In attempting to extract every last tonne of economic ore out of the ground, Curragh has driven into the wall of the Faro open pit. This underground mine has been going since 1990. The portal is situated in the southwest wall about 100 ft. above the pit floor. This was originally a 1.5-million-tonne deposit grading 12.25% combined Pb and Zn. (4.9% Pb, 7.35% Zn) and 73 g per tonne Ag). As of Dec. 31, 1991, the reserve was 304,119 tonnes grading 4.65% Pb, 6.92% Zn and 62 g per tonne Ag. The deposit, a massive sulphide in a sedimentary host rock, will be exhausted by mid-year, if not earlier.
Dipping at 25deg, the ore is in two zones — the first, on the south side, measures 1,000×1,000×35 ft., while the north side is about half the areal extent and 20 ft thick. It is mined by mechanized room-and-pillar, incorporating a 3-boom Montabert and a 2-boom and 1-boom Atlas Copco drill. This method provides 60% of total production, with 40% from development headings. The recovery is 70%. Dilution is 12%. The underground has been providing 15% of total millfeed.
“In spite of the fact that it is dwarfed by the massiveness of the open pit operations, this is a good-sized underground mine operating at 2,400 tonnes per day,” said Colin Benner, President, Operations.
The ramp, developed with a shanty back, measures 12.5×16 ft. Average daily advance is 100 ft. “The ore can be unpredictable,” said Leo Hwozdyk, Mine Project Superintendent. Diamond drills probe every 30 ft. along the ramp to maintain proper headings in ore.
Dilution is also a key concern. “The orebody has gone through five stages of deformation,” said Hwozdyk. Each round is mapped for tight ore control.
Steffen Robertson and Kirsten (B.C.) Inc. has worked closely with Curragh in designing pillars.
The underground will be closed by mid-year, not because the entire orebody has been exhausted but because the Faro pit will then be needed as a tailings pond.
“From the outset this has been a successful mine from the point of view of safety, productivity and cost control. That’s directly attributable to Canadian Mine Developments (the mining contractor) and Leo himself,” Benner said.
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