US20130127231A1

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Publication number: US20130127231A1
Application number: US13/811,354
Authority: US
Inventors: Ian Gray
Original assignee: Individual
Current assignee: Individual
Priority date: 2010-07-21
Filing date: 2011-07-21
Publication date: 2013-05-23
Also published as: WO2012009759A1; AU2011282475A1; CA2806084A1

Abstract

A mining system for extracting ore using directional chilling techniques to obtain access to the orebody. Spaced-apart roadways are formed in the ore formation, with a downhill roadway being lower in elevation than the other roadway, and the downhill roadway having a ditch therein draining downhill. A borehole is formed between roadways in the ore formation using the directional drill bit, and then the end of the drill string is equipped with a jetting nozzle. The jetting nozzle is moved within the borehole to erode the formation and mine the ore. In one embodiment, a slurry of mined ore and jetting fluid flows as a slurry down the intersection of the mined face and the floor towards a ditch formed in the downhill roadway. In another embodiment, a slurry of the mined ore and the jetting fluid flows down the borehole, and then down the ditch formed in the downhill roadway. In each case, the ore flows down the downhill roadway to a sump. From the sump, the ore is carried to the surface for transportation and eventual refining or use.

Description

RELATED PATENT APPLICATIONS

This PCT application claims the further benefit of Australian provisional application 2010903253 filed on 21 Jul. 2010, and Australian provisional application 2011900008 filed on 1 Jan. 2011.

BACKGROUND OF THE INVENTION

The production of many goods for commercial and private use requires the utilisation of numerous types of minerals, or orebodies, and the processing of the same from raw materials into finished goods. Similarly, the production of much of the heat and electrical energy in use today requires a substantial amount of coal. The minerals utilised in industry are obtained from the crust of the earth, usually by mining the same. Before mining machines were in general use, the mining of minerals was carried out manually by using picks and shovels, as well as wagons pulled by horses or mules. In order to increase the production level of minerals, mining machines were invented to allow the minerals to be more easily mined from the earth and transported to the refining and manufacturing sites.

Minerals are mined by different methods depending on where the minerals are found in the crust of the earth. When the minerals are found near the surface of the earth, the overburden is first removed and then the minerals are mined by surface equipment, such as power shovels, bulldozers, drag lines, etc. Minerals are also located underground to the extent that the mining thereof must be carried out by tunneling into the earth to extract the minerals. Numerous types of underground mining techniques have been developed to efficiently and safely recover the minerals.

The underground mining of tabular orebodies, and in particular coal or trona, generally involves the use of mining equipment which cuts roadways in the orebody. In one form of underground mining, a series of pillars are formed so that a portion of the ore is removed and a portion of the ore (the pillar) is left in place. The pillars support the roof of the mine and prevent it from caving in and filling the mine workings. This is referred to as either “bord and pillar” mining or “room and pillar” mining. Sometimes the pillars of ore are removed on retreat from the mine to extract the remaining pillars of ore. The removal of the pillars causes the roof to cave in and form a goaf or gob. In addition to this technique of underground mining, a more productive system involves extracting the ore using longwall mining techniques.

The longwall mining systems essentially divide the entire coal seam into a number of “panels” which are typically 3 to 4 km deep or long, 200 to 350 m wide and 1.5 to 5 m high. Roadways are initially excavated on each side of each panel to provide transportation of equipment, miners and allow transport of the mined coal during mining of the panel. One roadway is a main gate and the other roadway is a tail gate. The maze of roadways in a coal seam can be used to ventilate the working area and remove dangerous gases, such as methane and carbon dioxide, and provide fresh air.

A large and heavy mining machine is equipped with a rotating shearer which is moved laterally back and forth across the face of the panel to successively remove thick sheets or slices of coal. Because of the complexity and size of such mining machines, they are extremely expensive. The slice of coal removed during a single pass can be about I m thick. The chunks of coal which are removed from the face of the panel fall into an armoured face conveyor which moves the chunks of coal laterally to the main gate. At the main gate or roadway, the coal can be pulverised into smaller pieces and loaded onto a long conveyor to be transported along the main gate and eventually to the surface.

