A Low-Cost, Remotely Operated Mining Method

ROES® – A Low-Cost, Remotely Operated Mining Method I Gipps1, J Cunningham2, G Cavanough3, M Kochanek4 and A Castleden5 ABSTRACT ®

ROES is a proposed new mining system for underground hard rock mines. Ore is accessed from within a shaft, which is located close to or within the stope, and pitched either vertical or within approximately 20 degrees of vertical. The shaft is designed to exclude personnel entry so production drilling and explosive placement is done using remotely controlled or automated machines. Routine remotely controlled survey of the shaft, stope back and broken rock within the stope is typically done following each blast. The survey may include excavation geometry, rock fragmentation and geotechnical characteristics. Blastholes are surveyed before placement of explosives. This provides mine operators and engineers with real-time data, allowing them to monitor production performance and risk factors so that they can make rapid changes as required. ROES® is designed to apply to open stoping or sublevel caving situations either in disseminated, geologically defined, thick tabular or narrow vein orebodies. The technologies developed for ROES® will also have potential applications to block caving operations to reduce the risk of frozen ore and poor fragmentation. In a typical sublevel open stope application, ROES® will reduce the amount of stope-associated development by about half and therefore will allow ore to be brought on-stream sooner and at significantly reduced cost. Other savings are expected to flow from the centralisation of mining activities and operational data, reduction in mining fleet, reduction in ventilation requirements, improved occupational safety and reduced mine complexity. CSIRO and Orica Mining Services are developing the required technology and AMIRA is seeking sponsorship for a project to trial the mining method. This paper details the ROES® method, expected benefits and applications and includes typical stope and mining block designs and design requirements.

INTRODUCTION The Mining Industry is under continuous pressure to improve its performance in areas of safety, cost and productivity. This has been achieved in the past by improvements through mechanisation, scale-up of equipment size and occasionally changes in mining methods. The ability of underground mines to improve productivity by increasing equipment size is constrained by the trade-off between opening dimensions and ground support requirements. Another constraining factor is the increasing mining depth resulting in increased geotechnical risk, increased travel times and more hostile working environments for people. To overcome these constraints a considerable effort is being undertaken by equipment manufacturers, research organisations and mining companies into the remote control and automation of mining equipment. The mining industry currently has access to both remotely controlled and automated machinery for standalone mining activities. While the take-up of these technologies

1.

MAusIMM, Research Stream Leader, Non-Entry Underground Mining, Minerals Down Under National Research Flagship, CSIRO, QCAT Technology Court, Pullenvale Qld 4069. Email: [email protected]

2.

MAusIMM, Research Theme Leader, Transforming the Future Mine, Minerals Down Under National Research Flagship, CSIRO, QCAT Technology Court, Pullenvale Qld 4069. Email: [email protected]

3.

Mechatronics Research Engineer, CSIRO Exploration and Mining, QCAT Technology Court, Pullenvale Qld 4069.

4.

Research Physicist, CSIRO Exploration and Mining, QCAT Technology Court, Pullenvale Qld 4069.

5.

Mechanical Engineer, CSIRO Exploration and Mining, QCAT Technology Court, Pullenvale Qld 4069.

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is increasing, significant transformation will only come about when technologies are fully integrated or when a designed-forautomation mining system is introduced. Isolated introduction of remote control and automation may shift bottlenecks to other parts of the system. Mining methods based on block, panel and sublevel caving have been attractive for a number of reasons, including their low operating costs and high production rates (Brown, 2007). However, caving methods can be problematic when the cave does not perform as expected, especially when ground conditions are not suitable. Issues such as frozen ground, excessive dilution and poor fragmentation are difficult to remedy once a cave has been initiated. However, sublevel open stoping (SLOS) is more flexible, allows better control of fragmentation and can bring a mining block into production earlier. Unfortunately SLOS has higher operating costs. For some time, horidiam or raise mining geometries for drill and blast mining have been proposed and used for shaft expansion and stoping. For example: Mount Charlotte (Mikula and Lee, 2000), Mount Lyell (Usher and Kennewell, 1992) and Viscaria (Anon, 1983, 1984). These applications used manually operated equipment and therefore risked high exposure to hazardous environments. The protective measures applied to mitigate the risks limit productivity and the minimum shaft size. Mikula and Lee (2000) and others have observed that automation of the process should be possible and beneficial to overcome some of these drawbacks. Early concepts for automation have been proposed and discussed by various people (eg Adams, 1996) including equipment suppliers. The Curtin University of Technology, Western Australian School of Mines published a master’s thesis which examined an application for automated horidiam stoping (Fleetwood, 2002). This was proposed and sponsored by the CSIRO. More recently, Dorricott outlined a mining strategy using horidiam for underground uranium mines (Dorricott, Derrington and Horsley, 2006). CSIRO has develop a mining system concept called ROES®, which is based on horidiam geometries and aims to operate by remote and automated control. To achieve this, a system is proposed that uses the latest technology that will ultimately deliver a level of control and integration unprecedented in mining operations. ROES® will be a non-entry mining system and as such, allows more freedom in stope design than is available through conventional horidiam methods. Consequently, benefits of horidiam should be delivered beyond the reduction in sublevels. ROES® offers the benefits of SLOS at an operating cost close to that of caving methods when the latter includes amortisation of capital. Compared with caving it also offers deterministic control of fragmentation, recovery and dilution. CSIRO has worked with other parties, including Orica Mining Services, and the Curtin University of Technology during the development of ROES® concepts. CSIRO undertook and commissioned extensive evaluation of the technical and economic benefits of ROES® including mining block designs for a number of mineral deposits.

