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Geology of Nevadaby

Jonathan G. Price, Christopher D. Henry, Stephen B. Castor, Larry Garside, and James E. Faulds

Nevada Bureau of Mines and Geology, University of Nevada, Reno, Nevada 89557-0088

for publication in Rocks and Minerals magazine

November 1999 issue

The geology of Nevada is the foundation of its natural resources and is closely linked to itshuman history. The overall geologic history of Nevada, which spans more than 2.5 billion years(Table 1), has been assembled by geologists from information gathered from rock outcropsscattered throughout the state. This article outlines the complex geologic history of the state andhow it relates to such resources as minerals, water, and energy; to environmental issues; and tonatural hazards. The article draws heavily from the references listed in the bibliography for generalinformation on the geology of the state, particularly Stewart (1980) and Stewart and Carlson(1978).

The topography of the state is characterized by a patchwork of mountain ranges, which arecommonly about 10 miles wide and rarely longer than 80 miles, and intervening valleys. Thegeologic structure that controls this basin-and-range topography is dominated by faults. As can beseen on Figure 1, nearly every mountain range is bounded on at least one side by a fault that hasbeen active, with large earthquakes, during the last 1.6 million years. For the last several millionyears, these faults have raised and occasionally tilted the mountains and lowered the basins. Overthe years, these basins have filled with sediments (the yellow colors on fig. 1) that are derivedfrom erosion of the mountains and that are tens of thousands of feet thick in some places.

Many of the range-bounding faults are still active. Nevada is the third most seismically activestate in the nation (after California and Alaska). Over the last 150 years, a magnitude 7 or greaterearthquake has occurred somewhere in Nevada about once every 30 years. Most faults are"normal"; that is, the mountains rose and the valleys dropped along inclined fault planes(analogous to a tilted deck of cards). However, some Nevada faults are "strike-slip" faults, likethe San Andreas Fault in California, where opposite sides of the fault move horizontally. The mostapparent zone of strike-slip faults in Nevada is in a 50-mile wide swath along and parallel to thenorthwest-trending border with California. In fact, these northwest-trending faults areaccommodating part of the motion between the Pacific Plate and the North American Plate. TheSan Andreas Fault takes up most of the motion between these two plates. From Figure 1, one cansee that the generally north-south trend of mountain ranges in most of Nevada is deflected intonorthwest-trending ranges along the border with California.

The climate of Nevada is closely tied to the geologic structure and resultant topography.Judging from evidence of plants that grew in different parts of California and Nevada in the past(from fossils in sediments that were deposited in basins), the Sierra Nevada in California and farwestern Nevada rose to current elevations only within the last six million years. Today thesemountains trap moisture coming off the Pacific Ocean and leave Nevada the driest state in the

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nation. Only a few rivers leave Nevada. These include the Jarbidge and Owyhee Rivers innortheastern Nevada, which flow north into the Snake River in Idaho, and the White and VirginRivers in southeastern Nevada, which flow into the Colorado River. The Colorado, which is thebiggest river in Nevada, gets the bulk of its water from the Rocky Mountains to the east andprovides much of the municipal and industrial water for Las Vegas and other communities insouthern Nevada before flowing southward into the Gulf of California. Most of Nevada, however,is part of the Great Basin, a large area with no drainage to the ocean. The Great Basin is centeredon Nevada and includes parts of California, Oregon, Idaho, and Utah. The Truckee, Carson, andWalker Rivers, which provide much of the drinking, industrial, and agricultural water fornorthwestern Nevada, flow generally eastward from the Sierra Nevada to terminal lakes andlowlands in the desert (Pyramid Lake, the Carson Sink and Stillwater wetlands, and Walker Lake,respectively). The Humboldt River, which supplies much of northeastern Nevada with drinking,agricultural, and industrial water, flows southwestward into Humboldt Lake, and, when the lakefills, into the Carson Sink.

In addition to surface water from rivers and streams, groundwater is used throughout thestate, mostly from aquifers in alluvial basins. In some basins, groundwater has been pumped outmore rapidly than it is naturally recharged from rain and snowmelt; this causes significantlowering of the groundwater table and can even lower the land surface. In Las Vegas Valleycracks have developed locally in the ground (near preexisting faults), and in a few places the landhas subsided more than six feet in the last sixty years.

