Page 218 - The Geology and Ore Deposits of Sierra County, New Mexico - Bulletin 10

214 GEOLOGY AND ORE DEPOSITS OF SIERRA CO., N. M.
from the beds of the arroyos where the reworked and enriched portions of the gravels are to be found, and these enriched gravels occupy only about one-third of the area. The value of the thin blanket over the higher two-thirds of the terrane is largely unknown, but it is a question in the writer's mind if the gravels in these areas are of workable grade. There is also a question as to whether the sampling that has been done in the arroyos has been as complete and thorough as it should. Water is available in large amounts, but the placer gravels would be expensive to work, even should careful sampling prove them to be continuous and of fair grade, inasmuch as the 50 per cent of the total yardage believed to be on the hills would almost certainly have to be transported to a permanent central treatment plant located in one of the arroyos, or to one which would be moved from place to place in them as the work progressed.
DERRY MANGANESE DISTRICT
The Derry manganese district 69 is about 6 miles north- east of the town of Derry, and an equal distance southeast of the Shandon placers. Here the range is an anticline in limestone with axis trending north. Manganese occurs for a distance of two miles along the crest of the fold, and it is from this region that the manganese of the Shandon placers was possibly derived by secondary processes. These manganese deposits have not proved to be commercial.
COPPER DEPOSITS IN "RED BEDS"
LOCATION AND GEOLOGY
Outcrops of Permian "Red Beds" are extensive in Sierra County. The larger exposures are on the eastern slopes of the Fra Cristobal Range, Sierra Caballos and Sierra Cuchillo, and almost continuously along the eastern slope of the Black Range from Chloride to the Macho district. These rocks form low cuestas on the dip slopes or are present in tilted fault blocks. They are slightly warped in places and are cut by occasional east-west fractures. "Red Beds" of Triassic and Jurassic age, which are present in other parts of the State, are not known in Sierra County.
The lowest formation of the Permian series is the Abo sand- stone, composed principally of red to reddish-brown, coarse to fine sandy, and shaly members, intercalated with beds of yellow to buff sandstone, gray shale, some gypsum, and in places a few thin beds of limestone. The red sandy beds are in part arkosic. Overlying the Abo beds are great thicknesses of variegated gyp-
69Wells, E. H., op. cit. (Manganese in New Mexico), p. 64.