New Mexico Mineral Symposium — Abstracts

Although native silver is uncommon in the Magdalena mining district of Socorro County, New Mexico, it has nevertheless been reported from several mines. In particular, wire silver reputedly occurred at the Anchor mine in seams and crevices (Loughlin and Koschmann, 1942). This information, coupled with a report of large barite crystals on the dumps (B. D. Huntsman, pers. comm. 2002) inspired Mike Sanders, Chris Cowan, Tom Rosemeyer, and me to investigate the Anchor mine on January 25, 2003. The mine is reached by driving up Anchor Canyon at the north end of the Magdalena district. According to Loughlin and Koschmann (1942), it was opened about 1885 and is said to have produced rich silver ore with a total value of about $60,000, but it was abandoned about 1893 when the price of silver declined. It was reopened in 1924 and operated intermittently until 1926 when all operations ceased. Mine workings consist of an inclined (about 50°) shaft 170 ft deep from which two short levels have been driven and an adit level about 900 ft long. The adit level for most of its length is flooded, but a section at the bottom of the decline remains partially dry.

The average thickness of the vein is about 4 ft and consists primarily of quartz, barite, and calcite with some fluorite. Galena and sphalerite are the primary sulfide ore minerals. The vein exposed on the second level is quite rich in fluorite and galena, and rich ore samples were collected. At the bottom of the shaft (adit level), examination of the vein revealed numerous yellow tabular wulfenite crystals to 6 mm and cerussite crystals to 2.5 cm. Wulfenite in the Magdalena district is quite rare. It was found associated with azurite from the sixth level of the Kelly mine in 1987 by Chris Cowan and at the Mistletoe mine in 1993 by me. Wulfenite has also been found at the Linchburg mine by Brian D. Huntsman.

Following this trip, close inspection of the galena ore with a microscope revealed quartz-lined vugs containing small wires of silver. This discovery led to a second trip on January 30, 2003, by Mike Sanders, John Ottea, and me. A number of wire silver specimens were collected from the vein on the second level along with one specimen of yellow pyramidal wulfenite. The silver wires are mostly coiled and as long as 1 cm. Many of the wires are encrusted with small colorless quartz crystals and are partially altered to acanthite. Acanthite is also found coating sphalerite crystals in the vicinity of the silver. Additional minerals found on the dumps and in the shaft and adit include: pyrite, chalcopyrite, siderite, smithsonite, and hemimorphite. Identification of the acanthite, siderite, and hemimorphite was aided by microprobe analysis (Paul Hlava, pers. comm. 2003). Mine artifacts found at the bottom of the shaft suggest that mineral collectors had not previously visited this mine.

References:

1. Loughlin, G. F., and Koschmann, A. H., 1942, Geology and ore deposits of the Magdalena mining district, New Mexico: U. S. Geological Survey, Professional Paper 200, vii, 168 pp.