The mineral occurrences present and being sought in the Cieneguita and La India areas of the North Zone, as well as the Main Zone of the project area are volcanic-hosted, epithermal, high-sulphidation (HS) gold-silver deposits. Such deposits may be present as veins and/or disseminated deposits. Some of the most intensely studied and described HS deposits include Summitville, Colorado (Stoffregen, 1987; Gray and Coolbaugh, 1994), Goldfield, Nevada (Ransome, 1909; Ashley, 1974; Vikre, 1989), Lepanto, Philippines (Hedenquist et al., 1998) and Julcani, Peru (Petersen et al., 1977; Deen et al., 1994). Based on these studies and others, excellent compilations of general characteristics and genetic and empirical models have been presented by Hayba et al. (1985), Heald et al. (1987), Berger and Henley (1988) and Arribas (1995).

Numerous epithermal gold occurrences are exposed in small abandoned mines or exploration workings throughout the La India property. Host rocks include hydrothermal breccias, andesite, dacite porphyry, and volcaniclastic strata. Both high-angle structural and low-angle stratigraphic
controls are observed. Mineralized zones are characterized by alteration mineral assemblages that include alunite, dickite and/or pyrophyllite, accompanied by intense silica replacement of the host rock, with variable intensities of pyritization and/or hematization. Pyrite occurs both as disseminations and in microveinlets. In oxidized zones, relict hematite-limonite-goethite after pyrite is present. In some occurrences, primary hypogene specularite is associated with auriferous zones. The mineral occurrences for which resources have been estimated, the North and Main Zones, are described herein. Other mineral occurrences are described in Gray (2006).

The gold mineralization is confined to zones of argillitic alteration originally containing sulphides and subsequently oxidized. All of La India’s reserves are in oxidized material, amenable to heap leaching.

The La India mine is a collection of deposits grouped into three open pits – North, La India (Central) and Main – that will be mined over an estimated six-year life, providing ore for a heap leach pad located just west of the North pit. The mining rate is expected to be approximately 16,000 tonnes per day, using Caterpillar 992 front-end loaders (11.5-m3 capacity) and Caterpillar 777 haul trucks (90-tonne capacity), the same type of equipment used at Agnico Eagle’s Pinos Altos and Creston Mascota operations.

Three-stage crushing reduces the ore to 19 mm. Lime is added to the crushed ore to control the pH, and the ore is stacked in 8-metre-high lifts. The leach pad, which will be constructed in two phases, will have a capacity of up to 50 million dry tonnes, reaching an ultimate height of approximately 113 metres.

Cyanide leach solution percolates through the heap to the lined solution-collection ditch that routes it to a double-lined pregnant collection pond. A zero discharge water balance is maintained at the heap leach facilities with an event pond designed to contain the volume of solution that would be produced in the case of a 100-year/24-hour storm event.

The gold adsorption facility (ADR plant) consists of two parallel trains of five 3.5-tonne carbon adsorption columns and a Zadra strip with electrowinning. Gold-silver doré bars are produced in the refinery. The plant is designed to process leach flows from up to 6.0 million dry tonnes of ore per year (16,438 tonnes per day). Gold recovery is estimated at 80% with a 90-day leach time.