The PB-Zn ore deposits of San Felipe, Sonora, Mexico: "Detached" mineralization in the Basin And Range Province

Abstract

The lead-zinc-silver deposits of San Felipe, Sonora, Mexico are located in the vicinity of a metamorphic core complex, in its northeastern part. This structure is characterized by a denudation associated with Tertiary extension which affected northern Mexico and the western United States during Miocene. The units of the upper plate, including the Eocene porphyritic rhyolite which contain parts of the San Felipe deposits slided to the NE some kilometers from its original position along the El Amol detachment fault. This fault is exposed for about 40 km, with a general trend N 60g W and dips of 20 to 45g NE. The El Amol fault cuts the mineralized zone leaving the deeper parts (skarns) of the system in the lower plate, in the highest part of the Sierra de Aconchi. At least two other ore deposits in Sonora have been affected by extension, including a tungsten deposit in the west flank of the Sierra Mazatiin and part of the La Caridad mine (La Caridad fault). In Arizona, the San Manuel-Kalamazoo copper deposit was also affected by Tertiary extension. Effects of extension should be taken into account when exploring for new reserves in old districts.