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Geological Society of Nevada (GSN) Monthly Dinner Meeting—February 15

The Continua between Carlin-type Gold Deposits and Distal Disseminated and Epithermal Gold-Silver Deposits in Nevada

John Muntean

Nevada Bureau of Mines and Geology
University of Nevada, Reno
Faces of GSN: John Muntean

Abstract: Most research on Carlin-type deposits in Nevada has focused on four main camps that account for 95% of the production from Carlin-type deposits in Nevada – the Carlin Trend, Cortez, Getchell, and Jerritt Canyon. Though their local geologic settings differ slightly, they share many common characteristics, including lithologic and structural controls to fluid flow and ore deposition, an As-Hg-Sb-Tl geochemical signature and low Ag:Au ratios in the ores, hydrothermal alteration and ore paragenesis, relatively low temperatures and salinities of ore fluids, and lack of lack of mineral and elemental zoning. The shared characteristics suggest a shared origin, yet there is no consensus on their genesis. Future research should focus on Carlin-style deposits, such as distal-disseminated deposits that have a clear genetic association with magmatic-hydrothermal systems associated with intrusions and deposits that have characteristics of epithermal deposits.

There has been limited research on these Carlin-style deposits. An exception is the Cove distal disseminated deposit where Johnston et al.’s (2008) detailed study demonstrated both polymetallic and proximal Carlin-style mineralization, which led them to conclude that Cove represents a continuum between magmatic-hydrothermal systems and Carlin-type gold deposits in Nevada. New research utilizing recent deep drilling (Muntean et al., 2017) clearly shows Carlin-style mineralization overprints earlier polymetallic mineralization. The recent drilling also shows the Carlin-style mineralization is strongly zoned. The Ag/Au ratios of zones of Carlin-style mineralization and the Ag concentrations of pyrite decrease from the CSD zone underneath the open pit towards the Helen zone located 3 km to the northwest. Arsenian pyrite associated with Carlin-style mineralization in the CSD is coarser grained, euhedral, and becomes much finer grained with narrow arsenian rims in the Helen zone, very similar to the pyrite textures seen in the large Carlin-type deposits. The Kinsley deposit in eastern Nevada, shows very similar zoning features away from an Eocene intrusion. Over a distance of ~3 km, proximal W-(Mo) skarn adjacent to the intrusion zones outward to polymetallic quartz veins/mantos and distal Carlin-style mineralization that locally overprints polymetallic mineralization (Hill, 2016). The overprinting of polymetallic mineralization by Carlin-style mineralization at Cove and Kinsley could be the result of a separate later hydrothermal system. Alternatively, the zoning at Cove and Kinsley represent telescoped systems, where exhumation by erosion or by faulting led to the overprint.

Other Carlin-style deposits, mainly in eastern Nevada, have epithermal characteristics and appear to have formed at much shallower depths than the large Carlin-type deposits. Nutt and Hofstra (2003) pointed out many features at Alligator Ridge deposit consistent with formation at depths of <300 to 800 m, as did Ressel et al. (2015) for deposits in the Northern Pinon Range. The features include higher Ag/Au ratios, jigsaw mosaic quartz and feathery chalcedonic jasperoid suggestive of <180˚C, hydrothermal breccias, and Eocene lacustrine sediments with elevated As, Sb, Tl, and Hg. Quartz after lattice-textured calcite is present at the Gold Point deposit, where Castor and Hulen (1996) reported electrum occurring in banded quartz that filled matrices of brecciated stratiform jasperoid. The absence of the Roberts Mountain thrust in eastern Nevada is likely the main factor for the increase of epithermal characteristics. Where present the Roberts Mountains thrust and contractional deformation in the lower plate carbonates played a major role in forming the large Carlin-type deposits, by diverting upwelling hydrothermal fluids out of high-angle faults and into reactive carbonate rocks. In the absence of such a thrust in the upper crust, as in eastern Nevada, hydrothermal fluids rose toward the surface and interacting with increasing amounts of groundwater, resulting in extensive jasperoid formation.

Meeting Details

“The GSN Reno meeting is next Friday, February 15th, again at the NEW LOCATION: Great Basin Brewing’s Taps & Tanks facility, 1155 S. Rock Blvd., #490.  The entrance is ACTUALLY on McCarran Blvd. just south of the intersection w/Rock Blvd.

