DISPOSAL OF TAILINGS

Technical Field

The field of this disclosure relates to a method of mining to extract one or more desired materials/minerals from an underground ore body and to safely and economically dispose of any resulting tailings.

Background Art

Tailings are waste materials left after a target mineral/material or multiple such target minerals/materials have been successfully removed from a mined ore body. Such tailings may include crushed rock and/or ground rock, water, trace quantities of metals such as copper, gold, nickel, tin, mercury, cadmium, zinc etc, and additives of processing materials, if used, to extract the target mineral(s)/material(s) from the mined ore body, some of which may be dangerous. Conventionally, in the past, tailings generally in the form of a wet slurry, have been stored in tailings dams above ground behind an earth dam wall. It is currently estimated that world wide there are about 18,000 such tailing dams of which about 3,500 are currently active. It is well known that tailings dams have failed at rates higher than the failure rate for water supply reservoir dams, possibly because they are often poorly constructed and poorly maintained, particularly once a mine’s operational life ends. Failure of a tailings dam can have catastrophic effects on the surrounding regions, however, even without such failures occurring, above ground tailings dams are unpleasant and sometimes dangerous facilities. There has therefore been a tendency to try to take alternative tailings handling procedures to avoid having above ground tailings dams.

Some known tailings handling procedures have included:

(i) drying the tailings when they do not contain dangerous materials and spreading such dried tailings materials above ground; and

(ii) Taking the tailings material underground to fill mined underground voids or stopes with same. This has primarily been via pumping such tailings materials as semi liquid or paste. Such material has little or no strength and if this is required, often sufficient cement is dispersed in the semi liquid or paste material which allows the material to set underground with adequate strength. Filling underground voids or stopes is a desirable practice to avoid, as far as possible, ground instability resulting from too many such voids remaining underground once mining is complete or finished in a particular area. There are, however, certain disadvantages when an ongoing mining operation is occurring. If a void or stope is filled with semi liquid or paste tailings material, or dried tailings materials, that has no or little strength, then mining is prevented in an immediately adjacent region because the mining operation would be adversely affected by the adjacent tailings material of little or no strength. One solution is to leave part of the ore body to stabilise the tailings filled zone, however, this results in an unacceptable cost loading to the mining operation. This might be avoided by including sufficient cement in all of the tailings material whereby it would set with sufficient strength to maintain stability in the tailings material zone, however, cement is a costly material and this would also result in an unacceptably high cost loading for disposal of the tailings material. Also the mechanism to add cement to the tailings material and transport it to an underground location, is very expensive.

There is, however, a recognisable advantage in disposing of dried or semidried tailings material in any location including underground locations. This is that tailings material in paste form comprises typically 65% solids, whereas dried or semidried tailings material typically is much denser, having in the order of 93% solids. Thus, more tailings material can be disposed of for any given volume.

An objective, therefore, of the present disclosure is to provide a method of mining an underground ore body containing zone whereby a void or stope created by removing ore material therefrom is refilled with tailings material in a safe and economic manner without affecting subsequent removal of adjacent zones of the ore material from the ore body. Preferably the method minimises the use of cement or any other settable/stabilisation agent during placement of the tailings material.

Summary of the Invention

In accordance with one aspect of the development described in this disclosure, a method is provided for mining and removing ore body material from an underground ore body containing zone, said method including steps of:

(i) identifying a first volume section forming part of said ore body containing zone to be mined; (ii) positioning one or more access drives above and/or below at least said first volume section of said ore body containing zone;

(iii) mining and removing the ore body material from one or more first region(s) in said ore body containing zone immediately adjacent said first volume section and between said first volume section and a second volume section of said ore body containing zone;

(iv) filling the or each said first region with a settable mixture including an aggregate material and a setting agent whereby, when set, the settable material provides one or more stabilising structures;

(v) mining and removing ore material from said first volume section to create a first void;

(vi) introducing dried or semi dried filler material including at least some tailings material into said first void to substantially fill said first void with said dried or semi dried filler material;

(vii) repeating steps (iii), (iv) and (v) to create a second void in said second volume section; and

(viii) introducing dried or semi dried filler material including at least some tailings material into said second void to substantially fill said second void with said dried or semi dried filler material.

The method outlined in the preceding paragraph may have at least one first said access drive positioned at or below a lower level of said first volume section and at least one further said access drive positioned above the or each said first access drive(s) either passing through said first volume section at an intermediate level or at a second level positioned at or above an upper level of said first volume section.

