A bench mining method, particularly useful for open pit bench mining, which employs a combination of bulldozers and transversely movable apron feeders to provide the primary mechanism for removal of overburden.

CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is a division of U.S. patent application Ser. No. 11/575,273, filed Mar. 14, 2007, which is a section 371 national phase of PCT/US2005/032081, filed Sep. 9, 2005, which claims the benefit of U.S. Provisional Patent Application Ser. No. 60/610,081, filed Sep. 15, 2004, and U.S. Provisional Patent Application Ser. No. 60/639,829, filed Dec. 28, 2004. 
     
    
     FIELD OF INVENTION 
       [0002]    This invention relates to methods and apparatus for mining and in particular for open pit bench mining and apron feeders used in connection therewith. 
       BACKGROUND 
       [0003]    In modern mining, geologic surveys and other techniques estimate the size and shape of mineral and/or ore configurations before their removal in a mining operation. The ore and mineral deposits exist in layers or veins at varying depths below ground. For example, deposits of coal can be divided into multiple layers of substantially horizontal planes of varying thickness and at various depths such that several deposits or veins lie at different levels spanning hundreds of feet below ground. Such layers of mineral and ore deposits are often not completely horizontal but have a pitch or slope. Because of the three dimensional sloping layers, the deposits are generally mined from the shallowest end of the deposit in a down slope direction. 
         [0004]    In general the rock and earth disposed on top of a mineral or ore layer is referred to as “overburden”. In open pit mining, the overburden atop a first uppermost layer is removed to substantially expose a strip of the mineral or ore deposit. The exposed deposit is then accessible to be removed by mining the uncovered portion and transporting it from the mine for shipment or other processing. Overburden is then removed from above a next adjacent strip of the first layer deposit to substantially expose more of the first deposit layer for removal by mining and shipment. 
         [0005]    In open pit mining, once a portion of the uppermost deposit layer is mined and removed, the rock that had been sandwiched between the uppermost layer and the and the next lower deposit layer is exposed and is the overburden atop the next lower layer. Accordingly, the open pit process mining continues by removing strips of that overburden to generally expose the next deposit layer, in a sequential process that continues until successive deposit layers are exhausted. Depending on the size of the deposit, each strip may be several miles in length and is typically about 100 or more feet in width depending on the type of equipment used for the mining operation and other factors such as the size and pitch of the deposit layer. 
         [0006]    As open pit mining continues, overburden removal above each deposit layer forms steps or benches. At each step, multiple removal operations increase efficiency in mining the ore or other minerals within the deposits. Multiple operations, however, take some time, and can be cost prohibitive if projected mining yields are not sufficiently high. 
         [0007]    The valuable deposit layers are generally much smaller than the layers of overburden. Thus, the most labor intensive task in open pit mining is the removal of the overburden. 
         [0008]    In one conventional mining method, a bucket wheel excavator  500 , as illustrated in  FIG. 1A , loads overburden  29  onto dump trucks  180 . A single bucket wheel excavator  500  may cost on the order of One-Hundred Million Dollars ($100,000,000) and require a trained crew of 6 to 8 persons to operate. 
         [0009]    As an alternative to a bucket wheel excavator, shovels, drag lines or other bucket type equipment are often used to remove overburden. For example,  FIG. 1B  illustrates a conventional operation where a shovel  502  loads large oversized dump trucks  180  which deposit their materials into a hopper on a centrally located apron feeder  550 . The apron feeder  550  may feed a sizer that reduces oversized chunks of overburden to a size manageable by a conveyor  506  or other means of transport that carries the removed overburden away from the active mining area. 
         [0010]    In a conventional mining operation, the apron feeders  550  is typically located at a semi-permanent position where overburden is trucked and deposited to a feed end of the apron feeder. When initially positioned or relocated, an apron feeder  550  is traditionally moved in a direction aligned with the feeder's conveyor operation so that they are essentially backed into a desired location. It is known in the art to provide apron feeders  552  with wheels or crawler undercarriage in line with the feeder operation for the purpose of positioning the apron feeders  552  such as illustrated in  FIGS. 2A and 2B . 
         [0011]    Applicants have recognized that it would be desirable to provide a method and system of open pit mining that reduces or eliminates the need for reliance on complicated and expensive equipment such as bucket wheel excavators and efficiently uses the necessary equipment. Applicants have in particular recognized that more efficient mining can be conducted through the creative expanded use of apron feeders in the mining operation. 
         [0012]    Further, applicants have recognized that improved apron feeder designs may be employed to prevent costly operational stoppages due to the need for cleaning clogged material from an apron feeder. 
