Abstract

Archean gold-bearing quartz vein systems constitute one of the most important classes of precious metal deposits; however, their origin remains controversial. Mantle, granitoid, meteoric water, and metamorphic related models do not resolve this controversy. New N and nitrogen isotope data on hydrothermal muscovite from six gold camps from the Late Archean Superior Province of Canada, and biotite from nine Au-mineralized locations from the Norseman-Wiluna greenstone belt, Western Australia, are reported. The majority of muscovites and biotites have N contents of 20–190 ppm and δ15N of 10‰–20‰, and 10–70 ppm and 10‰–24‰, respectively. The δ15N of the mantle is −5‰, and of granitoids is 0‰–10‰, both with generally low N contents; organic N is 0‰–10‰; meteoric water is 1.9‰–9.4‰; and metamorphic rocks are 3‰–18‰, increasing with higher grade. Accordingly, the data appear to rule out a mantle hypothesis, granitoid-related magmatic processes, or meteoric water for the deposits, but are consistent with ore fluids derived by metamorphic dehydration reactions.

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