Conveniently, at least one first upper said access drive is positioned immediately above said ore body containing zone, and at least one second lower said access drive is positioned immediately below said ore body containing zone. In some possible further alternative arrangements, at least one third said access drive may be positioned through said ore body containing zone positioned between a said first upper access drive and a said second lower access drive. Conveniently, multiple said first upper access drives and multiple said second lower access drives may be provided. Preferably, the settable mixture in at least one of said first region(s) forms an isolating wall portion of said settable mixture. Alternatively, or in addition thereto, at least one and potentially more of said first region(s) form individual and spaced isolating pillar portions and/or isolating wall portions formed from set said settable mixture. The settable mixture may contain or substantially comprise tailings material containing a setting agent delivered to the or each said first region and may be delivered as a semi liquid or paste formulation. Preferably, the setting agent used may be cement.

Conveniently, in one preferred embodiment steps (iii), (iv) and (v) outlined above are further repeated to create further voids in further volume sections of said ore body containing zone with dried or semi dried filler material, preferably with at least some tailings material being introduced into said further voids to substantially fill said further voids. It is of course preferred that all tailings material produced during the mining operation while recovering desired target mined minerals/materials, are safely disposed of underground without adversely affecting further underground mining activities. This, however, may be achieved by mixing some of the tailings material into the aggregate material used for forming the stabilising structure(s) or by packing the dried or semi dried tailings material into the first or further voids. Alternatively or in addition, any other available access openings or spaces could be used to store dried or semidried tailings material.

The settable material may include an aggregate material including one or more of rock, crushed rock, ground rock material, and tailings material or a combination of any or all of these. These materials, individually, or in combination, may be combined with a settable agent such as cement to be used to form the one or more stabilising structures.

In a preferred arrangement, the ore body material removed from said first volume section, said second volume section, or any said further volume section, and from the or each said first region(s) occurs from a lower region of the ore body and is transported along a lower said access drive to a processing station located above ground with tailings material produced by said processing station being returned underground. In an alternative preferred arrangement, the ore body material removed from said first volume section, or any said further volume section, and from the or each said first region(s) is transported via a lower said access drive to a processing station located underground with tailings material produced by said processing station being returned to the first void, the second void, or any further void, or to voids formed in said one or more first regions. The dried or semi dried filler material including tailings material may be delivered to said void(s) as required via an upper said access drive.

Conveniently, a layer of crushed or ground based rock with or without tailing materials and a settable agent mixed therein can be laid on any suitable floor region within underground locations including any access drive.

According to another aspect of this invention, a mining method is provided for mining and removing ore body material from an underground ore body containing zone, said method including steps of

(i) identifying a first volume section forming part of said ore body containing zone to be mined;

(ii) positioning one or more access drives above and/or below said first volume section of said ore body containing zone;

(iii) identifying a second volume section forming part of said ore body containing zone to be mined positioned between the upper said access drive and the lower said access drive, the second volume section being located immediately adjacent said first volume section;

(iv) mining and removing ore body material from one or more first region(s) in said ore body containing zone between said first volume section and said second volume section;

(v) filling the or each said first region with a settable material including an aggregate material and a setting agent whereby, when set, the settable material provides one or more stabilising structures;

(vi) mining and removing the ore body material from said first volume section to create a first void; and

(vii) introducing dried or semi dried filler material including at least some tailings material into said first void to substantially fill said first void with said dried or semi dried filler material to be positioned at least partially against a said stabilising structure or structures.

One method outlined in the preceding paragraph may have at least one first said access drive positioned at or below a lower level of said first volume section and at least one further said access drive is positioned above the or each said first access drive(s) either passing through said first volume section at an intermediate level or at a second level positioned at or above an upper level of said first volume section.

The method outlined in the preceding paragraph may be further modified by identifying a third volume section forming part of said ore body containing zone, the third volume section being located immediately adjacent said second volume section or said first volume section, mining and removing ore body material from one or more said first region(s) positioned in said ore body containing zone between said third volume section and one of said first volume section or said second volume section, and filling the or each said newly formed first region(s) with a settable material including an aggregate material and a setting agent whereby, when set, the settable material provides one or more further said stabilising structures. Preferably the stabilising structure(s) formed between the first volume section and the second volume section, and between the third volume section and the first or the second volume section(s) are formed, prior to the mining and removing of the ore body material from the first volume section or the second volume section. In another alternative method, the stabilising structure(s) between the first volume section and said second volume section are formed prior to steps (vi) and (vii) outlined in immediately prior paragraphs, the stabilising structures being thereafter formed between the second volume section and third volume section; and further thereafter mining and removal of the ore body material from the second volume section to create a second void; and introducing dried or semi dried filler material into said second void to substantially fill said second void with said dried or semi dried filler material to be positioned at least partially against a said stabilising structure or structures.

