The Rocklands Project contains 11 main ore-bodies, 9 of which will be partially accessed in the first-stage 10-year mine plan.
Two of these orebodies (Las Minerale and Rocklands South) contain a unique supergene-enriched zone, characterised by pervasive high-grade coarse native copper and associated chalcocite ore, that persists from near-surface to depths of ~140m, widths up to ~45m and have a combined native copper/supergene zone strike length of ~1200m.
The planned mining method for Rocklands is a conventional open pit truck and shovel operation, using 180t and 190t class hydraulic excavators, in backhoe configuration, and 90t dump trucks. Drilling and blasting is conducted on 10 m high benches. Digging is conducted on flitches of 2.5 m height in the ore and up to 5 m high in bulk waste blocks.
The Las Minerale and Southern Rocklands Pit development will occur in stages. The Las Minerale Stage 1 is complete after reaching an RL of 152.5RL vs. a design of 150RL. Las Minerale Stage 2 has been partially developed to 170RL. Final design is to 100RL. Las Minerale Final has been partially pre-stripped to 215RL with a cutback to commence on completion of Stage 2. Initial pre-strip of the Southern Rocklands Pit has begun. The Southern Rocklands Pit will be developed in 2 stages with the potential for an additional small high grade pit to access native copper rich material.
Four Waste Dumps have been approved by the Department of Environmental and Heritage Protection (DEHP), East, West, North & South. Initial waste haulage is to the East and West Waste Dumps. As the pits get deeper these dumps are completed and haulage moves to the North and South dumps reducing the haul distances. Capacity of the combined dumps will meet the requirements for all currently planned pits.
Ore & Stockpile Management
Ore and stockpile management became a pivotal element of the life of mine scheduling plans at Rocklands when a report on aging studies indicated negligible losses were likely to occur to copper recoveries when processing aged ore through the Process Plant. Subsequent pit optimisation and scheduling studies resolved that higher rates of mining than required to meet process plant direct feed, combined with building of long-term stockpiles, resulted in superior project economics.
The optimal rate of mining was determined to be around 1.5 times the required mining rate, resulting in a scenario that would result in additional ore being mined each year and reporting to long-term stockpiles. On this basis, the pit is completed and all ore mined in around 7 years instead of 10. At the end of mining there will be around 6-9Mt of lower-grade ore remaining on the long-term stockpiles and waiting to be processed. With the mining fleet retired operating costs will reduce significantly, maximising the returns on this low-grade ore.
The benefit of higher mining rates is to deliver higher grades of ore from the pit to the mill in the initial years by providing more ore that can be selectively managed. The creation of long-term stockpiles also provides additional benefits, including building a contingent ore supply in the event the pit becomes inaccessible for any reason, and/or providing alternative monetisation options should they be considered.
A sophisticated ore control and stockpile management regime at Rocklands focusses on matching stockpiled ore characteristics to Process Plant requirements, not only to optimise recoveries but also to achieve maximum Net Present Value (NPV) for the project. Stringent ore identification and access procedures are also employed in the pit to minimise mining dilution and losses.
In its simplest form ore at Rocklands is separated into three classifications including oxide, chalcocite and chalcopyrite oretypes. These simple categories are then split into high and low grade versions of each, and further subdivided into native copper bearing ore or not, resulting in the following stockpile categories designed to match optimised process plant performance ranges:
Oxide ore – occurring in thin skin above water table where orebodies reach surface (water table just 10m below surface).
Supergene ore – high-grade enrichment has occurred from near surface to depths of 180m, including chalcocite and bonanza-grade coarse native copper that persists through oxide, supergene and primary ore types. Native copper ranges from sub millimetre fines to multi-tonne masses.
Primary ore – coarse patchy to massive primary copper mineralisation dominated by chalcopyrite that commences just 12m from surface in places.
The different ore types are stockpiled into 12 different ore type categories in order to match metallurgical and mineralogical characteristics of the various processing regimes. Segregation of Rocklands ore provides maximum flexibility for future adjustment to processing routes should the need arise, and results in direct costs savings when the gravity circuit is by-passed during processing of ore that does not contain native copper.