The first step is to detach the mineral from the mountain, which is performed by means of controlled explosions. The detached minerals are loaded with mechanical shovels onto trucks that carry them to a transfer hopper (orepass) that carries the ore to the cavern where the primary crusher is installed. There, the ore derived from surface operations is consolidated with ore from the underground mine. The crushed ore is transported through the tunnel to the intermediate ore sink by means of a conveyor belt that is 1647 m long. Once outside the tunnel, the ore is received by a second crushing unit, for secondary and tertiary crushing, which breaks down the rock until reaching the desired size for the next stage of the process. Then a set of conveyor belts carry the crushed ore to a leaching sink. The system used by Gualcamayo is to leach using a cyanide solution in a closed circuit.
The leaching sinks are waterproofed using a high-density polyethylene (HDPE) geo-membrane and a low-permeability layer of soil, made up mainly of compacted clay, with thickness of 30 cm (maximum permeability of clay is 10 -6 cm/s). Additionally, on top of the geo-membrane there is a system of collection pipes that lead the percolation solution off the leaching sink for the subsequent production stages. The rich solution (containing the leached gold) is transferred by gravity to an 18” pipeline laid inside a waterproofed channel to a tank or pool storage area. The ore in the leaching sinks is placed in piles, or production units, that are approximately 10 m tall by 86 m wide by 60 m long, by means of a radial stacker that receives the crushed ore from mobile conveyor belts.
A pump and pipeline system sends the leaching solution, called a “poor solution”, to the drip devices laid above the production unit, also called a “cell”. The leaching solution percolates through the ore, and during its downward flow it drags out the gold and other metals. When it reaches the bottom it finds the waterproof geo-membrane, and then flows to the collection pipelines that leads the “rich solution” (with gold)
by gravity to the Plant. There, the gold is extracted from the cyanide solution, which is returned to the leaching sink for a new cycle. The cyanide leaching solution works in a closed circuit between the leaching valley, the storage tanks and the gold recovery plant, which implies that no liquids are discharged into the environment at any time.
The leached gold is extracted from the rich solution by means of an activated carbon adsorption circuit. The activated carbon holds the gold inside its porous structure. Then the gold is stripped from the activated carbon using a cyanide solution at 145°C and a pressure of 450 kPa, a method called pressurized Zadra. The elution solution passes through the electrodeposition cells, where the gold in the solution is transformed into metal gold on the cathodes. The resulting sludge is filtered and dried prior to placing it in the melting oven along with fluxing agents. The sludge holds substantial quantities of gold, some silver and other metals to a lesser extent, most of which have no commercial value. The load is then melted in a gas oven, and the gold and silver are separated from other metals contained in the slag. When the molten load is poured from the oven, the gold and silver are collected in ingot molds and the slag is poured into slag containers.
The bullion’s contents are primarily 78% gold, 20% silver and 2% impurities or metals of no commercial value. Normally, between 3 and 4 ingots are obtained in each casting.