Geochemical and isotopic (Nd, O) data from Ordovician felsic plutonic and volcanic rocks of the Miramichi Highlands; petrogenetic and metallogenic implications for the Bathurst Mining Camp
Whalen Joseph, B.; Rogers Neil; van Staal Cees, R.; Longstaffe Frederick, J.; Jenner George, A.; Winchester John, A.
Canadian Journal of Earth Sciences = Revue Canadienne des Sciences de la Terre 35(3): 237-252
Middle Ordovician felsic magmatism contemporaneous with Bathurst Camp Pb-Zn volcanogenic massive sulphide (VMS) deposits consists of strongly altered volcanic to subvolcanic rocks, belonging to the Tetagouche Group, and relatively unaltered granitoid plutons, which are divided into northern, central, and southern groups within the Miramichi Highlands. Calc-alkalic felsic volcanic rocks and northern plus central plutons have epsilon (sub Nd) (T) values ranging from -8.2 to -1.9 and -4.0 to +0.3, respectively. They exhibit within-plate-type volcanic and transitional I- to A-type granite geochemical characteristics. Granitoid rock delta (super 18) O values range from +8.0 to +10.1 per mil. Published granitoid rock Pb isotopic compositions overlap unpublished galena data from Bathurst VMS deposits. Field, geochemical, and isotopic evidence indicate that these volcanic and granitoids rocks are consanguineous and mainly derived from Proterozoic or older infracrustal sources. Alkalic felsic volcanic rocks, and associated alkaline basaltic rocks, are more juvenile (epsilon (sub Nd) (T) = +3.2 to +4.2) and were possibly derived from slightly enriched mantle sources. Southern plutons exhibit continental arc-type features. The felsic magmatism and VMS deposits likely formed in an Okinawa-type back-arc basin developed from rifting the Early Ordovician Popelogan continental arc, of which the southern plutons are remnants. Correlations between pluton groups and volcanic formations indicate that felsic magmatism was erupted through and onto the Miramichi Group. As most felsic volcanic formations lack plutonic equivalents, the Tetagouche Group probably does not represent disrupted slices of an originally conformable stratigraphic section. This supports a model in which thrust slices juxtapose remnants of volcanic centres erupted at different locations within a back-arc basin.