ROES® SYSTEM ROES® is a system comprising equipment and software that will be used for the remote/automated mining of bulk underground stopes in hard rock mines and quarries as well as the stripping of shafts in mines and civil projects. This is a proposed new mining system currently being developed to fully utilise the benefits of

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remote and automated machine control without the constraints required by the presence of operators near the active working area. Rock fragmentation is achieved using drill and blast methods and the system includes integrated sensor technology for monitoring the mining equipment and stope environment. As all of the equipment and the processes are controlled remotely, or by automation there is no need for people to be in close proximity to the associated hazardous activities of mining. Rock is extracted at the base of the stopes via conventional draw points. ROES® operators and mine engineers will be able to use online software for design of blasting patterns and assessment of relevant mining conditions and monitoring product quality. ROES® is primarily designed as a replacement for sublevel open stoping (SLOS) with improved safety, lower costs and higher productivity, but can potentially be reconfigured for sublevel caving (SLC) or used to precondition block caving operations. It aims to solve many occupational health and safety hazards in mining, reduce the operating costs and reduce the time required to bring new stopes online. As a result of the lower cost structure, ROES® will also have the ability to increase ore reserves by shifting lower grade mineralised zones from subeconomic to economic. As shown in Figure 1, ROES® requires significantly less development compared with conventional SLOS, and the primary access to the ore for drilling and blasting is vertical (or near vertical inclined) rather than lateral access. This allows reductions in total development metres, generally smaller average development profiles and more efficient and effective use of development in both tonnes per metre of development and total metres required. ROES®, as a remote/automated system, will be configured to provide remote controlled and ‘real-time’ survey of the stope so that blasting patterns, blasthole loadings and stope shape can be modified easily during the production cycle as required.

ROES® DETAILS Pertinent aspects of the system are discussed below.

Stope access The stope access is provided on two levels:

• The lower or draw point access is developed to allow mining of the undercut and extraction of the broken rock from the stope. Current design for the system utilises a draw point layout similar to that used for SLOS and provides for

equipment ventilation and access between the draw points and ore passes or truck loading facilities. This design was adopted to increase confidence in using the system but it is expected that as experience is gained, a modified layout will be developed that utilises the ROES® equipment and shaft to develop the undercut bells. This will further reduce the lateral development associated with the undercut.

• The upper access as currently designed is developed above

the stope crown pillar and provides access to the ROES® raise and for equipment deployment. The development provides for access to the ROES® chamber and raise as well as flow-through ventilation for service and re-supply crews. While the design places the development above the crown pillar, if required this crown pillar could be extracted via a mass blast when the stope is near the end of its production.

The development for the top level is likely to be less than that required for a SLOS stope layout because access is required only to the raise rather than a number of suitable drilling locations for SLOS. This development will have drive dimensions similar to those currently in use.

