Geology and Ore Deposits of the Darwin Silver-Lead Mining District, Inyo County, California

The survey of the geology and ore deposits of the Darwin Hills presents two major problems. The first is the origin of the stratified silicate aureole about the Darwin stock. Such silication may be accomplished by pure thermal metamorphism or by additive processes. Field relations, supported by petrographic and chemical evidence, indicate that metasomatism played the dominant role. Considerable silica and other materials were introduced into the limestones by the magmatic emanations. The second major problem involves the origin and classification of the ore deposits. The deposition of all the ore bodies took place at a distinctly later time that the development of the silicate aureole. A period of tectonic fracturing in which most of the fissures of the district were developed intervened between the early silication period and the later metallization period. Three structural controls, igneous contacts, bedding planes, and fractures, dominated the location of the deposits. Genetically all three structural types are the same. The ore mineralization is not of the high temperature type and hence is not pyrometasomatic as classed by Knopf. Because of certain structural and textural features and the presence of such gangue minerals as fluorite and barite, the deposits are classed as upper mesothermal.