Linking Mississippi Valley-type deposit size to metal provenance

Mississippi Valley-type (MVT) deposits are important sources of Pb, Zn, and critical metals such as Ag, Ga, and Ge. However, their metal sources and the mechanisms behind the formation of giant deposits remain contentious. Here, we address these questions by studying Hg-Pb isotope signatures of MVT sulfides and potential source rocks in the southeastern Yangtze block. These data reveal that the ore metals come from at least two upper-crustal sources: shallower sedimentary rocks and deeper metamorphic basement. The giant deposits show isotopic signatures compatible with increased metal input from the deeper basement. Together with higher ore-fluid temperatures and salinities, as well as preferential localization of larger deposits along major fault intersections, this suggests that large MVT deposits form where specific geological factors coincide during regional orogeny, driving high fluid fluxes and deep fluid circulation. These can efficiently mobilize metals from basement rocks and concentrate them in shallow carbonate traps.