ROES® chamber The ROES® chamber will be above the stope and usually above the crown pillar to maximise development usage. It will be of similar cross-sectional dimensions required by a raise bore machine but will be longer than a conventional raise bore chamber. Again it is likely that once experience has been gained with the method, the length of the chamber may be reduced from that shown. Once the chamber has been developed then a raise is mined between the ROES® chamber and the draw point horizon. The chamber, as shown in Figure 2, will be equipped with a crane or hoist to lower and raise the ROES® modules in the shaft and to move the modules between the shaft and service, storage and resupply areas. The concept shown uses an overhead bridge crane with a 10 t capacity to deploy and store the ROES® modules. Alternative methods have been considered, including monorails, rail tracks, mobile, jib and pedestal cranes. The area will be laid out to allow easy movement of the modules as well as re-supply (consumables) and servicing in a safe environment. The chamber will be equipped with a communications node between the ROES® modules and the control station and mine network if required. Technology is also available to provide this functionality from a distant remote monitoring or control station via secure web communication protocol. Examples of this

SLOS Layout

SLOS Layout

ROES Layout

ROES Layout

®

FIG 1 - ROES layout.

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FIG 2 - ROES® chamber layout.

capability can be seen in the ACARP sponsored longwall automation project (ACARP, 2008). This initial chamber concept is recommended for the trial stages of the development program to provide maximum flexibility. A production version of ROES® may use a simplified concept.

ROES® raise Although the raise shown in Figure 2 is located centrally to the stope plan area and pitched vertically, this need not be the case. It can be located and pitched as required by geotechnical and orebody considerations. The top of the raise in this example is located towards the return air end of the chamber and set towards one side to allow easy movement of the various items of equipment past each other and around the chamber. The raise is expected to be 2.4 m in diameter, although final dimensions above this size, up to 3.0 m, may be justified. The raise would replace the cut-off slot raise as used in SLOS but a larger dimension (2.4 m to 3.0 m versus 1.4 m to 1.8 m) is required to accommodate the ROES® modules.

ROES® equipment modules The two main modules deliver drilling and explosives placement with a third module for survey. All modules have been designed to achieve a loaded weight well below the 10 t rating of the crane, including the weight of the ropes.

Drilling module The drilling module shown in Figure 3 consists of a drifter and power pack similar to that used in existing stoping drilling rigs. Modifications will be made to traditional boom, slide and drill carousel, in order to fit the smaller opening dimensions of the ROES® raise. Power and water are supplied to the platform from the ROES® chamber and compressed air is provided locally from an onboard air compressor. The rig carries sufficient consumables for several rings of drilling before re-supply is necessary. The system design anticipates that before drilling commences, hydraulically powered legs extend radially to the raise wall to lock the drill into position. This configuration, together with the more compact design of the boom and slide, is mechanically very stiff compared with existing stoping rigs,

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FIG 3 - Conceptual drilling module.

allowing increased collaring and drilling accuracy. The drill collar will be initiated orthogonal to the shaft walls, providing very accurate collar location. As the drill progresses in the collar, the orientation of the drifter changes to acquire the desired blasthole inclination. Once this is reached, the slide stinger extends to lock against the opposite side of the shaft so that all of the drilling reaction force is applied directly to the shaft wall. A specially developed drill control algorithm has been developed and will be applied to maintain the correct force on the bit as the rock type changes or the bit wears. As a result, the drill will be operating at its optimal performance while minimising wear, directional drift and risk of stalling. Additionally, any automatic change in the drilling control point will be logged and may be interpreted as a change in rock type, thus providing a level of ‘measurement while drilling’.

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Explosives module

Sublevels

The explosives module will be similar in size to the drilling module. It consists of storage and assembly area for the initiation components, emulsion and sensitiser storage and mixing and the robotic manipulators to load the components into the blasthole. Power and water are supplied to the platform from the ROES® chamber and compressed air is provided locally from an onboard air compressor. The rig carries sufficient emulsion and consumables for a ring of drill holes before resupply is necessary.

ROES® requires no sublevel development so that each sublevel removed is a saving of the total development for that level.

ROES® is shown as having the same development for this level as the SLOS system. If the draw point cones were to be developed using the ROES® drill and blast platforms, then some minor savings on this level would also be possible.

Survey module

Raising

This carries the instruments to accurately survey the stope void and map the exposed backs and walls of the stope. This module can operate independently of or in conjunction with the other two modules. Depending on requirements and local conditions, the survey will provide accurate dimensional data and possible block jointing patterns and a measure of fragmentation. Based on the data provided by the survey module, particularly the shape and location of the stope back, it will be possible to redesign the next blast round to correct any deficiencies with the previous round. Scanning lasers, millimetre radar and photogrammetry have been proven in similar applications and may be used for this survey.

