Geology of Nevada
Intense volcanism, the horst and graben landscape of the Basin and Range Province originating from the Farallon Plate, and both glaciers and valley lakes have played important roles in the region throughout the past 66 million years.
[1] The oldest rocks in Nevada are in the East Humboldt Range in the northeast, with lead isotope data suggesting an age of 2.5 billion years, at the boundary of the Archean and Proterozoic.
Metamorphic and igneous rocks formed 1.7 billion years ago underlie Clark County and the populous areas around Las Vegas.
[2] After the breakup of Rodinia, southern and eastern Nevada remained as a passive margin on the western edge of the proto-North American continent of Laurentia.
The Monitor, Egan, Schell Creek and Arrow Canyon ranges in the east are dominated by limestone and dolomite formed during 400 million years of marine conditions.
Sea levels rose over the eroded mountains in the late Paleozoic, although uneven rock surfaces remain as the Antler overlap sequence, which includes conglomerate, siltstone, limestone and sandstone deposited from the Pennsylvanian into the early Triassic.
High concentrations of the rare element iridium and jumbled mega-breccia deposits in the Guilmette Formation, made up of shattered limestone that re-cemented in deep water, has led geologists to infer the Alamo meteorite impact even around 382 million years ago in the Devonian.
Although an exact impact site has not been found, geologists have suggested a possible location in the Timpahute Range in southern Lincoln County, near Rachel, Nevada.
Due to conditions in the underlying crust, inferred to be a thinner section of the Farallon, intense volcanic activity began in the Eocene in northern Nevada around 43 million years ago, reaching the center of the state by the Oligocene and the south by the Miocene.
The volcanism was some of the most intense in Earth history, ejecting 17,000 cubic miles of material in 250 major eruptions and layering the landscape in tuff ash falls thousands of feet thick.
Some small cinder cones formed as recently as the Pleistocene and the Nye County Lunar Crater volcanic field was active only 15,000 years ago.
Dozens of large lakes filled the valleys in the region, accumulating fine silt and developing alkaline chemical conditions that precipitated tufa calcium carbonate mounds.
Polymetallic molybdenum, antimony, uranium, copper, gold zinc, lead and silver ores have been mined in the Reese River area since the 1800s.
Paleozoic limestone, formed at the ancient continental margin, contains nearly microscopic gold associated with pyrite and arsenic sulfides and particularly jasperoid in folds and faults.
Nevada is the leading producer of barite in the US, particularly at the Greystone Mine in Lander County, where it is found in deep sea black shale and argillite.
