Page 142 - The Geology and Ore Deposits of Sierra County, New Mexico - Bulletin 10

MINING DISTRICTS 141
shown in the following tabulation. In the preparation of th table Mr. W. H. Bucher of Hillsboro rendered invaluable assi: ance and supplied most of the figures.
MINE DESCRIPTIONS
GENERAL FEATURES OF WORKINGS
Mine workings are fairly extensive in the Hillsboro district,
but none of them are deep enough to have encountered serious difficulties from underground water. The deepest shafts in the district are the Richmond, Rattlesnake, Opportunity and El Oro, each of which reaches to approximately 500 feet below the sur- face. The Bonanza mine, developed by tunnels, has attained a depth of 500 feet under the highest point of the hill.
Development work has consisted chiefly of drifting along the veins on each level, following the high-grade streaks that occur within the veins, and of drifting between the walls of the veins where the ore has pinched out. The ore has been mined, as a rule, by a modified cut-and-fill method of stoping. The high- grade ore has been sorted or cobbed out of each cut made across the back of the stope and transported through stope chutes, and all low-grade material has been left behind as stope fill. If this low-grade material was not sufficient to fill the stopes, they were left open, or the filling was completed with waste rock. Due to