By expanding the mill at its Lone Tree mine near Winnemucca, Nev., Santa Fe Pacific Gold hopes to boost annual production to more than 200,000 oz. gold.
The heap-leach mine poured its first gold two years ago; in 1992, it produced 129,000 oz. Production this year is expected to be between 160,000 and 170,000 oz.
An oxide mill facility — the first phase of a US$67-million expansion project — is to start up by year-end. A new autoclave accounts for US$4 million of the US$16.6-million cost of installing a pressure oxidation segment for processing refractory gold ore.
The whole-ore autoclave, one of 14 in North America, is designed to process 2,500 tons per day of refractory ore by pressure-cooking it at 180C, under a pressure of
235 lb. per square inch. It measures 63 ft. in length and 14 ft. in diameter and weighs 322,000 lb.
Lone Tree has proven and probable reserves totaling 3.8 million oz., an increase of 0.6 million oz. since the end of 1992. This increase reflects ongoing developmental drilling in the southern extension of the deposit. Reserves include: 1.2 million tons of oxide mill ore grading 0.227 oz. gold per ton; 17.2 million tons of heap-leach ore grading 0.059 oz. gold per ton; 29.1 million tons of dump-leach ore grading 0.018 oz.; and 13.5 million tons of refractory mill ore grading 0.146 oz.
Santa Fe’s operations in Nevada and California are expected to produce about 600,000 oz. gold this year and 900,000 oz. in 1994. In June, the company acquired gold assets from Hanson PLC’s Goldfields Mining in a coal-for-gold exchange.
The Mesquite gold mine in California, acquired from Gold Fields, produced 206,000 oz. last year. Santa Fe combined its Rabbit Creek mine and Gold Fields’ former Chimney Creek mine to create the Twin Creeks mine in Nevada. The two operations cranked out a total of 411,000 oz. in 1992.
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