Caspiche Project Study Positive on Oxide-Sulphide Development

Development of Exeter Resources’ Caspiche gold/copper/silver project, pictured here, in northern Chile will
cost an estimated $4.8 billion for an open-pit mine/heap-leach operation.
Exeter Resource Corp. has reported the results of a positive prefeasibility study (PFS) for combined development of the oxide and sulphide ores at its Caspiche gold-copper-silver project in northern Chile. The study follows an earlier, posi-tive, stand-alone, oxides-only PFS that the company completed in June 2011 (E&MJ, July-August 2011, p. 16). The new study predicts an average annual production of 696,000 oz of gold, 244 million lb of copper, and 844,000 oz of silver over a 19-year mine life. The study is based on proven and probable gold reserves of 19.3 million oz and proven and probable copper reserves of 4.6 bil-lion lb.

Capital expenditures to develop the project are estimated at $4.8 billion.

The oxides-sulphides PFS evaluated three mining and processing options for the Caspiche deposit. All options in-cluded an open-pit to mine the near-sur-face, heap-leachable ore. The preferred development option is an open-pit opera-tion processing 150,000 mt/d of sul-phide ore and a heap-leach operation at an initial design production rate of 72,000 mt/d. The PFS envisages the heap leach operation will start before the main concentrator, with the leachable ore being removed as part of the pre-strip-ping operation.

A key component of the PFS is the inclusion of high-tonnage, in-pit crushing and conveying (IPCC) systems for the movement of waste rock. The cost savings per ton of total material moved using the IPCC system instead of a large truck fleet is estimated at about $0.25/mt, or $0.80/mt of ore mined. In addition to the operational savings, Exeter estimates an initial and sus-tainable capital saving of approximately $1 billion by building the tailings dam wall largely from a conveyor-stacker system rather than using conventional truck haulage for material movement. The waste dump would form the backbone of an engi-neered tailings dam face and provide a sig-nificant margin of safety in the event of an earthquake or other event.

The oxide ore and some low-copper sulphide ore would be treated in a con-ventional valley-fill heap leach operation. The sulphide orebody would be pro-cessed through a conventional concen-trator. The copper concentrate produced would be treated in an offsite roaster to ensure that its arsenic content is below 0.2%. Additional gold recovery would be achieved by leaching the flotation scav-enger tailings.

As featured in Womp 2012 Vol 02 -