       SUMMARY 
       [0013]    A bench mining system, mining method and related equipment are provided in which a combination of bulldozers and transversely movable apron feeders provide a primary mechanism for overburden removal. The mobility of teams of dozers along with the apron feeder, as described herein, is a significantly new and effective innovation in overburden removal. With an eye towards being able to move the entire mining operation, not only are the earth-moving pieces of equipment considered movable, but so is the entire infrastructure supporting the earth-moving equipment, including pump-houses, retaining walls, and the like. 
         [0014]    In a preferred embodiment, a mining floor or “bench” is defined adjacent to a section of a deposit layer and overburden. Preferably, the overburden and deposit layer have a combined height relative to the bench of between 50 to 150 feet. An apron feeder is disposed on the bench in front of a pre-blasted section of overburden which preferably runs about 300 feet along the bench and the apron feeder is preferably positioned in the approximate center of the 300 feet long section. Selective blasting, as is well known in the art, is used to loosen the overburden rock and/or other material of which it is composed while leaving the deposit layer substantially intact. Preferably, the loosened section of overburden in front of which the apron feeder is positioned is about 225 feet wide, extending away from the apron feeder. 
         [0015]    The invention further comprises bulldozers working in coordinated teams that push the overburden of the pre-blasted section onto the feed end of the apron feeder by preferably forming a natural hopper and relying on gravity to create a flow of the loosened overburden into the apron feeder. The bulldozers preferably work in defined zones and coordinate their efforts depending on the number of bulldozers employed. The apron feeder is then used to either load the bulldozed overburden onto trucks or onto a conveyor system for removal from the active mining area. After overburden removal, the substantially uncovered portion of the deposit layer is then mined using conventional methods. 
         [0016]    The operation preferably continues along the bench by blasting further sections of overburden and transversely relocating the apron feeder in front of the next loosened section whereat further bulldozing pushes the loosened overburden into the apron feeder, which in turn, feeds the trucks or the conveyor system. 
         [0017]    Where the layer deposits are in closely spaced intervals of less than 50 feet, a bench can be defined adjacent a section having an intermediate deposit layer within the overburden. In such case, selected blasting techniques known in the art are employed to blast the overburden atop the intermediate deposit layer as well as below the intermediate deposit layer. Then the bulldozing operation first removes the upper portion of overburden above the intermediate deposit layer and the intermediate deposit layer is mined and removed. Thereafter, the bulldozers are used to remove the lower portion of the overburden. The apron feeder can be either transversely displaced to a location for receiving another section of upper loosened overburden while the intermediate deposit layer is mined from the first section or remain at the same location for both upper and lower overburden removal operations. 
         [0018]    Where the layer deposits are spaced at an interval of more than 150 feet, a bench can be defined where there is no deposit layer of mineral or ore within the overburden. In such case, after blasting and removal of the loosened overburden by dozing it into the apron feeder, no mining operation is required on that bench. 
         [0019]    The blasting, dozer/apron feeder overburden removal, and deposit mining operations are preferably contemporaneously conducted on several benches where each operation is selectively transversely spaced from each other by a selected safety margin. 
         [0020]    In order to implement the system and operation thereof, the inventive apron feeders are preferably provided with a frame that permits engagement with a crawler for displacement of the apron feeder in a direction that is transverse to a conveying direction of the apron feeder. Alternatively, the apron feeder is provided with an innovative dedicated crawler affixed thereto or other means of transverse locomotion to facilitate efficient operations as the removal of overburden proceeds along one of the benches. 
         [0021]    Preferably, apron feeders used to conduct the inventive mining operation are provided with a self-cleaning mechanism to facilitate continuous operation without undue stoppage delays. In particular, the apron feeder is preferably provided with a scroll plate at its inlet end to catch overspill material as the apron feeder is loaded. Preferably, a “grizzly” component is mounted on an apron feeder flight that serves to break up and/or loosen material caught by the scroll plate and a wiper component is disposed on an apron feeder flight a selected distance behind the grizzly to clear the material from the scroll by pushing it back to the top of the apron feeder inlet end. 
         [0022]    The invention further comprises a method of open pit bench mining of selected material deposits by defining a bench disposed in front of a material deposit layer with overburden disposed atop the material deposit layer, providing an apron feeder having a feed end and an output end defining a conveying direction, selectively loosening overburden atop the material deposit layer in areas adjacent said bench, positioning the apron feeder at a first location on said bench at a first section of the material deposit layer where the overburden has been loosened such that the apron feeder's feed end is adjacent the material deposit layer and the apron feeder is oriented with its conveying direction substantially perpendicular to the material deposit layer, moving the loosened overburden onto the apron feeder's feed end to substantially uncover the first section of the material deposit layer, and removing the material deposits from the substantially uncovered first section of the material deposit layer. 