ROES® requires slightly more vertical development compared with SLOS because the chamber is placed above the crown drive. In addition to the extra length of raising, the ROES® raise is likely to be of a greater diameter than conventional existing slot raises.

ROES® design

• The drill module is held rigidly against the surface of the

Drilling and blasting The ROES® system will provide advantages in both drilling and blasting. The drilling advantages arise because: raise, reducing the opportunity for reactive forces to cause misalignments in drill collar location and/or hole direction.

Mine layout As the ROES® system only accesses the stope from two areas, the top and base, the mine layout will be significantly simplified and total development required will be reduced by up to 50 per cent dependent upon the stope height, orebody dimensions and orientation. Figure 1 gives some indication of the difference in development needed for a stope block of three by four stopes, Table 1 shows this comparison numerically. Obviously the total percentage saving will depend on the amount of declining and other capital development required per stope, but an overall saving of 50 per cent in development is certainly an achievable target.

Top level development There is a slight reduction in total metres of development required compared with SLOS because only one drive is required per stope versus two drill drives and a ballroom cross-cut for SLOS. However, ventilation development remains similar so that in the layout shown, a saving of about 20 per cent is possible for this level. 6.

Extraction level

This compares with SLOS where the aim is normally to maximise the height between sublevels (and hence blasthole length) to reduce development requirements.

• ROES® collars orthogonally into a machined surface (raise bore hole) before slowly acquiring the desired hole angle and this greatly improves collar location and accuracy. Collar slippage is expected to be nil.

• The axis of the drill slide can be accurately located in both position and orientation allowing the hole to be drilled in the exact location and in the orientation it was designed.

• Where the ROES® raise is within the orebody, the maximum drill hole length is reduced and drilling occurs in the plane that has the smallest dimension.6

• Improved drill accuracy should allow a reduction in total holes, total drill metres and explosives (and explosive consumables) as less allowance will be required for hole deviation. This also leads to improved control of fragmentation. Initial calculations show that ROES® requires slightly more total drill metres (zero to five per cent) for the same powder factor than would be used for SLOS. This is a result of the shorter holes being slightly less efficient in coverage of the volume to be blasted. These calculations, however, did not take into account the potential reduced powder factor as a result of more accurately placed drill holes.

TABLE 1 Development metres comparison. Item

ROES®

Stope height (m)

Variable

100 m

150 m

200 m

250 m

1500

1800

1800

1800

1800

0

1

2

3

4

1800

3600

5400

7200

Top level (m) Sublevels (number of) Distance at 1800 m

SLOS stope height

Draw points (m)

1800

1800

1800

1800

1800

Total (m)

3300

5400

7200

9000

10 800

Saving with ROES® (m)

2100

3900

5700

7500

Saving with ROES® (%)

40%

55%

62%

70%

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Rectangular (square)

Blasting advantages arise because:

• No blasting energy is required to ‘throw’ the rock clear of the face as broken material falls clear of the face that is being worked.

• The stope can be fired as single rings, multiple rings or as a mass blast (as can SLOS stopes).

• As no broken material will remain against the blast face, it may be possible that less material is required to be removed from the stope compared with SLOS before it is practical to fire the next ring blast. This may be of benefit where it is decided to maintain ore within the stope for wall support until the final extraction sequence.

This shape has been adopted for the initial feasibility comparisons with SLOS stopes during the early stages of ROES® development. It allows easy comparison with the SLOS system, which currently utilises square or rectangular plan shapes. In an area where square or rectangular stopes are optimal then the ROES® stopes may be arranged as shown in Figure 4, which shows a four by three stope block. Note that the ROES® chamber layout shown has a single pass airflow so that mine staff are isolated from air that leaves the stope. This is particularly useful for uranium mining.

Again initial calculations show a slight increase in blasting consumables (detonators and boosters) as a result of the shorter average drill hole length leading to more holes. This may be negated by reduced powder factor with improved drill hole location.

Ventilation ROES® also benefits the mine in other ways as a result of the reduced development and reduced complexity of the mining operation. One of these areas is mine ventilation, where ventilation requirements are reduced and simplified compared with conventional SLOS because:

• reduction of sublevels reduces ventilation requirements for drives by approximately 40 to 70 per cent,

• having fewer openings into stopes with no sublevel openings and only a single top level opening reduces short circuits through stopes,

• the reduced complexity of the ventilation system means less

management will be required to ensure that re-circulation is not occurring, and

• there will be reduced exposure of people to contaminants that

FIG 4 - Square/rectangular stopes.

