Geology and mineralization of Fireball Ridge, Churchill County, Nevada

Abstract

Fireball Ridge is underlain predominantly by a thick complex sequence of pelitic sedimentary and associated volcanic and volcaniclastic rocks of the Nightingale sequence which was deposited in a Triassic-Jurassic eugeosyncline, possibly in a back-arc setting. Regional greenschist metamorphism and large scale folding occurred during the Jurassic Nevadan orogeny prior to intrusion of a granodiorite stock of Cretaceous age. The initial phases of the granodiorite intrusion are dioritic in composition, later phases include granitic aplite which occurs in plugs. Faults and fractures related to stock emplacement helped localize later hypabyssal andesite and dacite dikes and facilitated migration of hydrothermal fluids. Contact metamorphism produced irregular zones of hornfelsed equivalents of the regionally metamorphosed host units.