Выпуск 83
Автор(ы):David W.Beaty, Peter T.Holland, Snow G.G.
Издание:Economic geology, 1988 г., 23 стр.
Comparative elemental and oxygen isotope geochemistry of jasperoid in the Northern Great Basin: evidence for distinctive fluid evolution in gold-producing hydrothermal systems

This comparative geochemical study of jasperoid in the northern Great Basin is based on 65 samples from 10 Carlin-type gold deposits and 22 similar but apparently barren hydro-thermal systems. Multielement geochemistry coupled with oxygen isotope data indicate that hydrothermal fluids in barren and mineralized systems evolved in different ways, and that there are fundamental geochemical differences among the various gold-producing deposits of the area.

Much of the variation in the jasperoid geochemical data can be explained in terms of seven abstract end-member components obtained through factor analysis. Three of these components (factors) dominate the results and are related to common products of alteration and mineralization in epithermal systems of the northern Great Basin. Element associations for these factors are: factor 1: Ti02, Al203, La, K20, Sr, Fe203, Th; factor 2: Au, Ag, Sb, Si02> As, Pb; and factor 3: W, B, V, Zn, Co, Au, CaO, Ni, Mn, Cu.

ТематикаПолезные ископаемые
Выпуск 1
Автор(ы):Mehrtens M.B.
Издание:Economic geology, 1986 г., 5 стр.
Case history and problem 1: the Tonkin Springs gold mining district, Nevada, U.S.A.

Geochemical techniques played a major role in exploration of the Tonkin Springs district and ultimately led to discovery of economically significant bodies of gold mineralization. Using some of the information obtained during the exploration program, it is possible to review the geochemical environment, secondary dispersion processes and survey techniques used successfully in this part of Nevada.

The Tonkin Springs district is located in west-central Eureka County, Nevada, within the Simpson Park Range approximately 65 km northwest of the town of Eureka (Figure 7.1). Topography is typical of the Basin and Range structural province being characterized by long narrow valleys and north easterly trending mountain ranges with elevations varying between 1,700 and 3,100 m. Precipitation is in the order of 400 mm per year, the major portion of which occurs in the higher elevations during winter and spring. Soils are light brown to brown desert soils of residual origin in locations above the gravel-filled valleys and pediments. Vegetation consists of sagebrush and sparse grass in the valleys with juniper, pinyon and mountain mahogany in the higher country.

ТематикаПолезные ископаемые
МеткиGold, Tonkin Springs gold mining district, Золото
Автор(ы):Arthur S.Radtke, Brent P.Fabbi, Chris Heropoulos, Mel Essington, Scheiner B.J.
Издание:Economic geology, 1972 г., 4 стр.
Data on major and minor elements in host rocks and ores, Carlin gold deposit, Nevada

The purpose of this communication is to summarize and make available a large amount of data on the content of major and minor elements in the host rocks and ores of the Carlin gold deposit and to show the changes in the abundance of these elements as a result of hydrothermal mineralization and subsequent oxidation. Other aspects of the study of minor elements in the Carlin deposit, including the correlation between elements in various types of ore and the influence of geologic features on spatial distribution, will be presented in a later paper. The Carlin gold deposit is located about 33 miles northwest of Elko, Nevada (Fig. 1).

The deposit is characterized by large disseminated replacement-type ore bodies in the upper beds of the Silurian Roberts Mountains Formation. Several of these ore bodies are currently exposed in the West, Main, and East Pit areas of the mine. Although detailed information on the depth of gold deposition and the geometry of individual ore bodies cannot be disclosed (by agreement with Newmont Mining Corporation), the host rocks have been hydro-thermally altered in some parts of the deposit to a depth of 800+ feet. Small amounts of gold are scattered throughout this depth, and larger amounts, concentrated in several zones, make up the ore bodies.

The host rocks for the ore bodies are dark- to medium-gray, thin-bedded, siliceous, argillaceous, dolomitic limestones. Mineralogically the rocks are made up of large and widely varying amounts of calcite, dolomite, illite, and quartz, plus minor kaolin, montmorillonite( ?), chlorite, K-feldspar, plagioclase, pyrite, zircon, barite, rutile, sphene, and carbonaceous materials.    Complete chemical analyses of the fresh carbonate rocks are given by Hausen (1967), Hausen and Kerr (1968), and Radtke and Scheiner (1970).