The longwall mining machine further includes a number of hydraulic jacks which extend across the width of the panel and function to support the roof of the mined area just in back of the face of the coal panel. The hydraulic support jacks move with the mining machine forwardly as the rotating shearer is moved forward to extract coal from the face of the panel. Once the mining machine moves forwardly during the mining operation, the portion of the roof that is no longer supported by the hydraulic support jacks caves in and forms a goaf. Each panel of coal is mined in the manner described until the entire coal seam is spent. The longwall mining system can either operate as advancing longwalls, or as retreating longwalls, depending on whether the gateroads are progressed with the face of the panel, or the face is retreated between the roadways. In either case, a goaf is formed between the gateroads in the waste zone of the mined area.

Where appropriate, hydraulic jet mining is used to recover ore from surface deposits or from underground deposits. The hydraulic mining system is particularly suited to the underground environment where the ore is weak and the roof and floor rocks are hard to provide support and guard against cave in of the roof. It is also a suitable method to use where the orebody is tabular and located on a slope. As the ore is manually eroded by the hydraulic jet, it is carried downwardly with the assistance of gravity along the slope of the mine floor. Hydraulic jet mining is generally accomplished by using high volumes of pressurised water projected at the orebody from a nozzle or monitor which is controlled by an operator. Limitations of hydraulic jet mining include the effective dispersal range of the jet, which is approximately 30 m, and the limited visibility afforded to the operators. Typical examples of such mining systems were Sunagawa Colliery in Japan, and the Strongman Mine in New Zealand.

Directional drilling has been in use for some time in the petroleum industry, and in coal mining where it is used for either gas drainage operations or for exploration. In its preferred form, directional drilling involves the use of a bottom hole assembly consisting of a downhole mud motor with a bent sub which drives a rotary drill bit. The drilling of the borehole is guided by the use of a survey system which determines the orientation of the borehole, as well as the toolface angle of the bent sub. Based on information from the survey system, the operator may rotate the drill string to re-orient the bent sub and thus steer the borehole in another direction. In addition to downhole motors, alternative bottom hole assemblies may be used for directional drilling. The use of offset jets has long permitted the direction of a borehole to be corrected. The process used is similar to that used for a downhole motor and bit, except the corrected borehole is drilled by high pressure jets. Other directional control systems are also used in drilling. These may involve a rotating drill string with a bottom hole assembly consisting of pressure pads which push the bit to one side of the borehole, or the other, so that a desired borehole path is followed.

SUMMARY OF THE INVENTION

In view of the foregoing, it can be seen that a need exists for a method of mining underground orebodies, where the equipment is much less expensive and complicated, as compared to the longwall mining technique. The various features of the invention combine both the practise of directional drilling and hydraulic mining to extract a sloping tabular ore body in an underground environment. In its preferred embodiment, roadways are driven or formed underground to permit ventilation and access in the normal manner. Gateroads are formed with a dip, and with respective ditches therein to provide downhill drainage of the mined slurry of ore and jetting water. The ditch in the downhill gateroad permits the transport of the slurry of the jetting fluid and ore down to a sump, from whence the slurry can be pumped to the surface. Alternatively, the ore may be separated from the fluid at the sump and transported to surface. Drilling is used to connect gateroads on each side of an ore panel with a borehole. Drilling is normally of a directional nature and orientated off of the dip direction of the ore body. Directional drilling between the gateroads may be achieved using downhole mud motors, water jets or other systems to provide directional control of the borehole formation. Such systems typically utilise a form of borehole survey system.

On reaching the opposite gateroad, the directional bottom hole assembly is exchanged for a jetting bit which erodes the formation laterally. This is done either physically by changing the bit, or by remotely changing the mode in which the bit operates, such as a method of pumping a sealing ball down the drill string and pressurising it until a pressure relief port blows, thus creating a lateral jet. In any event, the hydraulic jet at the end of the drill string is directed to the sidewall of the borehole adjacent to the goaf area to erode the ore, while moving along the borehole. The ore is thus effectively mined from the borehole between the roadways, except for the formation of a pillar, if desired. It can be appreciated that the initial borehole is formed at a location where the mining of the panel is to be commenced.

