Abstract 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

Abstract 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.

Abstract Lead-zinc deposits hosted by carbonate rocks in New Mexico account for 37% of the lead and 56% of the zinc production from the state. A thick sequence of carbonate rocks provides excellent host rocks for skarn and replacement mineral deposits. Six types of deposits containing lead and zinc in carbonate rocks are identified: Laramide skarn, carbonate-hosted Pb-Zn replacement, carbonate-hosted Ag-Mn (±Pb, Zn) replacement, alkalicrelated (Great Plains Margin) skarn, Rio Grande Rift barite-fluorite-galena (formerly sedimentary-hydrothermal deposits), and Mississippi Valley-type (restricted to the Permian Basin) deposits. These deposits range in age from Late Cretaceous to Miocene or younger and range in size from a few tons of low-grade material up to tens of millions of tons of 10% or greater lead and zinc. Most lead-zinc deposits in carbonate rocks in New Mexico are spatially associated with Late Cretaceous to Miocene calc-alkaline or Oligocene to Miocene alkaline igneous rocks. Geochemical and isotopic data indicate that the skarn and replacement deposits in New Mexico were probably formed by mixing of meteoric with local magma tic fluids. These fluids were heated by high-heat flow produced from the cooling of calderas and/or local intrusive plutons. Carbonate-hosted Pb-Zn and Ag-Mn replacement deposits have similar textures, tectonic setting, and formation temperatures as volcanic-epithermal vein deposits. These carbonate-hosted replacement deposits were probably formed from hydrothermal fluids that are similar to fluids forming volcanic-epithermal vein deposits. In contrast, other lead-zinc deposits hosted by carbonate rocks in New Mexico were formed by basinal brines migrating from sedimentary basins without any obvious association with intrusive rocks (Rio Grande Rift and Mississippi Valley-type deposits). Economically, the most important lead-zinc deposits in carbonate rocks in New Mexico are the deposits related to Late Cretaceous to Eocene calc-alkaline igneous rocks in the southwestern part of the state (Laramide skarns). Some of these skarn deposits are associated with porphyry-copper deposits (i.e. Santa Rita). Skarns are currently mined for copper at Chino and Continental mines; zinc is recovered as a by-product. Some of the lead-zinc deposits in carbonate rocks in New Mexico have yielded significant lead and zinc in the past and may have limited economic potential in the future. Potential for finding additional lead-zinc deposits in carbonate rocks in New Mexico is excellent.