Although Nevada is, on the average, quite dry (with about 10 inches of rainfall across thestate, but locally less than 5 inches in certain lowlands and over 40 inches in high mountains),major storms have caused significant floods and occasional landslides. Geologic evidence (andrecorded history) abounds for large floods on the major rivers and "dry" washes throughout thestate.

The ecological regions of Nevada are directly linked to the climate, elevations of themountains, and rocks. A combination of precipitation and rock type (with the help of ubiquitousmicrobes) dictates the types of soils that develop and the plants that grow, which, in turn, affectthe types of animals that survive. Geologic evidence (primarily fossils) shows us that climate haschanged substantially even within the last 10,000 years. For example, as recently as 11,000 yearsago, mammoths and camels lived near springs and what are presently dry lakes in Nevada.

During glacial times (most recently about 10,000 years ago), large expanses in the GreatBasin were covered by water. Great Salt Lake, Bonneville Salt Flats in Utah, and parts of fareastern Nevada were once part of ancient Lake Bonneville, while in western Nevada PyramidLake, the Carson Sink, and Walker Lake were connected in ancient Lake Lahontan. NativeAmericans occupied the shores of these lakes as early as 10,000 to 12,000 years ago. Glaciersexisted in the higher mountains, carving some of the spectacular U-shaped valleys in the RubyMountains and sculpting high-mountain topography in the Sierra Nevada. Small glaciers are stillpresent high in the Ruby Mountains and Snake Range in eastern Nevada.

Major events in the geologic history of Nevada are highlighted in Table 1. A westerncontinental margin, similar to the Atlantic coast of today, persisted for hundreds of millions ofyears before the more active, Pacific coast margin of today began to take shape about 400 millionyears ago. Repeated and prolonged periods of interactions between the North American Plate andoceanic plates to the west are recorded in the rocks and expressed as folds, thrust faults, strike-slip faults, normal faults, igneous intrusions, volcanism, metamorphism, and sedimentary basins.

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One of the most striking features of the generalized geologic map of Nevada (fig. 1) is theabundance of igneous rocks (colored red, pink, orange, and light green, with some also mixedwith other rock types colored green, blue, and brown). Nevada rocks record volcanic andintrusive igneous activity intermittently and repeatedly from earliest geologic history to within thelast few thousand years. Some of Nevada's igneous rocks are related to sea-floor spreading about450 million years ago (much like the Mid-Atlantic Ridge or the East Pacific Rise today), collisionsof ancient and modern plates, and hot spots in the Earth's mantle and perhaps outer core (someNevada volcanic rocks can be correlated with the Yellowstone hot spot, which, as a result of platetectonics, lay beneath southern Idaho and northern Nevada producing volcanoes). Some of thevolcanic rocks in western Nevada represent the precursor of the Cascades several million yearsago, and significant intrusions about 40, 100, and 160 million years ago are probably linked tosimilar plate-tectonic settings, whereby tectonic plates of the Pacific Ocean were being subductedbeneath western North America.

Most, but not all, ore deposits in Nevada are associated with igneous activity. In some cases,metals came from the magmas themselves, and in other cases, the magmas provided heat forcirculation of hot water that deposited metals in veins and fractured sedimentary rocks. Somespectacular mineral specimens occur in ore deposits that formed when magmas intruded andmetamorphosed sedimentary rocks. Even today, driven locally by deep circulation along faults andlocally by igneous activity, hot water shows up in numerous geothermal areas. Nevada producesapproximately $100 million worth of geothermally generated electric power annually, andgeothermal resources also are used for agriculture, industrial applications, and space heating.

Nevada produces more than $3 billion worth of mineral commodities each year. Nevada isthe nation's leading gold producer, accounting for approximately 70% of U.S. production and10% of world production. Much of the gold comes from a northwest-trending belt of ore depositsin northeast Nevada known as the Carlin trend. One of the interesting features of the Carlin trendis that nearly all the gold is contained in microscopic particles within Paleozoic sedimentary rocks.Although the sedimentary hosts for the gold are more than 250 million years old, the actualmineralization may have occurred much later (perhaps 40 million years ago) in association withigneous activity. Nevada, the Silver State, is also the nation's leading silver and barite producer.Other mineral commodities that are currently produced in Nevada include copper, gypsum, clays,limestone (for cement and lime), lithium, salt, magnesite, diatomite, perlite, silica sand, anddimension stone; and crushed rock, sand, and gravel for construction aggregate. In the past,Nevada has been a significant producer of lead, zinc, tungsten, molybdenum, and fluorite. Activeexploration and recent significant discoveries attest to the potential for finding additional oredeposits.

