Abstract

The Santa Barbara mines are grouped in a circle around the village of Santa Barbara located in the Parral mining district, in southern Chihuahua, Mexico. The mines are operated by American Smelting and Refining Company and the bulk of the mineral production comes from eleven vein systems.The pre-mineral rock types consist of a thick calcareous shale formation and andesite flows. The post-mineral rock types consist of dikes and sills of rhyolite and diabase, a thin conglomerate formation, basalt flows, and unconsolidated stream sediments. Pre-mineral faulting took place in two stages, forming four fault systems. Any fault within one system is similar in both strike and dip to another fault within that system. Movement along these faults, vertical in the first-stage faults and horizontal in the second-stage faults, formed openings, breccia zones, and in places horses and wedges of country rock in the faults. The location and explanation of these openings, breccia zones, horses and wedges are the main topic in this paper.Hydrothermal solutions, emanating from depth, were introduced into the faults. The walls and breccia fragments within the faults were silicated and silicified and the high-temperature silicates, garnet, pyroxene, epidote, and idocrase (?) were formed. Accompanying and following the formation of the silicates, the sulfides sphalerite, galena, chalcopyrite, pyrite, and arsenopyrite, with associated gold and an unknown silver mineral were introduced with quartz, calcite, and fluorite. Most of these minerals replaced the silicates and altered shale. The parts of the faults where wide pre-mineral openings, horses or wedges were formed, were filled with quartz and a higher ratio of sulfides than the narrow portions of the faults. Quartz, calcite, fluorite, and barite were among the last minerals deposited. The veins are assigned to the hypothermal class of hydrothermal deposits.

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