Chronology of gold mineralization in the Sierra Nevada Foothills from 40Ar/39Ar dating of mariposite
Cameron A. Snow 1,2
Dennis K. Bird 1
James Metcalf 1,3
Michael McWilliams 1,4
1. Department of Geological and Environmental Sciences, Stanford University, Stanford, CA 94305
2. Exploration and Production Technology, Apache Corporation, Houston, TX 77056
3. Department of Earth Sciences, Syracuse University, Syracuse, NY 13244
4. John de Laeter Centre of Mass Spectrometry, Curtin University, Perth, Australia
ABSTRACT
Mariposite (Cr-rich muscovite) formed during metasomatic replacement of serpentinite yield 40Ar/39Ar ages demonstrating that gold-quartz-carbonate mineralization in the Sierra Nevada Foothills occurred as early as 152 Ma and continued until at least 122 Ma. The earliest gold mineralization is found in the Grass Valley District; mineralization subsequently migrated southward along the Melones Fault Zone, forming the Mother Lode Gold Belt. These ages correspond with a lull in Sierra Nevada plutonism and with periods of ductile deformation along the Melones and related fault zones. Our data suggest that gold-quartz-carbonate mineralization was not associated with Sierra Nevada plutonism, but instead was related to changes in plate dynamics, and generation and migration of CO2-rich ore-forming metamorphic fluids. In this model, gold mineralization was produced by heating of the lower crust within the structural mélange of the Sierra Nevada as a response to an increase in dip of the subducting slab and oceanward migration of the saw-tooth thermal structure.
Published in International Geology Review, Vol. 50, 2008, p.1-16.