Geology of the Ravens Nest Quadrangle, Nevada
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See discussions, stats, and author profiles for this publication at: https://www.researchgate.net/publication/330924789 Preliminary Geologic Map of the Ravens Nest Quadrangle, Elko and Eureka Counties, Nevada Research · February 2019 CITATIONS READS 0 165 2 authors, including: Michael W. Ressel University of Nevada, Reno 41 PUBLICATIONS 387 CITATIONS SEE PROFILE Some of the authors of this publication are also working on these related projects: Eocene metallogeny of the Great Basin View project All content following this page was uploaded by Michael W. Ressel on 07 February 2019. The user has requested enhancement of the downloaded file. Text and references accompanying Nevada Bureau of Mines and Geology Open-File Report 18-5 Preliminary Geologic Map of the Ravens Nest Quadrangle, Elko and Eureka Counties, Nevada by Michael W. Ressel and Seth Dee Nevada Bureau of Mines and Geology, University of Nevada, Reno, NV 2018 Disclaimer: NBMG open-file reports are preliminary. They have not been thoroughly edited or peer reviewed. This geologic map was funded in part by the USGS National Cooperative Geologic Mapping Program under STATEMAP award number G17AC00212, 2018 SUMMARY GEOLOGY The Ravens Nest 7.5-minute quadrangle is located in Antler Orogeny the northern Piñon Range south of the town of Carlin in north-central Nevada. Mapping at Ravens Nest was The Ravens Nest quadrangle contains an unusually undertaken to address several components of the complex complete section across the Early Mississippian Antler geology of north-central Nevada, including the nature of orogen that includes highly deformed Devonian rocks of sedimentation and deformation associated with the leading the leading edge of its east-vergent allochthon, a partly edge of the Early Mississippian Antler allochthon, the deformed foreland basin consisting of fine- to coarse- effects of post-Antler contractional deformation, grained siliciclastic sedimentary rocks, and a coarse overlap development of the Eocene Elko basin and slightly younger sequence, in addition to pre- and post-Antler passive margin Robinson Mountain volcanic field, and deformation carbonate-dominant strata derived from easterly sources. associated with Cenozoic extension in the hanging wall of Thrusting associated with the Antler orogeny variably the Ruby Mountains-East Humboldt Range metamorphic affected Mississippian and older rocks at Ravens Nest. A core complex. Importantly, the northern Piñon Range lies major east-vergent thrust juxtaposes deformed Devonian to within the southern segment of the Carlin trend gold belt, Mississippian fine- to medium-grained siliciclastic rocks, which is one of the premier gold mining jurisdictions in the chert, and rare carbonate rocks over weakly to non-deformed world. Gold produced from disseminated, sedimentary rock- Mississippian to earliest Devonian medium- to coarse- hosted deposits, or Carlin-type deposits, in Nevada grained sandstone and a thick sequence of Late Devonian comprised about 90.5% of Nevada’s production and about and older carbonate rocks of the Paleozoic passive margin. 73.6% of U.S. production in 2016 (Muntean et al., 2017). A few important Early Mississippian units considered syn- The southern Carlin trend in the vicinity of the Ravens Nest orogenic (e.g., Poole, 1974; Smith and Ketner, 1975; 1978; quadrangle has seen several new Carlin-type gold Silberling et al., 1997; Mathewson, 2001; Trexler et al., discoveries since 2010 in non-traditional Paleozoic host 2003; 2004; Longo et al., 2002; Essman, 2011) likely strata. The Piñon Range and flanking Pine and Huntington straddle the orogenic front. These include the earliest valleys are also important areas for conventional and Mississippian Tripon Pass Limestone, which had an eastern unconventional hydrocarbon resources. The Blackburn and passive margin source but appears to have been deposited Tomera Ranch oil fields produce from Cenozoic and not only upon Devonian passive margin carbonate, but on Paleozoic rocks widely distributed in the Ravens Nest Devonian and Early Mississippian foreland basin rocks quadrangle, and the Elko basin has seen assessment of its largely derived from westerly sources in the allochthon. oil-bearing shale by the U.S. Bureau of Mines in the 1970s Conversely, the Early Mississippian Webb Formation was and since 2012 by energy companies. derived from Roberts Mountains allochthon sources, but its deposition extended far enough eastward such that it was also deposited conformably upon the Early Mississippian 1 Tripon Pass Limestone and older units of the Devonian Bullion stock and swarms of dikes of varying composition passive margin. Later south-vergent thrusting and reverse indicate multiple intrusions