MINERAL DEPOSITS AND THEIR GENESIS 497 Discovery of Further Mineral Deposits The AGI definition of economic geology includes the ‘application of geological knowledge and theory to the search for mineral deposits’, recognizing the fact that the extractive industries must meet future demands for new materials and replace mined out deposits with new discoveries Over the centuries the world’s need for mineral supplies has always been met by some combination of chance finds at outcrop, and indirect indications from prospecting methods such as panning, geophysical and geochemical surveys, aerial photography and earth satellite imagery Whether the search is for an extension to ore at a working mine or a new grassroots discovery, the choice of where to look for success is based on someone’s idea that a given part of the Earth’s crust will actually contain economic mineralization The best ideas are based upon two factors – superior knowledge of the observed and detailed characteristics and field associations of the type of deposit targeted, and a valid theory of its genesis These two factors have long been used empirically in prospecting, but over the past 20 years the available information has been systematically gathered and codified into a large number of ‘deposit models’ These models are continually being tested, improved, and added to as discoveries of new and unexpected types of mineralization are made For example, the huge Olympic Dam copper-uranium deposit, discovered under 350 m of barren cover rocks in South Australia in 1975, now represents a broad and complex group referred to as iron oxide-copper-gold deposits The search becomes more difficult as the number of undiscovered deposits decreases and the emphasis moves further towards deposits deeply buried and hidden under overlying rock cover This growing challenge is being met with an integrated approach of new and broader ideas backed by an ever-improving tool-kit of geophysical and geochemical field exploration technologies and elegant laboratory techniques The tool-kit also includes readily available space satellite imagery that now provides the broad perspective on which to study major crustal features and lineaments that may link the surface to the depths below the crust Economic mineral concentration is seldom an isolated event, but rather one result from a dynamic system linking tectonics, magmatism, volcanicity, and sedimentation in complex ways To guide exploration to best advantage the entire system should be investigated and understood as far as possible Twenty-first century economic geologists, striving to understand the ore forming systems in our complex Earth’s crust, may be poised to take the biggest step forward in the subject since 1556, when Georgius Agricola (Bauer) famously classified ore deposits and recorded the state of the art of mining in his classic work, De Re Metallica See Also Economic Geology Mining Geology: Exploration; Mineral Reserves; Hydrothermal Ores; Magmatic Ores Sedimentary Rocks: Banded Iron Formations; Ironstones Further Reading Cooke DR and Pongratz J (eds.) (2002) Giant Ore Deposits: Characteristics, Genesis and Exploration CODES Special Publication Hobart: University of Tasmania Craig JR, Vaughan DJ, and Skinner BJ (2001) Resources of the Earth: Origin, Use and Environmental Impact, 3rd edn New York: Prentice Hall Davis GR (1988) Is Metallogeny a Practical Exploration Tool? Episodes 11(2): 105 110 Derry DR (1980) World Atlas of Geology and Mineral Deposits London: Mining Journal Books Evans AM (1993) Ore Geology and Industrial Minerals, an introduction, 3rd edn Oxford: Blackwell Kirkham RV, Sinclair WD, Thorpe RI, and Duke JM (eds.) (1993) Mineral Deposit Modeling Geological Associ ation of Canada Special Paper 40 Selley RC (2000) Applied Sedimentology, 2nd edn San Diego: Academic Press Stanton RL (1972) Ore Petrology New York: McGraw Hill