This paper presents the results of an investigation of the geology and mineralization of the northeastern portion of the Humboldt Range, Nevada. The principal rock units of this area are keratophyric and rhyolitic volcanics overlain with apparent conformity by the Middle and Upper Triassic Star Peak limestones and associated clastic strata. These strata have been folded, faulted, and intruded by Late Jurassic or Early Cretaceous diabase, gabbro, syenite, and granite porphyry. Extensive mineralization and hydrothermal alteration have also taken place. Later deformation and igneous activity, which probably accompanied uplift of the present Humboldt Range by Pliocene “Basin Range” block faulting, are shown by olivine diabase dikes, by post-mineral faulting (in part), and by basalt, trachyte porphyry, and trachytic ash.
The hypogene ore deposits of silver, antimony, and gold are sulphide-bearing quartz fissure veins, bed veins, and stockworks in rhyolite, in granite porphyry, and in the lower Star Peak strata. Hypogene fissure filling and replacement have been accompanied by extensive wall-rock alteration. Supergene deposits comprise portions of the hypogene silver deposits enriched by supergene argentite and native silver. The ore deposits are grouped along major fault zones which trend roughly parallel to Jura-Cretaceous (?) folds and apparently were initiated during Jura-Cretaceous (?) orogeny. The forms of the hypogene deposits and the distribution of the hypogene vein minerals within them show a close control by structural features produced by deformation prior to and during mineralization.