New Mexico Mineral Symposium — Abstracts

The ore deposits of the Red Mountain district, Ouray and San Juan Counties, Colorado, occur as chimneys and less important veins that are associated with volcanic pipes. These pipes are confined to a belt of fractured and altered rocks along ring faults on the west and northwest sides of the Silverton caldera.

The volcanic pipes are usually vertical cylinder-like bodies that are elliptical to concentric in cross section. The pipes consist of breccias and intrusives of quartz latite porphyry and rhyolite. Brecciation occurred first from magmatic emanations that followed fracture zones. Volume and chemical changes resulted in cracking and slumping. The zone of brecciation spread outward from the fracture zone forming curved surfaces that formed the elliptical pipes. The pipes then were intruded by rhyolite and quartz latite porphyry. The breccias formed earlier were moved aside or were assimilated by the intrusive rocks.

The orebodies are of two types. The first formed within the pipes and occur as short veins and chimneys composed of massive sulfides. The second type formed at the margins or outside the pipes. This latter type is localized by structures related to the formation of the pipe, such as cone sheet pipe.

The common ore minerals include enargite, galena, sphalerite, tennantite, tetrahedrite, chalcopyrite, covellite, stromeyerite, and bornite. Rarer ore minerals are proustite, pyrargyrite, polybasite, and cosalite. Gangue minerals include quartz, sericite, dickite, barite apatite, and zunyite.

The district was active between 1882 and 1900 when the National Belle, Yankee Girl, Silver Bell, Guston, and Genessee mines were active. During the 1950's the Longfellow mine was discovered and operated. At present, no mines are operating in the area.