Fingerprinting the metal endowment of early continental crust to test for secular changes in global mineralization
Christien Thiart, Maarten J. de Wit, 2006. "Fingerprinting the metal endowment of early continental crust to test for secular changes in global mineralization", Evolution of Early Earth's Atmosphere, Hydrosphere, and Biosphere - Constraints from Ore Deposits, Stephen E. Kesler, Hiroshi Ohmoto
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Archean cratons are fragments of old continents that are believed to be more richly endowed with mineral deposits than younger terrains. The mineral deposits of different cratons are also diversely enriched with useful (to humankind) chemical elements. Cratons are therefore mineral diversity hotspots that represent regional geochemical heterogeneities of early Earth, the evidence for which remains encoded on each craton as unique metallogenic “fingerprints.” Using six selected elements groups from our extensive in-house GIS database of Gondwana mineral deposits, we derive the metallogenic fingerprints of 11 Archean cratons of the Southern Hemisphere, and compare these against metallogenic fingerprints of the same selected elements in younger crust of three of their host continents (Africa, Australia, and South America). After adjusting the mineral inventory of each craton to account for underexploration of regions lacking infrastructure and other political and economic conditions for mineral investment, we show that mineral deposit density and diversity of Earth's continental lithosphere has decreased with time. We conclude that metallogenic elements were transferred more efficiently from the mantle to the continental lithosphere in the Archean and/or that subsequent (younger than 2.5 Ga) recycling of these elements (mineral deposits) back into the mantle has become more effective. How most of these fragments of old continents inherited their rich and diverse metallogenic characteristics is unresolved, because different cratons are likely to represent only small remnants of once much larger and possibly more varied Archean continents, and part of the total metal inventory of Archean continents must have been recycled back into in the mantle. The latter has implications for understanding the secular change in the redox state of the Archean mantle and fluid envelope.