Page 64 - The Geology and Ore Deposits of Sierra County, New Mexico - Bulletin 10

MINING DISTRICTS 63
the walls, while the economic minerals consist of chalcopyrite, galena, sphalerite and pyrite, and varying amounts of gold and silver. There are also a few veins in the rhyolite, these being fissure fillings in which the gangue minerals are quartz and cal- cite, the quartz often of the amethystine variety, and the eco- nomic minerals consisting of gold, gold-silver, gold-silver tellu- rides, and gold- and silver-bearing sulphides. The second type of deposit is a replacement, either in fissure or blanket form, in the limestone, with lead-silver, silver-lead-manganese, and silver- lead-zinc mineralization.
Typical vein deposits in eruptive rocks are found in the Chloride district and the area to the north as far as the county line. South of Chloride several of the veins may be traced through the andesite into limestone, and in places in the lime- stone, as at the Midnight mine, contact metamorphism has taken place. Still farther south the veins are again in andesite, as at the Bald Eagle mine, where they contain lead, zinc and silver minerals. At Hermosa, Kingston, Tierra Blanca and Car- penter, most of the mineralization is of the replacement type, occurring along fractures and as blankets, and consisting of the minerals of lead, silver, manganese and zinc in varying propor- tions. At the Gray Eagle mine at the southern end of the King- ston district, and at the Lookout mine in the Tierra Blanca dis- trict, the ores, which are associated with rhyolite, occur as veins along the contacts of the dikes and the sediments. At the Gray Eagle mine, where silver was the chief metal and copper and gold were of moderate importance, the mineralization was clearly associated with the rhyolitic extrusions. At the Lookout mine, native gold associated with the silver telluride, hessite, and pos- sibly with the gold-silver telluride, calaverite, is found in pockets and stringers along the tops of small folds in close association with a rhyolite dike that expands locally into a small sill between the beds. (See figure 7.)
The workings throughout the region are shallow, no shaft reaching a vertical depth greater than 500 feet, and several adit tunnels reach a similar vertical depth, with lengths of 1,700 feet at the Silver Monument mine in the Chloride district, and of about 2,000 feet at the Lady Franklin mine in the Kingston dis- trict. The water level throughout the region varies between 50 and 400 feet from the surface. Little or no prospecting below water level has been done, and at only a very few places have even the main shafts or tunnels penetrated below this level. In the oxidized zone in the various workings, native gold, cerar- gyrite, cerusite, anglesite, copper carbonates and oxides, and manganese oxides occur. At and near water level native silver, secondary sulfides of copper, silver and lead, and perhaps some secondary gold are found in scattered grains or in concentrated bodies. The primary sulfide ores contain pyrite, chalcopyrite, bornite, tetrahedrite, argentite, galena and sphalerite. Tellu-