GB2152558A - Mining method and apparatus - Google Patents

Abstract

A mining method aimed at minimizing the use of ore handling equipment in underground situations, the method involving fragmenting the ore (10) to be mined, allowing the fragmented ore to gravitate freely through a lower ore pass opening (16) onto an inclined rill surface (18), and arranging an ore sizing opening (23) at or adjacent the lower edge of the rill surface (18) such that ore fragments below a certain size will pass by gravity there-through to a crushing installation (27) beneath the ore sizing opening (23). An underground mine arrangement for performing the mining method is also disclosed. <IMAGE>

Description

SPECIFICATION Mining method and apparatus The present invention relates to an improved method of mining, particularly in underground situations, and to elements in a system for carrying out the improved mining method.

Conventionally rock mining, either by glory hol ing or underground methods, throughout the world has been by discontinuous or batch processes. It has not been possible to bring fragmented rock, following blasting, to the point of discharge from a mine without the fragmented rock undergoing some form of discontinuous batching process.

Conventionally rock flow from the blasted area (stope) is stopped by any one of numerous methods such as providing flat bottoms to the stope or providing sufficiently small openings that will promote arching of the fragmented rock stopping flow through the opening. This is primarily to control the huge weights and volume of fragmented rock in the blasted stope. Secondly, it has not been possible to ensure, by blasting fragmentation, that one hundred percent of the rock fragments will be below a critical size permitting free flow through critical regions in the system such as ore passes and the rock crusher used in the system. Thirdly, it has been necessary to, in some way, handle the relatively large rock fragments by getting them into loaders, trucks or trains for transportation.Finally in conventional systems, because of the discontinuous approach, it has been necessary to provide storage facilities for the fragmented rock to be crushed.

Typically in large modern mines stopes are used having a number of relatively small draw points or drifts located at the bottom edges of the stope.

Rock is then extracted from the draw points by large machines such as diesel driven wheeled front loading diggers from moving the rock to subsequent processing stages. Without these machines in conventional mines, rock fragments would simply not move from the stope. These machines are usually adapted to sort out from each load those rocks too big to be handled by the crusher. Typically this is achieved by dumping the load onto a sized opening or grizzly. Those rocks which are too large to pass through the grizzly are then removed from the grizzly to a secondary breaking region for subsequent return to the grizzly after breaking. The rock fragments passing the grizzly generally gravitate to a controlled chute where it is batch loaded into haulage trucks for transport to a storage hopper for the crusher.The crusher may be located underground in one fixed high capital cost position which requires the fragmented rock to be hauled to it from all regions of ore body being mined. The rock fragments are then transferred from the storage hoppers to the crusher to be crushed to a size suitable for highly mechanized haulage such as conveying or high speed skip haulage to the discharge region from the mine. The capital costs of the machinery and the costs of the discontinuous handling of the rock in these conventional mine systems is extremely high and it is these high costs which often determine the profitability of an existing mine or the feasibility of proceeding with or not proceeding with mining of a particular min eral deposit.That is, the cost of physically extract ing the ore from a particular ore body with conventional methods may substantially outweigh the market value of that ore.

United States Patent No. 968,100 discloses a semi-automatic truck loading device for loading ore from a chute or ore pass directly into ore transport trucks located below the chute. The ar rangement deals with handling essentially sized ore, that is ore fragments of less than a predeter mined size, passing from the chute to the trucks.

The flow is divided at the base of the chute into two short oppositely inclined passages, each hav ing a control door such that any blockages are freed by alternate opening and closing of the respective lower passages. The method disclosed in this U.S. specification relates specifically to a type of mining known as glory holing around a particular ore pass and is in fact a batch wise process of handling ore so mined through a delivery chute which is not designed for free flow.

United States Patent No. 2,298,599 discloses a method of mining applicable only to block caving mining methods. These methods involve dividing the ore body into large blocks which are undercut one at a time and allowed to descend on the undercut area. Ideally, the ore body is crushed as it descends, due to its own weight and the weight of the overburden, into fragments of a size suitable for handling. in this specification, it is proposed that the fragmented ore be drawn from the base of the ore body through a number of finger raises leading to a mechanical conveyor drift located therebelow. The ore fragments are generally withdrawn at a slow rate consistent with the rate of caving to avoid packing of the ore fragments at the base of the ore body. Control of flow rate through the finger raises is achieved by adjustable slat gates.The specification does not consider the variation in ore fragment sizes which can normally be expected and simply assumes incorrectly that all descending ore fragments will be very fine. In practice, particularly in ordinary underground stope mining, the finger raises proposed in this specification, would choke and the slat gates would jam preventing the flow of ore therethrough. In practical situations the variation in, and the physical size of rock fragments would not allow the ore to be delivered onto a conveyor without some form of crushing.

