AP375A

AP375A - Selective mining method and apparatus.

Info

Publication number: AP375A
Application number: APAP/P/1992/000365A
Authority: AP
Inventors: Marc Octave Rene Ghilslain Buyer BUYENS; John Redvers Hunt; Peter Lance Desmond O'toole; Damien Pennefather; Anthony Ian Smith; Marthinus Johannes Taljaard
Original assignee: Advanced Mining Software Ltd
Priority date: 1991-03-01
Filing date: 1992-02-28
Publication date: 1995-01-11
Also published as: CA2062077A1; AP9200365A0; BR9200712A; AU1133292A; AU645663B2

Abstract

The method is

Description

BACKGROUND TO THE INVENTION

THIS invention relates to a selective mining method and apparatus.

In underground gold mines, the gold itself is often contained in a very narrow reef, typically with a width of 300mm or so. Traditionally, the reef is won from the working face of a stope which has a width great enough to permit personnel access to the working face. The end result is that a vast quantity of barren rock must be recovered, along with the reef, for subsequent processing, because the blasting that is used to advance the working face is non-selective in the sense that the reef becomes inextricably mixed up with the barren rock.

SUMMARY OF THE INVENTION

In its broadest terms, the present invention provides a selective mining method in which substantially only the mineral-bearing reef is won.

The invention provides a method of selectively recovering ore-bearing reef from a rock mass in a mine, the method comprising the steps of forming spaced apart access gullies in the rock mass, the gullies extending in the direction of mining, using a saw to form cuts in the rock mass, the cuts extending between the gullies and being situated just above and just below the reef, and recovering the reef from between the cuts while leaving barren rock above and below the reef intact.

Conveniently, the cuts are made using a diamond wire saw extending between the gullies.

In one version of the method, a hole is drilled from one gully to the next behind the mining face, a wire saw is threaded through the hole and is looped about the rock mass defined by the gullies, the hole and the mining face, and the wire saw is driven longitudinally in such a manner as to form a cut through the rock mass just above or just below the reef and extending between the gullies. The wire saw is preferably driven longitudinally along a path defined by a series of pulleys, and wherein the position of one of the pulleys is changed, as the wire saw is driven, in a manner to cause the wire saw form the cut in the rock mass.

In another version of the method, the wire saw is driven longitudinally and is pushed or pulled against the mining face, in the mining direction, to form a cut through the rock mass just above or just below the reef and extending between the gullies.

In either version, the cuts may be made separately or simultaneously.

After the cuts are formed, the reef can be broken out from between the cuts and is then moved sideways out of the face into one or other of the gullies for subsequent recovery. Various techniques are proposed for breaking out the reef from between the cuts, including hammering wedges into one or both cuts, blasting detonation cord threaded through one or both cuts, detonating explosives located in blastholes drilled into the reef from one or both gullies, and by means of an impact hammer.

After the reef has been broken out from between the cuts, it can in some cases be moved into a gully by means of water jets, or by mechanical or hydraulic rams.

For ease of removal of the reef, it is preferred that the cuts be formed in non-parallel planes.

The method summarised above finds particular, but not sole, application in the recovery of gold bearing reef in gold mining operations.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will now be described in more detail, by way of example only, with reference to the accompanying drawings in which:

Figure 1	shows a vertical cross-section at an underground location in a gold mine, looking in the direction of mining advance;
Figure 2	shows a diagrammatic plan view illustrating one method contemplated by the invention;
Figure 3	shows a diagrammatic plan view illustrating another method contemplated by the invention;
Figure 4	shows a cross-section illustrating a technique for breaking out the reef after sawing;
Figure 5	shows a similar cross-section illustrating another technique for breaking out the reef after sawing;
Figure 6	shows a similar cross-section illustrating a still further technique for breaking out the reef after blasting;
Figure 7	shows how the reef can be moved to the gully; and
Figure 8	shows a view similar to that of Figure 1 in which the saw cuts are not parallel.

- 5 DESCRIPTION OF EMBODIMENTS

In Figure 1, the numerals 10 and 12 refer to gullies which are formed in the rock mass in an underground gold mine. Each gully has dimensions sufficient to permit personnel access. The gullies may, for instance, have a width 14 of 1,2m or more. The gullies are spaced apart by about 15m or possibly more. Figure 1 illustrates a case in which the gullies are developed along the strike direction. Alternatively, they can be developed along the direction of dip.

The gold-bearing reef, which dips from right to left in Figure 1, is indicated with the numeral 16 and the numerals 18 and 20 indicate upper and lower cuts made respectively just above and just below the reef 16. The cuts 18 and 20 extend from one gulley to the other and will, in a typical case, be spaced apart by a vertical distance of about 300mm.

Referring now to Figure 2, the numeral 22 denotes the mining face i.e. the current position of the reef. It will be noted that the gullies 10 and 12 extend, in the mining direction 24, for quite some distance into the rock mass beyond the face 22. Ideally, the gullies are pre-developed, since this will greatly facilitate the reef recovery methods described below.

