Competition????https://www.faqs.org/patents/app/20080224527
atent title: CONTINUOUS EXTRACTION OF UNDERGROUND NARROW-VEIN METAL-BEARING DEPOSITS BY THERMAL ROCK FRAGMENTATION
Abstract:
A method for extracting minerals from a narrow-vein deposit by thermalfragmentation is provided. The method includes locating the vein anddetermining the extent thereof to form the boundaries of a stope. Accessto the stope is prepared by forming a panel having an upper drift and alower drift. Equipment for thermal fragmentation, including a burner, isinstalled from the upper drift. The burner moves along the panel surfacein a sweeping motion, while rock chips spalled from the rock panelsurface are collected. Multiple panels for processing can be realised,with lower panels being processed before upper panels, by excavating asub-level to separate the lower and upper panels.
Claims:
1. A method of extracting minerals from narrow-vein deposit comprising thesteps of:ascertaining the extent of the vein and establishing anextraction zone of material which extends beyond the extent of thevein;exposing a surface of the extraction zone;providing a source of heatcapable of inducing thermal fragmentation of the material in theextraction zone;moving the source of heat across the surface whilemaintaining sufficient proximity thereto to heat the material from thesurface inwardly so as to cause thermal fragmentation of the material onthe surface; andcollecting the fragmented material.
2. The method according to claim 1 wherein the movement of the source ofheat is in a repetitive sweeping pattern so as to remove layers of thematerial sequentially from the extraction zone.
3. The method according to claim 1 wherein the source of heat is a plasmatorch.
4. The method according to claim 1 wherein the step of collecting isperformed simultaneously with the thermal fragmentation step.
5. The method accordingly to claim 1, wherein the source of heat is movedat a rate which is sufficient so as to substantially avoid localizedfusion of the material on the surface.
6. The method accordingly to claim 5, wherein said rate is sufficient soas to break the surface of the deposit into fragments of a size of about2 cm or less.
7. A method for using a plasma torch for extraction of narrow-vein mineraldeposits, comprising:moving the plasma torch across a surface of thedeposit at a rate while maintaining sufficient proximity of the plasmatorch with the surface of the deposit, so that heat from the plasma torchheats the deposit from the surface inwardly so as to induce thermalfragmentation of a surface layer of the deposit.
8. The method of claim 7 wherein the plasma torch is moved in asemi-repetitive pattern to remove successive layers of the deposit.
9. The method for using a plasma torch as claimed in claim 7, wherein saidrate is sufficient so as to substantially avoid localized fusion ofmaterial on the surface of the deposit from the heat of the plasma torch.
10. The method for using a plasma torch as claimed in claim 7, whereinsaid rate is sufficient so as to break the surface of the deposit intofragments of a size of about 2 cm. or less.
11. A method for using a single plasma torch for extraction of narrow-veinmineral deposits, comprising:moving the plasma torch across an exposedsurface of the deposit at a rate while maintaining sufficient proximityof the plasma torch with the surface of the deposit, so that heat fromthe plasma torch heats the surface of the deposit so as to induce thermalfragmentation of a surface layer of the deposit.
12. The method of claim 11 wherein the plasma torch is moved in asemi-repetitive pattern to remove successive layers of the deposit.
13. The method of claim 11, wherein said rate is sufficient so as tosubstantially avoid localized fusion of material on the surface of thedeposit from the heat of the plasma torch.
14. The method of claim 11, wherein said rate is sufficient so as to breakthe surface of the deposit into fragments of a size of about 2 cm orless.
Description:
CROSS REFERENCE TO RELATED APPLICATIONS
[0001]This application is a continuation under 35 U.S.C. 120 of copendingU.S. application Ser. No. 10/836,616, filed May 3, 2004, which isscheduled to issue as U.S. Pat. No. 7,377,593 on May 27, 2008.
FIELD OF THE INVENTION
[0002]The present invention relates to a method for extracting mineralsfrom a narrow-vein mining deposit through utilization of athermal-induced rock fragmentation to channel out the mineralization.
