New Geologic Map—Welcome Quadrangle

Welcome

Title:  Geologic map of the Welcome quadrangle and an adjacent part of the Wells quadrangle, Elko County, Nevada
Author:  Allen J. McGrew[udayton.edu] and Arthur W. Snoke[uwyo.edu]
Year:  2015
Series:  Map 184
Format:  plate: 51 x 32.5 inches, color; text: 40 pages, color
Scale:  1:24,000; inset: 1:12,000

Located in central Elko County, the Welcome quadrangle and an adjacent part of the Wells quadrangle expose a remarkable array of critical relationships for understanding the geologic history of the state of Nevada and the interior of the southwestern U.S. Cordillera. Covering the northern end of the East Humboldt Range and adjacent Clover Valley and Clover Hill, this map includes the northern terminus of the Ruby Mountains–East Humboldt Range metamorphic core complex.

The oldest rocks in the state of Nevada (the gneiss complex of Angel Lake), and Nevada’s only exposures of Archean rock, form the core of a multi-kilometer scale, southward-closing recumbent fold-nappe, the Winchell Lake nappe (WLN). Although intensely metamorphosed and profoundly ductilely attenuated, the WLN folds a series of pre-metamorphic thrust allochthons that collectively form an essentially complete sequence of Paleoproterozoic to Mississippian metasedimentary rocks. The WLN transported what may be Nevada’s most deeply exhumed rocks, with peak pressures ranging to 10 kb, peak temperatures in excess of 750 ºC, and widespread partial melting and stromatic migmatization, all related to Late Cretaceous to Paleocene tectonism.

Overprinting the metamorphic core is a WNW-directed kilometer-scale shear zone that, together with the detachment fault that forms its roof, accommodated tens of kilometers of extensional displacement in mid- to late Cenozoic time, diachronously exhuming the terrain from mid-crustal depths by late Miocene time. In addition, the high-grade rocks are extensively intruded by one of the Nevada’s most diverse suites of magmatic rocks, ranging in age from Archean to Miocene and in composition from mafic to felsic. On the west flank of Clover Hill, a west-dipping detachment-fault system separates the high-grade metamorphic core from an overlying plexus of brittlely deformed, partly correlative but lower grade to non-metamorphosed Paleozoic rocks. In turn, a sequence of partly syntectonic volcanic and sedimentary rocks ranging in age from Eocene to Miocene structurally overlie the fault-bounded Paleozoic units. The Cenozoic sequence includes late Eocene and Oligocene ignimbrites and volcaniclastic rocks, Miocene sedimentary rocks and megabreccias, a Miocene rhyolite complex, and younger sedimentary rocks and vitric tuffs. The presence of the most distal northeasterly exposure of a key Oligocene volcanic marker, the 29 Ma tuff of Campbell Creek, suggests that a broad, low-relief (unfaulted) terrain was dissected by paleovalleys that extended at least 200 km to the west. Bracketed between the tuff of Campbell Creek and a 15.5 Ma tuffaceous sandstone at the base of the Miocene Humboldt Formation is a proximal sedimentary sequence known as the sedimentary sequence of Clover Creek that includes conglomerate, sedimentary breccia, sandstone, and megabreccia as well as intercalations of fossiliferous lacustrine strata. The megabreccias consist of unmetamorphosed mid-Paleozoic rocks (chiefly Upper Devonian Guilmette Formation) interpreted as rock-avalanche deposits shed from evolving normal-fault scarps inferred to have bounded the basin to the east. Disconformably overlying the sedimentary sequence of Clover Creek is a thick sequence of Miocene Humboldt Formation that is tilted steeply down against the detachment fault system, documenting large-scale displacement on the detachment system extending to at least as young ca. 9 Ma.

Finally, bounding the range today on both east and west are large, normal-fault systems that were active in Quaternary time, including the Clover Hill fault, which may represent a southerly extension of the blind fault that caused the 2008 Mw 6.0 Wells earthquake.

This map was prepared with support from the Geological Society of Nevada; National Science Foundation; University of Wyoming, Laramie; and the University of Dayton, Dayton, Ohio.

View or purchase Map 184 here: http://pubs.nbmg.unr.edu/product-p/m184.htm

New Geologic Map—Heelfly Creek Quadrangle

Heelfly

Title: Preliminary geologic map of the Heelfly Creek quadrangle and adjacent parts of the Tent Mountain, Soldier Peak, and Secret Valley quadrangles, Elko County, Nevada
Author: Seth M. Dee, Gregory M. Dering, and Christopher D. Henry
Year: 2015
Series: Open-File Report 15-4
Format: plate: 31 x 33 inches, color; text: 5 pages, b/w
Scale: 1:24,000

A 1:24,000-scale geologic map of the Heelfly Creek 7.5-minute quadrangle and adjacent parts of the Tent Mountain, Soldier Peak, and Secret Valley quadrangles, Elko County, Nevada. The map area covers the westernmost part of the East Humboldt Range, foothills west of the range front, and lowlands of Starr Valley. The quadrangle is traversed by numerous creeks flowing from the high topography in the east across lowlands occupied by ranching and farming communities toward the Humboldt River. New mapping has been integrated with data from previous bedrock and neotectonic studies to elucidate the structural and stratigraphic framework of the region. The relative timing and varying modes of Cenozoic extension documented here provide context for seismic hazard assessment as well as hydrocarbon and metallic mineral exploration.

