Low temperature lead-zinc-silver mineralization of Tertiary age characterizes the Palomas Mining District in the western part of Sierra County, in southwestern New Mexico. The ore occurs in fissure veins and replacement bodies in Paleozoic limestones and dolomitic limestones. Structural control of ore deposition has been exerted by fractures or shaly horizons. The principal hypogene minerals are galena, sphalerite, chalcopyrite, and argentite. Associated minerals are pyrite, polybasite, and tetrahedrite. The gangue consists mainly of talc, with associated calcite, quartz, barite, and clay minerals. Supergene minerals include covellite, native silver, limonite, carbonates of lead, zinc, and copper, silver halides, and a little vanadinite, descloizite, and pyromorphite.Talc, which occurs both as vein filling and in wall-rock alteration, is thought to have been formed by the action of silica-bearing hypogene solutions. Little transportation appears to have taken place during the early stages of oxidation, as evidenced by the intimate association of hypogene and supergene silver minerals. The mineralization is believed to have been brought about by alkaline hydrothermal solutions whose origin is in doubt, but may be connected with the sources of Tertiary volcanic activity in the area. An unusual feature of the deposits is the occurrence of talc as the chief gangue mineral.

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