Eureka copper mine, Nacimiento Mountains mining district, Rio Arriba County, New Mexico

Many people have heard of the Nacimiento sedimentary-hosted copper mine, in the Nacimiento Mountains east of Cuba, but another copper mine found high on the cliff (approximately 9000 ft elevation) east and above the Nacimiento mine is the Eureka mine. It is challenging to find and requires a 4-wheel drive vehicle and hiking. The Eureka mine is also a sedimentary-hosted copper mine. It was discovered in the 1880s and a 500 ft adit was first constructed before 1910, but has since collapsed. Later, the mine was patented, and in 1926, several adits and a quarry were constructed to mine copper ore. In 1956-1957, 231 short tons of copper and 841 ounces of silver were produced, worth $228,000. The ore is in the Triassic Agua Zarca Member of the Chinle Formation. The copper ore is confined to the lower Agua Zarca sandstone and conglomerate in a river-channel complex, approximately 280 ft long and 40 ft thick. Copper minerals replacing fossil logs and wood fragments are common in the walls and dump material. Azurite, malachite, chrysocolla, and bornite are the predominant copper minerals found at the mine. Other copper minerals found in the area include liberthenite, covellite, and chalcocite. NMBGMR geologists are examining sedimentary-hosted copper deposits for critical minerals potential. These deposits can contain copper, vanadium, and cobalt. Future reports will describe the geochemistry and mineralogy of these deposits. This work is funded in part by a DOE grant Carbon Ore, Rare Earth, and Critical Minerals (CORE-CM) assessment of San Juan River-Raton Coal Basin, New Mexico, DE-FE0032051.