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TitleOrigin of sulfur and crustal recycling of copper in polymetallic (Cu-Au-Co-Bi-U±Ag) iron-oxide-dominated systems in the Great Bear Magmatic Zone, NWT, Canada
AuthorAcosta-Gongora, P; Gleeson, S A; Samson, I M; Corriveau, L; Ootes, L; Jackson, S E; Taylor, B E; Girard, I
SourceMineralium Deposita 2017.,
Alt SeriesNatural Resources Canada, Contribution Series 20170088
Mediapaper; on-line; digital
File formatpdf
ProvinceNorthwest Territories; Nunavut
NTS86; 85M; 85N; 85O; 85P
AreaGreat Bear Magmatic Zone
Lat/Long WENS-120.0000 -114.0000 67.0000 63.0000
Subjectsgeochemistry; general geology; polymetallic ores; iron oxides; copper; gold; mineralization; magmatism; magmatic arcs; sulphur isotope ratios; copper geochemistry; source rocks; iron oxide copper-gold deposits (IOCG)
Illustrationslocation maps; photomicrographs
ProgramSouth Rae Province Bedrock/Surficial geology, GEM2: Geo-mapping for Energy and Minerals
AbstractThe Great Bear magmatic zone, in northwest Canada, contains numerous polymetallic deposits of the iron oxide copper-gold deposit (IOCG) family. The mineralization is hosted by the Treasure Lake Group and igneous rocks of the Great Bear arc, and was deposited concomitantly with the arc magmatism (ca. 1.88 to 1.87 Ga). In-situ ?34S (n=48) and ?65Cu (n=79) analyses were carried out on ore-related sulfides from a number of these deposits. The d34S values mainly vary between 0 and +5(permil), consistent with derivation of sulfur from the mantle. Lower d34S values (-7.7 to +1.4(permil)) from the Sue Dianne deposit may indicate SO2 disproportionation of a magmatic hydrothermal fluid. The delta65Cu values vary between -1.2 to -0.3(permil), and are lower than the igneous delta65Cu range of values (0.0±0.27(permil)). The S and Cu isotopic data are decoupled, which suggests that Cu (and possibly some S) was dissolved and remobilized from supracrustal rocks during early stages of alteration (e.g., sodic alteration), and then precipitated by lower temperature, more oxidizing fluids (e.g., Ca-Fe-K alteration). A limited fluid inclusion dataset and d13C and d18O values are also presented; the d18Ofluid values are consistent with a magmatic origin or a host-rock equilibrated meteoric water source, whereas the d13Cfluid values support a marine carbonate source. Combined, the S and Cu isotopic data indicate that while the emplacement of the Great Bear magmatic bodies may have driven fluid convection and may be the source of fluids and sulfur, metals such as Cu may have been recycled from crustal sources.
Summary(Plain Language Summary, not published)
This study comprises various Iron-Oxide-Copper-Gold mineral occurrences, prospects and deposits within the GBMZ zone, in the Canadian Northwest Territories. The investigation speculates about the source(s) of S and Cu obtained via in-situ isotopic analysis of chalcopyrite, pyrite and molybdenite and chalcopyrite, respectively,from these ore systems. The paper provides compelling evidence to support a magmatic source for S, and by the contrary, it suggests that Cu could have been leached from upper crustal litohologies. This manuscript is to our knowledge, the first of its kind to record the use of Cu isotopes applied to the origin of metals in IOCG deposits.