Page 196 - The Geology and Ore Deposits of Sierra County, New Mexico - Bulletin 10

MINING DISTRICTS 193
fault striking N. 25° W. and dipping 62° SW., which is highly silicified and intensely iron stained through a zone of gouge and breccia that averages 10 to 15 feet in width. Along the north escarpment the displacement has been in an eastward-trending shear zone. A fault with a displacement of approximately 100 feet marks the south side of this zone, and along it the white rhyolite breccia at the top of the hill has been dropped down against the rhyolite agglomerate, while the agglomerate on the north is now in contact with the andesite in the south wall of the fault. The northern end of the hill is strewn with fragments and blocks of the white silicified rhyolite and agglomerate. At the time of the faulting or shortly after, the rocks were silicified along the fault fissures and adjacent to many small fractures formed in the brittle rocks by the faulting. Complete silicifica- tion of the rhyolite breccia followed, and the rhyolite agglomerate was partly silicified.
Several shallow pits have been dug in this area, and on the west side of the hill tunnels have crosscut the breccia and gouge of the fault, and a 15-foot shaft has been sunk along the footwall of the fault. Where silicification has been most intense, reported assays indicate that the rock contains $3.00 to $4.00 in gold. Assays from other parts of the hill are said to be lower, and it has been stated that the mass of the silicified material will average between $2.00 and $3.00 to the ton, but these reports were not verified by the writer.
MUD SPRINGS MOUNTAINS
HOT SPRINGS DISTRICT
Six miles north of Las Palomas and about 3 miles west of Hot Springs there is a group of low hills that measures about 4 miles in length in a northwest direction, and about a mile and a half in greatest width. These mountains are called Sierra Cuchillo by Darton, 61 but in the present report, following local usage and that of Gordon, 62 the mountains east of Fairview have been called the Sierra Cuchillo and these hills the Mud Springs Mountains.
The Mud Springs Mountains have been carved out of a tilted fault block, the strata of which strike about N. 55° W. and dip approximately 20° NE. The range is approximately 500 feet high. From bottom to top along the southwest or fault-scarp face of the range, the same Paleozoic sequence that occurs in the Sierra Caballos has been recognized, beginning with a basement of pre-Cambrian granite and ending with the Magdalena (Penn- sylvanian) limestone. The northeast or dip slope of the range has been dissected by arroyos and their tributaries, which have
61-Darton, N. H., op. cit. (U. S. G. S. Buil. 794), p. 320, Plate 62. 622Gordon, C. H., op. cit. (U. S. G. S. Prof. Paper 68), p. 262.