The Geology And Hydrothermal Alteration And Mineralization Of The Black Gulch Creek Area Southern Breckenridge Mining District Colorado

The Breckenridge mining district is located in the Colorado mineral belt approximately 95 km west-southwest of Denver, Colorado. The district has been extensively mined for gold, silver, lead, and zinc since 1859. Recent work in the district has revealed surface expressions which suggest a possible mineralized porphyry complex at depth. The present study examines approximately one square mile in the south-central portion of the district, centered around Black Gulch creek. In the Black Gulch area the igneous bodies observed intrude a thick sedimentary layer including: (1) the Morrison formation, (2) the Dakota sandstone, and (3) the Benton-Niobrara undifferentiated. Associated with these igneous events are various stages of brecciation, alteration, and mineralization. The alteration varies from propylitic to phyllic but is not concentric around a source intrusion. The mineralization is locally in[crea]se with high geochemical concentrations of molybdenum, copper, lead, and zinc. The main zone of mineralization is localized in the Black Gulch Breccia and the Contact Breccia. Also a skarn zone is locally high in copper and zinc plus various amounts of molybdenum. There are many similarities with the Black Gulch area and Climax, Urad-Henderson, and Redwell Basin; the latter three being molybdenum deposits in the colorado mineral belt. Because of the high-level of erosin in the Black Gulch area the composition and configuaation of the mineralized zones at depth are difficult to judge. Quartz-molybdenumpyrite veining in the area indicate that molybdenum mineralization may be present at depth; and the high copper values suggest that a significant component of copper also may be associated with the molybdenum at depth within the complex. The surface data are encouraging and stronly suggest the presence of a multistage mineralization event emanating from a concealed source. Exploratory diamond drilling would add greatly to the knowledge of the igneous activity, and associated hydrothermal alteration and mineralization in the area.