46 BLOCK CAVING

Keeping up with caving Caving mining techniques are experiencing a surge of interest, thanks to a combination of favourable metal prices, high forecast demand and the need to exploit deeper, more complex orebodies at the lowest cost possible. Carly Lovejoy investigates the current market

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oth surface and underground mass SRK’s caving mining methods have generated experts at Bincreasing interest in recent years, Codelco’s as mining companies look to exploit large Chuquicamata orebodies faster and more economically. mine, Chile Underground mining methods such as block, panel and sub-level caving continue to be the premier choice for deeply situated massive orebodies, thanks to the high potential production rates and low operating costs involved. Recent technological developments and improved solutions for designing, planning and modelling caving operations mean that these techniques can now be applied at greater depths, in more competent rock masses with greater geotechnical challenges than ever before.

GLOBAL INTeReST A combination of factors that include relatively higher metal prices, high projected supply and demand forecasts and a lower discovery rate of significant new near-surface deposits have helped to drive global interest in cave mining methods. Simon Hanrahan, principal consultant (mining) based in SRK’s Perth office, explains: “In addition, a number of large open pit mines across the globe, some “Caving is producing in excess of 50,000t/d, are coming to the end of their lives. These the only make up the bulk of world copper underground production, and many mining companies bulk mining are examining the feasibility of shifting to low-cost, large-scale underground method operations in order to continue exploiting able to offer these orebodies. “Caving is the only underground bulk continued mining method that is able to offer production continued production at a comparably at a com- high rate and with low operating costs.” Aside from strip ratios, other factors parably high influencing the economics of open pit rate with low projects include the increasing escalation of energy prices, together with a focus on operating reducing carbon emissions. costs” A number of large-scale, low-grade underground operations are also considering expanding in order to access areas of the orebodies previously thought to be uneconomic to exploit. These are challenging applications that will require careful front-end investigation and analysis, innovative engineering design and a strict approach to development and operation. Sourcing of skilled labour is also a significant problem in the mining industry today, so a mining method such as caving that has a low reliance on skilled labour pools can be an interesting factor for mining companies to consider. Otto Richter, principal consultant at Snowden, says: “The recent interest in

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An LHD at work costs than many open pit mining methods at El Teniente and, in many cases, lower environmental mine in Chile impacts. However, it is very capital- Photo: Bloomberg Finance intensive, and one of the primary disadvantages is that it removes much of the supporting rock from under the overburden, which can lead to subsidence at the surface. Caving-induced subsidence might endanger mine infrastructure and is a major concern for operational safety. Changes to surface landforms brought about by subsidence can be dramatic and may lead to a pronounced environmental impact. Therefore, the ability to predict subsidence has become increasingly block caving comes down to two factors destroys its ability to support overlying important for operational hazard and envi- – less access to large orebodies near the rock, and fractures spread throughout the ronmental impact assessments. surface and an improvement in the rock mass, forming a cave. There are numerous variations of the knowledge of caving mining methods. Following extensive preparation and block caving technique that use different “It is becoming increasingly difficult to development work in order to access the layouts and extraction patterns. The find large, near-surface orebodies that are orebody at the correct depth, a set of choice will depend largely on the orebody suitable for open pit mining methods parallel, horizontal tunnels is created on characteristics, the nature of the host which will also yield high production rates the upper level, known as the undercut rock, and the associated development and low operating costs. Those open pit level. A set of holes are then drilled into and production costs. mines that are currently operating in these the roof, which are filled with explosives Panel caving allows the extraction of conditions are becoming deeper, and now and blasted. The tunnel collapses in very large orebodies by dividing them up have to consider closing operations or selected sections and broken rock is into ‘panels’, which are mined progres- changing to an underground method that removed via sections of the tunnel not yet sively, although, as with block caving, the will produce at a similar rate with low affected by blasting. This process initiates panel can in some cases cover the full operating costs.” the development of the upper cavern of footprint of the orebody. The fundamental “It is He adds: “In recent years a lot of effort broken rock, ie the block cave. difference between the methods is that has been applied to understand how the A second series of tunnels is then block caving produces from the full becoming internal mechanics of the caving process developed beneath the ore block, on the orebody footprint, while in panel caving increasingly works, thereby removing a lot of the production level, in which a series of the active caving zone moves across the difficult to uncertainty previously associated with tighter, vertical drill hole patterns are panel – ie while one end is being these mining methods. As caving has drilled into the broken rock above. These undercut, the other end is producing. find large proven to be a safe and effective mining allow the formation of funnel-shaped Once a panel becomes depleted, the orebodies method, its popularity has increased structures called drawbells, which act as adjacent panel is mined in sequence until around the world.” conduits for the broken ore and connect the orebody is exhausted. Like block cave suitable for the block to the production level. mining, panel caving offers low operating open pit BLOCK ANd pANeL CAVING From the drawbells, the ore is funnelled costs, and lower development costs due mining that Block caving is an underground mining into drawpoints. The broken ore is then to its progressive approach. method that uses gravity to exploit loaded by load-haul-dumpers (LHDs) and will also massive, steeply dipping orebodies delivered to ore passes or an under- SuB-LeVeL CAVING yield high located at depth, particularly those with ground crusher, prior to hoisting to the Sub-level caving is sometimes used where disseminated mineralisation or that are surface in skips or by conveyor. large open pit mining operations production low-grade in nature, but too deep to be Ore in the column is diluted by the transition to underground extraction rates and extracted using open pit methods. Block material in adjacent columns and methods, although it is often used for low oper- caving also depends on insitu stresses and ultimately by overburden and lateral independent underground projects too. the host rock’s ability to fracture in the waste. When the column drawdown is Once the orebody is developed, it is then ating costs” correct fashion, although this can now be complete and the drawpoint grade drops drilled and blasted on progressively lower overcome using preconditioning. below a minimum value, the drawpoint is levels until it is depleted. The waste rock The technique is commonly used to abandoned. above the orebody caves gradually extract low-grade copper, copper-gold, Technically, once the drawbells have upwards as the ore is extracted. iron and molybdenum ores, as well as been created, no further drilling is Sub-level caving is typically used where asbestos diamond-bearing kimberlite and necessary. The speed at which ore travels the orebody has a smaller footprint and/ lamprolite, although there are other through the drawbells is effectively or more competent rock mass that applications. controlled by the speed at which it is prevents the continuous caving required The term ‘block’ refers to the mine removed from the drawpoints. As broken for a block cave. Blasting of the entire layout, which usually divides the orebody ore from the block exits via the drawbells orebody is required to produce a into large sections, although in some and drawpoints, the roof of the cavern production ore flow. cases the block can represent the full gradually collapses under its own weight As sub-level caving uses a ‘top down’ footprint of the orebody. Upward caving to create more broken rock, forming a approach, it requires less upfront capital of the rock mass is induced by under- continuous process. than a block cave operation and much cutting the block and blasting it. This Block caving offers lower operating less time to reach full production. This

