Geology of the Fresnillo Mining District, Zacatecas
The Fresnillo Mining District is located in central Zacatecas State about 60 km northwest of the town of Zacatecas at geographic coordinates 23° 10′ 29″ and 102°52′39″ and an average elevation of 2,200 m (Fig. 1). Fresnillo is connected directly with Mexico City by Federal Highway 45 (Panamerican) and the México-Ciudad Juárez railroad; Zacatecas airport is 35 km southeast of the district.
The state of Zacatecas has been renowned for its mines since the time of the Spaniards; expeditions under Juan de Tolosa in 1546 discovered innumerable veins in the area of today’s town of Zacatecas. Francisco de Ibarra discovered Fresnillo farther north in 1554, naming it “Aguas del Fresnillo” (Isunza, 1981). Shortly after, he explored the area called Cerro Proaño where Diego Fernández de Proaño had already located some veins. These discoveries were followed by many others in the state, including Sombrerete, and ConcepciÃ³n del Oro (Fig. 1).