Abstract:
A process for extracting ore from a vein ( 10 ) comprises drilling spaced-apart boreholes ( 16 ) directly in the vein ( 10 ). The boreholes ( 16 ) are enlarged using thermal fragmentation generally up to the boundaries between the vein and surrounding waste. A blasthole ( 18 ) is then drilled in the vein between the thermally enlarged boreholes ( 17 ) for placement of explosive. The explosive is fired to break the ore between the enlarged boreholes ( 17 ) . The enlarged boreholes ( 17 ) act as weakening regions to direct the blasting effect and minimize dilution.

Description:
RELATED APPLICATIONS 
       [0001]    This is a continuation of International PCT Application No. PCT/CA2008/001372 filed on Jul. 24, 2008, which claims the benefit of U.S. patent application No. 60/953,555. 
     
    
     TECHNICAL FIELD 
       [0002]    The present application generally relates to a process for extracting mineral deposit using thermal fragmentation to provide directional blast. 
       SUMMARY 
       [0003]    It is an aim to minimize extraction costs by reducing ore dilution. 
         [0004]    Therefore, in accordance with a general aspect, there is provided a process for extracting ore from a vein, comprising: a) drilling spaced-apart boreholes directly in the vein, b) using thermal fragmentation, enlarging the boreholes generally up to the boundaries between the vein and surrounding waste to provide adjacent thermally enlarged boreholes, c) drilling at least one blasthole in the vein between two adjacent enlarged boreholes for placement of explosive, and d) detonating the explosive to break the ore between said two enlarged boreholes. 
         [0005]    In accordance with a further general aspect, there is provided a process for extracting ore from a vein having sidewalls extending along an axis, comprising providing two axially spaced-apart weakening regions along said vein, said weakening regions offering less resistance to pressure than said sidewalls, at least one of said weakening regions being obtained using thermal fragmentation, drilling a blasthole in said vein between said weakening regions, placing an explosive charge in the blasthole, firing the explosive charge to provide a blast, the blast being directed towards the weakening regions where there is less resistance. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0006]      FIG. 1  is a side elevation view of an underground ore vein extending between two excavated drifts extending along the course of the vein and providing access to the vein; and 
           [0007]      FIG. 2  is a top plan view of the ore vein shown in  FIG. 1 ; 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0008]      FIG. 1  illustrates an underground ore body  10  or vein extending between two horizontal drifts  12  and  14  accessible from the ground surface through a ramp or a vertical opening known as a shaft (not shown). As known in the art, the shaft is equipped with elevators by which the workers, machines and material can gain access to the galleries or drifts  12  and  14 . The drifts  12  and  14  are tunnels made in the rock with a size and shape to permit mining of the ore body  10 . Each drift defines a working level running through the ore body. The working levels can for instance be vertically spaced by about 18 m (59 feet). 
         [0009]    As shown in  FIGS. 1 and 2 , boreholes  16  (only two being shown in  FIGS. 1 and 2 ) are drilled at regular intervals along the vein  10 , each borehole extending vertically though the vein  10  from the top drift  12  to the bottom drift  14 . The diameter of these holes is typically in the range of 6 inches (15.2 cm). The diameter of the holes  16  is not critical but is preferably kept as small as possible to minimize drilling costs and time. The diameter must however be sufficient to permit hole enlargement by thermal fragmentation. Each borehole  16  can be drilled haft way through from the top drift  12  and the bottom drift  14  in order to limit hole deviation. It is however understood that the holes  16  can be completely drilled from the top drift  12  to the bottom drift  14 . As will be seen hereinafter, the spacing between adjacent boreholes  16  is selected such as to provide sufficiently closed expansion rooms or blast containing rooms such that the mass of ore between adjacent holes can be broken by a blast with minimum ore dilution in the surrounding waste. The boreholes  16  are used to contain as much as possible the blast within the boundaries of the vein  10 , thereby minimizing dilution. Satisfactory results have been obtained with a 6 m (19.68 ft) center to center distance between two consecutive boreholes. 
