Abstract:
A method for extracting minerals from a narrow-vein deposit by thermal fragmentation is provided. The method includes locating the vein and determining the extent thereof to form the boundaries of a stope. Access to the stope is prepared by forming a panel having an upper drift and a lower drift. Equipment for thermal fragmentation, including a burner, is installed from the upper drift. The burner moves along the panel surface in a sweeping motion, while rock chips spalled from the rock panel surface are collected. Multiple panels for processing can be realised, with lower panels being processed before upper panels, by excavating a sub-level to separate the lower and upper panels.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is a continuation under 35 U.S.C. 120 of copending U.S. application Ser. No. 10/836,616, filed May 3, 2004, which is scheduled 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 minerals from a narrow-vein mining deposit through utilization of a thermal-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 are associated with high operational constraints that interfere with mechanization. Conventional methods require a substantial amount of skilled manpower, which is becoming a scarce commodity. High operational costs results in the profitability of these deposits to be rather risky. In order to ensure the survival of this type of exploitation, it is crucial to develop innovative equipment and mining methods. 
         [0004]    The mineral inventory of a mining operation is classified into reserves and resources, reserves being the economically mineable part. Resources involve a level of geological knowledge that is usually insufficient to enable an appropriate economic evaluation or, in some cases, the estimated grade is lower than the economic grade. 
         [0005]    In recent years, the long-hole mining method has been used in some narrow-vein ore mining operations. Such a method is not always suitable to the operation conditions. Implementation of the method involves large blasts that damage the rock mass with several fractures that cause rock face instability resulting in frequent fall of waste rock. This waste mixes up with the broken ore and adds to the planned dilution in reserve estimate. 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 for extracting minerals from a narrow-vein deposit. Location of the vein and determination of the extent thereof forms the boundaries of the stope. Access to the stope is prepared by excavating an upper drift and a lower drift to form a panel therebetween. Equipment and a burner are installed from the upper drift. The burner is moved along a panel surface in a predetermined pattern, while spalled rock chips from the panel surface are collected at the lower drift. By providing highly selective extraction of ore, thermal fragmentation allows for substantial savings on ore transportation, ore processing and on the environmental level by reducing the generated waste volume. 
         [0007]    Another aspect of the invention relates to a method of extracting minerals from narrow-vein deposit including the step of ascertaining the extent of the vein and establishing an extraction zone of material, which extends beyond the extent of the vein. A surface of the extraction zone is then exposed after which a source of heat is provided, capable of inducing thermal fragmentation of the material in the extraction zone. The source of heat is moved across the surface while maintaining sufficient proximity to cause thermal fragmentation of the material on the surface. The fragmented material is collected. 
         [0008]    Another aspect of this invention includes the use of a plasma torch for extraction of narrow-vein mineral deposits. The plasma torch is moved across a surface of the deposit, in a sweeping movement, at a rate which, while maintaining sufficient proximity of the plasma torch with the surface of the deposit, induces thermal fragmentation to a layer of the deposit. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0009]    The following description will be more readily understood with reference to the drawings in which a preferred embodiment of the invention is illustrated. 
           [0010]      FIG. 1A  is an elevational view of a cross-section of a stope, with  FIG. 1B  being a plan view thereof, showing a first phase of the operation. 
           [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, with  FIG. 4B  being a plan view thereof, showing a fourth phase of the operation. 
           [0014]      FIG. 5A  is an elevational view of a cross-section of a stope, with  FIG. 5B  being a plan view thereof, showing a fifth phase of the operation. 
           [0015]      FIGS. 6A and 6B  are schematic diagrams in plan view comparing thermal torch fragmentation method versus the prior art long-hole mining method. 
       
    
    