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could be also advantageous where sufficiently weak to allow caving and have high-grade ore is located near the top suitably fine fragmentation, yet strong of the orebody. enough to ensure that the excavations will Mr Hanrahan explains to MM: “A last the 10- to 50-year life usually significant difference between sub-level associated with caving operations, caving and other caving techniques is that although preconditioning can be used to multiple levels of development are weaken rocks that would otherwise be required, many times more than a block unsuitable. It is of key importance that the cave requires, and ongoing ring blasting is hydraulic radius required to initiate caving used for production.” can be achieved and is typically exceeded. Mr Richter adds: “Sub-level caving In a block or panel cave only a relatively operations typically find applications small percentage of the orebody is drilled between the traditional large open and blasted to create the undercut. This stoping methods and block or panel removes the natural support of the rock, caving methods. allowing it to break up along natural and “The caved material forms a relatively stress-induced fractures. For this process small portion of the total production and to continue occurring (rather than forming is typically considered as external a natural, stable arch), the footprint of the mineralised dilution. Sub-level caving also cave must be sufficiently large. A suitable allows for a slightly more selective footprint is typically in excess of 100m, extraction of the orebody than is with some orebodies spanning almost attainable through block or panel caving. 1km across. Production rates achieved in sub-level Due to the initial undercut and caving operations are typically lower than extraction infrastructure required prior to for block caves but higher than for starting the main production phase, stoping methods.” caving operations have high initial capital of 50,000t/d, and newer operations are costs. Caving therefore requires a large being constructed with capacities in CAVING requIremeNts orebody that can produce at a high rate excess of 100,000t/d. However, there are Caving is a non-selective, bulk mining over a long period and at a low operating also some caves being planned with method. It requires large-scale mineralisa- cost, in order to offset the initial capital smaller scale and shorter mine lives – the tion in all three dimensions (length, width expenditure (CAPEX). Today, several key inputs will determine the value of a and height), in rock conditions that are caving operations are producing in excess project and its feasibility. Mr Hanrahan says: “Cave mining differs significantly from other typically more selective underground mining methods in a number of areas. Because cave mining is a ‘bottom up’ method that relies on first establishing a large fixed infrastructure underground that will provide a very long-term production platform, the initial capital costs are typically very high. This “Sub-level caving infrastructure consists of shaft and/or Mining and Construction decline access for men, materials, operations production hoisting and ventilation. typically find Today, this infrastructure is state-of-the-art applications in many instances and has a high degree of automation. Similar to providing a between the processing infrastructure ahead of traditional large production, this represents a large upfront expense.” open stoping He adds: “A noticeable difference in methods and building a caving operation [compared block or panel with other methods] is the finished build quality, particularly on the extraction level. caving methods” Because this level must remain in place and active for many years, ground support and roadway conditions are important. The production drives are finished with shotcrete, steel brow sets and, in certain situations, reinforced concrete. The roadways are completed with engineered roadway concrete that supports high-speed tramming of ore from the drawpoints to orepasses or crushers.” As a result of establishing a high- performance, large-scale infrastructure, it

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with most open pit operations. Typical (shaft or decline), which serves as a SRK mining production rates are in the range of platform to gain orebody knowledge,” engineers have 2-20Mt/y, with a few cave complexes Mr Hanrahan tells MM. worked on nearly able to produce in excess of 45Mt/y – “The benefit of establishing this every caving El Teniente is a good example. exploration access is that underground project globally conditions can be experienced firsthand, over the past GOING uNderGrOuNd particularly rock and stress conditions that decade As large open pits become deeper, they assist in determining cavability and often become uneconomic to continue to fragmentation. This early development is mine from surface, mainly due to material also of great benefit in determining movement costs. Where the orebody is development advance rates that can be suitable, many established operations used in project scheduling. An ultimate around the globe are opting to use caving benefit is that the infrastructure can then methods as they expand. be used to initiate a full project develop- Large open pit mining operations are ment programme or works.” typically associated with a large-scale Mr Richter points out that the wealth of processing facility. If a deposit continues orebody knowledge gained through open at depth, then there is often significant pit mining can also be extremely valuable project value to be achieved by when planning a subsequent underground continuing large-scale and low-cost operation. mining underground in order to feed what The main disadvantage of implementing is an already established high-volume a cave mining operation beneath an open processing facility. pit is that the geotechnical stability of the As open pits get deeper, the operation above can be compromised. waste-to-ore mining ratio becomes less Most caving operations that are situated is then possible for ongoing unit favourable. In addition, the environmental under large open pits have experienced “The disad- operating costs to be significantly cheaper impact and large footprint area required significant pit failures as the cave vantage of than lower-scale underground mining for a waste rock depository could prevent destabilises the pit walls. This can impact methods, particularly if a high degree of further continuation of surface mining. on existing infrastructure situated around choosing automation has been installed. Cave mining on the other hand has a the pit, and also increases the amount of cave mining Once a block cave mine is in produc- much smaller surface impact and almost dilution that can be expected in the cave. to replace a tion, logistics are relatively straightfor- no waste rock storage requirements. Concurrent mining of the pit and cave ward. The production footprint remains “Cave mining offers the advantage of to maintain the production rate is a safety surface fixed and mining consumables usually being the only underground mining and logistical challenge and needs to be mine is the revolve around secondary breaking method that can match the production carefully planned. The change-over period consumables, with campaign maintenance rate and low-cost profile of surface between an open pit and underground long lead within the production drives. The most mines,” explains Mr Hanrahan. “The operation can take several years, and care time significant logistics support is required for disadvantage of choosing cave mining to must be taken that the underground mobile equipment and fixed plant replace a surface mine is the long lead operation does not undermine or required for maintenance, which are normally time required for study work ahead of an destabilise the pit while it is still opera- study work supported by large underground investment decision, which often makes it tional, although SRK points out that several ahead of an maintenance facilities. challenging to provide a good level of open-pit and cave mines have successfully Very few other mining methods can be production continuity between a closing operated concurrently, even with active investment used to extract the large, typically open pit and a ramping-up underground cave subsidence. decision” lower-grade orebodies that are usually operation.” Peter Bray, product manager at Atlas selected for caving. If the orebody is near Given the high capital investment Copco, adds: “One of the main challenges the surface, a large open pit can be used required to establish a caving mine, the is to try to develop the block cave instead, while for higher-grade, deeper initial challenge when considering infrastructure ahead of the planned deposits, sub-level caving or large-scale whether to transition an operation from winding down of the surface mining open stoping with backfill can be used. open pit to underground is to carry out a activities. An operation that can achieve a The initial CAPEX required for a block thorough study in order to define project good hand-over from surface to under- or panel cave is always higher than for value, and understand and manage ground ore production will be better able other underground mining methods that project risk. One of the most critical items to maintain production targets without generally phase in CAPEX over time. in support of this is an adequate level of having idle mill and personnel capacity.” Large, modern-day caving projects orebody knowledge, including the typically report total CAPEX of anywhere geological, geotechnical and hydrogeo- deVeLOpmeNt/prOduCtION from US$500 million to in excess of logical characteristics. It takes time and The time taken to establish caving US$10 billion for ‘mega-caves’. However, often significant pre-project approval operations varies, and it is not uncommon operating expenditure (OPEX) for block or capital to obtain this data so that it can be to take a period of at least 10 years from panel caves is much lower than for other used in the study process. This data the time of study commencement to underground methods and is comparable provides the foundation for much of the achieving project approval. For some to open pit mining costs. Typical OPEX is study work in support of developing a large-scale planned caving operations, in the order of US$10-20/t. workable mine design and production studies have been under way for more The production rates of block and schedule. than 20 years with a final decision still yet panel caves are by far the highest of the “A number of projects today first to be made. underground methods and compare well establish some form of exploration access A major challenge is the time delay from

