Mining and mineralization of the Clear Lake region Active
The Geysers-Clear Lake area has been one of the most productive in the United States for mercury, and gold was mined in the late 1800s. Many of the deposits are directly associated with outcrops of early Clear Lake volcanic rocks.
For over a century, a correlation has been known between the mercury ore deposits, thermal springs, and volcanism at Clear Lake. No mercury deposits are known in the Coast Ranges north of Clear Lake. Gold and mercury mineralization (formation of minerals) occurs in rocks of the Great Valley sequence and the Coast Range at the eastern edge of the Geysers-Clear Lake area, as well as at the Sulphur Bank mine on the western shore of Clear Lake. First mined for borax in the 1850s and mercury for gold processing in the 1860s, the mine was closed in 1957 and was eventually declared a Superfund site in 1990 because of the presence of mercury-bearing mine tailings and wastewater. The hot springs which formed Sulphur Bank are monitored by CalVO for chemistry and temperature.
The McLaughlin gold mine is located farther south along the eastern edge of the Geysers-Clear Lake; it is a disseminated gold deposit that was discovered at the site of the former Manhattan mercury mine in the Knoxville district. Mineralization at this deposit is located in and adjacent to basaltic lava now dated at 2.2 Ma. Siliceous sinter deposits at the heart of the gold deposit indicate that mineralization is related to former hot springs; only relatively cool mineralized springs now emerge in the district
The Geysers-Clear Lake area has been one of the most productive in the United States for mercury, and gold was mined in the late 1800s. Many of the deposits are directly associated with outcrops of early Clear Lake volcanic rocks.
For over a century, a correlation has been known between the mercury ore deposits, thermal springs, and volcanism at Clear Lake. No mercury deposits are known in the Coast Ranges north of Clear Lake. Gold and mercury mineralization (formation of minerals) occurs in rocks of the Great Valley sequence and the Coast Range at the eastern edge of the Geysers-Clear Lake area, as well as at the Sulphur Bank mine on the western shore of Clear Lake. First mined for borax in the 1850s and mercury for gold processing in the 1860s, the mine was closed in 1957 and was eventually declared a Superfund site in 1990 because of the presence of mercury-bearing mine tailings and wastewater. The hot springs which formed Sulphur Bank are monitored by CalVO for chemistry and temperature.
The McLaughlin gold mine is located farther south along the eastern edge of the Geysers-Clear Lake; it is a disseminated gold deposit that was discovered at the site of the former Manhattan mercury mine in the Knoxville district. Mineralization at this deposit is located in and adjacent to basaltic lava now dated at 2.2 Ma. Siliceous sinter deposits at the heart of the gold deposit indicate that mineralization is related to former hot springs; only relatively cool mineralized springs now emerge in the district