WO2010017582A1

WO2010017582A1 - Mining system

Info

Publication number: WO2010017582A1
Application number: PCT/AU2009/001025
Authority: WO
Inventors: Collette Amos; John Clarence Box
Original assignee: Technological Resources Pty Ltd
Current assignee: Technological Resources Pty Ltd
Priority date: 2008-08-11
Filing date: 2009-08-11
Publication date: 2010-02-18
Anticipated expiration: 2011-02-11
Also published as: AU2009281697A1; CA2733640A1; US20110175429A1; ZA201101049B; CN102119261A; BRPI0917528A2; CL2011000312A1

Abstract

A method of mining ore in a mine pit (3) and a mine are disclosed. The method comprises drilling and blasting ore in a bench (19) of ore within the mine pit and collecting ore blasted from the bench from a floor (5) of the mine pit using at least one mobile excavation machine (11). The method also comprises delivering ore that has been collected by the mobile excavation machine to at least one mobile-in-pit crusher (41), and transporting crushed ore to outside the pit on at least one ladder conveyor (23) that extends up the wall of the pit.

Description

MINING SYSTEM

The present invention relates to mining ore that contains valuable metals.

The present invention relates particularly, although by no means exclusively to mining iron ore.

Conventional open pit mining of iron ore comprises progressively drilling and blasting sections of an ore body so that the ore can be picked up by shovels or other suitable excavators and transported from a pit on haulage trucks. It is known to mine iron ore in large blocks using a series of benches so that various mining activities can be carried out concurrently in a pit. A bench, which may be for example 40-200 m long by 20-100 m deep by 10-15 m high and containing many thousands of tonnes of ore and/or other material, is first drilled to form a pattern of "blast" holes . The material removed during the course of drilling the blast holes is analysed, for example by chemical analysis, to determine whether, on average, the ore is (a) high grade, (b) low grade or (c) waste material. The cut-off between high and low grades is dependent on a range of factors and may vary from mine to mine and in different sections of mines. The bench of ore is blasted using explosives, typically ANFO (ammonium nitrate/fuel oil) based, that are dispensed in specially designed bulk dispensing trucks which can regulate the explosive density prior to loading down the blast holes. The blasted material is picked up by earth moving vehicles in the form of excavators such as electric rope shovels, diesel hydraulic excavators, or front end loaders and placed into haulage vehicles such as trucks and transported from the mine pit. The ore is processed outside the mine pit depending on the grade determination. For example, waste ore is used as mine fill, low grade ore is stockpiled or used to blend with high grade ore, and high grade ore is processed further as required to form a marketable product.

The present invention is an alternative mining method to the above-described method.

The mining method of the present invention may be used as the only method of mining in a mine pit or as one of several mining methods in a mine pit.

According to the present invention there is provided a method of mining ore in a mine pit that comprises the steps of:

(a) drilling and blasting ore in a bench of ore within the mine pit;

(b) collecting ore blasted from the bench from a floor of the mine pit using at least one mobile excavation machine ;

(c) delivering ore that has been collected by the mobile excavation machine to at least one mobile in-pit crusher and crushing ore to an overall reduced size ore; and

(d) transporting crushed ore to outside the pit on at least one ladder conveyor that extends up the wall of the pit.

The mobile excavation machine may be in the form of an electric rope shovel, a diesel hydraulic excavator, or a front end loader, or any other suitable machine for collecting mined ore from the pit floor.

Step (c) of the method may comprise delivering ore that has been collected by the mobile excavation machine to at least one mobile flexible conveyor within the mine pit and transporting ore from the excavation machine on the conveyor and delivering ore to the in-pit crusher and crushing ore to the overall reduced size ore.

The term "mobile flexible conveyor" is understood herein to mean a conveyor that is both mobile and flexible and can move across the floor of the mine pit in a linear and a non-linear manner and can continue to operate while moving across the pit floor.

The term "mobile flexible conveyor" does not include conveyors that persons in the mining industry refer to as "shiftable" or "movable" conveyors, as described above. A "shiftable" or "movable" conveyor is a conveyor that can be repositioned in a mine after a period of mining has been completed. In other words, the conveyor is not mobile in the sense that it can move continuously, for example, to keep pace with a mobile excavation machine or other mobile machine while continuing to operate to transported ore along the conveyor.

