University of Tasmania, Australia

Characteristics, origins and controls on high grade gold mineralisation in the Caspiche porphyry – epithermal deposit, Chile

Caspiche is a newly discovered porphyry-epithermal system in the Maricunga Belt of Chile, 10 kilometres north of Cerro Casale and 15 km south of Refugio Mine. Exeter Resource discovered Caspiche in 2007, and their extensive drilling campaign since that time has defined an inferred mineral resource of 1,117 Mt @ 0.55 g/t Au and 3.81 g/t silver, including 1,017 Mt @ 0.22% copper. This equates to in-situ inferred resources of 19.6 million ounces of gold, 137 million ounces of silver and 4.84 billion pounds of copper, making Caspiche Chile’s second largest gold-rich porphyry deposit (in terms of contained gold). Caspiche is also one of the world’s largest gold-rich porphyry deposits, currently ranked 14^th in terms of contained gold.

As a newly discovered porphyry system, there are many potential research opportunities at Caspiche. One obvious aspect of the system that requires detailed investigation is the relationships between the porphyry and epithermal alteration stages, and a determination of the controls on high grade ore deposition. Possible research techniques include:

• Drill core logging and mapping, supplemented by LA-ICPMS zircon age dating to constrain the geological evolution of Caspiche, with emphasis on the intrusive history and its relationships to mineralisation
• Paragenetic studies of veins and altered rocks to determine timing relationships between the porphyry and epithermal stages of hydrothermal activity. This will be supplemented by geochronological investigations of hydrothermal minerals such as biotite and alunite to help constrain the timing and duration of the porphyry and epithermal events
• LA-ICPMS mapping of pyrite from the various paragenetic stages to help constrain the location and controls on gold mineralisation (both porphyry and epithermal), with metallurgical recovery implications

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