In accordance with a still further aspect of this disclosure, a mining method is provided for mining and removing ore body material having desired mineral/materials from an underground ore body containing zone, said mining method including steps of

(i) identifying multiple volume sections, each forming part of said ore body containing zone, being located either in side by side relation, in one above another relation, or in both side by side and one above another relation;

(ii) positioning at least one access drive providing access to said underground ore containing body containing zone;

(iii) mining and removing ore body material from one or more first region(s) positioned between at least two adjacent said volume sections of said underground ore body containing zone; (iv) filling the or each said first region with a settable material including an aggregate material and a setting agent whereby, when set, the settable material provides one or more stabilising structures, whereby at least one said volume section forming part of said ore body containing zone is at least partly contained by a said stabilising structure or multiple said stabilising structures;

(v) mining and removing the ore body material from one or more said volume section(s) that is, or are, at least partly contained by a said stabilising structure or multiple said stabilising structures to create one or more void(s); and

(vi) positioning dried or semi dried filler material including at least some tailings material into said void or said voids to substantially fill a said void or said voids while being stabilised by at least one said stabilising structure.

Preferably at least one said access drive is positioned at least partially above said underground ore body containing zone. Further, at least one said access drive may be positioned at least partially below said underground ore body containing zone. Still further, at least one said access drive may be positioned at least partially through said underground ore body containing zone.

In one preferred embodiment, steps (iii) and (iv) may be carried and to create one or more said first region(s) and said one or more stabilising structures being formed between multiple adjacent said volume sections forming part of said ore body containing zone, prior to carrying out steps (v) and (vi). Alternatively, steps (iii) and (iv) may be carried out to establish all said stabilising structures prior to carrying out steps (v) and (vi).

In a still further possible preferred embodiment, steps (iii) and (iv) may be carried out sequentially until all of said underground ore body containing zone has been mined, removed, and processed and replaced at least partially with dried or semi dried filler material stabilised with spaced said stabilising structures.

Mined or excavated ore material will normally be removed from lower regions of the ore body, either from an ore body volume section or from one or more said first region(s), via a lower said access drive. In one possible process step, any void formed as a said volume section may be filled with dried or semi dried filler material transported along an upper access drive, or multiple said upper access drive(s), located above the ore body region being mined. In some situations, such voids or stopes created via the mining process might be accessed by drilling a passage downwardly from the surface whereby dried or semi dried filler material might be delivered to the void or stope via such a drilled passage (or passages) from the surface. In such a case, an upper access drive positioned above the ore body being mined, may not be required.

Conveniently, the filler material positioned in a said void or at least some said voids is/are at least partially supported by rock or earth wall surfaces originally surrounding said underground ore body containing zone. In other situations, the filler material may be positioned in a said void or at least some said voids supported only by a surrounding said stabilising structure or structures. The stabilising structure, or structures, may comprise a variety of differing elements including a continuous wall structure, discontinuous and spaced shorter wall structure(s), a plurality of spaced pillar (or column) structures, and a combination of semi continuous wall section structures with spaced pillars. Pillars can be horizontal vertical or planar; they are typically used to isolate various parts of the underground workings, for stability or logistical reasons. In any case, the spacing between any such stabilising structures should be insufficient to allow the positioned dried and semi dried filler material (that may comprise a significant proportion of tailings material) in the respective void(s) to collapse through the spacing, particularly when an adjacent said volume section of ore body containing material is mined/excavated. Furthermore. It is preferred that the ore body material positioned between any such stabilising structures is also mined (excavated and processed) with this space also being occupied by the aforesaid filler material.

It will be appreciated that the methods outlined above allow for mining removal and processing of substantially all of the ore body material from an underground ore body containing zone, that is, it is unnecessary to leave any ore body material to support other adjacent zones being mined, and moreover a simple and economic process is provided for safe disposal of tailings material resulting from processed ore material mined.

