Page 88 - The Geology and Ore Deposits of Sierra County, New Mexico - Bulletin 10

MINING DISTRICTS 87
100 feet of drifting, and over 250 feet of open-cut and tunnel work near the surface. No ore has been blocked out, and there is not sufficient work to determine the value of the property in depth, but practically all work done to date has exposed ore that is of commercial grade. Besides several shipments of lead ore made in the past, it is estimated that 300 tons of ore assaying better than 10 per cent lead is stored on the surface. The ores can be mined from this property under proper conditions at about $3 per ton, and can be concentrated after relatively coarse grinding to save 90 per cent of the metals at a stated cost of $1 to $2 per ton milled. The ratio of concentration is estimated to be about 7 into 1, and it is said that there is probably sufficient water, which will require some development, to keep a 100-ton concentrating plant in steady operation.
SILVER MONUMENT MINE AND VICINITY
The Silver Monument mine is about 10 miles west of Chlor- ide at the head of Chloride Creek. The road from Chloride is in the rocky bed of the creek for the entire distance and requires extensive repairs after each severe storm before it is passable for even light cars. There are other claims in the district, among them the Black Night, which is reported to have more argentite and less bornite in the ore than the Silver Monument, but which otherwise is quite similar. Very little development work has been done at any of these outlying properties.
The Silver Monument mine is located in a fracture zone in andesite which strikes almost due east and dips to the north at about 70°. The vein is from 2 to 8 feet wide. The elevation of the top of the old shaft, which is said to be 350 feet below the crest of the range, is given as 7,650 feet. Along the walls of the veins the andesite has been much propylitized, with later bleaching and alteration due to the action of primary mineraliz- ing solutions and later descending surface waters. The vein consists of a well-defined hanging-wall, along which is a seam of gouge 2 inches to 2 feet thick. The mass of the vein consists of brecciated and altered andesite that merges gradually and indefinitely into the solid andesite footwall. The ore min- erals are bornite and chalcopyrite, with which are associated tetrahedrite and argentite. In the upper portions of the vein native silver, cerargyrite, azurite and malachite occur in small to moderate quantities. At greater depth chalcocite, covellite and argentite enrich the primary ore in a zone of indefinite extent, and below the 400-foot level an increasing amount of pyrite appears in the few openings that have been made into the vein. Figure 4 is a composite plan and figure 5 a longitudinal section of the Silver Monument workings. It is clear from the section that the ore occurs in three shoots pitching steeply to the east. The surface outcrops indicate the possible ex- istence of at least three other shoots, upon two of which no