CA1220232A - Open pit mining - Google Patents

Abstract

Abstract In open pit mining for tar sands ore, once the overburden has been removed, the ore is mined by forming an initial cut that extends longitudinally away from a dump station (extraction plant). Continued removal of overburden and mining of ore is accomplished by repeatedly widening this cut in such a way that the sides of the cut still extend at least approximately radially away from the dump station. The result is to form a first, generally triangular module. Subsequently, and preferably at least in part simultaneously, a second and subsequent triangular modules are formed. The ore is transported by trucks to one or more collection points below ground level, at which location it is loaded onto conveyors for transport to the dump station. The arrangement has improved efficiency and flexibility over prior mining schemes.

Description

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Open ~it mininq This invention relates to improvements in open pit mining and adopts procedures that are especially suited to the mining of tar sands. The invention is concerned with improvements in the layout and method of operation of such a mine.
In my prior Canadian patent No. 1,132,147 issued September 21, 1982, there is disclosed a method of open pit mining for tar sands ore that involves removing over-burden and mining the ore longitudinally along at least two strips to commence the formation of elongated cuts that diverge from each other away from a common dump station located adjacent an extraction plant. The strips diverge frcm each other at an angle between about 45 and about ~0, preferably around 60. The ore so mined is hauled along each cut by a fleet of trucks to the dump station. As mining continues each of the cuts is widened laterally. This is done by removing overburden and longitudinally mining ore from further strips adjacent and parallel to the initial strips~ The result is to cause each adjacent pair of the widened cuts to open to a track that becomes common to the two cuts. This common track extends to the dump station and acts as a route for hauling ore to the dump station from both the cuts.

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This arrangement was designed to shorten the haulage routes for the trucks travelling from the mining faces to the dump station, in comparison with prior designs of open pit mines.
The present invention represents an alternative scheme which incorporates some of the features disclosed in my earlier patent, but also provides some additional improvements.
The very high capital cost and long lead time necessary to put a "mega" sized tar sand project into operation, suggest that a less capital intensive approach should be sought. This lower capital approach may be accomplished by using the scheme of my earlier patent with mobile equip-ment, by developing the mine at a slow rate and expanding by adding more mobile mining equipment in increments, together with extra trains in the extraction and upgrading plants. The lower capital objective can also be accomplished by reducing the size of the sectors initially mined with the same "common track" haulage pattern.
However, as the size of the sectors is reduced, the length of the access ramps and other dimensional features require some modification of the patented scheme. The present invention will still involve mining a series of benches from the surface to the base oÇ the ore at each incremental advance of the mining faces from an initial slot. However, the present invention differs from the prior scheme in that the incremental advances are pie shaped (by which I mean the shape of a segment of a pie, i.e. essentially triangular) and take place in relatively small modules. For greater efficiency and flexibility it is ~referred to operate two modules simultaneously, although one may (and usually will) begin before the other, thus enabling the generation of revenue with a minimum of initial capital expenditure.

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In addition, in the present invention haulage by truck does not take place to the surface using a common track to the dump. Instead, the ore is trucked from the mining face on the bench to a collection point that is below surface level, preferably intermediate in level between the surface and the pit bottom. From this collection point the ore is transported by a conveyor to the surface and to the extraction plant dump. This combination of transporting means (first trucks, then a conveyor) provides a combin-ation of flexibility of operation and eCOnQmy of energy, since it is cheaper to convey the ore to the surface by a conveyor. While bringing the ore from the mining benches to the conveyor feeder at the collection point may require the trucks to do some lifting from levels below that of the collection point, this lifting is much less in vertical height than if the trucks were required to elevate the ore all the way to the surface.
The advantage of this system is thus relatively short haul by truck ~generally shorter than the patented scheme) and minimal lifting in elevation of material by truck (much less than in the patented scheme~. The lifting is more efficiently handled by conveyor~ and ultimately (as the mine expands by adding additional modules) ~airly long distance transport is also handled by conveyor. On the other hand, another advantage of the system, as compared with the dragline and bucketwheel schemes currently in use, is very short conveyors. Initially the conveyors would be a small fraction of the length of those used in the presently operating mines at Suncor and Syncrude in Alberta. The capital costs, as well as the operating costs, would thus be low in comparison. The modular approach to expansion, which is largely responsible for the lower initial costs, operates effectively and efficiently with the present ore transportation scheme, which would not be the case for large dragline and bucket wheel systems such as are in use at the Suncor and Syncrude projects.

