It is one of the company's newer projects, with the first copper cathode extracted in 2006. The mine reached design capacity in the third quarter of 2007, after which it was able to reach the current annual production rate of 200,000t of copper cathode.
Spence is the first greenfield large-scale mining project to be developed in Chile in six years and the first large SX-EW (solvent extraction and electrowinning) project constructed globally this decade.
Commenting at the opening, BHP Billiton president base metals, Diego Hernandez said: "This is an outstanding asset that incorporates global best operating practice and the latest technology."
Construction of the mine was undertaken at a cost of around $1bn, with annual capex estimated at around $20m. Around 90% of the engineering was undertaken in Chile, and 99% of the management team is Chilean nationals.
Spence has 663 full time employees – of which 70% are from the Antofagasta Region – and 489 contractors. Women make up about 8.5% of staff.
BHP Billiton has emphasised that design and the construction of the site was guided by best-practise safety standards, and the mine has already earned a number of awards for its achievements in this area. Mine life is currently estimated at 19 years.
Geology and reserves
The supergene enriched and partially oxidised porphyry copper deposit is of Upper Paleocene age (about 57 million years). The deposit is 100% covered by gravels and depth to mineralisation ranges from 80m to 100m below the surface. Oxide and supergene sulphide mineralisation is amenable to heap leaching (atacamite and chalcocite).
Proven and probable reserves of oxide ore as of the end of 2007 were 74.8 million tons at a grading of 1.24%. Total reserves of sulphide ore were 238.3 million tons with a grading of 1.08%.
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