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underground confirmatory programmes.” Snowden believes that the highest value in any block or panel cave project is achieved by getting the initial plan correct. When constructing a cave footprint infrastructure, there is little room for error, and any design issues can result in decreased recovery, increased dilution or increased operating costs. When determining the best approach for a project, Snowden says it combines the skills and experience of its mining personnel with its in-house design and optimisation software (Stopesizor and Evaluator) to select the best strategic plan within each project’s set of constraints. Once the strategy has been confirmed, more detailed planning and design work can start using cave planning software, such as Gemcom’s PCBC and PCSLC. “Greenfield and brownfield projects, and mine expansion programmes all have a unique set of constraints and require- The header the decision to proceed to the return on lished, which then allows incremental ments that can be incorporated into the frame and investment. Underground caving methods production to build up gradually. Typical optimisation,” says Mr Richter. winding room at can have a lead time of anywhere between production rates are in the order of “With greenfield projects we will build a shaft of five and 15 years before significant 150-300mm of insitu material drawn from the mine plan up from first principles and Newcrest production is realised. This is associated each drawpoint per day, or about 0.3t/m2 determine a zero-based cost and mining Mining’s Telfer with the amount of development work of footprint area per day. schedule, whereas brownfields projects mine in Australia required, and improving rates of advance Depending on the size and scale of the often have more accurate site-specific Photo: Bloomberg News for development is a key area of focus for operation, block/panel caves usually information available and current the mining industry. contain 200-500 drawpoints, with about operational constraints to be incorpo- Mr Hanrahan says: “Once approved, 60-80% in operation at any time. This rated. We understand that our clients project delivery time depends on a results in average production rates of know their operation and strategic number of aspects, including the depth 5–20Mt/y for most operating caves, objectives, which may impose a unique below the surface that is required for although there are some cave complexes set of constraints to be taken into account infrastructure to be established. Creation in the pipeline with thousands of for the evaluation.” of a 1,000-1,200m below-surface shaft can drawpoints, which will produce much The early stages of a block cave take up to three years, and a further three higher amounts of ore. However, development involve a high level of years might then be required for access orebodies suitable for this size operation construction activity, as the undercut and development before a production are few and far between. extraction infrastructure is created to last ramp-up can commence.” Mr Richter adds that multiple lifts do for the life of the orebody. “During the Mr Richter adds: “Due to the sheer not usually significantly increase the construction period, the total number of amount of data that needs to be gathered annual production capacity at caving personnel can easily reach 3,000 for a small to properly understand the geological, operations, due to the risk of lower panels block cave and up to 10,000 for a large “The period geotechnical and metallurgical nature of undermining higher panels. It does, block cave,” explains Mr Richter. “Once between such large orebodies, data collection and however, extend the life of the operation, steady state production is achieved, the analysis is frequently the most time- as lower panels can be brought into ongoing demand on logistics is drastically discovery consuming activity. operation as higher panels are depleted. reduced, and is low compared with other and steady “Another critical factor in the project Production rates also depend on factors underground mining methods.” state development timeline is undertaking such as: available orebody footprint, rock Once approved, establishing a cave negotiations with local land owners and mass competency and infrastructure in mine can be very complex. Speed is of production authorities to gain access and ownership. place. A number of large cave projects are the essence, and it is not uncommon for can be 15 For these reasons, the period between planning production rates above development in the order of tens or even initial discovery and steady state 100,000t/d but these high rates typically hundreds of kilometres to be required on years or production can be 15 years or more.” require multiple blocks or panels. some of the larger operations. This can be more” Mr Richter tells MM that detailed Mr Hanrahan says: “Greenfield challenging, particularly if ground design and study work (prefeasibility and projects, unlike an existing mine conditions are weak or wet in areas. feasibility studies) typically takes three to expansion and brownfield projects, are five years. The production ramp-up for a particularly challenging, since limited or equIpmeNt block or panel caving operation is no exposure of the orebody is available In the past, caving has generally only dependent on the size of the cave and there is no experience of the rock been considered for rock masses that footprint, but typically these are also in mass behaviour. This type of project cave and fragment readily. However, the three- to five-year range. requires a longer lead time and high improvements in mine planning and In an average rock mass, approximately capital investment for exploration drilling, design software, a better understanding five drawbells a month can be estab- laboratory and insitu testing and of geotechnical conditions and the

