Two-event genesis of Butte lode veins: Geologic and geochronologic evidence from ore veins, dikes, and host plutons

The long-standing ore-genesis model for world-class deposits of the Butte mining district, Montana, is of deep pre-Main Stage porphyry Cu-Mo and overlying Main Stage Ag-Zn-Cu-zoned lode veinsformed from discrete hydrothermal systems related to rhyolite dikes. The lode-specific model describes metals zones that formed in the lode veins as hydrothermal processes diminished in intensity (changing temperature and chemical characteristics) outward from the district center. New geologic and multi-method geochronologic studies pro- vide new timing constraints on the lode veins and reevaluation of geologic relations (Lund and others, 2018), leading to a new model for formation of the lode veins and their relations to stockwork Cu-Mo deposits and igneous events.