The petrogenesis of tin- and sulfide-lode mineralization at True Hill, southwestern New Brunswick

Abstract

The subvolcanic True Hill granite porphyry in southwestern New Brunswick is genetically related to the Beech Hill series of granites of Devono-Carboniferous age. Three True Hill (TH) greisenised granite porphyry cupolas host Bi-Sn-Mo-W mineralized zones that have similarities to the nearby W-Mo-Bi orebodies at Mount Pleasant (MP). Tin-bearing lodes (0.03 to 0.66 wt. % Sn) are developed along faults and fractures that cut both mineralized (Bi-Sn-Mo-W) and unmineralized True Hill granite porphyry and enclosing metasedimentary rocks of the Waweig Formation. Two types of mineralization are present, an early chlorite-sulfide assemblage (Stage 1) and a later hematite-phengite-cassiterite assemblage (Stage 2) that replaces, in part, the earlier Stage 1 assemblage. The composition of both Stage 1 and 2 assemblages in the lodes is controlled by the (i) host rock composition and (ii) the mineralizing hydrothermal fluids. The association of hematite and phengite with cassiterite mineralization is unique to this deposit. -from Authors