Abstract Chromitite genesis in ophiolites is indirectly related to spreading rate, controlling mantle fertility and depth of melt crystallization. The most favourable conditions for chromitite concentrations are found in ophiolites generated at moderate spreading rates, where the world's largest chromitite deposits reside. A huge extension of the Oman Ophiolite permits an overview of chromitite distribution in relation to ridge tectonics, yielding constraints on ophiolitic chromitite genesis. Chromite genesis requires large instantaneous melt delivery, coupled with increasing oxygen fugacity produced by hydrous fluids. Chromitites in the Oman Ophiolite reside either in the Moho Transition Zone or at depth in the mantle, along wide shear zones. Both locations are domains of large melt transfer. Thinner crust on top of mantle diapirs and large shear zones limiting propagating segments represent particular domains where seawater circulation at depth is favoured. The thermal structure of these domains may explain the preferential formation of Al-rich versus Cr-rich chromites. A frozen equilibrium with parent mid-ocean ridge basalt (MORB) in the Al-rich chromites could result from rapid cooling of chromitites formed close to the ridge axis. Alternatively, equilibrium with primitive melt and a variable oxidation state is explained here by fluid circulation along the shear zones, active during transition from spreading to detachment.

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

Abstract The Geological Survey of Portugal (Comissão dos Serviços Geológicos), was created in 1857, as a section of the Geodesic Division of the Ministry of Public Works, Trade and Industry. It benefited greatly from the workings of the ministry, which in trying to modernize the country was concerned to keep up with the latest technical and scientific developments occurring elsewhere in Europe. Since its foundation, the Geological Survey of Portugal showed a clear drive towards its participation in an international scientific dialogue and cooperation. This strategy encompassed subscription to specialized foreign books and journals; intense correspondence with foreign specialists; the regular publication of monographs and memoirs in French; occasional or permanent collaboration with foreign experts; and travelling. The main outcome of the ‘travel of negotiation’ undertaken in 1878 to Spain by the Portuguese geologist J. F. Nery Delgado, then adjunct to the Director of the Portuguese Geological Survey, in addition to improving relationships with the geologists of the neighbouring country, was the collection of field data that was useful for the geological characterization of the southern Portuguese regions. He was also able to negotiate and look for data which could persuade his Spanish colleagues to subscribe to interpretations consistent with the Portuguese geological map, published in 1876.