EARLY PALEOPROTEROZOIC (2.5–2.0 GA) GIANT SEDIMENT-HOSTED MINERAL DEPOSITS: A RESPONSE TO ENVIRONMENTAL CHANGES

Recognition of secular changes in the early Paleoproterozoic surface environment permits an understanding of the stratigraphic position of mineral deposits with respect to these tectonic, climatic, and biogeochemical events. The events in ascending order are: 1) a 2.48-2.45 Ga superplume event (SPE), 2) an extended glacial epoch (ca. 2.45–2.3 Ga) accompanied by carbon isotope excursions, 3) a period of enhanced weathering, 4) a major carbon isotope excursion between >2.2–2.1 Ga, not associated with known glaciation, 5) a great oxidation event (GOE), and 6) the 2.1-2.0 Ga breakup of the Kenorland supercontinent. BIFs of South Africa, Australia, and Brazil were deposited on continental margins contemporaneously with and in response to the SPE. Rifting of Kenorland was initiated by the SPE and associated sedimentary rift successions contain detrital uraninite. A rise in atmospheric pO₂ may have occurred episodically during the glacial epoch. Termination of glaciations was accompanied by a change from a stagnant glacial ocean to a well-mixed, post-glacial ocean resulting in the deposition of Mn- and Fe-rich sediments in open marine setting in South Africa and Botswana. The glacial epoch was followed worldwide by deposition of mature, Al-rich quartzites suggesting a change to greenhouse conditions and enhanced chemical weathering. Overlying carbonate successions deposited during the >2.2–2.1 Ga carbon isotope excursion contain pseudomorphs of sulfate minerals. These carbonates and associated siliciclastic deposits in North America and Fennoscandia contain Cu stratiform deposits, magnesite, and tourmaline formed in an evaporitic environment. The end of the 2.2-2.1 Ga carbon isotope excursion was accompanied by supercontinent breakup and voluminous mafic volcanism. Contemporaneous ocean overturn led to deposition of large Mn- and Fe-rich deposits, phosphorites, and organic carbon-rich deposits worldwide. The stratigraphic continuum of Paleoproterozoic mineral deposits therefore appears to be directly linked to tectonic revolutions and related changes in climate and the oxidation state of the oceans and atmosphere.