New Mexico Mineral Symposium — Abstracts

In the San Juan Mountains of southwestern Colorado, the Leadville Limestone of Mississippian age is the host rock for a number of small but outstanding mineral occurrences. Most of these non-commercial deposits are quartz veins and solution cavities that contain superb quartz crystals ranging up to 19 inches long and encrustation pseudomorphs of quartz after barite and calcite.

The Amphitheater, just east of Ouray, is an area that has produced large, world-class milky-quartz crystals from a large solution cavity and enormous milky-quartz crystals from a large vug in a crystalline-quartz vein.

Within the city limits of Ouray, a solution cavity was discovered that contained a number of fine encrustation pseudomorphs of quartz after large, bladed barite crystals. Just a short distance from this locality, another pocket produced large, brown calcite crystals implanted on small quartz crystals.

The Mineral Farm mine, which is one of the few economic operations in the Leadville Limestone, has produced fine quartz crystal groups along with crystallized tetrahedrite, sphalerite, and pyrite.

In the Ironton Park area, which is located south of Ouray, an igneous intrusion on the edge of the Leadville Limestone has produced a small skarn deposit. Superb micro crystals of prehnite, epidote, grossular, and magnetite have been collected from the contact metamorphic zone. Another contact metamorphic deposit just south of Silverton has produced an exotic array of minerals.