United States Patent Specification No. 4,377,310 recognizes the problem of ore fragment flow choking at the ore pass from normal underground mine stopes. The specification proposes a solution to this problem by arranging a very large reciprocating device directly beneath the ore pass. It is the effect of this reciprocating device that provides a shearing action on the base of the ore body fragments that effectively prevents ore flow blockages.

The proposal, however, involves considerable capital cost in the machinery required while also hav ing high energy consumption requirements which would make the use of the system disclosed uneconomical, particularly when mining lower grade ore bodies. The mining process disclosed does not propose any ore crushing installation in association with the ore withdrawn from the stope (other than conventional breaking of oversize ore fragments) and consequently the mining method is in essence a batch process in relation to the delivery of ore to the surface.

The principal objective of the present invention is to provide an improved underground mining method which provides the capability of a substantially continuous process without the problems and the substantial costs associated with the abovementioned conventional and other known processes. The present invention also aims at providing elements of a system for achieving the aforementioned method.

Accordingly the present invention provides a mining method comprising defining an underground stope to be mined whereby ore fragmented by any method within said stope gravitates to an opening in a lower region of the stope, said opening having dimensions sufficient to pass the fragmented ore freely therethrough to an inclined rill surface located beneath said opening, said rill surface having an angle of inclination sufficient to permit said fragmented ore to gravitage downwardly thereon and transversely relative to said opening, and providing an ore sizing opening (grizzly) at or adjacent to a lower edge of said rill surface whereby fragmented ore of a predetermined size passes therethrough for subsequent processing.Conveniently the ore sizing opening comprises a grill member arranged at an angle of inclination to the horizontal whereby ore fragments of said predetermined size or less pass through the grill member and oversize ore fragments gravitate downwardly beyond said ore sizing opening to a secondary breaking zone. In accordance with a preferred arrangement, an ore pass is provided immediately beneath said ore sizing opening to receive ore fragments therefrom and ore fragments from said secondary breaking zone after further fragmentation are delivered to said ore pass.

In accordance with a particularly preferred embodiment, an ore crushing machine is located beneath the ore pass leading from the ore sizing opening to receive ore fragments of said predetermined size or less directly from the ore pass. If desired flow control means rnay be provided to control the rate of flow of ore fragments to the crushing machine. Conveniently the crushing machine, after crushing the ore delivers the ore fragments to a continuous transport system for conveying the ore to a discharge region of the mine. The transport system preferably comprises a continuous conveyor means, however, it will be appreciated that other forms of transport such as trucks, trains, carriages, hoists, lifts or the like might also be employed.

According to another preferred arrangement, the crushing machine employed is of a mobile design whereby the crushing machine may be moved to be located beneath successive stopes to avoid unnecessary ore transportation (and associated costs) to a fixed crushing installation.

In the above described method, ore may be fragmented by blasting or by any other known method such as block caving in the desired stope and passed, in a substantially continuous manner from the stope downwardly under action of gravity through a sizing region to an ore crushing facility and therefrom to a mine discharge point without the need of any substantial ore handling or transport machinery. In consequence substantial cost savings may be achieved as compared to conventional methods. In some cases these savings may be sufficient to enable profitable mining of ore bodies which would otherwise be too costly to mine by conventional methods.

In accordance with another aspect of this invention there is provided in an underground mine having a stope region to be mined, an inclined rill surface located immediately beneath an opening in a lower region of said stope adapted to receive fragmented ore from the opening, said rill surface having an angle of inclination sufficient to allow fragmented ore to gravitate downwardly thereon, an ore sizing opening arranged at or adjacent to a lower edge of said rill surface to receive fragmented ore from the rill surface and to pass ore fragments of a predetermined size or less therethrough. Conveniently, ore flow control means are arranged to control the rate of flow of fragmented ore downwardly along the inclined rill surface.

Conveniently the ore flow control means may comprise a heavy chain curtain with means to selectably lift or lower the chains forming the curtain.

Preferably, the ore sizing opening forms a primary sizing means and comprises a grill member also arranged at an angle to the horizontal whereby fragmented ore of said predetermined size or less passes downwardly therethrough to an ore pass located beneath the grill member and oversized ore fragments gravitate beyond said grill member to a secondary breaking zone said secondary breaking zone having a secondary ore sizing means associated therewith permitting fragmented ore of said predetermined size or less to pass to said ore pass leading from the primary ore sizing means.

In accordance with a particularly preferred arrangement, the rill surface is constructed from steel members in a manner permitting the rill surface to be relocated under successive stope openings during mining of a particular ore body.

