AU2014200978A1 - Underground Mining Method - Google Patents

Abstract

Abstract A method of mining an underground ore body 12 is described. The method 5 comprising the steps of: (i) developing upper and lower level ore drives 10 through each of a plurality of mining levels along the strike of the ore body 12, an upper level drive being located above a lower level drive in each case; (ii) establishing a void vertically between the lower and upper level drives for a given mining level to allow expansion of blasted material during a stope 10 firing on each level; (iii) production drilling of rows of fanned blast holes 22 between upper and lower level drives over the width of the stope 20; (iv) loading the blast holes 22 with explosives and blasting towards the void previously established to form an open stope 20; (v) removing broken ore from the stope 20 as the production face retreats to an access drive; and, (vi) 15 repeating the steps of production drilling, loading of blast holes, blasting, and removing broken ore over the full length of the stope 20 wherein, in use, as the stope retreats back along the strike the hanging wall of the already mined open stopes will cave-in and sit on the footwall due to the foot wall angle of the stope 20 which is a reflection of the ore body dip. Drawing suggested to accompany Abstract: Figure 1

Description

ORIGINAL AUSTRALIA Patents Act 1990 COMPLETE SPECIFICATION Invention title: "UNDERGROUND MINING METHOD" Applicant: POSEIDON NICKEL LIMITED Associated Provisional Application No.: 2013900746 The following statement is a full description of the invention, including the best method of performing it known to me: 2 "UNDERGROUND MINING METHOD" Field of the Invention The present invention relates to an underground mining method and relates 5 particularly, though not exclusively, to a method for mining ore from a weak rock, flat-dipping underground ore body. Background to the Invention When considering the feasibility of mining a new ore body the selection of a 10 suitable mining method will affect ore recovery, production efficiency and economic viability. Many factors influence the selection of an appropriate method of mining for a particular ore body. These include: e Ore deposit characteristics e Rockmass quality 15 0 Environmental factors e Infrastructure 0 Equipment requirements * Cultural factors 0 Commodity prices 20 0 Economics. The nickel ore deposit at Cerberus has some unique characteristics which present particular challenges in the selection of a suitable mining method. Down dip extent in the Cerberus ore body is extensive (1,300 metres) and 25 flat-dipping (less than or equal to an average dip of 30*). The ore body and host rock range from poor to good quality. Ore body strike is also extensive (varies from a maximum of approximately 550 metres in places), but narrow in width (less than 8 metres on average).