Mining districts, which are the locations for many of the state's best mineral specimens, arescattered throughout Nevada in nearly every mountain range (fig. 2). Nevada became a State in1864, during the Civil War (hence the motto "Battle Born"), as a result of mineral wealth. The1859 discovery of silver-gold ores on the Comstock Lode enticed miners and prospectors, manyof whom had come to California a decade earlier in search of gold. Over the decades thatfollowed, they spread out from Virginia City, discovering other major mining camps andestablishing many towns in Nevada (Argenta, Aurora, Austin, Battle Mountain, Beatty, Carlin,Elko, Ely, Eureka, Goldfield, Henderson, Las Vegas, Lovelock, Nelson, Pioche, Searchlight,Tonopah, Unionville, Winnemucca, Yerington). Some of the old shafts, adits, pits, and glory holesat mine sites are dangerous. There are over 200,000 such sites in Nevada, and only some of those,

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which are close to towns and major roads, have been secured to warn people to "Stay Out andStay Alive."

Nevada also produces some oil, although small relative to amounts from major petroleumstates. An interesting aspect of Nevada petroleum production is that some of the oil is associatedwith hot water, much like the geothermal fluids that formed gold and silver deposits, althoughlower in temperature. Another curiosity is that some of the oil is trapped in fractured volcanicrocks, although the ultimate source of the petroleum was from organic matter in sedimentaryrocks. Most of the oil has come from the eastern part of the state, primarily Railroad and PineValleys.

Some environmental hazards are associated with the abundant igneous rocks in Nevada. Forexample, many groundwaters in Nevada contain elevated concentrations of radon, a naturallyoccurring, radioactive gas. Because radon is common in silica-rich igneous rocks (such as graniteand its volcanic counterpart, rhyolite), and because these rocks are widespread in the mountainsand make up much of the sediment in the valleys, radon occurs in groundwater, soil, and air.Similarly, arsenic is relatively abundant in certain types of igneous rocks and is locally a problemas a dissolved natural constituent in Nevada groundwater and surface water.

Most spectacular mineral and rock specimens from Nevada are directly related to the igneousrocks and associated hydrothermal (hot water) ore deposits. These include the porphyry copperand molybdenum deposits (such as the Robinson district near Ely in White Pine County), skarns(including some of the abundant scheelite deposits—skarns are types of contact metamorphicrocks that are directly associated with heat and hydrothermal fluids from magmas), different typesof epithermal veins (such as the Comstock Lode and the ores at Goldfield), hot-spring deposits(such as those at Steamboat Springs in Washoe County), and Carlin-type ores (named for theCarlin Mine in Elko County). Selected mineral localities are listed in Table 2. Many excellentmineral specimens can be found in the weathered and oxidized portions of ore deposits, and nearlyevery metallic mining district (fig. 2) has some metal oxide minerals.

Some rocks themselves are highly prized by collectors. An example is "wonderstone"(rock that is naturally stained with picturesque bands of red and orange iron oxide and hydroxide).In Nevada, some wonderstones are rhyolite lava flows, and some are sandstones. Thewonderstone near Grimes Point in Churchill County, which is used in lapidary, is a rhyolite tuffthat was altered by silica and pyrite from hydrothermal fluids.

Other prize specimens come from sedimentary rocks, but often with an igneous orhydrothermal connection. For example, in Humboldt County precious opal occurs as areplacement of wood fragments in sediments with high contents of volcanic material. The silicaneeded to form the opal probably came from the silica-rich volcanic material in the sediments.Near Fallon in Churchill County, fossil fish are exposed in diatomite (diatomaceous earth) mines.The growth of diatoms, single-celled plants that comprise most of the rock diatomite, is promotedby volcanic activity that produced abundant quantities of silica, the chief ingredient of thediatoms. At the Gerlach Mine in Pershing County, huge cleaved blocks of selenite are found inhydrothermal veins that record remobilization of sedimentary gypsum (fig. 3).

Nearly every rock type occurs in Nevada. With excellent rock exposures in the desert,generally good access to collecting localities on public lands, and fine tourist attractions in thetowns, Nevada is a wonderful state for rock and mineral enthusiasts.

