Page 210 - The Geology and Ore Deposits of Sierra County, New Mexico - Bulletin 10

206 GEOLOGY AND ORE DEPOSITS OF SIERRA CO., N. M.
calcite and fluorite. The ore minerals are galena, anglesite, ceru- site, wulfenite, and an occasional vanadinite crystal. In these veins fluorite should be considered as an ore mineral. The gangue minerals are calcite, barite, quartz, limonite, and pyrite. The south wall of the vein has been dissolved by surface waters, and a solution space has been formed, which varies from 1 to 4 feet in width and which stands open down to the 100-foot level. The galena occurs in the vein in single cubic crystals varying in size from one-sixteenth inch to 3 inches across. Aggregates of crystals are uncommon. Within the matrix of the vein these crystals are bright on fractured surfaces and show no evidence of alteration. Where exposed in the solution cavity, however, as shown in figure 18, they are rounded in outline and are covered with a thin layer of anglesite, and a thin outer layer of cerusite. En- crusted on the surface of the cerusite are crystals of wulfenite and scattered crystals of vanadinite. Away from the galena crystals the number of wulfenite crystals rapidly decreases, and on areas of the wall more than 1 foot away from a galena crystal, wulfenite is rarely found.
In the 40-foot shaft to the east of the tunnel the vein is 2 to 4 feet wide, and it is composed of galena, fluorite and calcite. In the bottom of the shaft the galena content of the vein is lower than at the surface. No wulfenite was noted in this shaft or on the dump.
The ore and gangue mineral assemblage in this vein indi- cates deposition from cool solutions at a great distance from the source, and the coarse crystallinity of the material indicates precipitation from extremely weak solutions. The galena crys- tals are sparsely distributed throughout the gangue, and the average lead content of the vein is probably not more than 3 per cent. The fluorite content is about 65 per cent. Mr. J. L. Walter, graduate student at the New Mexico School of Mines in 1931- 1932, kindly made several qualitative chemical tests on the galena specimens from this vein and from the surrounding shells of anglesite and cerusite, and in none of this material was he able to find a trace of vanadium or molybdenum. It seems probable, therefore, that these minerals were originally dissolved from some remote locality and were carried in soluble form in the percolating surface waters until they came in contact with the lead minerals of these veins, when they formed insoluble com- pounds that were precipitated on the nearest available surface.
The second vein in the series has a strike of N. 70° E. and is nearly vertical. The walls are 4 feet apart, but the galena-bear- ing calcite is 18 inches or less in width. This vein is developed by shallow tunnels and shafts, all of which have exposed some galena. Near the western end of the outcrop, considerable copper staining is visible. A cross vein striking N. 44° E. and dipping vertically was encountered in the main tunnel into this