Hexagonal and circular In areas where cemented fill is to be used, the stope may have a hexagonal or circular shape to improve drill hole efficiency and reduce exposed surface areas of fill in adjacent stopes (see Figure 5). In areas of low grade and in the absence of cemented fill, rock pillars are left between stopes and the ROES® stope shape could be circular to maximise drill hole efficiency and deliver improved geotechnical stability, or elliptical to match ground stress directions (Figure 6).

may be flushed from stopes into the ventilation circuit.

Dependent upon the amount of air required to ventilate stopes, the potential to save over 50 per cent of ventilation operating costs exists and significant reductions in capital cost may be available. In most mines with reduced openings into the stopes, very little stope ventilation air will be required. Also, ventilation air required for service crews does not need to pass through the stope, making control easier.

Stope filling The ROES® system provides the potential for improvements to the stope filling. In the ROES® stope it should be possible to tight fill against most of the crown as the fill can be placed through the raise, with the fill rising up the arched backs of the crown pillar and into the raise. The placement of dry fill through the raise borehole should also be safer than traditional practice via a drill drive. Large machinery cannot fall into the stope and the ground from which the equipment is operating should be more stable as it is above the crown pillar, not adjacent to the blasted void.

FIG 5 - Hexagonal stopes.

Stope design The design of ROES® stopes is reasonably flexible as the stope can accept several shapes and can be varied to follow the orebody profile or grade contours. While the early diagrams indicate a rectangular shape to the ROES® stopes, they need not be restricted and will conceivably migrate to other shapes as the system is introduced and mines become more confident about the method. Suggestions for other stope shapes are shown below. Various shapes considered to date include the following.

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FIG 6 - Circular stopes.

Inclined The stope does not need to be vertical as the raise can be pulled to match the ore orientation. The maximum inclination would currently be limited by the rill angle of the blasted material without modifications to the draw point layouts (see Figure 7).

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FIG 7 - Inclined stopes.

Shaped The ROES® stope does not need to have a constant plan area, or be vertical, as ground can be ‘made’ or ‘lost’ as required during the mining of the stope (as shown in Figure 8) to meet any combination of grade contours, geotechnical or infrastructure constraints. Since the location of the drilling rig and the location of the collar and its direction are also known very accurately for ROES®, the drill pattern can easily be changed from the control station as information is updated. The design of ROES® envisages that the drill holes will normally be subhorizontal but the angle from the horizontal can be varied as required and this allows the stope to either ‘make’ or ‘lose’ ground to match the desired stope profile. This is achieved by varying the amount of subgrade drilled, or preferentially by changing the angle that the drill holes intercept the profile shape, ie changing the amount of dump angle on the drill holes. Figure 9 shows how by varying the declination of the hole it would be possible to change the plan area of the stope and make ground. Increasing the dump angle (angle from the horizontal) should increase the gain angle by one degree for every one degree increase in the dump. As the initial design of the drill module allows angles of up to 40 degrees from the long axis of 7.

An angle lower than the rill angle could be obtained but would not be practical unless a modified extraction layout was developed.

FIG 8 - Shaped stopes.

the machine, it should be possible to gain ground at a rapid rate by decreasing the ring burden at the toe by increasing the dump angles with successive rings until the new profile has been reached. It should be possible to expand the plan area by achieving a gain of 30 - 40 degrees off the shaft axis. This is enough to allow the stope wall angle to approach the rill angle of the broken material.7 There can be several reasons for shaping stopes. These could be to follow geological or grade boundaries or to mine through areas that have existing development that intrudes through the

Ore outline

ROESTMTMshaft shaft

55 44

33

1. Dump angle to arch backs for geotechnical reasons.

22

2. Dump angle required to make blastholes perpendicular to required stope outline making ground. 3. Dump angle with added safety margin to allow for some loss of ground during blasting.

11

4. ‘Ground’ to be made to match ore outline. 5. Safety margin to allow for any losses.

FIG 9 - Making ground.

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stoping area. This development will intersect ROES® blastholes with the potential to cause ‘shadows’ or sterilised ore, as shown in Figure 10. With the reduced development resulting from the ROES® system there are fewer opportunities to locate a drilling rig close to the intrusive development except from the ROES® raise. A first solution might be to utilise the intrusive drives to drill the shadow zone; however, if these drives require rehabilitation before safe entry can be obtained then it may be preferable to avoid that task and fire the entire stope from the ROES® raise. The various ways this can be achieved are shown in the following diagrams and discussion.

