| Title | The mineralogical evolution of the clastic dominant-type zn-pb ± ba deposits at macmillan pass (Yukon, Canada)-tracing subseafloor barite replacement in the layered mineralization |
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| Author | Magnall, J M; Gleeson, S A; Creaser, R A; Paradis, S ; Glodny, J; Richard Kyle, J |
| Source | Economic Geology vol. 115, issue 5, 2020 p. 961-979, https://doi.org/10.5382/econgeo.4730 |
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| Year | 2020 |
| Alt Series | Natural Resources Canada, Contribution Series 20200683 |
| Publisher | Society of Economic Geologists |
| Document | serial |
| Lang. | English |
| Media | paper; on-line; digital |
| File format | pdf; html |
| Province | Yukon |
| Area | Canada |
| Lat/Long WENS | -142.0000 -121.0000 65.0000 55.0000 |
| Subjects | metallic minerals; Science and Technology; sedimentology; barite; feldspar; kaolinite; Selwyn Basin |
| Illustrations | location maps; cross-sections; stratigraphic columns; diagrams; photographs; tables; cross-plots |
| Released | 2020 08 01 |
| Abstract | Clastic dominant-type massive sulfide deposits are well preserved in Upper Devonian carbonaceous mudstones in the Macmillan Pass district (Yukon, Canada). The Macmillan Pass deposits have been
considered to be type examples of sedimentary exhalative Zn-Pb mineralization, whereby sulfides precipitated when hydrothermal fluids were vented into a euxinic (H2S-bearing) water column. We propose a new mineralization model, documenting the
mineralogical evolution of layered mineralization. We show that textures previously interpreted to form via depositional processes actually formed by subseafloor replacement of diagenetic barite. Mineral assemblages associated with barite dissolution
in the layered mineralization include (1) barium carbonate phases (witherite, barytocalcite, and norsethite), which are intergrown with Zn-Pb sulfides and represent localized Ba mass transfer, and (2) barium feldspar (celsian, hyalophane) that is
abundant in the mudstones surrounding the layered mineralization. The barium feldspar formed following transport of Ba in low-sulfate fluids on the margins of the subseafloor replacement system. This resulted in whole-rock Ba enrichments (up to 5 wt
%) in mudstones 15 m below and above the layered mineralization. High Ba in these surrounding mudstones is coupled with decreasing K/Al ratios, indicative of secondary illite and kaolinite. The source(s) of fluids related to the diagenetic (barite,
barytocalcite) and hydrothermal (ankerite) assemblages can be constrained using Sr isotopes. Whereas highly radiogenic 87Sr/86Sr values (>0.714) in ankerite correspond with host-rock alteration within the vent complex, the overlying barite and
barytocalcite preserve lower 87Sr/86Sr values (<0.714), providing evidence of mixing between a radiogenic fluid (likely a formation water) and Late Devonian seawater. The complex mineralogy and paragenesis contained within the layered mineralization
are linked to a protracted history of diagenetic and hydrothermal fluid events, all of which took place in and peripheral to a subseafloor replacement hydrothermal system. |
| GEOSCAN ID | 327971 |
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