BASE METALS — Triple 7 secures Flin Flon’s future

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 Anglo American (AAUKV-Q), faced depletion of resources at its operating mines. Flin Flon, an established mining camp in Manitoba, has traditionally provided enough ore to keep the company going, but the company’s Trout Lake and Callinan mines, and the Ruttan mine in Leaf Rapids 220 km to the northeast, were not going to last forever.

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.