The ore deposits of the Sunlight mining region, Park County, Wyoming

Abstract

The Sunlight mining region lies in the Absaroka Mountains, Wyo. The deposits are twenty miles from the nearest road and are not developed. The mineralization is genetically associated with an intrusive and volcanic center made up of a small stock of syenite and diorite, several basaltic plugs, hundreds of radially-arranged dikes, and a few cone sheets, all in the Early Basic Breccia Series of the Absarokas. The deposits are small, irregular fissure veins in fault zones and along dike contacts in the Tertiary Volcanic breccias.The common ore minerals are pyrite, chalcopyrite, galena, and tetrahedrite with pockety values in gold and silver. The gangue is essentially carbonates and quartz. The deposits have the banded and vuggy character of typical epithermal veins; they exhibit a vertical zoning that is well exposed due to the 3,000 foot relief, and seems to have been dependent on a vertical temperature gradient that existed in the roots of the volcano shortly after its activity had ceased. In the deepest zone are pyrite-quartz veins and above them successively, chalcopyrite-pyrite-gold, chalcopyrite, galena, and galena-silver veins in a 2,000 foot range.