This province extends from the Mexico/United States border between Sasabe in the east, through Nogales and Agua Prieta (Sonora), to the vicinity of Estacion Palomas (Chihuahua). Geographically, the metallogenic province coincides with the Sierra Madre Occidental Physiographic Province of Raisz (1959); on the west it is limited by the contact of the Gulf of California/Pacific Coastal Plains and on the east with the westernmost central Chihuahua valleys (Fig. 1). Over an area of almost 275,280 km2, its axis runs northwest-southeast from the American border to the city of Guadalajara (Jalisco).
The Sierra Madre Occidental exhibits a variable geologic character. The physiographically high altitudes above the coastal plain—1,500 to 2,000 m on the average, some higher than 3,000 m—evolved by effects of the differential erosion of thick extrusive volcanic sequences: intercalated andesites, rhyolites, tuffs, and ignimbrites making up a volcanic assemblage.
This assemblage overlies an older basement comprising Precambrian or Paleozoic metamorphic rocks and Mesozoic sedimentary or igneous rocks.