A preferred arrangement will now be described with reference to the accompanying drawings, in which: Figure 1 is a general schematic layout drawing illustrating the flow path taken by the ore in a preferred mining method; Figure 2 is a detailed elevation view of the ore handling region of the mining system shown in Figure 1; Figure 2A is a detailed view in the direction A of Figure 2; and Figure 2B is a detailed view in the direction B of Figure 2.

Referring first to Figure 1 there is shown schematically an underground ore body 10 to be mined. The ore body 10 is shown divided into a number of successive stopes 11, 11', 12, 12' and so on. An access drive 13 leading from a mine discharge point 15 at ground level 14 is provided to the ore body 10. The angle of inclination of the drive 13 might be 1 in 6, however, it will be appreciated that this could be varied depending on circumstances of the ore body mined and the equipment used. Conveniently the access drive 13 is produced by continuous tunnelling equipment with the earth/rock being carried to the surface by continuous conveyor system which might conveniently be used subsequently for transport of the fragmented ore from the ore body 10.

Conveniently the stopes 11. 11', 12, 12' and so on are arranged successively adjacent one another whereby the stopes can be successively mined as described hereinafter. Each stope is provided with a lower access opening 16 conveniently with the lower walls 17 of the stope being inclined at an angle y sufficient to ensure that fragmented ore in the stope will gravitate downwardly toward the opening 16. An angle y of about 55" to the horizontal would be an adequate inclination. The access opening 16 should be of a size sufficient for substantially all ore fragments produced by fragmentation blasting or by any other known fragmentation method in the stope to pass freely therethrough to avoid the use of any ore handling machinery at this point. It is considered that each stope outlet 16 should be regarded as a coarse ore bulk bin outlet and designed accordingly.Coarse materials are basically free flowing, that is, under consolidating pressure they do not develop any substantial unconfined yield strength.

However, in accordance with the present invention it is desired to design the stope opening 16 (to the best available knowledge) in such a way as to allow free flow through the opening. The design shape at the bottom of the opening should take into consideration: 1. fragmentation, to place a value on the percentage of rock size passing given sizes, including the maximum size allowed to enter the crusher; 2. the stope bottom shape; and 3. the shape of the opening itself.

The present state of knowledge would appear to indicate that the outlet opening 16 should have a generally oval or rectangular configuration where the ratio d/dm (where d is the outlet maximum dimension and dm is the diameter of the largest nominal rock in the designed blasts) is to have a minimum value of 10 and the outlet minimum dimension is to be six times dm. Conveniently dm and the maximum size allowed to enter the crusher would be, by design, the same.

These values may change as more precise methods of design are available, but the principle of designing to allow continuous free flow through the opening 16 is the concept of importance to the present invention.

Reference is now made to the detailed views of Figures 2, 2A and 2B as well as Figure 1. Beneath the opening 16, it is proposed to place an inclined steel fabricated rill 18 having an angle b to the horizontal. The rill 18 and its angle of inclination ss are such that the fragmented ore from the stope 11 passing through the opening 16 is supported by the rill and permits the fragmented ore to move downwardly and to the side relative to the opening 16. The angle b is of some importance and should be between 37 and 47" from the horizontal depending on the ore fragmentation. Usually an angle of about 40 inclination would be normal.

Arranged above the inclined rill 18 is a flow control means 19 comprising, in the embodiment illustrated, a chain curtain having a plurality of very heavy downwardly depending chain elements 20.

The chain elements 20 are such that they extend across the rill 18 to control the fragmented ore flow therealong. Conveniently the lower end of each chain element 20, or perhaps a group of chain elements 20, is/are connected by a cable 21 to a winch 22 to enable selective lifting or lowering of the particular chain elements to allow some ore fragments to pass thereby controlling the ore flow.

Alternate flow control means such as movable fingers or gates, stoppers or the like might also be used. At the lower end of the rill 18, there is provided a bar grizzly 23 covering an ore pass 24 leading downwardly therefrom. The angle of inclination to the horizontal of the bar grizzly 23 is conveniently such that ore fragments of a predetermined size (or less) will fall into the ore pass 24 while ore fragments greater than said predetermined size will pass over the grizzly 23 to a secondary breaking zone 25. An angle a of about 30 to the horizontal is believed to be adequate for this purpose.

Conveniently, the secondary breaking zone will include machinery such as drills, water canon hydraulic rock breakers or the like to break the oversize ore fragments down to a size less that said predetermined size. These broken fragments may then be transferred back to the grizzly 23 or more conveniently (as shown in Figure 1) pass through a secondary grizzly 26 leading to the ore pass 24.