It is SPONSOR APPRECIATION NIGHT and we will be recognizing all those generous donors who have bought the drinks for the members at the Reno meetings.  These bar tabs average at least $2,000.00 per meeting!  Please join us in showing our appreciation for their ongoing support of the GSN membership!

Dinner cost is $25/each and dinner reservations are due by MONDAY, FEBRUARY 11TH BY 4:00 PM!!  If you’d like to PREPAY for dinner please click on this link (by Jan 11th):   https://squareup.com/store/GSNV .

Or you can email your reservation to Laura Ruud at the GSN office: gsn@gsnv.org. (If you make a dinner reservation and No show/No cancel by Thursday, Feb. 14th at 9 am, you will be invoiced for $25 after the meeting, students included.)

PLACE: Great Basin Brewing’s Taps & Tanks, 1155 S. Rock Blvd., Reno, Nevada

TIMES: 6:00 p.m. – Drinks and dinner check-in begin

7:00 p.m. – Buffet dinner ($25 at the door or pre-pay online by clicking this link: https://squareup.com/store/GSNV )

7:30 p.m. – SPONSOR RECOGNITION BEGINS

7:45 p.m.  Announcements and Talk begin”

This message was forwarded from Laura Ruud, GSN Executive Manager. If you have any questions, you can contact her here: Phone (775) 323-3500; gsn@gsnv.org, www.gsnv.org .

Sorry for this late notice. Laura said that anyone is welcome to attend the lecture only (begins at 7:45) for free and no reservations are required for that. Of course, you would not get dinner or free drinks.

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Geologic map of the Terrill Mountains quadrangle, Churchill and Mineral counties, Nevada


Author: Chad W. Carlson
Year: 2018
Series: Map 187
Version: supersedes Open-File Report 2014-04
Format: plate: 33 x 27 inches, color; text: 16 pages, color
Scale: 1:24,000
View/download/purchase:

http://pubs.nbmg.unr.edu/Geol-Terrill-Mountains-quad-p/m187.htm

GIS version:

http://pubs.nbmg.unr.edu/CDP-Geol-Terrill-Mountains-quad-p/m187z.htm

The Terrill Mountains 7.5-minute quadrangle is located about 45 km south of Fallon and incorporates the bulk of the Terrill Mountains, southern Calico Hills, northwest Red Ridge, and part of the Rawhide Flats valley just east of U.S. Highway 95. The Terrill Mountains quadrangle has significant relevance to understanding the evolving tectonic framework of the region, as it straddles a major domain boundary in the Walker Lane. Positioned between the Sierra Nevada microplate and Basin and Range, the Walker Lane accommodates ~20% of the right-lateral transform motion between the North American and Pacific plates. This motion is accommodated on NW-striking right-lateral and ENE to E-W-striking left-lateral fault systems. The Terrill Mountains lie at the northern terminus of right-lateral fault zones translating crustal-blocks of the central Walker Lane and at the southeastern edge of left-lateral faults accommodating clockwise-rotation of blocks in the northern Walker Lane. As the mechanisms of strain transfer between these disparate fault systems are poorly understood, the thick Oligocene to latest Miocene volcanic strata of the Terrill Mountains make it an ideal site for studying the transfer of strain between regions undergoing differing styles of deformation and yet both accommodating right-lateral motions. Further, it contains several major Quaternary faults capable of producing large earthquakes and the Camp Terrill mining district.

Detailed geologic mapping of the Terrill Mountains quadrangle was completed to help elucidate the Neogene styles of, and changes in, strain accommodation for this region of the Walker Lane. The mapped Tertiary strata include at least nine late Oligocene ash-flow tuffs. Several tuffs, not previously identified in the Terrill Mountains, are tentatively correlated to regionally extensive units in the western Great Basin, including the 25.3 Ma Nine Hill Tuff. A distinct ~23 Ma paleosol is locally preserved below the tuff of Toiyabe and provides an important marker bed. This paleosol is offset ~6 km across a strand of the NW-striking, right-lateral Benton Springs fault that bounds the NE flank of the Terrill Mountains. Strain at the northernmost Terrill Mountains appears to be transferred from a system of NW-striking right-lateral faults to a system of ~E-W striking left-lateral faults with associated clockwise flexure. The northern Terrill Mountains may represent a localized region of strain transfer analogous to the greater transition between the central and northern Walker Lane.

