Ambient Redox and Hydrothermal Environment of the Wolverine Volcanogenic Massive Sulfide Deposit, Yukon: Insights from Lithofacies and Lithogeochemistry of Mississippian Host Shales

摘要

The Wolverine volcanogenic massive sulfide (VMS) deposit is a polymetallic, felsic-siliciclastic deposit hosted by similar to 352 to 347 Ma volcanic and sedimentary rocks of the Yukon-Tanana terrane, Yukon, Canada. Shales are located at various stratigraphic levels and in various mineralized zones within the Wolverine deposit area (e.g., Fisher, Puck, and Sable zones). Shales present along the mineralized horizon near the immediate hanging wall and footwall were deposited under anoxic conditions (e.g., low Mn, anoxic V-Cr-Mo-U systematics), whereas in the stratigraphically deeper footwall and uppermost hanging wall, the redox signatures imply deposition under suboxic to oxic conditions. The Mo-U systematics of the shales suggest that during the time of sulfide mineralization, the ambient basin was periodically euxinic with aqueous H2S present in the water column that this H2S contributed to the sulfur budget of the deposit. Furthermore, the Mo-U and C-org-Ni systematics favor deposition in a restricted basin (i.e., nutrient trap) where restriction of the water column led to H2S formation via sulfate reduction associated with excess organic carbon preservation. There is also evidence of a progressive shift upward in the stratigraphy to more oxygenated conditions in the uppermost hanging wall. The shift from euxinic to oxic-suboxic conditions is consistent with regional tectonic models that indicate a change from rifting during Wolverine deposit formation, where the basin was partially restricted with minimal circulation (i.e., restricted depocenter), to an incipient back-arc basin accompanied by extension and likely ingress of oxygenated seawater.