Page 103 - The Geology and Ore Deposits of Sierra County, New Mexico - Bulletin 10

102 GEOLOGY AND ORE DEPOSITS OF SIERRA CO., N. M.
izing solutions converted the host rocks to clay, sericite and residual quartz.
The secondary minerals include anglesite, cerusite, smith- sonite, malachite, azurite and cuprite. These are associated with kaolin, limonitic clay residues from limestone, and residual quartz. Free silver formed abundantly and is found in thor- oughly leached bodies of clay ; in places cerargyrite, the silver chloride, has been mined. Manganese oxides have formed from the rhodochrosite and manganiferous calcite.
Secondary enrichment has been important in this district. Most of the ore mined has been thus enriched, but several rich shoots are reported to have shown no evidence of enrichment and are considered to be due to local concentrations of primary silver- bearing sulfides.
The ore was introduced primarily along the northwestward- trending fractures in the district in areas of arched limestone where these rocks were overlain by an impervious shale, and the depositing solutions were brought in from below along the con- tacts of the intrusive masses, or along outlying fractures in the limestone generally parallel to these contacts, which are pre- sumed to have direct connection with the monzonite masses in depth. The minerals were deposited in the limestone by replace- ment of the wall rock along the fractures. In response to subse- quent adjustments in the region, the sedimentary beds were fur- ther disturbed. There was developed a new series of northeast fractures, which intersected the northwest ore-bearing series, and the northwest fractures were involved also in this later period of movement. Additional adjustment occurred along the major faults of the region, which were at that time extended through the later rhyolite flows. The development of this second series of fractures and the reopening of the older ones gave sur- face waters access to the primary ores, and these were oxidized, leached and secondarily enriched, particularly along pipelike channels at the intersections of the northwest and north- east fractures. Enrichment is considerably more advanced where the overlying beds have been eroded and the ore bodies exposed at the surface.
PRODUCTION
The main period of activity in the Kingston district drew to a close with the decline in the price of silver in 1893, and since then mining has been done only occasionally and on a very small scale. Shipments have been limited to small lots of high-grade ores and to a few carloads of moderate to low grade ores, many of them chiefly valuable for their fluxing properties at the smelter. Up to January, 1904, the estimated production as given byF.A.Jones41 was$6,250,000,mostofwhichwassilver.Since 1910 the records show that approximately 3,675 tons Of ore has
41 New Mexico mines and minerals, 1904.