     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 to the surface. The application of the method described herein enables a reduction in the required number of steps; drilling and blasting being replaced by a single step of continuous rock fragmentation. 
         [0017]    The present invention provides a method of using a burner to exploit underground 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 in common usage in mining operations, except for the plasma torch equipment and a vacuum system to draw off the ore. A plasma torch is used as the source of heat by which thermal fragmentation or spalling of a surface layer of the deposit is induced. While other types of burners could be utilized, plasma torches are preferred as they do not produce the emissions that combustible fuel torches do. Plasma torches produce intense heat and the higher rate of heating expedites the thermal fragmentation process. The intense heat, however, necessitates the movement of the torch in a sweeping pattern to avoid localized fusion of the rock. 
         [0018]      FIGS. 1A and 1B  illustrate the general arrangement of a standard stope  10 . In a first phase, cross-cuts  12 , 13  are developed to access the upper and lower levels of a mineralized block  14 . These accesses  12 , 13  are planned to intercept mineralization at the block centre  16 , thus separating 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 of  FIG. 1B  shows the stope accesses  12 , 13  leading to the drifts  18 , 20 . These drifts  18 , 20  represent the upper and lower limits of the stope  10  to be processed. Preferably, the maximum distance on either side of the stope access is limited to 50 meters, which will ensure proper efficiency of the vacuum devices and plasma torch. One skilled in the art would appreciate the distance may vary according to the limitations of different equipment. 
         [0019]    After the stope accesses  12 , 13  and drifts  18 , 20  are completed, a service raise  22  is excavated at the block centre  16 . The main purpose of the raise  22  is to enable workers to access sub-levels, transport equipment and to supply required ventilation, water, air and electric lines. 
         [0020]    From the service raise  22 , a sub-level  24  is preferably excavated to reduce the vertical mining distance in order to easily follow the mineralization, which is generally not rectilinear over long distances. Slot raises  26 , 28  are also developed at each stope extremity to allow initial installation of the plasma torch equipment (not shown in  FIGS. 1A and 1B ). Finally, small openings  30  are preferably excavated in the upper and lower stope cross-cuts accesses for the installation of the vacuum device and the equipment required to operate the plasma torch. The final arrangement of the various drifts and raises results in the mineral block  14  being sectioned into a plurality of panels  32 . 
         [0021]    Preliminary tests that were performed on granite blocks demonstrated that rock is broken into small chips or fragments by moving a plasma torch along the rock surface. This rock-fracturing through thermal fragmentation occurs as a result of thermal shock created by the plasma torch flame on contact with the rock surface. The generated chips have a dimension that is usually less than 2 cm. 
         [0022]    As shown in  FIGS. 2A and 2B , burner equipment  34  is installed from the sub-level  24  or from the drift located above the section to be extracted. During fragmentation, the burner  36  is moved from top to bottom in a back-and-forth movement, as well as from left to right between the sidewalls of the panel. When the spalling efficiency diminishes, a mechanism associated with the equipment  34  brings the burner  36  closer to the rock face  38 . Once the mechanism reaches a maximum extension, all of the equipment  34  is brought closer to the face  38  and spalling continues. Preferably the burner  36  is moved at a controlled rate through a predetermined pattern. 
         [0023]    As indicated above, the preferred embodiment of the stope  10  is separated into four panels  32  and each panel  32  is extracted consecutively in a predetermined sequence. After the extraction of a panel  32  as shown in  FIG. 3A , an opening is created between two drifts or, in the case of  FIG. 3A , between the lower drift  20  and the sub-level  24 ; consequently, it will be impossible to travel in the lower drift. Thus, extraction should begin in the lower panels  32   a ,  32   b  and then move upward. 
         [0024]    As the burner  36  sweeps along the rock face  38 , the rock chips  42  are extracted. Since this mining method is directed towards a highly selective ore extraction, the excavated rock volume is low while the grade of the rock is high. The low rock volume produced to be handled enables a simple mucking system to be implemented at a low cost. An example of such a system is shown in  FIGS. 2A and 2B  which uses a metal container  44  that can hold up to 8 tons of ore. The container  44  is positioned directly under the work face  38  at the base of the opening  40  to recover the falling rock fragments  42 . The winch  52  hoists the container to follow the mining process. Afterwards, the accumulated ore is vacuumed by the vacuum system  46  through vacuum hoses  48  into a mine car  50 . It is suggestible to perform mucking twice per work shift, thereby eliminating the requirement of having a full-time employee on mucking operations. 
         [0025]    The mining sequence of the preferred stope embodiment is shown in  FIGS. 2A to 5A . Firstly, the plasma torch equipment  34  is installed in the sub-level  24  above panel  32   a , as shown in  FIG. 2A . The ore container  44  and the winch  52  are installed in the lower drift. The vacuum system  46  is located in the lower stope access  13  and a hose  48  of sufficient length is used to vacuum the accumulated ore from inside the container  44 . The burner  34  is moved across the rock surface  38  in a repetitive sweeping movement to remove successive layers of rock  38 , while the container  44  is moved in unison with the burner equipment  34  to continuously catch the falling rock fragments  42 . Preferably, not the entire panel  32   a  is removed so as to leave a supporting pillar  54  (see  FIG. 3B ). Once panel  32   a  is complete, the equipment  34  is transferred to the opposite lower panel  32   b  for use in a similar arrangement, as shown in  FIG. 3B . 
         [0026]    In order to extract upper panels  32   c ,  32   d , the plasma torch equipment  34  is mobilized in the upper drift  18  and the mucking equipment is 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. 2A and 3A , extends through the sub-level floor an approximate width of 45 cm, as shown in  FIG. 6A . Therefore, workers should be secured during their displacement, such as by securely tying themselves to a lifeline. Furthermore, depending on ground conditions, construction of a floor could be required to block access to the opening. 
         [0027]    The vacuum system  46  remains in the lower access  13  throughout the extraction of the stope  10  and the suction hose  48  is extended as required. As mentioned previously, the service raise  22  or slot raises  26 , 28  are used to move equipment inside the stope  10 . 
         [0028]    The application of the thermal fragmentation method with a burner or plasma torch allows for high selectivity, the possibility of mechanization, continuous mining, immediate ore recovery, and elimination of the use of explosives.  FIG. 6A  shows that the opening  40  formed with the present thermal fragmentation method is 4 times smaller than the opening  60  formed through traditional long-hole mining with explosives as seen in  FIG. 6B , therefore much less waste  62  is generated. The boundaries of the extraction zone  64  for the thermal fragmentation method, shown by dotted lines  66  in  FIG. 6A , which extend beyond the ascertained width  68  of the vein  70 , can be much narrower than the required extraction zone  74  for the long hole blasting method, shown by dotted lines  76  in  FIG. 6B , which extend significantly beyond the ascertained width  78  of the vein  80 , thus leading to greater amount of waste  62  in the mined ore. 
         [0029]    Furthermore, after the extraction, the walls  82  have more stability than walls  84  that have been massively fractured, as through long-hole blasting methods. Mineral recovery is immediate, as compared to conventional methods in which the mineral may remain underground in inventory for a period of time, sometimes being non-recoverable due to stope instability, which results in significant financial loss. 
         [0030]    As shown in Table 1, selective mining allows for a substantial reduction in extracted tonnage. A smaller volume of rocks for handling and processing directly impacts operation costs. Moreover, a continuous penetration in the rock allows dynamic readjustment of the extraction in order to stay inside the mineralized zone and consequently avoid dilution from mining. 
         [0031]    The method of the present invention allows for continuous extraction since the process do not generate large amount of gas compared with the explosives. A 7-day work schedule is therefore possible, rather than the typical 5-day work schedule currently employed in narrow-vein mines. Such a work schedule would increase annual production, thereby decreasing indirect operational and depreciation costs. 
         [0000]    
       
