New Mexico Mineral Symposium — Abstracts

The Apache mine is in the bootheel region of southwest New Mexico. Deposits in the area were first worked by Mexican miners who shipped silver ore back to Chihuahua City, Mexico. The Apache No. 2 mining district (also known as the Anderson district) was located by Bob Anderson in 1878. Mining was continuous from 1878 to 1929, at which time the main stope collapsed at the Apache mine. The district is credited with the production of about 100,000 tons of silver-copper and silver-lead ore. Interest in the district continues to the present day with recent claims (May 1996) posted at the mine.

Two types of ore deposits are known in the district. Copper skarns are found at the contact zone between a 27 Ma monzonite porphyry and Cretaceous limestones (Peterson, 1976). Mineralogy of these deposits is typical for a copper skarn and consists of garnet, diopsidic pyroxene, epidote, quartz, and calcite with sulfide minerals of chalcopyrite and pyrite. Much of the ore is oxidized to malachite and chrysocolla. Vein replacement deposits represent the second type of mineralization in the district. These veins are associated with the McKinley fault zone. Calcite is the dominant vein material, containing pods or blebs of oxidized ore minerals. Geology of the fault zone is complex with many subsidiary faults juxtaposing limestone, shale, and skarn units. The dominant ore minerals are malachite and chrysocolla with minor amounts of secondary bismuth minerals.

Bismuth minerals are restricted to the upper parts of the ore deposit. Bismutite, Bi₂(CO₃)O₂, is the most common bismuth mineral, reported to be a pseudomorph of bismuthinite. Yellow rims surrounding bismutite surrounded by calcite have been identified as kettnerite, CaBi(CO₃)OF, by x-ray diffraction. The paragenetic relationship of bismutite, calcite, and kettnerite indicates the calcite post-dates oxidation of primary bismuth ore minerals and probably represents cavern filling. Other bismuth minerals, tentatively identified by optical examination and crystallographic habit include: perite, PbBiO₂Cl; bismite, Bi₂O₃; and bismoclite, BiOCl. These minerals were observed only in material that was devoid of calcite from above the 200 level. The calcite-free material, no longer available, was collected at the mine by Mahlon T. Everhart in the 1930s and later donated to the NMBMMR Mineral Museum in 1990. Chiorargyrite, AgCl, is fairly abundant in the calcite-free material and represents the major silver-bearing phase in the deposit. The abundant copper, silver, and bismuth secondary minerals suggest that the primary bismuth sulfide was not bismuthinite, but was possibly a silver-copper-bismuth sulfosalt of the pavonite group.
 

References:

1. Peterson, S. L., 1976, Geology of the Apache No. 2 mining district, Hidalgo County, New Mexico: Unpublished MS thesis, University of New Mexico, 86 pp.