Variations in the Distribution of Mineral Deposits with Time

Abstract

Volcanogenic base metal deposits and related precious metal deposits were formed in the crust at least as long as 2700 m.y. ago, at the time of craton formation. The Rhodesian and Kaapvaal cratons were the source of the immense gold and important uranium deposits of the Witwatersrand basin (2700 m.y.); the Superior craton of Canada was the source of uranium in the Blind River uranium deposit (~2400 m.y.). These placer deposits carry detrital pyrite and appear to have been eroded and transported under an oxygen-deficient atmosphere. The principal period of banded iron formation occurred 2500–2000 m.y. ago at a time when sufficient oxygen had accumulated in the ocean-atmosphere system to bring about iron oxide precipitation in favorable basins. Stratiform lead-zinc deposits in sediment-hosted environments formed in mobile belts marginal to the cratons 2000–1400 m.y. ago. About the same time (1800–1100 m.y.), uranium deposits, sometimes with associated gold, silver, copper, nickel, or cobalt, were forming in the Cahill basin of Northern Australia and in the Athabasca basin of Canada. Sedimentary copper deposits of the Zambian or Kupferschiefer type developed from 1400 m.y. to 200 m.y. ago. The setting of these deposits suggest extensive oxidation and red bed conditions on the neighboring land masses. Economic phosphorites are late Precambrian through Phanerozoic in age and show clear biospheric control. Volcanogenic base metal deposits reappear in the Paleozoic Appalachian orogenic belt at Bathurst, Canada and in the Miocene of the Kuroko district of Japan. Mississippi Valley lead-zinc deposits occur in platform carbonates from late Precambrian (Nanisivik, Gayna River) through Paleozoic (Missouri, Polaris, Pine Point) into Mesozoic times (Silesia). Porphyry coppers of late Phanerozoic age occur for the most part in subduction-related volcanic belts of the Circum-Pacific and Alpide orogenic regions. A recently recognized class of ultra-fine gold-silver deposits occurs in Phanerozoic areas of former hot spring activity, formed by the interaction of meteoric waters with shallow seated igneous intrusives.