Abstract

The origin of Precambrian banded iron formations is controversial. One type of evidence is a comparison of different occurrences. Three of the best-preserved basins of Precambrian iron formation deposition are here denned and compared systematically: the Hamersley Basin of Western Australia, the Animikie Basin of North America, and the Transvaal System Basin of South Africa. After a brief summary of the broad structural and stratigraphic evolution of each basin, their differences and similarities are reviewed. They differ mainly in: major stratigraphic sequence, thickness of iron formation, thickness variation, stratigraphic continuity, lithology of iron formation, nature of sedimentary structures, conspicuousness of varves (micro-banding), clastic association, and abundance of diagenetic riebeckite. With some reservations, they resemble each other in: age, basin size, chemistry and mineralogy, broad time-structural evolution of basin, precedence of chert, volcanic association, and in the restricted, medial and transitional stratigraphic status of the main iron formation. It is concluded that the Western Australian and South African iron formations are very closely similar, but that both differ markedly from the Animikie iron formations of the Lake Superior area. However, all three are more closely similar in chemistry than is required by the fact that their definition is chemical. Quantitative geochemical argument indicates a direct volcanic contribution of iron to the Hamersley Basin; it is possible that such vulcanicity is restricted to a limited medial part of basin development in a particular kind of basin-forming process.

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