The Baie D'Alembert showing, an example of base-metal mineralization in mafic to intermediate volcanic rocks of the Blake River Group, Abitibi Greenstone Belt, Quebec

Abstract

The Archean Blake River Group contains numerous volcanogenic massive sulphide (VMS) deposits, many of which are spatially associated with rhyolite domes and related volcaniclastic rocks. Therefore, most base-metal exploration in the Blake River Group has historically focused on rhyolite-rich areas. Yet the rhyolite-poor sectors may have VMS potential as well, and to illustrate this point, a recently discovered Cu-Zn showing, found in mafic to intermediate volcanic rocks, is described. Mineralization in the Baie D'Alembert showing occurs at, and stratigraphically below, the contact between aphyric lavas (transitional basalts and basaltic andesites) and a plagioclase-rich volcaniclastic unit known as the D'Alembert tuff (calc-alkaline basaltic andesites and andesites). The sulphide minerals are found within a marker horizon at this contact, and as stringers and impregnations below it. Mineralization formed in part by sub-seafloor replacement; several mafic to intermediate volcaniclastic units from the periphery of the Blake River Group could represent good hosts for replacement-style VMS mineralization.