It will be understood that any terms such as “comprises”, “comprising”, “includes”, and/or “including” when used in this specification, specify the presence of stated features, items, steps, operations, elements and/or components, but do not preclude the presence of or addition of one or more other features, items, steps, operations, elements, components and/or groups thereof. Preferred embodiments of the method of this disclosure will hereinafter be described with reference to the accompanying drawings. It will be appreciated that the drawings represent only an illustrative representation in two dimensions of an underground ore body to be mined. In the real world an underground ore body will be three dimensional, i.e. extended into and out of the page, and will have a variety of volume shapes. The drawings illustrate sequential stages in one preferred mining process, however, other intermediary and alternative stages are possible within the scope of the accompanying patent claims.

Brief Description of the Drawings

Fig 1 illustrates diagrammatically an ore body containing zone in an underground location with surrounding earth or rock over burden;

Fig 2 represents diagrammatically, a first mining stage where the ore body containing zone of Fig 1 has upper and lower access drives positioned above and below the ore body and identifying a first volume section and a first region in the mining process of this disclosure;

Fig 3 represents diagrammatically establishing a reinforced surface layer of cement rock fill (CRF) along at least a floor zone of the lower access drive shown in Fig 2;

Fig 4 represents diagrammatically establishing a floor zone or space underneath the first volume section shown in Fig 3 with the floor zone or space also including a reinforcing surface layer of cement rock fill (CRF) being an extension of the reinforcing layer along the lower access drive or drives;

Fig 5 represents diagrammatically, a further mining stage including mining and removal of ore body material from the first regions or regions;

Fig 6 represents diagrammatically, a still further stage in the mining process where a void or voids creating the first regions region(s) have been filled with a settable material mixed with a setting agent and further represents diagrammatically, mining and removal of ore body material from the first volume section;

Fig 7 represents diagrammatically yet another stage in the mining process where the void formed by removing ore body material from the first volume section has been filled with dried or semi dried filler material, and further, a further first region or regions defining a second volume section of the ore body is defined;

Fig 8 represents diagrammatically a still further stage in the mining process where the further first region or regions have been excavated and filled with a settable material to form a stabilizing structure or structures and the second volume section has been excavated; and

Fig 9 represents diagrammatically a further mining stage following that illustrated schematically in Fig 8 where the ore body material in the second volume section has been removed and replaced with dried or semi dried filler material that may include at least some tailings material.

Description of Preferred Embodiments

Fig 1 represents schematically ore body material 10 in an ore body containing zone 11 underground with a surrounding earth or rock over burden 12. The aim of the process steps disclosed herein is to remove substantially all of the ore body material 10, process same to recover any desired target mineral or other materials that may be commercially worth recovering, and to safely and economically return any tailings material resulting from processing the ore body material 10 to the underground position defined by the zone 11. It will of course be recognised that in any mining operation, the tailings material may also come from any previously mined zone. The ore body material has a side edge wall surface 17 being the left hand edge wall in Fig 1, however this simply representative of any desired starting point for mining the ore body 10.

Fig 2 represents the ore body material 10 in the ore body containing zone 11 with an upper access drive 13 and a lower access drive 14 generally positioned above and below the ore body containing zone 11. Preferably each access drive 13, 14 has a relatively planar lower surface to permit mine and mining machinery to traverse along the respective access drives 13, 14 as required from time to time. Conveniently, the access drives 13, 14 may be inclined and/or include other drainage means to permit liquids to drain away from the ore body containing zone 11 where mining processes applied to the ore body material 10 will occur. Normally transversely extending access drives (not illustrated) will be provided to enable access to parts of the ore body material 10 located into or out of the two dimensional representation illustrated in Fig 2. The transverse access drives connect to the upper and lower access drives 13, 14 or any further positioned upper/ lower access drives generally to the illustrated access drives 13, 14. Fig 2 further represents schematically, a first region 15 disposed vertically and extending transversely across the ore body material 10, or two or more such first regions 15 aligned and extending across the ore body material 10 separated by sections of the ore material, and further extending between the upper and the lower access drives 13, 14. In this manner the first region(s) 15 might be a series of individual spaced vertical zones adapted to form pillar or column sections which form stabilising structures as described hereafter. The first region(s) 15 may also be configured to form a continuous wall section, or discontinuous shorter wall sections, or a combination of pillars and discontinuous wall sections. A first volume section 16 of the ore body material 10 is located between the upper and the lower access drives 13, 14, and between the first region or regions 15 and the left hand (in the drawing) side limit face 17 of the ore body material 10. The rock or earth wall face 17 of the overburden (or waste rock) 12 is positioned at the left hand side face of the ore body material 10. It will be appreciated that the upper and the lower access drives 13, 14 have sections (not shown) leading to above ground locations to allow suitable mining machinery to get to the mining site and to allow mined ore materials to be transported to the above ground locations. In some cases the mined ore body materials might be processed under ground and in this case tailings material would be returned from such an underground position as described hereafter. In this case, any target minerals or materials would need a route to the above ground locations.

