40Ar/39Ar dating of mica-bearing pyrite from thermally overprinted Archean gold deposits

Abstract

Research Article| May 01, 2006 40Ar/39Ar dating of mica-bearing pyrite from thermally overprinted Archean gold deposits David Phillips; David Phillips 1School of Earth Sciences, Predictive Mineral Discovery Cooperative Research Centre (pmd*CRC), University of Melbourne, Parkville, 3010 VIC, Australia Search for other works by this author on: GSW Google Scholar John M. Miller John M. Miller 1School of Earth Sciences, Predictive Mineral Discovery Cooperative Research Centre (pmd*CRC), University of Melbourne, Parkville, 3010 VIC, Australia Search for other works by this author on: GSW Google Scholar Author and Article Information David Phillips 1School of Earth Sciences, Predictive Mineral Discovery Cooperative Research Centre (pmd*CRC), University of Melbourne, Parkville, 3010 VIC, Australia John M. Miller 1School of Earth Sciences, Predictive Mineral Discovery Cooperative Research Centre (pmd*CRC), University of Melbourne, Parkville, 3010 VIC, Australia Publisher: Geological Society of America Received: 03 Oct 2005 Revision Received: 03 Jan 2006 Accepted: 05 Jan 2006 First Online: 09 Mar 2017 Online ISSN: 1943-2682 Print ISSN: 0091-7613 Geological Society of America Geology (2006) 34 (5): 397–400. https://doi.org/10.1130/G22298.1 Article history Received: 03 Oct 2005 Revision Received: 03 Jan 2006 Accepted: 05 Jan 2006 First Online: 09 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn Email Permissions Search Site Citation David Phillips, John M. Miller; 40Ar/39Ar dating of mica-bearing pyrite from thermally overprinted Archean gold deposits. Geology 2006;; 34 (5): 397–400. doi: https://doi.org/10.1130/G22298.1 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 SocietyGeology Search Advanced Search Abstract Previous studies have suggested that pyrite may armor potassium-bearing mineral inclusions from alteration-induced argon loss, thus providing improved 40Ar/39Ar age results. To test this hypothesis, matrix muscovite and pyrite crystals hosting muscovite inclusions were selected from two variably overprinted Yilgarn gold deposits (Western Australia) and analyzed by combined single crystal 40Ar/39Ar laser probe and "in vacuo" crushing methods. Pyrite grains from the ca. 2.60 Ga Mount Charlotte gold deposit exhibit evidence of minor argon loss, but give concordant high-temperature ages averaging 2594 ± 8 Ma (2σ), indistinguishable from previous age estimates. Matrix mica from the ca. 2.63 Ga Kanowna Belle gold deposit yielded a discordant age spectrum with all ages younger than 2.5 Ga, indicating substantial 40Ar* loss related to Middle Proterozoic thermal overprinting. Crushing and low-temperature heating experiments on pyrite crystals from Kanowna Belle produced anomalously old apparent ages (up to 7.0 Ga); however, in contrast to the matrix mica, total-gas pyrite ages generally approach or overlap the inferred time of gold mineralization. This behavior is attributed to diffusion of 40Ar* to internal muscovite-pyrite grain boundaries in response to the Middle Proterozoic thermal event, with limited external loss of argon. It is concluded that pyrite acts as a partially closed system for argon, but that the 40Ar/39Ar pyrite dating method has the potential to see through later thermal and/or alteration events and resolve controversial aspects of ore deposit geochronology. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.