The bulk of mining is achieved through the mechanism of erosion brought about by pumping a pressurised fluid from a lateral jet. The jet is controlled in order to drill in the direction of the orebody on the waste or goat side of the face of the orebody. If the mode of operation is that the borehole is drilled updip, fluid and ore flow downhill and back towards the borehole along the solid bottom edge of the orebody. Where the borehole is essentially drilled down dip, the slurry of fluid and ore proceed down the intersection of the solid edge of the panel face with the floor of the orebody to the roadway at the lower level of the panel being mined, from thence flowing to the sump.

Where the borehole is drilled essentially up dip, the borehole must be of a sufficiently large diameter to permit the fluid and ore to pass back through the borehole while the drill string is still in the borehole. A useful method to enlarge the borehole and remain in line with the mining system is to use a fluid jet to erode the borehole and enlarge the diameter thereof. After the enlargement of the drilled borehole, the lateral jet bit is used to mine the ore. Where the borehole is drilled up dip, the preferred sequence is to drill the borehole from one roadway to the other roadway, ream it out, re-enter the borehole with a jetting bit which will erode laterally, and then mine on the waste side of the panel face with the ore and fluid passing down the borehole to the lower roadway and thence to the sump. Depending on the pressure of the fluid used with the hydraulic jet, it is possible to mine the face of the ore panel with a height greater than the vertical diameter of the initial borehole.

Once a first pass of the mining operation is accomplished through the first borehole, a second borehole is formed downhill and parallel to the first borehole. A subsequent mining pass is accomplished using the second borehole to erode a further layer of ore from the formation. Subsequent boreholes arc formed to allow additional mining passes to deplete the panel of ore located between the roadways.

It can be appreciated that rather than using expensive and extremely heavy machinery for longwall mining, essentially the same result can be accomplished using directional drilling to sequentially form boreholes between roadways, and then use a high pressure jet which traverses each borehole to erode the ore panel. The mining of the ore continues in each borehole until the panel is spent. According to this technique, the equipment can be easily moved from one ore panel to another in a short period of time, thereby making the technique very cost effective. The nature of the equipment means that it can be easily retrieved should a collapse of the borehole or face occur. Another borehole may then be drilled and the mining process is recommenced through erosion. In the event that the drill string is lost then its cost is small compared to that of conventional longwall equipment.

BRIEF DESCRIPTION OF THE DRAWINGS

Further features and advantages will become apparent from the following and more particular description of the preferred and other embodiments of the invention, as illustrated in the accompanying drawings in which like reference characters generally refer to the same parts, functions or elements throughout the views, and in which:

FIG. 1 shows a plan view of a panel being mined. The dip of the orebody is down the page. The boreholes are drilled down dip along the line2-2 and the jetted face is along the line3-3;

FIG. 2 shows a sectional view, taken along the line2-2 ofFIG. 1, through a panel where the boreholes are drilled down dip and extraction is taking place;

FIG. 3 shows a sectional view through a panel where the boreholes are drilled up dip and extraction is taking place;

FIG. 4 shows a section taken along4-4 ofFIG. 1, through the mining zone; and

FIG. 5 shows a plan view of a panel being mined with boreholes which are drilled up dip.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 illustrates a plan view of a mineral panel that is being mined by drilling down dip. The mining operation of the panel proceeds in the drawing ofFIG. 1 to the right, with the goaf (2) to the left and the unmined orebody (3) to the right. The angle or dip of the panel of ore being mined is shown inFIG. 2, where the gateroad (10) is lower in elevation than the gateroad (5). The panel of ore of interest includes the solid deposit of ore (3) to be mined, as well as the goaf (2) that has been mined. The dip direction is marked by an arrow (18) inFIG. 1. illustrated also is a neighbour goaf (1) that was formed in the area of the previously mined neighbour panel. The neighbour goaf (1) is separated from the current mining panel, i.e. solid ore (3) and associated goaf (2), by gateroads (4,5). On the lower side of the panel (2,3) undergoing the mining operation are the lower elevation gateroads (10,11). The gateroads (4,5,10,11) slope downhill to the right of the figure and include respective ditches (not shown) to drain the slurry of ore and water down to a sump (12).