         [0023]    The invention further comprises a method of open pit bench mining of selected material deposits from a mining area by providing an apron feeder having a feed end and an output end defining a conveying direction and at least one extension wall disposed at either side of the apron feeder, the feed end disposed at a bench adjacent a material deposit layer with overburden disposed atop of the material deposit layer, using a bulldozer to push loosened overburden atop the material deposit toward the feed end of the apron feeder to form a natural hopper adjacent the feed end of the apron feeder, and using the bulldozer to push the loosened overburden atop the material deposit layer along the natural hopper toward the feed end of the apron feeder by substantially relying on gravity to create a flow of loosened overburden along the natural hopper. 
         [0024]    Other objects and advantages of the present invention will be apparent from the following detailed description and the accompanying drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0025]      FIG. 1A  is a perspective illustration of a prior art bucket wheel excavator used in conventional open pit mining. 
           [0026]      FIG. 1B  is a schematic illustration of a conventional open pit mining operation where a shovel loads short haul dump trucks that transport the shoveled material to a relatively stationary fixed position apron feeder in a conventional open pit mining operation. 
           [0027]      FIG. 2A  illustrates the mobility of a conventional apron feeder in line with the feeder's conveying operation utilizing a crawler. 
           [0028]      FIG. 2B  illustrates the mobility of a conventional apron feeder in line with the feeder's conveying operation utilizing wheels. 
           [0029]      FIG. 3A  is an overall perspective view of an open pit bench mining system in accordance with the teachings of the present invention. 
           [0030]      FIG. 3B  is a perspective schematic diagram of the mining system of  FIG. 3A  wherein a bench is adjacent to a formation that includes multiple deposit layers. 
           [0031]      FIG. 4  is an elevated side view of an apron feeder configured for use in the mining operation depicted in  FIGS. 3A and 3B . 
           [0032]      FIG. 5A  is an illustration of a preferred apron feeder and transporter. 
           [0033]      FIG. 5B  is an illustration of a transport tractor. 
           [0034]      FIG. 5C  is an illustration of a preferred apron feeder with extension walls and a sizer attached to the outlet end of the apron feeder. 
           [0035]      FIG. 5D  is an illustration of an apron feeder with extension walls. 
           [0036]      FIG. 5E  is an illustration of an alternate embodiment of the transport tractor and apron feeder. 
           [0037]      FIG. 6A  is an elevated side view of the feed end of an apron feeder fitted with a scroll element. 
           [0038]      FIG. 6B  is a perspective illustration of a self-cleaning mechanism of an apron feeder. 
           [0039]      FIG. 6C  is a perspective illustration of a top view of a preferred apron feeder. 
           [0040]      FIGS. 7A and 7B  are side and top views of an initial push to an apron feeder.  FIGS. 7C-E  show three successive cuts of overburden. 
           [0041]      FIG. 8  illustrates a top view of a successive dozer push towards an apron feeder. 
           [0042]      FIG. 9  illustrates a top view of a first embodiment of a method of loading the apron feeder. 
           [0043]      FIG. 10  illustrates a top view of a second embodiment of a method of loading an apron feeder. 
           [0044]      FIG. 11  illustrates a top view of a third alternate embodiment of a method of loading an apron feeder. 
           [0045]      FIGS. 12A-H  illustrate iterative steps in a top view of a fourth method for loading a movable apron feeder. 
           [0046]      FIGS. 13A-H  illustrate iterative steps in a top view of a fifth method for loading a movable apron feeder. 
           [0047]      FIG. 14A-I  illustrate iterative steps in moving an apron feeder used in the invention. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Overview of Operation and Equipment 
       [0048]      FIG. 3A  illustrates an open pit mining operation  20  wherein three benches  22 ,  24 ,  26  are at different levels relative to deposit layers  28 ,  30 ,  32  respectively. A layer of overburden  29 ,  31 ,  33 , which a removal operation carries away, covers each level of deposit layer  28 ,  30 ,  32 . Once the mineral or ore deposit is exposed, a mining operation removes the deposit layer  28 ,  30 ,  32  for further processing. 
         [0049]    Preferably, the benches  22 ,  24 ,  26  are defined such that the height H of the deposit  28 ,  30 ,  32  and overburden  29 ,  31 ,  33  to which they are adjacent is between 50 and 150 feet. Each bench itself preferably has a width of at least 100 feet extending from the deposit and overburden to which it is adjacent. 
         [0050]    On each bench, an apron feeder is disposed in front of a pre-blasted section S 1  of loosened overburden  29 L,  31 L,  33 L which preferably has a length L which runs about 300 feet along the bench. The apron feeder is preferably positioned at the approximate center of the 300 feet long section S 1  Preferably, the loosened section S 1  of overburden in front of which the apron feeder is positioned has a width W of about 225, extending away from the apron feeder. With the apron feeder  150  in place, bulldozers  200  push the loosened overburden  29 L,  31 L,  33 L of the section S 1  into the feed end  152  of the apron feeder  150  using one of the methods shown in  FIGS. 7-13 , and discussed in more detail below. 
