Page 193 - The Geology and Ore Deposits of Sierra County, New Mexico - Bulletin 10

190 GEOLOGY AND ORE DEPOSITS OF SIERRA CO., N. M.
may at some future time be sorted or milled at a profit. The veins in most places are 4 to 5 feet wide, but stoping has been confined to a width of 2 or 21/2 feet in the richest part. Further- more, the Anniversary vein may be considered with some degree of assurance to carry moderately profitable ore to a depth of 300 feet, and as only 30 per cent of the ground has been removed from the stopes and development headings within this area, it appears that there may be enough ore on the dumps and in place in the veins to run a 50-ton mill for a period of nearly three years. Development work below the 300-foot level is insufficient to warrant including any ore from this horizon in an estimate of possibilities, but when it is considered that the highest grade ore shipped from the mine was reported from just above the 300- foot level from a stope that is between 200 and 300 feet long, it is reasonable to expect that there may be substantial tonnage of profitable ore below the 300-foot level.
SAN MATEO MOUNTAINS GOLDSBOROUGH DISTRICT LOCATION AND GEOGRAPHY
The San Mateo Mountains, which occupy an elliptical area of approximately 800 square miles, are mainly in Socorro County, but the south end extends about 8 miles into Sierra County. The major axis of the ellipse trends southwest and is about 12 miles west of the Elephant Butte reservoir. The range is rugged and travel is difficult. The canyons in their upper reaches are con- fined between precipitous cliffs, and the courses of the stream- beds are broken by sheer falls of as much as 30 feet. In the lower parts of the mountains the valleys are more open, and the low hills between are rounded and gently sloping. South of the main range are several prominent landmarks, consisting of outliers of the more resistant rocks that project through the valley fill as hills and ridges.
GEOLOGY
The San Mateo Mountains consist of volcanic rocks, which
in the southern portion show the normal sequence of flows as found elsewhere in the county. These are, from the bottom up- ward, andesite breccias, flows, and tuffs ; latite flows ; and rhyo- lite tuffs, flows and breccias. Dikes of rhyolite, latite and basalt are abundant in the lower flows. In the canyon near the Red Rock ranger station a small cropping of a rock resembling gab- bro was noted, but its nature was not determined. Older sedi- mentary rocks were not observed anywhere in this part of the range. No large faults were seen, but the higher cliffs of the range may be due in part to faulting. The volcanic rocks are, however, traversed in all directions by cracks and fractures