GEOLOGICAL SETTINGS OF MASSIVE SULFIDE DEPOSITS IN THE BATHURST MINING CAMP: A SYNTHESIS

Of the 46 known massive sulfide deposits within the Ordovician Bathurst Supergroup, 32 are in the Tetagouche Group (TG) and 13 are in coeval rocks of the California Lake Group(CLG). Most are associated with the first felsic volcanic cycle in each group; nine are in second cycle rocks.

In the TG, the first cycle comprises quartz-feldspar crystal tuffs of the Nepisiguit Falls Formation. The deposits are all stratiform proximal type; they are mostly within chloritic mudrocks that are at or near the top of the formation, the so-called “Brunswick Horizon”, and are associated with oxide iron formation. However, at least one, the Heath Steele deposit, sits beneath quartz-feldspar porphyry in the lower part of this formation. The second cycle is dominated by aphyric rhyolites of the Flat Landing Brook Formation. Both stratiform proximal and stratabound replacive deposits occur in this formation and oxide iron formation is absent. The former type is relatively low in the formation, whereas the latter type is within fragmental felsic rocks that can occur anywhere in the pile.

In the CLG, the first volcanic cycle consists of feldspar-phyric tuffs and lavas of the Mount Brittain and Spruce Lake formations. Deposits in the Spruce Lake Formation occur in three stratigraphic positions. Deposits such as Caribou are stratiform proximal type and hosted by dark grey shales at or near the bottom of the formation. Deposits like Armstrong A are stratabound replacive type and occur within felsic volcanic rocks, whereas those like Orvan Brook are stratiform distal type and hosted by fine grained clastic rocks that overlie the volcanic pile. Deposits in the Mount Brittain Formation also occur at the base of and within the felsic volcanic pile. Regardless of host formation, the largest deposits in the CLG are at or near the base of the group.