         [0051]    The apron feeder  150  conveys the loosened overburden  31 L,  33 L onto trucks  180  for removal from the active mining area. Alternatively, loosened overburden  29 L is fed into a sizer  185  for removal on a conveyor system  210 . After removal of the overburden  29 L,  31 L,  33 L, a substantially uncovered section D of the deposit layer  28 ,  30 ,  32  is then mined using conventional methods. As a practical matter, trucks are preferred for the deeper benches, but this is dependent on the type and availability of conveying equipment to serve as an alternative means. 
         [0052]    Selective blasting to loosen the overburden  29 ,  31 ,  33  is performed using techniques well known in the art to loosen the rock and other overburden material while leaving the deposit  28 ,  30 ,  32  intact. A second section S 2  of overburden may be loosened by blasting before the apron feeder/dozer overburden removal operation is conducted. In practice, both safety considerations and operational efficiency are preferably used to determine when and whether multiple sections of overburden are to be blasted to loosen the overburden for the overburden removal operation. 
         [0053]    In accordance with conventional practice, the exposed sections D resulting from the dozer/apron feeder overburden removal operation will include a relatively small overlying buffer layer of rock material so that the mineral or ore deposit itself is not contaminated by the blasting process. That relatively thin buffer layer is removed using conventional methods and the mineral or ore is removed by mining in a relatively pure form and is transported out of the open pit mine for further processing and/or shipment. 
         [0054]    Preferably on each bench  22 ,  24 ,  26 , the operations continue laterally along each bench and can be conducted contemporaneously at spaced locations on each bench. In general, the blasting overburden operation precedes the dozer/apron feeder overburden removal operation which in turn precedes the mining of the mineral or ore deposit. Each of the upper benches, such as benches  24  and  26 , are in fact defined by overburden for a lower bench. Accordingly, the blasting of sections of overburden  29  is performed after that area has already completed its service in forming a base for removal operations of the higher overburden and mining of the upper deposits. 
         [0055]    As illustrated in  FIG. 3A , contemporaneous operation of the three procedures, blasting, overburden removal and mining, can be laterally spaced along each bench with the active areas respectively being laterally spaced to produce a very efficient mining operation with relatively inexpensive equipment. 
         [0056]    Variations Due to Spacing of Mineral or Ore Deposits 
         [0057]    As noted above, the benches are preferably defined such that the adjacent overburden and deposit combination is in a range from 50 to 150 feet in height H. Where the layer deposits are spaced in close interval of less than 50 feet, a bench can be defined where there is an intermediate deposit layer within the overburden. 
         [0058]    In such case, selected blasting techniques known in the art are employed to blast the overburden  31  atop the intermediate layer  30   i  as well as below the intermediate deposit layer. Preferably, a bulldozing operation first removes the upper overburden above the intermediate deposit layer, the intermediate deposit layer is mined and removed, and then bulldozers are used to remove the lower portion of the overburden. The apron feeder may be transversely displaced to a location for receiving another section of upper loosened overburden and then transversely returned. Alternatively, the apron feeder may remain at the same location during removal of the intermediate deposit for both overburden removal operations. 
         [0059]    For example,  FIG. 3B  illustrates an intermediate deposit layer  30   i  within the overburden  31  adjacent to bench  24 . The intermediate deposit layer  30   i  could, for example, be five feet thick having a forty feet of overburden all of which is disposed above the lower deposit layer  30  that is ten feet thick having forty feet of overburden sandwiched between the deposits  30   i ,  30 . In such an example, the bench  24  is defined at the level of the lower layer deposit  30  at a depth of ninety-five feet below the top of the overburden of the intermediate deposit  30   i . After blasting to loosen both portions of the overburden  31 L in section S 1 , bulldozers are then used to first push the upper forty feet of overburden onto the apron feeder  150  stationed therebelow and the five foot thick intermediate deposit  30   i  is then removed. Bulldozers then remove the remaining forty feet of overburden lying atop the lower layer deposit  30  which permits the mining of the lower deposit material. 
         [0060]    After the overburden atop intermediate deposit  30   i  is removed through the dozing operation, the apron feeder is preferably transversely moved along the bench where a next section S 2  of blasted overburden is removed through a bulldozing operation while the deposit is removed from the first five foot thick upper deposit layer  30   i . Thereafter, the bulldozers and apron feeder can be returned to the first site S 1  to remove the lower forty feet of overburden  31 L disposed on the lower deposit layer  30 . 