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Drilling, bolting fragmentation of rock masses, plus the weeks earlier than conventional and mesh availability of more advanced equipment development methods can mean millions installation at for drill-and-blast and load-and-haul of dollars in advance earnings.” Oyu Tolgoi mine, duties are enabling mining companies to Production tasks for cave mines are Mongolia exploit more competent orebodies with dominated by loaders taking ore from the Photo: SRK coarser fragmentation than was previously drawpoints and transporting it to another thought to be economical. Operators also location. Many of the repetitive tasks have greater control over development associated with moving ore from and production rates at these operations drawpoints to ore passes carry the “Methods than ever before. potential for automation, and many Most mining companies realise the equipment manufacturers are able to offer and control importance of time when developing semi- or even fully automated loading systems caving infrastructure, and many are equipment. looking at methods and equipment that Other production tasks may involve previously will speed up the process. As a result, secondary breaking, crushing, conveyors only used equipment, methods and control systems and shaft haulage. The trend in this area is in civil that were previously only used in civil the ability to automate and monitor as tunnelling have started to migrate to the many activities as possible using a tunnelling underground mining environment. Other mine-wide control and monitoring have started areas under consideration include: network. This allows for better efficiencies overbreak control, drilling accuracy, long in equipment utilisation, people to migrate rounds, blasting fragmentation, type of management, safety and energy to the explosives, fumes and re-entry times, consumption. underground haulage speeds, loader and truck Automated and semi-automated capacity, and adaptive ground support equipment is often able to perform tasks mining schemes. faster than the manned equivalent and, mines and other underground mass environment” “Companies are also finding ways to more importantly, automated systems do mining methods (which is addressed in a reduce wasted time and inefficiencies, not carry the human error factor, meaning separate article in this issue), this section and refining the development process to less equipment damage and operating examines some recent trends in the a predictable and repeatable process. mistakes. application of more traditional equipment Time after all costs money,” explains Mr Leaving aside the obvious advent of for development and production activities Bray. “The ability to produce even a few equipment for rapid development in cave at caving operations.

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Whereas horizontal jumbos are used to more accurate than top hammer drilling, create the access levels, vertical especially for longer holes (greater than in-the-hole (ITH) and top hammer 30-35m). However, most undercut and production drills are more commonly drawbell development work does not used in developing the block cave. require longer holes. Hence, top hammer “Drilling Three main factors must be taken into drilling is the method most commonly accuracy for consideration when drilling for both employed.” Regardless of the drilling undercut and drawbell development. First method, it is important to select the drill up-holes is a are the rock properties; these will influence rig and string that maximises drilling prerequisite, the powder factor required to fracture the accuracy results, particularly for drawbell as this rock mass when blasting (powder factor is development. a combination of explosive type/power, Harold Jonker, applications engineer at affects the hole diameter and hole spacing). Rock Cubex, agrees. “Drilling accuracy for undercut properties also play an important role up-holes is a prerequisite, as this affects when considering rock mass damage due the undercut and extraction level stability and to blasting. due to the elimination of pillars on the extraction “This is especially important when undercut,” he says. “Customers are level developing the drawbells,” says Mr Bray. demanding better operational efficiencies “As drawbells need to remain in place for and more maintainable machines. Trends stability” a long time (often the life of the mine), it is in terms of measuring the efficiency of the advisable to practise smooth-wall blasting various processes are developing. This techniques.” This entails using lower- entails on-board and vital signs power explosives coupled with close- monitoring, as well as measurement of spaced holes along the desired final the drilling process in order to deliver to design boundary in order to create a the planned production requirements.” DrILLING AND BLAstING pre-split. The resulting rock boundary is The third factor is the capabilities of The creation of the block cave from the less likely to be fractured and will remain the drill rig. This can be expressed as a undercut level and the drawbells from the more stable. combination of possible drilling angles, production level require specific drill The second factor is the drilling hole diameter range, the stability of the patterns and depths of holes, and accuracy required to achieve the desired drilling platform, the length of hole therefore certain drill rigs and drilling blasting results. Mr Bray explains: “It is possible and automation capabilities. methods are more suitable for each task. often considered that ITH drilling is far “There is a wide selection of long-hole

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Atlas Copco has drill rigs available on the market today,” have high levels of automation. The face delivered a advises Mr Bray. “So be sure to evaluate drills feature COP 3038 rock drills to Boomer E2 C rig the criteria desired when selecting assist with increased drive development to Rio Tinto’s equipment.” rates. Mr Bray says that to date the Northparkes During mine development, there are machines have been running well, and the mine in Australia typically many kilometres of drives to be customers are very pleased with the excavated, and many thousands of metres results. that need to be drilled for undercut and Atlas Copco has recently delivered a drawbell development. Due to the Boomer E2 C30 face drill to Rio Tinto’s quantities involved, and the requirement Northparkes operation. The machine will for rationalising and improving efficien- be used to access and develop a new cies, the use of semi- or fully automated block caving area. “There are high equipment has high potential. Drill rigs expectations that the machine will “During that have on-board drill plans and the contribute to faster development rates, mine ability to drill automatically between shifts due to the use of the 30kW Cop 3038 develop- are just one example of how equipment rock drill, long rounds and accurate utilisation and therefore development drilling systems,” says Mr Bray. ment, there rates can be increased. Given the extreme quantities of lateral are typically Atlas Copco has supplied equipment development required at caving to many of the world’s existing and operations, mine operators are keen to many developing block caving operations. minimise overbreak for several reasons; kilometres Customers include: Codelco, Climax firstly, it creates excessive rock to handle of drives Molybdenum’s Henderson mine, during development, and secondly, it Newcrest’s Cadia East project, Rio Tinto creates a larger void that will require to be and Ivanhoe Mines’ Oyu Tolgoi mine, and secondary support. excavated” Rio Tinto’s Northparkes mine. To help minimise overbreak, many drill Oyu Tolgoi copper mine in Mongolia rig manufacturers have developed precondition a rock mass ahead of caving. has a drilling fleet that includes Atlas automated programmes that allow Preconditioning involves drilling a series Copco Boomer M2 C30, Boomer E2 C30 increased accuracy when drilling a face. of holes into the lower portion of the rock face drills, and Boltec MC and Cabletec Where a rock mass does not have mass that is to be caved and then, by LC bolting machines. These share enough natural inherent jointing to cave, means of either hydrofracturing or common intelligent control systems and operators are often now looking to explosives, inducing manmade fractures

