They seem to be counting on leaching the low-grade stockpiles to extend the mine life. It seems like a lot of money for a short-term operation. I wonder what they do with the railroad after the mine closes? They are now required to pay for the costs of reclamation at the end of the mine.

Pinto Valley is an open cut gold and copper mine located about 125km east of Phoenix in the US state of Arizona.

Wholly owned by BHP Billiton, Pinto Valley was acquired through the acquisition of Magma Copper Company in 1996.

Sulphide mining operations stopped in 1998, after which the operation continued to produce small amounts of copper cathode through residual dump leaching SXEW operations.

Following a Feasibility Study on a re-start of the sulphide mining operations in 2006, the Re-Start Project was approved in January 2007 with first concentrate production occurring in October 2007.

The Miami unit of Pinto Valley Operations is an in situ leach plus SX-EW operation within the upper parts of an oxidised and enriched porphyry copper deposit. The Miami unit is currently on care and maintenance status, except that the SX-EW unit is processing leach solutions that continue to be cycled through the leachable resources.

BHP estimates that current reserves at Pinto Valley will support mining for a further four years.

Geology and reserves

The Pinto Valley mine produces concentrate and cathode from a low-grade porphyry copper characterised by chalcopyrite mineralisation within potassically-altered quartz monzonite.

As of 2008 proven ore reserves – copper – 7mt low grade leach, 42mt sulphide. Measured resources as of 2008 were 15mt low grade leach, 54 mt sulphide, 446 mt sulphide stockpiles.

The changes in Ore Reserves are due to lowering the mill feed cut-off from 0.27% Cu in 2007 to 0.25% Cu, changed haulage ramp design and other mine parameters, and a revised resource model, including revised classification. Mine life only considers the extraction of the intact sulphide ore. Copper recovery of the low-grade sulphide stockpiles is estimated from the expected leach production during mine life.

Changes to the resource declaration include revised methods of resource modelling and classification, and updated economic and geotechnical parameters.

--http://www.mining-technology.com/projects/pinto-valley/