The gateroads (4,5,10,11) are connected to main roadways (7,8,9) which are used for access and ventilation during development of the mine. The sump (12) collects the slurry of ore and fluid. Drilling of the borehole (17) is initiated at the gateroad (5) at (19). The borehole is shown as (17) and is drilled to gateroad (10) at (13). The borehole (17) can be drilled with diameters between about 0.1 m and 0.3 m, and preferably about 0.15 m. The length of the borehole (17) is about the same as the distance between opposite roadways, namely about 300 m. This distance is to a significant extent controlled by ventilation needs. The angle or dip of the borehole (17) with respect to a horizontal reference can be anywhere between about 6 degrees and 45 degrees. It is noted that these dimensions and numerical limitations are not critical to the operability of the methods of the invention. In any event, while drilling the borehole (17), the ore removed is also mined and recovered by way of a slurry at the sump (12).

At the terminal location (13) of the drilled borehole (17), the directional drill bit is changed to a lateral jetting device (not shown) and the zone to the left of the borehole (17) is eroded. The goaf (2) is thereby formed. In the figure, the eroding bit is at (16) and a panel face (15) is formed which is advanced up dip. The eroded ore and fluid flow down the lower face (14) to downhill gateroad (10) into a ditch (23 inFIG. 2), and thence down the ditch (23 inFIG. 2) to the sump (12). Once the ore has been mined from the initial borehole (17), the drill pipes are removed and the drilling equipment is moved downhill a short distance to drill a subsequent borehole where another mining operation is again carried out using the jetting nozzle. Depending on the roof behaviour, it may be possible to erode all the ore from the eroding bit (16) to the goaf edge. If, however, roof control becomes an issue and it is not possible to erode back to the goaf edge, the preferable approach is to leave a pillar parallel to the borehole (17) to provide roof support. This pillar can be designed to crush as the goaf (2) fully forms, or to remain standing.

The ore is transported to surface from the sump (12) either as a pumped slurry or is separated at (12) and is carried to surface by such a device as a conveyor while the water is pumped separately.

A pillar (6) is formed because the eroding jet is controlled so as not to erode the formation all the way to the roadway (5). The pillar (6) is Conned adjacent to the gateroad (5) where the directional drilling equipment is located.

In another embodiment of the invention, it is possible to pre-drill all of the boreholes (17) in the panel and use them for drainage of water and/or gas prior to mining.

FIG. 2 illustrates a borehole cross-section through the panel ofFIG. 1. Up dip, the roadway (4) has a goat zone (1) uphill from it and is therefore damaged. Drilling of the borehole (17) in this embodiment begins at the higher elevation roadway (5), and proceeds down to the lower elevation roadway (10). As noted above, at borehole location (13), a laterally eroding jet bit (not shown) is attached to the drill string (not shown) in the borehole (17). The jetting bit is shown at location (16) having eroded the zone (26). The shaded area (6) near roadway (5) depicts the pillar zone where mining does not take place so as to preserve the roadway (5) and the drilling machinery (27) located therein. The drill pipe in the borehole (17) is pulled back by the drill (27) which is used to manipulate the orientation of the drill string in the borehole (17) and with it the jetting bit. The roof above the orebody is marked as (21) and the floor as (20). Drainage ditches are formed in the floor of the roadways at (23,24,25). The ditch (23) carries the slurry of fluid and ore away from the mining area as originally did the up dip ditch (25) for the previously mined up dip panel. The ditch (24) carries drill fluid away from the directional drilling operation. The borehole spacing might be typically 5 to 10 m, limited by the eroding capability of the jetting bit within the particular ore type. While not shown, the borehole (17) is drilled at desired locations between roadways (5,10) using directional and/or spatial sensors and other equipment well known in the art. A survey and mapping of the formation can be made to determine where the various roadways should be made before the mining operation is commenced. The actual mining operation can be carried out using a camera or other visualisation device such as an acoustic scanner located at the jetting nozzle so that the operation can be observed and controlled by an operator at a remote location. Cameras utilising self cleaning lenses can be used to provide an unobstructed view of the mining operation and the need for adjustment thereof. Using a joystick, the operator can control the orientation of the jetting nozzle to selectively erode the ore panel, and at the same time remotely view the jetting operation to verify that it is progressing as desired. At times, if the drainage of the slurry is slowed due to blockage by excessive ore on the mine floor, borehole or ditches, the jetting erosion can be temporarily suspended so that the additional fluid can be used to flood the area and clear the drainage way of the excess ore. The advantage of the remote control of the jetting operation is that workers arc not in the area where there is a risk of the mine roof collapsing, or being overcome by dangerous gasses or outbursts.

