Geology of the Batopilas mining district, Chihuahua, Mexico, volumes 1 and 2

The Batopilas mining district is located in the southwestern portion of Chihuahua, Mexico in highly dissected terrain consisting largely of Cretaceous and Tertiary intrusive and extrusive rocks of intermediate to felsic composition, forming the upper and lower igneous series of the Sierra Madre. An early, 85 MY granodioritic phase was followed by Tertiary quartz dioritic phase at 50 MY, and another granodioritic phase at 45 MY. The upper volcanic series occurred at 28 MY. A map of the surface geology eas made at a scale of 1:25,000 covering an area of 60 sq km. The Batopilas area was near the source of several of the igneous stages which vented, resulting in great variability in extrusive units. An intrusive phase associated with the 45 MY Las Tahonas unit developed a small porphyry copper deposit to the west of the town, which is presently in a stage of excellent exposure. The numerous silver deposits occur in a broad arc around the prophyry and several kilometers out. The silver zone is separated from the porphyry by a poor quartz-galena zone. Several genetic models of Batopilas mineralization are discussed.