Geology and mineral deposits of the sedimentary-copper deposits in the Scholle Mining District, Socorro, Torrance and Valencia counties, New Mexico

Small, uneconomic, stratabound sedimentary-copper deposits at the Scholle mining district are restricted predominantly to the lower member of the Abo Formation, with minor occurrences in the upper member of the Bursum Formation and the Meseta Blanca Sandstone Member of the Yeso Formation. Spanish settlers likely mined copper from the district sometime after the founding of the Abo and other Salinas missions in the area in 1629. Sedimentary-copper deposits were rediscovered by modern prospectors in the Scholle district as early as 1902, but production did not begin until 1915. From 1915 to 1961, 15,037 short tons of ore were produced and yielded 1,122,468 lbs Cu, 8,147 oz Ag, and 426 lbs Pb. Copper and uranium minerals in the Abo Formation occur: (1) as disseminations within bleached arkose, limestone-pebble conglomerate and siltstone; (2) along bedding planes and fractures at or near sandstone-shale, sandstone-siltstone and sandstone-limestone contacts; (3) as replacements of wood and other organic materials; and (4) as replacements of clay or calcite cement within the host sandstone. Copper and other metals were probably transported in low-temperature brine solutions through permeable sediments and along bedding planes and faults shortly after burial. Oxidizing waters could have leached copper and other metals from at least three sources: (1) clay minerals and detrital mineral grains and rock fragments within the red-bed sequences, (2) Proterozoic rocks enriched in these metals, and (3) Proterozoic base-metal deposits. Most sedimentary-copper deposits in the Scholle district, as elsewhere in New Mexico, are too low grade, low tonnage, and far from existing copper mills for current development of copper. However, increases in copper and silver prices have sporadically renewed interest in some of the larger deposits, such as in the Scholle district. 249