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two Cubex ITH drills have been used for for drill rigs at caving operations. Due to drilling service and preconditioning holes the tight constraints and narrow up to 240m in length. This is part of cave passageways, miners need safe, portable, propagation in lift 2 of the E26 orebody. compact equipment. Codelco’s El Teniente mine in Chile has Boart Longyear recommends its also utilised a Cubex ITH drill for drawbell StopeMaster and StopeMate rigs for development. A contractor has drilled 200 production drilling at caving operations. raises, each 760mm in diameter and 15m These feature heavy-duty hydraulic hoses in length. The average total time per raise and guarding to protect the driller from was 24h including mobilisation, setup, pilot ruptures and moving parts. Miners can hole drilling, reaming and de-mobilisation. operate the rigs from up to 25m away via Cubex ITH rigs are also at work at New a remote positioning system. The rigs Gold’s New Afton block cave mine in have emergency stop circuits to cut the Canada, where they are being used to power in the event of an incident. develop drawbells. Twin 760mm pilot For low-profile situations, the rigs can holes are used for the drawbell construc- tram through openings just under 1.5x2m, tion using the V-30 drilling method. and can be used for back height drilling In some mines, oversized rock can be a as low as 2.4m. Both Stope drills feature major challenge in the production cycle. hydraulically driven wheels to allow for “There Mr Hanrahan of SRK explains: “Given that skid-steer mobility, maximising manoeu- are ITH some of the more competent orebodies vrability in tight spots. are now being caved with consequent The smaller, lightweight StopeMate machines coarser fragmentation, a sophisticated drill accommodates drilling depths of available secondary breaking fleet is often required 12-15m. It weighs 3.7t and is small to quickly and efficiently reduce oversized enough to be loaded into a lift cage. The today that material ahead of transport to the primary rig can also be broken down into six can have into the rock mass to increase the ability crusher. Much of this material may have to manageable pieces in order to gain over 60m of to cave and/or to reduce block sizes. This be handled within the throat of the access to captive areas. task is typically performed by long-hole drawpoint (up in the drawbell area). The StopeMaster HX model was used mechanised drill rigs. Due to the long hole lengths and “Mobile equipment has been extensively in the development of Rio rod handling larger hole diameters required for this developed to drill and charge in this zone Tinto’s Palabora block cave mine in South type of work, it may also be worth remotely, so that no personnel are Africa. The extensive infrastructure capacity” considering ITH drill rigs. “There are ITH exposed to this task other than from a required rapid drilling of the drawbells machines available today that can have remote control cabin. Additional and for ground support cables. Boart over 60m of mechanised rod handling equipment such as water cannons has also Longyear says the HX drill helped to keep capacity, thereby improving the safety and been developed to blast hang-ups with a work within schedule. productivity of the preconditioning stream of high-pressure water and Mining contractor and equipment process,” comments Mr Bray. Mr Jonker dislodge them for treatment in a more manufacturer Redpath specialises in adds: “Due to the height of the caves, accessible location.” raisedrilling and shaft sinking for mine preconditioning holes can extend beyond Jay Klinko, senior global product development, and frequently uses 100m in length.” manager at Boart Longyear, says that boxhole boring and Alimak for work at Cubex has developed a heavy hoist mobility and flexibility are also a challenge caving projects. feed system that is designed to drill preconditioning holes beyond 250m, and has added drill rod handling systems to its rigs in order to eliminate manual handling. Mr Jonker says that Cubex’s Constellation and Megamatic range of underground ITH drill rigs are suitable for preconditioning when fitted with the heavy hoist feed, and matched with an appropriate high-pressure booster compressor or water pump. At PT Freeport Indonesia’s DOZ and Big Gossan block caves, Cubex compact LH1 top hammer drills and 6200 ITH drills with booster compressors are being used successfully in undercut and drawbell development. With the addition of remote controls, the drills are also used for secondary breaking in the drawbells. At Newcrest Mining’s Cadia East block cave mine in Australia, a Cubex ITH drill is drilling 165mm-diameter and 150m-long Atlas Copco’s blast pre-conditioning holes in lift 1, and Simba E7 C drill at Rio Tinto’s Northparkes mine (Australia) rig in action

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Mike Kelly, senior vice-president of the projects to allow setups in drifts under mines. The company’s scope of work Redpath group, explains: “Raisedrilling is 3.2m in height,” says Mr Kelly. “At PT covered constructing the Big Gossan “Raise- the fastest and safest method of Freeport’s mines we use an Alimak shaft, excavating roughly 2,500m per drilling is developing raises, provided you have the machine for raises. This has proven to be month of lateral drifts, providing mass infrastructure (and power) to utilise the the most effective method there, in part excavation for crusher stations and the fastest method. Workers do not have to enter the due to the time lag in getting power conveyor ways, as well as raiseboring and and safest raise, you do not have to support the distribution in place that a raisedrill Alimak services. “We have a workforce of method of ground, and the capital cost of the would require. To streamline the 1,100 at present and another three years equipment is relatively low.” operation, we developed a ‘portable on our current contract,” says Mr Kelly. developing The company is currently undertaking nest’, which significantly reduced the “We have been at this site for 28 years.” raises” boxhole boring at Codelco’s Andina and traditional setup times and makes Alimak Redpath has developed four drills El Teniente operations using its Redbore cost effective.” specifically for use in block cave 50 machine. “We are also manufacturing Redpath is the primary development operations: the Redbore 30 for small a Redbore 30 for future use at these contractor for the Freeport underground boxhole raises (up to 0.9m diameter) in low back height applications; the Redbore 40UR for raises to 1.2m in diameter; Redbore 50 for raises to 1.3m in diameter in low back applications; and the Redbore 70 for downreaming 1.2m raises to Operations experience connect to ore passes. can change theoretical In Mongolia, Redpath is the primary development contractor for shafts and solutions into practical and lateral development at the Oyu Tolgoi profitable outcomes. A copper mine. The company has 500 staff simple change to a client’s working on the project, and has completed the OT#1 shaft, which is 6.8m mining method turned a in diameter and 1,000m deep. It has also theoretical loss into a very completed 400m of the OT#2 shaft (10m profitable outcome. diameter and 1,375m deep), and will begin shaft sinking on OT#5 (6.7m Mines don’t just happen… diameter, 1,250m deep) in June. Shaft they are made. OT#4 will measure 11m in diameter and 1,375m deep. Work will start on this in the June quarter of 2013. Mr Kelly adds: “We also have two development crews working at North- parkes in Australia doing lateral development. Redpath is currently involved with over 25 shafts around the world. We have the world’s largest underground fleet of Alimak climbers, and the largest capacity raisedrill package on the planet: the Redbore 100.”