Redesign stoping boundaries If possible the stopes and stope block should be redesigned so that:

• The stope is designed to ensure that the drives are as close as possible or coincident with the boundary of the stopes and running parallel to the boundary. This minimises the size of the shadow at it may be decided to leave the relatively small remnant material at the edge of the stope.

• The stoping layout is designed so that the ROES® raise

passes through the drive. As it is possible to locate the ROES® shaft non-central to the stope, this offers some scope for avoiding the creation of a shadow.

Access the drive This is a solution provided that the drive is in good condition and can be easily accessed and has not been already isolated from the mine access development. This enables conventional stope drilling rigs and explosive loading equipment to access the drive so that they can drill and fire material that would otherwise be left behind. The length of the drill holes in the ROES® rings contracts and re-expands to cover the rest of the material. However, if the drive is in a remnant part of the mine the costs of doing this may not be justified, particularly if the material is low grade. This solution will probably also require rehabilitation of accesses leading to the intersecting-stope drive. Figure 11 shows the drill pattern around a rehabilitated drive. Note that in order to ensure safe access, explosive loading from the drive would need to be done prior to firing at least three ROES® rings below the drive. Hence this system would probably require firing of at least five rings in combination, ie at least three ROES® rings below the drive plus two that intersect it in a sequenced firing.

FIG 10 - Drill shadows.

Managing intrusive development One of the perceived problems with adoption of a ROES® system is that first applications will probably occur in mines using SLOS and the first stopes mined are likely to occur in areas with existing sublevel development. The problem then becomes that some of the ROES® stopes may have existing development drives within the stoping area that will give rise to ‘shadows’ that can not be accessed by the standard ROES® drill pattern. While the occurrence of narrow natural voids can be accommodated by the drilling and explosive loading modules, these development drives are too large to be managed in a practical way. The magnitude of the challenge is determined by:

• the location of the drive relative to the ROES® shaft, • the location of the drive relative to the edges of the stope, and • the size of the drive relative to the drill pattern spacing and burden. The main approaches to avoiding a significant loss of ore as a result of existing development causing drill shadows can be divided into the following categories:

• redesign of the stoping block and individual stopes to relocate the development in a suitable position relative to stope boundaries and the stope raise,

• access the drive and use it for some drilling, • leave ore grade material in place, and • reconfigure the ROES® rings to drill the shadow from above and below.

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FIG 11 - Rehabilitated drive.

Leave grade material behind The material within the shadow and some material both above and below would have to be left in place so that ground could be lost and regained around the shadow area while forming a bulge into the stope (as shown in Figure 12). This provides a reasonably easy solution if the material does not have a high value and is adjacent to the edge of the stoping region; however, this solution may not be possible if adjacent areas are of fill as there would be insufficient strength to hold the bulge in place.

Reconfigure ROES® rings The flexibility of the ROES® system allows the material in the shadow to be accessed by modifying the ring drilling parameters and design. There are two main solutions required:

• where drilling and firing occurs a single ring at a time, and • where drilling and firing is on multiple rings (or mass blast).

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• The inclination of the holes within a ring is adjusted from 15 degrees down to flat or inclined slightly upward in the region of the development. The ring spacing at the collars of the hole decreasing to half that at the hole toes so that the ring burden remains constant at the toe location.

• Just below the base of the development the rings are drilled horizontal or with a slight upward inclination to access material behind the drive.

• At the level of the drive the rings are drilled horizontal. • Above the drive one or two shortened rings are drilled horizontal or on a very low downward inclination to create the cone.

• From further above the drive, the rings will move to a steep downward inclination to pick up material within the drill shadow.

• Each subsequent ring will be drilled at a lower inclination until the standard inclination has been reached. Again the collar burden between the rings is half that of the ring burden at the toes until the standard inclination has been achieved.

FIG 12 - Loose ground.

