The Huizopa Property is situated within an extensive package of Tertiary volcanic rocks which comprise the Sierra Madre Occidental Mountains of northern Mexico. These rocks host the Sierra Madre Gold-Silver Belt. The site is defined by an unusually high concentration of historic and newly discovered low-sulfidation to high-sulfidation epithermal polymetallic gold-silver deposits within a belt ranging up to 200 km east to west and 1,200 km north to south. Some of the largest precious metal mining districts in Mexico, including Ocampo, Batopilas, San Dimas, Tayoltita, Topia, Guanaceví and recent discoveries such as Pinos Altos, Palmarejo, Dolores, Mulatos and El Sauzal fall within the Sierra Madre Gold-Silver Belt. The Huizopa Property falls almost on a straight line between the large gold mines at Dolores and Mulatos.
The Sierra Madre Occidental Mountains, a north-northwest-trending volcanic plateau that separates the southward extension of the Basin and Range Province of the southwestern United States into two parts; Sedlock et al. (1993) suggested calling these two areas of extension the eastern and western Mexican Basin and Range provinces. The major rock types of the Sierra Madre Occidental Mountains are characterized by two distinct packages of volcanic rocks: one group of early Oligocene age (28 to 36 million years old), which are unconformably overlain by younger rocks of Miocene age (18 to 24 million years old). The Oligocene-age formations represent widespread magmatism and are known as the Lower Volcanic Group, and are characterized by a predominant pile of andesitic flows and volcano clastic rocks which typically crop out at the bottom of the deep barrancas. They are generally massive in nature and show extensive propylitic alteration, related to the intrusion of coarse grained to porphyritic intrusive rocks.
Even though the volcanism is predominantly andesitic, the upper parts, towards the contact with overlying Miocene volcanics (Upper Volcanic Group), tend to become more felsic and thick beds of rhyodacite and rhyolite are intercalated with andesites and dacites. The Upper Volcanic Group forms a one-kilometer-thick unit that unconformably overlies the Lower Volcanic Group andesitic rocks. The basement lithology is hidden beneath the Lower Volcanic Group. However, where the underlying basement rocks are exposed in other parts of the Sierra Madre Occidental Mountains they are typically Cretaceous to early Tertiary sedimentary and volcanic rocks. The basement rocks are often cross-cut by slightly younger intrusive rocks of diorite to granitic compositions.