McDermitt Caldera


The McDermitt Caldera is a large, oval-shaped caldera west of McDermitt in southeastern Oregon and northern Nevada in the United States. It is about wide north to south and wide east to west. The western part of the caldera is in the Trout Creek Mountains, and the northern part is in the Oregon Canyon Mountains.
McDermitt Caldera is possibly the oldest caldera in a sequence of calderas formed by the Yellowstone Hotspot. The caldera was formed when a lava dome made of rhyolite collapsed in an eruption between 16.37 and 16.41 million years ago. The lava dome had been built by volcanic eruptions starting about 19 million years ago. The highest point in the McDermitt Caldera is Jordan Meadow Mountain, part of the Montana Mountains, which is at its peak elevation.
A lake formed after the caldera collapsed, and it deposited varved sediments, diatomite, horizons with opal or carbonaceous material, and mafic lavas. Significant ore deposits are buried in the caldera, including mercury and uranium, 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. 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 at the Moonlight mine on the caldera's southwestern edge, from a rhyolite brecciated fault zone. 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 Ma. Other deposits in the caldera contain ores of antimony, cesium, and lithium. 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.