The report details the existing gold dump leach operation at La Arena Mine and the proposed stand-alone La Arena II process facilities.
Report context
The La Arena 2018 Technical Report (M3-PN170043, 20 February 2018, Revision 0) describes current mineral recovery methods at the La Arena Mine and presents the proposed design for the La Arena II Project. The existing facility exploits oxide gold Mineral Reserves by open pit methods using conventional drill, blast, load and haul. The La Arena II Project is described as a stand-alone project independent of the current mine and not an extension or expansion of the existing operation.
Processing route
Existing La Arena Mine gold dump leach operation
Ore is truck dumped directly onto leach pads with no crushing or agglomeration required prior to leaching. The operation has a capacity of 40,000 tonnes per day, using 90 tonne trucks to haul run-of-mine ore to the leach pad, with one Caterpillar D6T dozer to spread the ore. Side slopes of the heap are covered with HDPE to control rain water influx for proper water balance.
Cyanide leach solution is applied by drip emitters at a rate of 0.175 kg per tonne of ore. Pregnant solution collects in a 73,000 m³ pond and is pumped to the ADR plant for gold recovery.
The ADR plant begins with 35 carbon adsorption columns (2.82 m diameter by 3.75 m height) operated in parallel in five circuits. Two additional carbon columns (2.1 m diameter by 2.7 m height) run in series to scavenge gold from solution bled to the effluent treatment plant through the clarification circuit.
Target gold loading on carbon is 4,000 to 6,000 g per tonne. Loaded carbon is pumped to one of two pressure strip vessels (1.42 m diameter, 6.8 m height, capacity 4 tonnes of carbon per batch) where gold is desorbed using the standard pressure Zadra method. Gold in the pregnant solution is precipitated as metallic gold by electrolysis in 8 units of electrowinning cells (total volume 12 m³). Gold metal collected in the electrolytic cathodes is smelted and molded into bullions.
La Arena II Project proposed process
With the exception of the ADR plant currently in use, no other existing process facilities are included in the La Arena II Project mineral recovery facilities. All oxide material encountered during La Arena II mining would be hauled directly to a new leach facility built within the dry stack tailing facility. Current carbon adsorption columns would be relocated adjacent to this new facility. Loaded carbon would be transported to the current ADR plant for stripping, and stripped carbon would be transported back to the new leach facility.
La Arena II sulfide material would be hauled to a crusher and then crushed and ground to liberate copper and gold for flotation. Comminution begins with a gyratory crusher to crush ROM sulfide material in preparation for semi-autogenous grinding (SAG). The SAG mill discharges to a trommel-vibrating screen combination. Screen oversize goes to a pebble crusher before returning to the SAG mill. SAG mill product is further ground by two ball mills operated in closed circuit with hydrocyclone clusters. Hydrocyclone underflow reports back to the ball mill, while overflow proceeds to rougher flotation cells.
Copper is recovered with three stages of flotation: a rougher stage followed by two stages of cleaning. Concentrate grade is limited to 23% copper to minimize loss of gold in the tailing with pyrite. Copper concentrate is filtered and shipped to smelters for copper revenue with gold credits. Copper flotation tailing is further processed by flotation to remove pyrite from the final mill tailing. Mill tailing and pyrite tailing would be filtered separately and deposited by mobile conveyors to separate storage facilities.
Key reported parameters
| Parameter | Value | Basis |
|---|---|---|
| Existing operation capacity | 40,000 tonnes per day | Operating data |
| Average gold recovery (oxide) | 86% | Historical operating data (reported by La Arena S.A.) |
| Cyanide application rate | 0.175 kg per tonne ore | Operating data |
| Pregnant solution pond volume | 73,000 m³ | Existing facility |
| Carbon adsorption columns (main) | 35 units, 2.82 m dia. × 3.75 m height | Existing facility |
| Carbon adsorption columns (scavenger) | 2 units, 2.1 m dia. × 2.7 m height | Existing facility |
| Target gold loading on carbon | 4,000–6,000 g per tonne | Operating target |
| Pressure strip vessels | 2 units, 1.42 m dia. × 6.8 m height, 4 tonnes carbon per batch | Existing facility |
| Electrowinning cells | 8 units, total volume 12 m³ | Existing facility |
| La Arena II copper concentrate grade limit | 23% Cu | Proposed design |
Project website: https://panamericansilver.com/news/pan-american-silver-announces-the-sale-of-la-arena-for-us245-million-cash-upfront-and-us50-million-contingent-payment/
Project website: https://panamericansilver.com/news/pan-american-silver-completes-the-sale-of-la-arena-2/
Project website: https://www.mining-technology.com/projects/la-arena-gold-copper-project/
Technical qualifications
The report does not present metallurgical testwork results or performance data for the proposed La Arena II process. No recovery estimates are provided for the sulfide flotation circuit. The description of the La Arena II process is a proposed design only; all oxide material and sulfide material processing descriptions for La Arena II are prospective and not based on operating data.
Source: La Arena Project , 2018 Technical Report, M3-PN170043, 20 February 2018, Revision 0, Section 17 Recovery Methods.