In the embodiment illustrated in Figure 1, the fragmented ore passing down the ore pass 24 progresses directly to a crushing machine 27 located in a substantially horizontal drive 28 having access to the mine access drive 13. Flow control means may be provided in the ore pass 24 to control the flow of ore to the crusher. Crushed ore fragrnents leaving the crusher 27 pass via a conveyor system 29 through the drives 28 and 13 to the mine discharge point 15. As will be seen in Figure 1 it is possible that more than one stope 11, 11' may have access to the ore pass 24 leading to the crusher 27 and it will be appreciated that further adjoining stopes might be connected in gravitational flow relation to the ore pass 24 leading to the crusher site. In a preferred aspect of this invention, the crusher 27 is of a mobile type permitting the movement thereof to subsequent locations such as 27' to service adjacent ore passes 24' leading from the subsequent stopes 12. 12'.

Nothing in the present invention precludes the use of boring machines, mass blasting or other mining procedures nor does it preclude the use of pillars between stopes, irregular stoping or the use of various stoping methods as dictated by consideration of rock mechanics or geology. Drilling may be effected from the surface or underground. The method is primarily concerned with coarse ore handling below ground, not with detailed stoping or drilling.

In consequence of the above described arrangements fragmented ore flow may be made to gravitate through a flow path to a crusher unit and therefrom to the mine discharge zone in a substantially continuous manner without the need of expensive handling and transportation system. It is believed therefore that substantial savings to the cost of extracting crushed ore from an ore body can be achieved.

Claims (16)

1. A mining method comprising defining an underground stope to be mined, whereby ore fragmented by any method within the stope gravitates to an opening in a lower region of the stope, said opening having dimensions sufficient to pass the fragmented ore freely therethrough to an inclined rill surface located beneath said opening, said rill surface having an angle of inclination sufficient to permit said fragmented ore to gravitate downwardly thereon and transversely relative to said opening, and providing an ore sizing opening at or adjacent to a lower edge of said rill surface whereby fragmented ore of a predetermined -size passes therethrough for subsequent processing.

2. A method according to claim 1 wherein the ore is fragmented in said stope by blasting.

3. A method according to claim 1 or claim 2 wherein the ore sizing opening comprises a grill member at an angle of inclination to the horizontal whereby said ore fragments of a predetermined size or less passing from the inclined rill surface pass through the grill member and oversize ore fragments of a size greater than said predetermined size gravitate downwardly beyond said ore sizing opening to a secondary breaking zone.

4. A method according to any one of claims 1 to 3 wherein the rate of flow of fragmented ore from said opening to said inclined rill surface is controlled by flow control means,

5. A method according to any one of claims 1 to 4 whereby said fragmented ore passing through said ore sizing opening gravitates directly to an ore crushing machine.

6. A method according to claim 5 wherein an ore pass is provided leading from said ore sizing opening to said crushing machine, said ore pass receiving fragmented ore directly through said ore sizing opening and from said secondary breaking zone.

7. A method according to claim 5 or claim 6 wherein continuous conveyor means is provided to continuously convey ore from said crushing machine to a surface discharge region.

8. In an underground mine having a stope region to be mined, an arrangement including an inclined rill surface located immediately beneath an opening in a lower region of said stope adapted to receive fragmented ore from said opening, said rill surface having an angle of inclination sufficient to allow fragmented ore to gravitate downwardly and transversely thereon, and an ore sizing opening arranged at or adjacent to a lower edge of said rill surface to receive fragmented ore from said rill surface and to pass ore of a predetermined size or less therethrough.

9. An arrangement according to claim 8 including ore flow control means arranged to control the rate of flow of fragmented ore downwardly along said inclined rill surface.

10. An arrangement according to claim 9 wherein said ore flow control means comprise a heavy chain curtain and means to selectably lift or lower chains forming said chain curtain relative to said rill surface.

11. An arrangement according to any one of claims 8 to 10, wherein said ore sizing opening comprises a grill member arranged at an inclination to the horizontal whereby fragmented ore of a size greater than said predetermined size gravitate beyond said grill member to a secondary breaking zone having a secondary ore sizing means.

12. An arrangement according to claim 11 wherein fragmented ore passing through said ore sizing opening and said secondary ore sizing means flow to a common ore pass.

13. An arrangement according to any one of claims 8 to 12 wherein fragmented ore from said ore sizing opening flows directly by gravity to a crushing installation.

14. An arrangement according to claim 13 wherein said crushing installation is adapted for movement between different locations whereby fragmented ore can be received from separate stopes.

15. An arrangement according to claim 13 or claim 14 wherein continuous conveyor means is provided leading from said crushing installation to a surface discharge region.

16. An arrangement substantially as described herein with reference to the accompanying drawings.