Regional Report: Lordsburg District, Pyramid Mts, Hidalgo Co., New Mexico, USA

Ref.: USGS Bulletin 885. The Lordsburg District is located in the extreme northern part of the Pyramid Mountains. It is an elongate District which trends N-S and is about seven miles long by three miles wide. Latitude-longitude and UTM location is for the Eighty-Five Mine, one of the largest mines in the district. This is the most important district in Hidalgo County in terms of total production value and the 4th ranking district in New Mexico for copper production. Total value of production from 1870 to 1975 has been estimated at 60 million dollars. Average ore grade at the Eighty-Five Mine was 2.8% Cu, 1.23 oz Ag/ton, and 0.11 oz Au/ton. The northern part of this district contains deposits of the copper-tourmaline class of veins which are the most productive deposits of this type in the United States. Ore occurs in E- to NE-striking veins but the largest ore bodies are found in the NE-striking veins. The Emerald vein, at the Eighty-Five Mine, has been mined continuously for a strike length of more than 4000 feet and a vertical depth of about 2000 feet. The average width of the Emerald Vein is about 6.5 feet. Exposed rocks in the district are extrusive and intrusive volcanics ranging in age from Upper Cretaceous to Pliocene but consisting chiefly of basaltic andesite flows intruded by a porphyritic granodiorite stock. Major faults trend N-S along the margins of the Pyramid Mountains. This district contains some of the deepest workings in New Mexico and includes several well-developed mines which exceed 2000 feet in depth. The most extensive workings are in the Eighty-Five Mine, the Bonney Mine and the Atwood-Henry Clay Mine. Although mainly an underground mining district, some small open pit operations have been attempted.

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