El Antimonio, Caborca Municipality, Sonora, Mexicoi

Regional Level Types
El Antimonio	- not defined -
Caborca Municipality	Municipality
Sonora	State
Mexico	Country

The El Antimonio district is in the northwestern part of the Estado de Sonora, Mexico, about 160 kilometers by road west of Santa Ana, the nearest shipping point, and 100 kilometers south of Ajo, Arizona. Its estimated past production is about 20,000 or 25,000 tons of metallic antimony. This amount has been exceeded by only one or two other antimony districts in Mexico.
The bedrocks of El Antimonio district consist largely of sandstone, siltstone and conglomerate of Triassic and Lower Jurassic age unconformably overlying limestone of Permian age. These rocks are intruded by dikes and irregular bodies of quartz porphyry, diorite, and trachyte. The Triassic rocks are cut by thrust faults of small displacement, more or less parallel to the stratification, and by small cross faults. The thrust faults and in places the cross faults are occupied by veins containing quartz, oxides of antimony, and locally gold, chloride and bromide of silver, and chalcedony. Postmineral faults are common, but all of them are of small displacement.
Two formations consisting of indurated gravel occur in the district. One is distinctly older than the other, but both are of Recent age. They have been mapped separately. The present stream channels contain unconsolidated gravels which are younger than the indurated gravels; these have not been mapped. All the gravel deposits contain antimony minerals, and all except the oldest have been worked as placers.
The district contains 22 mines working the largest and the richest of the veins, which are mostly in the Triassic siltstone but partly in the Triassic sandstone and intrusive igneous rocks. In addition, a hundred or more smaller veins are known.
The ore is generally localized in the flatter-dipping parts of the veins and at or below the intersections of the main veins with premineral faults and fractures.

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