Authors: Andrew V. Zuza, Christopher D. Henry, Michael W. Ressel, Charles H. Thorman, Seth Dee, and Jeffrey E. Blackmon
Series: Open-File Report 2018-04
Format: plate: 39 x 31 inches, color; text: 12 pages, b/w
The Independence Valley NE 7.5-minute quadrangle encompasses the northern Pequop Mountains and adjacent Goshute Valley in eastern Elko County. Active mining in the northeast corner of the quadrangle is focused on newly recognized Carlin-type gold deposits in the east-tilted Pequop Mountains that are hosted in a geographic and geologic setting distinct from similar deposits elsewhere in Nevada. Mapping was conducted in 2017 and 2018.
The northern Pequop Mountains are comprised of east-southeast-dipping Cambrian through Permian sedimentary rocks. Cambrian and Ordovician rocks are metamorphosed and strongly foliated. Although contacts on the geologic map suggest a parallel undeformed stratigraphy, the lower and middle Paleozoic units are variably deformed with local boudinage development, shearing, thrust faulting, and folding. Upper Paleozoic rocks exhibit open folds. This deformation is strongly partitioned to the mechanically weaker horizons, with some beds completely undeformed. Well-developed lineations and asymmetric shear fabrics across the range suggest top-southeast shear. A large thrust fault, named the Independence thrust, cuts across the western and central parts of the map area, juxtaposing lower Paleozoic rocks over younger Paleozoic rocks with an apparent southeast transport direction (present-day orientation). Total offset along this thrust fault is a minimum of two kilometers, based on mapped cutoff relationships. Sparse Jurassic sills and dikes intrude the Paleozoic stratigraphy, including the Independence thrust, which requires this structure to be older.
In the northern map area, the Pequop structural plate consists of Devonian rocks thrust over Pennsylvanian-Permian strata, which are juxtaposed over Ordovician rocks along the enigmatic Pequop fault. This fault has been regarded as a thrust (Thorman, 1970) or a low-angle normal fault (Camilleri, 2010). We interpret that the Pequop plate consists of the structurally highest part of the Independence thrust system—i.e., hanging wall Devonian rocks thrust over footwall Permian strata—that was faulted over Ordovician rocks via the low-angle Pequop normal fault system during an unconstrained phase of post-Jurassic extension. Eastward tilting and exhumation of the entire range was accommodated by late Cenozoic high-angle normal fault activity on the western flank of the range.
In Goshute Valley, lacustrine gravels are deposited in beach bars, and spits recording the high-stand and recessional stages of latest Pleistocene Lake Clover (Munroe and Laabs, 2013). Lacustrine sediments are buttressed against Pleistocene fan deposits (Qfi) along a lake high-stand shoreline at an elevation of approximately 1765 m.
This geologic map was funded in part by the USGS National Cooperative Geologic Mapping Program under STATEMAP award number G17AC00212, 2018.
Read about the authors
Mike Ressel, author of two of these newly released maps, was featured in the Geological Society of Nevada “Faces of GSN” in November. You can read his story here:
NBMG staff pages
You can also read about the other geologic mappers and their work on the individual NBMG staff pages: