It has always been the lot of mining towns to watch ore reserves decline and hope some new feed will come along. When a mining town has been around as long as Flin Flon, that feeling will have come around several times before.
So it was in the early 1990s, when Hudson Bay Mining & Smelting, the Canadian presence of South African mining house
But the Triple 7 discovery has changed that picture substantially. Feasibility studies having given the deposit a thumbs-up, the company has now approved a $5-million capital investment to develop the deposit, which is about 700 metres south of the currently producing Callinan mine. Triple 7 makes a big difference to Hudson Bay’s reserves, adding 13.4 million tonnes of ore with better grades than the operation has been used to in recent years: 3.32% copper and 5.78% zinc, plus 2.7 grams gold and 38 grams silver per tonne.
The discovery of Triple 7 in November 1993 was a victory for HBM&S’s long-standing program of mine-scale geological exploration. The target was the main Flin Flon mine horizon, where it was crossed by a southeast-striking fold axis part way between the mined-out Flin Flon orebody and the Callinan.
A surface drilling program intersected the first massive sulphides at a depth of 1,200 metres, and the succeeding holes delineated two lenses of massive-sulphide mineralization — one mainly zinc-rich, with precious metal credits, and the other copper-rich.
The company’s interpretation is that the shallower, copper-rich lens is near the vent of the exhalative system that formed the deposit, and the deeper zinc-rich lens is a more distant zone. The vent feeders themselves appear in the footwall of the copper-rich lens as altered volcanic rocks with chlorite, biotite, muscovite, talc, magnetite and carbonate. Stringers of chalcopyrite and pyrrhotite extend from the footwall rocks into the copper-rich lens.
The metal zoning at Triple 7 resembles the zoning of the Flin Flon deposit, which also had copper-rich and zinc-rich zones. The Callinan, on the other hand, is lower-grade and mainly zinc-rich, and the mineralized zones carry fragmental volcanic material.
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