New Mexico Mineral Symposium — Abstracts

Recent mineral discoveries in the Cuchillo Negro mining district indicate a virtually untapped collecting area for New Mexico mineral enthusiasts. The Cuchillo Negro district is in Sierra County southeast of the small town of Winston. The district was mined extensively in the early 1900's for lead, copper and zinc; however, most prospects were small operations and thus mine workings are generally not very large. Because little has been known about this district, few collectors have been to the area. Thus, the variety and quality of minerals will come as somewhat of a surprise to seasoned New Mexico collectors.

The mines are situated at the contact between Pennsylvanian Magdalena limestone and a Tertiary monzonite porphyry. Shafts and tunnels intercept the contact-metamorphic ore deposits. Five major groups of mines in the district were investigated. These included the Dictator, Covington, Vindicator, Black Knife, and Confidence mines. Mineral assemblages at each mine are distinctive.

At the Dictator mine, superb discoidal willemite crystals to 7 mm across were found on the dumps in recrystallized limestone. The crystals are colorless to yellow, highly lustrous and often transparent. The willemite fluoresces green under short wave while the calcite fluoresces crimson red. Willemite crystals are also found inside the main tunnel of the mine but are more typical of the species, being gray, hexagonal prisms about 1-2 mm long. Lustrous brown crystals of descloizite are also found imbedded in calcite on the dumps. Additional minerals found are mottramite, vanadinite, smithsonite, cerussite, wulfenite, azurite, malachite, galena, and sphalerite.

No noteworthy mineral specimens were found at the Covington group of mines about 0.5 km west of the Dictator mine.

The Vindicator mine at the northern end of the Sierra Cuchillo range produced very aesthetic fluorite specimens. Grass-green octahedrons to 2 cm, often coated with a thin crust of white adularia crystals, were collected from two large pockets in the main inclined shaft. Small, water-clear, sceptered quartz crystals along with very small (0.5 mm) black crystals of mottra¬mite occur in association with the fluorite. Calcite scalenohe¬drons replaced by quartz and coated with olive-green, earthy mottramite also occur here.

The Black Knife mine about 1 km south of the Vindicator mine and on the east side of the range produced unique specimens of calcite and fluorite. The scalenohedral calcite crystals are for the most part replaced by quartz and intimately associated with light-green fluorite octahedrons. The fluorite has been etched and the luster is dull, but crystals to 3 cm occur here. Olive-green to dark-green mottramite "crusts" often coat these speci¬mens. Ramsdellite has been confirmed from this mine in 0.5-1 mm crystals in association with purple fluorite.

The Confidence mine is on the west slope of the range about 2 km due west of the Dictator mine. Wulfenite and willemite specimens are common at this mine. Bright-yellow to orange crystals of wulfenite in tabular, blocky, and pyramidal habits to 0.8 mm are found in vugs associated with cerussite and willemite. Hexagonal prisms of willemite to 0.5 mm are common, but the luster is dull and the pinkish color is not particularly attractive. Hemimorphite and vanadinite microcrystals can also be found here and, rarely, linarite and brochantite.