         
               
             
               
               
               
               
             
               
               
               
             
               
               
               
               
               
             
           
               
                 TABLE 1 
               
               
                   
               
               
                 Comparison of thermal fragmentation with 
               
               
                 plasma torch and long-hole mining methods 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                   
                 Calculated Tonnage base on a 
                 Thermal 
                 Long- 
               
               
                   
                 reserve block of 100 m by 45 m 
                 Fragmentation 
                 hole 
               
               
                   
                   
               
               
                   
                 Grade in situ (oz/s. ton) 
                 1.70 
                 1.70 
               
               
                   
                 Width in situ (cm) 
                 30 
                 30 
               
               
                   
                 Ore development 
               
               
                   
                 Development tonnage (s. ton) 
                 6 506 
                 8 130 
               
               
                   
                 Development grade (oz/s. ton) 
                 0.22 
                 0.22 
               
               
                   
                 Mining 
               
               
                   
                 Geological reserves (s. ton) 
                 3 166 
                 2 965 
               
               
                   
                 Grade of geological 
                 1.70 
                 1.70 
               
               
                   
                 reserves (g/t) 
                 45 
                 180 
               
               
                   
                 Minimum width (cm) 
                 50% 
                 500%  
               
               
                   
                 Planned dilution 
                  0% 
                 35% 
               
               
                   
                 Walls dilution 
                 95% 
                 85% 
               
               
                   
                 Stope recovery 
                 4 511 
                 20 413  
               
               
                   
                 Planned mining reserves (s. ton) 
                 1.13 
                 0.21 
               
               
                   
                 Mined grade 
               
               
                   
                 Mill recovery 
                 95% 
                 95% 
               
               
                   
                 Produced ounces 
                 6 220 
                 5 757 
               
               
                   
                 (stope and development) 
               
               
                   
                   
               
             
          
           
               