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A scheme embodying the present invention is illustrated by way of example in the accompanying drawings, in which:
Figure 1 is a plan view of an initial cut;
Figure 2 is an isometric view of Figure l;
Figures 3A and 3B extend into one another and represent a section on A-A' in Figure l;
Figure 4 is a section on B-B' in Figure l;
Figure 5 is a plan view corresponding to Figure 1 but at a later stage in the mining operation;
Figure 6 is an isometric view of Figure 5;
Figure 7 is a section on A-A' in Figure 5;
Figure 8 is a plan view of the mining operation at a still later stage;
Figure 9 is an isometric view of Figure 8;
Figures lOA and lOB (with Figure 7) extend into each other and represent a section on A-A' in Figure ~;
Figures llA and llB extend lnto each other and represent a section on B-B' in Figure;
Figure 12 is a plan view of yet a further stage 20 illustrating the division of the mine into modules;
Figure 13 is an isometric view of Figure 12;
Figure 14 is a plan view of the mine showing further modules;
Figure 15 is an isometric view of Figure 14; and Figure 16 shows a completed layout diagrammatically.
Figures 1-4 illustrate an initial cut extending from an extraction plant 10 which will include a dump station (not separately shown). These views show the situation at a stage when a sector of overburden (shown generally by 30 horizontal hatch lines) has been removed and mining of ore has begun. At this stage, ore from the pit bottom 11 is trucked up a ramp 12 to a hopper/breaker 13 ~or breaking up the ore if necessary and loading it onto the foot of a conveyor 14 which has a first upwardly inclined section 35 14a, followed by a flat section 14b at ground level and a ~2~3,q~

final, upwardly inclined section 14c extending into the dump station portion of the extraction plant 10. The ore will have been mined by conventional methods (not shown) such as large power shovels.
Overburden stripping is continuing in an area 15 and is just about to commence at a location 16, these regions being connected to the pit by ramps 17 and 18 respectively.
Other ramps 19 to 23, some of which are constructed as permanent roads, interconnect the various areas and eventually lead up to the ground level including providing access to additional, back-up hopper/breakers 24 situated at ground level and feeding to a further section 14d of the conveyor 14. The arrows on the ramps and roads indicate the direction of upward incline (typically 8%) 1~ and the arrows on the conveyor sections indicate their feeding direction. The arrows at the side of the cut in Figures 1 and 2 indicate the direction of mining, as will be more apparent from the next series of views (Figures 5-7) showing a somewhat later stage in the mining 2Q operation, Figures 5 to 7 show development of the mine as a result of continued widening of the cuto It will be noted that the portions of the sides of the cut furthest from the extraction plant 10 are widened more than the nearer portions so that these sides continue to extend substant-ially radially from the extraction plant 10, i.e. the cut has begun to take on the general shape of a pie segment~
This result is achieved by continuing to strip overburden at areas 30 and 31, as before, and to mine ore at various 3Q shovel faces 32 to 35. The hopper/breakers 13 and 24 are unchanged as is the conveyor 14 and the general ramp and road system. More permanent roads 36 and 37 have been provided to facilitate the transportation of ore to the hopper/breaker 13~ and a waste dump 38 for the stripped overburden has been begun. In making the preliminary cut (Figures 1-~) it had been necessary to haul the overburden away to an external waste dump (not shown), but this is now no longer necessary.
Eventually the mine will have developed to the status shown in Figures ~-11, by which time the triangular shape of the cut in plan view is clearly evident. The waste dump 38 now has roads 39 and 40 on it for bringing the stripped overburden to the dump. It also has a central ramp 41 for conveying road construction material from a limestone quarry ~2 assuming that such rock is available below the level of the pit bottom. Otherwise the operation continues essentially as already described, there now, however, being additional permanent roads 43-45 constructed to facilitate haulage. The roads 43 and 44 are for truck-ing ore to the hopper/breaker 13 and the road 45 for hauling reject to the dump. Overburden stripping continues along the sides at 30 and 31, as before, and mining continues at shovel faces 46, 47 and backhoe ~ace 48. In additional to indicating up-grades, some of the arrows in Figures 8 and 9 now represent travel directions and mining directions.
It should be noted in comparing the three stages illustrated so far (compare, for example, Figures 1, 5 and 8) that the cut has not only been continuously widened towards a triangular form but simultaneously lengthened in the direction away from the extraction plant. Eventually the outwardly expanding sides will reach a position in which they are substantially perpendicular to each other and encompass the laterally projecting portion containing the road 22. Thus completed, the area, which will now be referred to as module 1, is an shown on the left hand side of Figure 12 or 13, having the shape of an isosceles tri-angle with its longest side 50 remote from the extraction plant 10.