Typically, the mobile flexible conveyor has to meet any one or more of three basic requirements, namely (a) be sufficiently mobile to keep pace with an associated mobile excavation machine or other mobile machine while operating and transporting ore on the conveyor, (b) allow lateral, flexible movement whilst operating and transporting ore on the conveyor and, by way of example be capable of moving up or down steps of up to 400 mm in a pit floor, and (c) allow lengthwise extension and contraction while operating and transporting ore on the conveyor.

The mobile flexible conveyor may be of a type described in Australian patent 767395 in the name of

Michael Pietsch. The disclosure in the Australian patent is incorporated herein by cross-reference. The method may comprise delivering ore that has been collected by the mobile excavation machine to at least one mobile holding and feeding device within the mine pit and delivering the ore via the mobile holding and feeding device to the mobile flexible conveyor.

The method may comprise delivering ore via multiple flexible mobile conveyors to the in-pit crusher.

The in-pit crusher may be located proximate blasted ore to minimise the travel distance to the crusher.

In this connection, the in-pit crusher may be a mobile crusher and the method may comprise moving the crusher about the mine pit from time to time in response to increasing pit depth and/or change of location of mining activities.

The method may comprise transporting crushed ore from the in-pit crusher in at least one haulage truck within the mine pit to the ladder conveyor.

The method may comprise transporting crushed ore from the in-pit crusher on at least one mobile trunk conveyor that extends along a section of the pit floor to the ladder conveyor.

The term "mobile trunk conveyor" is understood herein to mean conveyors that persons in the mining industry refer to as "shiftable" or "movable" conveyors. A "shiftable" or "movable" conveyor is a conveyor that can be repositioned in a mine after a period of mining has been completed. In other words, the conveyor is not mobile in the sense that it can move continuously, for example, to keep pace with a mobile machine while continuing to operate to transport ore along the conveyor. The conveyor is mobile in the sense that it can be shifted or moved periodically to a new location.

The mobile trunk conveyor may be located on the pit floor in a lower region of the pit.

The mobile trunk conveyor may follow a linear path or a non-linear path.

The method may comprise periodically adjusting the mobile trunk conveyor in response to a lowering of the pit floor from time to time.

The in-pit crusher may be located proximate the ladder conveyor.

In that event, the method may comprise delivering ore that has been collected by the mobile excavation machine to at least one mobile trunk conveyor that extends from a location proximate the blasted ore and along a section of the pit floor to the in-pit crusher.

In addition, in that event, the method may comprise (a) delivering ore that has been collected by the mobile excavation machine to at least one mobile flexible conveyor located proximate the blasted ore, (b) transporting the ore along the mobile flexible conveyor to the trunk conveyor, and (c) transporting the ore along the trunk conveyor to the in-pit crusher.

The term "ladder conveyor" as used herein is understood to mean a conveyor that is able to transport ore from a mine pit directly up a wall of the mine pit from the pit floor, with the wall being a steep wall at an angle of at least 20° to the horizontal. The wall of the mine pit may be at least 30°, in many instances at least 65° to the horizontal.

The pit wall may be at least 20 m and typically at least 40 m.

The ladder conveyor may be a single conveyor from the pit floor to a rim of the pit and extend up the pit wall without transfer points along the length of the conveyor, i.e. without the ore being off-loaded at an upper end of one section of the conveyor and loaded onto a lower end of a successive section of the conveyor.

The ladder conveyor may extend up the pit wall without a switchback.

The method may comprise extending the ladder conveyor in response to a general lowering of the pit floor.

The method may comprise transferring crushed ore that has been transported up the wall of the pit along the ladder conveyor onto at least one main conveyor and transporting the ore along the main conveyor to a processing plant and/or a load out station.

Step (d) may comprise transporting crushed ore to outside the pit on at least two ladder conveyors that extend up the wall of the pit and transferring crushed ore onto the main conveyor via separate transfer points for each ladder conveyor.

The main conveyor may be located generally on a rim of the pit or at a base of a local topography surrounding the pit and follows the toypography thereof.

The main conveyor may receive ore from more than one part of the pit or from a series of pits. According to the present invention there is also provided a mine that comprises at least one pit having a pit floor and a pit wall that defines at least a part of the pit, at least one mobile excavation machine for collecting ore that has been blasted from a bench in the pit, at least one mobile-in-pit crusher for crushing the ore to an overall reduced size ore, and at least one ladder conveyor that extends up the wall of the pit for transporting crushed ore from the pit.

