Cenozoic Pb--Zn--Ag mineralization in the Western Alps.

Metallogenic models of polyphase mountain belts critically rely on robust geochronology. We combine petrology with Rb--Sr and U--Th--Pb in situ geochronology, paired at thin-section scale, to date mineralization in deformed hydrothermal Pb--Zn--Ag deposits along an east-west transect in the Western Alps, France. The Pb--Zn--Ag veins occur in shear zones with kinematic structures consistent with the mylonitized host rocks. The ore consists mainly of galena in a quartz-phengite gangue. The paragenesis can be related to hydrothermal crystallization during periods of variable strain. Both isotope systems yield only Cenozoic ages (ca. 35 Ma and 15-20 Ma) without any pre-Alpine inheritance, clearly indicating orogenic mineralization. The metallogenic model proposed here includes significant fluid circulation along major tectonic contacts between basement and sedimentary cover during Alpine convergence. [ABSTRACT FROM AUTHOR]