BACKGROUND OF THE INVENTION
[0003]Exploitation of narrow-vein deposits represents great challenges.Highly selective mining methods for this type of exploitation areassociated with high operational constraints that interfere withmechanization. Conventional methods require a substantial amount ofskilled manpower, which is becoming a scarce commodity. High operationalcosts results in the profitability of these deposits to be rather risky.In order to ensure the survival of this type of exploitation, it iscrucial to develop innovative equipment and mining methods.
[0004]The mineral inventory of a mining operation is classified intoreserves and resources, reserves being the economically mineable part.Resources involve a level of geological knowledge that is usuallyinsufficient to enable an appropriate economic evaluation or, in somecases, the estimated grade is lower than the economic grade.
[0005]In recent years, the long-hole mining method has been used in somenarrow-vein ore mining operations. Such a method is not always suitableto the operation conditions. Implementation of the method involves largeblasts that damage the rock mass with several fractures that cause rockface instability resulting in frequent fall of waste rock. This wastemixes up with the broken ore and adds to the planned dilution in reserveestimate. Like the ore, this waste rock must be mucked and processed,significantly increasing operation costs.
SUMMARY OF THE INVENTION
[0006]One aspect of the present invention relates to a method forextracting minerals from a narrow-vein deposit. Location of the vein anddetermination of the extent thereof forms the boundaries of the stope.Access to the stope is prepared by excavating an upper drift and a lowerdrift to form a panel therebetween. Equipment and a burner are installedfrom the upper drift. The burner is moved along a panel surface in apredetermined pattern, while spalled rock chips from the panel surfaceare collected at the lower drift. By providing highly selectiveextraction of ore, thermal fragmentation allows for substantial savingson ore transportation, ore processing and on the environmental level byreducing the generated waste volume.
[0007]Another aspect of the invention relates to a method of extractingminerals from narrow-vein deposit including the step of ascertaining theextent of the vein and establishing an extraction zone of material, whichextends beyond the extent of the vein. A surface of the extraction zoneis then exposed after which a source of heat is provided, capable ofinducing thermal fragmentation of the material in the extraction zone.The source of heat is moved across the surface while maintainingsufficient proximity to cause thermal fragmentation of the material onthe surface. The fragmented material is collected.
[0008]Another aspect of this invention includes the use of a plasma torchfor extraction of narrow-vein mineral deposits. The plasma torch is movedacross a surface of the deposit, in a sweeping movement, at a rate which,while maintaining sufficient proximity of the plasma torch with thesurface of the deposit, induces thermal fragmentation to a layer of thedeposit.
BRIEF DESCRIPTION OF THE DRAWINGS
[0009]The following description will be more readily understood withreference to the drawings in which a preferred embodiment of theinvention is illustrated.
[0010]FIG. 1A is an elevational view of a cross-section of a stope, withFIG. 1B being a plan view thereof, showing a first phase of theoperation.
[0011]FIG. 2A is an elevational of a cross-section of a stope, with FIG.2B being a plan view thereof, showing a second phase of the operation.
[0012]FIG. 3A is an elevational of a cross-section of a stope, with FIG.3B being a plan view thereof, showing a third phase of the operation.
[0013]FIG. 4A is an elevational view of a cross-section of a stope, withFIG. 4B being a plan view thereof, showing a fourth phase of theoperation.
[0014]FIG. 5A is an elevational view of a cross-section of a stope, withFIG. 5B being a plan view thereof, showing a fifth phase of theoperation.
[0015]FIGS. 6A and 6B are schematic diagrams in plan view comparingthermal torch fragmentation method versus the prior art long-hole miningmethod.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0016]A mining method generally consists of four distinct steps: drilling,blasting, mucking, and transport of the ore to the shaft for hoisting tothe surface. The application of the method described herein enables areduction in the required number of steps; drilling and blasting beingreplaced by a single step of continuous rock fragmentation.
