Exeter Resource Corp., a Vancouver-based Canadian junior company, has received a positive prefeasibility study (PFS) from Jacobs Engineering for development of a stand-alone, oxides-only heap leach mine at its Caspiche project in the Maricunga region of northern Chile. Such development would be based on the thick oxide blanket that covers the very large underlying Caspiche sulphide deposit. A combined oxide-sulphide development is the subject of a much larger PFS currently under way and scheduled for release in the fourth quarter of 2011.
The purpose of the Caspiche oxides-only PFS was to demonstrate the commercial viability of a relatively low-capital-cost, low-risk mine producing 210,000 oz/y of gold and 364,000 oz/y of silver over five years. The study established the oxide ore leaches exceptionally well and will be an important cash-flow generator whether it is developed independently or in concert with the main sulphide deposit.
Oxide processing throughput would be at a rate of 62,000 mt/d. Mine trucks would discharge run-of-mine ore to a bin ahead of a primary jaw crusher. Where required, primary crushed product would be further reduced in a secondary crushing circuit. Following addition of lime to control cyanidation pH, the ore would be trucked to a valley heap leach. Pregnant leach solution would be processed through a counter-current carbon-in-column (CIC) circuit, electrowinning and smelting to produce doré gold-silver bullion.
Average cash operating costs for the heap leach operation are estimated at $524/oz of gold, after the silver credit. Initial capital costs are estimated at $335.6 million. At a $1,320/oz gold price, payback would be 3.2 years after initial construction.
The Caspiche oxides-only PFS was based on NI 43-101 compliant proven and probable reserves totaling 1.35 million oz of gold at an average grade of 0.41 g/mt and 5.36 million oz of silver at an average grade of 1.64 g/mt in 102 million mt of ore. Several opportunities to improve project economics, including supply of power from the national grid, were not incorporated into the PFS.