Magmatic-epithermal transitions in alkalic systems: Porgera gold deposit, Papua New Guinea

Abstract

Research Article| June 01, 1992 Magmatic-epithermal transitions in alkalic systems: Porgera gold deposit, Papua New Guinea Jeremy P. Richards Jeremy P. Richards 1Department of Geological Sciences, University of Saskatchewan, Saskatoon, Saskatchewan S7N 0W0, Canada Search for other works by this author on: GSW Google Scholar Author and Article Information Jeremy P. Richards 1Department of Geological Sciences, University of Saskatchewan, Saskatoon, Saskatchewan S7N 0W0, Canada Publisher: Geological Society of America First Online: 02 Jun 2017 Online ISSN: 1943-2682 Print ISSN: 0091-7613 Geological Society of America Geology (1992) 20 (6): 547–550. https://doi.org/10.1130/0091-7613(1992)020<0547:METIAS>2.3.CO;2 Article history First Online: 02 Jun 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation Jeremy P. Richards; Magmatic-epithermal transitions in alkalic systems: Porgera gold deposit, Papua New Guinea. Geology 1992;; 20 (6): 547–550. doi: https://doi.org/10.1130/0091-7613(1992)020<0547:METIAS>2.3.CO;2 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 Fluid-inclusion and stable isotope evidence are presented for the transition from magmatic-related mesothermal to meteoric water-dominated epithermal activity at the giant Porgera gold deposit, Papua New Guinea. Reflecting this transition, Au-Ag mineralization occurs in two main stages: disseminated auriferous pyrite in phyllic alteration zones (stage I); and fault-related, quartz-roscoelite-cemented hydrothermal breccias and veins carrying locally abundant free gold and Au-Ag-tellurides (stage II). The deposit is spatially and temporally associated with a late Miocene (6 Ma) epizonal intrusive complex emplaced in continental crust immediately prior to an early Pliocene continent- island-arc collision. Stage I ore formation was associated in part with fluids of magmatic origin (∼200 to >500 °C, 7 to 12 wt% and 31 to 58 wt% NaCl equivalent [eq.], δ18O = 8.1‰ to 9.4‰, δD = -50‰ to -32‰) and appears to represent a new type of Au-rich, Cu-poor, porphyritic, intrusion- related mineralization associated with volatile-rich, mafic, alkalic magmatism in a continent island-arc collision environment. Stage II vein-type mineralization crosscuts this earlier disseminated orebody; it formed at depths of 2 to 3 km from lower temperature, lower salinity, isotopically exchanged ground waters (∼180 °C, 3 to 10 eq. wt% NaCl, δ18O = 3.1‰ to 6.4‰, δD = -62‰ to -34‰), similar to fluids from other Au-Ag-Te epithermal deposits. Gold in these late veins was probably remobilized from deeper stage I-type mineralization, and stable isotope and textural evidence suggest that Au was deposited following tectonically induced fluid phase separation. This content is PDF only. Please click on the PDF icon to access. First Page Preview Close Modal You do not have access to this content, please speak to your institutional administrator if you feel you should have access.