Abstract

The Mendip–Bristol veinfield is one of a number of British Mississippi Valley-type deposits, the genesis of which has never been fully explained. The Mendip–Bristol Pb-Zn–Ba vein mineralization is hosted in Carboniferous, Permo-Triassic and Jurassic sediments. The metal sources involved during mineralization were investigated using Pb-isotope analysis of vein galenas.206Pb/206pb values range from 18 311 to 18.594,207Pb/204Pb values from 15.601 to 15.688 and 208Pb/204Pb values from 38.257 to 38.565. The data show three isotopically different mineralizing fluids, which it is suggested reflect fluid expulsion from adjacent Mesozoic sedimentary basins, as a result of overpressuring due to rapid subsidence in the Triassic–Jurassic.

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