ТематикаПолезные ископаемые
Выпуск 15
Автор(ы):Bedell R., Coolbaugh M., Craig L., Jessica Smith, Marilyn Miller, Ronald Parratt, Struhsacker E.
Издание:Economic geology, 2010 г., 28 стр.
The Pequop Mining District, Elko County, Nevada: an evolving new gold district

Several gold deposits discovered since 1990 in the central Pequop Mountains of Elko County, northeastern Nevada, make up the new Pequop mining district. The most advanced projects, including Long Canyon and West Pequop, have a combined resource exceeding 42.5 tonnes Au and growing. Favorable open-pit mining economics are generated by high-grade, oxidized gold deposits above the water table.

The deposits exhibit characteristics typical of Carlin-type gold deposits, including limestone and calcareous siliciclastic host rocks, collapse breccias, and <5 micron gold grains in rims of oxidized arsenian pyrite grains. Host rocks are decalcified, argillized, and locally silicified (jasperoid). Some gold mineralization, particularly at Long Canyon, occurs along the margins of competent blocks of Cambrian Notch Peak dolomite in contact with limestone.

ТематикаПолезные ископаемые
МеткиElko County, Gold, The Pequop Mining District, Золото
Выпуск 59
Автор(ы):Eric Seedorff, Jean S. Cline, John L. Muntean, Marcus K.Johnston, Mark D.Barton, Michael W.Ressel
Издание:Economic geology, 2004 г., 9 стр.
Controversies on the Origin of World-Class Gold Deposits, Part I: Carlin-type Gold Deposits in Nevada

This article and a future article in the SEG Newsletter will serve as previews to an SEG-sponsored forum to examine and discuss the origins of gold deposits in the Carlin and Witwatersrand camps. The forum will be held in Reno, Nevada, on May 14, 2005, in conjunction with Geological Society of Nevada’s Symposium 2005 – Window to the World. Both districts have been the focus of major controversies. In this article, three short papers discuss the origin of Carlin-type deposits in north-central Nevada. Over the last few decades, Carlin-type deposits have been seen as shallow hot spring deposits, distal products of porphyry copper deposits, and the uppermost parts of deep mesother-mal systems. The first paper, by Jean Cline, provides an introduction to the characteristics of Carlin-type deposits and a framework for discussions of their origin. The second paper, by Marcus Johnston and Michael Ressel, argues for a magmatic origin for the deposits, and specifically that plutons are the source of heat and probably fluids and metals. The third paper, by Eric Seedorff and Mark Barton, discusses amagmatic models for the origin of Carlin-type deposits, as well as pointing out shortcomings in magmatic models. These authors will give talks at the May 2005 forum, which will be followed by panel and open discussions with the aim of identifying what we need to know to better understand and explore for these deposits.

ТематикаПолезные ископаемые
Выпуск 98
Автор(ы):Constance J.Nutt, Hofstra A.H.
Издание:Economic geology, 2003 г., 17 стр.
Alligator Ridge District, East-Central Nevada: Carlin-type gold mineralization at Shallow Depths

Carlin-type deposits in the Alligator Ridge mining district are present sporadically for 40 km along the north-striking Mooney Basin fault system but are restricted to a 250-m interval of Devonian to Mississippian strata. Their age is bracketed between silicified ca. 45 Ma sedimentary rocks and unaltered 36.5 to 34 Ma volcanic rocks. The silicification is linked to the deposits by its continuity with ore-grade silicification in Devonian-Mis-sissippian strata and by its similar δ18O values (~17‰) and trace element signature (As, Sb, Tl, Hg). Eocene reconstruction indicates that the deposits formed at depths of ≤300 to 800 m. In comparison to most Carlin-type gold deposits, they have lower Au/Ag, Au grades, and contained Au, more abundant jasperoid, and tex-tural evidence for deposition of an amorphous silica precursor in jasperoid. These differences most likely result from their shallow depth of formation.

ТематикаПолезные ископаемые
МеткиAlligator Ridge District, Carlin type gold, East-Central Nevada, Gold, Shallow Depths, Золото
Выпуск 98
Автор(ы):Heitt D.G., Jackson R.G., Tommy B.Thompson, W.Warren Dunbar
Издание:Economic geology, 2003 г., 29 стр.
Geology and geochemistry of the Deep Star gold deposit, Carlin Trend, Nevada

Deep Star is a high-grade Carlin-type gold deposit located in the northern part of the Carlin trend. The deposit averages 34.0 g/t Au and by year end 2000 had produced 37.8 t (1,217,000 oz) gold with a remaining reserve of 16.0 t (513,698 oz) gold. The deposit is primarily hosted in brecciated calc-silicate rocks of the Devonian Popovich Formation, with a minor amount of gold in the Jurassic Goldstrike diorite. Intrusion of the syn- and postore Deep Star rhyolite constrains the age of the mineralization. The postore rhyolite is composi-tionally and mineralogically similar to the synore dike and yielded an average 40Ar/39Ar isochron age of 38.3 Ma. Eocene rhyolite dikes intruded active, dilatant north- to northeast-striking faults and/or fractures, providing an important age constraint on the local stress regime at Deep Star during mineralization. Essentially horizontal, west-northwest-directed Eocene extension (291°) is consistent with dextral-normal oblique slip observed on north-south-striking, east-dipping portions of the Gen-Post fault system and dilation and sinistral shear on dike-filled, northeast-striking structures. A right-stepping, releasing bend in the Deep Star fault at its intersection with northwest- and north-northwest-striking subsidiary structures created a deep-tapping dilatant conduit for gold-bearing hydrothermal fluids.

