Page 77 - The Geology and Ore Deposits of Sierra County, New Mexico - Bulletin 10

76 GEOLOGY AND ORE DEPOSITS OF SIERRA CO., N. M.
nearly east-west. In the latter system a roughly radial pattern' is discernible, and in a broad way the character of the ore varies in the two systems. The veins of the north-south system are val- uable chiefly for their gold and silver content, with copper occur- ring sparingly in places. The east-west or radial system, as ex- emplified in the Silver Monument vein, is valuable chiefly for its silver and copper content. Near Monument Creek, in the extreme southern part of the Apache district, the Bald Eagle group of claims contains vein deposits that are of the galena-sphalerite- pyrite type, with associated silver and gold and chalcopyrite lo- cally present. Although included within the Chloride area, these veins appear to be much more closely associated with the type of ore found in the Hermosa district, 7 miles to the south.
The gold-silver veins in the district occur in a belt 2 to 3 miles wide that extends from the northern boundary of the coun- ty to Monument Creek on the south and follows approximately the contact of the limestone and andesite. This belt includes the greater part of the gold-bearing veins, most of which strike due north, although others in this system, such as the Apache and U. S. Treasury veins, strike northwest, and still others strike northeast. These veins have many features common to the epi- thermal or low-temperature type and range in width from 2 to 8 feet. They are single fissures filled with delicately banded and crustified vein matter, usually with a seam of gouge along one wall, or they are in sheared and broken zones with a seam of gouge usually following one wall of the vein, and the vein matter filling the irregular fractures and spaces in a mass of brecciated wallrock, which passes gradually into the solid ground of the other wall. These veins are persistent, and some of them, such as the Pye lode south of Hagen's Peak and the main or "Great Master" lode in the northern part of the district, may be traced continuously for several miles. The vein filling consists of band- ed quartz, calcite and locally barite, with which have been de- posited pyrite associated with gold and silver, and locally chal- copyrite. Later quartz has filled fractures within the original vein filling and has in part replaced the original calcite. Most of the mines in the region have encountered sulfides at depths varying from 50 to 500 feet below surface, but the great bulk of the ore shipped has been free-milling oxidized ore. In the upper portion of the veins, silver chloride and free gold, and in places oxides and carbonates of copper, have been the valuable min- erals. It is reported that native silver, argentite, and chalcocite have been found near water level. In the sulfide zone the ore is lower in metallic content, but within the ore shoots it is con- sidered to be of good milling grade and is said to average $10 to $15 per ton. Ore shoots within the veins are irregular, and al- though they are 200 to 300 feet in vertical dimension, they are apt to be at short stoping length along the levels. (See footnote, page 59.)