Petrogenesis of the low sulfidation gold mineralization in the Williams Brook area, Tobique-Chaleur Zone, New Brunswick

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University of New Brunswick


Gold mineralization in the Williams Brook area occurs within the Siluro-Devonian bimodal volcano-sedimentary rocks of the Tobique-Chaleur Zone in northern New Brunswick (Wapske Formation). Geotectonic discrimination diagrams show A-type signatures. Such compositions indicate a transpressive tectonic setting and suggest that oblique convergence of Gondwana and Laurentia as the driving force for basin formation and coeval magma generation. Gold occurs in two types of mineralization, which show slightly different Ar-Ar (muscovite) ages: 412 Ma from altered rhyolites and 408 Ma from quartz veins. This younger age is supported by similar U-Pb zircon ages determined from the rhyolite host rocks. A -414 Ma age of muscovite from a foliation fabric suggests that there is a structural control to the gold mineralization. Sphalerite, pyrite, and galena are the main hypogene sulfides associated with the gold mineralization; however, supergene oxyhydroxides such as goethite and hematite are also common. Stable isotopic (0, H, S) and radiogenic Pb evidence suggest fluids and metals are from a magmatic source. Fluid inclusions and stable isotope geothermometers suggest gold deposition was at an approximate temperature of 200°C, which is interpreted to be via mixing with meteoric waters. Evidence from different scales determined in this study support the theory that the study area is part of a low sulfidation epithermal style mineralizing system, thus making the Tobique-Chaleur Zone prospective for this style of mineralization.