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BIBLIOGRAPHY (references and suggested reading)

Anonymous 1976. Continents adrift and continents aground, readings from Scientific American.San Francisco: W. H. Freeman and Company.

Anonymous 1982. Volcano. Chicago: Time-Life Books, Inc.

Castor, S. B., and others, in preparation for publication in 2000, Minerals of Nevada. NevadaBureau of Mines and Geology bulletin.

Cox, Allan, and R. B. Hart 1986. Plate tectonics: how it works. Palo Alto, California: BlackwellScientific.

Decker, Robert, and Barbara Decker 1981. Volcanoes. San Francisco: W. H. Freeman andCompany.

DeMouthe, J. F. 1994. An introduction to the geology of California: Rocks and Minerals69(6):360-365.

Harris, S. L. 1990. Agents of chaos: earthquakes, volcanoes, and other natural disasters.Missoula, Montana: Mountain Press.

Jordan, T. H., and J. B. Minster 1988. Measuring crustal deformation in the American west.Scientific American 259(2):48-58.

Lush, A. P., A. J. McGrew, A. W. Snoke, and J. E. Wright 1988, Allochthonous Archeanbasement in the East Humboldt Range, Nevada. Geology 16:349-353.

Macdonald, G. A. 1972. Volcanoes. Englewood Cliffs, New Jersey: Prentice-Hall, Inc.

McPhee, John 1980. Basin and Range. New York: Farrar Straus Giroux.

Murphy, J. B., and R. D. Nance 1992. Mountain belts and the supercontinent cycle. ScientificAmerican 266(4):84-91.

Murphy, J. B., S. L. Nichols, and J. H. Schilling 1975. Rockhound's map of Nevada. NevadaBureau of Mines and Geology special publication 1, 1:1,000,000 scale.

Papke, K. G., and D. A. Davis, D.A. 1996. Mining claim procedures for Nevada prospectors andminers, 4th ed. Nevada Bureau of Mines and Geology special publication 6.

Press, Frank, and Raymond Siever 1978. Earth. San Francisco: W. H. Freeman and Company.

Price, J. G., J. V. Tingley, D. D. LaPointe, R. H. Hess, H. F. Bonham, H.F., Jr., S. B. Castor, andD. A. Davis 1998. The Nevada mineral industry - 1997: Nevada Bureau of Mines andGeology special publication MI-1997.

Purkey, B. W., E. M. Duebendorfer, E. I. Smith, J. G. Price, and S. B. Castor 1994. Geologictours in the Las Vegas area. Nevada Bureau of Mines and Geology special publication 16.

Purkey, B. W., and L. J. Garside 1995. Geologic and natural history tours in the Reno area.Nevada Bureau of Mines and Geology special publication 19.

Smith, G. H., and J. V. Tingley 1997. The history of the Comstock Lode. Nevada Bureau ofMines and Geology special publication 24.

Stewart, J. H. 1980. Geology of Nevada. Nevada Bureau of Mines and Geology specialpublication 4.

Stewart, J. H., and J. E. Carlson 1977. Geologic map of Nevada. Nevada Bureau of Mines andGeology map 57, 1:1,000,000 scale.

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Stewart, J.H., and J. E. Carlson 1978. Geologic map of Nevada. U.S. Geological Survey,1:500,000 scale.

Tingley, J. V. 1998. Mining districts of Nevada. Nevada Bureau of Mines and Geology report 47,2nd ed.

Tingley, J. V., R. C. Horton and F. C. Lincoln 1993. Outline of Nevada mining history. NevadaBureau of Mines and Geology special publication 15

www.nbmg.unr.edu (the Web site of the Nevada Bureau of Mines and Geology).

About the authors:

Dr. Jonathan G. Price is the Nevada State Geologist and director of the Nevada Bureau of Minesand Geology (NBMG). He has 27 years of experience in industry, academia, and government,chiefly in the areas of exploration and mining, environmental geochemistry, igneous petrology,geologic hazards, and geologic mapping. The other authors are NBMG research geologists. Dr.Christopher D. Henry has 30 years of research experience in geologic mapping, igneous geologyand geochemistry, geochronology, volcanology, and environmental geology. Dr. Stephen B.Castor has 34 years of industrial and research experience in mining and exploration, geologicmapping, and igneous petrology. Larry Garside has 34 years of research experience in geologicmapping, volcanic geology and ore deposits, energy resources, and geochronology. Dr. JamesFaulds has 18 years of teaching and research experience in structural geology, tectonics, geologicmapping, paleomagnetism, and geochronology.