The mine may comprise at least one flexible mobile conveyor in the pit for transporting ore from the excavation machine and delivering ore to the in-pit crusher.

The mine may comprise at least one mobile trunk conveyor that extends along a section of the pit floor for transporting ore at least a part of the distance from the mobile excavating machine to the ladder conveyor.

The in-pit crusher may be located proximate the mining activity in the mine to minimise travel distance to the crusher.

The in-pit crusher may be a mobile crusher. The in-pit crusher may be located proximate the ladder conveyor.

In that event, the mine may comprise at least one mobile trunk conveyor that extends along a section of the pit floor for transporting ore at least a part of the distance from the mobile excavating machine to the in-pit crusher.

In addition, in that event, the mine may comprise at least one mobile flexible conveyor within the mine pit for transporting mined ore from the mobile excavating machine to the mobile trunk conveyor.

The pit wall may be a steep wall, i.e. at least 20°, more typically at least 30°, in many instances at least 65° to the horizontal.

The pit wall may be at least 20 m and typically at least 40 m high.

The ladder conveyor may be a single conveyor from the pit floor to the rim of the mine pit and extends up the pit wall without transfer points along the length of the conveyor, i.e. without the ore being off-loaded at an upper end of one section of the conveyor and loaded onto a lower end of a successive section of the conveyor.

The ladder conveyor may extend up the pit wall without a switchback.

The mine may comprise a main conveyor outside the pit for transporting mined and/or collected ore from the pit to a processing plant or a load-out station. There may be at least two ladder conveyors that extend up the wall of the pit for transferring crushed ore onto the main conveyor.

There may be separate transfer points for each ladder conveyor .

The mine may comprise a plurality of pits and at least one main conveyor outside the pits for transporting mined and/or collected ore from the pits to a processing plant or a load-out station.

The mine may be an iron ore mine.

The present invention is now described by way of example only with reference to the accompanying drawings of which:

Figure 1 is a schematic diagram of a layout of a mine pit that illustrates a number of embodiments of the method of mining iron ore in accordance with the present invention and a number of embodiments of the mine in accordance with the present invention; and

Figure 2 is a schematic diagram of a layout of a mine pit that illustrates a number of other embodiments of the method of mining iron ore in accordance with the present invention and a number of other embodiments of the mine in accordance with the present invention.

The following description of both Figures is in the context of mining iron ore. It is understood that the present invention is not limited to mining iron ore and extends to mining other ores . It is also understood that the mine layouts shown in both Figures are schematic and are intended to represent mine layouts in a very general sense.

The same reference numerals are used in both Figures to describe the same features .

With reference to Figure 1, a mine pit generally identified by the numeral 3 and having a pit floor 5 is defined at least in part by mine walls 7. The mine walls 7 are shown as opposed straight walls for convenience only and the present invention is not limited to this arrangement. The pit floor 5 may be at one level. Alternatively, as shown in the Figure, the pit floor 5 is on multiple levels which form a series of benches, which may be isolated from each other or interconnected by ramps 33.

Each mine wall 7 may comprise a series of steps or be one continuous wall.

The mine pit 5 comprises two benches 19 that are being drilled and blasted in blocks, typically for example 40 m long by 20 m deep by 10 m high and containing 8,000 tonnes of ore, by mobile drilling machines 51 and produce blasted ore on the lower benches of the pit floor 5. The blasted ore varies in size from large rocks to fines.

A plurality of mobile excavation machines 11 collect blasted ore from the pit floor 5. The mobile excavation machines 11 may be any suitable type of machine. By way of example, the mobile excavation machines 11 may be in the form of electric rope shovels, diesel hydraulic excavators, or front end loaders.

The mobile excavation machines 11 (and other equipment) shown in Figure 1 may be controlled remotely or by operators on the machines. In either case, typically the paths of movement of the mobile excavation machines 11 (and other equipment) within the mine pit 3 are in accordance with a mining plan.

One group of the mobile excavation machines 11 shown in Figure 1 transfers collected ore directly onto in-pit crushers 41. The mobile crushers 41 reduce the size of the ore to a suitable size for downstream materials handling and processing. This option is identified by the letters "A" in Figure 1.

The crushed ore is transported from the in-pit crushers 41 to ladder conveyors 23, i.e. "shiftable" or "movable" conveyors, either by a mobile trunk conveyor 27 or by trucks 37.