3 Clearly not all mining methods would be appropriate for Cerberus, particularly when the shallow dipping nature of the ore body is taken into consideration. The flat-dipping, long-strike, weak-rock nature of the deposit (referred to hereinafter as "Cerberus Type" deposits) excludes most conventional mining 5 methods from being applied. Historically, room and pillar mining would have been applied to Cerberus Type deposits, but in modern times safety and cost issues now generally preclude that method in these circumstances. Stoping is another method that can be employed in flat-dipping deposits, but 10 that method requires a sufficient rock mass quality for a modest stable unsupported span if there is to be high productivity. The effect of very weak foliation and the shallow dip would be frequent stope instability at modest spans. Cerberus Type deposits can only achieve very modest productivity with stoping methods. 15 US2010/0295359 (Bodley) relates to a method of underground mining that involves stoping. Bodley discloses collapsible cushion (30) that can be positioned in a stope (22) after the first panel (11) has been blasted and hauling operations associated with the broken rock generated in excavation of the first panel and stope generation have been completed, but before 20 backfilling operations commence. The cushion (30) creates a void into which fragmented rock can expand during subsequent blasting operations for a second or subsequent panel. The void is maintained after blasting operations occur, and then the cushion (and void) is collapsed to accommodate the fragmented ore generated during blasting operations. It is clear that in the 25 underground mining method of Bodley backfilling operations are employed (paragraph [0042]), rather than sub-level caving as in the present invention. The cushion (30) of Bodley is positioned between the ore body facing wall (40) and a backfill segment of pre-defined volume which is designated for 30 subsequent backfilling (23). The cushion (30) is a fluid-tight container designed to create a collapsible void prior to backfilling operations. The void 4 created by the cushion (30) is maintained during backfilling operations, and then collapsed, depending on backfill material selection, either during or just prior to blasting operations. By contrast, no backfilling is employed in the method of the present invention, and hence there is no need to maintain a 5 void. Instead, as the stope retreats back along the strike the hanging wall of the already mined stopes are allowed to cave-in and sit on the footwall. The present invention was developed with a view to providing a modified open stoping underground mining method suitable for Cerberus Type deposits, although it will be apparent that the method may also have wider 10 application. References to prior art in this specification are provided for illustrative purposes only and are not to be taken as an admission that such prior art is part of the common general knowledge in Australia or elsewhere. 15 Summary of the Invention According to one aspect of the present invention there is provided a method of mining an underground ore body, the method comprising the steps of: 20 developing upper and lower level ore drives through each of a plurality of mining levels along the strike of the ore body, an upper level drive being located above a lower level drive in each case; establishing a void vertically between the lower and upper level drives for a given mining level to allow expansion of blasted material during a stope firing 25 on each level; production drilling of rows of blast holes between upper and lower level drives over the width of the stope; loading the blast holes with explosives and blasting towards the void previously established to form an open stope; 5 removing broken ore from the stope as the production face retreats to an access drive; and, repeating the steps of production drilling, loading of blast holes, blasting, and removing broken ore over the full length of the stope wherein, in use, as the 5 stope retreats back along the strike the hanging wall of the already mined open stopes will cave-in and sit on the footwall due to the foot wall angle of the stope which is a reflection of the ore body dip. Typically the step of establishing a void for the first stope firing involves establishing a slot raise vertically between the levels running the entire height 10 of the stope. Once all the broken ore has been removed for the full length of an open stope the cycle begins again from production drilling at the next level down. A slot raise will typically not be required as the mining method is continuous and generally no rib pillars will be left. Preferably stopes are mined over multiple levels simultaneously. At peak 15 production stoping will preferably occur on up to four levels. Preferably rows of fanned blast holes are drilled from the lower level to the upper level as up holes. Preferably the broken ore is removed using remote controlled underground loaders. 20 Optionally rib and chain pillars may be left in situ where major structures are encountered and as an aid to controlling waste rilling into the active stopes where needed. Typically rib and chain pillars may be used to address difficulties introduced by flat-dip, namely, dilution, a lack of cave material flow, and high deformation at draw point brows. Preferably chain (temporary, 25 crushing) pillars are left where needed to help slow waste rilling and aid recovery. Preferably temporary crush (Rib) pillars are used to control deformation at the brow.

