New Mexico Mineral Symposium — Abstracts

In September 1984 I was searching the Taylor Creek mining district for tin prospects that might be hosts for the mineral durangite. Access to most of the prospects is via forest roads connected to NM-59, sometimes referred to as the "Beaverhead Highway." I was investigating the Squaw Creek tin mine, located in sec. 34, T9S, R11W, when microscopic red crystals were seen in both outcrop and randomly scattered loose rock near the mine's upper portal. Any assumptions that the material was durangite were subsequently proved incorrect by Paul Hlava's microprobe analyses and Eugene Foord's x-ray diffraction results. Research showed the red crystals were a new durangite-like arsenate. In the same material was found a new cassiterite-like oxide, recently named squawcreekite, and a new yellow chernovite-like arsenate. Chernovite (YAsO4) was also identified in the groundmass of the rhyolite.

In the weeks following the initial analyses I collected a significant amount of rhyolite that had specimen potential. It was eventually broken up and checked under a microscope. In addition to the three new minerals, the following were observed: cassiterite, hematite, pseudobrookite, quartz, tridymite, mordenite, heulandite, and stellerite(?).

Field identification of the new minerals is difficult because of their small grain size and their color similarity. Generally, the new red arsenate resembles cassiterite in color but has a slight orange tint compared to a dark blood red, almost purplish tint, for the cassiterite. The crystals can be recognized by their monoclinic morphology. The red arsenate also tends to form nice euhedral crystals in lithophysae; the cassiterite tends to form aggregates on or near seams. The red arsenate is altered more easily by ground-water activity and sometimes may resemble cassiterite when it is altered. Hematite is ever present in most of the samples, but when hematite crystals are in contact with cassiterite, the cassiterite tends to smear/spread out over the crystals; the red arsenate does not exhibit this characteristic. It is also common to have squawcreekite crystals growing on tiny hematite crystals. The squawcreekite can have an epitaxial overgrowth of Fe-Sb-rich cassiterite, but this apparently does not affect the overall color. Squawcreekite is less common than the red arsenate and tends to be amber to root-beer brown in color. Generally, the finer grained the squawcreekite is, the lighter its color tends to be. For example, an aggregate of squawcreekite may be a golden-brown color, but a single tiny crystal sitting adjacent to it may be a light-amber color (yellow with brown tints). Tiny, easily recognizable tetragonal crystals, resembling natrolite in form, are quite rare. The new yellow arsenate is apparently visually similar in color to chernovite, but chernovite is apparently rarer and hence not likely to be seen. The chernovite-like arsenate is strictly lemon yellow in color, very fine grained and usually found as grains in the groundmass. Generally, if a tiny yellow grain has any hint of a brown tint, then it is more likely to be the more prolific squawcreekite and not the new yellow arsenate.

I wish to thank Paul Hlava, Eugene Foord, and Charley Maxwell for their lab and/or field work and Arnold Hampson for microphotography.
 

References:

1. Foord, E. E., Oakman, M. R., and Maxwell, C. H., 1985, Durangite from the Black Range, New Mexico, and new data on durangite from Durango and Cornwall: Canadian Mineralogist, v. 23, pt. 2, pp. 241-246
2. Foord, E. E., and Maxwell, C. H., 1986, Mineralogy of the Black Range tin district, Sierra and Catron Counties, New Mexico (abs.): New Mexico Inst. Mining and Tech., New Mexico Mineral Symp.; New Mexico Geology, 1987, v. 9, no. 1, pp. 20-21
3. Fries, Carl, Jr., and Butler, A. P., 1940, Geologic map of the Black Range tin district, New Mexico: U.S. Geol. Survey, Bulletin 922-M, 1 sheet