Page 195 - The Geology and Ore Deposits of Sierra County, New Mexico - Bulletin 10

192 GEOLOGY AND ORE DEPOSITS OF SIERRA CO., N. M.
movement and the subsequent introduction of subordinate vein material.
Along the first of the shear zones noted above are several pits, open cuts and shallow shafts, from which only a few hun- dred pounds of hand-sorted ore has apparently been shipped. On the second shear zone are two shafts within 15 feet of each other, one 30 feet and the other 65 feet deep, with a crosscut 30 feet long at the bottom trending N. 15° W. along the strike of the shear zone. These workings are all in rhyolite. One hundred feet east of the shafts and near the east side of the property is an open cut 50 feet long, which gains 20 feet in depth in that dis- tance. This open cut has been driven in the rhyolite along a zone of shearing and brecciation that trends S. 25° W. In all workings the walls of the shear zones are well defined and stand without support.
The vein material consists essentially of quartz and pyrite. Near the surface the rhyolite of the shear zones and near the fractures has been flooded with iron-bearing solutions and has been stained bright red and yellow. A slaggy appearing botry- oidal form of limonite, almost black in color, lines the spaces between the breccia particles and locally is associated with minute quartz crystals. In places near the surface a small amount o,f silica box-work is associated with the slaggy iron ox- ide, and weak staining by manganese has occurred. Where the rocks are tight the original quartz-pyrite gangue of the fractures and shear zones appears within 25 feet of the surface, while in the more open channels oxidation extends to depths of 50 to 100 feet. Native gold is reported to have been found in the shear planes during the sinking of the shafts, and pannihgs of surface outcrops are said to show a small amount of gold. Assays of the vein matter vary from a trace to $420 per ton, but only single assays of commercial grade have been obtained in any one place, and there is nowhere an indication of a continuous vein or ore shoot. On the whole, the mineralization of the district is weak.
QUARTZ MOUNTAIN DISTRICT
Quartz Mountain is one of the outliers of more resistant rock projecting through the valley fill about 2 miles from the southern end of the San Mateo MoUntains. The hill is located about 4 miles west of the Red Rock ranger station on the old Monticello road. It attains a height of about 150 feet and is essentially a tilted fault block, the strata of which strike N. 70° E. and dip 15° SE. The base of the block consists of an andesite flow that is visible for just a few feet above the detrital material which laps gently up against the sides of the escarpment. Above this is a rhyolite agglomerate about 70 feet thick, and above this on the north end of the hill is a mass of white silicified rhyolite breccia 50 to 80 feet in thickness. The block is cut off on the west by a