Cobre has secured 150,000 tonnes of low-cost ENAMI oxide material while testing two ways to recover copper from Sierra Atacama’s old leach infrastructure. The initiatives could lift SX-EW utilisation, although the historical pad opportunity remains early-stage and non-JORC.
- 150,000 tonnes of ENAMI material secured at about US$9/t
- Planned deliveries of approximately 30,000 tonnes per month
- Historical pads producing copper-rich solution grading up to 2 g/L Cu
- Copper recovery from historical ponds targeted by quarter-end
- Historical pad volume is not a JORC Mineral Resource
ENAMI ore gives Sierra Atacama a defined near-term feed source
Cobre Limited (ASX:CBE) has secured a relatively concrete way to keep Sierra Atacama’s processing plant busy: approximately 150,000 tonnes of crushed and previously leached copper oxide material from Empresa Nacional de Minería, or ENAMI, at an estimated purchase and delivery cost of about US$9 per tonne.
The stockpile averages approximately 0.65% total copper and sits within 55 kilometres by road of the project. Cobre plans to move roughly 30,000 tonnes a month to Sierra Atacama, blending the material with underground ore as mining ramps up and the company advances its planned open-pit operation. Metallurgical testing returned 58% copper recovery in columns, but Cobre is using a more conservative assumption of about 50% recovery at industrial scale.
That feed strategy fits neatly with the company’s recently outlined expansion plan. Cobre has previously mapped a path from its existing configuration towards 18,000 tonnes per annum of copper cathode, then 25,000 tonnes, with a larger 50,000-tonne case under consideration. The ENAMI agreement does not itself establish those production outcomes, but it gives the existing leach and SX-EW circuit an additional source of material while the mine develops.
Old leach pads are being tested for residual copper
The more speculative opportunity lies on site. Historical mining used stacked leach pads up to 30 metres high, with reported copper recoveries of roughly 50% to 55%. Cobre says its current practices, including finer crushing, lower stack heights and dynamic leaching, achieve approximately 72% to 82% recovery, suggesting that some copper may remain in the old pads.
Initial irrigation trials using recycled solution have generated copper-rich pregnant leach solution, with the announcement reporting concentrations of up to 2 grams per litre of copper in the current programme. Cobre is now optimising irrigation rates and solution chemistry, and plans to assess injection leaching during the December 2026 quarter.
There is a sizeable-looking number attached to the pads, but it comes with a large qualification. LIDAR-based volumetric estimates indicate the historical material may exceed 10 million tonnes, yet Cobre expressly says this is not a Mineral Resource and that sampling is insufficient for JORC reporting. The pad programme is therefore an operating test, not a declared inventory of recoverable copper.
Pond recovery could reach production sooner
A separate programme is targeting copper-rich precipitates and sediments in four historical lixiviant ponds. Cobre says water is being circulated through the accumulated material to dissolve readily soluble copper sulphates, with the resulting solution filtered and introduced into the existing pregnant leach solution circuit. First copper production from this workstream is targeted by the end of the quarter.
Both on-site programmes are designed to use infrastructure already in place and are expected to require relatively little additional acid, an advantage the company highlighted amid elevated acid prices. The ENAMI testwork, however, points to the importance of monitoring the numbers in practice: laboratory acid consumption was approximately 45 kilograms per tonne, while the filing’s parameter table lists projected industrial consumption of 18.3 kilograms per tonne and its narrative refers to a more conservative 30 kilograms per tonne planning assumption.
The next evidence will be operational rather than promotional: how consistently ENAMI deliveries arrive and blend, what recovery and acid consumption look like at scale, and whether the old pads and ponds produce enough solution to matter commercially. Cobre is trying to make a regional copper-processing hub from three feed sources, but only one of them currently has defined tonnage and a purchase arrangement.
Bottom Line?
The ENAMI material provides the clearest near-term support, while the pad and pond programmes must convert promising solution flows into repeatable copper production.
Questions in the middle?
- Can the ENAMI stockpile deliver the assumed recovery and acid consumption at industrial scale?
- How much copper can the historical pads produce once irrigation and injection methods are optimised?
- Will pond and pad recovery become material enough to change Sierra Atacama’s production profile during the underground ramp-up?