6 Preferably a slope distance of 18 metres is adopted to ensure that once the stope is extracted the hanging wall will fail, but during mining it will remain in situ. The ore drives are preferably mined as a shanty back to reflect the shallow 5 dip of the ore body. Typically the ore body has an average dip of 30*. The ore drives are preferably mined to a width of 4.0 metres, the hanging wall side 3.0 metres in height and the foot wall side 5.25 metres in height to provide a dip of 300 in the backs which simulates the average dip of the ore body. The ore drives are preferably offset approximately two metres from the 10 foot wall to ensure ore drives are developed within the extents of the ore body. Throughout the specification, unless the context requires otherwise, the word "comprise" or variations such as "comprises" or "comprising", will be 15 understood to imply the inclusion of a stated integer or group of integers but not the exclusion of any other integer or group of integers. Likewise the word "preferably" or variations such as "preferred", will be understood to imply that a stated integer or group of integers is desirable but not essential to the working of the invention. 20 Brief Description of the Drawings The nature of the invention will be better understood from the following detailed description of a specific embodiment of the underground mining method, given by way of example only, with reference to the accompanying 25 drawings, in which: Figures 1(a) and 1(b) are a plan view and an isometric view respectively of the ore body illustrating a preferred embodiment of the underground mining method according to the present invention; Figure 2 illustrates a proposed global layout for the Cerberus 30 underground mine; 7 Figure 3 illustrates a typical level plan for the Cerberus underground mine showing a central access to the ore drives; Figure 4 illustrates a typical level plan for the Cerberus underground mine showing end access to the ore drives; 5 Figure 5 illustrates in section view the preferred positioning of an ore drive in the ore body; Figure 6 illustrates the use of rib and chain pillars to control the flow of caved material and dilution of newly blasted material; Figure 7 (a) and (b) are plan view and an isometric view respectively of 10 the ore body illustrating the underground mining method of Figure 1 using rib and chain pillars; and, Figure 8 is an enlargement of part of the proposed global layout of Figure 2 illustrating the possible location of rib and chain pillars. 15 Detailed Description of Preferred Embodiments A preferred embodiment of an underground mining method in accordance with the invention, as illustrated in Figure 1, comprises a long hole open stoping drill and blast method in which human entry into the stopes can be 20 minimised. The underground mining method is similar to open stoping except once extracted the hanging wall is allowed to cave-in as stopes are retreated back to the access. Such a mining method without rib pillars has not been demonstrated in low global rock strength such as the <1OmPa experienced at Cerberus and may be considered a high risk mining method. 25 A typical step by step mining cycle in accordance with the method of the invention is detailed below: 1. Development - Ore drives 10 (see also Figures 2, 3 and 4) for extracting and drilling are developed through each mining level along the strike of the ore to the economic extremity of the ore body 12 using jumbos 26. A level 8 must be developed above to allow top access. As the stoping panel is retreated towards a central access 14 the top level needs to lead the bottom level as this method is a top down mining method. 2. Slot Raises - Once the upper and lower level development has been 5 established for a given level, a slot raise 16 is established vertically between the levels running the entire height of the stope 20. The initial slot raise can be established using handheld machinery. The purpose of the slot 16 is to offer a void for the expansion of blasted material which swells during the first stope firing on each level. 10 3. Slot Drilling - The slot raise is expanded to cover the entire width of the stope 20. Rows of blast holes 22 are drilled around the initial slot raise 16, with the slot raise offering a void for the expansion of blasted material. Using drill holes 22 the slot raise is gradually expanded to the full width of the stope 20. The process is iterative with material removed using loaders 24 after 15 each blast. With each successive blast and removal of material the void created is increased allowing for more material to be blasted until the slot has been expanded to the desired width. 4. Production Drilling - Once the slot raise has been established more rows of fanned blast holes 22 are drilled between levels. The blast holes are 20 preferably drilled from the lower level to the upper level as up-holes. It is planned that blast holes are drilled with a forward dump of 15'. This will facilitate broken ore being fired off the footwall therefore reducing hang up and increasing recovery. 5. Production Firing - Once a predetermined number of fanned drill holes 22 25 have been drilled in a ring the holes are loaded with explosives and blasted towards the void previously established. 6. Production Bogging - Once broken, the blasted ore 18 is removed using remote controlled underground loaders 24. Due to the shallow dipping nature of the Cerberus ore body there may be a degree of hang-up experienced on 30 the footwall. This can washed off the footwall by using water monitors 9 (cannons). To minimise the chance of hang-up and increase the efficiency of washing down the footwall, rock fragmentation should be as small as is optimal. In a shallow dipping ore body such as this, drill and blast quality is critical to ensuring minimal hang-up on the footwall. 