From a metallogenetic standpoint, mineralisation in the Quinchía district is genetically linked to the emplacement of a cluster of Miocene-aged hypabyssal porphyry bodies. A variety of magmatichydrothermal Au (Cu) and Au-Ag (Pb, Zn, Cu) deposit types are associated with the geochemical and cooling history of the porphyry bodies.

Retreat longhole open stoping with backfill is the mining method proposed. This method permits the extraction of the ore at maximum hydraulic radius after backfilling the stopes. The backfill assumed is waste material from mining and fine tailings material. Backfill is required for both stability and environmental reasons, allowing all waste material generated by the mining operation to be redeposited as fill in the mine.

All the mine accesses will be developed in rock mass with good geotechnical conditions. The first 80m of the decline ramp will be developed in basalt before transitioning to breccia.

The process facility is designed to treat 474,500 tonnes of ore per annum (1,300 tonnes per day). The wet plant is scheduled to operate seven days per week at a nominal treatment rate of 59 dry t/h.

Crushing Circuit
A run-of-mine (ROM) pad for storage of ore delivered by mine haul trucks will be established adjacent to the crushing plant feed bin (ROM bin). Ore will be reclaimed from the ROM stockpiles and delivered in the required blend to the ROM bin by a front-end loader.

A three-stage crushing plant will be provided to crush the ROM ore. The crushing plant has been designed to operate five days per week, 12 hours per day, at an effective utilisation of 70%, at a crushing rate of 220 t/h to produce sufficient product for the mill throughput of 474,500 dry t/a. The crushing circuit design will have sufficient capacity to build fine ore stocks to accommodate non-operational periods and tolerate shutdowns for maintenance requirements. The crushing plant product will have a maximum particle size P100 of 13mm and a P80 of 9mm.

Grinding, Gravity Recovery and Classification
The grinding circuit will consist of a single stage overflow ball mill that will operate in closed circuit with hydro-cyclones to a product size P80 of 106 µm. The circuit will also comprise of centrifugal gravity concentrators, with feed screen, and an intensive cyanidation reactor to leach the recovered gravity concentrate.

The recovered concentrate will be subjected to intensive cyanidation in a CS2000 Consep Acacia dissolution module to dissolve the contained gold and silver. The intensive cyanidation module will be located within a secure area and concentrate dumped periodically from the gravity concentrators will flow by gravity to the intensive cyanidation storage cone.

The intensive cyanidation reactor will be an up- flow fluidised bed leach reactor whereby the gravity concentrate will be exposed to a high concentration cyanide solution at elevated temperature in the presence of a leach accelerant chemical known as ‘Leach Aid’. At the completion of the leach cycle the pregnant solution will be transferred to a gravity pregnant solution tank for controlled delivery to the zinc precipitation circuit.

Flotation
The flotation circuit will consist of a conditioning stage and conventional, forced air addition flotation cells for the roughing/scavenging and cleaning duties. Concentrate from the rougher and scavenger cells will be pumped to the cleaner flotation conditioning tank where it will combine with the cleaner scavenger concentrate.

Concentrate Thickening and Leaching
The cleaner flotation concentrate will be thickened in the concentrate thickener. The concentrate pulp will be thickened in a 5m diameter high rate thickener fitted with an auto- dilution feed system to increase the settling rate. Flocculant will be added as a solution to settle the solids to approximately 60% solids w/w.

The concentrate will be pumped to a feed box ahead of the intensive leaching circuit which will comprise four agitated tanks arranged in series. The box will have two discharge outlets and dart plugs which allow the feed to be directed to either the first or the second leach tank. Barren solution from the zinc precipitation circuit will be used to dilute the thickened pulp to a density of 30% solids w/w. The leaching train will consist of four 103 m³ agitated leach tanks, resulting in a minimum residence time of 48 hours at the design treatment rate.

Gold and Silver Recovery
The unfiltered pregnant solution from the concentrate leach residue thickener overflow will report to the unfiltered pregnant solution tank. Gravity leach pregnant solution will also report to this same tank. The combined solution will be clarified to remove a majority of the contained suspended solids which may otherwise be detrimental to the zinc precipitation process.

The filtered pregnant solution will then be pumped to a de-aeration tower. Vacuum pumps (duty/standby) are fitted to the tower to aid the de-aeration process. The dissolved oxygen concentration of the pregnant solution will be decreased to below 1ppm to minimise its impact on the zinc precipitation efficiency. Zinc powder will be added to the de-aerated pregnant solution. Dilute lead nitrate solution will also be added to aid the zinc precipitation process.

The solution containing precipitate will then be pumped to nominally one of two (duty/standby) zinc precipitation filters. The canister-type filters will be coated with diatomaceous earth to aid the filtration process. The precipitated precious metals, some precipitated base metals and the zinc remnants will be recovered in the filters.

Zinc precipitate from the zinc precipitation filters will be transferred to the calcining oven. The oven will be fitted with an exhaust hood and exhaust fan. After drying overnight the residual cake will be cooled and then mixed with flux reagents. The mixed cake will then be loaded into an electric furnace for smelting. The tilting furnace will discharge slag and bullion into moulds. The recovered bullion will be cleaned, weighed and then stored within a vault in preparation for shipment.