ABSTRACT

Mineralized zones in the southern Absaroka Mountains, Wyoming, are confined to a belt of intrusive rocks extending approximately 100 kilometers along the northwest-trending central axis of the Absaroka volcanic field. Plutonic rocks within this belt are calc-alkalic and include basalt, andesite, granodiorite, diorite, quartz monzonite, dacite, and rhyodacite. The most common plutons are stocks typically 1 to 5 km.².2 in size but ranging up to 30 km.².2. Sills, laccoliths dike swarms, and some breccia are also common. The igneous history involving periods of multiple intrusion, and the larger centers, in particular the Stinkingwater and Kirwin districts, contain several separate mineralized zones Most, perhaps all, of the mineralized intrusive centers were also extrusive centers, and the presently exposed piutonic masses constitute lower-level vent fillings in old stratovolcanoes and shield volcanoes.

The mineralized areas are best described as relatively small porphyry deposits having a central zone of disseminated copper and molybdenum surrounded by a poorly developed halo of small, discontinuous base and precious metal veins. Propylitically altered rocks are common in all of the mineralized areas, and some areas also contain phyllic, potassic, and argillically altered rocks. Quartz-bearing porphyritic rocks are closely associated with all of the mineral deposits, and most of the mineralized centers have distinct northwest- and northeast-trending faults and fracture systems.