Using drilling equipment (not shown) in one of the gullies, a hole 26 is formed from one gully to the next at a level just above the upper surface of the reef 16, i.e. at the level of the cut 18. At the same time, another hole 28 is formed from one gully to the next at a level just below the lower surface of the reef 16, i.e. at the level of the cut 20.

An endless diamond impregnated wire saw 30 is threaded through the hole 26, is looped about the exposed surface 34 in the gully 12, and is passed across the face 22 back to the gully 10 where it is looped about a drive pulley 36. As it enters the hole 26, the wire saw passes about a guide pulley 38 and as it reaches the end of the face 22 at the gully 10, it passes about a further guide pulley 40. It will be seen that the wire saw forms an endless loop about the various surfaces and pulleys.

The drive pulley 36 is connected to a drive mechanism 42 which drives the pulley in rotation. The drive mechanism is also capable of driving itself along a track 44 located in the gully 10.

In use, with the drive mechanism operative, the wire saw moves continuously in the direction indicated by the arrows 46. At the same time, the drive mechanism 42 moves slowly along the track in the direction of the arrow 48. This causes the wire saw to cut into the rock, the broken lines in Figure 2 illustrating successive positions of the wire saw as cutting proceeds. Eventually the wire saw cuts right through the rock mass between the gullies. Thus the cut 18 is formed.

Thereafter, the lower cut 20 is made by following the same procedure at the lower level. Figure 4 illustrates the resultant situation. It is anticipated that the rock mass 50 formed between the cuts 18 and 20 may break off at the line 52 under its own weight if favourable fracture patterns are present.

It should be noted that the cuts 18 and 20 could be formed simultaneously, after initial drilling of the relevant inter-gully holes, with a single wire saw formed into a double-loop configuration. This would have the advantage that it would be possible to provide a single wire saw drive for forming both cuts. As a further alternative, separate wire saws, each with its own drive, could be used to form the cuts simultaneously.

If the mass 50 does not break off under its own weight, wedges 54 (Figure 4) can be hammered into the cut 18 as illustrated to encourage breaking. As an alternative to wedges, ribbon-type elongate explosive charges 53 (Figure 5) can be threaded into the cuts 18 and 20 and detonated to initiate the desired breakage. The charges may, for instance, be constituted by appropriate lengths of detonating cord. The threading operation can be carried out with the aid of a stiff wire fed through the relevant cut, tied to the detonating cord and pulled back through the cut. The detonating cord may be embedded in inert packing material shaped for the blast to be directional i.e. upward or downward as required.

In cases where the cuts 18 and 20 have closed and it is impossible to insert wedges or detonating cord as just described, a blasting technique can be employed to liberate the reef from between the cuts. In this case, blastholes are drilled sideways from the gullies into the rock mass which exists between the upper and lower cuts, i.e. into the plane of the paper in a Figure such as Figure 4. The blastholes are charged with explosive which is then detonated to break up the rock between the cuts, thereby facilitating later removal. The presence of the cuts prevents damage to the rock above the upper cut and below the lower cut respectively.

- 8 Another technique that could be used in situations where closure of the cuts prevents insertion of wedges or detonating cord is that of employing a low profile impact hammer, operating sideways from the gullies, to break up the rock mass between the cuts. When compared to the explosive method just described, the use of impact hammers would allow mining to take place substantially continuously without the necessity to stop mining operations during blasting.

Yet another technique for severing the mass 50 is illustrated in Figure

6. In this case, a vertical slot 55 is formed between the cuts 18 and 20 using an endless wire saw of a kind similar to that used for the cuts 18 and 20. The wire saw is fed through the cut 18 from the gully 10, is looped over the end of the mass 50 in the gully 12 and is fed back through the cut 20 to the gully 10 where a drive mechanism operating in a manner similar to that of the drive mechanism 42 is provided. Naturally, appropriate direction-changing guide pulleys are also provided where appropriate.

Figure 3 illustrates another method for forming the cuts 18 and 20. In this case, the diamond impregnated wire saw 30 is looped about pulleys 70, 71, 72, 74 and 76 and is initially arranged in the manner illustrated in solid lines. The pulley 76 is connected to a drive mechanism 78 which rotates the pulley 76 and is also capable of driving itself along a track 80 in the direction 81. The pulleys 70, 71, 72 and 74 are fixed in position.

With the drive mechanism operative, the wire saw is pulled through the rock mass in the direction of the arrow 82. The broken lines in Figure 3 indicate successive positions of the relevant run of the diamond wire saw 30 as cutting proceeds. As in the case of Figure 2, the cuts 18 and 20 are made either separately or simultaneously.

As an alternative to the drive mechanism moving in the direction of the arrow 81, the pulleys 70 and 72 could be moved apart from one another as indicated by the arrows 84, or in the mining direction as indicated by the arrows 86. The driven pulley 76, and the pulley 74, would in this case be fixed in position.

Having made the cuts 18 and 20 with the technique of Figure 3, the rock mass 50 is separated from the surrounding rock using the appropriate one of the techniques described above.

Having achieved separation of the mass 50 from the surrounding rock, it is necessary to recover it for subsequent winning of the gold which it contains. This will be facilitated if the mass 50 itself breaks up into smaller rock pieces as a result, for instance, of favourable fracture patterns in the mass.