FIG. 3 illustrates another embodiment showing a sectional view through an ore panel where the borehole (17) has been drilled up dip from roadway (10) to roadway (5). The borehole (17) has then been reamed to a large size. The drill string (not shown) equipped with a jetting nozzle has then been re-inserted into the borehole (17). The eroding jet bit is shown at location (33), and is moving downhill toward the roadway (10). The zone up dip of the eroding bit at (33) and below the roadway (5) has been removed by the action of fluid erosion. The ore and fluid mined has passed back down the enlarged borehole (17) to the drainage ditch (23). The zone (30) is not mined so as to form a barrier pillar and prevent caving damage to roadway (10). In its preferred embodiment, the enlarged borehole (17) is eroded to a larger size than the original borehole (17) by the use of a combination of different eroding bits, water flow or eroding time duration to suit requirements. The reaming of borehole (17) may also be accomplished by other means such as rotating mechanical reamers.

FIG. 4 is an enlarged view of the mining face at section4-4 of the operation depicted in

FIG. 1. Here, the lateral jetting bit is at (16) in borehole (17). The jetting bit (16) has lateral port(s) in it which make it jet laterally from the bit (16). The jets which issue from the lateral port(s) may be directed to sweep at different orientations by twisting the drill string within the borehole (17) using the drilling machine. This twisting is controlled by the operator working under the guidance of the survey system and visualisation system contained within the drill string and delivering information to the operator.

The roof of the orebody is shown at (21) and the floor at (20). The face which has been eroded is at (15) and solid ore is to the right of the jetting bit (16) and between the roof (21) and floor (20). A goat is formed at (2), because the roof of the excavated portion of the panel can no longer support the weight of the material thereabove. Angular movement of the jet (22) cuts ore from the face (15) which then flows down the floor (20) to the face at (16) and thence along the intersection of the eroded face (14) and the floor (20) into the ditch in the roadway (not shown) and outward.

While it is not shown in this figure, the potential exists to not use the jet (22) to cut the full way to the goaf (2) but rather leave a narrow pillar between, which is parallel to borehole (17). This pillar then serves to control the failure of the roof (21) into the area where flow of the mined ore slurry takes place. The use of such parallel pillars also retards goaf formation and permits ventilation of the mining area.

FIG. 5 illustrates the drilling operation conducted up dip from roadway (10). The dip direction is marked by an arrow (18). Here, the roadway (5) is at a higher elevation than the roadway (10), but the mining with the hydraulic jet starts at the higher end of the panel. The drill rig is positioned in the downhill roadway (10) at (31) and has drilled up grade to position (32) in the roadway (5). The borehole (17) is then reamed out and a lateral jetting bit (not shown) is attached to the end of the drill string (not shown). In the figure, the jetting bit is at location (16) and is shown cutting the face (15) of the ore panel. The mined ore and fluid flow down the borehole (17) to location (31) and thence into the ditch (not shown) in the roadway (10).

