Abstract Basement outcrops are rare in northeastern Mexico, but the effect of older basement structures on the current structural plan is clear. Two large structures, the San Marcos fault and the northern edge of the Sierra Madre Oriental, are oriented roughly east-west, and have been postulated as sites of the Mojave-Sonora megashear. Both structures were probably active in the late Jurassic. The San Marcos fault continued to be active into the Cretaceous, while the northern edge of the Sierra Madre Oriental became inactive. Both structures were strongly reactivated during the Laramide orogeny. Potential fields data integrated with regional geologic mapping suggests a series of horsts and grabens were created during Middle-Late Jurassic rifting of the basement, but that relative displacements are far less than those proposed for the Mojave-Sonora megashear system. The northern edge of the Sierra Madre Oriental, with its large left-step along the Monterrey salient, is kinematically more compatible with the postulated left-lateral offset along the Mojave-Sonora megashear, while the San Marcos fault has numerous right-stepping offsets, which is kinematically incom-patible with the Mojave-Sonora megashear hypothesis. In general, however, these data do not support the concept of a large-offset left-lateral megashear in northeastern Mexico.

Abstract Spain has a great variety of metallic and industrial rock and mineral deposits, as well as important energy and water resources. Within the European Union it has a pre-eminent position, being the country with the highest level of production of raw materials for its own use (Table 19.1 ). Spain is a first-rank producer of several non-metallic minerals such as celestite, sodium sulphate, magnesite, potassium and sepiolite, and ornamental rocks such as granite and marble. There are huge quarrying operations currently active in gypsum, clays, slate and aggregate. Spanish ores include examples of world-class deposits such as Almadén, by far the largest mercury deposit in the world, and the Iberian Pyritic Belt with its giant and supergiant massive sulphide deposits that include the world’s largest at Rio Tinto. Exploration programmes developed in the 1990s have resulted in the discovery of new deposits, both in already active mining districts (e.g. Migollas, Aguas Teñidas, Las Cruces and Los Frailes in the Pyritic Belt, and new mercury reserves in Almadén) and in new areas (e.g. El Valle-Carl és for gold, Aguablanca for nickel). However, despite the large reserves of metallic minerals that exist in the country, mining is only currently active for copper, mercury, gold and zinc (Table 19.2 ). One legacy of the long mineral exploitation history in Spain results from the fact that, before the 1980s, environmental damage was considered to be an inevitable consequence of the extractive Spanish mining industry. This has produced many environmental problems associated with