FIGURE CAPTIONS

Figure 1. Generalized geologic map of Nevada (reprinted with permission of the Nevada Bureauof Mines and Geology, Educational Series E-30).

Figure 2. Locations of mining districts in Nevada (modified from Tingley, 1998, and NevadaBureau of Mines and Geology Educational Series E-31, digital shaded relief map of Nevada).

Figure 3. Large cleaved masses of clear gypsum (selenite) from the Selenite pit at the EmpireMine, Pershing County. The mine and nearby wallboard plant in Washoe County are operated byU.S. Gypsum Corporation. J.G. Price photograph.

TABLES

Table 1. Geologic time scale with major events in Nevada history.

Table 2. Selected mineral occurrences in Nevada.

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120

42

41

40

39 120

38

118

119

37

117

116 36

115

36

37

38

39

40

41

42

114

115 116 117 118 119 120 114

NEVADA BUREAU OF MINES AND GEOLOGY EDUCATIONAL SERIES E-30 GENERALIZED GEOLOGIC MAP OF NEVADA

GENERALIZEDGEOLOGIC MAP OF NEVADA

Modified from Nevada Bureau of Mines and Geology Map 57, Million-Scale Geologic Map of Nevada, by John H. Stewart and John E. Carlson, 1977; and fault maps by Craig M. dePolo, 1998.

NEVADA BUREAUGEOLOGYMACKAY SCHOOL OF MINES

First edition, first printing, 1999; 5,000 copies Printing: Bear Industries, Sparks, Nevada Cartography: Susan L. Tingley For sale by the Nevada Bureau of Mines and Geology, Mail Stop 178Mackay School of Mines, University of Nevada, Reno, Nevada, 89557-0088(775) 784-6691, ext. 2; nbmgsales@unr.edu; www.nbmg.unr.edu

0

0 20 40 60 80kilometers

10 20 30 40 50miles

County boundaries

Quaternary and suspected Quaternary faults, less than 1.6 Ma (million years old), dashed where age uncertain

Lakes and reservoirs

Alluvial and playa deposits

Volcanic rocks, less than 6 Ma

Upper volcanic rocks, 6–17 Ma

Tuffaceous sedimentary rocks, 6–17 Ma

Lower volcanic rocks, mostly 17–43 Ma

Intrusive rocks, Mesozoic and Tertiary

Igneous and metamorphic complex, Jurassic or Cretaceous

Sedimentary, volcanic, and intrusive rocks, Mesozoic

Sedimentary and volcanic assemblage, upper Paleozoic

Carbonate and other sedimentary rocks, upper Paleozoic

Sedimentary and volcanic assemblage, lower Paleozoic

Carbonate and other sedimentary rocks, lower Paleozoic and Late Proterozoic

Metamorphic and intrusive rocks, Early and Middle Proterozoic

120¡

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40¡

39¡120¡

38¡

118¡

119¡

37¡

117¡

116¡36¡

115¡

36¡

37¡

38¡

39¡

40¡

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42¡114¡115¡116¡117¡118¡119¡

0

0 20 40 60 80 kilometers

10 20 30 40 50 miles

County boundaries

Metallic districts

Nonmetallic districts

Elko

Carlin Argenta

Winnemucca

Unionville

Lovelock

BattleMountain

AustinEureka

Ely

Virginia City

RenoFallon

Carson City

Minden Yerington

Aurora

Hawthorne

Goldfield

TonopahPioche

Beatty

LasVegas

Henderson

Nelson

Searchlight

Figure 2. Locations of mining districtsin Nevada (modified from Tingley, 1998, and Nevada Bureau of Mines and GeologyEducational Series E-31, digital shaded reliefmap of Nevada)

Figure 3. Large cleaved masses of clear gypsum (selenite) from the Selenite pit at theEmpire Mine , Pershing County. The mine and nearby wallboard plant in Washoe Countyare operated by U.S. Gypsum Corporation. J.G. Price photograph

Table 1. Geologic time scale with major events in Nevada history.Million yearsbefore present******************************************************************************************************************

CENOZOIC Quaternary Modern earthquakes, mountain building, volcanism, and geothermal activity are expressions of Basin and Range extension

that began in the Tertiary Period. The crust is being pulled apart in Nevada, causing valleys to drop relative to mountains.Prior to 10,000 years ago, ice ages caused glaciers to form in the higher mountains and large lakes to develop, in placesconnecting today's valleys.