LOADING AND hAuLING The fixed footprint and layout of a block or panel cave lends itself well to partial or full automation, especially for the production loading equipment, and truck or train haulage of loaded material. Mr Hanrahan says one of the systems that have proved most effective is LHD automation. At operations/projects that use this system, significantly higher productivities have been achieved at a lower unit operation cost due to lower manning costs, increased tramming speeds (fewer loaders are >1,000 professionals, >40 offices, required for the same production throughput) and minimal damage. Higher 20 countries, 6 continents effective utilisation is also possible due to the elimination of operator constraints. solutions Expert independent advice. However, automation does not come without challenges; it requires much stricter safety controls, such as completely .com removing people from the working area. Roadways must also be well maintained to

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realise the full benefits of the higher Codelco’s El Teniente mine tramming speeds. Currently, manual uses Sandvik’s AutoMine intervention is still common in the form of load and haul system tele-remote loading, as this typically results in improved bucket fill factors. People will always be required as part of the operation to perform routine inspections and maintenance, but full or partial automation can reduce the exposure time of personnel in the production environment. Sandvik was one of the first suppliers to introduce automated systems for underground hard rock operations with its AutoMine automated loading and hauling system. AutoMine is a flexible modular system that can be adapted to small- or large-scale block caving operations. The system incorporates functions and applications that allow it to interface with third-party IT systems at mine sites. AutoMine allows operators who would “Automation does otherwise drive a single vehicle underground to work from a control room not come without on the surface, and simultaneously challenges; it monitor the movement of a fleet of requires much driverless loaders or trucks underground. Sandvik loaders or trucks navigate stricter safety between the load and discharge points controls, such as under the control of a supervisory system, which manages traffic and monitors the removing people machines. from the working Sandvik says increased fleet utilisation area” ensures constant performance level enhancements and optimum use of the workforce, so there are no breaks during shift changes. Increased productivity is achieved through a continuous process enabling integration of information on site. Codelco’s El Teniente mine has been using the AutoMine system for a number of years. The company invested in two systems to exploit its Pipa Norte and Diablo Regimiento deposits more efficiently. The Pipa Norte system was installed in 2005 and commissioned by December 2009. The mine currently uses Mining Contractors and Engineers LHD517 17t LHDs in three tunnels. The system for the larger 28,000t/d Diablo

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An employee CurreNt/future prOjeCts works in a There are a number of established mines control room at globally that use cave mining techniques the El Teniente to exploit orebodies successfully, and due copper mine, to newly realised economies of scale, owned and there are a large number of greenfield operated by and brownfield caving projects, as well as Codelco, near mine expansions in the feasibility/ Rancagua in development pipeline. The following Chile section looks at how a few of the most Photo: Bloomberg Finance prominent projects are progressing. Of the international-scale operators, Codelco has the greatest experience of developing and operating caving projects, followed closely by Rio Tinto. Codelco also operates the world’s largest cave mining operations, including El Teniente “The mine (the largest) in Chile. Other companies include: Newcrest Mining and Ivanhoe layout and Mines, which are relatively new to the activities are caving arena; LKAB, which specialises in Regimiento is in early stages of operation. product support team in the Cadia Valley. sub-level caving; and Freeport McMoRan, repeated Three semi-automated LHDs were used in Mr Richter comments: “Typical modern which is involved with caving via its at high the first phase, but the fleet could block and panel caves are designed to subsidiaries PT Freeport Indonesia (which frequency potentially increase to 10 LHDs when the efficiently utilise large, mechanised operates the Grasberg mining complex in full production stage is reached. trackless equipment fleets. The mine Indonesia) and Climax Molybdenum Co with little Other mines that use AutoMine include layout and activities are designed to be (which operates the Henderson mine in variability. Newcrest’s Ridgeway Deeps mine in repeated at high frequency with little Colorado, US). Australia, which has five LHD514Es (electric variability. This makes caving one of the This makes loaders). Rio Tinto’s Northparkes E48 mine, mining methods most suited to automat- rIO tINtO caving most Australia, also has five electric loaders, and ing loading and drilling equipment. Rio Tinto says its main mines/projects that suited to Petra Diamond’s Finsch diamond mine in “While fully autonomous loading is use caving techniques are: Northparkes South Africa (formerly of De Beers) also currently possible, it has not yet been (Australia), Palabora (South Africa), Oyu automating uses an automated trackless load and haul widely implemented, and typically Tolgoi (Mongolia), and Resolution Copper loading and fleet. In addition, Oyu Tolgoi mine will have tele-remote loading of the loaders forms and Kennecott Utah Copper (both US). more than 40 automated LHDs when a crucial part of the operation. Likewise, Northparkes and Palabora are operating drilling operating at full capacity. some manual intervention is required in mines, while Oyu Tolgoi and Resolution equipment” In September 2011, Sandvik won a setting up drill rigs before drilling can be are in development. contract to supply 14 fully automated performed as an automated activity.” Rio Tinto is currently transitioning one of LH517 LHDs for the initial production The fixed layout of a caving operation its most established operations, Kennecott phase at Newcrest’s Cadia East mine in also lends itself to utilising electrical Utah Copper (KUC), to an underground New South Wales, Australia. The equipment, which offers a reduction in block caving operation, which will be machines are now on site and being used noise, heat and diesel particulates. located beneath the Bingham Canyon in Lift 1 as part of Sandvik’s AutoMine New technologies are continuously open pit mine. The company increased its system. The project is slightly behind being tested, such as using vibrator plate copper resource for the mine in late 2011 Mongolian schedule so the machines have not yet feeding of trucks instead of loaders, and by 20Mt to 106Mt. The resource, known as mining officials been used to their full potential, but utilising road header equipment instead the North Rim Skarn, is a high-grade at Rio Tinto’s Sandvik says the results so far have been of traditional drill and blast techniques for copper-gold deposit located 300m below Oyu Tolgoi promising. Service and support for the development. However, these technolo- the current pit. Rio Tinto has committed copper mine loaders is being carried out by Sandvik’s gies have to meet the safety requirements US$165 million to complete the next stage Photo: SRK Orange service centre, plus an onsite of each operation and prove that they will of exploration and development studies by outperform the current tried and tested 2014. The prefeasibility programme methods before they will be widely includes final shaft rehabilitation, an access accepted. decline from the pit and further under- Accurately tracking material as it flows ground exploration drilling. The investment through the cave is critical for understand- follows the approval of US$238 million to ing the internal mechanics of the advance studies extending the open pit life operation, and for predicting grades and to 2028 and to purchase associated dilution. Mr Richter explains that research long-lead time equipment. is under way to develop ‘smart markers’ Northparkes in NSW, Australia, boasts that can be placed inside the cave to track both open cut and underground mining the material flow throughout the life of operations. The E26 underground block the operation. These markers require long cave mine was Australia’s first, and lift 1 operating lives and must be extremely reached design production of 3.9Mt/y in durable to survive while moving through 1997. Northparkes commissioned its the cave. second block cave mine, E26 lift 2, in