[0017]The present invention provides a method of using a burner to exploitunderground narrow-vein metalliferous deposits by thermal fragmentation,through sweeping in a sequence across the height and width of the vein.Most of the items or equipment required to perform the method are incommon usage in mining operations, except for the plasma torch equipmentand a vacuum system to draw off the ore. A plasma torch is used as thesource of heat by which thermal fragmentation or spalling of a surfacelayer of the deposit is induced. While other types of burners could beutilized, plasma torches are preferred as they do not produce theemissions that combustible fuel torches do. Plasma torches produceintense heat and the higher rate of heating expedites the thermalfragmentation process. The intense heat, however, necessitates themovement of the torch in a sweeping pattern to avoid localized fusion ofthe rock.
[0018]FIGS. 1A and 1B illustrate the general arrangement of a standardstope 10. In a first phase, cross-cuts 12,13 are developed to access theupper and lower levels of a mineralized block 14. These accesses 12,13are planned to intercept mineralization at the block centre 16, thusseparating the stope 10 in two. From the upper and lower accesses 12,13,upper and lower drifts 18,20 are developed in the ore. The plan view ofFIG. 1B shows the stope accesses 12,13 leading to the drifts 18,20. Thesedrifts 18,20 represent the upper and lower limits of the stope 10 to beprocessed. Preferably, the maximum distance on either side of the stopeaccess is limited to 50 meters, which will ensure proper efficiency ofthe vacuum devices and plasma torch. One skilled in the art wouldappreciate the distance may vary according to the limitations ofdifferent equipment.
[0019]After the stope accesses 12,13 and drifts 18,20 are completed, aservice raise 22 is excavated at the block centre 16. The main purpose ofthe raise 22 is to enable workers to access sub-levels, transportequipment and to supply required ventilation, water, air and electriclines.
[0020]From the service raise 22, a sub-level 24 is preferably excavated toreduce the vertical mining distance in order to easily follow themineralization, which is generally not rectilinear over long distances.Slot raises 26,28 are also developed at each stope extremity to allowinitial installation of the plasma torch equipment (not shown in FIGS. 1Aand 1B). Finally, small openings 30 are preferably excavated in the upperand lower stope cross-cuts accesses for the installation of the vacuumdevice and the equipment required to operate the plasma torch. The finalarrangement of the various drifts and raises results in the mineral block14 being sectioned into a plurality of panels 32.
[0021]Preliminary tests that were performed on granite blocks demonstratedthat rock is broken into small chips or fragments by moving a plasmatorch along the rock surface. This rock-fracturing through thermalfragmentation occurs as a result of thermal shock created by the plasmatorch flame on contact with the rock surface. The generated chips have adimension that is usually less than 2 cm.
[0022]As shown in FIGS. 2A and 2B, burner equipment 34 is installed fromthe sub-level 24 or from the drift located above the section to beextracted. During fragmentation, the burner 36 is moved from top tobottom in a back-and-forth movement, as well as from left to rightbetween the sidewalls of the panel. When the spalling efficiencydiminishes, a mechanism associated with the equipment 34 brings theburner 36 closer to the rock face 38. Once the mechanism reaches amaximum extension, all of the equipment 34 is brought closer to the face38 and spalling continues. Preferably the burner 36 is moved at acontrolled rate through a predetermined pattern.
[0023]As indicated above, the preferred embodiment of the stope 10 isseparated into four panels 32 and each panel 32 is extractedconsecutively in a predetermined sequence. After the extraction of apanel 32 as shown in FIG. 3A, an opening is created between two driftsor, in the case of FIG. 3A, between the lower drift 20 and the sub-level24; consequently, it will be impossible to travel in the lower drift.Thus, extraction should begin in the lower panels 32a, 32b and then moveupward.
