The Chino mine

A copper pit started in 1909 and still being dug

The Chino mine, 15 miles east of Silver City in southwestern New Mexico, is an open-pit porphyry copper mine and the largest porphyry copper deposit in the state. The pit is about 1.75 miles across and 1,350 feet deep, and it is the third oldest active open-pit copper mine in the world, after Bingham Canyon and Chuquicamata. It is also called the Santa Rita mine, after the village it swallowed: Santa Rita was removed in the 1950s as the workings spread. An overlook with educational displays stands on the south side of Highway 152 east of Hanover.

Apaches were the first to notice native copper lying on the ground in a valley northwest of Santa Rita Mountain, and Apaches, Spaniards, Mexicans and Americans have all taken copper from it since. In 1800 an Apache showed the site to the Spanish officer José Manuel Carrasco, who named it Santa Rita del Cobre and in 1804 sold it to Francisco Manuel de Elguea. Elguea brought in convict labour, built a presidio to house the convicts and protect them from the Apache, and sent mule trains loaded with copper to Chihuahua. Robert McKnight and Stephen Courcier worked it from 1828 to 1834 and made a large fortune. A massacre of Apache by John Johnson in 1837 is often placed here, though it more likely happened near the Animas Mountains, and it provoked the Apache rather than cowing them. The mine was cut off from supplies, and in 1838 the 300 to 400 people of Santa Rita fled toward the presidio at Janos, 150 miles south; nearly all were killed on the way. The mine reopened after Cochise made peace with the United States in 1873. John M. Sully and Spencer Penrose founded the Chino Copper Company in 1909, and the open pit was begun in 1910.

The copper lies in and around the Santa Rita stock, a granodiorite pluton 58 million years old, one of many intruded across southern Arizona and southwestern New Mexico during the Laramide deformation. Porphyry deposits are low grade, under 0.8 percent copper, spread through fractures that pressurised steam and gas broke open as the magma cooled. Above the southeast side of the pit stands the Kneeling Nun, a landslide block of 34.9 million-year-old tuff, and there is concern for its stability as the mining moves toward it.

The mine became part of Freeport-McMoRan in 2007. Mining and milling were suspended in 2008 and about 600 of the 830 workers laid off, and the mine reopened in 2011. It is a working industrial site, best seen from the overlook.