The geologic environments of formation of three types of massive, pyritic, largely stratiform orebodies of western Europe are compared. The largest concentration of such ores, the pyrite belt of Spain and Portugal, seems to have resulted from volcanic-hydrothermal precipitation on the sea floor largely in or adjacent to quartz keratophyre eruptive centers. The smaller deposits of northwestern Germany, important for their content of zinc and lead and with abundant barite, are in pelites close to reef limestones. They apparently are shallow-water accumulations, largely organically precipitated. The third and economically least important pyritic ores are those of southern Tuscany. The original sulfide accumulations appear to have formed in stagnant deep-water basins associated with calcium sulfate evaporites. The Triassic ores of Tuscany have been strongly modified and mobilized during a near-surface thermal event accompanied by a few intrusions during the Pliocene.

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