Research Article| December 01, 1998 Eocene magmatism: The heat source for Carlin-type gold deposits of northern Nevada Christopher D. Henry; Christopher D. Henry 1Nevada Bureau of Mines and Geology, University of Nevada, Reno, Nevada 89557 Search for other works by this author on: GSW Google Scholar David R. Boden David R. Boden 21445 High Chaparral Drive, Reno, Nevada 89511 Search for other works by this author on: GSW Google Scholar Author and Article Information Christopher D. Henry 1Nevada Bureau of Mines and Geology, University of Nevada, Reno, Nevada 89557 David R. Boden 21445 High Chaparral Drive, Reno, Nevada 89511 Publisher: Geological Society of America First Online: 02 Jun 2017 Online ISSN: 1943-2682 Print ISSN: 0091-7613 Geological Society of America Geology (1998) 26 (12): 1067–1070. https://doi.org/10.1130/0091-7613(1998)026<1067:EMTHSF>2.3.CO;2 Article history First Online: 02 Jun 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation Christopher D. Henry, David R. Boden; Eocene magmatism: The heat source for Carlin-type gold deposits of northern Nevada. Geology 1998;; 26 (12): 1067–1070. doi: https://doi.org/10.1130/0091-7613(1998)026<1067:EMTHSF>2.3.CO;2 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 SocietyGeology Search Advanced Search Abstract The origin of Carlin-type or sediment-hosted, disseminated gold deposits of the Great Basin, the major source of gold in the United States, is poorly understood. We propose that Eocene magmatism was the heat source that drove the hydrothermal systems that generated these deposits in the Carlin trend and Independence Mountains in northern Nevada. This interpretation is based on a strong spatial and temporal association of Eocene intrusive-volcanic centers with the gold deposits of this region. Our new work and published 40Ar/39Ar dates indicate that magmatism was particularly intense between 39 and 40 Ma throughout northeastern Nevada, especially in and around the area of gold deposits. Carlin-type deposits may have formed preferentially during Eocene magmatism because it was (1) more intense in the area than other magmatic episodes, (2) somehow compositionally distinct, or (3) accompanied by extension that promoted hydrothermal flow. However, large-scale extension does not appear to have been a factor in generating Carlin-type deposits. This content is PDF only. Please click on the PDF icon to access. First Page Preview Close Modal You do not have access to this content, please speak to your institutional administrator if you feel you should have access.
The Tuscarora district lies within an Eocene volcanic field that covers [approximately]800 km[sup 2] in the northern Tuscarora Mountains in northwest Elko County. Geologic mapping of [approximately]100 km[sup 2] at Tuscarora and vicinity and new K-Ar age determinations reveal a complex, rapidly evolving volcanic history. Volcanism began with construction of a poorly preserved andesitic stratovolcano(s) at 42+ Ma. Subsequently, the 7- by 10-km Mt. Blitzen graben developed between 41--42 Ma. The graben filled with the tuff of Mt. Blitzen. Graben subsidence occurred along NE to ENE and NNW to NW faults, and a variety of dikes and plugs, including the 39.8-Ma Mt. Neva granodiorite, locally intruded the bounding faults. Rocks of the graben strike NE, dip moderately to steeply, and are cut by penecontemporaneous NE-striking dikes, indicating that the graben formed in response to NW-SE-directed extension. Collapse of the rhyolitic Big Cottonwood Canyon caldera truncated the northern part of the Mt. Blitzen graben between 40.6 and 41.0 Ma. Rocks of the Mt. Blitzen graben range from silicic andesite to rhyodacite, whereas rocks of the Big Cottonwood Canyon caldera are rhyolite and high-silica rhyolite. Mineralization at Tuscarora occurs near the southeast margin of the Mt. Blitzen graben and mainly as quartz-adulariamore » veins filling ENE, N, and NW faults. New K-Ar analyses on adularia from the Dexter and Grand Prize veins yield ages of 38.9 and 39.9 Ma, respectively. Although closely developed in space and time, the Ag-rich, base-metal-bearing mineralization, characterized by the Grand Prize vein, and the Au-rich, base-metal-poor Dexter vein zone likely represent separate, unrelated hydrothermal events. In general, alteration in the district, as observed in outcrops and drill-hole cuttings, changes from fault or fracture controlled in the north to more pervasive in the Dexter pit area and eastward under pediment.« less
Geothermal energy stands out because it can be used as a baseload resource. This book, unlike others, examines the geology related to geothermal applications. Geology dictates (a) how geothermal resources can be found, (b) the nature of the geothermal resource (such as liquid- or vapor-dominated) and (c) how the resource might be developed ultimately (such as flash or binary geothermal plants). The compilation and distillation of geological elements of geothermal systems into a single reference fills a notable gap.
