(Left) Location of the Boulder Batholith in relation to the Idaho Batholith. (right) Geologic map of the Boulder Batholith
Rounded brown-weathering boulders give the Boulder Batholith its name.
The Boulder Batholith is a relatively small batholith in southwestern Montana, United States, exposed at the surface as granite (more specifically quartz monzonite) and serving as the host rock for rich mineralized deposits at Butte and other locations. The batholith lies roughly between Butte and Helena, and between the Deer Lodge (Upper Clark Fork) Valley and the Broadwater (Upper Missouri) Valley. The volcanic Elkhorn Mountains are a large mass of forested lava associated with the batholith.
The batholith is composed of at least seven, and possibly as many as 14, discrete rock masses called plutons, which had formed beneath the Earth's surface during a period of magma intrusion about 73 to 78 million years ago (Late Cretaceous time).[1] The rising buoyant plutons resulted from subduction along what was then the west coast of North America, which was near today's border between Montana and Idaho. Regional uplift brought the deep-seated granite to the surface, where erosion exposed the rocks and the extremely rich mineral veins they contained. Hundreds of millions of dollars of copper, silver, gold, zinc, lead, and other metals have been mined from the batholith, both using underground mining and pit mining.
The Butte Granite makes up the bulk of the batholith (about 70%), with additional named intrusions along the periphery consisting of granodiorite, monzogranite, and minor syenogranite. The batholith intruded into Mesoproterozoic and Mesozoic sedimentary rocks, including the Elkhorn Mountains volcanics. The origin of these igneous rocks is related to subduction and continental magmatic arc processes associated with the Late Cretaceous western margin of North America. Later hydrothermal vein activity along fault and shear zones within the Butte quartz monzonite and its contact with adjacent rocks, resulted in major ore deposits of lead, zinc, and silver.[2][3]
The Boulder Batholith was named for the prominent rounded boulders that typify its landscape, the result of spheroidal weathering of fractured granite. It measures approximately 75 miles (121 km) north-south by about 25 miles (40 km) east-west, rather small in comparison to most batholiths.
^Johnson, B.R., and others, 2004, Reexaming the geochemistry and geochronology of the Late Cretaceous Boulder Batholith, MT Archived 2012-04-06 at the Wayback Machine
^Meyer, Charles; Shea, Edward; Goddard, Charles; Staff, JR. (1968). Ridge, John (ed.). Ore Deposits at Butte, Montana, in Ore deposits of the United States, 1933-1967. New York: The American Institute of Mining, Metallurgical, and Petroleum engineers, Inc. pp. 1373–1416.
^du Bray, E.A.; Aleinikoff, J.N.; Lund, Karen (2012). "Synthesis of petrographic, geochemical, and isotopic data for the Boulder batholith, southwest Montana: U.S. Geological Survey Professional Paper 1793" (PDF). USGS. Retrieved 1 July 2020.
The BoulderBatholith is a relatively small batholith in southwestern Montana, United States, exposed at the surface as granite (more specifically quartz...
A batholith (from Ancient Greek bathos 'depth', and lithos 'rock') is a large mass of intrusive igneous rock (also called plutonic rock), larger than...
The Sierra Nevada Batholith is a large batholith that is approximately 400 miles long and 60-80 miles wide which forms the core of the Sierra Nevada mountain...
mountains, such as the Tobacco Roots were formed from the BoulderBatholith. The batholith is composed of at least seven, and possibly as many as fourteen...
The Butte mining district is characterized by the Late Cretaceous Boulderbatholith which metamorphosed surrounding rocks during the Laramide orogeny...
the range is occupied by the Tobacco Root Batholith, thought to be a satellite pluton of the BoulderBatholith. This Late Cretaceous granitic body intrudes...
Jefferson County Montana and implications for the generation of the Boulderbatholith (M.S. thesis). Missoula: University of Montana. "West Musgrave". integra...
Northwest Montana: Implications for Palinspastic Restoration of the BoulderBatholith and Elkhorn Mountains Volcanics". PALAIOS. 15 (5): 476–482. Bibcode:2000Palai...
silver, lead, zinc and tungsten. In the Idaho Batholith, BoulderBatholith and Tobacco Root Batholith, intrusive granite bodies are particularly common...
western United States, investigating mineral deposits in Alaska, the BoulderBatholith in Montana, and the Gold Country of California. Knopf was a member...
Volcanics are extrusive rocks related to the plutonic granites of the BoulderBatholith. Volcanic flows, lahars, and ash falls from sources in the Elkhorn...
south extrusive volcanic activity occurred in association with the BoulderBatholith collectively called the Elkhorn Volcanics. Most of the vertebrate...
1130/GSAB-44-989. Grout, F. F.; Balk, R. (1934). "Internal structures in the Boulderbatholith". Geological Society of America Bulletin. 45 (5): 877–896. Bibcode:1934GSAB...
Northwest Montana: Implications for Palinspastic Restoration of the BoulderBatholith and Elkhorn Mountains Volcanics." Palaios. 15:5 (October 2000). Hyndman...
intermediate calc-alkalic rocks, such as the granodiorites of the Boulder Creek batholith. The accompanying amphibolite facies metamorphism is characterized...
magma chamber, made of Half Dome granodiorite of the Tuolumne batholith. Tuolumne batholith (also, the Tuolumne Intrusive Suite) dates to Late Cretaceous...
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monzonite.[citation needed] A large pluton in the Atlanta lobe of the Idaho Batholith, near McCall, Idaho, is made of quartz monzonite. The Guilford Quartz...
Dominica, Lesser Antilles: The Surface Expression of an Island-Arc Batholith. Boulder, Colorado: Geological Society of America. pp. 20, 44. ISBN 978-0-81372-496-6...
1966 she devoted herself to completing his research regarding the BoulderBatholith but health complications arose for her. She died in 1974 from arteriosclerosis...
continental margin were deformed, metamorphosed and intruded with granite batholiths. Interpretations of rock forms in Antarctica during the 1980s suggested...
Hookuhu'eeno) is a 13,577-foot-elevation (4,138-meter) mountain summit in Boulder County, Colorado, United States. Chiefs Head Peak is set along the Continental...
northeast and the Stellenbosch batholith a bit further to the north. The characteristic spheroidal shapes of granite boulders are a result of preferential...
Pagoda Mountain is a 13,497-foot-elevation (4,114-meter) mountain summit in Boulder County, Colorado, United States. Pagoda Mountain is located one mile east...
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