Sequence of Deformational Events and the Recognition of Eocene(?) Deformation in the Alligator Ridge Area, East-central Nevada

Abstract

Abstract The Alligator Ridge district hosts disseminated gold deposits (Alligator Ridge, Yankee deposits) in Mississippian and Devonian clastic and carbonate rocks. The deposits are about 70 miles (113 km) northwest of Ely, Nevada, along the southern projection of the Carlin trend (Fig. 1), and east of the Roberts Mountain thrust. The area is underlain by lower-plate Paleozoic miogeoclinal carbonate and clastic rocks, Eocene(?) sedimentary rocks; and Oligocene and younger volcanic rocks. Jurassic plutonic rocks are exposed to the north at Bald Mountain (Hitchbom et a/., 1996) (Fig. 2). Hitchbom eta/. (1996) propose that at Bald Mountain tungsten, molybdenum, zinc, and precious metal deposits, including disseminated gold, are associated with the Jurassic pluton and are Jurassic in age, and that Alligator Ridge and Yankee are related distal deposits. The well-exposed Alligator Ridge area is ideal for unraveling the geologic history of ea.stem-facies rocks, and, in particular, documenting Mesozoic and Tertiary deformation and their controls on ore. An improved understanding of the tectonic history in the Alligator Ridge district may also help to identify Mesozoic and Tertiary structures in the Carlin trend which is underlain by eastern- and western-facies rocks that were deformed during the late Devonian-early Mississippian Antler and late Permian Sonoma orogenies, as well as during the Mesozoic and Tertiary tectonic events. Previously published geologic maps have depicted the Alligator Ridge-Bald Mountain area as a relatively undeformed uplift between the isoclinally folded and thrusted Diamond Mountains on the west side of Newark Valley and the broad syncline comprising the Butte Mountains