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2004 and an extension, E26 lift 2 North, in resume in September. Construction of 2008. In 2006 Northparkes began Shaft #2 at Hugo North is progressing well construction of E48 lift 1, its third major and the headframe has now reached a block cave mine, with full production height of 78.5m above surface. The final achieved in 2010. E48 extends the life of height of the shaft will be 97m. The Northparkes’ operations until 2024. headframe and ancillary buildings were Palabora operates a very successful 87% complete at the end of March and block cave mine, which has been ahead of schedule. Shaft-sinking activities producing around 30,000t/d of copper ore began in December 2011 and had reached since 2005. The mine is something of a 224m below surface on May 12. benchmark, due to the high competency The Resolution copper project is in of its orebody. The production footprint Arizona, US, near the depleted Magma measures 650m long by 200m wide, with mine. Rio Tinto has a 55% share in the 20 production cross-cuts and 320 draw project in partnership with BHP Billiton. points. The coarse fragmentation of the The project has an inferred resource of orebody means that a high degree of 1,600Mt of copper and operations are secondary breaking activity is required to expected to last 40 years. The prefeasibil- treat hang-ups and oversized material. ity study is currently under way, and is Oyu Tolgoi in Mongolia is the world’s expected to be complete by 2013, with largest undeveloped copper-gold project, production at the new mine targeted to containing 81,000Mlb of copper and start in 2021, eventually ramping up to 46Moz of gold in measured, indicated and 500,000t/y of copper. Resolution will use “Oyu Tolgoi inferred resources. The project is owned by panel caving methods to extract the ore, is the world’s a joint venture consisting of Rio Tinto, which is located 2km below the surface. largest Ivanhoe Mines and the Government of Temperatures at this depth can reach 70oC. Mongolia, although Rio Tinto is managing In addition, Rio Tinto took the decision undeveloped the development of the operation. in 2005 to extend the Argyle diamond copper-gold Construction of the Oyu Tolgoi complex mine in Australia, with an underground duction from the DOZ orebody began in is advancing toward its planned start-up block caving project at a cost of US$760 1989 using open stope methods, but was project, later this year and commercial production million, which would prolong its life by at suspended in 1991 in favour of the containing in the first half of 2013. The project is least another 11 years. However, in January Grasberg deposit. Production resumed in 81,000Mlb initially being developed as an open-pit 2009, the decision was made to slow the September 2000 using block caving and is operation, with the first phase of mining to development of the underground project expected to continue until 2019. of copper start at the near-surface Southern Oyu in response to global market conditions. Beginning in 2015, Freeport plans to and 46Moz deposits, which include Southwest Oyu Construction was scaled down to only ramp up production at the Deep Mill and Central Oyu. An 85,000t/d under- critical development activities, resulting in Level Zone (DMLZ) block cave mine, of gold” ground block cave mine is also being a workforce reduction and a demobilisa- which lies below the DOZ mine and is developed at the Hugo North deposit. The tion of contractors. currently under development. throughput capacity of the concentrator The Big Gossan mine lies underground plant is expected to be 160,000t/d of ore PT FreePOrT and adjacent to the current mill site. It is a when underground production begins. PT Freeport’s Grasberg complex in tabular, near-vertical orebody. Production Overall construction of the project was Indonesia includes both open pit and began in the December quarter of 2010 82% complete at the end of April 2012, underground operations. Open-pit mining and is to ramp up to 7,000t/d by mid-2013. and approximately US$4.6 billion has been of the Grasberg orebody began in 1990 invested so far. and is expected to continue until LKAB Underground lateral development at the mid-2016, at which point the underground Swedish iron ore miner LKAB took the Hugo North Deposit was suspended in mining operations – the Deep Ore Zone decision in 2008 to expand its Kiruna and February as planned to enable the (DOZ) and Big Gossan mines – will take Malmberget sub-level caving operations. upgrading of hoisting equipment at Shaft over the bulk of production. New main levels are being built at both #1. This is expected to continue until The DOZ orebody lies below the now operations; Kiruna’s at a depth of 1,365m August. Development is scheduled to depleted Intermediate Ore Zone. Pro - and Malmberget’s at 1,250m. The new

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Newcrest and will be the deepest block The block cave cave in Australia. The mine is expected to operation below produce 1.6Moz of gold and 210,000t of the Chuquica- copper over the project life of eight years. mata open pit The mine began transitioning from conains 1,700Mt Ridgeway to Ridgeway Deeps ore in 2010, of copper and ramp-up of production is currently Photo: Bloomberg News under way to 8Mt/y. Newcrest expects the cost of mining at Ridgeway Deeps to be significantly lower than at Ridgeway due to the combined impact of lower block cave mining costs and the use of semi-auto- mated LHDs. A capital cost for the project of US$551 million comprised: construction of the block cave, extension of the existing underground ore handling system (including two new primary underground crushers), development of bulk under- ground mining technologies, including the application of automated remote loaders, and modifications to the processing plant (adding additional secondary crushing and regrind facilities). Exploration drilling below the Ridgeway Deeps block cave has also indicated a continuation of the orebody, and M1250 level at Malmberget will be sub-level caving mines (in operation), and preliminary assessments are being designed to handle the extraction of 18Mt the Ridgeway Deeps block cave and undertaken into the potential development of crude ore, plus 1-2Mt of waste per year. Cadia East panel cave projects. of a second block cave. Workable ore reserves are estimated to be Ridgeway is one of the largest The Cadia East project is located on the around 140Mt, which will yield around underground mining operations in eastern edge of the Cadia Hill orebody 84Mt of finished product. An annual Australia. The mine produces 5.6Mt/y of (one of Newcrest’s open pit operations.) production of 8-10Mt will extend the gold-copper ore. Ore is accessed through The project, which is currently under operating life of Malmberget by about 10 a series of horizontal tunnels and dumped construction and about to enter produc- years to approximately 2020. Sections of into ore passes for transfer to the primary tion, will be Australia’s first, and the world’s the new main level were put into operation underground crusher. Crushed ore is deepest, panel cave operation. in the September quarter of 2010. transported up a 3.5km decline by a The Cadia East orebody holds a reserve At Kiruna, the new KUJ 1365 level will conveyor, then deposited on surface of 18.7Moz of gold and 3.1Mt of copper, accommodate remotely controlled stockpiles adjacent to the Ridgeway which Newcrest expects will underpin shuttle-train traffic, similar to the concentrator. In 2005, Ridgeway made the production for at least the next 30 years. present-day haulage level. Remote- transition from contract mining to The estimated capital cost of the project is “The Cadia controlled trains will transport the ore owner-operated mining. approximately US$1.9 billion, and to date East project from gravity shafts to the crusher, and Underground production at Telfer it remains on schedule and in budget. from there it will be skip-hoisted in two began in March 2006, the mine reached its The project also requires expansion and will be stages 1.4km vertically to processing nameplate production of 4Mt/y in February upgrade of the existing Cadia Valley Australia’s plants at surface level. 2007 and has since increased this to over processing plant as the ore at Cadia East is first, and Mining will take place in 10 production 6Mt/y. The initial phase of underground harder than that at Cadia Hill and areas, each with its own access road, mining uses sub-level caving as higher Ridgeway. Capacity will also be increased the world’s media systems, gravity shafts and ore grades occur at the top of the orebody. from 24Mt/y to 26Mt/y. deepest, chutes. Ore will be mined in stages The development of the mine is based on The project will increase production between today’s 1,045m track level and procedures and techniques similar to those from Newcrest’s Cadia Valley operations panel cave the new 1,365m level. Based on an annual used at the Ridgeway operation. The main to 700-800koz of gold and 75-100kt of operation production of around 19Mt, the operating difference at Telfer is that crushed copper per year over the first 10 years. life of the Kiruna mine will be extended to underground ore is hoisted to the surface The project is 75% complete with first 2030. Operations are expected to begin via a 1,100m deep haulage shaft. commercial production scheduled for the in the first sections later this year. Newcrest has a number of projects in December quarter this year. the pipeline. The Ridgeway Deeps project The Cadia East panel cave will be NewCrest MINING involves development of the resource conducted in two lifts. Mining will extend Newcrest Mining is focused on securing below the current Ridgeway mine. The from 500m below the surface to 1,450m. high-quality gold-copper resources and Newcrest board approved full project Work is currently under way to establish converting them into low-cost, high- execution in June 2007 to extend the panel cave 1 and the associated margin operations. To help achieve this, depth of the original mine by 300m to under ground infrastructure. Development the company has chosen to employ 1,100m below the surface by block caving. of the decline toward the deeper panel caving methods at a number of its mines. Ridgeway Deeps is the first natural cave 2 is also under way. Preconditioning These include the Telfer and Ridgeway caving operation to be developed by blasts are now complete in panel cave 1

