{"title":"Fluid-rock sulfidation reactions control Au-Ag-Te-Bi precipitation in the Val-d’Or orogenic gold vein field (Abitibi subprovince, Canada)","authors":"","doi":"10.1007/s00126-024-01247-6","DOIUrl":null,"url":null,"abstract":"<h3>Abstract</h3> <p>The Val-d’Or vein field (VVF), located in the southern Abitibi subprovince (Québec, Canada), is host to ~ 47 Moz gold and is therefore an example of a greenstone-hosted orogenic gold district. Gold is contained in quartz-tourmaline-carbonate veins that cut As-poor intermediate to mafic volcanic and intrusive rocks, including dioritic, granodioritic and gabbroic sills, dikes, stocks, and plutons. Five investigated orebodies (Goldex, Triangle, Plug #4, Pascalis Gold Trend, Beaufor) host gold in vein- and wallrock-hosted pyrite-rich sulfide aggregates (> 95 vol%) that show a porous core domain (Py1), with abundant inclusions of carbonate, silicate, and Fe-oxides up to several tens of µm in size. A homogeneous pyrite rim domain (Py2) surrounds Py1 and contains most of the gold as native gold and polymetallic (Au-Ag-Te-Bi) inclusions, primarily calaverite and petzite. The two pyrites show different Au and As contents (Py1 = Au ≤ 30 ppm; As ≤ 67 ppm; Py2 = Au ≤ 1250 ppm; As ≤ 550 ppm). Pyrite shows a ubiquitous shift in δ<sup>34</sup>S values of up to + 3.0‰ from Py1 (δ<sup>34</sup>S = − 0.4‰ to 5.8‰, <em>n</em> = 32) to Py2 (δ<sup>34</sup>S = 0.0‰ to 6.3‰, <em>n</em> = 59) and records a small, slightly negative Δ<sup>33</sup>S signature between – 0.20‰ and 0.01‰. The δ<sup>34</sup>S shift suggests that removal of reduced sulfur species from auriferous hydrothermal fluids causes the formation of inclusion-hosted gold in Py2 by a decrease in the fluid sulfur fugacity (<em>f</em>S<sub>2</sub>) through wallrock sulfidation of Fe-oxides. The shift also correlates with locally enriched Co and Ni concentrations in Py1 (< 1 wt%), compared to lower, oscillatory zoned concentrations (< 0.1 wt%) in Py2, respectively, indicating an overall decrease in fluid oxygen fugacity (<em>f</em>O<sub>2</sub>). Contemporaneously, a decrease in fluid tellurium fugacity (<em>f</em>Te<sub>2</sub>) drives polymetallic inclusion-hosted gold formation in Py2, initially as calaverite followed by increasingly Ag-bearing petzite and hessite. The multiple sulfur isotopes and trace element compositions recorded in pyrite in the VVF indicate that a homogeneous fluid reservoir introduced gold-sulfide complexes. Even if considered a localized process at the ore-shoot scale, fluid-wallrock sulfidation reactions can lead to a coupled decrease in <em>f</em>S<sub>2</sub>, <em>f</em>O<sub>2</sub>, and <em>f</em>Te<sub>2</sub> of auriferous hydrothermal fluids in a greenstone-hosted As-poor gold district.</p>","PeriodicalId":18682,"journal":{"name":"Mineralium Deposita","volume":"22 1","pages":""},"PeriodicalIF":4.4000,"publicationDate":"2024-02-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":"0","resultStr":null,"platform":"Semanticscholar","paperid":null,"PeriodicalName":"Mineralium Deposita","FirstCategoryId":"89","ListUrlMain":"https://doi.org/10.1007/s00126-024-01247-6","RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":null,"EPubDate":"","PubModel":"","JCR":"Q1","JCRName":"GEOCHEMISTRY & GEOPHYSICS","Score":null,"Total":0}
引用次数: 0
Abstract
The Val-d’Or vein field (VVF), located in the southern Abitibi subprovince (Québec, Canada), is host to ~ 47 Moz gold and is therefore an example of a greenstone-hosted orogenic gold district. Gold is contained in quartz-tourmaline-carbonate veins that cut As-poor intermediate to mafic volcanic and intrusive rocks, including dioritic, granodioritic and gabbroic sills, dikes, stocks, and plutons. Five investigated orebodies (Goldex, Triangle, Plug #4, Pascalis Gold Trend, Beaufor) host gold in vein- and wallrock-hosted pyrite-rich sulfide aggregates (> 95 vol%) that show a porous core domain (Py1), with abundant inclusions of carbonate, silicate, and Fe-oxides up to several tens of µm in size. A homogeneous pyrite rim domain (Py2) surrounds Py1 and contains most of the gold as native gold and polymetallic (Au-Ag-Te-Bi) inclusions, primarily calaverite and petzite. The two pyrites show different Au and As contents (Py1 = Au ≤ 30 ppm; As ≤ 67 ppm; Py2 = Au ≤ 1250 ppm; As ≤ 550 ppm). Pyrite shows a ubiquitous shift in δ34S values of up to + 3.0‰ from Py1 (δ34S = − 0.4‰ to 5.8‰, n = 32) to Py2 (δ34S = 0.0‰ to 6.3‰, n = 59) and records a small, slightly negative Δ33S signature between – 0.20‰ and 0.01‰. The δ34S shift suggests that removal of reduced sulfur species from auriferous hydrothermal fluids causes the formation of inclusion-hosted gold in Py2 by a decrease in the fluid sulfur fugacity (fS2) through wallrock sulfidation of Fe-oxides. The shift also correlates with locally enriched Co and Ni concentrations in Py1 (< 1 wt%), compared to lower, oscillatory zoned concentrations (< 0.1 wt%) in Py2, respectively, indicating an overall decrease in fluid oxygen fugacity (fO2). Contemporaneously, a decrease in fluid tellurium fugacity (fTe2) drives polymetallic inclusion-hosted gold formation in Py2, initially as calaverite followed by increasingly Ag-bearing petzite and hessite. The multiple sulfur isotopes and trace element compositions recorded in pyrite in the VVF indicate that a homogeneous fluid reservoir introduced gold-sulfide complexes. Even if considered a localized process at the ore-shoot scale, fluid-wallrock sulfidation reactions can lead to a coupled decrease in fS2, fO2, and fTe2 of auriferous hydrothermal fluids in a greenstone-hosted As-poor gold district.
期刊介绍：
The journal Mineralium Deposita introduces new observations, principles, and interpretations from the field of economic geology, including nonmetallic mineral deposits, experimental and applied geochemistry, with emphasis on mineral deposits. It offers short and comprehensive articles, review papers, brief original papers, scientific discussions and news, as well as reports on meetings of importance to mineral research. The emphasis is on high-quality content and form for all articles and on international coverage of subject matter.
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