Portal de Periódicos da CAPES

Application of U-Th-Pb Phosphate Geochronology to Young Orogenic Gold Deposits: New Age Constraints on the Formation of the Grass Valley Gold District, Sierra Nevada Foothills Province, California

2015; Volume: 110; Issue: 5 Linguagem: Inglês

10.2113/econgeo.110.5.1313

1554-0774

Ryan D. Taylor, Richard J. Goldfarb, Thomas Monecke, Ian R. Fletcher, Michael A. Cosca, Nigel M. Kelly,

earthquake and tectonic studies

Research Article| August 01, 2015 Application of U-Th-Pb Phosphate Geochronology to Young Orogenic Gold Deposits: New Age Constraints on the Formation of the Grass Valley Gold District, Sierra Nevada Foothills Province, California Ryan D. Taylor; Ryan D. Taylor † 1U.S. Geological Survey, Denver Federal Center, Denver, CO 802252Department of Geology and Geological Engineering, Colorado School of Mines, 1516 Illinois Street, Golden, CO 80401 †Corresponding author: e-mail, rtaylor@usgs.gov Search for other works by this author on: GSW Google Scholar Richard J. Goldfarb; Richard J. Goldfarb 1U.S. Geological Survey, Denver Federal Center, Denver, CO 802253State Key Laboratory of Geological Processes and Mineral Resources, China University of Geosciences, Beijing 100083, China4Centre for Exploration Targeting, School of Earth and Geographical Sciences, University of Western Australia, Crawley, WA 6009, Australia Search for other works by this author on: GSW Google Scholar Thomas Monecke; Thomas Monecke 2Department of Geology and Geological Engineering, Colorado School of Mines, 1516 Illinois Street, Golden, CO 80401 Search for other works by this author on: GSW Google Scholar Ian R. Fletcher; Ian R. Fletcher 5Department of Applied Geology, Curtin University, Kent Street, Bentley, WA 6102, Australia Search for other works by this author on: GSW Google Scholar Michael A. Cosca; Michael A. Cosca 1U.S. Geological Survey, Denver Federal Center, Denver, CO 80225 Search for other works by this author on: GSW Google Scholar Nigel M. Kelly Nigel M. Kelly 6Department of Geological Sciences, University of Colorado at Boulder, 2200 Colorado Ave UCB 399, Boulder, CO 80309 Search for other works by this author on: GSW Google Scholar Author and Article Information Ryan D. Taylor † 1U.S. Geological Survey, Denver Federal Center, Denver, CO 802252Department of Geology and Geological Engineering, Colorado School of Mines, 1516 Illinois Street, Golden, CO 80401 Richard J. Goldfarb 1U.S. Geological Survey, Denver Federal Center, Denver, CO 802253State Key Laboratory of Geological Processes and Mineral Resources, China University of Geosciences, Beijing 100083, China4Centre for Exploration Targeting, School of Earth and Geographical Sciences, University of Western Australia, Crawley, WA 6009, Australia Thomas Monecke 2Department of Geology and Geological Engineering, Colorado School of Mines, 1516 Illinois Street, Golden, CO 80401 Ian R. Fletcher 5Department of Applied Geology, Curtin University, Kent Street, Bentley, WA 6102, Australia Michael A. Cosca 1U.S. Geological Survey, Denver Federal Center, Denver, CO 80225 Nigel M. Kelly 6Department of Geological Sciences, University of Colorado at Boulder, 2200 Colorado Ave UCB 399, Boulder, CO 80309 †Corresponding author: e-mail, rtaylor@usgs.gov Publisher: Society of Economic Geologists Received: 21 Jul 2014 Accepted: 14 Jan 2015 First Online: 09 Mar 2017 Online ISSN: 1554-0774 Print ISSN: 0361-0128 © 2015 Society of Economic Geologists. Economic Geology (2015) 110 (5): 1313–1337. https://doi.org/10.2113/econgeo.110.5.1313 Article history Received: 21 Jul 2014 Accepted: 14 Jan 2015 First Online: 09 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn Email Permissions Search Site Citation Ryan D. Taylor, Richard J. Goldfarb, Thomas Monecke, Ian R. Fletcher, Michael A. Cosca, Nigel M. Kelly; Application of U-Th-Pb Phosphate Geochronology to Young Orogenic Gold Deposits: New Age Constraints on the Formation of the Grass Valley Gold District, Sierra Nevada Foothills Province, California. Economic Geology 2015;; 110 (5): 1313–1337. doi: https://doi.org/10.2113/econgeo.110.5.1313 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyEconomic Geology Search Advanced Search Abstract The Grass Valley orogenic gold district in the Sierra Nevada foothills province, central California, the largest historic gold producer of the North American Cordillera, comprises both steeply dipping E-W veins located along lithologic contacts in accreted ca. 300 and 200 Ma oceanic rocks and shallowly dipping N-S veins hosted by the Grass Valley granodiorite; the latter have yielded about 70% of the 13 million ounces of historic lode gold production in the district. The oceanic host rocks were accreted to the western margin of North America between 200 and 170 Ma, metamorphosed to greenschist and amphibolite facies, and uplifted between 175 and 160 Ma. Large-scale magmatism in the Sierra Nevada occurred between 170 to 140 Ma and 120 to 80 Ma, with the Grass Valley granodiorite being emplaced during the older episode of magmatism.Uranium-lead isotope dating of hydrothermal xenotime yielded the first absolute age of 162 ± 5 Ma for the economically more significant N-S veins. The vein-hosted xenotime, as well as associated monazite, are unequivocally of hydrothermal origin as indicated by textural and chemical characteristics, including grain shape, lack of truncated growth banding, lack of an Eu anomaly, and low U and Th concentrations. Furthermore, the crack-seal texture of the veins, with abundant wall-rock slivers, suggests their formation as a result of episodic fluid flow possibly related to reoccurring seismic events, rather than a period of fluid exsolution from an evolving magma. The N-S veins are temporally distinct from a younger 153 to 151 Ma gold event that was previously reported for the E-W veins.Overlapping U-Pb zircon (159.9 ± 2.2 Ma) and 40Ar/39Ar biotite and hornblende (159.7 ± 0.6–161.9 ± 1.4 Ma) ages and geothermobarometric calculations indicate that the Grass Valley granodiorite was emplaced at ca. 160 Ma at elevated temperatures (~800°C) within approximately 3 km of the paleosurface and rapidly cooled to the ambient temperature of the surrounding country rocks (<300°C). The age of the granodiorite is indistinguishable from that of the N-S veins, as recorded by the U-Pb age of xenotime in those veins. Consequently, the N-S veins must have formed between 162 and 157 Ma, the maximum permissive age of magma emplacement and the youngest permissive xenotime U-Pb age, respectively, during an E- to ENE-directed compressional regime. The geochemistry of the Grass Valley granodiorite is consistent with it being the product of arc magmatism. It served as a receptive host for mineralization, but it is has no direct genetic relationship to gold mineralization. Initial uplift of the intrusive mass correlates with the initial voluminous fluid flow event and vein formation at depths of no greater than 3 km. The E-W gold-bearing veins hosted within greenschist-facies country rocks adjacent to the intrusion formed during a second hydrothermal event 5 to 10 million years later than the magmatism and were contemporaneous with a shift to transtensional deformation denoted by sinistral strike-slip faulting. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.