John F. Slack Gerald T. Cebula Harald H. Mehnert 1979 <p>The San Juan Mountains of southwestern Colorado are famous for rich vein deposits of base and precious metals and for patterns of conspicuous hydrothermal alteration. Areas of acid-sulfate alteration, characterized by extensive base leaching of volcanic rocks or hypabyssal plutons, are of current interest because of their local association with Au, Ag, and, in some cases, U mineralization (Lipman and others, 1976; Cunningham and others, 1978; Steven and others, 1979). Potential may also exist for recovery of aluminum from altered rocks rich in alunite (Hall, 1978). Alunite has been shown to be suitable for K-Ar dating in other mining districts (Mehnert and others, 1973b; Ashley and Silberman, 1976). We report here two concordant K-Ar ages determined on hydrothermal alunite from Red Mountain, in the Lake City area of the western San Juan Mountains.</p> application/pdf 10.3133/ofr791642 en U.S. Geological Survey K-Ar age of alunite alteration at Red Mountain, Lake City area, western San Juan Mountains, Colorado reports