at depth (Hollingsworth et al., faulting and folding affect Early to Middle Mississippian 2017; Henry et al., 2015; Ressel and Henry, 2006). rocks of the Chainman Formation and Melandco formation. Widespread Carlin-type gold mineralization occurred in a The contrast in vergence with earlier Antler deformation shallow Eocene setting at or near the paleosurface, and therefore in proximity to Eocene lakes and shallow suggests that this deformation may entirely postdate Antler intrusions. Constraints on mineralization age and depth are deformation (e.g., Long et al., 2014; Rhys et al., 2015) or summarized in table 3 of the Appendix (from Hollingsworth alternatively, represent protracted Antler deformation that et al., 2017). changed vergence (Trexler et al., 2003; 2004). New biostratigraphic ages on units are provided in table 1 of the Miocene and Younger Basins and Appendix. Extension Eocene Basins, Magmatism, Extension, Miocene through Pleistocene basin deposits in the map and Carlin-type Gold Deposits area record ongoing extension and deposition into a hydrologically closed Pine Valley. Subsequent integration The Eocene geologic record in northern Nevada and of Pine Valley into the Humboldt River watershed in the specifically, Ravens Nest, is extensive. Following middle Pleistocene resulted in widespread dissection of the contractional deformation associated with the Late deposits and numerous large landslide complexes. Fault Cretaceous Sevier orogeny, the region is widely considered scarps in middle Pleistocene fan deposits demonstrate to have been a high elevation orogenic plateau with major ongoing extension of the area and the potential for drainage both east and west from a northerly axis near the earthquake hazards. Piñon Range (Henry, 2008). Lacustrine deposition from ~47 to 38 Ma (Smith et al., 2017; Mulch et al., 2015; Horner, 2015; Haynes, 2003; Solomon et al., 1979) was widespread DESCRIPTION OF MAP UNITS near the Eocene drainage divide and probably consisted of several moderate-sized lake basins developed in a half- Quaternary and Other Late Cenozoic graben setting in the hanging wall of the incipient Ruby Deposits Mountains-East Humboldt Range metamorphic core complex (Horner, 2015; Henry, 2008). The Elko bas in , Qmd Mine disturbance (Anthropocene) Excavations, which includes rocks in the eastern part of the Ravens Nest mine dumps, heap leach, and tailings of the Rain Mine. quadrangle, was sufficiently long-lived to produce an abundance of organic-rich sediments that would later Qg wd Groundwater discharge deposits (Holocene) develop into hydrocarbon resources (Horner, 2015). Deposits of eolian and alluvial, sand and silt with organic Lacustrine deposition waned by ~38.5–38 Ma as volcanic clay, in areas surrounding intermittently discharging rocks of the 38.5–34 Ma Robinson Mountain volcanic field springs. Exposed thickness of the unit is typically 1–4 m. (RMVF) inundated the Elko basin at Ravens Nest and surrounding areas. Magmatism in the RMVF was most Qfy Young alluvial-fan deposits (Holocene) Coarse-to concentrated in a ~1 m.y. span from ~38.5 to 37.5 Ma (tables fine-grained alluvial deposits in intermittently active alluvial 2 and 3 of Appendix); magmatism was characterized by the fans and perennial tributary channels; locally sandy, pebble- emplacement of numerous rhyolite and dacite flow domes to cobble-sized gravel with silt and boulders, or sandy silt and associated small-volume ash-flow tuff. The domes are with coarse-grained material in discontinuous horizons. spatially associated with numerous intrusions (stocks, dikes, Clasts are subrounded to subangular. Fan surfaces and sills) of rhyolite, dacite, granite porphyry, and commonly have distributary flow patterns with morphology granodiorite that were emplaced into Paleozoic rocks and ranging from subdued bar-and-channel forms to slightly strongly recrystallized them to hornfels and marble over an smoothed surfaces. Map unit includes young alluvial exposed area at least 43 km2. Intrusions are spatially and deposits in incised channels along axial drainages. In Pine temporally related to numerous historically mined skarn and Valley, Qfy deposits are present in drainages that are incised polymetallic carbonate replacement deposits of the Railroa d >100 m below Qfo surfaces. The large magnitude of incision mining district, which contained copper, gold, silver, lead, is the result of base level change associated with the and zinc (Ketner and Smith, 1963; Koehler et al., 2015; integration of Pine Valley into the Humboldt River basin in Jackson et al., 2015). Peripherally distributed around the the middle Pleistocene. Qfy fans typically have weak to no largest intrusion, the Bullion composite stock, are many soil development. If present, soil development is sedimentary rock-hosted gold deposits,