To demonstrate the ability of the ROES® system to overcome this issue an example is shown based on assumed design parameters of:

• spacing and burden at stope boundaries are: • 4 m spacing between holes, • 3 m ring burden, and • dump angle on holes from the horizontal of 15 degrees down. When the stope is mined by drilling and blasting a single ring at a time the hardest problem is presented. The constraint of the single ring at a time firing being that additional rings can not be drilled through the plane of standard rings, making it harder to access the material within the shadow. Figure 13 shows a potential solution by modifying the drilling as the stope approaches the development, causing the drill shadow. The following modifications are made:

In practice the ring locations would be designed to minimise the number of rings that would occur within the elevation of the development and the amount of inclination and extra dump on holes in rings around the development would vary with the location of the drive and its height relative to the ring burden. Note in Figure 13 the light blue rings at the base and top represent rings drilled on the standard ring pattern. The purple rings represent drill patterns where the rings have been adjusted. Note that this ring design is provided to show that it is possible to modify rings to overcome shadows and does not represent an optimal ring design. Where multiple rings are fired in combination it is possible to interweave the rings to improve the solution. In this case, shown in Figure 14, one extra part ring is drilled from below and one extra part ring is drilled from above the drive to intersect material in the shadow. As the rings are fired in multiples it is possible to fire the lower purple ring in combination with the three rings above and the upper purple ring in combination with the rings below.

FIG 14 - Multi-ring firing.

Stope block and development layout

FIG 13 - Single ring firings.

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One of the advantages of the ROES® system is that the top lateral development is not required to be coincident with the top of the stope. It thus becomes possible to handle rapid variations in the thickness of the ore zone by varying the thickness of the crown pillar. As shown in Figure 15, as the top level of the ore varies

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®

FIG 15 - ROES generalised layout.

the development can remain on one level by varying the thickness of the crown pillar for individual stopes. The only additional cost of this approach is due to the additional metres of raising for some stopes. This compares with SLOS where a number of options might be used, including an additional sublevel, acceptance of additional waste within the stope boundaries (dilution), loss of economic grade material that might be above the drill horizon. For orebodies that are close to the surface or near the base of an open pit, it is possible to deploy and service the ROES® equipment from the surface while still leaving an intact crown pillar. A significant advantage of this ability to vary stope height without changing the development levels is that it then becomes possible to delay making decisions about the economics of mining marginal grade material until much later in the mining process, ie when the material is in fact being mined. Where mineralisation slowly declines with elevation it is possible to plan development well above the stope and cease drill and blast only when the actual grade falls below the cut-off grade. The cost of this extra economic freedom is only the additional metres of raising undertaken.

Stope scheduling Stope scheduling becomes slightly easier using ROES® than for SLOS as the removal of all sublevels and the placement of the chamber and access above the crown pillar means that the stope sequence is not constrained by the requirements of access to the middle rows of stopes if the stoping block is more than two stopes wide. Additionally, less development needs to be sacrificed as each stope is completed for ventilation and services. The stope can, if required for geotechnical or production reasons, retain most of the blasted material to act as support for the walls up until the final extraction sequence, as the blast face

is advancing vertically not horizontally. Only sufficient ore must be extracted between blasts to allow for expansion of the next blast. Hence for most of the stope life, the height of exposed wall can be less than for SLOS stopes.8

Production Of major concern for the introduction of any new mining method is the likely production rate compared with existing systems. As part of the detailed feasibility work undertaken for ROES® a study was undertaken to model the performance of the ROES® stope and to compare these results with the SLOS stopes from an operating mine. It was determined that for a single stope, the drilling rig dedicated to the stope spent 85 per cent of its available time drilling, six per cent of its available time travelling (up and down the shaft) and the remaining time was spent waiting for blasting to occur. This utilisation was significantly above that achieved by conventional stoping rigs, principally because the machine spent less time travelling between the various sublevels within a stope. A similar modelling of the explosives module showed that it was required for 14 per cent of the time loading, five per cent travelling and 80 per cent free, indicating that it would be reasonable to expect one explosive module to service four stopes at a time, while still allowing time to travel between stopes. The study also indicated that a single ROES® drilling module would be able to supply significantly more than the daily scheduled production from the stope for the comparison mine. In fact the drilling and blasting rate was in excess of twice the scheduled production rate for a stope.

TECHNOLOGY DEVELOPMENT ®

8.

This may be particularly important when extracting against a filled stope.

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The ROES technology development program is designed to minimise costs, time and first-trial risks. It will use existing equipment to the fullest extent possible to deliver confidence and

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maintain compatibility with existing mine equipment fleets. However where necessary, it will also use recent advances in communications, remote and automated equipment control, sensing and machine guidance which have been proven in other projects undertaken by CSIRO and Orica Mining Services. Many of these technologies have been commercialised and some are in the commercialisation stage. Technology to remotely place explosives is currently being developed by Orica Mining Services, with assistance from CSIRO. This will be the third generation of the remote placement technology. To minimise the risk during trials, the trial stope will be designed so that it is compatible with SLOS layouts so that mining can revert easily to sublevel stoping methods at any time during the trials if required. This eliminates the risk of sterilising ore and minimises ‘sunk costs’ during the trial phase. Conversely, it will not use an optimum design for ROES®. Sponsorship for a mining trial is currently being sought through AMIRA International.