Fig 3 is a view similar to Fig 2 but further illustrating that the lower floor surface of the lower access drive 14 may be further excavated to a depth of about 1 metre to enable a cement rock fill (CRF) reinforcing layer 21 to be positioned along, at least the zone beneath the ore body 10. Fig 4 is a view similar to Figs 2/3 but further illustrating that the earth or rock burden material 12 immediately below the first volume section 16 of the ore body material 10 to be mined is excavated to form an open volume zone 30 extending int and/or out of the page of the drawing below the first volume section 16. The floor of this zone 30 is further excavated to allow formation of cement rock fill (CRF) reinforcing layer 31 being essentially an extension of the reinforcing layer 21 of the or each layer access drive 14. The reinforcing layers 21, 31 may act as a strengthening isolating layer to allow a lower ore body zone to be mined utilising process techniques outlined in this specification. In such circumstances, the thickness of these layers 21, 31 would be selected to have required performance characteristics.

Fig 5 is a view similar to Fig 2 but showing the first region or regions 15 have been mined to remove ore body material therefrom as represented by the pile 32 of such ore body material with such ore body material being conveyed via the lower or other lower said access drives 14 to an above ground or below ground processing site. The ore body material removed from the first region or regions 15, after processing, produces desired target minerals/materials to be sold and waste materials (tailings) that are intended to be returned to an underground position in accordance with processes described in this specification. As represented in Fig 6, wall or pillar stabilising structure(s) 18 is/are formed in the open volume or spaces formed in the first region or regions 15 (Fig 5) by packing a settable material therein. The settable material may be any of:

(i) cement rock fill (CRF) comprised of suitable rock aggregate, cement and water;

(ii) cement rock fill (CRF) as described in (i) together with a suitable volume of tailings dried or partially dried and formed into an aggregate; and

(iii) a quantity of dried tailings material formed into an aggregate together with cement and water.

Cement rock fill (CRF) is known in mining industries and the ability to provide a set stabilising material from the aforesaid materials of adequate strength and other performance characteristics would be within the knowledge of the skilled addressee.

As is shown in Fig 6, the ore material in the first volume section 16 is excavated by any suitable mining/ excavating method to form ore material 35 that is dropped to the floor layers 21, 31 and removed for processing along the lower access drive (or drives) 14.

As shown in Fig 7, once the stabilising structure or structures 18 have been formed, and the first volume section 16 has been mined (Fig 6) by any suitable mining techniques or machinery including, but not limited to, blasting, drilling and excavating machinery, and the ore body material is removed from the first volume section 16 for processing (above or below ground). A void is formed in the first volume section 16 that has a floor level generally the same as the floor surface of the lower access drive 14. The void formed in the first volume section 16 may then be filled with dried or semi dried filler material 20 via the upper access drive 13 or by any other suitable means such that the filler material 20 rests against the stabilising structure or structures 18 as well as the opposed wall face 17. The filler material 20 may include dried or semi-dried tailings material or consist substantially of such dried or semi dried tailings material. Tailings material leaving ore processing equipment is usually in the form of a slurry and this can be processed to effectively remove all or a substantial part of the liquid therefrom. This can be done by any water/liquid filtering machine, by centrifuging machinery, by cyclone separation, or by any other machinery for dewatering the tailings material. The dry or semi dry tailings material 20, in the region of the lower access drive 14, will sit on the lower layer 21 or 31 stabilizing floor layer of CRF material or other similar material described above. This dry or semi dry filler material 20 essentially fills the first volume section 16 and is supported by the stabilising structure or structures 18 on one side, and on an opposed side by the wall face 17 of the surrounding rock or earth material. The dry or semi dry filler material 20 is also supported underneath in sections by the surrounding rock or earth material, or by such a base with a reinforcing layer (e.g. CRF) covering same, and by the floor layers 21, 31. In this configuration, the stabilising structure or structures 18, support the filler material 20 permitting further mining/excavation of ore body material adjacent to the filler material 20 protected by the supporting structure or structures 18. Fig 7 further illustrates identification of a further first region or regions 22 (similar to first region or regions 15 (Figs 2-4)) adapted to form a void or voids that can be filled with a settable stabilizing material to form a second stabilizing structure or structures 28 (Figs 8/9).

