Page 155 - The Geology and Ore Deposits of Sierra County, New Mexico - Bulletin 10

MINING DISTRICTS 153
the contact in the andesite. This branch vein is 18 inches wide and carries quartz stringers 1 to 3 inches in width. Pockets of valuable ore occur in these quartz stringers. The whole width of the vein is said to assay $6, with the quartz seams and pockets assaying approximately $70 per ton. Three hundred feet farther north a short surface tunnel in the andesite breccia crosscuts two fractures striking N. 55° E. and N. 60° E. respectively. At the Eureka shaft and tunnel the vein is in a sill of latite porphyry and is much broken up and disturbed. At the portal of the tun- nel a latite dike striking northwest has offset the vein on the north side a short distance to the west. The ground here is almost entirely altered to a mass of kaolin over a width of 30 feet. Shearing planes and seams of fault gouge can be traced through this mass along the trend of the vein, and stringers and seams of mineralized quartz are abundant and tend to follow these planes of movement. The full width of this zone is min- eralized and contains, according to report, $7.50 per ton. From it a large tonnage of ore was mined in open cuts and in stopes near the surface, and this ore was treated in the local mill with a recovery of $4.50 per ton. Farther north in the tunnel the vein contains higher grade ore along a seam of fault gouge 2 to 4 feet in width. Much low-grade ore is supposed to remain in these workings.
The Snake, Bobtail, and Eureka shafts are caved, and hence no examination could be made of the various underground levels. Figure 13 shows a longitudinal section of the Snake vein adapted from the old maps and from an engineer's map made at the time of the most recent work done in the mine.
Quartz is the most abundant gangue mineral, and it encloses most of the sulfides and gold. The quartz veins occur in shoots from a few feet to 100 feet in length on the strike of the vein, and these are said to vary in width from 1 inch to 12 feet. In one place a width of 30 feet is reported. Often there are two quartz seams in the vein, separated by 12 to 30 feet of country rock. In places the country rock or fractured vein rock carries bunches and stringers of mineralized quartz in sufficient quantity to make the mass of the vein a low-grade milling ore. Irregular bodies of oxidized ore were mined from the surface to the 500-foot level, and sulfide ore was found from surface down, alternating with the oxidized ore.
Estimates of possible reserves in this mine Old their classi- fication, and possible profits from working them are given in the reports of several private investigators. The Snake and Oppor- tunity mines together are reported to have produced a total of $2,170,000 in shipping ore, concentrates and bullion. Of this total the Snake is given credit for $1,500,000. Shipments from the mine consisted of ore that would assay better than $12 per ton, and anything under that figure w as left unmined in the stopes or was hand sorted and the reject used as stope