Sulfur isotopes of host strata for Howards Pass (Yukon–Northwest Territories) Zn-Pb deposits implicate anaerobic oxidation of methane, not basin stagnation

Geology
By: , and 

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Abstract

A new sulfur isotope stratigraphic profile has been developed for Ordovician-Silurian mudstones that host the Howards Pass Zn-Pb deposits (Canada) in an attempt to reconcile the traditional model of a stagnant euxinic basin setting with new contradictory findings. Our analyses of pyrite confirm the up-section 34S enrichment reported previously, but additional observations show parallel depletion of carbonate 13C, an increase in organic carbon weight percent, and a change in pyrite morphology. Taken together, the data suggest that the 34S enrichment reflects a transition in the mechanism of pyrite formation during diagenesis, not isotopic evolution of a stagnant water mass. Low in the stratigraphic section, pyrite formed mainly in the sulfate reduction zone in association with organic matter–driven bacterial sulfate reduction. In contrast, starting just below the Zn-Pb mineralized horizon, pyrite formed increasingly within the sulfate-methane transition zone in association with anaerobic oxidation of methane. Our new insights on diagenesis have implications for (1) the setting of Zn-Pb ore formation, (2) the reliability of redox proxies involving metals, and (3) the source of ore sulfur for Howards Pass, and potentially for other stratiform Zn-Pb deposits contained in carbonaceous strata.

Additional publication details

Publication type Article
Publication Subtype Journal Article
Title Sulfur isotopes of host strata for Howards Pass (Yukon–Northwest Territories) Zn-Pb deposits implicate anaerobic oxidation of methane, not basin stagnation
Series title Geology
DOI 10.1130/G40274.1
Volume 46
Issue 7
Year Published 2018
Language English
Publisher Geological Society of America
Contributing office(s) Alaska Science Center, Crustal Geophysics and Geochemistry Science Center, Eastern Mineral and Environmental Resources Science Center, Central Mineral and Environmental Resources Science Center
Description 4 p.
First page 619
Last page 622
Country Canada
State Northwest Territories, Yukon
Other Geospatial Howards Pass