New Mexico Mineral Symposium — Abstracts

Turquoise is not a well-known gem material from Colorado, but the state has four localities that have produced significant amounts of turquoise in the past, two of which are still worked today. All the deposits are associated with Tertiary-age felsic igneous rocks, though at Leadville and Cripple Creek the productive turquoise veins are hosted by adjacent Precambrian granite. The turquoise occurs as near-surface supergene veins and veinlets, which are characteristically free of other normally common secondary copper minerals such as azurite, malachite, or chrysocolla.

The King turquoise mine is in Conejos County, in the San Luis Valley, about 9 mi east of Manassa and 19 mi west of the town of San Luis. The workings are in a hill composed of chalky, hydrothermally altered silicic volcanic rock, part of the Conejos Formation of Oligocene age. Turquoise was discovered here by Israel Pervoise King in 1890, but extensive Native American workings already existed and tools made of stone and horn have been found here (Harvey and Harvey, 1938). The most extensive mining took place in the 1940s and included open cuts, inclines, and shafts. An 8.75-lb nugget was reported to have been recovered in 1941 (Pearl, 1951). The property is still worked sporadically by Bill King of Manassa, who markets silver jewelry set with the material. Polished turquoise from the mine includes blue-green material intergrown with brown limonitic matrix in an attractive pattern, and sky-blue turquoise that tends to be more solid but does require some stabilization treatment (King, pers. comm. 2002).

The Hall turquoise mine is about 8 mi northwest of Villa Grove in Saguache County. It lies about 5 mi east of the Bonanza mining district and near the head of the Turquoise Gulch drainage. Said to have been developed first as a copper mine, turquoise production was reported by Kunz (1894), who described the workings as the Blue Gem and Manitou mine. The turquoise veinlets occur in a highly fractured and altered, light-colored silicic volcanic rock, near the edge of the Bonanza caldera. The visible mine workings consist of a pit (now partially water filled) and open cuts. The mine is said to have also once included underground workings. Pearl (1941a,b) reported that 4-5 tons per day of dump material were hand sorted daily to produce several pounds of turquoise, valued at $15—$45 a pound. Colorado Bureau of Mines records show that the most extensive production was during the mid-1950s. The patented mining claims are currently inactive and posted.

Most of the turquoise reported from Cripple Creek has come from the Florence mine, located on the south side of Mineral Hill at the northern edge of town. Mining for turquoise was begun here by Wallace C. Burtis in 1939 and continues today on a small scale. Turquoise occurs as residual weathered nuggets and as veins along fractures in moderately weathered Pikes Peak Granite at the northwest edge of the Cripple Creek volcanic center. Two slabs of pure turquoise, each weighing slightly over 6 lb, were recovered around 1987 by Burtis' son, Wallace F., who now works the property to produce silver and turquoise jewelry. Contiguous workings slightly higher on Mineral Hill are operated by David and Harriet Graham (business name, The Bad Boys of Cripple Creek), who also mine, polish, and sell the turquoise. Limonitic vein material in some of the Grahams' turquoise is reported to contain flecks of native gold (Jones, 2001). The nearby Roanoke shaft is also known to have intersected turquoise veins.

The Turquoise Chief and nearby smaller mine workings are in Lake County, about a mile north of the center of Turquoise Lake. They are about 6 mi northwest of the Leadville mining district, and closer to (about 1 mi southeast of) the St. Kevin mining district. The Turquoise Chief mine is reported (Pearl, 1951) to have been initially worked by two Navajos in 1935, at which time a thousand pounds of turquoise is said to have been mined over a 2 yr period. Excavations apparently continued over the next half century, but little has been published about the deposits or the mining history. The present workings consist of a relatively large open pit at the Turquoise Chief mine proper and several smaller open cut workings (the Josie May mine) about 1/4 mi to the southwest, adjacent to San Isabel National Forest Road 103. Turquoise occurs as veinlets and nodules in variably altered Silver Plume-age (1.4 Ga) St. Kevin Granite.

In addition to the references cited, Murphy and Modreski (2002) summarize the history and mining activity at the four deposits and give additional literature references. The location of and information about these deposits is being incorporated into a database on Colorado gemstone occurrences at the Denver Museum of Nature and Science (Murphy, 2002).

Small amounts of turquoise have also been reported from Creede, Summitville, the Holy Cross mining district in Eagle County, and the Sugarloaf district in Lake County, south of Turquoise Lake.

References:

1. Eckel, E. B., 1997, Minerals of Colorado, updated and revised by Cobban, R. R., Collins, D. S., Foord, E. E., Kile, D. E., Modreski, P. J., and Murphy, J. A.: Golden, Colorado, Fulcrum Publishing, 665 pp.
2. Harvey, J. R., and Harvey, R., 1938, Turquoise among the Indians and a Colorado turquoise mine: Colorado Magazine v. 15, pp. 186-192.
3. Jones, R., 2001, Cripple Creek turquoise: Rock & Gem, v. 32, no. 5, pp. 48-51.
4. Kunz, G. F., 1894, Precious stones; in Mineral resources of the United States for 1893, U.S. Geological Survey, pp. 680-702.
5. Murphy, J. A., 2002, Colorado gemstone survey???a database and locality map for a museum internet program; in Gemstone deposits of Colorado and the Rocky Mountain region, Program and Abstracts: Golden, Colorado, Friends of Mineralogy, Colorado Chapter, Colorado School of Mines Geology Museum, Denver Museum of Nature and Science, and U.S. Geological Survey, pp. 7-13.
6. Murphy, J. A., and Modreski, P. J., 2002, A tour of Colorado gemstone localities: Rocks & Minerals, v. 77, no. 4, pp. 218-238.
7. Pearl, R., 1941a, Colorado turquoise localities: The Mineralogist, v. 9, pp. 3-4, pp. 24-27.
8. Pearl, R., 1941b, Turquoise deposits of Colorado: Economic Geology, v. 36, pp. 335-344. Pearl, R., 1951, Colorado gem trails: Colorado Springs, Mineral Book Co., 125 pp.