5 Once the stope is bogged clean the cycle begins again from production drilling. A slot raise will not be required as the mining method is continuous and generally no rib pillars will be left. Rib and chain pillars may be left in situ where major structures are encountered and as an aid to controlling waste rilling into the active stopes where needed. As the stope 20 retreats back 10 along strike the hanging wall of the already mined open stopes upper levels will fail (cave-in) and sit on the footwall. Stopes are preferably mined over multiple levels simultaneously. At peak production stoping will typically occur on up to four levels. A lead/lag not exceeding 40 meters should be followed as a stoping front between adjacent levels. 15 Figure 2 illustrates a preferred level design for the Cerberus mine, showing in perspective view the preferred layout of decline, access and ore drives in relation to the ore body. Level intervals are primarily determined by the following three variables: 1. Ore Geometry (primarily dip and width) 20 2. Geotechnical conditions 3. Length of blast holes that can be accurately drilled between levels. Due to the preferred mining method a recommended slope distance of 18 metres is adopted to ensure that once the stope is extracted the hanging wall will fail, but during mining it will remain in situ. The Cerberus ore body has 25 varying dip and therefore the level spacing has been calculated on a level by level basis, with the constant being the 18 metre slope distance down dip. A summary of levels is presented in Table 1 below. Level RL Level RL Level RL Change Change Change (M) (M) (M) 349.9 122.4 9.5 -109.8 9.5 339.8 10.1 112.9 9.5 -119.3 9.5 10 329.7 10.1 103.4 9.5 -128.8 9.5 319.4 10.3 93.9 9.5 -138.8 10.0 309.1 10.3 84.4 9.5 -147.8 9.0 298.5 10.6 74.9 9.5 -157.3 9.5 288.7 9.8 64.8 10.1 -166.8 9.5 278.9 9.8 54.7 10.1 -176.3 9.5 269.1 9.8 44.6 10.1 -185.8 9.5 259.3 9.8 34.5 10.1 -196.1 10.3 249.5 9.8 24.4 10.1 -206.4 10.3 239.7 9.8 14.3 10.1 -216.7 10.3 229.9 9.8 4.2 10.1 -227.0 10.3 220.4 9.5 -5.9 10.1 -237.3 10.3 210.9 9.5 -16.0 10.1 -247.6 10.3 201.4 9.5 -26.1 10.1 -257.9 10.3 191.3 10.1 -36.7 10.6 -268.2 10.3 181.2 10.1 -47.3 10.6 -278.5 10.3 171.1 10.1 -57.9 10.6 -288.8 10.3 161.0 10.1 -68.5 10.6 -299.1 10.3 150.9 10.1 -79.5 11.0 -309.4 10.3 141.4 9.5 -89.7 10.2 -319.7 10.3 131.9 9.5 -100.3 10.6 Table 1. Cerberus Level Summary Typically the sublevel interval is also constrained by long hole drilling capability which then affects hole drilling accuracy. Increasing the vertical level interval has the advantage of lowering the overall 5 mining cost by reducing the development cost that each recovered tonne has to pay. The two risks that increase with increasing level spacing are: " Drill hole deviation resulting in dilution " Deviation resulting in bridging producing hang-ups and potential ore loss. 10 In the case of Cerberus it is not long hole drilling capability but geotechnical conditions which determine level spacing. Hole length will be approximately 12 metres based on these level intervals. Over this distance hole deviation and accuracy will not be an issue. Preferably 64mm blast holes are utilised. Figures 3 and 4 illustrate typical level designs. Each primary access 30 has 15 another access 28 developed off of it to access the intermediate level between the two primary accesses. The Cerberus ore body is preferably accessed via a central access, as illustrated in Figure 3. Central accesses 11 will be suitable until level RL-1 57.3 where the ore body will be accessed end on from the north. This is based on geotechnical recommendations. Figure 4 illustrates end-on access to the ore body at depth, showing level -309.4. Level operating development is considered as the ore drives 10 on each 5 level. As a rule the level accesses 28, 30 have been situated as close as possible to the centre of the ore body 12 with the ore drives 10 developed to the north and south to the economic extents of the ore body. The ore drives form the horizons within the underground mine from which production activities such as blast hole drilling and stope bogging will take 10 place. It is important that the position of the ore drive is excavated with careful consideration for production drilling to ensure achievable and realistic drill angles, and therefore full extraction of the ore zone. Due to the shallow dip of the Cerberus ore body and the 'shanty back' design of the ore drives, the ore drives 10 should be developed in the foot wall to facilitate ease of 15 long hole drilling. This will help to increase grade of ore development by ensuring the ore body is located within the extents of the ore development as demonstrated in Figure 5. Figure 5 shows in cross-section view a typical shanty back shape of an ore drive 10, as well as its position within the ore body 12. 20 Ore drives 10 are preferably mined as a shanty back to reflect the dip of the ore body, an average dip of 300 has been used. Ore drives 10 should preferably be mined to a width of 4.0 metres, the hanging wall side 3.0 metres in height and the foot wall side 5.25 metres in height. This provides a dip of 30* in the backs which simulates the average dip of the ore body 12. 25 Ore drives should preferably be offset approximately 2 metres from the foot wall to ensure ore drives are developed within the extents of the ore body 12. The shanty back design is important to reflect the dip of the ore for both ore recovery and geotechnical purposes, to minimise stress and damage to the hanging wall.

