Metallogeny of the Mesoproterozoic Belt-Purcell Basin, Northern Rocky Mountains, USA-Canada

Abstract Metasedimentary rocks of the Mesoproterozoic Belt Supergroup in the United States and correlative Purcell Supergroup in Canada contain diverse types of mineral deposits with a variety of commodities including base metals, precious metals, and critical metals. The economically most important deposits (≥ 10 Mt past production + reserves + resources) are stratabound Pb–Zn–Ag ores at the Sullivan mine in southeastern British Columbia, Ag–Pb–Zn–(Cu) veins of the Coeur d’Alene district in northern Idaho, stratabound sediment-hosted Cu–Ag deposits of the Spar Lake, Montanore, and Rock Creek deposits in western Montana, stratabound Co–Cu–Au–(Bi–Y–REE) ores of the Idaho cobalt belt, and stratiform Cu–Co–Ag at the Black Butte deposit in western Montana. Minor deposits in the region, also hosted in strata of the Belt and Purcell supergroups, are stratabound Pb–Zn–Ag deposits in southeastern British Columbia, and Th–REE–(Cu) veins of the Lemhi Pass district in northern Idaho and western Montana. Small prospects and occurrences include gold-quartz veins, Ag–Pb–Zn veins, Fe–(Cu–Au) deposits, and a variety of rare metals (Th, REE, Nb, Be, Sn) in pegmatites and carbonatites. High-precision geochronology of ore and gangue minerals, like in the Sullivan deposit, has yielded only Mesoproterozoic ages, but other deposits (Blackbird, Rock Creek, Coeur d’Alene, Lemhi Pass) have U–Pb and/or Re–Os ages that suggest Neoproterozoic, Paleozoic, and/or Mesozoic to Tertiary overprinting of older Mesoproterozoic mineralization, possibly linked in some cases to fluid flow during reactivation of deep basement structures. Some of the Paleozoic and younger ages are also attributed here to dissolution-reprecipitation of dated minerals and not to new metal introduction. An integrated assessment of the geochronological data reveals growing evidence for previously underappreciated roles of major mineralizing events occurring during the East Kootenay orogeny (1379 − 1325 Ma) and the Grenvillian orogeny (1150 to 980 Ma), with important implications for mineral exploration in many parts of the Belt-Purcell Basin.