         [0061]    The return of the apron feeder to finish overburden removal may be after several sections of overburden atop intermediate deposit  30   i  are removed. Alternatively, a second set of dozers and a second apron feeder may be used on the same bench  24  to follow the removal of the intermediate deposit  30   i . The second set of dozers and second apron feeder would then remove the lower forty feet of overburden to permits a second mining operation to proceed with respect to removing the lower deposit layer  30 , preferably using a second set of deposit removal equipment. In either case, the transverse mobility of the apron feeders greatly facilitates the efficiency of the operation. 
         [0062]    Where the layer deposits are spaced at an interval of more than 150 feet, a bench can be defined where there is no deposit layer of mineral ore within the overburden. In such case, after blasting and removal of the loosened overburden by dozing it into the apron feeder, no mining operation is required on that bench. 
         [0063]    The movement of the bulldozers and apron feeders along the benches allows for efficient removal of both overburden and mineral deposits simultaneously, without extended equipment down time. 
         [0064]    Apron Feeder Equipment 
         [0065]    As best seen in  FIGS. 4 ,  5 A- 5 E, and  6 A- 6 C, a preferred apron feeder assembly  150  is shown which is designed specifically for efficient implementation of mining operations in accordance with invention by facilitating transverse apron feeder movement. The apron feeder assembly includes a feed end  152 , which receives material (overburden) that is conveyed to an outlet end  156  thus defining a conveying direction of the feeder. The apron feeder  150  is preferably comprised of  180  flights  146 , each ten inches wide, which are horizontally pivotally connected in a continuous loop. This loop defines a conveyor with a top surface  146   a  that transports material from the feed end  152  to the outlet end  156  of the apron feeder  150 , and a bottom surface  146   b . The inlet end  152  of the apron feeder is conventionally enclosed within a strong metal box  155  called a “dog house” to protect it from impact and from compacted surrounding material during operation. 
         [0066]    The apron feeder  150  is mounted at a desired angle upon a selectively configured frame  154  such as shown in  FIG. 4 . The desired angle is preferably 14 to 15 degrees above horizontal. Preferably, the frame  154  supports the apron feeder so that its outlet end  156  is located at a height sufficient to fill a dump truck  180  positioned beneath the outlet end  156 . Alternatively, as depicted in  FIG. 5C , a sizer  185  can be attached to the outlet end  156  of the apron feeder  150  to reduce large size chunks of overburden to a manageable size for conveying by a conveyor system  210  which is then disposed beneath a conveyor loading apparatus  186  associated with the sizer  185 . 
         [0067]    Where a conveyor system is used, the conveyor system  210  then transports the overburden from the active mining site such as illustrated in  FIG. 1B . As illustrated in  FIG. 3A , the conveying system  210  can extend along a bench  22  so that the entire apron feeder  150  and sizer  185  combination can simply move transversely from in front of a section S 1  to a subsequent section S 2  for a highly efficient overburden removal process without any alteration to the conveying system. Other alternatives for transporting overburden material from the apron feeder may be used alone or in combination with the examples provided above. 
         [0068]    The frame  154  preferably includes a selectively defined opening for access by a transport crawler  190  in a direction that is transverse to the conveying direction of the apron feeder  150 . As best seen in  FIGS. 5A ,  5 B, and  5 E, the transport crawler  190  preferably has treads  192  or other motive means suitable for the strip mining environment and preferably includes a vertically displaceable support bed  194 . 
         [0069]    In lieu of having a separate crawler  190 , the apron feeder assembly  150  can include a dedicated transport crawler attached thereto. In Either case, the crawler  190  may optionally have a relatively rotatable support bed  194  associated with the transport crawler  190  to enable the crawler treads  192  to be turned relative to the apron feeder  150  to be in either a transverse or an aligned orientation with respect to the conveying direction of the apron feeder  150 . With such an option, the transport crawler  190  can move the apron feeder assembly  150  in a conventional manner as is done with the apron feeders shown in  FIGS. 2A and 2B  and also move the apron feeder assembly  150  in a transverse manner by changing the directional orientation of the crawler treads. 
         [0070]    When the apron feeder assembly  150  is to be relocated on a bench, the transport crawler  190  preferably travels beneath the apron feeder assembly  150  in the space defined by the frame  154 , lifts the apron feeder assembly  150  on the support bed  194  above the bench and transversely repositions the apron feeder assembly  150  along the bench to a new location where it is lowered onto the bench. Preferably the frame  154  is structured so that the transport crawler  190  engages the apron feeder  150  directly below the center of mass of the entire apron feeder assembly  150 . As shown in  FIG. 5C , where the apron feeder  150  is used in connection with the sizer  185 , a similar crawler  188  is preferably provided to transversely relocate the sizer  185  and its associated conveyor loading apparatus  186 . 