Figures 12 and 13 also show module 2 which will have been started after module 1 began but before module 1 was completed. Obviously, the particular sequence and overlap of module construction can be varied to suit conditions on the site and the capital and labour available. Frequently, the preferred sequence will be to have some overlap between module development while keeping them to some degree out of phase. For example, Figures 12 and 13 show module 1 complete, module 2 nearly complete, module 3 started and module 4 also started but somewhat behind module 3 in development.
The further development of module 1 shown in Figures 12 and 13 includes an extension 14' of the conveyor 14 to a hopper/breaker 13l located on the pit bottom along the side 50, i.e. at the end of the basic cut remote from the extraction plant 10. The conveyor extension 14' passes under a road at 51 and on an overpass at 52. Numeral 53 designates a quarry below pit bottom level and 53' a site for a future extension of such quarry. It will be noted that the road 22 is common to ~he road systems of modules 1 and 2, which latter module does not yet include the conveyor extension 14' but soon will. At present t~e early stages of module 4 are supported by the road system of module 2, while conveyance of material from module 3 will be carried out principally by the extended and original conveyors of module 1. Module 2 will not require any equivalent to the back-up hopper/breakers 24 or conveyor section 14d because of the common road 22 interconnecting the modules.
The shape of modules 3 and 4 will necessarily differ to some extent from that of their respective parent modules 1 and 2. For example, the sides 54 and 55 of module 3 will be rotated about a centre located approximately in the vicinity of the hopper/breaker 13i as this module is expanded, the angle between these sides ~z~

eventually reaching 180, in contrast to the final angle between the sides of module 1, which is 90~ Hence module

2 eventually achie~es the shape of an isosceles triangle but this time with the apex at the remote corner. This arrangement will be best understood from Figures 14 and 15 which show modules 1, 2 and 3 complete, module 4 almost complete and modules 5 and 6 in different stages of early development. Another ma~or addition to the mine shown in these latter ~igures is a trunk conveyor 56 and a parallel road 57 extending from the extraction plant 10 along the adjacent edges of modules 1 and 2 to a hopper/breaker 58 at the remote ends of such edges, namely at a new pivotal centre from which modules 5 and 6 grow and expand.
Figure 16 shows diagrammatically an area of ground (typically ~ km x 4km) in which a pattern of eight modules 1-8 have been mined in this way over a period of say thirty years. Lines 60 and 61, i.e. the limits of modules 1 and 2, might typically be approximately the mining limits for the first seven and a half year, and lines 62 and 63 (limits of modules 3 and 4) the mining limit for year 15, although as already mentioned the left and right hand sides of the mine will preferably not be mined exactly simultaneously with each other. Lines 64 and 65 represent the approximate 22 1/2 year limit and lines 66 and 67 the 30 year lirnit. The hopper/breakers 13 and 24 will be used typically for about the first 7 1/2 years; then the hopper/
breakers 13' for a second 7 1/2 years. Conveyance to the extraction plant 10 during the second 15 years will be along the trunk conveyor 56 from hopper/breaker 58. The arrows show the mining directions.
I~ desired this entire pattern can be repeated in the region 68 below the extraction plant 10 as seen in Figure 16, either subsequently, simultaneously or partly simultaneously.

g Advantages of the mining scheme described and illustrated are as follows:
1. The modular concept shortens conveying and hauling distances.
2. Mining radially, i.e. in pie or fan shapes that are expanded laterally, also shortens these distances.

3. Locating the hopper/breakers below ground level ]imits the amount of lifting by trucks; it is cheaper to lift by conveyor.
. The module repeat pattern allows use of a trunk conveyor for servicing the later modules.
5. The modular concept also lends itself to a large variety of configurations that can be adapted to the shape of the ore body.
6. The geometry of the modules shortens haulage routes and permits the sharing of roads between modules; the distances for trucking waste are reduced as well as the distances for hauling ore;
7. The o~lter limits of the first module form a straight line that provides a desirable base for the third module and so on.
8. Since it is usually necessary to construct roads with rock when mining tar sands, the scheme provides ready access to the pit bottom to form quarries at convenient locations for the work areas.
9. The direct dumping of overburden in the pit is facilitatedO
10. The modular concept facilitates starting on a small scale and mining even only a single module economically, until capital for expansion is available. There is no need for bucket wheel and drag line equipment which is very expensive.