1.6 - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - Tertiary Basin and Range extension began about 30 to 40 million years ago. Igneous activity during the Tertiary Period was

caused not only by extension but also by subduction (descent of oceanic crust into the Earth's mantle) of oceanic platesbeneath the North American Plate and, in northern Nevada, by motion of the crust over the Yellowstone hot spot in themantle. Numerous Nevada ore deposits, including most major gold and silver deposits and the copper ores near BattleMountain, formed during this time. Gypsum deposits formed from evaporating lakes in southern Nevada.

65 ****************************************************************************************************************MESOZOIC Cretaceous The Cretaceous Period and Mesozoic Era ended abruptly with the extinction of dinosaurs and many marine species;

chemical, mineralogical, and other geological evidence suggests that these extinctions were caused by a largemeteorite striking the Earth. Numerous granitic igneous intrusions, scattered throughout Nevada, originated fromsubduction along the west coast of North America. Much of the granite in the Sierra Nevada formed at this time. Theigneous activity caused many metallic mineral deposits to form, including the copper-gold-silver-lead-zinc ores atRuth, near Ely in White Pine County, copper-molybdenum ores north of Tonopah in Nye County, and tungsten ores inseveral mining districts. In southern and eastern Nevada, sheets of rocks were folded and thrust from the west to theeast during the Sevier Orogeny (mountain building), which began in Middle Jurassic time and ended at or beyond theend of the Cretaceous Period.

144 - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - Jurassic A subduction zone to the west caused igneous intrusions, volcanism, and associated ore deposits, including copper

deposits near Yerington. Sandstones, including those in the Valley of Fire, were deposited in southeastern Nevada,and sedimentary gypsum deposits formed in northwestern Nevada.

208 - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - Triassic The general geography of Nevada during the Triassic Period was similar to that during the Jurassic Period—igneous

activity in the west and deposition of sedimentary rocks in continental to shallow marine environments to the east.Explosive volcanism produced thick ash-flow tuffs in west-central Nevada. Economically important limestone,gypsum, and silica-sand deposits formed in southern Nevada. The Sonoma Orogeny, which began during LatePermian time and ended in Early Triassic time, moved rocks from the west to the east along the Golconda Thrust incentral Nevada. The large marine reptiles at Berlin-Ichthyosaur State Park lived during the Triassic Period.

245 ***************************************************************************************************************PALEOZOIC Permian Volcanism to the west and deposition of thick limestones to the east were characteristics of much of the Paleozoic Era

in the Great Basin. Some marine gypsum deposits formed in southern Nevada.286 - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -

Pennsylvanian The Antler highland, formed earlier, was eroded and shed sediments into the basins to the east. Carbonate rocks weredeposited in eastern and southern Nevada.

320 - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - Mississippian During the Antler Orogeny, from Late Devonian to Early Mississippian time, rocks were folded and thrust from the

west to the east. The Roberts Mountains Thrust, below which many of the gold deposits in north-central Nevadaoccur, formed at this time. Conglomerate, sandstone, siltstone, and shale were deposited in the thick basin ofsediments derived from the Antler highland, and carbonate rocks were deposited further east.

360 - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - Devonian Limestone was deposited in eastern Nevada, and shale, chert, and economically important barite were deposited in

northereastern and central parts of the state. No record of middle to lower Paleozoic rocks exists in the western part ofthe state. The quiet, shallow-marine tectonic setting that persisted earlier in the Paleozoic Era began to change, assmall land masses from the Pacific Ocean collided with western North America.

408 - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - Silurian Carbonate rocks (dolomite and limestone) in the eastern part of the state and silica-rich rocks (shale, sandstone, and chert) in

the central part of the state record similar deposition to that during the rest of the middle to lower Paleozoic Era.438 - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -

Ordovician Marine deposition during the Ordovician Period was similar to that during the rest of the early Paleozoic Era, with theexception of basalts (metamorphosed to greenstones) locally interbedded with sedimentary rocks found today in thecentral part of the state. Some sedimentary barite deposits and copper-zinc-silver ores formed in sea-floor sedimentsduring this time.

