Page 219 - The Geology and Ore Deposits of Sierra County, New Mexico - Bulletin 10

MINING DISTRICTS 215
sum beds, shale and sandstone of the Yeso or Lower Chupadera formation, and over this the gray San Andres limestone or Upper Chupadera formation.
The problem of the origin of the "Red Beds" has had long consideration by geologists, and differences of opinion still exist as to the source and origin of the sediments and of the red hematitic coloring matter comprising the cementing matrix of the rocks from which they derive their name. 70
ORE DEPOSITS AND WORKINGS
At many exposures of the "Red Beds" in Sierra County, weak copper mineralization has been found. At a few localities, as in Palomas Gap in the Sierra Caballos, at Chloride, near Her- mosa, and near Kingston, the surface showing has been such as to warrant some prospecting, and a few tons of high-grade hand- sorted ore has been shipped. The mineralization has been localized in these beds in several ways ; in fractures cutting across the bedding planes, as nodules replacing the calcareous cement and kaolinized feldspar of the arkosic beds, as replace- ment of carbonaceous matter such as old tree trunks, twigs, coaly material, etc., and as a replacement of shaly beds. The sulfide minerals include pyrite, chalcopyrite, bornite, covellite and chal- cocite ; the oxidized minerals are limonite, hematite, cuprite, melaconite, malachite and azurite ; and the gangue minerals con- sist of quartz, calcite, barite, gypsum and dolomite. No gold and only small amounts of silver are associated with the copper
minerals.
Mineralization is not entirely confined to the red sandstones
of the Abo formation, although it is the principal horizon in this respect. The underlying Magdalena limestone, particularly the sandy and shaly members, and the overlying sandy horizons as far up in the geological column as the Cretaceous have been sparsely stained and sporadically mineralized in a manner sim- ilar to the mineralization in the Abo beds. The workings at these deposits consist entirely of surface pits and a few short tunnels and shallow shafts.
As these ores consist generally of mixtures of sulfides and oxides or carbonates in a siliceous gangue, the problem of local concentration is a difficult one, and hand sorting and direct ship- ment to the smelter must be resorted to. The stimulus of a high price for copper is required before they can be profitably shipped. At no place within the county do the ore deposits of this type so
70Tomlinson, C. W., Origin of the "Red Beds" : Jour. Geology, Vol. 24, No. 2, pp. 153- 179, No. 3, pp. 238-253, 1916.
Dorsey, G. E., Origin of the color in "Red Beds": Jour. Geology, Vol. 34, No. 2, pp. 131-143, 1926.
Lee, W. T., "Red Beds" of the Rio Grande region in central New Mexico, Jour. Geol- ogy, Vol. 15, No. 1, p. 52, 1907.
Hager, D. S.. Factors affecting color of sedimentary rocks : Am. Assoc. Petroleum Geologist Bull. 12, No. 9, pp. 901-938, 1928.