Another group of mobile excavation machines 11 shown in the Figure transfers collected ore onto mobile flexible conveyors 13 and the conveyors 13 transport the ore to a mobile feed system 15 located at a forward end of a mobile trunk conveyor 27 and the conveyor 27 transports the ore to an in-pit crusher 41 located proximate the ladder conveyors 23. This option is identified by the letter "B in the Figure.

Another group of mobile excavation machines 11 shown in the Figure transfers collected ore directly onto the mobile feed system 15 located at the forward end of the mobile trunk conveyor 27 and the conveyor 27 transports the ore to the in-pit crusher 41 located proximate the ladder conveyors 23. This option is identified by the letter ^WC" in Figure 1.

The mobile crushers 41 may be of any suitable type. The mobile feed systems 15 may be hoppers or be any other suitable feed system.

The mobile flexible conveyors 13 may be of any suitable type. By way of example, the mobile flexible conveyors 13 may be as manufactured by International Conveying Systems International and described in Australian patent 767395 in the name of Michael Pietsch.

The mobile trunk conveyors 27 may be of any suitable type. By way of example, the mobile trunk conveyors 27 may be the same design as the mobile flexible conveyors 13, such as manufactured by International Conveying Systems International and described in Australian patent 767395, but operated in a more static mode.

The mobile flexible conveyors 13 and the mobile trunk conveyors 27 make it possible to reduce the reliance on trucks for transporting mined ore from a mine pit 3. This is a benefit in terms of operating costs, particularly in large, deep mine pits where travel distances and time from mining areas to crushers and other processing equipment can be significant.

The ladder conveyors 23 are arranged to transport ore directly up the wall 7. The ladder conveyors may be in fixed locations against the side wall 7 or may be mounted for movement along the length of the side wall 7. In the latter case, the trunk conveyors 27 are arranged to be shiftable or movable or otherwise be able to be extended to accommodate changes in location of the ladder conveyors 23. In both cases, the ladder conveyors 23 may be extendable in length as the pit depth increases.

The ladder conveyors 23 may be any suitable conveyor. By way of example, the ladder conveyor 23 may be of the type manufactured by International Conveying Systems International and described in Australian patent 767395 in the name of Michael Pietsch.

The ladder conveyors 23 transfer the crushed ore via separate transfer points 61 onto a conveyor assembly 29 that extends along the rim of the mine pit 3 and interconnects a series of pits and/or different sections of the same pit and transports the ore to a processing station, such as a crusher.

The conveyor assembly 29 may be of a type that facilitates separation of ore into two process streams, with one stream, such as a high grade ore, being transported for processing in a crusher, and the other stream, such as waste ore, being transported to a stockpile for subsequent use as a fill material.

It is relevant to note that the arrangement shown in Figure 1 represents a section of a pit only and the mining method illustrated with reference to the Figure is repeated in other sections of the pit 3. It may also be the case that other mining methods are used in different sections of the pit 3. In any event, the mined ore is transported from the mine via ladder conveyors 23 and is delivered to the conveyor assembly 29.

As is indicated above, Figure 2 is a schematic diagram of a layout of a mine pit that illustrates a number of other embodiments of the method of mining iron ore in accordance with the present invention and a number of other embodiments of the mine in accordance with the present invention.

With reference to Figure 2, a mine pit generally identified by the numeral 3 and having a pit floor 5 is defined at least in part by mine walls 7. The mine walls 7 are shown as opposed straight walls for convenience only and the present invention is not limited to this arrangement. The pit floor 5 may be at one level. Alternatively, as shown in the Figure, the pit floor 5 is on multiple levels which form a series of benches, which may be isolated from each other or interconnected by ramps (not shown) .

Each mine wall 7 may comprise a series of steps or be one continuous wall.

The mine pit 5 shown in Figure 2comprises two benches 19 that are being drilled and blasted in blocks, typically for example 40 m long by 20 m deep by 10 m high and containing 8,000 tonnes of ore, by mobile drilling machines 51 and produce blasted ore. The blasted ore varies in size from large rocks to fines.

The mobile excavation machines 11 (and other equipment) may be controlled remotely or by operators on the machines. In either case, typically the paths of movement of the surface miners 11 (and other equipment) within the mine pit 3 are in accordance with a mining plan.