Research Article| January 01, 1986 Eruptive history and structural development of the Toquima caldera complex, central Nevada DAVID R. BODEN DAVID R. BODEN 1Department of Geology, Stanford University, Stanford, California 94305 Search for other works by this author on: GSW Google Scholar Author and Article Information DAVID R. BODEN 1Department of Geology, Stanford University, Stanford, California 94305 Publisher: Geological Society of America First Online: 01 Jun 2017 Online ISSN: 1943-2674 Print ISSN: 0016-7606 Geological Society of America GSA Bulletin (1986) 97 (1): 61–74. https://doi.org/10.1130/0016-7606(1986)97<61:EHASDO>2.0.CO;2 Article history First Online: 01 Jun 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn Email Permissions Search Site Citation DAVID R. BODEN; Eruptive history and structural development of the Toquima caldera complex, central Nevada. GSA Bulletin 1986;; 97 (1): 61–74. doi: https://doi.org/10.1130/0016-7606(1986)97<61:EHASDO>2.0.CO;2 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 SocietyGSA Bulletin Search Advanced Search Abstract The Toquima caldera complex, located in the Toquima Range of central Nevada, consists of three overlapping to nested calderas. The Moores Creek caldera is the largest (∼30 by 20 km); it formed ∼27.2 Ma in response to eruption of the high-silica rhyolite tuff of Moores Creek. Because of recurrent volcanic activity and subsequent basin-range faulting, only the northern segment of the Moores Creek caldera is preserved; its eastern and western margins are downfaulted below valley fill, and its southern part was obscured by collapse of the Mount Jefferson caldera. Eruption of the tuff of Mount Jefferson resulted in collapse of the 18- by 20-km Mount Jefferson caldera ∼26.5 Ma. The ash-flow tuff exposed at Round Mountain is a silicic outflow-facies equivalent of the compositionally zoned (76–67 wt % SiO2) intracaldera tuff of Mount Jefferson. Pyroclastic eruptive activity in the complex concluded ∼23.6 Ma with formation of the comparatively small 8- by 10-km Trail Canyon caldera. With time, caldera size diminished, and the focus of volcanic activity shifted progressively southeastward. The southeastward migration of volcanism in the complex approximately parallels regional northwest-striking faults, suggesting fundamental structural control in the rise and eruption of magma.Arcuate faults and small, aphyric to porphyritic plugs outline the structural margins of the calderas. Some plugs, on the basis of gradational textural changes from vitroclastic in the tuff to flow-layered and porphyro-aphanitic in the plug, appear to represent lava-choked, ash-flow-tuff, feeder vents. Caldera collapse breccias are locally well exposed in all three calderas.Caldera resurgence is not strongly developed in the Toquima caldera complex. The Mount Jefferson massif, which dominates the complex at an elevation of 3,640 m, is an artifact of young basin-range block faulting. The limited development of resurgence in the Mount Jefferson caldera is attributed to ponding of the bulk of erupted material within the caldera.Intermediate to mafic volcanic rocks, premonitory or coeval to silicic ash-flow tuff, are volumetrically minor over central Nevada and are lacking in the Toquima caldera complex. The less silicic magma apparently became lodged in the middle to lower crust below an extensive zone of more silicic, less dense magma. First Page Preview Close Modal You do not have access to this content, please speak to your institutional administrator if you feel you should have access.