DESKTOP STUDIES Over time, a series of desktop studies have been undertaken to help develop the concept. The first of these was a Masters Thesis by K Fleetwood in 2002 (Fleetwood, 2002), this was a major study undertaken to look at all aspects of the system including rock mechanics, stope scheduling, design of the draw point and top levels, ring design and timing of activities. This study was based on a standard mine design layout of a 12 stope (three by four) block. Three subsequent major studies have since been undertaken. While the results of the studies remain confidential to the companies involved they clearly demonstrated that ROES® offered significant cost reductions over conventional SLOS stoping. In the first of these studies, undertaken by WASM at the request of CSIRO, operating savings of six per cent, 14 per cent, 16 per cent and 20 per cent per tonne were shown for ROES® compared with SLOS. Subsequently CSIRO has undertaken with two mining companies studies showing savings of approximately 20 per cent for ROES®, compared to SLOS, for blocks of stopes. One of these studies included detailed modelling of stope production based on typical drilling performance achieved at the mine and scheduled production rates from stopes.

SUMMARY OF ROES® ADVANTAGES Economic and safety advantages of ROES® will arise from:

• No one working near the openings into open stopes – all equipment can be housed, serviced and launched from the ROES® chamber or from the surface if the raise opens to the surface for shallow orebodies.

• Reduced lateral development length, leading to: • improved safety with reduced exposure of operators to the development cycle,

• reduced costs with lower capital and operating costs, and • reduced time to bring ore production online. • Improved drill/blast performance: • more accurate hole collar location, • shorter and more accurate holes,

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• improved fragmentation control, and • simple ‘real-time’ control of blasting pattern during the production cycle.

• Reduced ventilation requirements due to: • less development to ventilate; • no ‘through stope’ ventilation required to provide ventilation for stope drill and blast crews; and

• smaller, simpler ventilation circuits with reduced risk of short circuiting.

• Potential to improve geotechnical performance due to: • improved ability to arch the stope backs, and • improved ability to increase wall support (broken rock to support walls).

• Improved stope backfilling due to: • fewer entries into stope, • able to arch stope crown, and • able to close fill to stope crown through ROES® raise. • Improved ability to monitor and hence control stope performance:

• real-time acquisition of survey and equipment data during operation; and

• opportunity to integrate control of mining production with other operational tasks, including processing.

REFERENCES ACARP, 2008. Longwall automation web site. Available from: . Adams, M, Hannigan, T, Horsley, T, Cunningham, J B, et al, 1995 - 1997. Personal communication. Anon, 1983. Viscaria – A new copper mine in Northern Sweden, Mining Magazine, October:226-233. Anon, 1984. High grade spurred Viscaria development, Engineering and Mining Journal, 185(2):33-35. Brown, E T, 2007. Block Caving Geomechanics, The International Caving Study, second edition (Julius Kruttschnitt Mineral Research Centre: Brisbane). Dorricott, M, Derrington, A and Horsley, T, 2006. Underground mining strategies for uranium deposits, in Australia’s Uranium 2006 – Program/Abstracts, pp 19-20 (The Australasian Institute of Mining and Metallurgy: Melbourne). Fleetwood, K G, 2002. The development and evaluation of the automated horadiam stoping method, Thesis, Master of Science by Research – Mining Engineering, Curtin University of Technology, October. Mikula, P A and Lee, M F, 2000. Bulk low-grade mining at Mount Charlotte Mine, in Proceedings MassMin 2000, pp 623-635 (The Australasian Institute of Mining and Metallurgy: Melbourne). Ulrich, W, 1983. Critical Heuristics of Social Planning, second edition (University of Chicago Press: Chicago). Usher, R E and Kennewell, G J, 1992. Evolution of mining and current practices in the Prince Lyell orebody, Mount Lyell Mining and railway Company Limited, in Proceedings Fifth Underground Operators’ Conference, pp 37-46 (The Australasian Institute of Mining and Metallurgy: Melbourne).

Launceston, TAS, 14 - 16 April 2008

Tenth Underground Operators’ Conference