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The McDermitt Caldera is a large, oval-shaped
caldera A caldera ( ) is a large cauldron-like hollow that forms shortly after the emptying of a magma chamber in a volcano eruption. When large volumes of magma are erupted over a short time, structural support for the rock above the magma chamber is ...
west of McDermitt in southeastern
Oregon Oregon () is a U.S. state, state in the Pacific Northwest region of the Western United States. The Columbia River delineates much of Oregon's northern boundary with Washington (state), Washington, while the Snake River delineates much of it ...
and northern
Nevada Nevada ( ; ) is a U.S. state, state in the Western United States, Western region of the United States. It is bordered by Oregon to the northwest, Idaho to the northeast, California to the west, Arizona to the southeast, and Utah to the east. N ...
in the
United States The United States of America (U.S.A. or USA), commonly known as the United States (U.S. or US) or America, is a country Continental United States, primarily located in North America. It consists of 50 U.S. state, states, a Washington, D.C., ...
. It is about long north–south and wide east–west. The western part of the caldera is in the Trout Creek Mountains, and the northern part is in the Oregon Canyon Mountains. The highest point of the McDermitt Caldera is Jordan Meadow Mountain at , which is part of the Montana Mountains of Humboldt County, Nevada. McDermitt Caldera is possibly the oldest of a sequence of calderas formed by the
Yellowstone hotspot The Yellowstone hotspot is a volcanic hotspot in the United States responsible for large scale volcanism in Idaho, Montana, Nevada, Oregon, and Wyoming, formed as the North American tectonic plate moved over it. It formed the eastern Snake Riv ...
. The caldera was preceded by a
lava dome In volcanology, a lava dome is a circular mound-shaped protrusion resulting from the slow extrusion of viscous lava from a volcano. Dome-building eruptions are common, particularly in convergent plate boundary settings. Around 6% of eruptions ...
that had been built by volcanic eruptions of
rhyolite Rhyolite ( ) is the most silica-rich of volcanic rocks. It is generally glassy or fine-grained (aphanitic) in texture, but may be porphyritic, containing larger mineral crystals ( phenocrysts) in an otherwise fine-grained groundmass. The miner ...
starting about 19 million years ago. This lava dome collapsed into a caldera in an eruption between 16.37 and 16.41 million years ago. A lake subsequently formed in the caldera, and it deposited varved sediments,
diatomite Diatomaceous earth (), diatomite (), or kieselgur/kieselguhr is a naturally occurring, soft, siliceous sedimentary rock that can be crumbled into a fine white to off-white powder. It has a particle size ranging from more than 3 μm to le ...
,
opal Opal is a hydrated amorphous form of silica (SiO2·''n''H2O); its water content may range from 3 to 21% by weight, but is usually between 6 and 10%. Due to its amorphous property, it is classified as a mineraloid, unlike crystalline form ...
, carbonaceous material, and mafic lavas. Significant ore deposits are buried in the caldera, including mercury and
uranium Uranium is a chemical element with the symbol U and atomic number 92. It is a silvery-grey metal in the actinide series of the periodic table. A uranium atom has 92 protons and 92 electrons, of which 6 are valence electrons. Uranium is weak ...
, which were mined at more than eight sites in the caldera during the 20th century. Mercury at these mines was extracted in large amounts, and it came mostly from
cinnabar Cinnabar (), or cinnabarite (), from the grc, κιννάβαρι (), is the bright scarlet to brick-red form of mercury(II) sulfide (HgS). It is the most common source ore for refining elemental mercury and is the historic source for the bri ...
. The McDermitt Mine, located on the eastern edge of the caldera in Nevada, was the last active mercury mine in the United States before it shut down in 1992. Uranium was discovered in the caldera in 1953, and it was extracted mainly from a rhyolite brecciated
fault zone In geology, a fault is a planar fracture or discontinuity in a volume of rock across which there has been significant displacement as a result of rock-mass movements. Large faults within Earth's crust result from the action of plate tectoni ...
at the Moonlight mine on the caldera's southwestern edge. The uranium ore minerals include
uraninite Uraninite, formerly pitchblende, is a radioactive, uranium-rich mineral and ore with a chemical composition that is largely UO2 but because of oxidation typically contains variable proportions of U3O8. Radioactive decay of the uranium causes ...
and coffinite. The age of the uranium formation is assumed to be the same as the caldera tuff, which is approximately 16.1 million years. Other deposits in the caldera contain ores of
antimony Antimony is a chemical element with the symbol Sb (from la, stibium) and atomic number 51. A lustrous gray metalloid, it is found in nature mainly as the sulfide mineral stibnite (Sb2S3). Antimony compounds have been known since ancient ti ...
,
cesium Caesium (IUPAC spelling) (or cesium in American English) is a chemical element with the symbol Cs and atomic number 55. It is a soft, silvery-golden alkali metal with a melting point of , which makes it one of only five elemental metals that ar ...
, and
lithium Lithium (from el, λίθος, lithos, lit=stone) is a chemical element with the symbol Li and atomic number 3. It is a soft, silvery-white alkali metal. Under standard conditions, it is the least dense metal and the least dense soli ...
. The
Thacker Pass lithium deposit The Thacker Pass Lithium Mine is a proposed lithium clay mining development project in Humboldt County, Nevada which is the largest known lithium deposit in the US, and one of the largest in the world. There has been significant exploration of T ...
, located within the caldera, is a prospect that in 2017 was said to be the most significant lithium-clay resource in the U.S. File:Kleinite-Calcite-285098.jpg, Kleinite, a rare yellow mineral containing mercury (formula: (Hg2N)(Cl,SO4)·nH2O) from the McDermitt Mine File:USGS McDermitt caldera geologic map.png, Location of Aurora uranium deposit at McDermitt caldera margin File:USGS McDermitt caldera geologic cross-section.png, Cross-section showing Aurora uranium deposit in McDermitt caldera File:USGS McDermitt caldera geologic cross-section 2.png, Schematic cross-section of Aurora uranium deposit ore zones


See also

*
Basin and Range Province The Basin and Range Province is a vast physiographic region covering much of the inland Western United States and northwestern Mexico. It is defined by unique basin and range topography, characterized by abrupt changes in elevation, alternating ...


References


External link

*{{commonscatinline Calderas of Nevada Calderas of Oregon Extinct volcanoes Landforms of Harney County, Oregon Landforms of Humboldt County, Nevada Landforms of Malheur County, Oregon Landforms of the Great Basin Miocene calderas VEI-7 volcanoes Volcanoes of Nevada Volcanoes of Oregon Yellowstone hotspot