Gold Deposits of Northern Sonora, Mexico

The first part of the route is southward from Tucson to Nogales. The geology and tectonic fabric is variable and includes from north to south the Santa Catalina-Rincon mountains metamorphic core complex, Late Cretaceous and Early Tertiary volcanic rocks of the Tucson Mountains, several porphyry-copper deposits associated with Laramide siliceous intrusion, and Precambrian units, imbricate fault slices of Paleozoic formations, and the Early Cretaceous Bisbee Group in the Santa Rita Mountains. The route follows the valley of the Santa Cruz River in which abundant Plio-Pleistocene gravel deposits are located to the international line. Further south, in northernmost Sonora, the route continues along the valley of the upper reaches of Rio Magdalena. This valley is largely surrounded by Jurassic volcanic flows and intrusions as far south as Magdalena de Kino where another core complex is situated. The route then turns eastward across the Magdalena extensional basin where borate and gypsum deposits have been discovered in Miocene age continental deposits. After crossing a drainage divide at Puerto Cucurpe, where ignimbrites are exposed in Sierra Torreón, the route turns northward through the valley-fills deposits exposed by Arroyo Las Rastras to the Santa Gertrudis, Carlin-type, disseminated gold deposit.

0.0 Buenos Dias! Turn right (west) on Speedway. The first part of the route (Fig. 1) is from Tucson to Nogales, parallel to the Santa Cruz River. Travel west towards 1-10. 2.1

2.1 To the north are the Santa Catalina Mountains. The Santa Catalina-Rincon metamorphic core complex is shown in Figure 2. The mylonite zone is 10-15 km wide and appears to have formed in the Middle Tertiary (37 ± 8 Ma) at a depth of 9.3 ± 1.9 km (Anderson et al., 1988). Lower plate rocks include Pinal Schist, Oracle Granite (1.4 Ga), Apache Group, Cambrian through Mississippian strata, and Lower Cretaceous Bisbee Group. Plutonic rocks include Tertiary quartz diorite and granites that form the bulk of the range except for the southwestern and northeastern flanks that comprise the upper plate (Naruk and Bykerk-Kauffman, 1990). 4.6

6.7 Cross Alvermon Way. Tucson Mountains straight ahead (12:00) on skyline. The Tucson Mountains form a low desert range on the west side of Tucson. They are underlain by Upper Cretaceous volcanic rocks that have been interpreted as parts of the fill of a large ash-flow caldera (Lipman, 1993). 1.6

8.3 Cross Country Club Road 1.8

10.1 Cross Campbell Street; University of Arizona football stadium and