[0024]As the burner 36 sweeps along the rock face 38, the rock chips 42are extracted. Since this mining method is directed towards a highlyselective ore extraction, the excavated rock volume is low while thegrade of the rock is high. The low rock volume produced to be handledenables a simple mucking system to be implemented at a low cost. Anexample of such a system is shown in FIGS. 2A and 2B which uses a metalcontainer 44 that can hold up to 8 tons of ore. The container 44 ispositioned directly under the work face 38 at the base of the opening 40to recover the falling rock fragments 42. The winch 52 hoists thecontainer to follow the mining process. Afterwards, the accumulated oreis vacuumed by the vacuum system 46 through vacuum hoses 48 into a minecar 50. It is suggestible to perform mucking twice per work shift,thereby eliminating the requirement of having a full-time employee onmucking operations.
[0025]The mining sequence of the preferred stope embodiment is shown inFIGS. 2A to 5A. Firstly, the plasma torch equipment 34 is installed inthe sub-level 24 above panel 32a, as shown in FIG. 2A. The ore container44 and the winch 52 are installed in the lower drift. The vacuum system46 is located in the lower stope access 13 and a hose 48 of sufficientlength is used to vacuum the accumulated ore from inside the container44. The burner 34 is moved across the rock surface 38 in a repetitivesweeping movement to remove successive layers of rock 38, while thecontainer 44 is moved in unison with the burner equipment 34 tocontinuously catch the falling rock fragments 42. Preferably, not theentire panel 32a is removed so as to leave a supporting pillar 54 (seeFIG. 3B). Once panel 32a is complete, the equipment 34 is transferred tothe opposite lower panel 32b for use in a similar arrangement, as shownin FIG. 3B.
[0026]In order to extract upper panels 32c, 32d, the plasma torchequipment 34 is mobilized in the upper drift 18 and the mucking equipmentis installed in the sub-level 24, as shown in FIGS. 4A and 5A. However,the opening 40 created during the extraction phases, as shown in FIGS. 2Aand 3A, extends through the sub-level floor an approximate width of 45cm, as shown in FIG. 6A. Therefore, workers should be secured duringtheir displacement, such as by securely tying themselves to a lifeline.Furthermore, depending on ground conditions, construction of a floorcould be required to block access to the opening.
[0027]The vacuum system 46 remains in the lower access 13 throughout theextraction of the stope 10 and the suction hose 48 is extended asrequired. As mentioned previously, the service raise 22 or slot raises26,28 are used to move equipment inside the stope 10.
[0028]The application of the thermal fragmentation method with a burner orplasma torch allows for high selectivity, the possibility ofmechanization, continuous mining, immediate ore recovery, and eliminationof the use of explosives. FIG. 6A shows that the opening 40 formed withthe present thermal fragmentation method is 4 times smaller than theopening 60 formed through traditional long-hole mining with explosives asseen in FIG. 6B, therefore much less waste 62 is generated. Theboundaries of the extraction zone 64 for the thermal fragmentationmethod, shown by dotted lines 66 in FIG. 6A, which extend beyond theascertained width 68 of the vein 70, can be much narrower than therequired extraction zone 74 for the long hole blasting method, shown bydotted lines 76 in FIG. 6B, which extend significantly beyond theascertained width 78 of the vein 80, thus leading to greater amount ofwaste 62 in the mined ore.
[0029]Furthermore, after the extraction, the walls 82 have more stabilitythan walls 84 that have been massively fractured, as through long-holeblasting methods. Mineral recovery is immediate, as compared toconventional methods in which the mineral may remain underground ininventory for a period of time, sometimes being non-recoverable due tostope instability, which results in significant financial loss.
[0030]As shown in Table 1, selective mining allows for a substantialreduction in extracted tonnage. A smaller volume of rocks for handlingand processing directly impacts operation costs. Moreover, a continuouspenetration in the rock allows dynamic readjustment of the extraction inorder to stay inside the mineralized zone and consequently avoid dilutionfrom mining.
[0031]The method of the present invention allows for continuous extractionsince the process do not generate large amount of gas compared with theexplosives. A 7-day work schedule is therefore possible, rather than thetypical 5-day work schedule currently employed in narrow-vein mines. Sucha work schedule would increase annual production, thereby decreasingindirect operational and depreciation costs.
