2.05-Ga Isotopic Ages for Transvaal Mississippi Valley–Type Deposits: Evidence for Large-Scale Hydrothermal Circulation around the Bushveld Igneous Complex, South Africa
نویسندگان
چکیده
The known dimensions of hydrothermal fluid circulation associated with emplacement of the 2.055-Ga Bushveld Igneous Complex (BIC) are extended with new isotopic ages for Paleoproterozoic mineral deposits in wallrocks (Transvaal Supergroup) surrounding the BIC. A fluorite-rich Mississippi Valley–type (MVT) deposit in the Zeerust district, dated at 2.05 Ga (Sm-Nd isochron age), has Nd isotopic compositions that are identical to coeval F-rich Lebowa Granite late in the BIC intrusive sequence, suggesting transport of magmatic fluids ∼100 km beyond the present margins of the BIC. Hydrothermal illite from the Zn-Pb MVT Bushy Park deposit, dated at 2.05 Ga by K-Ar geochronology, links widespread MVT deposits of the Kaapvaal craton to large-scale basinal brine circulation associated with emplacement of the BIC. These data, in combination with gold vein, phosphate mineral, and paleomagnetic resetting ages, indicate a regional-scale Bushveld-age hydrothermal system circulating 700 km outward from the present margins of the BIC. Online enhancement: appendix.
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