New Mexico Mineral Symposium — Abstracts

Fluorite is a common gangue mineral in many of the mines located in the San Juan Mountains of southwest Colorado, often forming large euhedral crystals associated with quartz, rhodochrosite, calcite, pyrite, sphalerite, galena, and other minerals. Encrustation pseudomorphs of quartz after fluorite are also relatively common in quartz outcrops throughout the San Juans. Although fluorite is relatively common in the mines of the San Juans, it has not been widely exploited commercially, possibly because it rarely forms massive veins that could be mined at a profit. An exception was the Thistledown mine, along the Camp Bird road, about a mile southwest of the town of Ouray, where mining was specifically for fluorite. This overview is intended to provide a survey of the mines that have produced a significant amount of well-formed crystallized fluorite.

Some of the finest crystallized fluorite specimens come from the Sunnyside mine, located in San Juan County, about 5 mi northwest of Silverton along Cement Creek at the old site of Gladstone. Specimens are composed of octahedra or cubes of fluorite to as much as 4 inches on edge, typically on a matrix of drusy white quartz, often associated with rhodochrosite, pyrite, and other sulfides. Color includes pale green, emerald green, pale lavender, and grayish green. At the mouth of Arrastra Gulch, about 2 mi north of Silverton, is a prospect known as the Genoa claim. It has produced fine groups of encrustation pseudomorphs of quartz after octahedra of emerald-green fluorite to 2 inches on edge, in plates to as much as 10 inches across. Occasional encrustation pseudomorphs of quartz after barite are also found interspersed with the fluorite at this locale. The Ransom mine, just above the town site of Eureka, has yielded some beautiful gemmy, pale-green complex cuboctahedra of fluorite to nearly 2 inches on edge, implanted on large, milky-white barrel-shaped quartz clusters. In and near Hematite Gulch, west of the Animas River and opposite the mouth of Cunningham Gulch, several mines and prospects contain pale-green octahedra of fluorite, sometimes coated with a thin crust of drusy quartz.

In the Red Mountain mining district, between Silverton and Ouray, the Longfellow mine contains occasional cubes of lavender or white fluorite cubes to 1.5 inch on edge on plates of bright enargite crystals. The Idarado mine, which runs from Red Mountain Pass on the east all the way to the Telluride side on the west, contains occasional vugs with pale-lavender cubes and octahedra to 1 inch in association with quartz, minor sulfides, and other less-common species. At the north end of the Red Mountain district on the west edge of Ironton Park is a small prospect, the Gertrude claim. This claim contains large (to 2 inches on edge) bright-green fluorite octahedra coated with a druse of quartz and associated with scalenohedral calcite crystals to 0.5 inches.

The Grizzly Bear mine, in Ouray County, about 1 mile south of Ouray, has numerous vugs that contain fluorite crystals from 1-inch cubes of lavender to roughly 0.75-inch cuboctahedra of pale-green perched on plates of milky quartz crystals and associated with small rhodochrosite crystals. The Camp Bird mine, about 5 mi southwest of Ouray, also has numerous vugs containing fluorite crystals. Large encrustation pseudomorphs of quartz over emerald-green cubes of fluorite were found on the 14 Level of the East Camp Bird, whereas small, gemmy clusters of fluorite were found with cream-color doubly terminated calcite crystals on the 21 Level. Other vugs have produced colorless to pale-green fluorite in various parts of the mine. The Thistledown mine, which was mined for a short time around the First World War for fluorite, has yielded some of the largest emerald-green octahedra of fluorite crystals ever found in Ouray County. One crystal measures more than 3 inches on edge and is found on a plate of etched, white quartz crystals.

Although fluorite has no significant economic value in the mines of the San Juans, it forms fine large euhedral crystals and attractive crystal specimens in a range of color and habit and deserves its reputation as one of the most desirable collectible species from this area.