Abstract

The Matagami mining camp in the northern Abitibi greenstone belt of Canada contains 19 known Archean volcanogenic massive sulfide (VMS) deposits, 11 of which have collectively produced 46.5 Mt of zinc-rich ore to date. The VMS deposits occur in three NW-SE– to WNW-ESE–oriented trends called the north flank, the south flank, and the west camp, which are composed of a felsic to mafic volcanic sequence cut by mafic to intermediate, synvolcanic sills and dikes. In order to clarify stratigraphic relationships between the south flank and the west camp, and to constrain the temporal evolution of volcanic activity, six new high-precision U-Pb zircon ages have been obtained. These data show that the total duration of felsic volcanism in the south flank was no more than 2.5 m.y., with the rhyolites extruded in the following order: Watson Rhyolite (2725.9 ± 0.8 Ma), Bracemac Rhyolite (2725.8 ± 0.7 Ma), Dumagami Rhyolite at the Persévérance Mine (2725.4 ± 0.7 Ma), and Dumagami Rhyolite in the Orchan West VMS deposit area (2724.9 ± 0.7 Ma). A hiatus in effusive volcanism is represented by the Key Tuffite, an important marker horizon in the camp. The hiatus probably lasted on the order of 0.5 m.y. Significantly, the rhyolite from the footwall of the Caber VMS deposit in the west camp has an age of 2725.9 ± 1.2 Ma, identical to that of the Watson Rhyolite on the south flank.

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