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|Palaeolatitudinal controls of Phanerozoic sediment-hosted mineral deposits
|Grainger, Susan Elizabeth
|The distribution of Phanerozoic sediment-hosted mineral deposits appears to be influenced by latitudinal zoning. The palaeolatitudes of the host rocks were determined using standard palaeomagnetic procedures - the most reliable results being for the Mesozoic and Cenozoic with early Palaeozoic palaeolatitudes least reliable. The palaeolatitudes derived from Tarling and BP palaeogeographic reconstructions are in general agreement i. e. +/- 10°, although greater discrepancies occur for India and Central America. It is shown that some types (e. g. sandstone copper, sandstone lead) have a preference for low latitude arid regions whilst conditions in the equatorial and temperate rainfall belts were more favourable to the formation of other deposits (e. g. sandstone uranium-vanadium, oolitic ironstone). Using climatic modelling assuming uniformitarianism of the principles governing the Earth's atmospheric and oceanic circulation patterns, the climatic conditions affecting the distributions of sediment-hosted deposits were evaluated. It is concluded that local climatic effects are influential in the genesis of limestone base-metal, oolitic ironstone, sandstone copper, sandstone lead, shale base-metal, sedimentary exhalative, sandstone uranium-vanadium, manganese, laterite and phosphate deposits. These climatic conditions affect the nature and degree of chemical weathering, erosion, abundance of organic matter, ground water chemistry and volume in a particular region. However in some instances, such as placer deposits, the major control on deposit distribution was the availability and distribution of source rocks. Such palaeolatitudinal/palaeoclimatic control on the distribution of some deposit types places genetic constraints upon their formation. It also has obvious implications in the evaluation of potential sites for exploration and development.
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|School of Civil Engineering and Geosciences
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