From the foregoing, it can be seen that ore panels can be mined without the utilisation of heavy and expensive equipment which is difficult to move from one panel to another. According to a feature of the invention, the mining of a panel of ore is commenced by forming a borehole from one roadway on one side of the panel, to the opposite roadway on the other side of the panel. The roadways are preferably sloped to carry the mined slurry of ore and a liquid used to erode the face of the panel. Similarly, the borehole is sloped so that the mined ore can be carried as a slurry either in it or along its former position to the downhill roadway. Once the initial borehole is formed through the ore panel to the opposite roadway, the drill bit is changed to a hydraulic jet, and a pressurised liquid is used to erode the sidewall of the borehole as the hydraulic jet is withdrawn back down the borehole. The sweeping up and down of the hydraulic jet as it is moves down the borehole forms a face of the ore panel. Once the first pass of the hydraulic jet is made to erode the sidewall of the borehole and the orebody across the panel, a second borehole is formed through the ore panel, and the hydraulic jet is again used to erode a subsequent slice of the panel face. The process continues until the entire panel of ore has been mined. During the mining of the ore using the hydraulic jet, the ore and liquid form a slurry that is carried down the bottom of the mined area, and again down the downhill roadway to a sump. A goaf is formed after an area has been mined, as the mined area can no longer support the roof. Should the roof of the mine prematurely collapse, a new borehole can be formed and the mining operation again commenced to continue mining the ore panel. Even if the ore formation is not oriented on slope, which is optimum, the mining operation can be carried out by forming the opposite gateroads with different elevations so that the slurry of ore is nevertheless carried downhill by the action of gravity. The system is best but not exclusively suited to narrow orebodies which are soft and thus easily eroded while having a hard roof and floor which is not easily eroded and which does not cave near the face. Thus an open area is left adjacent to the face and between it and the goaf to permit ventilation between the gateroads. The prudent use of the system would involve the capability to ventilate the upper and lower gate roads independently in the event of a face collapse which blocks air flow between gateroads. The use of the system following gas drainage drilling could be advantageous as the gas drainage boreholes could be re-used as the boreholes from which mining is undertaken by the described methods. Another advantage of the system is that the maximum amount of mining hardware that is at risk is the drill string, survey and surveillance tools and either a downhole motor and bit or the jetting assembly. This is significantly less machinery than is involved in conventional longwall mining operations.

While the preferred and other embodiments of the invention have been disclosed with reference to specific mining methods, structures and equipment, it is to be understood that many changes in detail may be made as a matter of engineering choices without departing from the spirit and scope of the invention, as defined by the appended claims.

Claims

1. A method of mining ore from a formation, comprising:

forming an underground upper roadway and an underground lower roadway in said formation to define an ore panel therebetween;

forming said lower roadway at an elevation generally below said upper roadway, and sloping the lower roadway downhill;

locating borehole drilling equipment underground in one of said upper roadway or said lower roadway;

forming a sloping borehole with a drill string connected to said drilling equipment, said sloping borehole formed from one said roadway to the other roadway and through the ore panel to be mined, and moving the drilling equipment in the roadway each time a different sloping borehole is formed;

using a jetting nozzle attached to the end of the drill string to produce a high pressure jet of a liquid;

moving the jetting nozzle through said borehole to erode the ore panel, where the pressurized liquid forms a slurry with the mined ore; and

allowing the slurry of mined ore and liquid to flow down the lower roadway to a sump.

2. The method of mining ore as described inclaim 1, further including forming a face in the ore panel by the erosion process, and forming a floor as the face of the ore panel recedes during the erosion process, and forming the floor with the solid panel of ore on one side, and a goaf on the other side.

3. The method of mining ore as described inclaim 1, further including creating a series of enlarged holes from whence ore is removed, with pillars of the ore panel standing therebetween.

4. The method of mining as described inclaim 1, further including sloping the upper and lower roadways and forming ditches therein for the conveyance of the slurry of mined ore to the sump.

5. The method of mining as described inclaim 1, further including drilling the bore hole from the upper roadway through the ore panel to the lower roadway;

connecting the lateral jetting nozzle to the drill string at the lower roadway;

using the drill string to move the jetting nozzle uphill toward the upper roadway, and controllably rotate the jetting bit so that an enlarged hole or face is formed in the ore panel by the jet of high pressure liquid; and

producing an ore bearing slurry by the erosion, and transporting the ore bearing slurry down the enlarged hole of the mining face created by the erosive process, to the lower roadway.

6. The method of mining as described inclaim 1, further including drilling the borehole from the lower roadway through the ore panel to the upper roadway;

attaching a reaming system to the drill string at the upper roadway;

reaming the borehole to a larger diameter;

attaching a lateral jetting bit to the drill string; and

using the jetting bit to erode the ore panel, starting at the upper level of the borehole, where the eroded ore then flows as a slurry back down the enlarged borehole to the lower roadway.