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Discovery Metals strike length of 2km and is situated is developing a immediately under the Zeta open pit, sub-level caving extending from 150m to 630m below the operation at the surface. The operations will be accessed Boseto copper via a decline from twin portals, one project in developed from within the Zeta open pit Botswana and one from the surface. It is planned that all lateral development will be within ore. Access on each level will be developed to the periphery of the orebody and the sub-level caving conducted on retreat to the decline access points. The opportunity exists to trial the sub-level caving method at relatively shallow depths (55m below surface) in the southern end of the planned underground mining area. This will allow confirmation of the feasibility assumptions early in the development phase of the mine. Ore from both the development and caving operations will be trucked to the surface, and its drawbells continue to be fired, with of 140,000t/d of ore. stockpiled and then trucked approxi- the first ore from the blasted drawbells and Work is also under way at El Teniente’s mately 8km to the Boseto concentrator. undercut processed in the March quarter New Mine Level Project, which began The optimum extraction and process- this year. To date, over 300,000t of ore has construction in 2011. The new level (an ing sequence for the combined been treated through the process plant. addition to El Teniente’s current operations at Boseto has not yet been The crushers for the underground underground workings) will extend the life determined, with the final sequence being materials handling system remain a work of the mine by another 50 years using dependent on the timing of the planned in progress and the conveyor system is panel caving. The level will be developed expansion of the Boseto concentrator to a largely complete. Newcrest says that an at a depth of approximately 1,880m throughput of 3Mt/y. Discovery intends to “The new accelerated temporary crushing capability above sea level and adds around 2,000Mt maintain the option for an early start date and a substantially complete conveyor of reserves to the mine. Production from at Zeta while these studies continue. level at El system will allow the ramp-up of the new level will begin in 2017. El To that end, recruitment of a project Teniente production from panel cave 1, albeit at Teniente has been successfully using development team for the underground will extend lower initial rates than expected. Sandvik’s AutoMine system since 2005 to operation has started and Discovery plans On the surface, the concentrate exploit the Pipa Norte and Diablo to award the mining contract in early the life of handling, power, tailings and water Regimiento deposits and is expected to 2013, with development to provide under- the mine by infrastructure have been commissioned. use a similar system at the new level. ground access beginning in late 2013. The flotation plant and the regrind Infrastructure completion is slated for the another 50 Vertimill are both now complete and are dIsCOVery MetALs December quarter of 2013. years using in the final stages of commissioning. The Discovery Metals has just completed the panel high-pressure grinding rolls circuit is also definitive feasibility study for the Zeta Others well advanced, and commissioning took underground mine at its 100% owned SRK recently completed a contribution to caving” place in May. Boseto copper project in northwest a scoping study for Oz Minerals’ Botswana. Open-pit mining operations Carrapateena deposit in South Australia. COdeLCO have already begun at Zeta, and The study examined a range of mining Codelco has a number of caving projects in production is due to start later this year. methods appropriate to the deposit, the pipeline. The Chuquicamata mine The underground mine at Zeta was a key including sub-level open stoping, complex in Chile currently produces component of the Boseto Development sub-level caving and block caving. SRK copper from two open pit operations Plan, which anticipates open cut and conducted the sub-level caving and block (Chuquicamata and Mina Sur). However, underground mining to produce 35,000t/y caving studies. these will cease to be profitable in the next of copper for at least 15 years. Work on the scoping study by Oz decade, and construction work began in Discovery says that sub-level caving has Minerals will continue in parallel with 2011 for a new underground mine. been chosen for the underground portion diamond drilling of the orebody from The operation, situated below the of the project, as it is the most appropri- surface. In addition, SRK mining engineers current Chuquicamata pit, is estimated to ate mining method that took into account have been involved in aspects of cave contain 1,700Mt of copper (0.7% grade) the safety of operating personnel and the design and operation on almost all caving and molybdenum (502ppm) reserves. The mine itself, maximisation of resource projects globally over the past decade. project will use block caving to extract recovery, capital and operating costs and Snowden recently completed an ‘macro blocks’ of ore. Work has begun to operating risk (Zeta has weak hanging options study, followed by a detailed establish the four production levels; a wall conditions and it is the hanging wall scoping study, for a caving project in Asia, 7.5km-long main access tunnel; five clean that contains the mineralisation). Sub-level allowing the project to progress to the air injection ramps; and two air-extraction caving allows maximum extraction of the prefeasibility stage. The company has also shafts. Development is expected to be ore at the lowest mining cost. recently completed a number of caving complete by 2019 with a production rate The underground mine extends over a reviews in Australasia.

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