High-Sulfidation Epithermal Pyrite-Hosted Au (Ag-Cu) Ore Formation by Condensed Magmatic Vapors on Sangihe Island, Indonesia

Research Article| September 01, 2014 High-Sulfidation Epithermal Pyrite-Hosted Au (Ag-Cu) Ore Formation by Condensed Magmatic Vapors on Sangihe Island, Indonesia* Julia King; Julia King † 1Department of Earth and Planetary Sciences, McGill University, 3450 University Street, Montréal, Québec, Canada H3A 0E8 †Corresponding author: e-mail, julia.j.king@gmail.com Search for other works by this author on: GSW Google Scholar A.E. Williams-Jones; A.E. Williams-Jones 1Department of Earth and Planetary Sciences, McGill University, 3450 University Street, Montréal, Québec, Canada H3A 0E8 Search for other works by this author on: GSW Google Scholar Vincent van Hinsberg; Vincent van Hinsberg 1Department of Earth and Planetary Sciences, McGill University, 3450 University Street, Montréal, Québec, Canada H3A 0E8 Search for other works by this author on: GSW Google Scholar Glyn Williams-Jones Glyn Williams-Jones 2Department of Earth Sciences, Simon Fraser University, 8888 University Drive, Burnaby, British Columbia, Canada V5A 1S6 Search for other works by this author on: GSW Google Scholar Author and Article Information Julia King † 1Department of Earth and Planetary Sciences, McGill University, 3450 University Street, Montréal, Québec, Canada H3A 0E8 A.E. Williams-Jones 1Department of Earth and Planetary Sciences, McGill University, 3450 University Street, Montréal, Québec, Canada H3A 0E8 Vincent van Hinsberg 1Department of Earth and Planetary Sciences, McGill University, 3450 University Street, Montréal, Québec, Canada H3A 0E8 Glyn Williams-Jones 2Department of Earth Sciences, Simon Fraser University, 8888 University Drive, Burnaby, British Columbia, Canada V5A 1S6 †Corresponding author: e-mail, julia.j.king@gmail.com Publisher: Society of Economic Geologists Revision Received: 31 Mar 2013 Accepted: 09 Dec 2013 First Online: 09 Mar 2017 Online ISSN: 1554-0774 Print ISSN: 0361-0128 © 2014 Society of Economic Geologists. Economic Geology (2014) 109 (6): 1705–1733. https://doi.org/10.2113/econgeo.109.6.1705 Article history Revision Received: 31 Mar 2013 Accepted: 09 Dec 2013 First Online: 09 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn Email Permissions Search Site Citation Julia King, A.E. Williams-Jones, Vincent van Hinsberg, Glyn Williams-Jones; High-Sulfidation Epithermal Pyrite-Hosted Au (Ag-Cu) Ore Formation by Condensed Magmatic Vapors on Sangihe Island, Indonesia. Economic Geology 2014;; 109 (6): 1705–1733. doi: https://doi.org/10.2113/econgeo.109.6.1705 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 Although gold in high-sulfidation epithermal deposits generally occurs as the native metal or electrum, in some deposits, a significant proportion of the gold is hosted in pyrite. Here we use a combination of petrography, whole-rock geochemistry, pyrite chemistry, crystallography, and phase stability relationships to determine how gold was transported and incorporated into pyrite in two relatively young high-sulfidation epithermal deposits, where the gold occurs almost exclusively in solid solution or as nanoparticles in pyrite.The genetically related Bawone and Binebase Au (Cu-Ag) deposits, located 1 km apart on the volcanic island of Sangihe, northeastern Indonesia, are hosted by andesitic volcaniclastic rocks that were altered to a proximal advanced argillic association of quartz + pyrite (py I) + pyrophyllite + natroalunite + alunite + dickite + kaolinite and a more distal intermediate argillic association of quartz + pyrite (py I) + kaolinite + dickite + illite. The economic mineralization takes the form of multiple generations of auriferous pyrite, the first of which, pyrite I (py I), developed during advanced argillic alteration. Mass balance calculations show that all elements were mobile with the exception of Nb, Ti, some rare earth elements, and possibly Al.The highest gold concentration is in pyrite II (py II), which occurs in veins that cut pyrite I. This drusy variety of pyrite is characterized by complex growth and sector zoning, and contains as much as 6.0 wt % Cu. The elevated Cu concentrations correlate positively with Au and As concentrations, whereas the Ag concentration correlates strongly with Au but not Cu. Later barite-enargite mineralization exploited py II veins and vugs, and significant concentrations of Ag and Au are hosted by enargite, although the Au concentration in enargite is lower than in py II or py I.A model is presented in which the fluid responsible for advanced argillic and intermediate argillic alteration and associated stage 1 gold mineralization was a condensed magmatic vapor derived from an oxidized magma. The gold and other metals were transported as hydrated species that ascended through the volcanic pile via fractures and zones of enhanced permeability to a depth between 900 and 1300 m, where the vapor condensed at a temperature between 250 and 340°C to form an acidic liquid with a pH of ~2.5; fo2 ranged up to four log units above the hematite-magnetite buffer. Interaction of this liquid with the host andesites caused advanced argillic and intermediate argillic alteration, including sulfidation of mafic minerals to form py I. During crystallization of py I, Au, Cu and Ag were adsorbed onto the surface of the pyrite and deposited as nanoparticles, or were incorporated in the pyrite structure. Adsorption of Au, Cu, and Ag from the condensed vapor reached a peak during the crystallization of vein-hosted py II, and the uptake of Ag and minor Au continued during later crystallization of enargite. From the distribution of metals among growth and sector zones in py II, incorporation of gold and other metals appears to have been maximized when physicochemical conditions were relatively stable. This is in contrast to the requirement for native gold precipitation, namely that physicochemical gradients be steep to ensure supersaturation of gold in the ore fluid. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

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