Abstract

Between the late 1890s and the present, the Gold Hill mining district produced gold, arsenic, lead, zinc, copper, molybdenum, and tungsten from numerous mines. Shallow marine strata of Cambrian through Pennsylvanian age underlie most of the Gold Hill area. At least fifteen distinct deformational events occurred between Late Triassic and Miocene. These included Mesozoic folding, thrust faulting and extensional faulting; Late Mesozoic-Early Tertiary strike-slip and low-angle normal faulting; and Tertiary low- and high-angle normal faulting. Two plutons intruded the strata, a granodiorite at 152 Ma and a quartz monzonite at 38 Ma. The combination of deformational and intrusive events produced as many as six periods of mineralization. These include: (1) Late Jurassic tungsten skarns and polymetallic intrusion-related deposits, (2) Post-Late Jurassic (Tertiary?) polymetallic veins and replacement deposits containing gold, silver, copper, and base metals, (3) Pre-Late Eocene (Tertiary?) polymetallic veins and replacement deposits containing primarily silver and lead, with variable amounts of gold, copper, barium, and zinc, (4) Late Eocene tungsten skarns, (5) Tertiary disseminated gold deposits in selected strata and gold enrichment in local veins and zones that were previously mineralized, and (6) Miocene beryllium-bearing quartz-adularia veins.

The Gold Hill area is structurally segmented and divided into blocks with internally distinct patterns of deformation that are bounded by faults. This segmentation strongly affected the patterns of mineralization and distribution of mineral deposits. The development of structural blocks with discontinuous fault patterns could reflect the position of Gold Hill in a Cenozoic transverse zone, one of a sequence of structural zones in the Basin and Range that strike roughly parallel to the direction of regional extension. These zones served as loci for magmatic activity and internally contain discontinuous patterns of faulting and rigid-body rotation of fault-bounded blocks. To explain similar deformation and intrusion patterns that formed before the Tertiary, Gold Hill may have been situated in a similar, although more localized, transverse zone during the Late Jurassic.