New Mexico Mineral Symposium — Abstracts

The Silver Hill subdistrict is located in the western half of the North Magdalena mining district, about 2 miles northwest of Magdalena, New Mexico. The district has produced a small amount of copper and silver from fissure veins in basaltic andesite.

Recently, small crystals resembling fornacite (Pb, Cu)₃[(Cr, As)O₄]₂(OH) were found on the Bullfrog #2 claim about 1/2 mile southwest of Silver Hill. SEM and microprobe analysis have shown the material to contain Pb and Cu in the +2 valence site and Mo and minor As, V, and Cr in the +5, +6 valence site in the structure. X-ray diffraction shows the mineral to have the structure of fornacite. This chemistry and structure would make the material identical to a newly described (as yet, unnamed) mineral from Tsumeb. The mineral is associated with descloizite, willemite, mimetite, chrysocolla, and hematite.

Other recent finds of micro-crystalsin the district from other mines and prospects include duftite, PbCu(AsO₄)(OH), conichalcite, CaCu(AsO₄)(OH), and apatite Ca₅(PO₄)₃F. Iranite Pb₁₀Cu(CrO₄)₆(SiO₄)₂(F,OH)₂ is also reported from the district, but has not been confirmed.