Page 123 - The Geology and Ore Deposits of Sierra County, New Mexico - Bulletin 10

122 GEOLOGY AND ORE DEPOSITS OF SIERRA CO., N. M.
15 to 20 feet in height, and in practically all places mining has been discontinued with the workings still in a good grade of mill- ing ore.
On the Covington claims development work has been con- fined largely to the sinking of prospect shafts and to a moderate amount of drifting along the contact of the limestone with the monzonite. On the Covington No. 3 claim, near the east end and adjoining Dictator ground, a 40-foot shaft sunk on the contact cut a heavily epidotized rock stained with iron and manganese the full distance. From the surface to a depth of 20 feet the ore is oxidized, but below this depth grains and bunches of sulfides coated with oxidized material appear. Ore produced from this shaft is reported to have averaged around 6 per cent copper, 6 oz. silver, 14 per cent lead and 15 to 20 per cent zinc. This ore was transported to the mill on pack animals. The ore occurs in a shear zone 10 to 12 feet wide, which strikes N. 15° W. It is esti- mated that along this zone of shearing the monzonite to the west has been dropped about 100 feet and displaced to the south about 600 feet relative to the block on the east. Erosion of the lime- stone along the contact has left the monzonite east wall standing as a steep scarp along an arroyo which has cut its way into the shear zone. Near the shaft the surface zone of alteration is as much as 50 feet wide. Northward from the contact this shear zone may be followed through the Magdalena limestone to a point east of the Black Knife- claims as a wide zone of silicification con- taining some calcite and subordinate fluorite. No development work has been done along this shear zone at places other than the contact of the limestone and monzonite. The bottom of this shaft is in ore, and it is possible that mineralized ore shoots will be en- countered at intervals along this shear zone.
On the Covington No. 2 claim a shaft 50 feet deep is located near the east end of the claim. Drifts having a combined length of 25 feet extend N. 80° E. and S. 80° W. from the bottom of the shaft, all in mineralized ground. At the surface in this shaft, partly oxidized lead-zinc ore containing 3 to 6 ounces of silver was mined. In places this ore contained oxidized copper min- erals, and where these were present silver rose to as high as 20 ounces per ton. The copper minerals were malachite, azurite and some cuprite in a gangue of limonite and manganese oxides that contained scattered specks of chalcopyrite and chalcocite In the bottom of the shaft, galena, sphalerite and chalcopyrite consti- tute the usual association, with smaller amounts of oxidized minerals. The contact was apparently not cut in the develop- ment work done, although it was closely approached, as indicated by the much-fractured and highly altered appearance of the limestone. Fracturing of the limestone is very pronounced for a distance of 100 to 150 feet from the contact, and the limestone is much altered throughout, being replaced by silica, epidote and garnet. Closer to the contact the fractures and cavities are filled