Evidence for Large-Magnitude, Post-Eocene Extension in the Northern Shoshone Range, Nevada, and Its Implications for the Structural Setting of Carlin-Type Gold Deposits in the Lower Plate of the Roberts Mountains Allochthon

Abstract

Research Article| November 01, 2014 Evidence for Large-Magnitude, Post-Eocene Extension in the Northern Shoshone Range, Nevada, and Its Implications for the Structural Setting of Carlin-Type Gold Deposits in the Lower Plate of the Roberts Mountains Allochthon Joseph P. Colgan; Joseph P. Colgan † 1U.S. Geological Survey, Denver Federal Center, Bldg. 25, PO Box 25046, Lakewood, Colorado 80225 †Corresponding author: e-mail, jcolgan@usgs.gov Search for other works by this author on: GSW Google Scholar Christopher D. Henry; Christopher D. Henry 2Nevada Bureau of Mines and Geology, Mail Stop 178, University of Nevada, Reno, Nevada 89557 Search for other works by this author on: GSW Google Scholar David A. John David A. John 3U.S. Geological Survey, 345 Middlefield Rd., Menlo Park, California 94025 Search for other works by this author on: GSW Google Scholar Author and Article Information Joseph P. Colgan † 1U.S. Geological Survey, Denver Federal Center, Bldg. 25, PO Box 25046, Lakewood, Colorado 80225 Christopher D. Henry 2Nevada Bureau of Mines and Geology, Mail Stop 178, University of Nevada, Reno, Nevada 89557 David A. John 3U.S. Geological Survey, 345 Middlefield Rd., Menlo Park, California 94025 †Corresponding author: e-mail, jcolgan@usgs.gov Publisher: Society of Economic Geologists Received: 25 Jun 2013 Accepted: 08 Mar 2014 First Online: 09 Mar 2017 Online ISSN: 1554-0774 Print ISSN: 0361-0128 © 2014 Society of Economic Geologists. Economic Geology (2014) 109 (7): 1843–1862. https://doi.org/10.2113/econgeo.109.7.1843 Article history Received: 25 Jun 2013 Accepted: 08 Mar 2014 First Online: 09 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation Joseph P. Colgan, Christopher D. Henry, David A. John; Evidence for Large-Magnitude, Post-Eocene Extension in the Northern Shoshone Range, Nevada, and Its Implications for the Structural Setting of Carlin-Type Gold Deposits in the Lower Plate of the Roberts Mountains Allochthon. Economic Geology 2014;; 109 (7): 1843–1862. doi: https://doi.org/10.2113/econgeo.109.7.1843 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyEconomic Geology Search Advanced Search Abstract The northern Shoshone and Toiyabe Ranges in north-central Nevada expose numerous areas of mineralized Paleozoic rock, including major Carlin-type gold deposits at Pipeline and Cortez. Paleozoic rocks in these areas were previously interpreted to have undergone negligible postmineralization extension and tilting, but here we present new data that suggest major post-Eocene extension along west-dipping normal faults. Tertiary rocks in the northern Shoshone Range crop out in two W-NW–trending belts that locally overlie and intrude highly deformed Lower Paleozoic rocks of the Roberts Mountains allochthon. Tertiary exposures in the more extensive, northern belt were interpreted as subvertical breccia pipes (intrusions), but new field data indicate that these “pipes” consist of a 35.8 Ma densely welded dacitic ash flow tuff (informally named the tuff of Mount Lewis) interbedded with sandstones and coarse volcaniclastic deposits. Both tuff and sedimentary rocks strike N-S and dip 30° to 70° E; the steeply dipping compaction foliation in the tuffs was interpreted as subvertical flow foliation in breccia pipes. The southern belt along Mill Creek, previously mapped as undivided welded tuff, includes the tuff of Cove mine (34.4 Ma) and unit B of the Bates Mountain Tuff (30.6 Ma). These tuffs dip 30° to 50° east, suggesting that their west-dipping contacts with underlying Paleozoic rocks (previously mapped as depositional) are normal faults. Tertiary rocks in both belts were deposited on Paleozoic basement and none appear to be breccia pipes. We infer that their present east tilt is due to extension on west-dipping normal faults. Some of these faults may be the northern strands of middle Miocene (ca. 16 Ma) faults that cut and tilted the 34.0 Ma Caetano caldera ~40° east in the central Shoshone Range (<5 km south of Mill Creek), but further mapping is necessary to trace the faults through the highly deformed Paleozoic rocks that surround the isolated Tertiary outcrops. Significant post-Eocene extensional faulting in the northern Shoshone Range may have important implications for both the structure of the Roberts Mountains allochthon and the exposure of potentially mineralized rocks in its lower plate, both of which were likely east-tilted and repeated by west-dipping faults together with overlying Tertiary rocks. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.