Geology and mineral deposits of the Pyramid district, southern Washoe County, Nevada
AuthorWallace, Andy Bert
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The Pyramid district is thirty miles north-northeast of Reno, Nevada in the northern Pah Rah Range. Known mineralization in the district is confined to west and northwest trending veins along fracture zones and faults cutting the Late Oligocene to Miocene ash-flow tuffs of the Hartford Hill Rhyolite. The vein mineralization is only slightly younger (1-3 million years) than disseminated copper and molybdenum mineralization in the Guanomi quartz monzonite stock exposed six miles from the district. Post-mineralization rocks in the area include dacite stocks and lavas, and also lacustrine sediments, basaltic tuff-breccias, basalt flows, and ash- flow tuffs of the Pyramid Sequence. Hypogene mineralization in the district displays well- defined zoning with a central enargite (luzonite)-pyrite zone, an intermediate polymetallic zone with tetrahedrite, sphalerite, galena, chalcopyrite, bornite, and pyrite, and an outer zone with galena and pyrite. The ash-flow tuffs of the Hartford Hill are pervasively propylitized with sericitic envelopes around veins, and in the central enargite-pyrite zone, advanced argillic alteration occurs between the veins and the sericitic envelopes. Mineralization in the Pyramid district is similar to several Peruvian polymetallic vein systems, Butte, Montana, Chinkuashih, Taiwan, several Japanese polymetallic vein deposits, and also to districts in the San Juan Mountains of Colorado. At least one of the polymetallic vein systems in Peru (Morococha) is known to directly overlie a porphyry copper deposit and it is suggested that such an exploration target may lie beneath the central zone of the Pyramid district.
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Pah Rah Range
Late Oligocene ash-flow tuffs
Miocene ash-flow tuffs
Hartford Hill Rhyolite
Guanomi quartz monzonite stock
ash-flow tuff of the Pyramid sequence
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