TABLE-US-00001TABLE 1Comparison of thermal fragmentation withplasma torch and long-hole mining methodsCalculated Tonnage base on a Thermal Long-reserve block of 100 m by 45 m Fragmentation holeGrade in situ (oz/s. ton) 1.70 1.70Width in situ (cm) 30 30Ore developmentDevelopment tonnage (s. ton) 6 506 8 130Development grade (oz/s. ton) 0.22 0.22MiningGeological reserves (s. ton) 3 166 2 965Grade of geological 1.70 1.70reserves (g/t) 45 180Minimum width (cm) 50% 500%Planned dilution 0% 35%Walls dilution 95% 85%Stope recovery 4 511 20 413Planned mining reserves (s. ton) 1.13 0.21Mined gradeMill recovery 95% 95%Produced ounces 6 220 5 757(stope and development)Thermal fragmentation Long-holeUnit cost Total Unit cost Total$/s. ton $ $/s. ton $Development 354 252 462 889Mining cost ($/t) 58.20 262 564 19.00 387 852Mucking 5.00 22 557 4.00 81 653Transport to mill 5.50 24 813 5.50 112 273(stope)Transport to mill 5.50 35 785 5.50 44 714(development)Milling (stope) 10.37 46 783 12.20 249 042Milling 12.20 79 377 12.20 99 183(development)TOTAL 826 131 1 437 607CAN$ per short ton 74.98 50.37CAN$ per ounce 132.82 249.71US$ per ounce 0.65 86.34 162.31
Experimental Setup
[0032]A test case was conducted by elaborating a mining concept usingthermal rock fragmentation with a plasma torch to mine extremely narrowveins. The test case was developed according to commonly found stopedimensions in mining operations. A stope height of 45 meters wasselected, which corresponds to the standard distance between two levels.For equipment operational reasons, the maximum length was fixed to 100meters. Table 2 lists the details of development of the stope.
TABLE-US-00002TABLE 2Details of developmentsWidth Height Length(m) (m) (m)Upper access 2.7 2.7 10Lower access 2.7 2.7 10Upper ore drift 2.4 2.4 100Lower ore drift 2.4 2.4 100Service raise 2.4 2.4 40Sub-level 2.4 2.4 98Slot raises 1.8 1.8 76Excavation for plasma torch equipment 3.0 2.4 4.5Excavation for vacuum 3.0 2.7 4.5
[0033]One skilled in the art will appreciate that variations in the numberof panels is possible. As an example, excavation could be performed in asingle lower panel 1 or 2 without forming or expanding to the upperpanels 3 or 4.
[0034]Another variation exists in the sweeping of the burner. The burnercan be swept from left to right or right to left, while progressing fromthe top of the stope panel to the bottom. Alternatively, sweeping canoccur from top to bottom, while progressing from left to right or rightto left. The pattern and rate of motion of the burner/plasma torch willbe dependent on several factors, including but not limited to thephysical dimensions of the deposit, the composition of the deposit,variations in the deposit, desired fragmentation rate/volume, type andoutput of the burner/plasma torch, etc. The rate and pattern can bepredetermined through theoretical considerations and/or empiricalevaluation of test samples. The rate and pattern can also be adapteddynamically during the process to ensure optimization of fragmentation.Optimization does not necessarily mean increased fragment size, asfragment size can have an affect on the removal process in the case ofvacuum removal, for example, or on subsequent processing steps.Volumetric removal rate (yield) is typically a better indicator ofefficiency.
[0035]Another embodiment of the present invention provides for automaticoperation of the equipment. Thus, the operator can safely remain in aworkplace outside of the stope, while the automatic equipment operateswithin the stope. Cameras can be used to monitor progress. Furthermore,automatic detection of surface edges could be employed, further reducinginput required from an external operator and eliminating the need forcameras. In such an automatic system, the burner could be provided on aplatform extending up from the floor of the lower drift.
[0036]While there has been shown and described herein a method forcontinuous extraction of deposits in narrow-vein mining applications, itwill be appreciated that various modifications and or substitutions maybe made thereto without departing from the spirit and scope of theinvention.