A Middle Devonian basin-scale precious metal enrichment event across northern Yukon (Canada)

J.M. Peter,D. Hnatyshin,S. Gouwy,T. Fraser,M.G. Gadd,R. Creaser

doi:10.1130/g46874.1

J.M. Peter, D. Hnatyshin + Show 4 more

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https://doi.org/10.1130/g46874.1

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Abstract

AbstractHyper-enriched black shale (HEBS) Ni-Mo-Zn-Pt-Pd-Au-Re mineralization is geographically widespread across the Richardson trough in northern Yukon (Canada), where it discontinuously outcrops at the regional contact between the Road River Group and overlying Canol Formation. Stratigraphic relationships indicate that the contact is Middle Devonian, but there are no precise age constraints for the HEBS. We apply Re-Os geochronology to HEBS mineralization from two localities that are 130 km apart, the Nick prospect and the Peel River showing, to date directly the age of sulfide mineralization. The Nick prospect yields an isochron age of 390.7 ± 5.1 (2σ) Ma, whereas the Peel River showing yields an isochron age of 387.5 ± 4.4 (2σ) Ma. Within error, these ages are identical and overlap with the biostratigraphically constrained age of the sedimentary host rocks, indicating that mineralization and sedimentation were coeval. Significantly, the ages of the HEBS overlap those of Middle Devonian Kačák, pumilio, and Taghanic global-scale biotic events which are characterized by eustatic sea-level rise and black shale deposition. Linkage of the Yukon HEBS to one (or more) of these bio-events indicates that sea-level rise may have been requisite to formation of basin-scale HEBS mineralization in northwestern Canada during latest Eifelian and Givetian time.

Highlights

Hyper-enriched black shales (HEBS), or polymetallic shales, are an important global resource for Zn, Ni, Cu, Mo, Se, U, V, ± Cr, Co, Ag, Au, platinum group elements (PGEs), and rare earth elements (REEs) (Jowitt and Keays, 2011; Johnson et al, 2017)
Precise age constraints are required for mineralization to test the favored model that elemental enrichments in HEBS originate from ambient seawater (Gadd and Peter, 2018; Crawford et al, 2019; Gadd et al, 2019a, 2019b), and they can provide a clearer understanding of the broader environmental parameters that may have facilitated mineralization
An early Re-Os geochronologic study on HEBS mineralization at the Nick prospect (Horan et al, 1994) determined a Devonian age for the HEBS, which only broadly agreed with established stratigraphic relationships

Summary

Introduction

Hyper-enriched black shales (HEBS), or polymetallic shales, are an important global resource for Zn, Ni, Cu, Mo, Se, U, V, ± Cr, Co, Ag, Au, platinum group elements (PGEs), and rare earth elements (REEs) (Jowitt and Keays, 2011; Johnson et al, 2017). The HEBS at each of the two localities in this study is conspicuously situated at a regional stratigraphic contact between the Road River Group and the Canol Formation (Fig. 2A).

Results

Conclusion