Page 192 - The Geology and Ore Deposits of Sierra County, New Mexico - Bulletin 10

MINING DISTRICTS 189
No lateral development work is known to have been done from this shaft.
At 1,000 feet northeast of the main shaft and on another of the radiating dikes is an old shaft about which even less informa- tion could be gathered. The shaft is perhaps 150 feet deep, and probably little or no lateral work has been done. The dump rock from this shaft indicates that the shaft follows the contact of a latite dike and brecciated andesite wallrock, both of which are
well leached and altered. This rock contains considerable man- ganese oxide, probably psilomelane, which has partly filled the open spaces between the fragments of altered andesite and latite as botryoidal masses. At a later period carbonate-bearing waters penetrated the remaining open spaces and filled them with cal- cite, so that on fracture faces small spherical shots of black psilomelane appear to be completely embedded in the calcite. No minerals of value were seen on this dump, and no production has been reported from this shaft.
SECONDARY ENRICHMENT
The upper portions of the veins in the district have been
partly oxidized and leached by meteoric waters. From the sur- face to a depth of 60 to 70 feet, pyrite has been completely altered
to limonite. The leached outcrops have a rusty cellular appear- ance, due to the formation of silica boxwork in the space formerly
occupied by the pyrite crystals. Manganese oxides and limonite form black to dark brown slaggy coatings in the silica boxwork,
botryoidal bunches and stalactites in the open spaces of the vein, and thin films in the fractures of the wall rock. The manganese may have been leached from the minerals of the adjacent rocks
or derived from the small amount of manganiferous calcite in the veins. In the oxidized zone the galena has been altered in
part to anglesite and cerusite. Most of the sphalerite has been leached, but small amounts of calamine and smithsonite remain in the oxidized ore.
A short distance below water level pyrite occurs in subordi- nate amounts, and the zinc in the ore ranges from 0.4 to 7.2 per cent. This zinc represents largely the primary sphalerite of the vein, but it includes also a part of the zinc leached from the upper portion of the veins, transferred downward in circulating waters, and redeposited in the reducing zone. Lead shows only a slight relative increase between the 80-foot level and the lower work-
ings (20.0 per cent to 26.1 per cent as shown in the table on page 187), which may be due to an accidental distribution of the metal or to the deposition of a small amount of secondary galena.
POSSIBILITIES OF THE DISTRICT
According to records and estimates, 2,640 tons of ore and
concentrates has been shipped from the Macho district in the
past and approximately 10,000 tons of material in the dumps