New Mexico Mineral Symposium — Abstracts

The San Juan Mountains of southwestern Colorado have been an exceptionally productive area for micromineral crystals. Many of the mine dumps, as well as some of the uneconomically mineralized volcanic areas, have provided us with fine crystallized
specimens.

In the Summitville district of Rio Grande County, thin hexagonal plates of deep-blue covellite may be found on the dumps of the Reynolds tunnel. Occasionally, these covellite crystals are partially altered to chalcopyrite. The nearby Missionary shaft produces sharp lustrous black crystals of enargite as well as tabular barite.

Careful searching of the dumps of the Bessie G mine in the La Plata district has uncovered several telluride minerals occurring very occasionally as euhedral crystals. Krennerite occurs at the Bessie G as tin-white lath-shaped crystals while sylvanite is found as bladed crystals. Coloradoite, the most common telluride, occurs only rarely as subhedral iron-black crystals having a "melted" surface appearance. Gold, in wire form, has been found with the tellurides. Barite in sharp thin plates has been found at the May Day mine along with sylvanite and sphalerite.

The old dumps of the Longfellow mine on Red Mountain Pass, San Juan County, Colorado, have recently yielded wurtzite, a new species for Colorado, that occurs as dark-brown hexagonal hemimorphic crystals. This locality also produces fine euhedral crystals of tetrahedrite, enargite, and octahedral pyrite. Also in San Juan County in the Silverton district, dumps of the Zuni mine continue to yield well-formed tetrahedrons of zunyite and octahedrons of pyrite. Fine specimens of huebnerite occur on the dumps of the Yukon tunnel located along Cement Creek north of Silverton. The Sunnyside mine, also north of Silverton, has been a noted locality for rhodochrosite, gold, huebnerite, helvite, tetrahedrite, and pyroxmangite.

In nearby Ouray County, the Micky Breen mine has yielded fine euhedral crystals of rhodochrosite and chalcopyrite as well as sphalerite and fluorite. The Zannett tunnel, also in Ouray County, has produced crystals of rhodochrosite, chalcopyrite and huebnerite, as well as sphalerite and fluorite.

Near Ophir in San Miguel County, cassiterite has been found, along with molybdenite and ferrimolybdite.

At Dunton in Dolores County, nice bladed crystals of stibnite occur.

The volcanics of the Treasure Falls area near Wolf Creek Pass, Mineral County, have yielded some well-crystallized zeolites. Mordenite, heulandite, analcime, and natrolite occur in moderate abundance along with the rarer species new to the area, gmelinite and wellsite. These zeolites are associated in amygdaloidal cavities with celadonite, nontronite, calcite, quartz, and semiopal.