57. Geology of the Christmas Mine and Vicinity, Banner Mining District, Arizona

The Banner mining district is about 70 miles northeast of Tucson in the southern part of Gila County, Arizona. Production from the district, valued at about $26 million, is chiefly from copper-silver-lead zinc ores. The stratigraphic section consists of Precambrian conglomerates, quartzites, dolomites, and limestones, Cambrian quartzites; Devonian limestones; dolomites, and shales; Mississippian limestones; Pennsylvanian limestones and shales; and Cretaceous volcanic and sedimentary rocks. Deformation of these rocks presumably started near the end of the Cretaceous, and extended into the late Tertiary. The sedimentary rocks were folded, faulted, and intruded by fine grained diorite, quartz mica diorite, and dacite porphyry. At least four distinct stages of mineralization are recognized. In the first stage of contact metamorphism and the second stage of hydrothermal alteration, favorable zones were prepared for ore deposition. Metallization occurred in three of the mineralizing stages. Magnetite, pyrite, and hematite were deposited near the end of the second stage of hydrothermal alteration. The third stage included the main deposition of sphalerite, chalcopyrite, bornite, and galena. In the fourth and final stage, minor amounts of sulfide minerals were deposited with a late anhydrite and quartz gangue. The ore deposits in the form of veins and veinlets, pipes, irregular massive replacements, and bedded replacements are localized by the extent and distribution of metamorphic and hydrothermal alteration, by the proximity to the intrusive contacts, and by the effects of structural development. Oxidized ores of copper, lead, and zinc constituted the principal production of the district prior to 1940, but, for the most part, supergene enrichment was of minor economic importance. The ore bodies of the district are in the mesothermal class of deposits, occurring as normal metasomatic replacement and vein types.