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Application of molybdenum and thallium isotopes as indicators of paleoredox conditions and genesis of hyper-enriched black shale deposits, Peel River, Yukon, Canada

Isobel Crawford, Daniel Layton-Matthews, Jan M. Peter, Michael G. Gadd, Alexandre Voinot, Matthew I. Leybourne and Peir Pufahl
Application of molybdenum and thallium isotopes as indicators of paleoredox conditions and genesis of hyper-enriched black shale deposits, Peel River, Yukon, Canada
The Canadian Mineralogist (September 2021) 59 (5): 1085-1110

Abstract

Hyper-enriched black shale (HEBS) deposits in northern Yukon, consist of thin (<10 cm), laterally extensive (tens of thousands of km (super 2) ) stratiform sulfide mineralization layer(s) that are hyper-enriched in Ni, Mo, Zn, platinum group elements, Re, and Au. The genesis of HEBS deposits and the ambient paleoenvironment in which they formed are the subject of vigorous debate. Non-traditional stable isotopes, particularly molybdenum and thallium, are robust paleoredox indicators and we have employed these isotope systems in this study of Yukon HEBS. Systematic sampling and Mo and Tl isotopic analysis of a continuous 200 m stratigraphic section through the Yukon HEBS mineralization and footwall and hanging-wall strata at the Peel River north and south bank showings (spaced five km apart) give delta (super 98) Mo -1.24 to -0.53 ppm and -8.1 to -5.2 epsilon -units for the mineralization and -0.70 to 0.60 ppm and -6.5 to -2.0 epsilon -units for the unmineralized strata. These values preclude a hydrothermal origin and strongly suggest that redox processes were responsible for the Yukon HEBS mineralization. The isotopic compositions, together with rare earth element (REE) systematics (REE profile, Y positive anomalies, Ce negative anomalies, and Y/Ho values) and other bulk geochemical redox indicators (Mo, V, Re/Mo, Ni/Co, U/Th, and V/Cr) indicate that the Peel River HEBS mineralization formed because of metal scavenging from seawater in a quiescent, euxinic basinal paleoenvironment.


ISSN: 0008-4476
EISSN: 1499-1276
Coden: CAMIA6
Serial Title: The Canadian Mineralogist
Serial Volume: 59
Serial Issue: 5
Title: Application of molybdenum and thallium isotopes as indicators of paleoredox conditions and genesis of hyper-enriched black shale deposits, Peel River, Yukon, Canada
Affiliation: Queen's University, Queen's Facility for Isotope Research, Kingston, ON, Canada
Pages: 1085-1110
Published: 202109
Text Language: English
Publisher: Mineralogical Association of Canada, Ottawa, ON, Canada
References: 125
Accession Number: 2021-070820
Categories: Isotope geochemistryEconomic geology, geology of ore deposits
Document Type: Serial
Bibliographic Level: Analytic
Illustration Description: illus. incl. strat. cols., 3 tables, geol. sketch maps
N65°00'00" - N67°00'00", W138°00'00" - W135°00'00"
Secondary Affiliation: Geological Survey of Canada, Ottawa, ON, CAN, Canada
Country of Publication: Canada
Secondary Affiliation: GeoRef, Copyright 2021, American Geosciences Institute. Abstract, copyright, Mineralogical Association of Canada. Reference includes data from GeoScienceWorld, Alexandria, VA, United States
Update Code: 2021
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