Figure 7 illustrates one possible technique for removing the mass 50 for subsequent processing. In Figure 7, high pressure water jets 60 located in the gully 10 are used to drive the broken material of the mass 50 in the down dip direction into the gully 12 from where it can be removed with conventional scrapers or the like.

As an alternative to the use of high pressure water jets, another possibility is to used mechanical or hydraulic ram devices in the gully 10 to push the broken material into the gully 12 for subsequent removal.

The latter technique will be particularly useful in situations where the rock mass 50 does not itself break up markedly, since water jets in such situations will be unlikely to be capable of moving very large rock pieces in the desired manner.

The job of pushing the mass 50 into the gully 12 is further facilitated if the cuts 18 and 20 are not parallel, as indicated in Figure 8, since the resultant mass 50 will have a wedge shape that is less likely to jam when attempts are made to push it towards the gully 12.

As mining proceeds, and the gullies 10 and 12 advance, worked out areas thereof can be filled up with waste rock or backfill.

It is believed that the practice of the invention as described above can lead to a number of important advantages including inter alia, the following:

1. The mining method is selective in the sense that substantially only the reef, and little other rock, is removed from the mine for subsequent processing to liberate the gold. The surface processing equipment may therefore have a far lower capacity than in the case of conventional stoping techniques. Alternatively, with the same surface processing capacity, the recovered ore can be treated for a longer period of time, increasing the percentage recovery of the desired mineral.

2. Aside from the formation of the gullies, which will probably be achieved using conventional blasting techniques, the mining can proceed around the clock This is in contrast to conventional stoping practice, where there is considerable down-time after each blast while personnel wait for blast-created gases to dissipate.

3. Except near the gullies, there may be no need to provide the conventional array of temporary and permanent stope supports to support the hanging wall. The mined out areas will of course close with time in the normal way.

4. Because there is a far smaller mined area when compared to a conventional stoping system, it is anticipated that refrigeration and ventilation requirements will be substantially reduced.

5. In view of the smaller mined volume, and accordingly the smaller the change in the rock environment it is anticipated that the rock mass will be less prone to rockbursts.

A possible disadvantage of the method described above is the fact that it may not be appropriate in cases where the reef is non-tabular, i.e. the reef undergoes a number of steps and changes in direction, although in cases where the rock mass is faulted, it is expected that prior knowledge of the geology could enable the gullies to be positioned in such a manner as to allow efficient reef extraction with a minimum distance between the cuts.

Claims

1.

A method of selectively recovering ore-bearing reef from a rock mass in a mine, the method comprising the steps of forming spaced apart access gullies in the rock mass, the gullies extending in the direction of mining, using a saw to form cuts in the rock mass, the cuts extending between the gullies and being situated just above and just below the reef, and recovering the reef from between the cuts while leaving barren rock above and below the reef intact.

2.

A method according to claim 1 wherein the cuts are made using a diamond wire saw extending between the gullies.

3.

A method according to either one of the preceding claims wherein a hole is drilled from one gully to the next behind the mining face, a wire saw is threaded through the hole and is looped about the rock mass defined by the gullies, the hole and the mining face, and the wire saw is driven longitudinally in such a manner as to form a cut through the rock mass just above or just below the reef and extending between the gullies.

4.

A method according to claim 3 wherein the wire saw is driven longitudinally along a path defined by a series of pulleys, and wherein the position of one of the pulleys is changed, as the wire saw is driven, in a manner to cause the wire saw form the cut in the rock mass.

5.

A method according to either one of claims 1 or 2 wherein the wire saw is driven longitudinally and is pushed or pulled against the mining face, in the mining direction, to form a cut through the rock mass just above or just below the reef and extending between the gullies.

6.

A method according to any one of the preceding claims wherein the cuts are made separately.

7.

A method according to any one of claims 1 to 5 wherein the cuts are made simultaneously.

8.

A method according to any one of the preceding claims wherein, after the cuts are formed, the reef is broken out from between the cuts and is moved sideways out of the face into one or other of the gullies for subsequent recovery.

9.

A method according to claim 8 wherein the reef is broken out from between the cuts by hammering wedges into one or both cuts.

10.

A method according to claim 8 wherein the reef is broken out from between the cuts by detonating detonation cord threaded through one or both cuts.

11.

A method according to claim 8 wherein the reef is broken out from between the cuts by detonating explosives located in blastholes drilled into the reef from one or both gullies.

12.

A method according to claim 8 wherein the reef is broken out from between the cuts by means of an impact hammer.

13.

A method according to any one of claims 8 to 12 wherein the reef, after it has been broken out from between the cuts, is moved into a gully by means of water jets.

14.

A method according to any one of claims 8 to 12 wherein the reef, after it has been broken out from between the cuts, is moved into a gully by mechanical or hydraulic rams.

15.

A method according to any one of the preceding claims wherein the cuts are formed in non-parallel planes.

16.

A method according to any one of the preceding claims when used in the recovery of gold bearing reef.