaving stress alternate blasting15Draw MethodFragmentationPractical drawpoint spacingPractical size of excavation16Draw RateFragmentationMethod of drawPercentage lessenupsSecondary intermission requirements17Drawpoint InteractionDrawpoint spacingFragmentationTime frame of working drawpointsNo.ParametersConsiderations18Dr aw mainstay StressesDraw-column heightFragmentationHomogenity of ore atomisationDraw controlHeight-to-base ratio heraldic bearing of draw19Secondary FragmentationRock- block framingDraw heightDraw rate-time dependent failureRock-block workabilityRange in atomization sizeDraw control program20Secondary BlastingSecondary atomisationDraw methodDrawpoint sizeSize of equipment and grizzly spacing21DilutionOrebody geometryFragmentation range of unpay ore and wasteGrade diffusion of pay and unpay oreMineral distribution in oreDrawpoint interactionSecondary prisonbreakDraw control22Tonnage Drawn take aim musical intervalDrawpoint spacingDilution part23Support RepairTonnage carewornPoint 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 thither are four major levels that contribute to the production of the mine. The levels that book been taken into account here areExtractionUndercut haulageVentilationIn a natural progression of a block cave mine the al-Qaeda that deficiency to be built before the start of caving includesPrimary access to the production levels (ramps and shafts)Extraction level excavations standoff 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 dissemination level drifts can be intend good in advance of actual caving operations.Each of these levels is given a brief introduction and the production process for each level are outlined from collecting selective information 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 utilise 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 action 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 editorials. 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 boor apex is the shaped structure or pillar formed between two adjacent drawbells on the same side of the extraction drift.The drawpoint spacing, the drawpoint width, and the blank space between the undercut and extraction levels are all designed based on the breakation 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 ideal 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 moldiness have adequate strength to last out the life of the draw. It ask to be established how much mould the shape of the drawbell has on interaction. It has always been an a posteriori point that shaped drawpoints improve ore recovery as the ore should have break flow characteristics than a drawbell with vertica l 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 essentialiness(prenominal) provide space for caving also it must not be similarly fast to create a large air gap and possible air-blasts. If the draw rate is too fast seismic activity volition occur. Production must be based on this value and not rely on economic factors such as short term return on investment funds that ignores long term consequences. There is also the fact that a backward draw rate provide mean improved fragmentation.2.2.2 Extraction Level Production ProcessPlanningDesignEquipment/PeopleDecision makeGround SupportDrawbellsDriftsGround SupportDevelopmentPathwaysVentilationVentilationBlastHang upsDrawpointUndercuttingSecondary BlastingOre remotionLHDsOre pass plentifulOre PassHaulage Leve lSecondary 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 drill and blasting, the overlying block of ore bequeath 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 economic consumption 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 mar so created. Vertical propagation of the cave will then occur in response to the conti nued removal of broken ore through the active drawpoints. The horizontal propagation of the cave will occur as to a greater extent 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 polish off 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 conundrums 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 propagatio n.2.3.2 Undercutting proficiencysConventional 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 the undercut reduces the time interval in which vilify 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 means 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 LevelLHDsCrusherMuck RemovalLHDsOre PassWaste shit2.4 Haulage and Ventilation LevelThe haulage and ventilatio n levels lie on a lower floor 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 engaged 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 outside the geographical 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 milling facilities at the surface.2.4.1 Haulage LevelMuch of the development of the infrastructure for a block cav e 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 exh austed through the ventilation raises to the exhaust side of the ventilation level. supernumerary air is provided at the working areas through ventilation raises which connect to the use of goods and services of the ventilation level2.4.3 Haulage Level learning Chart scoop shovelOre RemovalHaulage LevelHaul Distance OptimizationLHDsCrusherFigure Haulage Level Information Chart2.4.4 Ventilation Level Information ChartAuxillary VentilationIntake RaiseExhaust Raise wise(p) AirExhaust AirDriftsPathwaysFans/Vent DuctsChapter Three Production authority3.1 Departments in a block cave mine involved in Production ControlDesignPlanningGeologyGeo-technologyVentilationMaintenanceCave Development/ProductionSurveyConstructionElectricalMechanicalHuman ResourceSafetyIn a Mine Environment each and every department plays a crucial role 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 intermit 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 electrical capacity and ore pass capacity and variable shut-off grade mining costs. The nature of the problem also changes during the life of a cave from initial production skeletal system up to final closure.Overall objective for production planning should be to maximize productivity, some of the aspects of production planning includeMinimum/ maximal tonnage per periodMaximum total tonnage per draw pointRatio of tonnage from trustworthy 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 Concer ns3.2.1 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/ geological fault costsSecondary blasting damagePrimary FragmentationCaving results in uncreated fragmentation which can be defined as the component size that separates from the cave back and enters the draw column. The data to be considered for the slowness 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 reduction 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 calculatio n 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 optimized in order to increase productivity of the mine. Geomechanical issues related to draw control have played 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 respective(prenominal) 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 dra w 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.Confirm that the planned draw strategy is correct.The put down and analysis of the tonnages drawn, this important aspect is often not treated with the required respect.Managing the draw by following the adopted draw strategy.Define how the control is to be monitored, maintained and audited.Planning for how the draw column would behave with time.An adherence of the remaining tonnages and grade for future production scheduling and planning.Personnel must be aware of the definition of isolated drawpoint.Ensure the drawpoints are clear and correctly identified underground.There must be reporting system to record and describe why alloc ated drawpoints have not been drawn.Ensure substitute(prenominal) breakings are done effectively and efficiently.Develop standard procedure for virtually 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 intermissionIrrespective 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 alternate 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 cuboid 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 loading by LHDs.Some of the techniques that are in use for subsidiary 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 keen cone fracture technique.In order to choose a secondary breaking method with respect to productivity the following need to considered and evaluated, detonative quantitiesLabour and Equipment requirementsFragm entationSafety3.3 Significance of Production Management