Re-Os PYRITE GEOCHRONOLOGY OF THE YELLOWHEAD-TYPE MINERALIZATION, PEND OREILLE MINE, KOOTENAY ARC, METALINE DISTRICT, WASHINGTON

Pend Oreille, a carbonate-hosted Zn-Pb sulfide deposit, is the only base metal mine recently in production within the historically prolific Kootenay arc belt. The deposit consists of two spatially and lithologically distinct types of stratabound, carbonate-hosted Zn-Pb mineralization: Josephine and Yellowhead. The Yellowhead-type sulfide mineralization, the focus of this study, consists of en échelon tabular to lensoidal pyrite-sphalerite–rich orebodies hosted by the middle Cambrian to Early Ordovician Metaline Formation. The Yellowhead-type mineralization is characterized by carbonate replacement and open-space filling textures, indicating diagenetic and epigenetic origin. As with most low-temperature deposits not directly associated with igneous activity, the timing of sulfide mineralization has traditionally been difficult to constrain using radiometric methods. In this study, we present a new Re-Os age of 512 ± 17 Ma from the Yellowhead mineralization. Combining this age date with the Cambrian-Ordovician fossil record of the host Metaline Formation and detailed textural analysis of the mineralization, we conclude that the Yellowhead sulfide mineralization is largely diagenetic in origin. Such an origin for the Yellowhead mineralization is similar to that of Irish-type deposits worldwide. For explorationists, the presence of Irish-type deposits in the United States portion of the Kootenay arc opens the possibility of discovering similar mineralization in the Canadian extension of the Kootenay arc.