505 - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - Cambrian Middle and Upper Cambrian deposition resembled that during much of the Paleozoic Era, with carbonate rocks to the

east and shale plus sandstone to the west. Lower Cambrian and uppermost Precambrian rocks are characterized byquartzite and metamorphosed siltstone throughout much of Nevada.

570 ***************************************************************************************************************PRECAMBRIAN

The oldest rocks in Nevada (at least 2,520 million years old in the East Humboldt Range in northeastern Nevada and atleast 1,740 million years old in southern Nevada) are metamorphic rocks (including gneiss, schist, marble, andmetamorphosed granite, pyroxenite, hornblendite, and pegmatite). Precambrian rocks also include granites (about1,450 million years old) and younger sedimentary rocks. Beginning approximately 1,100 million years ago,Antarctica and Australia may have rifted away from western North America, setting the stage for the development of awestern continental margin that is similar to the Atlantic coast of today. A shallow marine, tectonically quiet settingpersisted in eastern Nevada for the next 700 million years.

Table 2. Selected mineral occurrences in Nevada.

Minerals that are parts of igneous rocksBeryl Ruby Mountains, Elko County (in pegmatite)Epidote, feldspar, fluorite, & quartz Eldorado & Newberry Mountains, Clark County

(in cavities in granite)Orthoclase feldspar Goodsprings district, Clark County (in syenite)Plagioclase feldspar, olivine, & clinopyroxene Easy Chair Crater, Nye County (in basalt)Quartz & albite Incline Village, Washoe County (in pegmatite)Spessartine garnet Garnet Hill, near Ruth, White Pine County (in rhyolite)Topaz & amazonite Gillis Range, Mineral County (in pegmatite)

Minerals that are parts of sedimentary rocksBarite Argenta, Clipper, & Greystone Mines, Lander CountyGypsum Empire Mine, Pershing CountyHalite Humboldt Marsh, Churchill CountyPrecious opal Virgin Valley, Humboldt CountySaponite, sepiolite, & montmorillonite Ash Meadows, Nye CountyUlexite, halite, & trona Columbus Salt Marsh, Esmeralda County

Minerals that are parts of metamorphic rocksAndradite garnet, zoisite, & quartz Nightingale district, Washoe County (in skarn)Epidote Julie Claim, Mineral County (in skarn)Magnesite, brucite, & callaghanite* Gabbs district, Nye County (in skarn)Scheelite, galenobismutite, & bismuth Tem Piute district, Lincoln County (in skarn)

Minerals that formed from geothermal or hydrothermal fluidsAcanthite, polybasite, electrum, uytenbogaardite*, Comstock Lode, Virginia City, Storey County & quartz (amethyst)Barite & calcite Meikle Mine, Elko CountyCarlinite* & frankdicksonite* Carlin Mine, Eureka CountyCassiterite & hematite Izenhood district, Lander CountyCinnabar Poverty Peak district, Humboldt CountyCorderoite*, kenhsuite*, mcdermittite*, McDermitt Mine, Humboldt County & radtkeite*Galkhaite, getchellite*, orpiment, & realgar Getchell Mine, Humboldt CountyElectrum & adularia Round Mountain Mine, Nye CountyEnargite & pyrite Pyramid district, Washoe CountyGold, goldfieldite*, bismuthinite, enargite Goldfield district, Esmeralda County famatinite, & mackayite*Huebnerite* Ellsworth (Mammoth) district, Nye CountyMetastibnite*, cinnabar, and sulfur Steamboat Springs, Washoe CountyQuartz Petersen Mountain, Washoe CountyStibnite Murray Mine, Elko County & White Caps Mine, Nye CountySulfur Sulphur district, Humboldt County

Minerals that formed from oxidation of other mineralsAdamite, mimetite, & beudantite San Rafael Mine, Nye CountyArthurite, olivenite, parnauite, phamacosiderite Majuba Hill, Pershing County & scoroditeCerussite, hydrozincite, linarite, & smithsonite Goodsprings district, Clark CountyChlorargyrite Treasure Hill, White Pine CountyChrysocolla, azurite, and malachite Yerington Mine, Lyon CountyCopper, cuprite, and azurite Robinson district, White Pine CountyLinarite & brochantite Old Soldier Mine, Churchill CountyMalachite Pioche district, Lincoln CountyTurquoise Bullion district, Lander CountyWulfenite Eureka district, Eureka County