12 An average dip was measured on each level RL with an average taken over four measurements. Two measurements were recorded to the north of the access and two to the south of the access. An average was taken for each level and an overall average for the total ore body. An average cumulative 5 dip of the ore body has been calculated to be 33.10 degrees. Client: Poseidon Nickel SGS Job No: 10855 Sample Identification: Cerberus Ore Composite PNDRC0169 (-2 mm) Date: 8/02/2012 Test Sample Cone Diameter of Diameter of Angle of No. Description Diameter (D) Side (dl) Side (d2) Repose cm cm cm Degrees 1 Cerberus Ore 19.4 11.7 11.8 34.4 2 19.3 11.0 11.3 30.1 3 19.1 11.0 11.8 33.1 Av 19.3 11.2 11.6 32.6 Table 2. Rill Angle Testing Results: Angle of Repose Based on the angle of repose results presented in Table 2 above the following recovery rates were applied to stope ore tonnes. The angle of 10 repose relates directly to the foot wall angle of the stope which is a reflection of the ore body dip. <30* = 80% recovery 30-34* = 85% recovery >340 = 90% Recovery 15 Dilution was calculated using the following constants: For stopes < 1 Metre 0.4 = Dilution thickness (0.2 metres on the foot wall and 0.2 metres on the hanging wall) 10 = Average stope distance along dip in metres 20 20 = Stope length in metres For stopes > 1 Metre 13 235 = Tonnes of dilution applied to stopes greater than 1 metre. Calculated as follows: 0.4 x 10 x 20 x 2.9 = 232 (rounded up to 235), where 0.4 = Dilution thickness (0.2 metres on the foot wall and 0.2 metres on 5 the hanging wall) 10 = Average stope distance along dip in metres; 20 = Stope length in metres 2.9 = Average ore density Based on these assumptions, the total dilution should account for about 23% 10 of mined ore material over the life of the mine. The underground mining method of the invention is in some aspects similar to conventional longitudinal sub level caving (SLC), but certain essential elements critical to the viability of the method in Cerberus type deposits differ or are contrary to conventional SLC practice. The similarities to conventional 15 SLC lie in the general configuration of drives, and drill and blast practice. Some key differences are in the management of cave flow and cave propagation. Where an SLC method must achieve steady-state cave propagation, the present method may not do so and, generally, this is most often likely to be 20 an advantage of the method. Recovery may be reduced or similar to a conventional SLC method, but dilution from overlying waste will be lower. In a conventional SLC method, the caved material flows and mixes with newly blasted ore 18. In the method of the invention there may be design measures to control this that are not present for conventional SLC. The flat dip of the 25 Cerberus Type deposit is also a limiting factor. One possible control measure is the use of rib and chain pillars as shown in Figures 6 to 8. In a conventional SLC method, pillars negatively affect performance substantially. In the method of the present invention they may be used to address difficulties introduced by the flat-dip, namely, dilution, a 30 lack of cave material flow, and high deformation at draw point brows. Preferably chain (temporary, crushing) pillars 40 would be planned where 14 needed to help slow waste rilling and aid recovery. Preferably temporary rib (crush) pillars 42 would be used to control deformation at the brow. The method of the invention does require that the hanging wall collapse a short distance behind the active stopes. If the un-collapsed span becomes 5 excessive, in extreme cases there would be an air blast risk. Therefore procedures to promote instability before this occurs are necessary. Preferable means for controlling instability include: " Drive spacing down dip/sub-level interval " The option to leave behind rib pillars 42 of various sizes, to augment 10 the chain pillars 42 " Omission of the chain pillars 42 " Drill and blast into the hanging wall. The use of rib and chain pillars 42 and 40 forces a loss in the amount of ore available to recover as the ore is left behind in the goaf in these rib and chain 15 pillars, and this results in more dilution (see Figures 6 and 8). Figure 6 shows the progressive goaf collapse and subsidence process as the mining front retreats along a stope 20. As mining progresses the chain pillars 40 and rib pillars 42 are crushed and do not survive. Figures 7 (a) and (b) show the pillars that are in the caved/goaf area marked "chain pillar (caved)" and "rib 20 pillar (caved)." The word "caved" is used instead" of "crushed" to represent that the pillars are destroyed as mining progresses. While possible future pillars outside the caved/goaf area have the words "future rib pillar" and "future chain pillar." In the preferred method of the invention the use of rib and chain pillars 42 and 40 may not be required, however the method can fall 25 back to the use of rib and chain pillars if necessary. Now that a preferred embodiment of the mining method has been described in detail, it will be apparent that the described embodiment provides a number of advantages over the prior art, including the following: (i) It makes mining of an ore body considered uneconomical by 30 conventional mining methods more viable.

