Page 205 - The Geology and Ore Deposits of Sierra County, New Mexico - Bulletin 10

MINING DISTRICTS 201
The structure of the Sierra Caballos is further complicated by transverse overthrust faults. One of these in the northern end of the range shows considerable movement of the overthrust block toward the south. In the southern end of the range near the county line, an overthrust block of Magdalena limestone has moved to the north over Abo beds for a distance of several hun- dred feet. 65
ORE DEPOSITS
The ore deposits of the Sierra Caballos are principally fluor-
spar deposits and lead-vanadium-molybdenum deposits. Most of the fluorspar deposits are in the Magdalena limestone along the face of the range, but one fluorspar vein has been found in the San Andres limestone of the foothills southeast of Palomas Gap. Some of the fluorspar veins contain small amounts of galena. The deposits of lead, vanadium and molybdenum, which are also in the Magdalena limestone, are in and near Palomas Gap on the east side of the range. The Abo sandstone is stained with copper in places, and copper showings have been prospected in the Mag- dalena limestone along the face of the range. The Shandon placers near the southern end of the range have yielded small amounts of gold.
The lode deposits are almost entirely in true fissure veins, with only a. moderate amount of replacement of the wall rock. With the possible exception of the copper in limestone, the de- posits are all of the low-temperature type. There is a gradual transition southward from the deposits of the metallic minerals in and around Palomas Gap through a galena-fluorite type to a fluorite-calcite-silica type at the southern end of the range. All of the veins of this region may be connected with a deep-seated mass of Tertiary intrusive rock, probably monzonitic in charac- ter, located near Palomas Gap. This mass has two outcrops, one in the west face of the Fra Cristobal Range, and the other west of Cutter on the east slope of the Sierra Caballos.
The ore minerals are galena, anglesite, cerusite, vanadinite, wulfenite, descloizite, pyromorphite, chalcopyrite, bornite, mala- chite, azurite, and cuprodescloizite, and small amounts of sec- ondary sulfides and oxides of copper. Fluorite is classed as an ore mineral or a gangue mineral, depending on its abundance and mode of occurrence in the deposits. In most places where fluor- ite is not the mineral of chief economic importance in the veins, it occurs in such quantity and condition that its utilization as a by-product to be recovered along with the important mineral or minerals is worthy of consideration. Among the gangue min- erals are pyrite, silica, calcite, barite, and a little gypsum.
65Johnston, W. D., Jr., Fluorspar in New Mexico, New Mex. Sch. of Mines, State Bur. of Mines and Min. Res. Bull. 4, pp. 28-29, 1928.