Although the formation of metalliferous mineral deposits by processes active in sedimentary basins depends ultimately on physical and chemical conditions at the site of deposition, the style, scale and timing of mineralization are influenced by tectonic and magmatic events, which relate to the evolution of the crustal environment as a whole. During the Archaean era, when geothermal gradients were high and igneous activity widespread, sedimentary processes played little part in mineralization. The development of cratonic crustal massifs at the beginning of the Proterozoic era was followed by an increase in the variety and size of deposits formed in sedimentary basins. From this time onward the cratonic cover formations have provided important sites for the deposition of metals. These metals entered the basins from a variety of sources, some being derived from weathering and erosion of the basement and others being transferred to surface levels by magmas and volatiles originating in the mantle or lower crust. It is suggested that the timing of mineralization is related to that of the major magmatic and tectonic happenings determined by the global tectonic regime.

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