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11. The scheme is adapted to the use of relatively less expensive equipment, namely, trucks, shovels and backhoes.
12. Use of shovels permits selective mining, i.e.
picking off layers of good ore and centre re]ect, avoiding contaminating good ore with bad ore and reducing tailings and the handling thereof.
13. The modular concept also provides the alternative of rapid expansion, since many modules can be developed and mined simultaneously.
14. Multiple conveying with relatively short conveyors to a single point, i.e~ a dump station at an extraction plant, is efficient and reliable.
15. The modular concept further enables ~he initial cut of each module to choose the area with the best ore. The configuration need not in practice be as symmetrically laid out as in the drawings, but may be modified and adapted to the shape of the ore body. An initial cut need not necessarily be central to the shape of the final module.
16. This flexibility facilitates the omission of any area with bad ore. Conventional mining layouts have usually involved mining through a bad area because to do otherwise would disrupt the entire operation.

Claims (8)

Claims:

1. A method of open pit mining comprising (a) removing overburden and mining ore to form an initial cut extending generally longitudinally away from a dump station, (b) continuing to remove overburden and to mine ore by repeatedly widening said cut, each stage of widened cut so formed having sides extending generally radially from a location in the vicinity of the dump station whereby eventually to form a first mined module of generally triangular shape with the dump station at or near an apex thereof, and (c) transporting the ore obtained by such continued mining to the dump station and the overburden so obtained to a waste dump.

2. The method of claim 1, including repeating steps (a) to (c) for a second module of generally triangular shape having the dump station at or near an apex thereof, the mining of such second module taking place at least partially simultaneously with the mining of the first module.

3. The method of claim 1 or 2, including prior to or simultaneously with step (b) in the formation of each module, setting up a conveyor to extend from a collection point located part way along said initial cut at an elevation below ground level, and carrying out the transportation of ore under step (c) by hauling said ore by a fleet of trucks to said collection point for transport to the dump station by the conveyor.

4. The method of claim 1 or 2, wherein in the formation of each module, the waste dump for the overburden is formed on the pit bottom generally centrally of the widened cut.

5. The method of claim 2, wherein the initial cut taken under step (a) during the mining of each of said first and second modules includes a portion projecting laterally from the general longitudinal extent of such initial cut, such portion being employed to provide a road from the mine to the ground surface, the two modules being located with their edges adjacent each other and with said laterally projecting portions overlapping whereby at least a part of each said road is common to the two modules.

6. The method of claim 1, including (d) prior to or simultaneously with step (b), setting up a conveyor to extend to the dump station from a collection point located part way along said initial cut at an elevation below ground level, and carrying out the transportation of ore under step (c) by hauling said ore by a fleet of trucks to said collection point and subsequently transporting the ore to the dump station by the conveyor, and (e) subsequently commencing a further module in accordance with steps (a) to (c), except that the cut of said further module, as it is widened, radiates generally from a location at or near the end of the initial cut of the first module remote from the dump station, and extending the conveyor of the first module into the further module for transport of ore mined in the further module along such extended conveyor and the original conveyor of the first module to the dump station.

7. The method of claim 2, including (d) prior to or simultaneously with step (b) in the formation of each module, setting up in each module a conveyor to extend to the dump station from a collection point located part way along the initial cut at an elevation below ground level, and carrying out the transportation of ore under step (c) in each module by hauling said ore by a fleet of trucks to said collection point and subsequently transporting the ore to the dump station by the conveyor, and (e) subsequently commencing third and fourth modules in accordance with steps (a) to (c) except that the cuts of the third and fourth modules, as they are widened, radiate generally from respective locations at or near the ends of the initial cuts of said first and second modules remote from the dump station, and extending the conveyors of the first and second modules into the third and fourth modules for transport of ore mined in said third and fourth modules along the extended and original conveyors of the first and second modules to the dump station.

8. The method of claim 2 or 7, including setting up a trunk conveyor to extend from the dump station along adjacent edges of the first and second modules to a transfer point at the remote end of said edges, and subsequently mining at least one further module with mined ore being transported to the dump station along a conveyor of the further module to the transfer point and hence along the trunk conveyor to the dump station.