Multi-stage orogenic gold mineralization of the Pine Lake greenstone belt: evidence from the Seabee Gold Operation, Trans-Hudson orogen, northern Saskatchewan

The Seabee Gold Operation, located within northern Saskatchewan, Canada, hosts the Seabee and Santoy deposits, as well as important exploration targets, including the Fisher property. These properties occupy the Pine Lake greenstone belt, hosted within the Glennie domain of the larger Paleoproterozoic Trans-Hudson orogen. At the Seabee Gold Operation, auriferous quartz veins are hosted within shear zones, such as the Santoy shear system, that are focussed along basalt-intrusion contacts, extending south onto the Fisher property. The systematics of gold mineralization and relationships therein between the properties along the Santoy shear system are largely undefined, including the role that intrusions play during ore genesis. In this study, mineralized samples from the Santoy Mine Complex and Fisher property along the Santoy shear system were studied to compare the lithological, mineralogical, and mineralization characteristics associated with sulfide-gold mineralization, in terms of associated major, minor, and trace-element variations within alteration and sulfide minerals, respectively. This study also provides new Re-Os and U-Pb geochronological data to constrain Seabee Gold Operation events relative to the Glennie domain and Trans-Hudson orogen. The mineralized host rocks primarily comprise lower greenschist to lower amphibolite-grade sheared metabasalt to chlorite-hornblende-biotite ± garnet schist, with intrusive rocks dominated by granodiorite and tonalite. Analogous quartz vein generations (V1-V3) cut these lithologies and yield synchronous alteration assemblages and mineralization. This includes i) syn-late D3 distal sericite-biotite-chlorite-clinozoisite ± albite, titanite to vein-adjacent to coarse-grained diopside-K-feldspar-albite-actinolite ± apatite, titanite calc-silicate alteration, associated with main-stage Py3a, 3b-Cpy2-Po1-Au (syn-late D3) mineralization; ii) remobilized, fracture-filling Py4-Po2-Cpy3-Au-Tbi-Ttd (late D3) mineralization within the calc-silicate assemblage; and iii) and early colloform Py2 (late-D2 to early-syn-D3) and intrusion-hosted, inclusion-rich Py1 (Pre-D1). Microprobe analyses reveal similar mineralogical trends between Fisher and Santoy alteration minerals, typical of orogenic gold systems. Empirical geothermobarometric calculations of gold-associated vein-adjacent and vein-hosted chlorite and biotite exhibit orogenic-style formation conditions (~320-330 °C, 3 kbar, ~9 km depth). In conjunction with microprobe analyses, petrographic and trace-element analyses on synchronous Fisher and Santoy sulfide phases further indicate that hydrothermal processes between the properties were a consequence of an interconnected, multi-stage gold-mineralizing system, dominated by orogenic processes. These analogous hydrothermal events along the Santoy shear system have been progressively overprinted and include the i) influx of polymetallic magmatic-hydrothermal fluids pre-D1 (Py1); ii) late D2 to early-syn D3 injection of metamorphic fluids during diachronous metamorphism at different levels in the crust and the onset of orogenic-style mineralization (Py2); iii) influx of metamorphic fluids syn-late D3 from diachronous metamorphism at different levels in the crust, generating main-stage mineralization, including V2a and V2b veins, distal- to vein-adjacent alteration, and Py3a, 3b-Cpy2-Po1-native Au mineralization; and iv) continuous late D3 remobilization from diachronous metamorphism or devolatilization during uplift of the crust, resulting in the deposition of fracture-filling Py4-Po2-Cpy3-native Au-Tbi-Ttd mineralization, which occurred under more intensity at Santoy. The characteristics and relative timing of these mineralization stages, as well as the determined Re-Os age of ca. 1764 Ma for gold associated Fisher highly radiogenic Py4, agree with other gold-mineralizing systems in the Trans-Hudson orogen, including the ca. 1756 Ma U-Pb age of gold-associated hydrothermal titanite previously identified for Santoy. Additionally, this proxy age for orogenic mineralization is outside of analytical uncertainty (2s) of the weighted mean 207Pb/206Pb age for a granodiorite intrusion at Mac south (ca. 1882 Ma), eliminating magmatic fluids as a source for gold during syn-late-D3 mineralization. This study also presents the first direct weighted mean 207Pb/206Pb zircon age for Assemblage A (Footprint tuff) at 1885.58 ± 0.80 Ma. In summary, this study presents evidence for an inter-related, multi-stage, orogenic-dominated gold-mineralizing system along the Santoy shear system, which was subject to the geodynamic settings during the evolution of Trans-Hudson orogen. As such this study provides implications for the presence of earlier mineralizing systems within the Trans-Hudson orogen as well as other dynamically evolved orogenic terranes.

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