Eva Yu, BSc
E. Yu1, D. Gregory1, M. Reynolds2
1Department of Earth Sciences, University of Toronto, Toronto, Ontario, Canada, 2Northwest Territories Geological Survey, Yellowknife, Northwest Territories, Canada
The Howard Pass district spans the Yukon-Northwest Territories border and contains an estimated 400.7Mt of mineralization grading at 4.5% Zn and 1.5% Pb, which accounts for over 30% of global Zn and Pb resources. Mineralization is hosted in the Ordovician to Silurian Duo Lake Formation, which consists of carbonaceous and siliceous mudstone. There are multiple proposed genetic models of a modified exhalative environment including Zn-Pb-rich brines permeating sulfidic muds by downward percolation of the metalliferous brine into unconsolidated sediments, or selective replacement of reactive strata during early diagenesis. Therefore, redox conditions at the time of sediment deposition may play an important role in controlling mineralization. A recent study suggests that global Ordovician through Early Devonian anoxic marine waters were commonly ferruginous (nonsulfidic). Previous workers have used whole rock multi-element geochemical proxies to show that at Howards Pass the redox conditions during host sediment deposition fluctuated from suboxic to sulfidic, but the occurrence of ferruginous conditions has not been fully investigated. This study employs Fe-speciation to test for ferruginous conditions in the strata hosting Zn-Pb mineralization at Howards Pass. Sequential leach analyses will quantify different forms of iron hosted in hosted in the carbonaceous and siliceous mudstones and determine ferrous-ferric oxide phases. Additionally, sulfur from pyrite, sphalerite, and galena will be characterized through extraction of acid-volatile sulfides, chromium-reducible sulfides and bulk analysis of S isotope composition. This study aims to address knowledge gaps in sediment-hosted massive sulfide deposits by interpreting the relationship between redox environments and mineralization processes. The geochemical analyses will elucidate how redox fluctuations impact metal concentration and preservation in sediment, potentially offering broader implications for sediment-hosted ore-deposit exploration. Further, this study will provide empirical data to assess the effects of hydrothermal systems on Fe-speciation analyses.