                   
                 Thermal fragmentation 
                 Long-hole 
               
             
          
           
               
                   
                 Unit cost 
                 Total 
                 Unit cost 
                 Total 
               
               
                   
                 $/s. ton 
                 $ 
                 $/s. ton 
                 $ 
               
               
                   
               
               
                 Development 
                   
                 354 252  
                   
                 462 889 
               
               
                 Mining cost ($/t) 
                 58.20 
                 262 564  
                 19.00 
                 387 852 
               
               
                 Mucking 
                 5.00 
                 22 557 
                 4.00 
                  81 653 
               
               
                 Transport 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 
                 249 042 
               
               
                 Milling 
                 12.20 
                 79 377 
                 12.20 
                  99 183 
               
               
                 (development) 
                   
                   
                   
                   
               
               
                 TOTAL 
                   
                 826 131  
                   
                 1 437 607   
               
               
                 CAN$ per short ton 
                   
                 74.98 
                   
                 50.37 
               
               
                 CAN$ per ounce 
                   
                 132.82 
                   
                 249.71 
               
               
                 US$ per ounce 
                 0.65 
                 86.34 
                   
                 162.31 
               
               
                   
               
             
          
         
       
     
       Experimental Setup 
       [0032]    A test case was conducted by elaborating a mining concept using thermal rock fragmentation with a plasma torch to mine extremely narrow veins. The test case was developed according to commonly found stope dimensions in mining operations. A stope height of 45 meters was selected, which corresponds to the standard distance between two levels. For equipment operational reasons, the maximum length was fixed to 100 meters. Table 2 lists the details of development of the stope. 
         [0000]    
       
         
               
             
               
               
               
               
             
               
               
               
               
             
           
               
                 TABLE 2 
               
             
             
               
                   
               
               
                 Details of developments 
               
             
          
           
               
                   
                 Width 
                 Height 
                 Length 
               
               
                   
                 (m) 
                 (m) 
                 (m) 
               
               
                   
                   
               
             
          
           
               
                 Upper access 
                 2.7 
                 2.7 
                 10 
               
               
                 Lower access 
                 2.7 
                 2.7 
                 10 
               
               
                 Upper ore drift 
                 2.4 
                 2.4 
                 100 
               
               
                 Lower ore drift 
                 2.4 
                 2.4 
                 100 
               
               
                 Service raise 
                 2.4 
                 2.4 
                 40 
               
               
                 Sub-level 
                 2.4 
                 2.4 
                 98 
               
               
                 Slot raises 
                 1.8 
                 1.8 
                 76 
               
               
                 Excavation for plasma torch equipment 
                 3.0 
                 2.4 
                 4.5 
               
               
                 Excavation for vacuum 
                 3.0 
                 2.7 
                 4.5 
               
               
                   
               
             
          
         
       
     
         [0033]    One skilled in the art will appreciate that variations in the number of panels is possible. As an example, excavation could be performed in a single lower panel  1  or  2  without forming or expanding to the upper panels  3  or  4 . 
         [0034]    Another variation exists in the sweeping of the burner. The burner can be swept from left to right or right to left, while progressing from the top of the stope panel to the bottom. Alternatively, sweeping can occur from top to bottom, while progressing from left to right or right to left. The pattern and rate of motion of the burner/plasma torch will be dependent on several factors, including but not limited to the physical dimensions of the deposit, the composition of the deposit, variations in the deposit, desired fragmentation rate/volume, type and output of the burner/plasma torch, etc. The rate and pattern can be predetermined through theoretical considerations and/or empirical evaluation of test samples. The rate and pattern can also be adapted dynamically during the process to ensure optimization of fragmentation. Optimization does not necessarily mean increased fragment size, as fragment size can have an affect on the removal process in the case of vacuum removal, for example, or on subsequent processing steps. Volumetric removal rate (yield) is typically a better indicator of efficiency. 
         [0035]    Another embodiment of the present invention provides for automatic operation of the equipment. Thus, the operator can safely remain in a workplace outside of the stope, while the automatic equipment operates within the stope. Cameras can be used to monitor progress. Furthermore, automatic detection of surface edges could be employed, further reducing input required from an external operator and eliminating the need for cameras. In such an automatic system, the burner could be provided on a platform extending up from the floor of the lower drift. 
         [0036]    While there has been shown and described herein a method for continuous extraction of deposits in narrow-vein mining applications, it will be appreciated that various modifications and or substitutions may be made thereto without departing from the spirit and scope of the invention.