15 (ii) It avoids the added expense of back-filling of stopes (iii) Reduced dilution compared with conventional sublevel caving techniques. 5 It will be readily apparent to persons skilled in the relevant arts that various modifications and improvements may be made to the foregoing embodiment, in addition to those already described, without departing from the basic inventive concepts of the present invention. For example, during production drilling, the blast holes may also be drilled from the upper level to the lower 10 level as down-holes. Therefore, it will be appreciated that the scope of the invention is not limited to the specific embodiments described.

Claims (16)

1. A method of mining an underground ore body, the method comprising the steps of: 5 developing upper and lower level ore drives through each of a plurality of mining levels along the strike of the ore body, an upper level drive being located above a lower level drive in each case; establishing a void vertically between the lower and upper level drives for a given mining level to allow expansion of blasted material during a stope firing 10 on each level; production drilling of rows of blast holes between upper and lower level drives over the width of the stope; loading the blast holes with explosives and blasting towards the void previously established to form an open stope; 15 removing broken ore from the stope as the production face retreats to an access drive; and, repeating the steps of production drilling, loading of blast holes, blasting, and removing broken ore over the full length of the stope wherein, in use, as the stope retreats back along the strike the hanging wall of the already mined 20 open stopes will cave-in and sit on the footwall due to the foot wall angle of the stope which is a reflection of the ore body dip.

2. A method of mining an underground ore body as defined in claim 1, wherein the step of establishing a void for the first stope firing involves establishing a slot raise vertically between the levels running the entire height 25 of the stope.

3. A method of mining an underground ore body as defined in 1, wherein once all the broken ore has been removed for the full length of an open stope the cycle begins again from production drilling at the next level down. 17

4. A method of mining an underground ore body as defined in 3, wherein a slot raise will not be required as the mining method is continuous and generally no rib pillars will be left.

5. A method of mining an underground ore body as defined in any one of 5 claims 1 to 4, wherein stopes are mined over multiple levels simultaneously.

6. A method of mining an underground ore body as defined in 6, wherein at peak production stoping will occur on up to four levels.

7. A method of mining an underground ore body as defined in claim 1, wherein rows of fanned blast holes are drilled from the lower level to the 10 upper level as up holes.

8. A method of mining an underground ore body as defined in claim 1, wherein the broken ore is removed using remote controlled underground loaders.

10. A method of mining an underground ore body as defined in claim 4, 15 wherein rib and chain pillars may be left in situ where major structures are encountered and as an aid to controlling waste rilling into the active stopes where needed.

11. A method of mining an underground ore body as defined in 10, wherein rib and chain pillars are used to address difficulties introduced by flat-dip, 20 namely, dilution, a lack of cave material flow, and high deformation at draw point brows.

12. A method of mining an underground ore body as defined in 11, wherein chain (temporary, crushing) pillars are left where needed to help slow waste rilling and aid recovery. 25 13. A method of mining an underground ore body as defined in 11, wherein temporary crush (Rib) pillars are used to control deformation at the brow.

14. A method of mining an underground ore body as defined in any one of the preceding claims, wherein a slope distance of 18 metres is adopted to 18 ensure that once the stope is extracted the hanging wall will fail, but during mining it will remain in situ.

15. A method of mining an underground ore body as defined in 1, wherein the ore drives are mined as a shanty back to reflect the shallow dip of the ore 5 body.

16. A method of mining an underground ore body as defined in 15, wherein the ore body has an average dip of 30'.

17. A method of mining an underground ore body as defined in 16, wherein the ore drives are preferably mined to a width of 4.0 metres, the hanging wall 10 side 3.0 metres in height and the foot wall side 5.25 metres in height to provide a dip of 30* in the backs which simulates the average dip of the ore body.

18. A method of mining an underground ore body as defined in 17, wherein the ore drives are offset approximately two metres from the foot wall to 15 ensure ore drives are developed within the extents of the ore body. Dated this 21st day of February 2014 20 Poseidon Nickel Limited by its Patent Attorneys 25 Wrays