Fig 7/8 represent a further step or stage in an essentially sequential mining process where a second volume section 23 of the ore body material 10 to be mined between the first stabilizing structure(s) 18 and the second stabilizing structure(s) 28, being at least partially dropped by any suitable mining process to a lower floor level being effectively an extension of the floor level of the lower access drive 14 as shown at 27 to be removed along the drive 14 for processing, either above ground or below ground. The lower floor level in regions adjacent the lower access drive 14 may also include a layer of reinforcing material (e.g. CRF) as positioned along the lower drives 13, 14. Preferably a floor space or cavity 33 similar to the space 31 (Figs 4, 5, 6) may be formed under the ore body material in zone 23 extending into and/ or out of the page (Fig 7). The space or cavity 33 may have a stabilizing or reinforcing layer 34 essentially being an extension of the layer 21 forming a base layer of the lower access drive 14. This arrangement and processing is essentially similar to the arrangements and processing as described with reference to Figs 3 to 6. Once the ore body material has been removed from the second volume section 23 (Fig 8), the void may be filled with filler material 26 (Fig 9) from the upper access drive 13 with the filler material 26 being similar to the dry or semi-dried filler material 20. Typically, it will include or substantially consist of dried or semi dried tailings material without any setting agent (e.g.) cement. The process described in the foregoing may sequentially continue across the ore body containing zone 11 until all of the ore body material 10 has been mined (removed for processing) and replaced by dried or semi-dried filler material typically including or substantially consisting of dried or semi dried tailings material, supported by spaced stabilising structures 18, 28, etc. Any method step described in relation to one stage of the mining process, may equally be followed in relation to another stage where it appears appropriate to do so.

While the foregoing describes one preferred mining method embodiment, there are a number of possible variations to this process that might be employed from time to time. A first possible variation might be where the ore body containing zone 11 is particularly extensive, for example into and out of the page in the diagrammatic drawings annexed hereto. In this circumstance, it may be desirable to divide the first volume section 16, the second volume section 23 and any further volume sections into two or more subsections by providing a stabilising structure or structures in a longitudinal direction relative to the transversely disposed stabilising structure(s) 18, 28 described in the preceding. Otherwise, the “further” stabilising structure(s) including their formation might be as previously described for the stabilising structure(s) 18, 28. Similarly, for particularly extensive ore body containing zones in a vertical direction, it may be desirable to divide each, or at least some of the first, second, etc. volume sections 16, 23 into two or more, subsections by providing a stabilising support wall or other means between the vertically disposed subsections. In this regard, it may be desirable to locate one or more access drives between the upper access drive 13 and the lower access drive 14.

While the foregoing describes a sequential mining process of mining subsections (e.g. first and second volume sections 16, 23) of an ore body containing zone 11, some variations are possible where a strict sequential regime may not need to be followed. For example, in some preferred situations, it may be desirable to form all the stabilising structure(s) 18, 28 or any similar further such stabilising structure(s), (e.g. floor stabilising walls 21, 31, etc.) prior to mining and removing (for processing) any of the remaining ore body material from the first, second, or further, volume sections 16, 23 etc. In one possible variation, the ore body material might be sequentially removed from each or the first, second or further volume sections 16, 23 and replaced by dried or semi-dried filler material before moving onto mining/removing ore body material from an adjacent volume section to be mined. In a still further possible variation, all of the first, second and further volume sections 16, 23 etc. might be mined with the ore body material being removed for processing before any of the volume sections are refilled with dried or semi-dried filler material. It will also be recognised that if access along the upper access drive 13 does not need to be maintained, the space of the upper access drive or drives 13 also may be filled with dried or semi dried filler material including or consisting of tailings material. It will be recognized by those skilled in this art that a number of variations are possible to the concepts disclosed herein within the scope of the claims annexed hereto. The annexed claims are hereby made part of the disclosure of this specification.