Page 112 - The Geology and Ore Deposits of Sierra County, New Mexico - Bulletin 10

MINING DISTRICTS 111
or over fair mountain roads 9 and 11 miles in length from the small hamlets, Sherman and Swartz, on the Mimbres River in Grant County. On the whole, the district is difficult of access. In two localities some important prospects have been developed and some mining has been done, and if provided with suitable transportation facilities, profitable mines might be made of them. One of these is the old Grand View group, located about 7 miles southwest of Kingston, and the other the Grand Central group, 4 miles south-southeast of Grand View camp.
GEOLOGY
The area in and around the Carpenter district is the only part of the Black Range known to the writer where the sediments of the western limb of the arch are exposed to view near its crest. According to Gordon, 43
The range is flanked on the west at this point by lower Paleozoic (Ordo- vician) rocks covered in places by flows of andesites and rhyolites and cut by large dikes of granite porphyry and lesser ones of diabase. In the vicinity of the mines the sedimentary formations consist of blue and white crystalline limestones alternating with beds of quartzite evidently belonging near the base of the Mimbres limestone. Both limestones and quartzites show marked indications of metamorphism, the limestone in places resembling marble. About half a mile west of the Grand View mine these formations are cut on the west by a mass of granite porphyry, which constitutes a prominent ridge running north and south for 2 or 3 miles. A dike of a similar rock 20 feet wide was observed on the trail a short distance north of the mine, cutting across the limestones toward the southeast.
About 2 or 3 miles north of this locality occurs a cliff of limestone seamed with chert closely corresponding in appearance to the Abrigo lime-
stone (Cambrian) described by Ransome 44 in his report on the Bisbee quad- rangle, Arizona.
At the Grand View (Mitch-Gray) mine the sedimentary fornlations dip 30° to 35° W. They appear to flatten out somewhat toward the southeast and at the Grand Central (Royal John) locality the dip is not more than 15°.
ORE DEPOSITS
Character of the ores.—At the Grand View camp the ores consist chiefly of galena, with some zinc sulphide and a large amount of iron pyrites in quartz gangue. The ore is of low grade and carries little or no gold or silver. The Grand Central properties show a higher content of zinc, with considerably less of lead and iron sulphides.
Geologic relations.—In both places the ores occur along sheer zones cutting the crystalline limestones. At the Grand View the shear zone is about 30 feet wide and extends N. 53° E. for a distance of 1,000 feet or more. At the Grand Central mines the shear zone is about 25 feet wide and extends nearly due north. The ore is distributed somewhat irregularly along the zone, which appears to dip at a high angle to the east. The openings, which are superficial, are on the east side of a small valley; on the west side the westward-dipping limestones are covered by a flow of rhyolite. The lime- stone along the vein on the foot-wall side is altered to a hard siliceous rock containing bunches and stringers of ore. No intrusive rocks were observed, but the general relations strongly suggest their presence near at hand.
Much of the following information regarding the mining
43Gordon, C. II., op. cit. (U. S. G. S. Prof. Paper 68), p. 272.
44Ransome, F. L., U. S. Geol. Survey Geol. Atlas, Bisbee folio (No. 112), 1904.
MINE DESCRIPTIONS