Petrographic study of hydrothermal alternations in Upper Cretaceous Shale from Breckenridge, Colorado

Abstract

A petrographic investigation was conducted on several surface samples of Upper Cretaceous Shale from the eastern portion of the Breckenridge Mining District in Summit County, Colorado. Shales associated with known and speculated ore bodies were studied as well as shales from a nearby area not known to be associated with an ore body. The presence of hydrothermal alteration assemblages are described and interpreted following guidelines taken from the literature. The results strongly suggest that altered shales may be good guides to ore.