The March 2012 pre-feasibility study for Coro Mining's San Jorge project in San Juan Province, Argentina describes crushing to 13 mm, retreat stacking in 6 m lifts, ILS and raffinate irrigation, 880 m3/h of PLS at 4 g/L and an electrowinning tankhouse of 90 cells.
San Jorge is a copper leach project in San Juan Province, Argentina. Coro Mining Corporation commissioned the Preliminary Feasibility Study of the San Jorge 25kt/y Copper Leach Project, prepared by Sergio Alvarado, Heriban Soto and Enrique Quiroga with an effective date of the 1st of March, 2012. The process design runs from crushing through agglomeration, stacking, heap leaching, solvent extraction and electrowinning to cathode copper. Crushing circuit design is set by a target product size of P80 13 mm, based on leach recovery at various crush sizes in the initial column leach test work, and by the run-of-mine ore top size of 1,000 mm delivered to the circuit.
Critical Data
| Parameter | Value | Unit | Notes |
|---|---|---|---|
| Cathode production | 25,000 | t/y | LME Grade A specification |
| ROM top size | 1,000 | mm | Fed by 50 t mine trucks |
| Crusher product | 13 | mm P80 | Three-stage open circuit |
| Railcars | 14 | x 56 t | Ore haul to the process plant stockpile |
| Agglomerator | L:D about 3:1 | Not applicable | Up to 15 rpm, rubber-lined |
| Radial stacker cells | 82 wide x 6 high | m | 6 m retractable stinger |
| Heap lifts | 10 | x 6 m | Leach pad 990 m x 630 m |
| Leach pad panels | 12 | x 82.5 m | 1.5 mm HDPE, 2% grade |
| Irrigation cells | 6 per panel | 82 m x 100 m | 13 mm dripper tube |
| Solution cycling rate | 883 | m3/h | Pond sizing basis |
| PLS pond live storage | 10,600 | m3 | 12 hours |
| ILS pond live storage | 7,070 | m3 | 8 hours |
| Raffinate pond live storage | 8,850 | m3 | 10 hours |
| PLS grade | About 4 | g/L Cu | 880 m3/h to SX |
| Copper recovery | 85 / 66 | % | Two-stage leach of 0.57% CuT oxide and 0.61% CuT enriched ore |
| Tankhouse | 90 | cells | 18 scavenger, 72 commercial |
| Current density | 310 | A/m2 | Maximum 340 A/m2; 92% current efficiency |
Overview
The leaching strategy is a two-stage leach that maximizes the copper tenor of the pregnant leach solution (PLS) delivered to the solvent extraction (SX) plant. Agglomerated ore on the leach pads is irrigated first with intermediate leach solution (ILS) and then with raffinate from the SX plant. Heap run-off goes to the PLS pond or the ILS pond depending on its copper concentration.
Key Process Stages
Crushing
A three-stage open circuit crushing plant is fed directly by 50 t mine trucks and by front-end loader from a small ROM stockpile. A vibrating grizzly feeder from the ROM dump bin feeds the primary jaw crusher, which has a rock breaker and an air-conditioned control cabin. Primary crushed ore goes to a single deck secondary scalping screen, whose oversize goes to the secondary cone crusher. Screen undersize and secondary product go to a surge bin and double deck tertiary scalping screens, where oversize goes to the tertiary cone crusher. The product stockpile feeds 14 railway carriages of 56 t capacity that carry ore to the process plant stockpile in San Juan province.
Agglomeration and stacking
The agglomerator is an inclined mild steel rubber-lined drum with an L:D ratio of about 3:1 and a variable speed of up to 15 rpm. Concentrated sulphuric acid is sprayed on the ore over the first third of the drum, and raffinate adds moisture. The tumbling action binds fine particles to larger ones and mixes them with acid and raffinate. A conveyor loads 20 t trucks that deliver ore to a radial stacker with a 6 m retractable extension, which stacks cells 82 m wide and 6 m high. Retreat stacking lets freshly stacked ore go under irrigation as soon as enough area is available.
Heap leaching and leach pad
Ten 6 m lifts are needed on a nominal 990 m by 630 m pad, with ramps built to reach the top of the heap as it rises. The pad sits across an alluvial plain, divided into 12 panels of 82.5 m with 2.5 m batters, 1 m containment bunds and 1.5 mm HDPE liner, and is graded at an average 2%. Each panel connects by pairs of HDPE pipes to trapezoidal lined PLS and ILS drains, with valves to choose which solution leaves. A leak detection system of under-liner mole drains runs down each panel. Pre-production ore placement is significant, since PLS grade and the ability to meet the production target early depend on the tonnage and grade placed. The study recommends considering pre-production mining in the next phase.
Ponds and irrigation
Storm water runoff can bypass the process ponds through an overflow weir to an environmental storm water pond. Ponds have two layers of 1.5 mm HDPE with a biaxial mesh geocomposite between them for primary leak detection, side slopes of 1V:2.5H, depths limited to 4 m and bund crest widths of 5 m. Each panel has six cells irrigated through two ring mains of 110 mm HDPE feeding a 13 mm dripper tube network, with six 250 mm collection pipes at the edge of the panel.
Solvent extraction and electrowinning
The SX plant starts as a 2E x 1S series circuit, with provision for an extra mixer settler to make a series-parallel arrangement if the design PLS grade cannot be maintained. The tankhouse is an ISA Process type or equivalent with 90 cells holding 46 anodes and 45 cathode mother plates each, at 104 mm electrode spacing and a seven day harvest cycle. A semi-automatic stripping machine with a flexing station strips the cathodes.
Additional Interesting Data and Summary
The study calls for site earthworks, a control system, surface protection and fire protection, and describes reagents and a storm water pond in separate sections. The report states that the leach mass balance gives about 85% total copper recovery on 0.57% CuT oxide ore and 66% on 0.61% CuT enriched ore.
Key Processes
- Three-stage open circuit crushing to 13 mm
- Acid and raffinate agglomeration in a rubber-lined drum
- Radial stacker retreat stacking in 6 m lifts
- Two-stage ILS and raffinate heap leaching
- Solvent extraction in a 2E x 1S circuit
- Electrowinning and cathode stripping to LME Grade A copper
Source: Preliminary Feasibility Study, San Jorge 25kt/y Copper Leach Project in San Juan Province, Argentina, March 1, 2012.
