1. Sulfur isotopic systematics of granitoids from southwestern New Brunswick, Canada: implications for magmatic-hydrothermal processes, redox conditions, and gold mineralization.
- Author
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Yang, Xue-Ming and Lentz, David
- Subjects
SULFUR isotopes ,SULFATES ,OXIDATION-reduction reaction ,IGNEOUS intrusions ,MAGNETIC susceptibility ,SEDIMENTARY rocks - Abstract
Bulk δS values, sulfur contents, and magnetic susceptibility were determined for 12 gold-related granitoid intrusions in southwestern New Brunswick, the Canadian Appalachians. The sulfur isotope compositions of sulfide minerals in some of the granitoid samples were also analyzed. This new dataset was used to characterize two distinctive groups of granitoids: (1) a Late Devonian granitic series (GS) and (2) a Late Silurian to Early Devonian granodioritic to monzogranitic series (GMS). The GS rocks have a large range in δS values of −7.1‰ to +13‰ with an average of 2.2 ± 5.0‰ (1σ), low bulk-S contents (33 to 7,710 ppm) and low magnetic susceptibility values (<10 SI), consistent with reduced ilmenite-series granites. The GMS rocks have a relatively narrower variation in δS values of −4.4‰ to +7.3‰ with an average 1.2 ± 2.9‰ but with larger ranges in bulk-S contents (45 to 11,100 ppm) and high magnetic susceptibility values (>10 SI), indicative of oxidized magnetite-series granites. The exceptions for the GMS rocks are the Lake George granodiorite and Tower Hill granite that display reduced characteristics, which may have resulted from interaction of the magmas forming these intrusions with graphite- or organic carbon-bearing sedimentary rocks. The bulk δS values and S contents of the GMS rocks are interpreted in terms of selective assimilation-fractional crystallization (SAFC) processes. Degassing processes may account for the δS values and S contents of some GS rocks. The characteristics of our sulfur isotope and abundance data suggest that mineralizing components S and Au in intrusion-related gold systems are dominantly derived from magmatic sources, although minor contaminants derived from country rocks are evident. In addition, the molar sulfate to sulfide ratio in a granitic rock sample can be calculated from the δS value of the whole-rock sample and the δS (or δS) value of sulfide and/or sulfate mineral in the sample on the basis of S-isotope fractionation and mass balance under the condition of magmatic equilibrium. This may be used to predict the speciation of sulfur in granitic rocks, which can be a potential exploration tool for intrusion-related gold systems. [ABSTRACT FROM AUTHOR]
- Published
- 2010
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