The detailed mapping of the Terrill Mountains quadrangle was completed through the EDMAP component of the National Cooperative Geologic Mapping Program in cooperation with the U.S. Geological Survey (Agreement No. G13AC00106), and supported by a grant from the National Science Foundation (EAR1419724). This mapping has provided a robust foundation for structural, paleomagnetic, and geochronologic investigations in the region.

Award-winning map!
Chad Carlson won first place in the 2014 Student Geologic Map Competition at the annual meeting of the Geological Society of America in Vancouver on October 21, 2014 for his Geologic Map of the Terrill Mountains, Western Nevada.

Here is a YouTube video of the students at GSA talking about their winning posters:

https://www.youtube.com/watch?v=9_MA-757UK4

Preliminary geologic map of the Independence Valley NE quadrangle, Elko County, Nevada

Authors: Andrew V. Zuza, Christopher D. Henry, Michael W. Ressel, Charles H. Thorman, Seth Dee, and Jeffrey E. Blackmon
Year: 2018
Series: Open-File Report 2018-04
Format: plate: 39 x 31 inches, color; text: 12 pages, b/w
Scale: 1:24,000
View/download/purchase:

http://pubs.nbmg.unr.edu/Prel-geol-Indep-Valley-NE-p/of2018-04.htm

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:

http://www.gsnv.org/about/faces-of-gsn.php?face=mressel

http://www.gsnv.org/about/faces-of-gsn.php

NBMG staff pages

You can also read about the other geologic mappers and their work on the individual NBMG staff pages:

http://www.nbmg.unr.edu/Staff.html

Preliminary geologic map of the Ravens Nest quadrangle, Elko and Eureka counties, Nevada

Authors: Michael W. Ressel and Seth Dee

Year: 2018

Series: Open-File Report 2018-05

Format: plate: 37 x 30 inches, color, 2 cross sections; text: 20 pages, color

Scale: 1:24,000

View/download/purchase:

http://pubs.nbmg.unr.edu/Prel-geol-Ravens-Nest-p/of2018-05.htm

The Ravens Nest 7.5-minute quadrangle is located in the northern Piñon Range south of the town of Carlin in north-central Nevada. Mapping at Ravens Nest was undertaken to address several components of the complex geology of north-central Nevada, including the nature of sedimentation and deformation associated with the Early Mississippian Antler orogeny, the effects of post-Antler contractional deformation, development of the Eocene Elko Basin and slightly younger Robinson Mountain volcanic field, and deformation associated with Cenozoic extension in the hanging wall of the Ruby Mountains–East Humboldt Range metamorphic core complex. Importantly, the northern Piñon Range lies within the southern segment of the Carlin trend gold belt, which is one of the premier gold mining jurisdictions in the world. Gold produced from disseminated, sedimentary rock-hosted deposits, or Carlin-type deposits, in Nevada comprised about 90.5% of Nevada’s production and about 73.6% of U.S. production in 2016 (Muntean et al., 2017). The southern Carlin trend in the vicinity of the Ravens Nest quadrangle has seen several new Carlin-type gold discoveries since 2010 in non-traditional Paleozoic host strata. The Piñon Range and flanking Pine and Huntington valleys are also important areas for conventional and unconventional hydrocarbon resources. The Blackburn and Tomera Ranch oil fields in Pine Valley produce from Cenozoic and Paleozoic rocks widely distributed in the Ravens Nest quadrangle, and the Elko Basin has seen assessment of its oil-bearing shale by the U.S. Bureau of Mines in the 1970s and in 2012-15 for its hydrofracture potential by energy companies.

Mapping shows that three principal Paleozoic structural-stratigraphic domains exist at Ravens Nest. In particular, Late Devonian to Early Mississippian strata, which straddle the leading edge of the Roberts Mountains allochthon, are interpreted to comprise: 1) the deformed base of the allochthon, 2) the incipiently deformed foreland basin, and 3) the least-deformed passive margin. The allochthonous rocks are separated from rocks of the passive margin by a west-dipping thrust or thrusts. In addition, a fourth domain, the Antler overlap sequence, consists of relatively undeformed Late Mississippian through Permian strata widespread at Ravens Nest, which overlies all three other Paleozoic domains. The Early Mississippian Chainman Shale, previously mapped as a component of all three domains, is herein restricted to an allochthonous shale-dominant Lower Mississippian facies that occurs in the western half of the Ravens Nest quadrangle. The Chainman along with underlying deformed units of the Webb and Woodruff Formations were thrust upon a coarse chert- and quartzite-grain sandstone and fine conglomerate formerly assigned to the Chainman Shale by Smith and Ketner (1978) but herein attributed to the Melandco Sandstone. Two key Early Mississippian units, the Webb of allochthon derivation, and the Tripon Pass of passive margin derivation, straddle allochthon, foreland basin, and passive margin, and thus, provide important ties between Antler tectonic domains. Late south-vergent reverse faults cut some Lower Mississippian rocks, indicative of a change from Antler east vergence that may reflect either post-Early Mississippian (i.e., post-Antler) contraction, or local variation of Antler deformation through time and space.