         [0071]    As best seen in  FIGS. 5C and 5D , the apron feeder assembly  150  is preferably used in connection with massive extension walls  170 ,  172  and a hydraulic assembly housing  174  having skids that permit them to be dragged by a bull dozer for placement at a desired location. Unlike conventional apron feeder walls which are semi-permanently erected such as illustrated in  FIG. 2A , the walls  170 ,  172  are selectively designed with a large foot print and sufficient weight to remain immobile during the dozing operations used to feed the apron feeder, while remaining sufficiently mobile and easily transportable for quickly establishing a subsequent apron feeder operational site. 
         [0072]    The hydraulic assembly housing  174  provides the motive power to the apron feeder and typically includes both hydraulic and electrical equipment for operation the apron feeder. The hydraulic assembly housing  174  may be designed with sufficient strength and bulk to serve as one of the extension walls. However, it is preferred to provide an extension wall disposed in between the dozing operations and hydraulic assembly housing  174 . 
         [0073]    As shown in  FIG. 5D , preferably, a signal light  176  is provided which is controlled by the apron feeder operator having red and green lights. The signal light is advantageously used to signal to the operators of the bull dozers which load the apron feeder; a green light indicating when the feeder is ready to receive material and a red light indicating no loading should occur. Typically a red light indication will be given when there is a change of trucks at the outlet end. 
         [0074]    For apron feeder operation, the walls  170 ,  172  are positioned proximate the inlet end  152  of the apron feeder  150  and serve to protect the apron feeder operators and to assist in the formation of the natural hopper  40  formed during the dozing operations. The wall  170  also serves to protect the transport crawler  59  and to keep clear the area beneath the apron feeder frame  54  for the transport crawler to easily engage the apron feeder assembly  50  for transport. 
         [0075]    Apron Feeder Self-Cleaning Mechanism 
         [0076]    The dog box  155  provides protection to the front and sides of the feed end  152  of the apron feeder  150 . However, during the dozing operation to load the feeder, some material spills into a gap  162  defined between the apron feeder's feed end  152  and the dog box  155 . Although such spillage is a lesser problem when the apron feeder is loaded with dry material, material build up is exponentially increased where the apron feeder is loaded with wet sludge or slurry material. Typically the problem of such spillage build up results in periodic stoppage of apron feeder operation to remove built up spillage. 
         [0077]    As illustrated in  FIGS. 6A-6C , in order to prevent or reduce the buildup of overspill material, the apron feeder  150  is provided with a self cleaning mechanism that includes a spillage catching scroll  140 , a grizzly element  142 , and a wiper element  144 . The scroll element  140  comprises a strong metal sheet that is mounted to the dog box at the gap  162  and extends substantially parallel to the apron feeder fights  146  in front of the feed end of the feeder for a selected distance parallel the bottom surface  146   b  of the feeder  150 . Preferably the scroll  140  is approximately 22 feet long. 
         [0078]    The grizzly element  142  is mounted on one of the feeder flights  146  to define a row of metal teeth spanning transversely across the conveying surface. An associated wiper element  144  is mounted on one of the feeder flights  146  at a selected distance behind the grizzly  142  to define a raised blade spanning transversely across the conveying surface. 
         [0079]    In operation, as the apron feeder is loaded, material that spills through the gap  162  is caught by scroll  140  where it collects. With each complete revolution to the apron feeder, the grizzly  142  travels along the scroll and breaks up the collected overspill material caught by the scroll. The wiper  144  then follows the grizzly  142  to push the broken up overspill back up onto the top surface  146   a  of the feeder  150 . After the wiper  144  passes, the scroll  140  has been cleared to again begin to catch spillage into the gap  162 . 
         [0080]    More than one grizzly/wiper set can be provided so that the scroll is cleared multiple times during one complete revolution of the apron feeder. Preferably, two evenly spaced grizzly/wiper sets are provided, as illustrated in  FIGS. 6A and 6B . 
         [0081]    Dozer/Apron Feeder Overburden Removal 
         [0082]    With reference to  FIGS. 7A-7E  and  8 , details of a preferred dozer/apron feed overburden removal operation are illustrated. With the apron feeder  150  disposed on the bench  22  in front of the loosened section S 1  of overburden  29 L, the dozers  200  perform an initial push to form a slope  34  and natural hopper  40 . The dozers push an uppermost layer of overburden  29 L 1  towards the apron feeder  150  to form the slope  34  between the overburden section S 1  and the bench  22 . The slope  34  angles downward to form overburden chute walls  39  on either side of the apron feeder  150 . These chute walls  39  define a natural hopper or chute  40  sized and shaped to direct dozer-pushed overburden  29  to the inlet of the apron feeder  150 . 