7. The method of mining as described inclaim 1, further including using a directional bottom hole assembly attached to the drill string to enable the drilling of a directionally controlled borehole in the ore panel.

8. The method of mining as described inclaim 1, further including moving the jetting nozzle through the borehole to erode a sidewall thereof and form a face of the ore panel, and then continuing the movement of the jetting nozzle laterally across the face of the ore panel to mine the ore of the formation.

9. The method of mining as described inclaim 1, further including moving the drill string into a different borehole to mine a new slice of the ore panel.

10. The method of mining as described inclaim 1, further including forming a pillar adjacent to one said upper or lower roadway to protect the roadway from collapsing, and forming said pillar by leaving the panel intact at the location of the pillar.

11. The method of mining as described inclaim 6, further including eroding a face in the ore panel to form a shape to induce backflow of the slurry toward the borehole to mine the ore panel.

12. The method of mining as described inclaim 6, further including forming the borehole at an angle with respect to a horizontal reference so that the slurry is carried downhill by the borehole.

13. The method of mining as described inclaim 1, further including using the jetting nozzle that produces a narrow jet of high pressure liquid oriented generally in plane perpendicular to the drill string so as to permit erosion of the ore panel.

14. The method of mining as described inclaim 1, further including forming a goaf at locations where the mined ore is removed from the ore panel.

15. The method of mining as described inclaim 2, further including mining the ore panel by sweeping a high pressure liquid jet across the face of the ore panel to mine the face of the ore panel and cause the ore panel face to recede and form the sloping floor, and allow the ore bearing slurry to flow down the sloping floor along the solid ore panel of ore, away from the goaf and toward the lower roadway.

16. The method of mining as described inclaim 1, further including using a visual survey system at a mining location where the ore panel is eroded by the jetting nozzle to provide a remote video representation of the operation.

17. The method of mining as described inclaim 1, further including using an acoustic or other survey system at a mining location where the ore panel is eroded by the jetting nozzle to provide a remote representation of the operation.

18. The method of mining as described inclaim 1, further including using a survey system to provide an operator with knowledge of the orientation of the jetting nozzle.

19. The method of mining ore as describe inclaim 1, further including moving the drilling equipment downhill in one said upper or lower roadway each time mining of a slice of an ore panel has been completed.

20. The method of mining ore as described inclaim 1, further including forming a lateral roadway perpendicular to both said upper roadway and said lower roadway, said lateral roadway sloping downhill from said upper roadway to said lower roadway so that a slurry of mined ore from an ore panel located above said upper roadway can flow down said lateral roadway to said lower roadway and then to said sump.

21. The method of mining ore as described inclaim 1, further including sweeping the jetting nozzle about an arc from a floor of the formation to a roof of the formation, and moving the jetting nozzle axially along said borehole to cause a face of the ore panel to recede in the direction of movement of the jetting nozzle, and allowing the slurry to flow downhill on the floor toward the borehole and then perpendicular downhill to the lower sloping roadway.

22. The method of mining ore as described inclaim 21, further including moving the jetting nozzle downhill from one borehole to a subsequent borehole to mine subsequent slices of said ore panel.

23. A method of mining ore from a formation, comprising:

defining plural panels of ore to be mined in said formation;

forming an underground upper roadway and an underground lower roadway in said ore panel;

forming said lower roadway at an elevation lower than said upper roadway, and sloping said lower roadway downhill;

locating borehole drilling equipment underground in one of said roadways;

forming a sequence of adjacent sloping boreholes with a drill string and drill bit connected to said drilling equipment from one roadway to the other roadway and through an area of the ore panel to be mined, and moving the drilling equipment in the roadway each time a sloping borehole is formed;

moving the jetting nozzle axially through each borehole to erode a slice of the ore panel between boreholes, and eroding the ore panel with the pressurized liquid to form a slurry of the mined ore, the eroding of the ore panel forming a sloped junction where a face of the unmined ore panel joins a floor formed by the mined ore panel; and

allowing the slurry of the mined ore and liquid to flow down the sloped junction to the downhill sloping lower roadway, and then to a sump.