Rocks of the Eocene Elko Basin unconformably overlie Paleozoic rocks at Ravens Nest. The basin developed as primarily lacustrine sedimentation from ~45 Ma to 38 Ma, and only a small part of the lacustrine facies is present in the far northeast corner of the Ravens Nest quadrangle. An Eocene basal fluvial-alluvial gravel is present in many places in and near Ravens Nest quadrangle, which in previous mapping was commonly assigned a Paleozoic age (Hollingsworth et al., 2017). By ~40 Ma at Ravens Nest, significant volcanic input is evident in strata of the Elko Basin, as distally derived small-volume ash-flow tuff and tephra. By ~38.5 Ma, significant local volcanic input began, and lacustrine deposition completely ceased by ~38 Ma, during major deposition of volcanic products of the nearby Robinson Mountain volcanic field (RMVF). Activity associated with the RMVF was short-lived, with abundant rhyolite and dacite lavas and domes with lesser tuff emplaced between ~38.5 and 37.5 Ma. Coeval with calc-alkaline volcanism was the emplacement of the Bullion granodiorite to high-silica rhyolite intrusion in the Railroad district as well as other smaller stocks and swarms of silicic to intermediate sills and dikes. The intrusions of the Railroad district are responsible for polymetallic skarn and carbonate-hosted replacement deposits. In addition, widespread marble and hornfels occurs over 40 km2 in the southern half of the quadrangle, indicative of a much larger underlying pluton. Carlin-type gold deposits are coeval with Eocene intrusions and occur peripherally to them and higher-temperature polymetallic deposits (Henry et al., 2015; Hollingsworth et al., 2017).

The mid-Miocene Humboldt Basin partly overlapped the Elko Basin in the vicinity of the Ravens Nest quadrangle. However, extensive areas of lacustrine shale and siltstone, tuff, and fluvial and alluvial gravels occur over a large area in the southwest part of the quadrangle where lacustrine deposition postdated emplacement of the Palisade Rhyolite (Wallace et al., 2008). Strata of the Humboldt Basin were faulted against Paleozoic bedrock along north striking normal faults on the eastern margin of Pine Valley. Pliocene and younger gravels and extensive tuffaceous lacustrine deposits of the Hay Ranch Formation were deposited synextensionally into a hydrologically closed Pine Valley. Quaternary normal faulting along the western margin of the Piñon Range has continued at least into the middle Pleistocene. The effects of the stream capture of Pine Creek and integration of Pine Valley into the Humboldt River watershed during the middle Pleistocene include deeply incised drainages, oversteepened hillslopes and extensive landslide deposits.

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:

http://www.gsnv.org/about/faces-of-gsn.php?face=mressel

http://www.gsnv.org/about/faces-of-gsn.php

NBMG staff pages

You can also read about the other geologic mappers and their work on the individual NBMG staff pages:

http://www.nbmg.unr.edu/Staff.html

Preliminary geologic map of the Mount Rose NW quadrangle, Washoe County, Nevada


Authors:
Nicholas H. Hinz, Alan R. Ramelli, and Christopher D. Henry
Year:
2018
Series:
Open-File Report 2018-03
Version:
supersedes Open-File Report 2016-06
Format: plate: 35 x 29 inches, color; text: 4 pages, B/W
Scale:
1:24,000
View/download/purchase:

http://pubs.nbmg.unr.edu/Prel-geol-Mount-Rose-NW-p/of2018-03.htm

This quadrangle straddles the north end of the Carson Range directly west-southwest of Reno and abuts the Nevada-California border. The Truckee River and Interstate 80 transect the northwest quarter of the quadrangle. Parts of the City of Reno urban area and Steamboat irrigation ditch fall within the northern part of the quadrangle, and part of a rural community along Thomas Creek is in the southeast quarter.

