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In Situ 87Sr/86Sr of Scheelite and Calcite Reveals Proximal and Distal Fluid-Rock Interaction During Orogenic W-Au Mineralization, Otago Schist, New Zealand

2018; Volume: 113; Issue: 7 Linguagem: Inglês

10.5382/econgeo.2018.4603

1554-0774

Emma J. Scanlan, James M. Scott, Victoria J. Wilson, Claudine H. Stirling, Malcolm Reid, Petrus le Roux,

Geochemistry and Geologic Mapping

Research Article| November 01, 2018 In Situ 87Sr/86Sr of Scheelite and Calcite Reveals Proximal and Distal Fluid-Rock Interaction During Orogenic W-Au Mineralization, Otago Schist, New Zealand Emma J. Scanlan; Emma J. Scanlan 1 Department of Geology, University of Otago, Dunedin 9054, New Zealand †Corresponding author: e-mail, scanlan.emma@gmail.com Search for other works by this author on: GSW Google Scholar James M. Scott; James M. Scott 1 Department of Geology, University of Otago, Dunedin 9054, New Zealand Search for other works by this author on: GSW Google Scholar Victoria J. Wilson; Victoria J. Wilson 1 Department of Geology, University of Otago, Dunedin 9054, New Zealand Search for other works by this author on: GSW Google Scholar Claudine H. Stirling; Claudine H. Stirling 2 Department of Chemistry, University of Otago, Dunedin 9054, New Zealand3 Centre for Trace Element Analysis, University of Otago, Dunedin 9054, New Zealand Search for other works by this author on: GSW Google Scholar Malcolm R. Reid; Malcolm R. Reid 2 Department of Chemistry, University of Otago, Dunedin 9054, New Zealand3 Centre for Trace Element Analysis, University of Otago, Dunedin 9054, New Zealand Search for other works by this author on: GSW Google Scholar Petrus J. Le Roux Petrus J. Le Roux 4 Department of Geological Sciences, University of Cape Town, Rondebosch 7700, South Africa Search for other works by this author on: GSW Google Scholar Economic Geology (2018) 113 (7): 1571–1586. https://doi.org/10.5382/econgeo.2018.4603 Article history accepted: 02 Oct 2018 first online: 19 Nov 2018 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation Emma J. Scanlan, James M. Scott, Victoria J. Wilson, Claudine H. Stirling, Malcolm R. Reid, Petrus J. Le Roux; In Situ 87Sr/86Sr of Scheelite and Calcite Reveals Proximal and Distal Fluid-Rock Interaction During Orogenic W-Au Mineralization, Otago Schist, New Zealand. Economic Geology 2018;; 113 (7): 1571–1586. doi: https://doi.org/10.5382/econgeo.2018.4603 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 ability of hydrothermal scheelite (CaWO4) and calcite (CaCO3) to bind Sr in their crystal lattices makes them useful minerals for tracing fluid-rock interaction in mineralizing systems. Strontium isotopes in scheelite, calcite, and epidote were measured in situ by laser ablation-multicollector-inductively coupled plasma-mass spectrometry to assess the extent of fluid-rock interaction for Early Cretaceous orogenic W-Au mineralization occurring in the Otago Schist in New Zealand. Scheelite Sr isotope populations, regardless of their geographical location or stage of mineralization, are mostly homogeneous and cluster between 87Sr/86Sr = 0.7068 and 87Sr/86Sr = 0.7087, with the lack of Rb indicating that these are the initial ratios of the mineralizing fluids. However, while scheelite 87Sr/86Sr values in the Hyde-Macraes shear zone and the Barewood and Bendigo deposits overlap with the age-corrected 87Sr/86Sr values of the host Rakaia terrane, scheelite 87Sr/86Sr values in the Glenorchy and Waipori deposits are commonly more radiogenic than the age-corrected values of the host Caples terrane rocks. Because the Caples terrane was thrust over more radiogenic rocks before mineralization, the Caples terrane scheelite deposits are interpreted to result from fluids that were derived from deep crustal dehydration reactions within the underlying radiogenic and dominantly metaturbiditic (grayschist) Rakaia and Aspiring terranes, and/or that acquired their Sr isotope signatures from extensive fluid-rock reaction with Rakaia and Aspiring terrane grayschists during ascent. It is also evident that the scheelite 87Sr/86Sr values in the Caples terrane become more similar to the host-rock values with increasing incorporation of wall rock at the deposit scale as well as with increasing distance above the Caples-Rakaia/Aspiring terrane boundaries. Late-stage calcite that has replaced scheelite takes on the scheelite Sr isotope composition, whereas tabular calcite grains in the same samples have less radiogenic compositions that are equivalent to the wall rock. Application of in situ 87Sr/86Sr analysis therefore reveals that (1) there was extensive fluid-rock exchange of Sr during the formation of orogenic W-Au deposits, and (2) the Cretaceous W-Au mineralizing fluids in the Otago Schist were mobile over at least km-scale and probably greater vertical distances. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.