ТематикаПолезные ископаемые
МеткиCarlin type gold, Deep Star gold deposit, Gold, Золото
Выпуск 98
Автор(ы):Eric A.Lauha, Griffin G.L., Hofstra A.H., Hutchinson R.W., Poul Emsbo
Издание:Economic geology, 2003 г., 37 стр.
Origin of high-grade gold ore, source of ore fluid components, and genesis of the Meikle and Neighboring Carlin-type deposits, Northern Carlin Trend, Nevada

The Meikle mine exploits one of the world’s highest grade Carlin-type gold deposits with reserves of ca. 220 t gold at an average grade of 24.7 g/t. Locally, gold grades exceed 400 g/t. Several geologic events converged at Meikle to create these spectacular gold grades. Prior to mineralization, a Devonian hydrothermal system altered the Bootstrap limestone to Fe-rich dolomite. Subsequently the rocks were brecciated by faulting and Late Jurassic intrusive activity. The resulting permeability focused flow of late Eocene Carlin-type ore fluids and allowed them to react with the Fe-rich dolomite. Fluid inclusion data and mineral assemblages indicate that these fluids were hot (ca. 220°C),of moderate salinity (<6 wt % NaCl equiv), acidic, and H2S rich. Gold-rich pyrite formed by dissolution of dolomite and sulfidation of its contained Fe. Where dissolution and replacement were complete, ore-stage pyrite and other insoluble minerals were all that remained. Locally, these minerals accumulated as internal sediments in dissolution cavities to form ore with gold grades >400 g/t.

ТематикаПолезные ископаемые
МеткиCarlin type gold, Gold, Meikle, Neighboring, Золото
Выпуск 9
Автор(ы):Keith Bettles
Издание:Economic geology, 2002 г., 24 стр.
Exploration and geology, 1962 to 2002, at the Goldstrike Property, Carlin Trend, Nevada

The Goldstrike property, located in the Carlin Trend in Nevada, contains a diverse group of Carlin deposits, including some of the largest and highest grade examples known. The largest deposit, Betze-Post, has a gold endowment of approximately 1,250 metric tons (t) Au, and the Meikle deposit, which contains 220 t Au, has a grade of 24.7 g/t Au. Goldstrike is part of the larger Blue Star-Goldstrike subdistrict, which has an areal extent of 58.5 by 2 km and a total gold endowment of 1,970 t. The first discovery of gold at Goldstrike was in 1962. Subsequent exploration culminated in the discovery in 1986 of large high-grade orebodies beneath smaller, lower grade orebodies. Exploration over a 40-yr period has relied on the evolution in understanding of geology and ore controls, supported by the application of geochemical and geophysical exploration techniques.

ТематикаПолезные ископаемые
Выпуск 96
Автор(ы):Jean S. Cline
Издание:Economic geology, 2001 г., 16 стр.
Timing of gold and arsenic sulfide mineral deposition at the Getchell Carlin-type gold deposit, North-Central Nevada

Pregold mineralization at the Getchell Carlin-type gold deposit includes quartz and base metal vein mineralization associated with intrusion of a Cretaceous granodiorite stock. The veins contain minor pyrite and trace chalcopyrite, arsenopyrite, galena, and sphalerite. The pyrite is moderately coarse and, in thin section, has high relief, is well polished, and is fractured and locally cemented by the gold ore assemblage. White micas are associated with veins near the granodiorite intrusion. Gold was not observed or detected by fire assay analyses of samples or electron microprobe analyses of pyrites. Microprobe analyses show that pregold pyrites have near-stoichiometric compositions. Variable, low arsenic is present in pyrite in samples overprinted by gold mineralization. Secondary ion mass spectrometry (SIMS) analyses detected trace gold in the coarse, near-stoichiomet-ric pyrite in overprinted samples. The pregold vein assemblage was fractured and cemented by gold ore-stage mineralization

ТематикаПолезные ископаемые
МеткиCarlin type gold, Getchell gold deposit, Gold, Золото
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