Origin of sulfur and crustal recycling of copper in polymetallic (Cu-Au-Co-Bi-U ± Ag) iron-oxide-dominated systems of the Great Bear Magmatic Zone, NWT, Canada

• Published in: Mineralium deposita 2018-03, Vol.53 (3), p.353-376
• Main Authors: Acosta-Góngora, P., Gleeson, S.A., Samson, I.M., Corriveau, L., Ootes, L., Jackson, S.E., Taylor, B.E., Girard, I.
• Format: Article
• Language: English
• Subjects: Arc deposition; Breccia; Carbonates; Cobalt; Convection; Copper; Disproportionation; Earth and Environmental Science; Earth Sciences; Fluids; Geology; Gold; Heavy metals; Igneous rocks; Iron; Iron oxides; Isotopes; Lakes; Low temperature; Magma; Metals; Meteoric water; Mineral Resources; Mineralization; Mineralogy; Oxidation; Rock; Silver; Sulfur; Sulfur dioxide; Sulphur
• ISSN: 0026-4598; 1432-1866
• DOI: 10.1007/s00126-017-0736-6

The Great Bear Magmatic Zone, in northwest Canada, contains numerous polymetallic mineral occurrences, prospects, and 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 δ 34 S ( n  = 48) and δ 65 Cu ( n  = 79) analyses were carried out on ore-related sulfides from a number of these systems. The δ 34 S values mainly vary between 0 and +5‰, consistent with derivation of sulfur from the mantle. Lower δ 34 S values (−7.7 to +1.4‰) from the Sue-Dianne breccia may indicate SO 2 disproportionation of a magmatic hydrothermal fluid. The δ 65 Cu values vary between −1.2 and −0.3‰, and are lower than the igneous δ 65 Cu range of values (0.0 ± 0.27‰). 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 δ 13 C and δ 18 O values are also presented. The δ 18 O fluid values are consistent with a magmatic origin or a host-rock equilibrated meteoric water source, whereas the δ 13 C fluid 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 could have been recycled from crustal sources.