Archean Komatiitic Sill-hosted Chromite Deposits in the Zimbabwe Craton

摘要

Lenticular chromite deposits of widely varying age, metamorphic grade and strain rate, as well as size, shape, and ore quality, are widespread in greenschist to amphibolite grade greenstonegneiss terrain in the south-central part of the Zimbabwe craton and in granulite grade equivalents in the Northern Marginal zone of the Limpopo belt in the far south. In order of age and, very approximately, decreasing abundance, they form three groups: (1) early Archean (3.5–3.2 Ga) deposits associated with amphibolite grade greenstone remnants in the 3.6 to 3.35 Ga Tokwe gneisses (e.g., Hornet, Valley) and on the amphibolite grade eastern flank of the Shurugwi greenstone belt, and granulite grade greenstone remnants in the Northern Marginal zone (e.g., Inyala, Rhonda); (2) mid-Archean deposits within the ca. 3.0 Ga Shurugwi Group in the main greenschist part of the Shurugwi belt (e.g., Peak, Railway Block) and associated with the ca. 3.0 Ga Belingwean Supergroup in several other belts; and (3) late Archean (ca. 2.74 Ga) deposits mostly in the western segment of the Masvingo belt (e.g., Prince).