Middle Proterozoic through Devonian sedimentary and metamorphic rocks (Ely Formation, Diamond Peak Formation, Guilmette Formations, Eureka Quartzite, Horse Creek assemblage and Proterozoic crystalline basement) are exposed along the high relief East Humboldt range front. These rocks are part of the Ruby Mountains–East Humboldt Range metamorphic core complex, a package of complexly deformed Proterozoic orthogneiss interfolded with Paleozoic metasedimentary rocks exhumed from mid-crustal depths along several low-angle faults during Tertiary extension. The crystalline and Paleozoic sedimentary rocks of the East Humboldt Range front are juxtaposed against middle Miocene sedimentary and volcanic rock along a north-striking, high-angle normal fault. The fault is locally buried by a mega-landslide deposit of presumed mid-Pleistocene age. Activity on this fault likely ended in the middle Pleistocene when uplift stepped 4–5 km west to the currently active frontal fault trace. Late Quaternary uplift along the active frontal fault trace exposed a section of largely northeast-dipping tuffaceous sandstone, shale and conglomerate of the Miocene Humboldt Formation. The stratigraphically lowest Cenozoic deposits, exposed near the southern map boundary in a broad anticline, may be as old as Eocene and equivalent to the Elko Formation. The Miocene sediments are locally overlain by coarsely porphyritic lavas chemically correlated with Jarbidge Rhyolite, which is widely distributed across northeastern Nevada.

Quaternary deposits in the map area include numerous inset Pleistocene surfaces beveled onto the Miocene sediments, early Pleistocene to Tertiary lacustrine and fluvial basin deposits, glacial outwash likely from the Lamoille and Angel Lake glaciations, and several inset late Pleistocene through Holocene alluvial fan and fluvial terrace deposits. Repeated late Quaternary surface-rupturing earthquakes along the active trace of the frontal fault system are recorded by increased uplift of Quaternary surfaces as a function of relative age.

This map was prepared with support from the Nevada Division of Minerals.

View or purchase Open-File Report 15-4 here: http://pubs.nbmg.unr.edu/product-p/of2015-04.htm

New Geologic Map—Robinson Mountain Volcanic Field / NW Huntington Valley

of2015-2_plate1

Title: Preliminary geologic map of Cenozoic units of the central Robinson Mountain volcanic field and northwestern Huntington Valley, Elko County, Nevada
Author: Jens-Erik Lund Snee[earth.stanford.edu] and Elizabeth L. Miller[earth.stanford.edu]
Year: 2015
Series: Open-File Report 15-2
Format: two color plates and color text; plate 1 (geologic map): 41 x 54 inches, plate 2 (cross sections): 43 x 21 inches, text: 42 pages
Scale: 1:24,000

Huntington Valley is situated east of the Piñon Range, in the hanging wall of a shallowly west-dipping detachment system bounding the west side of the Ruby Mountains–East Humboldt Range (RMEH) metamorphic core complex. This geologic map of Cenozoic sedimentary, volcanic, and subvolcanic rocks of the central Robinson Mountain volcanic field and northwestern Huntington Valley provides important information about the history of Cenozoic crustal extension, magmatism, sedimentation, and paleogeography near the RMEH.

Depositional rates in the Elko Basin were minor from Cretaceous to Oligocene time, and became rapid in the middle Miocene. Late Cretaceous(?)–Eocene(?) conglomerate, sandstone, siltstone, and limestone “redbeds” (TKcs) and limestone (TKl) are exposed at the base of the Cenozoic section in places, where they each reach thicknesses of ~600 m, but they are not exposed at all in other locations. The overlying Eocene Elko Formation is only ~180 m thick at its greatest in the map area. Detrital zircon geochronology conducted on two samples collected near its base yields a maximum depositional age of ~45.9 ± 1.0 Ma, and a third sample collected near the top of this unit yields a maximum depositional age of 37.9 ± 0.5 Ma.

