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Geology and Isotope Geochemistry of the Wainaulo Cu-Au Porphyry Deposit, Namosi District, Fiji

2018; Volume: 113; Issue: 1 Linguagem: Inglês

10.5382/econgeo.2018.4546

1554-0774

E Orovan, David R. Cooke, Anthony C. Harris, Ben Ackerman, Erin Lawlis,

Mining and Resource Management

Research Article| January 01, 2018 Geology and Isotope Geochemistry of the Wainaulo Cu-Au Porphyry Deposit, Namosi District, Fiji Evan A. Orovan; Evan A. Orovan 1Transforming the Mining Value Chain, the Australia Research Council Industrial Transformation Research Hub, University of Tasmania2Centre of Excellence in Ore Deposits (CODES), University of Tasmania, Hobart, Tasmania 7001, Australia † Corresponding author: e-mail, Evan.Orovan@utas.edu.au Search for other works by this author on: GSW Google Scholar David R. Cooke; David R. Cooke 1Transforming the Mining Value Chain, the Australia Research Council Industrial Transformation Research Hub, University of Tasmania2Centre of Excellence in Ore Deposits (CODES), University of Tasmania, Hobart, Tasmania 7001, Australia Search for other works by this author on: GSW Google Scholar Anthony C. Harris; Anthony C. Harris 3Newcrest Mining Limited, 600 St. Kilda Road, Melbourne, Victoria 3004, Australia Search for other works by this author on: GSW Google Scholar Ben Ackerman; Ben Ackerman 3Newcrest Mining Limited, 600 St. Kilda Road, Melbourne, Victoria 3004, Australia Search for other works by this author on: GSW Google Scholar Erin Lawlis Erin Lawlis 2Centre of Excellence in Ore Deposits (CODES), University of Tasmania, Hobart, Tasmania 7001, Australia Search for other works by this author on: GSW Google Scholar Author and Article Information Evan A. Orovan 1Transforming the Mining Value Chain, the Australia Research Council Industrial Transformation Research Hub, University of Tasmania2Centre of Excellence in Ore Deposits (CODES), University of Tasmania, Hobart, Tasmania 7001, Australia David R. Cooke 1Transforming the Mining Value Chain, the Australia Research Council Industrial Transformation Research Hub, University of Tasmania2Centre of Excellence in Ore Deposits (CODES), University of Tasmania, Hobart, Tasmania 7001, Australia Anthony C. Harris 3Newcrest Mining Limited, 600 St. Kilda Road, Melbourne, Victoria 3004, Australia Ben Ackerman 3Newcrest Mining Limited, 600 St. Kilda Road, Melbourne, Victoria 3004, Australia Erin Lawlis 2Centre of Excellence in Ore Deposits (CODES), University of Tasmania, Hobart, Tasmania 7001, Australia † Corresponding author: e-mail, Evan.Orovan@utas.edu.au Publisher: Society of Economic Geologists First Online: 27 Feb 2018 Online Issn: 1554-0774 Print Issn: 0361-0128 © 2018 Society of Economic Geologists.Society of Economic Geologists Economic Geology (2018) 113 (1): 133–161. https://doi.org/10.5382/econgeo.2018.4546 Article history First Online: 27 Feb 2018 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation Evan A. Orovan, David R. Cooke, Anthony C. Harris, Ben Ackerman, Erin Lawlis; Geology and Isotope Geochemistry of the Wainaulo Cu-Au Porphyry Deposit, Namosi District, Fiji. Economic Geology 2018;; 113 (1): 133–161. doi: https://doi.org/10.5382/econgeo.2018.4546 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 late Miocene, calc-alkalic, Wainaulo Cu-Au porphyry deposit of the Namosi district, Fiji, hosts distinct styles of alteration and mineralization that overlapped to produce a substantial porphyry Cu-Au resource. The early stages produced medium-grade Cu, low-grade Au and concentric calc-potassic to propylitic alteration that is zoned around the early-stage diorite intrusions. Discrete zones of high-grade Cu and Au and calc-sodic alteration were then superimposed during the intrusion of the main-stage quartz diorites and the formation of quartz-sulfide and epidote-sulfide veins. As the magmatic-hydrothermal system waned, lower Cu and Au grades, with a weaker intensity of calc-sodic alteration and lower density of veins, were produced coincident with emplacement of subsequent quartz diorite intrusions. Late-stage anhydrite-pyrite veins and chlorite-illite alteration overprinted the quartz diorite intrusive complex. The final hydrothermal event consisted of argillic alteration that was concentrated in and around steeply dipping, ENE-trending shears. These structures appear to have controlled the emplacement of the quartz diorite complex and distribution of high-grade Cu-Au mineralization, suggesting they were active during the pre- and synmineralization stages.Stable and radiogenic isotopic data provide evidence for direct seawater contributions to the magmatic-hydrothermal system. Measured δ34Ssulfide (–5.0 to 3.8‰) and δ34Ssulfate (9.0–16.8‰) values are consistent with a predominantly magmatic source, whereas an elevated bulk sulfur composition (6.7‰) suggests mixing with an isotopically heavy fluid (e.g., seawater). Estimates of δDfluid derived from epidote (–9.1 to 11.3‰) and δ18Ofluid from epidote and anhydrite (–0.2 to 4.7‰) approach that of Vienna standard mean ocean water, and the initial Sr isotope ratios of epidote (0.70364–0.70378) suggest a component of seawater Sr ranging from 3.2 to 5.8%. These results are consistent with the inferred submarine paleogeographic setting and may explain the abundance of albite- and epidote-rich alteration assemblages at Wainaulo. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.