Page 120 - The Geology and Ore Deposits of Sierra County, New Mexico - Bulletin 10

MINING DISTRICTS 119
Hot Springs-Fairview highway. Mineralization along the con- tact consists of sulfides and carbonates of copper, lead and zinc occurring in cross fractures located mainly in the tops of slight folds in the limestone. The ore occurs in bunches and shoots along the contact with the underlying porphyry. The limestone near the ore is garnetized, sometimes completely so, and in some places away from the fractures and veinlets of ore it has been slightly marbleized or recrystallized. Development work consists of a 175-foot shaft sunk on the contact, which here dips 25° slightly north of east, and several other shallow shafts and pros- pect holes. On the whole, except for the work in the shaft, which disclosed a persistent though small shoot of ore for the full depth, the work done on this property has been insufficient to determine the size and exact mode of occurrence of the important ore shoots.
BLACK KNIFE GROUP
This group of three claims lies southeast of the Vindicator-
West Contact claims and near the southern end of the porphyry exposure, as seen on the map, figure 8. The overlying beds of Magdalena limestone strike N. 20° W. and have a dip of 25° NE. The beds are slightly folded, with axes pitching down the dip of the beds, and in many of these folds the top of the arch has been fractured along what appears to be a tension crack. The ore occurs in bunches and shoots within or in close proximity to these cracks. Lead is the chief metal, and subordinate amounts of copper, silver and zinc are present ; the minerals are galena, cerusite, anglesite, azurite, malachite, cerargyrite, sphalerite and smithsonite. The gangue minerals are quartz and calcite, with a small amount of manganese oxides. Occasionally a small amount of fluorspar is noted. Pyrite was an original constituent of the ore, but it has been altered to limonite, which now occupies the original pyrite spaces and has stained the adjacent rock yellow to brown. Along the contact of the limestone and the porphyry, the limestone is greatly silicified. Silica has been deposited in the tension cracks above the ore zone to the surface, and it is an indicator of ore below wherever development work has opened the ground for inspection. Many of these surface occurrences of silicia have not as yet been prospected along the contact. The fractures are nearly vertical and extend at right angles to the strike of the limestone beds. In general the ore shoots are about 2 feet in width and occur from the contact upwards for from 3 feet to as much as 20 feet, with a pitch that follows the dip of the strata.
Development consists of an inclined shaft about 150 feet deep following the dip of the beds. This shaft connects at the bottom with a tunnel from the surface, driven along the strike at the contact of the porphyry and limestone. Half way down the shaft a vertical winze 30 feet deep connects with a crosscut