The calcic to calc-alkalic Robinson Mountain volcanic field records early peraluminous to weakly metaluminous “ignimbrite flare-up” volcanism of basaltic andesite to trachydacite and rhyolite composition, which occurred mostly between about 38.5 and 36.8 Ma. Early eruptions were roughly synchronous with the end of deposition of the Elko Formation, and no significant unconformity is observed beneath the volcanic units. The only Eocene–Oligocene sedimentary rocks exposed above the Eocene Elko Formation are thin, fluviolacustrine deposits interbedded within the volcanic rocks. For this reason, the “Indian Well Formation” name for Eocene–Oligocene volcanic and sedimentary rocks has been abandoned. The rhyolitic, Oligocene-age tuff of Hackwood Ranch is significantly younger than the Eocene deposits of the Robinson Mountain volcanic field. This tuff was erupted at ~31.1 Ma, which coincides with a lull in regional volcanism, but could represent far-traveled deposits from a distant volcanic center.

Significant, approximately westward tilting developed a shallow angular unconformity between ~37.3 and 33.9 Ma (10–15°). Subsequently, between ~31.1 and 24.4 Ma or later, 10–15° additional westward tilting occurred. These westward tilting events were likely associated with slip on east-dipping normal faults in the Piñon Range. Following the second episode of westward tilting, a basin rapidly developed near the present-day RMEH, as recorded by thick deposits of the mostly Miocene Humboldt Formation that dip gently eastward toward the RMEH. Greater than 1 km of the sedimentary strata previously mapped as Eocene–Oligocene age has been reassigned to the Miocene Humboldt Formation as a result of our geologic mapping and supporting geochronology.

Detrital zircon geochronology yielded a coherent age group at ~24.4 Ma for one tuffaceous pebble conglomerate and sandstone sample at the base of the Humboldt Formation, but it is unlikely that this maximum depositional age constrains the timing of the start of basin sedimentation. Deposition accelerated at ~16–15 Ma, when most of Humboldt Formation pebble conglomerate, sandstone, siltstone, marl, and air-fall tuff were deposited in Huntington Valley. Locally, pre-Tertiary rocks were exposed by faulting by ~16 Ma (although this depositional age is not well constrained), and RMEH provenance is not detected until ~14 Ma, suggesting that the metamorphic core complex was not exposed until about this time. Greater than 2100 m of Humboldt Formation strata were deposited in the study area alone (thickening further eastward toward the RMEH), and deposition continued until at least ~8.2 Ma, but the rate apparently decreased before ~12 Ma.

Miocene or later fault slip occurred along a well preserved, east-dipping normal fault system exposed at the east side of the Piñon Range, partially synchronous with faulting at the RMEH. Uplift and erosion of Eocene- to Quaternary-age sedimentary and volcanic deposits on the west side of Huntington Valley support a significant magnitude of slip on west-dipping normal faults west of the study area during or after Miocene time. Open folding of the Humboldt Formation occurred during or after the middle–late Miocene, perhaps due to normal fault slip offsetting underlying Paleozoic basement.

This geologic mapping study thus supports the hypothesis that surface-breaking extensional faulting in and near the mapped area was minor from the Late Cretaceous(?) through the early Miocene, and that most surface-breaking extension and sediment deposition occurred in middle Miocene time.

This map covers all of the following 1:24,000-scale quadrangles: Robinson Mountain, Cedar Ridge, and Red Spring and a portion of the following quadrangles: Bailey Mountain, Bullion, and West of Lee.

This map was prepared as part of the EDMAP component of the National Cooperative Geologic Mapping Program in cooperation with the U.S. Geological Survey and with support from the Geological Society of Nevada.

View or purchase Open-File Report 15-2 here: http://pubs.nbmg.unr.edu/product-p/of2015-02.htm

New Interactive Mining District Map

Rachel (Wearne) Micander, GIS Specialist with the NBMG Cart/GIS group, has created a new interactive mining district map, and you can view the beta test of that map here.

New: Beta test of the interactive mining districts web mapping application and how-to guide.

Please send any comments and suggestions that you may have to Rachel Micander: rwearne@unr.edu

Creation of map services and interactive maps are an important component of the Nevada Bureau of Mines and Geology mission. Interactive maps are developed as a tool for users who may not have access to their own datasets or GIS software. Users can download specific databases, excel files and PDF’s, search layer information, and view updated data without any special skill other than internet familiarity.

The Mining District Files consist largely of historical and current maps, reports, articles, photographs, correspondence, assays, production reports, and reserve information on all aspects of mining in Nevada. These have largely been donated to the NBMG over the years from individuals, companies, and other government agencies.

Over the last several years, Nevada Bureau of Mines and Geology has undertaken the digital conversion of these paper documents into scanned images. The files contained in the mining district files are in PDF file format. The digital file conversion project at NBMG is ongoing. Some records are copyrighted and have no link associated with them in the search results. However, these documents are available for viewing at NBMG’s Great Basin Science Sample and Records Library.

