New Mexico Mineral Symposium — Abstracts

The Victorio mining district, located in the Victorio Mountains, Luna County, hosts three types of deposits. These are (1) carbonate-hosted lead-zinc replacement, (2) tungsten-beryllium-molybdenum skarn-vein-tactite, and (3) porphyry-type molybdenum deposits.

Most of the production from the district came from the carbonate-hosted Pb-Zn replacement deposits that occur as oxidized replacements and veins within Ordovician and Silurian dolomites and limestones. The more productive deposits are along faults or fractures that strike N30°-65°E and dip steeply east. Brecciation, dissolution, and recrystallization of the dolomites are common in the vicinity of the mineral deposits. Ore minerals include galena, smithsonite, cerussite, and anglesite with rare sphalerite, galena, and chalcopyrite in a gangue of quartz, calcite, and iron oxides. Lead typically exceeds zinc and copper in abundance. Ore at the Rambler mine averaged 12.5% Pb and 3.9% Zn. Gold assays range as high as 5,500 ppb. Carminite, kolfanite, adamite, vanadinite, and wulfenite have also been reported (Beyer, 1997).

Drill cores collected in the vicinity of the Victorio Mountains yield mineralogically diverse samples, and examples of what appear to be skarn-associated vein and replacement-texture deposits, as well as igneous granite, were studied using the electron microprobe. Using this instrument, textural relationships as well as quantitative and qualitative chemical compositions of metal-bearing and gangue minerals were investigated. A diverse mineral assemblage was found within the gangue minerals of the samples that were interpreted to be replacement-texture and vein skarn deposits. Garnet, a wide compositional range of pyroxenes, actinolite, serpentine, phlogopite, calcite, quartz, talc, and fluorite were recognized. The assemblages present in the samples that appear to be replacement-texture deposits are indistinguishable from those that are veins and are likely to represent the same mineralization event. The mineral assemblage, particularly the presence of serpentine, magnesian pyroxene, phlogopite, and talc and the absence of wollastonite and apatite, suggests that the Victorio Mountains skarn system should be classified as magnesian rather than calcic (e.g. Kwak, 1994). The presence of fluorite further suggests that the skarn-related fluids were F-rich. Mineralogy and textural relationships observed in both replacement-texture and vein deposits suggest that remnants of a primary, or prograde, skarn assemblage are present, as well as a number of secondary, or retrograde phases. In one sample, large (-1 cm) complexly zoned garnets, interpreted to be part of a prograde skarn assemblage, are present in an open-space filling vein. In a nearby part of the same sample, smaller garnets co-exist with phlogopite, serpentine, and talc and are interpreted to be part of a retrograde facies. Other samples record similar ranges of mineral phases. In one case, delicate, fan-shaped masses of phlogopite appear to have crystallized in open-space cavities, which possibly formed during prograde skarn evolution. Serpentine, a mineral that would form at a later stage of prograde evolution than phlogopite, is found around and intergrown with the phlogopite. Hence, the replacement-texture and vein samples from Victorio Mountains appear to record an extended history of skarn formation, spanning a range of fluid concentrations and formation temperatures.

A range of metal-bearing minerals is observed in the skam-related samples. These include euhedrel rods or masses of molybdenite, masses of molybdenum-bearing scheelite, and an iron sulphide. The metal-bearing minerals are more abundant in the vein samples than in the replacement-texture samples. In some cases, bands of concentrated metal-bearing phases are present along vein margins, suggesting an interval of favorable conditions for ore formation during the growth of the veins.

One sample of granite from the Victorio Mountains area was analyzed and appears to contain a normal mineral assemblage of quartz, potassic feldspar, biotite, albite, and magnetite. However, in addition to these phases, the granite contains abundant pinkish, manganese-rich garnets that include a high abundance of heavy-mineral inclusions and fluorite. These inclusions include hafnium-rich zircon and thorium-, uranium-, and yttrium-rich allanite. These phases appear to have crystallized from the granitic magma and may suggest that the Victorio Mountains granite may be anomalously enriched in heavy elements, as well as fluorine. Molybdenite and scheelite have also been observed in the Victorio Mountains granite.

The carbonate-hosted Pb-Zn replacement deposits in the Victorio district are epithermal deposits as evidenced by ore textures, ore controls, and correlations with similar carbonate-hosted replacement deposits in southwestern New Mexico that are also believed to be epithermal. The skarn-vein-tactite and porphyry-type Mo deposits are magmatic-hydrothermal deposits that appear to be related to the Victorio Mountains granite as evidenced by ore textures and similar mineralogy, metal associations, and alteration assemblages. However, the relationship between the carbonate-hosted replacement and skarn—porphyry-Mo deposits remains unknown. All three deposit types may be genetically related, or more than one mineralization event occurred forming the deposits at different times.

Selected minerals found in the Victorio mining district, Luna County (from Holser, 1953; Griswold, 1961; DeMark, 1992; Northrop and LaBruzza, 1996; Beyer, 1997; Gulf Minerals company reports; this study). Minerals in bold are newly reported in this study. Type of deposit in parenthesis: 1-carbonate-hosted Pb-Zn replacement deposits, 2-Be-Mo-W skarn-vein-tactite deposits, and 3-porphyry Mo deposits.
 

References:

1. Beyer, J., 1997, A second New Mexico carminite locality, Victorio Mountains, Luna County, New Mexico (abs.): New Mexico Geology, v. 19, pp. 26-27.
2. DeMark, R. S., 1992, New Mexico mineral locality index: Rocks and Minerals, v. 67, pp. 314-327,330-331.
3. Griswold, G. B., 1961, Mineral deposits of Luna County, New Mexico: New Mexico Bureau of Mines and Mineral Resources, Bulletin 72,157 pp.
4. Holser, W. T., 1953, Beryllium minerals in the Victorio Mountains, Luna County, New Mexico: American Mineralogist, v. 38, pp. 599-611.
5. Kwak, T. A. P., 1994, Hydrothermal alteration in carbonate-replacement deposits: ore skarns and distal equivalents; in Lentz, D. R. (ed.), Alteration and alteration processes associated with ore-forming systems: Geological Association of Canada, Short Course Notes, v. 11, pp. 381-402.
6. Northrop, S. A., and LaBruzza, F. A., 1996, Minerals of New Mexico: University of New Mexico Press, Albuquerque, New Mexico, 356 pp.