636 MINING GEOLOGY/Hydrothermal Ores Figure Schematic model for formation of carbonate hosted Mississisppi Valley type Pb Zn ores, via lateral gravity driven flow of basinal brines from an upland region (Reproduced with permission from Evans AJ (1993) Ore Geology and Industrial Minerals: An Introduction, 3rd edn Oxford: Blackwell.) compaction and overpressuring of basin sediments, promoting the flow of warm pore fluids Pore fluids in deforming sedimentary basins adjacent to uplifting forelands can be forced to flow laterally in response to gravity, a scenario that is best developed during continental plate collisions A widely accepted theory for the origin of many carbonate-hosted Mississippi Valley-type (MVT) Pb–Zn deposits in central and eastern North America is westward gravity-driven flow of warm basinal brines, caused by Late Palaeozoic collisions between the ancient North American and European continents (Figure 6) Compositional and colour banding (‘sphalerite stratigraphy’), fluid inclusions, and other geochemical features of the ores are remarkably consistent over long distances between the Pb–Zn deposits, supporting the occurrence of regional fluidflow events Gravity-driven lateral flow of basinal brines has emerged as the most effective mechanism that can account for the thermal and mass balances in many MVT systems Overthrusting and consequent sediment compression in fold-mountain belts may also drive the flow of deeper, warmer fluids into shallower or more peripheral environments Shale-hosted stratiform copper deposits such as the Kupferschiefer (Europe) and White Pine (North America) may have formed via this type of mechanism Dehydration reactions associated with regional metamorphism can also provide sources of hot fluids, although they are initially low in salinity and high in CO2 Such fluids may have been responsible for hydrothermal gold deposits associated with CO2 metasomatism, found in shear zones and faults in Archaean and younger greenstone belts Earthquake-induced seismic pumping could provide a mechanism of fluid flow along fault zones See Also Economic Geology Gold Minerals: Native Elements; Sulphides Mining Geology: Hydrothermal Ores Tectonics: Hydrothermal Activity Further Reading Barnes HL (1979) Geochemistry of Hydrothermal Ore Deposits, 2nd edn New York: Wiley Interscience Barnes HL (1997) Geochemistry of Hydrothermal Ore Deposits, 3rd edn New York: John Wiley Barton PB, Rye RO, and Bethke PM (2000) Evolution of the Creede Caldera and its relation to mineralization in the Creede mining district, Colorado In: Bethke PM and Hay RL (eds.) Ancient Lake Creede; Its Volcano Tectonic Set ting, History of Sedimentation, and Relation to Mineral ization in the Creede Mining District, vol 346, Special Paper Geological Society of America, pp 301 326 Berger BR and Bethke PM (1985) Reviews in Economic Geology, vol 2: Geology and Geochemistry of Epithermal Systems El Paso, Texas: Economic Geology Publishing Company Cox DP and Singer DA (1986) Ore Deposit Models US Geological Survey Bulletin 1693 Craig JR and Vaughan DJ (1994) Ore Microscopy and Ore Petrography, 2nd edn New York: Interscience Evans AJ (1993) Ore Geology and Industrial Minerals: An Introduction, 3rd edn Oxford: Blackwell Giggenbach WF (1992) Magma degassing and mineral de position in hydrothermal systems along convergent plate boundaries Economic Geology 87: 1927 1944 Guilbert JM and Park CF Jr (1986) The Geology of Ore Deposits New York: WH Freeman