Crystal Graphite

Location: Montana, United States (45.103, -112.505 approx.)

Commodities: graphite

Deposit model: 37g - Graphite veins

Geology

“The recent study of Duke and others (1990) provides compelling C-isotope and fluid inclusion evidence that the Crystal Graphite and nearby deposits formed when relatively low temperature (T <350˚C) hydrothermal fluids leached disseminated graphite out of marbles that had been previously metamorphosed to T >800˚C, and reprecipitated the graphite in structurally controlled veins and lodes.” (Berg and Gammons (2021)) “Graphite occurs in veins in gneiss and pegmatite, as disseminations and irregular small masses in pegmatite, and as disseminations mainly in biotite gneiss. The veins pinch and swell, within a few inches forming bunches and pockets of graphite as much as 6 feet thick, and are generally 10 to 20 feet in vertical and horizontal dimensions. The veins can be grouped into mineralized zones 100 to 150 feet across that are believed to be continuous from upper to lower levels. Disseminated graphite is more abundant in the wall rock adjacent to the vein. In the gneiss the graphite is fine grained, being interlayered with the minerals of the gneiss and parallel to the gneissic structure. The graphite in the pegmatite is coarse grained and may occur in blades, rosettes, or irregular masses an inch or two across.” (Geach (1972))

Recorded production

• Crystal Graphite, Crystal Graphite mine: produced 2,000 metric tons of graphite, 1902–1920 (Geach (1972), Page 155 — Geach, R.D., 1972, Mines and mineral deposits (except fuels) Beaverhead County, Montana: Montana Bureau of Mines and Geology Bulletin 85, 194 p., http://www.mbmg.mtech.edu/mbmgcat/public/ListCitation.asp?pub_id=10086&.)

Exploration and site history

• Active — Intermittent production 1902-1920, where primary production occurred from 1917-1920. Concentrate milled from the mine dumps in 1944 and 1948 (1), 1902–1948 (Geach (1972))
• Inactive — Property has been inactive since 1948 (1), 1948 (Geach (1972))
• Discovery — Deposit was discovered in 1899, 1899 (Geach (1972))

Record imported from USGS USMIN ver. 4.0 (June 2019). Developments after that date appear on facility records, not here; see the methodology.