Research Article| March 01, 2015 Gold Refining by Bismuth Melts in the Iron Oxide-Dominated NICO Au-Co-Bi (±Cu±W) Deposit, NWT, Canada P. Acosta-Góngora; P. Acosta-Góngora † 1Department of Earth and Atmospheric Sciences, University of Alberta, Edmonton, Alberta, Canada T6G 2E3 †Corresponding author: e-mail, Pedro.AcostaGongora@NRCan-RNCan.gc.ca Search for other works by this author on: GSW Google Scholar S. A. Gleeson; S. A. Gleeson 1Department of Earth and Atmospheric Sciences, University of Alberta, Edmonton, Alberta, Canada T6G 2E3 Search for other works by this author on: GSW Google Scholar I. M. Samson; I. M. Samson 2Department of Earth and Environmental Sciences, University of Windsor, Windsor, Ontario, Canada N9B 3P4 Search for other works by this author on: GSW Google Scholar L. Ootes; L. Ootes 3Northwest Territories Geoscience Office, Yellowknife, Northwest Territories, Canada X1A 2L9 Search for other works by this author on: GSW Google Scholar L. Corriveau L. Corriveau 4Geological Survey of Canada, 490 rue de la Couronne, Québec, QC, Canada G1K 9A9 Search for other works by this author on: GSW Google Scholar Author and Article Information P. Acosta-Góngora † 1Department of Earth and Atmospheric Sciences, University of Alberta, Edmonton, Alberta, Canada T6G 2E3 S. A. Gleeson 1Department of Earth and Atmospheric Sciences, University of Alberta, Edmonton, Alberta, Canada T6G 2E3 I. M. Samson 2Department of Earth and Environmental Sciences, University of Windsor, Windsor, Ontario, Canada N9B 3P4 L. Ootes 3Northwest Territories Geoscience Office, Yellowknife, Northwest Territories, Canada X1A 2L9 L. Corriveau 4Geological Survey of Canada, 490 rue de la Couronne, Québec, QC, Canada G1K 9A9 †Corresponding author: e-mail, Pedro.AcostaGongora@NRCan-RNCan.gc.ca Publisher: Society of Economic Geologists Received: 16 Dec 2013 Accepted: 29 Jul 2014 First Online: 09 Mar 2017 Online ISSN: 1554-0774 Print ISSN: 0361-0128 © 2015 Society of Economic Geologists. Economic Geology (2015) 110 (2): 291–314. https://doi.org/10.2113/econgeo.110.2.291 Article history Received: 16 Dec 2013 Accepted: 29 Jul 2014 First Online: 09 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation P. Acosta-Góngora, S. A. Gleeson, I. M. Samson, L. Ootes, L. Corriveau; Gold Refining by Bismuth Melts in the Iron Oxide-Dominated NICO Au-Co-Bi (±Cu±W) Deposit, NWT, Canada. Economic Geology 2015;; 110 (2): 291–314. doi: https://doi.org/10.2113/econgeo.110.2.291 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 NICO Au-Co-Bi(±Cu±W) deposit is located in the Great Bear magmatic zone, NWT, Canada, where numerous polymetallic, iron oxide-dominated mineralized systems have been recognized. Petrographic, electron microprobe analysis (EMPA), and laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) studies of host-rock alteration and ore mineralogy, together with sulfarsenide geothermometry, have been carried out to constrain the nature of alteration and/or mineralization assemblages in this deposit.Metasedimentary rocks of the Treasure Lake Group host NICO and are pervasively altered to an assemblage of ferrohornblende I + actinolite I + biotite I + magnetite I ± orthoclase, which is cut by barren veins composed of quartz ± ferrohornblende-orthoclase-calcite (Set 1). These alteration events are overprinted by metasomatic prograde and retrograde mineralized assemblages and both brittle and ductile deformation accompanied the metasomatism. The prograde assemblage (>400°C) consists of cobaltite, Co-rich loellingite, and Co-rich arsenopyrite (stage I), magnetite II, ferrohornblende II, actinolite II, biotite II, pyrite, and minor scheelite and orthoclase. The earliest retrograde mineralization consists of arsenopyrite (stages II and III), which contains variable amounts of Co, together with native Bi (±bismuthinite) and Au, with lesser magnetite, marcasite, pyrite, hastingsite, and minor quartz. The preservation of solidified native Bi droplets suggests a temperature range of 270° to <400°C for precipitation of this assemblage. The final stage of retrograde mineralization consists of a chalcopyrite-bismuthinite-hematite-chlorite assemblage, together with hastingsite ± emplectite, which formed at temperatures of less than 270°C.Textural and trace element evidence indicates that the Au and Bi present within arsenides and sulfarsenides in the NICO system resulted from the initial partitioning of structurally bound Au and/or "invisible" (nanometer-sized particles) of Au and Bi into the prograde sulfarsenide and arsenide phases, which contain up to 81 ppm Au. The Au and Bi were remobilized following retrograde alteration of those minerals to arsenopyrite II. Molten Bi droplets are interpreted to have scavenged Au insitu, resulting in the formation of the Bi-Au inclusions observed in arsenopyrite II. The second mechanism of gold refining is explained by the occurrence of contemporaneous Bi (±Te) melt and hydrothermal fluids that also could have fractionated gold during transport in solution and deposited it in fractures, interstitially to earlier mineral grains, and as disseminations within Ca-Fe-amphibole-magnetite-biotite-altered rocks. Overall, the gold upgrading at NICO is consistent with the liquid bismuth collector model, suggesting that this process was an important control on gold concentration in this and potentially other Au-Bi-Te-Fe-As-S-rich iron oxide-copper-gold (IOCG) deposits. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.