One group of the mobile excavation machines 11 shown in Figure 2 transfers mined ore directly onto mobile flexible conveyors 13. Another group of mobile excavation machines 11 shown in Figure 2 transfers collected ore via mobile feed systems 15 located at forward ends of the conveyors 13.

The mobile feed systems 15 may be hoppers or be any other suitable feed system.

The mobile flexible conveyors 13 make it possible to operate a mine without trucks as a main option for transporting mined ore from a mine pit 3. This is a benefit in terms of operating costs, particularly in large, deep mine pits where travel distances and time from mining areas to crushers and other processing equipment can be significant.

The mobile flexible conveyors 13 may be of any suitable type. By way of example, the mobile flexible conveyors 13 may be as manufactured by International Conveying Systems International and described in Australian patent 767395.

The collected ore is transported via the mobile flexible conveyors 13 within the mine pit 5 to mobile crushers 41 located on the pit floor 5. The mobile crushers 41 reduce the size of the ore to a suitable size for downstream materials handling and processing.

The mobile crushers 41 may be of any suitable type.

The crushed ore produced by the mobile crushers 41 is transported either (a) directly to ladder conveyors 23 that are arranged to transport crushed ore from the mine pit 3 up the mine wall 7 or (b) to internal trunk conveyors 27 that extend along the pit floor 5 and transport the ore to the ladder conveyors 23. The ladder conveyors 23 may be in fixed locations against the side wall 7 or may be mounted for movement along the length of the side wall 7. In the latter case, the trunk conveyors 27 are arranged to be movable or otherwise be able to be extended to accommodate changes in location of the ladder conveyors 23. In both cases, the ladder conveyors 23 may be extendable in length as the pit depth increases.

The ladder conveyors 23 may be any suitable conveyor. By way of example, the ladder conveyors 23 may be of the type manufactured by International Conyeying Systems International and described in Australian patent 767395 in the name of Michael Pietsch.

The ladder conveyors 23 transfer the crushed ore via separate transfer points 61 onto a conveyor assembly 29 that extends along a rim of the mine pit 3 and interconnects a series of pits and/or different sections of the same pit and transports the ore to a processing station, such as a crusher.

It is relevant to note that the arrangement shown in

Figure 2 represents a section of a pit only and the mining method illustrated with reference to the Figure is repeated in other sections of the pit 3. It may also be the case that other mining methods are used in different sections of the pit 3. In any event, the mined ore is transported from the mine via ladder conveyors 23 and is delivered to the conveyor assembly 29. Many modifications may be made to the method of the present invention summarised in the Figure and described above without departing from the spirit and scope of the present invention.

Claims

1. A method of mining ore in a mine pit that comprises the steps of:

(a) drilling and blasting ore in a bench of ore within the mine pit;

(c) delivering ore that has been collected by the mobile excavation machine to at least one mobile-in-pit crusher for crushing ore to an overall reduced size ore; and

2. The method defined in claim 1 wherein step (c) comprises delivering ore that has been collected by the mobile excavation machine to at least one mobile flexible conveyor within the mine pit and transporting ore away from the excavation machine on the conveyor and delivering ore to the in-pit crusher and crushing ore to the overall reduced size ore.

3. The method defined in claim 2 wherein the mobile flexible conveyor meets any one or more of three basic requirements, namely (a) is sufficiently mobile to keep pace with an associated mobile excavation machine or other mobile machine while operating and transporting ore on the conveyor, (b) allows lateral, flexible movement whilst operating and transporting ore on the conveyor and, by way of example be capable of moving up or down steps of up to 400 mm in a pit floor, and (c) allows lengthwise extension and contraction while operating and transporting ore on the conveyor .

4. The method defined in claim 2 or claim 3 comprises delivering ore that has been collected by the mobile excavation machine to at least one mobile holding and feeding device within the mine pit and delivering the ore via the mobile holding and feeding device to the mobile flexible conveyor.

5. The method defined in any one of the preceding claims wherein the in-pit crusher is located proximate blasted ore to minimise the travel distance to the crusher.

6. The method defined in claim 5 wherein the in-pit crusher is a mobile crusher and the method comprises moving the crusher about the mine pit from time to time in response to increasing pit depth and/or change of location of mining activities.

7. The method defined in any one of the preceding claims comprises transporting crushed ore from the in-pit crusher in at least one haulage truck within the mine pit to the ladder conveyor.

