440 ECONOMIC GEOLOGY Figure Development of the theory of plate tectonics in the 1960s led rapidly to a new view of the genesis of some ore deposits as shown on this early diagram in 1972 Reproduced with permission from Evans AM (1995) Introduction to Mineral Exploration Oxford: Blackwell, p 40 (modified from Sillitoe 1972) Table Life cycle of extractive industry activities Activity Applied geology input Discovery of new deposits Feasibility studies and mine development Mineral extraction Dominant role End of life of deposit Major role in defining reserves and critical technical parameters Essential engineering role in operational efficiency Long term environmental assessment deposit models’ These models marshal all the pertinent facts concerning related deposits that are seen as ‘types’ Modern advances in nearly all fields of geology are of relevance and application to some aspect of economic geology For example structural geology from the scale of electron microscopy in rock deformation studies to megastructures on satellite imagery; evolution and structure of sedimentary basins; the geochemistry of sediments as source rocks for hydrocarbons and metalliferous brines; the volcanic realm and its diverse products; magma generation and crystallization; metamorphic effects on rock structures and mineral chemistry; and even the profound effects of major meteorite impacts on the Earth’s crust Specialist fields of knowledge are required for each phase of the industrial cycle of activity (Table 2) in each branch of the extractive industries, and economic geologists have formed several specialist groups such as petroleum geologists, mining geologists and exploration geologists Discovery of New Deposits To maintain a stable extractive industry long term, the huge tonnages of minerals extracted each year must be replaced, on average, by discovery and/ or development of an equivalent amount of new materials The difficulty imposed by this high demand is compounded by the fact that new mineral fields and individual deposits become progressively harder to discover as the easier finds are made Scientifically based mineral exploration has developed into a sub-industry, in which the participants include government agencies, mineral resource companies of all sizes, and specialist groups offering contract and consulting services Exploration objectives are targeted on either certain commodities or certain regions of interest The search area for bulk materials such as aggregates or low-grade coal is restricted by transportation costs and environmental factors; some mines concentrate their search close to existing infrastructure; and state organizations are of course interested in their own territories Most mineral commodities are internationally traded, and exploration money and effort tend to favour countries that offer the most attractive combination of geology, political stability, mining taxation and operational infrastructure Commoditytargeted exploration is based solidly on favourable