         [0010]    The drilled boreholes  16  are individually thermally enlarged as per the way described in U.S. Pat. No. 6,913,320 issued on Jul. 5, 2005, the content of which is herein incorporated by reference. More specifically, each borehole  16  is enlarged by lowering a burner B ( FIG. 1 ) into the borehole, by igniting it and then gradually raising it until the borehole is completely enlarged from a bottom end to a top end thereof. A plug P is installed in the bottom of the boreholes  16  to seal the same and provide for a build-up of temperature in the borehole. The heat generated by the burner B raises the temperature in the hole up to 1800° C. This creates thermal stresses that spall the ore. In simple terms, spalling is considered to be a form of decrepitation caused by an unequal expansion of mineral crystals which overcomes molecule cohesion. The broken or fragmented material produced during this process ranges in size from fine grain to 4 cm (1.6 inch). The plug is removed and the broken material is recuperated by any suitable methods. The boreholes  16  are typically enlarged up to the sidewall of the vein (i.e. the boundaries between the ore body and the surrounding waste) to provide thermally enlarged boreholes  17  as schematically shown in dotted lines  FIG. 2 . For illustrative purposes, the spacing between the boreholes  16  can be selected to leave about 1 m (3.28 feet) of ore between two adjacent enlarged boreholes  17  for a vein having a width ranging from about 13 inches (33 cm) to about 15 inches (38.1 cm). The spacing between adjacent holes is not only function of the width of the vein but also of the explosive that will be used to break the ore between the so enlarged weakening holes. As mentioned herein above satisfactory results have been obtained with a distance of 6 m (19.69 feet) between the centers of adjacent boreholes  16 . 
         [0011]    Once the first two drilled holes have been thermally enlarged and emptied as described hereinabove, at least one blasthole  18  is drilled through the vein  10  between two adjacent enlarged holes  17 , as shown in  FIGS. 1 and 2 . If only one blasthole  18  is drilled it is generally located midway between the enlarged holes  17 . Each blasthole  18  is generally spaced by 80 cm (31.5 inches) from the periphery of the adjacent enlarged hole  17 . The blasthole  18  can be drilled haft way through from the upper drift  12 , the other haft being drilled from the lower drift  14 . Alternatively, the blasthole can be fully drilled from the upper drift  12 . The diameter of the blasthole  18  is typically in the range of 2 ½ inches (6.4 cm). It is understood that the blasthole diameter can vary depending on the type of explosive to be loaded therein. 
         [0012]    The selected explosive charge is loaded into the blasthole  18  and is then fired to break the ore present between the two enlarged holes  17 . As shown by arrows  20  in  FIG. 2 , the blast is substantially contained within the boundaries of the vein  10  between the enlarged holes  17 . When an explosive charge explodes a powerful force is exerted in generally all directions but most movement occurs along the line of least resistance or least confinement. The enlarged boreholes  17  provide weakening regions of less resistance than that of the sidewall of the vein. The propagation or explosive force will thus be directed toward the enlarged holes  17  in the vein  10  and not into the surrounding waste which offers greater resistance, thereby minimizing dilution. By so providing boreholes in the vein on opposed sides of the blasthole  18 , the blasting effect can be contained generally longitudinally along the vein. In other words, the enlarged boreholes  17  define the blasting propagation line. 
         [0013]    Once a given section of the vein has been broken by a directional blast as described above, another borehole is drilled in the vein  10  at a selected distance from the initial blasted site. The drilled borehole is then enlarged by thermal fragmentation as described hereinabove and a second blasthole is drilled in the vein at an intermediate location between the exploded site and the newly enlarged bore hole. The blasthole is then filled with an explosive charge, which is then fired to break the ore between the first exploded site and the newly enlarged borehole. Again, the blast propagation take place where there is least resistance, in other words along the line between the first exploded site and the newly enlarged borehole. This process is repeated as required to recover the desired quantity of ore from the ore vein. It is also understood that all the boreholes and the blastholes can be drilled in a first time followed by the thermal fragmentation of the boreholes. The vein can then be blasted in sequence. Other drilling and blasting sequence are contemplated as well.