New Mexico Mineral Symposium — Abstracts

Molybdenum mining at Questa, New Mexico has drawn to a close after almost 100 years of on-and-off-again production.
Prior to 1916, the soft black mineral and earthy yellow material found along Sulphur Gulch were thought to be graphite and sulfur. However, in 1916, the true nature of the minerals (molybdenite and ferrimolybdite) was recognized. Thus began the history of moly mining along the Red River highway about six miles east of the village of Questa.

In 1918, the R&S (Rapp and Savery) Molybdenum Company was formed and production began in 1919 (Clark and Read 1972). Shortly thereafter, Molycorp of America (MCA) acquired the property and by 1941, an 850-foot pit had been excavated (Shilling 1990). Mining ceased in 1958, but open-pit mining began once again in 1965. Underground mining commenced in 1983, however operations shut down once again in 1986 due to a soft market for Molybdenum. The mine reopened in 1989 and MCA was taken over by Chevron Mining Inc. in 2005. In 2011, the mine was declared a “superfund site” by the EPA and on the 2nd of June, 2014, the mine was declared permanently closed by David Partridge, the President and CEO of Chevron Mining, Inc., at an employee meeting in Questa. Mine closure, including the demolition of mine structures is estimated at one to two years. “Full” reclamation could take decades.

Minerals from the mine of interest to collectors, in descending importance include: Molybdenite, fluorite, fluorophlogopite, fluorapatite, celestine, beryl, orthoclase, pyrite, calcite, hübnerite and rutile. Mindat lists 31 entries from the mine of which 25 are valid species. Molybdenite crystals are most noteworthy: They occur as platy, single and aggregate crystals up to 2.0 cm and hexagonal rosettes to 1 cm. These are often found in association with brown mica crystals that have been variously reported to be biotite or phlogopite, but have been more recently identified as fluorophlogopite (Lueth, pers. Comm. June 2015). Thin, bladed, white to colorless crystals to 1 cm have been identified as celestine by microprobe analysis (Hlava, pers. Comm. 2003). Tabular, water-clear crystals, collected by Klaus Althammer on an Albuquerque Gem and Mineral Club (AGMC) field trip in June 2002 have been visually identified as barite, but are most likely celestine. Rex Nelson found beryl crystals on the June 2002 field trip. These crystals are light blue, acicular prisms up to 1.5 cm and transparent to translucent. The beryl was found in the seams of a fine-grained, silicic rock. Staff geologists found beryl reputed to be emerald in December 2004, but microprobe analysis determined that there was insufficient Cr or V to classify it as emerald (Hlava, pers. Comm. June, 2015). Fluorite is found in anhedral masses and as cubo-octahedral crystals to 2.0 cm. Pale green is the most common color, but purple also occurs. Fluorapatite crystals are uncommon and are usually intergrown with crystals of fluorophlogopite. These are cream colored to colorless prisms with a pyramidal termination and fluoresce orange under short-wave UV illumination. Crystals are generally less than 5 mm. Blocky orthoclase crystals to 1 cm often have a slightly pink color and occur in vugs with molybdenite, quartz and fluorophlogopite crystals. Hübnerite crystals to 3 mm are tabular, brown and associated with a glassy colorless, anhedral scheelite. Pyrite crystals as simple cubes, to 3 mm are common. Phil Bové found irregular rutile crystals in sericite to 1 mm in March, 1989. Light purple cleavages of anhydrite have been collected and yellow coatings of ferrimolybdite are common. Rhodochrosite has been reported from the Questa mine but specimens are at best rare and not noteworthy. Colorless calcite crystals less than 1mm sometimes occur as a “fringe” on fluorophlogopite crystals. Scalenohedral crystals also occur.

This description of minerals from the Questa mine is not complete, but is intended topartially familiarize the mineral collector community with the mineral assemblage that did exist and will probably not be seen again from a mine that now appears to be “extinct”.

References:

1. Clark, K. F. and Read, C. B. (1972) Geology and ore deposits of the Eagle Nest area, New Mexico, NMBGMR Bull. 94,149pp.
2. Shilling, J. H. (1956) Geology of the Questa molybdenum (moly) mine area, Taos County, New Mexico, NMBGMR Bull. 51, 87pp.
3. Shilling, J. H. (1965) Molybdenum resources of New Mexico, NMBGMR Bull. 76, 76pp.
4. Shilling, J. H. (1990) A history of the Questa molybdenum (moly) mines, Taos County, New Mexico, New Mexico Geol. Soc. Guidebook, 41st field conf., pp. 381–386.