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Basaltic andesites of the Ongeluk Formation, Transvaal Supergroup in Griqualand West constitute part of a large flood volcanic province that extruded at ca. 2.22 Ga onto the partly submerged Kaapvaal Craton. Pods and short veins of megaquartz, with albite, epidote and traces of calcite and Cu-Ni-Co sulphides are closely associated with beds and pods of jasper and chert that are products of low-temperature...
This is the first report about silica-rich hydrothermal precipitates which were sampled together with hydrothermal sulfides (chimney fragments) in an extinct vent field in the Central Indian Ocean. There are two kinds of silica-rich rocks: a jasper which is impregnated and replaced to various degrees mainly by sphalerite, and to a lesser extent by barite, pyrite and traces of chalcopyrite, and an...
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