The material covered over this six-day field trip explores the regional stratigraphy, tectonic setting, and mineral deposits of the central Sierra Madre Occidental and western part of the Mesa Central in Mexico. The course builds on similar field trips held in 1997, 2003, and 2014, adding updates of the geology based on new studies and opening of new roads in this rugged and poorly accessible region. A completely new section presents a detailed overview of the geology of the classic San Dimas mining district and the Sabinas and La Colorada mines. A road trip log with descriptions of each stop is included.

The material covered over this six-day field trip explores the regional stratigraphy, tectonic setting, and mineral deposits of the central Sierra Madre Occidental and western part of the Mesa Central in Mexico. The course builds on similar field trips held in 1997, 2003, and 2014, adding updates of the geology based on new studies and opening of new roads in this rugged and poorly accessible region. A completely new section presents a detailed overview of the geology of the classic San Dimas mining district and the Sabinas and La Colorada mines. A road trip log with descriptions of each stop is included.

Abstract Rincón de Parangueo is a Quaternary maar that has been recently desiccated. The crater was partially occupied by a soda lake, and near the shoreline microbialites have formed. Evaporites (mainly trona and halite) precipitated as the water level dropped. Active subsidence of the lake floor (c. 24 m since 1980) produced countless structures close to the lakeshore, where deformation is extensional. Closer to the depocentre, in the western half of the basin, gliding/spreading produced folds and mud-injection domes. The most remarkable structure throughout the basin is a monocline that forms a ring-like, nearly continuous scarp, approximately 15 m high, which in the eastern half of the basin was produced as a fault-propagation fold developed above the buried diatreme–country rock boundary. A more diffuse (wider) monocline, locally associated with compressive structures, occurs in the western half of the basin. These structures are interpreted as having developed above a gently inclined, irregular lake sediment–country rock (andesite) interphase. The monocline was modified by high-angle extensional faults/fractures with large heaves/apertures. In the eastern half of the basin, there is a second (outer) scarp, approximately 13 m high, formed by a high-angle, listric, normal fault. Rollover antiforms occur in the hanging wall of this structure. Rincón is an example of centripetal gravitational gliding/spreading.

Abstract Silver and gold mineralization was discovered in the late 1600s in the epithermal sulfide-rich veins of Mineral de Pozos Mining District, northeast Guanajuato state, Mexico. The main exploitation period of this mining district was between 1888 and 1922, with sporadic activities until 1942. Exploitation of the deposit is estimated at 1,200,000 tons of ore with average of 202 g/ton silver, and 11.83 g/ton Au. Mineral waste materials (more than 1 million tons) are scattered along the area on the main creeks and in the ancient processing plants (Haciendas de Beneficio). In this field guide, we present brief descriptions of the mineralization, the geology of the area, some of the ancient processing plants, and the potential dispersion of metals derived from the mine tailings into the environment (soil, sediments, and groundwater). Despite the relatively high concentrations of As and Pb in groundwater (0.011–0.090 mg/l As and 0.025–0.035 mg/l Pb), we consider that these values represent natural background values rather than contamination derived from anthropogenic input. However, we consider that Zn is the only metal potentially derived from mining activities being released to the environment. The historical processing plants offer a very interesting perspective of the more than a century old mining activities.

The low-temperature epigenetic and stratabound Pb-Zn-Cu-Ba-F-Sr–bearing ore deposits enclosed within sedimentary columns historically have been major sources of metals. Exploration companies still find these deposits to be a profitable exploration target due to their simple mineralogy as well as the large tonnage that can present, always considering the mineral districts as a whole. In northeastern México, several nonmagmatic, low-temperature Pb-Zn-F-Ba deposits have been systematically considered as magmatic-related (skarns, high-temperature replacement deposits, epithermal deposits, etc.). Recently, these deposits have been restudied and placed within a scenario of deep fluid circulation of basinal brines through the Mesozoic sedimentary series, enriched in Ba, F, and metals during fluid flow and water-rock interactions. These fluids gave rise to a series of strata-bound epigenetic ore deposits scattered throughout the whole Mesozoic carbonate platform and can be shown to be unrelated to any period of magmatism. There is no intense alteration to the host rocks. Commonly there is a close association with organic matter, either liquid hydrocarbons or bitumen; they have a very simple mineralogy of barite, celestine, fluorite, sphalerite, galena, and have low formation temperatures (90–105 °C) combined with variable salinities. These characteristics make these deposits similar to the Mississippi Valley–type deposits, possibly most similar to the Alpine-Appalachian subtype.