The Parral mining district is situated in the centre of the Mexican silver belt epithermal silver-gold vein districts. The geology of this belt is characterized by two volcanic sequences of Tertiary age, discordantly overlying deeply eroded Mesozoic sediments and older metamorphic rocks. The physiography of the belt resembles the basin and range area in the western USA, with wide, flat valleys and narrow, relatively low mountain ranges and hills. The precious metal-bearing fissure vein type of mineral deposit is the most widespread and economically important type of deposit found in the belt. The belt has been recognized as a significant metallogenic province, which has reportedly produced more silver than any other equivalent area in the world.

Tailings from the Mina la Prieta mill were impounded on dry ground to the north of the mine and milling complex. The tailings were deposited over many years in flat, consistent layers, dewatered and eventually built up in 5 m lifts into raised heaps reaching a final height of 50 m. The physical consistency of the material is uniform and has an average particle size distribution of 80% passing 0.255 mm.

The Parral Project is a surface mining operation using conventional excavation equipment and on road haulage trucks. The scale of production will require mining rates on the order of 5,200 t/d or 1.8 Mt/a of tailings. Waste handling quantities will be minimal.

Due to the nature of the tailings deposit, no drilling and blasting will be required. All of the tailings material will be free digging with a hydraulic excavator. The tailings have an insitu bulk density of 1.68 t/m3 and an expected loose bulk density of 1.40 t/m3.
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The Plant at the Parral Project is used to re-treat old tailings from the tailings dump from the Mina la Prieta silver and base metal mine, which operated periodically from the 1600’s to 1990.

The Plant is designed to process a minimum of 5,000 t/d. The extraction process is by conventional heap leach using sodium cyanide as the leaching reagent. Recovery of gold and silver from cyanide solution is by zinc precipitation. The very high silver content of the ore makes this process more cost effective than a carbon-in-leach or carbon in-pulp process.

The Plant comprises of tailings reception with a temporary 40,000 tonnes re-mined tailings stockpile, an agglomeration and stacking circuit, a heap leach circuit, a Merrill-Crowe plant, a copper-acid leaching and precipitation circuit and neutralisation circuit.