         [0083]    Once the dozers  200  form the natural chute  40 , the dozers  200  begin the task of removing the overburden  29 L proceeds in removal of successive layers  29 L 2 ,  29 L 3 , and  29 L 4  as illustrated in  FIGS. 7C-E . Gravity provides assistance in this part of the operation since the angle of repose of the material being pushed in the natural hopper  40  is such that the material naturally slides down the slope  34  to the apron feeder  150 . However, for the lower most overburden layer  29 L 4 , the dozers  200  may need to push the overburden material upward to inlet of the apron feeder. This is somewhat dependent on the thickness of the underlying deposit. 
         [0084]      FIGS. 9-14  illustrate several alternative methods for dozing the overburden  29 L into the apron feeder  150 . The general objective to maximize the efficiency of the dozers  200  which generally means to keep the dozers in constant motion. Accordingly, communication between the apron feeder, supervisors, dozer operators, and other personnel is desirable to achieve for maximum efficiency. 
         [0085]      FIG. 9  shows a first embodiment for dozing loosened overburden  29 L in a section S 1  into the apron feeder  150 , in which several dozers  200  operate in discreet zones  50 ,  52 ,  54 ,  56 , and  58 . The dozers  200  in zones  50 ,  54 , and  58  drive the overburden  29 L to a staging area  59 , where the dozers  200  operating in areas  52  and  56  take turns dozing the overburden  29 L through the staging area  59  into the chute  40  to the apron feeder  150 . The dozers  200  in zones  50 ,  54 , and  58  preferably advance while the dozers in zones  52  and  56  retreat and vice versa to provide a system of continuous operation for all of the dozers. 
         [0086]      FIG. 10  shows a second embodiment for dozing loosened overburden  29 L in a section S 1  into the apron feeder  150 , in which the dozers  200  in zones  52  and  56  doze the overburden  29  to the staging area  59  and dozers  200  in zones  50 ,  54  and  58  doze the overburden down the chute  40  to the apron feeder  150 . Again, the dozers  200  in zones  50 ,  54 , and  58  preferably advance while the dozers in zones  52  and  56  retreat and vice versa to provide a system of continuous operation for all of the dozers. 
         [0087]      FIG. 11  shows a third embodiment for dozing loosened overburden  29 L in a section S 1  into the apron feeder  150 , in which the dozers  200  in zones  61  and  63  feed overburden  29 L to dozers  200  in zones  60 ,  62 ,  64 , and  66 . The dozers  200  in zones  60 ,  62 ,  64 , and  66  in turn feed overburden  29 L into a slot  69 . Another dozer  200  then dozes all of the overburden  29 L in the slot  69  down the chute  40  to the apron feeder  150 . The third embodiment's advantage is that it allows for more dozers  200  to work in concert with each other over a wider mining area  36 . Further, because only the dozer  200  in the slot  69  feeds the apron feeder  150 , there is little chance of a traffic jam at the slot  69 . 
         [0088]      FIGS. 12A-H  illustrate iterative steps of a fourth embodiment for dozing loosened overburden  29 L in a section S 1  to the apron feeder  150 . This embodiment uses five dozers, one in each of four zones  70 ,  72 ,  74 , and  76  and the fifth in a slot  75  to feed overburden  29 L to the chute  40  and down to the apron feeder  150 . The apron feeder  150  is illustrated loading dump trucks  180 . Each truck  180  leaves the area once it is full of overburden  29 L, and another takes its place. 
         [0089]    In the step shown in  FIG. 12A , all dozers advance towards the slot  75 , with the dozer  200  in zone  70  arriving in the slot  75  first, where it dumps its load of overburden. In the step in  FIG. 12B , the dozer  200  in zone  70  begins its retreat through its zone  70  to gather another load, and the dozer  200  in the slot  75  prepares to drive a load to the hopper  40 . The other dozers in the zones  72 ,  74 , and  76  advance. In  FIG. 12C , the dozer  200  in zone  74  has dumped its load of overburden and begins its run to pick up more overburden. The dozer  200  in zone  70  continues its run to pick up overburden, while the dozers in zones  72  and  76  advance. 
         [0090]    In  FIG. 12D , the dozers in zones  70  and  76  advance and the dozers in zones  72  and  74  are still returning to pick up overburden. In  FIG. 12E , the dozers in zones  70 ,  74 , and  76  advance while the dozer  200  in zone  72 , having dumped its load of overburden, returns to pick up more overburden. In  FIG. 12F , the dozer  200  in zone  76  has dumped its overburden, and returns to pick up overburden, while the dozers in zones  70 ,  72 , and  74  advance. 