8. The method defined in any one of the claims 1 to 6 comprises transporting crushed ore from the in-pit crusher on at least one mobile trunk conveyor that extends along a section of the pit floor to the ladder conveyor.

9. The method defined in any one of claim 1 to 4 wherein the in-pit crusher is located proximate the ladder conveyor .

10. The method defined in claim 9 comprises delivering ore that has been collected by the mobile excavation machine to at least one mobile trunk conveyor that extends from a location proximate the blasted ore and along a section of the pit floor to the in-pit crusher.

11. The method defined in claim 10 comprises (a) delivering ore that has been collected by the mobile excavation machine to at least one mobile flexible conveyor located proximate the blasted ore, (b) transporting the ore along the mobile flexible conveyor to at least one trunk conveyor that extends along a section of the pit floor to the in-pit crusher, and (c) transporting the ore along the trunk conveyor to the in- pit crusher.

12. The method defined in any one of the preceding claims comprises transferring crushed ore that has been transported up the wall of the pit along the ladder conveyor onto at least one main conveyor and transporting the ore along the main conveyor to a processing plant and/or a load out station.

13 The method defined in claim 12 wherein step (d) comprises transporting crushed ore to outside the pit on at least two ladder conveyors that extend up the wall of the pit and transferring crushed ore onto the main conveyor via separate transfer points for each ladder conveyor .

14. A mine that comprises at least one pit having a pit floor and a pit wall that defines at least a part of the pit, at least one mobile excavation machine for collecting ore that has been blasted from a bench in the pit, at least one mobile in-pit crusher for crushing the ore to an overall reduced size ore, at least one ladder conveyor that extends up the wall of the pit for transporting crushed ore from the pit .

15. The mine defined in claim 14 comprises at least one flexible mobile conveyor in the pit for transporting ore away from the excavation machine and delivering ore to the in-pit crusher.

16. The mine defined in claim 15 wherein the mobile flexible conveyor meets any one or more of three basic requirements, namely (a) is sufficiently mobile to keep pace with an associated mobile excavation machine or other mobile machine while operating and transporting ore on the conveyor, (b) allows lateral, flexible movement whilst operating and transporting ore on the conveyor and, by way of example be capable of moving up or down steps of up to 400 mm in a pit floor, and (c) allows lengthwise extension and contraction while operating and transporting ore on the conveyor .

17. The mine defined in any one of claims 14 to 16 comprises at least one mobile trunk conveyor that extends along a section of the pit floor for transporting blasted ore at least a part of the distance from the mobile excavating machine to the ladder conveyor.

18. The mine defined in any one of claims 14 to 17 wherein the in-pit crusher is located proximate the mining activity in the mine to minimise travel distance to the crusher.

19. The mine defined in claim 18 wherein the in-pit crusher is a mobile crusher.

20. The mine defined in any one of claims 14 to 19 wherein the in-pit crusher is located proximate the ladder conveyor .

21. The mine defined in claim 20 comprises at least one mobile flexible conveyor within the mine pit for transporting mined ore at least a part of the distance from the mobile excavating machine to the in-pit crusher.

22. The mine defined in any one of claims 14 to 21 wherein the pit wall is a steep wall, i.e. at least 20°, more typically at least 30°, in many instances at least 65° to the horizontal.

23. The mine defined in any one of claims 14 to 22 wherein the pit wall is at least 20 m and typically at least 40 m high.

24. The mine defined in any one of claims 14 to 23 wherein the ladder conveyor is a single conveyor from the pit floor to a rim of the mine pit and extends up the pit wall without transfer points along the length of the conveyor, i.e. without the ore being off-loaded at an upper end of one section of the conveyor and loaded onto a lower end of a successive section of the conveyor.

25. The mine defined in any one of claims 14 to 24 comprises a main conveyor outside the pit for transporting mined and/or collected ore from the pit to a processing plant or a load-out station.

26. The mine defined in any one of claims 14 to 25 comprises a plurality of pits and at least one main conveyor outside the pits for transporting mined and/or collected ore from the pits to a processing plant or a load-out station.

27. The mine defined in claim 25 or claim 26 wherein there are at least two ladder conveyors that extend up the wall of the pit for transferring crushed ore onto the main conveyor.

28. The mine defined in claim 27 wherein there are separate transfer points for each ladder conveyor.