The timing of epigenetic gold mineralization on the Baie Verte Peninsula, Newfoundland, Canada: new evidence from Re–Os pyrite geochronology |
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| Authors: | Andrew Kerr and David Selby |
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| Institution: | (1) Geological Survey of Newfoundland and Labrador, Department of Natural Resources, PO Box 8700, St. John’s, NL, Canada, A1B 4J6;(2) Department of Earth Sciences, University of Durham, Durham, DH1 3LE, UK |
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| Abstract: | The absolute timing of epigenetic mineralization, including most types of gold deposits, is difficult to resolve due to the
absence of suitable minerals in veins and replacement zones. However, gold is commonly closely associated with pyrite and
arsenopyrite, which may be amenable to Re–Os geochronology, providing sufficient Re and Os are present within them. This short
paper outlines the use of this method to date two gold deposits in Newfoundland using pyrite. Although the Os contents of
the pyrites are extremely low (≪0.1 ppb), the Os is almost exclusively radiogenic 187Os, and data are amenable to model age calculations, as used in Re–Os molybdenite dating. The pyrites from these deposits
correspond to low-level highly radiogenic sulphides, as defined by other studies. The Stog’er Tight and Pine Cove gold deposits
yield mean Re–Os model ages of 411 ± 7 Ma (n = 4) and 420 ± 7 Ma (n = 5), respectively, which agree with isochron regression of 187Os against 187Re. The Re–Os age for Stog’er Tight is within uncertainty of a previous U–Pb age from ‘hydrothermal’ zircon (420 ± 5 Ma) in
spatially related alteration. A latest Silurian–earliest Devonian age for the mineralization is consistent with indirect age
constraints from some other gold deposits in central Newfoundland and suggests a broad temporal link to the mid-Silurian Salinic
Orogeny. However, the gold mineralization appears to be younger than most plutonic activity associated with this event. The
results illustrate the potential value of Re–Os pyrite geochronology in understanding the temporal framework of epigenetic
mineralization, especially if future improvements in analytical precision and reductions in procedural blanks allow wider
application to material with similarly low Re and Os concentrations. |
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