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Stratigraphic control and distal hydrothermal footprint of the Ursa Zn-Pb-Ag prospect, Selwyn Basin, Yukon Territory, Canada

Engström, Fredrik
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Monecke, Thomas
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Date
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2024
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Keywords
base metals
 clastic-dominated
 geochemistry
 hydrothermal
 Selwyn Basin
 stratigraphic control
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2024 - Mines Theses & Dissertations
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Engstrom_mines_0052N_316/ursa_sulfur_isotopes_appendix.xlsx
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Engstrom_mines_0052N_316/ursa_element_analysis_methods.xlsx
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Engstrom_mines_0052N_316/ursa_geochemistry_appendix.xlsx
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https://hdl.handle.net/11124/179219
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Abstract
Clastic-dominated deposits are an important source of Zn, Pb, and Ag worldwide. While it is widely accepted that the hydrothermal alteration halos around these deposits can be laterally extensive, the mineralogical and geochemical signature of the distal alteration footprint is currently not well understood. This severely limits greenfield exploration for this deposit type. The Ursa project in the Selwyn Basin, of the Yukon Territory of Canada, is a Zn-Pb-Ag prospect located 60 km north of the famous Macmillan Pass district. Extensive Zn and Ag anomalies in soil- and silts occur across the property which could indicate the presence of an undiscovered deposit. The present study aimed to understand stratigraphic control on the location of the prospect and to determine the distal alteration signatures of the Ursa prospect. The research involved detailed fieldwork across Ursa to map its stratigraphic setting and to determine the chemostratigraphic characteristics of favorable units through whole-rock geochemical analysis. It is demonstrated that the weakly altered sedimentary rocks at Ursa are stratigraphically equivalent to the host rocks of the Macmillan and Howards Pass districts. Optical microscopy, scanning electron microscopy, and the analysis of sulfur isotopes of pyrite, sphalerite and other sulfur-bearing minerals have been used to systematically evaluate the textural, mineralogical, and isotopic characteristics of the weakly altered, reduced, calcareous, and barite-bearing sedimentary units hosting the Ursa prospect. The most widespread and conspicuous hydrothermal phases include pyrite, sphalerite, and pyrite replacing earlier barite. The weakly altered rocks contain siderite and witherite. The results of this study provide new guidelines on how the distal signature of clastic-dominated deposits in the Selwyn Basin can be identified and used as potential vectors to mineralization.
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