New Mexico Mineral Symposium — Abstracts

Many mines and mineral localities are along the Rio Grande trench in south-central and southwestern New Mexico. Many of the best localities are along the Black Range, particularly south of Alamosa Creek. (The well-known tin deposits on the west side of the range are not discussed here because many recent papers have described them.) The best-known mineral locality is the Iron Mountain deposit in the Sierra Cuchillo, east of the main Black Range, about 2 mi east of the junction of the road to Dusty and NM-52. Many minerals have been reported in the iron manganese skarn at Iron Mountain, including helvite, danalite, fluorescent fluorite, and fluorescent molybdenum-bearing sheelite (Richard Jahns and J. J. Glass, U.S. Geological Survey, Bulletin 945). Manganoan calcite that fluoresces red and hypogene pale-yellow granular willemite that fluoresces bright yellow-green (similar to that at Franklin, N.J.) are also common in the main tunnel workings and at the adjacent large ore bin. Both minerals are intergrown with banded andradite garnet, magnetite, and inconspicuous danalite. Nonfluorescent supergene grayish-pink transparent willemite crystals occur in vugs. The helvite occurs in yellow-brown tetrahedrons; the danalite, where present as euhedral crystals, has a similar habit but is pale brown to pink.

South of NM-52, 1.2 miles into the Black Range, a mine road leads southward to the Great Republic mine in a branch of Poverty Creek, where large open pits expose gold-quartz veins. The veins contain beautiful coarse amethyst crystals that are suitable for slabbing, bands of silver-copper minerals, sparse grains of gold, and pale-green chlorargyrite. A rocky point of andesite, adjacent to the north side of the Winston-Chise road, 7 mi south of Winston, contains crystals of heulandite, stilbite, and uncommon natrolite. Along the same road 6.1 miles south of Winston, Cuchillo Negro Creek is joined by a valley from the south that becomes Coyote Canyon. South 1.1 miles, on a 4-wheel-drive road up the canyon, along the northwest side of the road, are outcrops of semiprecious white opal. West of Chloride, about 14 miles up Chloride Creek on a 4-wheel drive road, are the dumps of the Silver Monument mine. The dumps contain beautifully colored massive bornite and much nearly microscopic native silver. South of NM-152, 2.5 mi east of Hillsboro, a passable road extends down Ready Pay Gulch to the east end of Percha Creek Box. Here old vanadium mines have well-formed pale-yellow crystals of endlichite (arsenian vanadinite), orange vanadinite, wulfenite, and yellow-brown descloizite. Far to the south of the Black Range, 2.3 mi due south of Deming and 10 mi south on NM-517, are the old silver-lead mines of the Mahoney mining area that are at the foot of the northwest corner of the Tres Hermanas Mountains. These mines and their dumps have well-formed supergene crystals of willemite and smithsonite, masses of cerussite, pale-green fornacite (Pb,Cu)₃[(Cr,As)O₄]₂(OH), wollastonite, hyrozincite, malachite, and hemimorphite.