See other interactive maps created by the NBMG Cart/GIS group here:
http://www.nbmg.unr.edu/Mapping/InteractiveMaps.html

Take a five minute vacation with this geologic photo tour of Nevada:
http://nbmg.maps.arcgis.com/apps/MapTour/?appid=32bc91f8e5b84522828663f9b6516410#[nbmg.maps.arcgis.com]

Job Announcements from BLM

blm-logo Message from BLM:  We are pleased to announce new, exciting positions available at BLM – BUREAU OF LAND MANAGEMENT.   It is our hope that qualified, career oriented individuals at your organization or other professionals known to you will actively consider this position and apply accordingly.  Efforts on your part to disseminate this information are greatly appreciated. Position Information: Job Description:  Civil Engineer; Announcement Number:  OR-DEU-2015-0169; Location(s) of position:  Eugene, OR, US; Salary:  $58,562 – $76,131; Applications will be accepted until:  07/07/2015. For additional information on this job posting, please click here. Position Information: Job Description:  General Engineer; Announcement Number:  AZ DEU-2015-0039; Location(s) of position:  Phoenix, AZ, US; Salary:  $71,791 – $93,333; Applications will be accepted until:  07/09/2015. For additional information on this job posting, please click here. Position Information: Job Description:  Archeologist; Announcement Number:  OR-DEU-2015-0168; Location(s) of position:  Roseburg, OR, US; Salary:  $70,192 – $91,255; Applications will be accepted until:  06/30/2015. For additional information on this job posting, please click here. Position Information: Job Description:  Contact Representative; Announcement Number:  OR-DEU-2015-0164; Location(s) of position:  Eugene, OR, US; Salary:  $39,570 – $51,437; Applications will be accepted until:  07/07/2015. For additional information on this job posting, please click here.  Position Information: Job Description:  Range Technician (ESI Team); Announcement Number:  OR-DEU-2015-0157; Location(s) of position:  Vale, OR, US; Salary:  $39,570 – $51,437; Applications will be accepted until:  07/01/2015. For additional information on this job posting, please click here. 

Remembering Harold F. Bonham, Jr.

Bonham

We are very sad to inform you that Harold F. Bonham, Jr. passed away of natural causes on Saturday June 6, 2015. The family will hold a private memorial service.

Hal was a research geologist at Nevada Bureau of Mines and Geology for thirty-three years (1963–1996) and Acting State Geologist and Acting Director at NBMG for two years (1993–1995).

Hal was an internationally recognized expert in the geology of mineral deposits, volcanology, and exploration of precious metal deposits. He had more than thirty years of experience in geologic investigations and mapping in Nevada.

Hal’s contributions to Nevada geology are evident in this list of selected publications which include million-scale commodity maps for gold, silver, copper, lead, and zinc; many urban maps in the greater Reno area; and the geology and mineral resources bulletin for Washoe and Storey counties.

You can read more information about Hal’s career here:

NBMG resume
Biography from Geological Society of Nevada Honorary Member Page

Sincerely,

Jim Faulds (Director) and all of Hal’s many friends at NBMG
Nevada Bureau of Mines and Geology
University of Nevada, Reno, MS 178
Reno, NV 89557
(775)-682-8751

USGS Webinar: Using The National Map services to enable your web and mobile mapping efforts

Are you a developer, firm, or organization using mobile or web applications to enable your users?  The USGS has publicly available geospatial services and data to help your application development and enhancement.

The USGS’ National Geospatial Technical Operations Center (NGTOC[ngtoc.usgs.gov]) will be hosting a 30- minute webinar on “Using The National Map services to enable your web and mobile mapping efforts” on June 16 at 9am Mountain Time.

This webinar will feature a brief overview of services, data and products that are publicly available, a quick overview on how AlpineQuest (http://alpinequest.psyberia.net/[alpinequest.psyberia.net]), a leading private firm, is leveraging this public data to benefit their users, and a Question & Answer session with a USGS developer to help you get the most out of the national geospatial services.

“This is an opportunity from NGTOC to bring developers and users together for some demonstrations and starting some dialogue,” said Brian Fox, the NGTOC Systems Development Branch Chief.  “The webinar format allows us to improve awareness of USGS geospatial services and develop a better understanding of what users and developers need to make our data and services more available and usable.”

To access the webinar, you’ll need to activate Cisco WebEx and call into the conference number (toll free) 855-547-8255 and use the security code: 98212385.  The webinar will display through WebEx, and you can access it via this address: http://bit.ly/1RHayxY[bit.ly]

To ensure that you have the appropriate players installed for this WebEx enabled webinar: https://usgs.[usgs.webex.com]
webex[usgs.webex.com].com/usgs/systemdiagnosis.php[usgs.webex.com]

The session will be recorded and closed caption option is available during the webinar at: https://recapd.com/w-a3c704[recapd.com]

To find out more about this and other NGOC webinar conferences, go to: http://ngtoc.usgs.gov/webinars/webinar_june2015.html[ngtoc.usgs.gov]

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