McDermitt Caldera is a

Miocene The Miocene ( ) is the first epoch (geology), geological epoch of the Neogene Period and extends from about (Ma). The Miocene was named by Scottish geologist Charles Lyell; the name comes from the Greek words (', "less") and (', "new") and mea ...

caldera A caldera ( ) is a large cauldron-like hollow that forms shortly after the emptying of a magma chamber in a volcanic eruption. An eruption that ejects large volumes of magma over a short period of time can cause significant detriment to the str ...

west of McDermitt in southeastern

Oregon Oregon ( , ) is a U.S. state, state in the Pacific Northwest region of the United States. It is a part of the Western U.S., with the Columbia River delineating much of Oregon's northern boundary with Washington (state), Washington, while t ...

and northern

Nevada Nevada ( ; ) is a landlocked state in the Western United States. It borders Oregon to the northwest, Idaho to the northeast, California to the west, Arizona to the southeast, and Utah to the east. Nevada is the seventh-most extensive, th ...

in the

United States The United States of America (USA), also known as the United States (U.S.) or America, is a country primarily located in North America. It is a federal republic of 50 U.S. state, states and a federal capital district, Washington, D.C. The 48 ...

. The oval caldera is about wide 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 at McDermitt Caldera is above sea level at Jordan Meadow Mountain, which is part of the Montana Mountains of Nevada. McDermitt Caldera is possibly the oldest of a sequence of calderas formed by the Yellowstone hotspot. The caldera was preceded by a lava dome 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 (geology), texture, but may be porphyritic, containing larger mineral crystals (phenocrysts) in an otherwise fine-grained matri ...

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, depositing varved sediments, diatomite,

opal Opal is a hydrated amorphous form of silicon dioxide, silica (SiO2·''n''H2O); its water content may range from 3% to 21% by weight, but is usually between 6% and 10%. Due to the amorphous (chemical) physical structure, it is classified as a ...

, and carbonaceous material amidst lava flows and tuffs. Significant ore deposits are buried in the caldera, including mercury and

uranium Uranium is a chemical element; it has chemical symbol, 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. Ura ...

, which were mined at more than eight sites in the caldera during the 20th century. Mercury at these mines was extracted in large amounts, predominantly from

cinnabar Cinnabar (; ), or cinnabarite (), also known as ''mercurblende'' is the bright scarlet to brick-red form of Mercury sulfide, mercury(II) sulfide (HgS). It is the most common source ore for refining mercury (element), elemental mercury and is t ...

. 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 at the Moonlight mine on the caldera's southwestern edge. The uranium ore minerals include uraninite 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; it has chemical symbol, symbol Sb () and atomic number 51. A lustrous grey metal or metalloid, it is found in nature mainly as the sulfide mineral stibnite (). Antimony compounds have been known since ancient t ...

, cesium, and

lithium Lithium (from , , ) is a chemical element; it has chemical symbol, symbol Li and atomic number 3. It is a soft, silvery-white alkali metal. Under standard temperature and pressure, standard conditions, it is the least dense metal and the ...

(potentially, one of the biggest lithium mines in the world). The Thacker Pass lithium deposit, 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 the Aurora uranium deposit at the McDermitt Caldera margin File:USGS McDermitt caldera geologic cross-section.png, Geologic cross-section showing the Aurora uranium deposit in McDermitt Caldera File:USGS McDermitt caldera geologic cross-section 2.png, Schematic cross-section of Aurora uranium deposit ore zones

References

External links

*{{commons category-inline Calderas of Nevada Calderas of Oregon Extinct volcanoes of the United States 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

See also

References

External links