         [0091]    In  FIG. 12G , the dozer  200  in zone  76  retreats, while the others advance. Finally, in  FIG. 12H , the dozer  200  in zone  70  has dumped its load and returns for another, while the other dozers in zones  72 ,  74 , and  76  advance. During these various advances through the zones, the dozer  200  in the slot  75  moves back and forth, driving the dumped loads into the natural hopper  40 , with all dozers taking care not to interfere with one another and cause any work stoppage. 
         [0092]      FIGS. 13A-H  illustrate iterative steps of a fifth embodiment for dozing loosened overburden  29 L in a section S 1  to the apron feeder  150 . This embodiment uses four dozers, one in each of three zones  80 ,  82  and  84  and the fourth in a slot  85  to feed the natural hopper  40  leading to the apron feeder  150 . The apron feeder  150  is illustrated loading dump trucks  180 . Each truck  180  leaves the area once it is full of overburden  29 L, and another takes its place. 
         [0093]    The consecutive steps of dozer movements are shown  FIGS. 13A-H .  FIG. 13A  shows the dozers  200  in zones  80 ,  82 , and  84  advancing to the slot  85 , and  FIG. 13B  shows the same dozers further advanced towards the slot  85 . In  FIG. 13C , the dozer  200  in zone  80  has dumped its load of overburden and is beginning its return for another load, while the dozers in zones  82  and  84  advance towards the slot  85 . In  FIG. 13D , the dozer  200  in zone  82  begins its return for another load following the dumping of a load into the slot  85 , while the dozer  200  in zone  80  continues its return run, and the dozer  200  in zone  84  advances. 
         [0094]    In  FIG. 13E , the dozers in zones  80  and  84  advance, while the dozer  200  in zone  82  retreats for another load of overburden. In  FIG. 13F , the dozers in zones  80 ,  82  advance, while the dozer  200  in zone  84  begins its return for another load, having just dumped its load in the slot  85 , and  FIG. 13G  shows the further advance of the dozers following the step shown in  FIG. 13F . Finally,  FIG. 13H  shows the dozers in zones  82  and  84  advance while the dozer  200  in zone  80  retreats to get another load of overburden, having just dumped its own load. 
         [0095]    During these various advances through the zones, the dozer  200  in the slot  85  moves back and forth, driving the dumped loads into the natural hopper  40 , with all dozers  200  taking care not to interfere with each other. 
         [0096]    The various methods can be used in a single mining site. In addition, variants thereof may be used that employ more or less dozers  200 . For example if one or more zones has a deeper cut of overburden  29  to remove, it may be advantageous to position more than one dozer in that zone, or split the zone into subzones. If too much overburden accumulates in a single dozer slot, and the dozer  200  therein falls behind, a staging area for two or more dozers may be more efficiently employed. 
         [0097]    Apron Feeder Relocation 
         [0098]    Once the dozers  200  remove the overburden from a section S 1 , the apron feeder  150  is then moved to a new location, such as adjacent the next section of loosened overburden S 2 .  FIGS. 14A-I  illustrate a preferred sequential procedure for moving the apron feeder  150  after the overburden removal operation is completed from section S 1 . 
         [0099]    As the dozers  200  are completing the dozing of the lowest layer of the overburden  29 L of a section S 1  into the apron feeder  150  ( FIG. 14A ), a single dozer  200  or other equipment cleans out overburden spillage on the right hand side of the apron feeder until it is clear as shown in  FIG. 14B . 
         [0100]    Once the right hand side of the apron  150  is clear, a dozer  200  or other equipment removes the right hand wall  170  of the apron feeder  150 . With the right hand wall  170  removed, a dozer  200  or other equipment removes further overburden spillage,  FIG. 14C , to completely clear right hand side of the apron feeder. 
         [0101]    A dozer  200  then cleans away any overburden spillage about the left hand wall  172  and removes the wall  172  as shown in  FIG. 14D . Any remaining overburden spillage  89  adjacent the hydraulic housing  174  on the left side is then also removed as shown in  FIG. 14E . Thereafter, the hydraulic housing  174  is disconnected from the apron feeder  150 , and a dozer  200  removes the housing  174  for final cleaning on the left hand side, as shown in  FIG. 14F . Finally, as shown in sequential steps  14 G-I a transporter  190  moves in from the right of the apron feeder, lifts it and carries the apron feeder  150  to its new location, such as adjacent another section S 2  of loosened overburden whereat the hydraulic housing  174  and walls  170 ,  172  are reattached. 
         [0102]    While specific embodiments of the invention are disclosed they are not limiting in nature. Those of ordinary skill in the art will recognize a variety of variations in parameters, equipment and processes which can be employed within the scope of the invention.