The bedrock exposures in the quadrangle consist of Mesozoic granitic and metamorphic basement, and Tertiary volcanic and sedimentary rocks. The Tertiary section includes a complex section of lavas, intrusions, and volcanic sedimentary rocks. Tertiary volcanic and sedimentary rocks in the northern part of the quadrangle are part of an ~1112 Ma ancestral Cascades volcanic center. Generally north-dipping Miocene basalt (~10 Ma) and fluvial-lacustrine sediments rest on the ~11–12 Ma volcanic rocks. Many of the volcanic and sedimentary rocks in the southern part of the quadrangle were derived from a ~6–7 Ma volcanic center in the Mount Rose quadrangle, directly south of this quadrangle. Plio-Pleistocene basaltic andesite lavas locally rest on these late Miocene volcanic rocks in the middle part of the quadrangle. Principal surficial deposits include late Pliocene to modern alluvial fan and fluvial deposits, deposits of the Truckee River, Quaternary glacial deposits, and extensive late Quaternary mass wasting deposits. Notable deep-seated landslide complexes reside in all major drainages—including Thomas Creek, Hunter Creek, Bronco Creek, and the smaller catchments along the west edge of the quadrangle. Most of the Carson Range is west-tilted with west-dipping Cenozoic strata. However, within the Mount Rose NW quadrangle, the dip domain flips and most all the Cenozoic strata dips east with numerous west-dipping normal faults. These west-dipping normal faults are cut by younger east-dipping normal faults of the Mount Rose fault zone on the east side of the range. East-facing Quaternary fault scarps occur on the east side of the range, west-facing Quaternary fault scarps occur on the west side of the range, and the crest of the range is cut by a complex zone of mostly west-facing faults.

This geologic map was funded in part by the USGS National Cooperative Geologic Mapping Program under STATEMAP award numbers G15AC00240, 2016, and G17AC00212, 2018.

Preliminary geologic map of the central East Range, Pershing County, Nevada

Authors: Sandra J. Wyld, James R. Nutaitis, and James E. Wright

Year: 2018

Series: Open-File Report 18-7

Format: plate: 51 x 38 inches, color, with 3 cross sections and photos; text: 14 pages, b/w

Scale: 1:24,000

View/download/purchase:

http://pubs.nbmg.unr.edu/Prel-geol-central-East-Range-p/of2018-07.htm

This is a new geologic map of the central East Range, including bedrock and Cenozoic geology. Text on stratigraphic units and structural relations accompanies map. Panels illustrating structures and elements of stratigraphy are included. The study documents several important new discoveries. Ductilely deformed and metamorphosed rocks of the Cambrian Preble Formation underlie the Lee Peak Window, but are not as extensive as previously inferred, and Ordovician fossils thought to be from the Preble are actually from the structurally overlying Ordovician Valmy Formation. A fault between these two units is present everywhere (Lee Peak fault) and probably originated as a Paleozoic thrust (Roberts Mountains thrust?) but was later domed upward, along with Window units, during intrusion of the 165 Ma Lee Peak pluton. Unconformably overlying the Valmy Formation is the Mississippian to Pennsylvanian(?) Inskip Formation, which is extensively deformed by the newly defined Jurassic top-to-the-east Buena Vista ductile shear zone. We distinguish a new unit, the Permian Buena Vista unit, from the upper Inskip Formation. A newly defined dextral strike-slip fault (Jurassic Rockhill Canyon fault, previously shown as part of a “Willow Creek thrust”) is identified in Rockhill Canyon, and separates Paleozoic units listed above from a thin selvage of Havallah Formation overlain by Triassic strata of the Koipato, Star Peak, and Auld Lang Syne Groups. Triassic units were deformed by NW-SE shortening in the Jurassic, primarily manifested by folds and foliation. Jurassic structures (shear zone, strike-slip fault, folds and foliation) are related to shortening in the Fencemaker fold-thrust belt.

The map covers most of the Dun Glen and Natchez Pass 1:24:000-scale quadrangles and the southern portion of the Inskip Canyon and Lee Peak quadrangles.

Geologic mapping was supported by the Tectonics Program of the National Science Foundation and the Geological Society of Nevada.