Magmatic conditi ons inferred from the composition of the Fish Canyon Tuff by Whitney &Stormer (J. Petrology, 26, 726–62 (1985)) and Stormer & Whitney (Am. Miner. 70, 52–64 (1985)) differ from studies of other ash-flow tuff and caldera systems, in that they consider the magma to have been unzoned and to have resided at ˜9 kb pressure just prior to eruption. We find these conclusions unconvincing because of incomplete sampling of the Fish Canyon Tuff, alteration of the tuff after emplacement, and, in particular, serious limitations of coupled Fe-Ti oxide and two-feldspar geothermobarometry.
Abstract The Tuscarora volcanic field (TVF), the largest Eocene volcanic field in Nevada, lies just north of major gold deposits of the Carlin Trend and west of deposits in the Independence Mountains (Fig. 1). Ongoing detailed mapping documents at least five voluminous volcanic-intrusive centers in the southeastern part of the TVF (Figs. 1, 2). 40Ar39 Ar dates show that the five centers developed between 39.9 and 39.2 Ma during a brief, intense period of magmatism. Precious-metal mineralization at Tuscarora formed at about 39.3 Ma, contemporaneous with a major intrusive episode, and is the oldest Tertiary volcanic-hosted epithermal deposit in Nevada. Compilation of 40Ar39 Ar dates indicates that magmatism was particularly intense between 39 and 40 Ma throughout northeastern Nevada. Given that several Carlin-type deposits are now interpreted to have formed in the Eocene (Hofstra, 1995~ Emsbo, 1996~ Leonardson and Rahn, 1996~ Phinisey et al., 1996~ Rota, 1996), contemporaneous with this activity, we suggest that Eocene magmatism was directly or indirectly the heat source to drive hydrothermal circulation that generated Carlin-type deposits (see also Hofstra, 1995).
The Tuscarora mining district contains the oldest and the only productive Eocene epithermal deposits in Nevada. The district is a particularly clear example of association of low-sulfidation deposits with igneous activity and structure, and it is unusual in that it consists of two adjoining but physically and chemically distinct types of low-sulfidation deposits. Moreover, Tuscarora deposits are of interest because they formed contemporaneously with nearby, giant Carlin-type gold deposits. The Tuscarora deposits formed within the 39.9 to 39.3 Ma Tuscarora volcanic field, along and just outside the southeastern margin of the caldera-like Mount Blitzen volcanic center. Both deposit types formed at 39.3 Ma, contemporaneous with the only major intrusive activity in the volcanic field. No deposits are known to have formed during any of the intense volcanic phases of the field. Intrusions were the apparent heat source, and structures related to the Mount Blitzen center were conduits for hydrothermal circulation. The ore-forming fluids interacted dominantly with Eocene igneous rocks.
The two deposit types occur in a northern silver-rich zone that is characterized by relatively high Ag/Au ratios (110–150), narrow alteration zones, and quartz and carbonate veins developed mostly in intrusive dacite, and in a southern gold-rich zone that is typified by relatively low Ag/Au ratios (4–14), more widespread alteration, and quartz-fissure and stockwork veins commonly developed in tuffaceous sedimentary rocks. The deposit types have similar fluid inclusion and Pb and S isotope characteristics but different geochemical signatures. Quartz veins from both zones have similar thermal and paragenetic histories and contain fluid inclusions that indicate that fluids cooled from between 260° and 230°C to less than 200°C. Fluid boiling may have contributed to precious-metal deposition. Veins in both zones have relatively high As and Sb and low Bi, Te, and W. The silver zone has high Ca, Pb, Mn, Zn, Cd, Tl, and Se. The gold zone has high Hg and Mo. A few samples from an area of overlap between the two zones share chemical characteristics of both deposit types. The deposit types could represent a single zoned or evolving system in which hydrothermal fluids rose along structures within the silver zone, preferentially deposited Ag and base metals, and then spread into the gold zone. Alternatively, the deposit types could represent two distinct but temporally indistinguishable hydrothermal cells that only narrowly overlapped spatially.
As noted in previous studies, the hydrothermal fluids that generated the Tuscarora and other epithermal deposits could have evolved from Carlin-type fluids by boiling and mixing with meteoric water. If so, the Tuscarora deposit may represent epithermal conditions above Carlin-type deposits, and Carlin-type deposits may lie beneath the district.
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