Multiple mineralization events in the Zhaxikang Sb–Pb–Zn–Ag deposit and their relationship with the geodynamic evolution in the North Himalayan Metallogenic Belt, South Tibet

Abstract

The Zhaxikang Sb–Pb–Zn–Ag deposit, the only super-large deposit identified within the North Himalayan Metallogenic Belt (NHMB), is still debated to date with perspectives of mineralization age and genesis. The previous genetic models mainly include hot-spring, magmatic hydrothermal fluid, coarse-grained hydrothermal Pb–Zn vein overprinted by Sb-rich magmatic hydrothermal fluid, and SEDEX overprinted by hydrothermal fluid. Here, we present new and credible isotope geochronological evidence to discuss the genesis and mineralization age of Zhaxikang deposit. The isotopic ages of minerals from different mineralization stages in Zhaxikang deposit coincide with the mineralization ages of three main regional mineralization events. In detail, the older 206Pb/238U (218 ± 10 Ma), Sm–Nd (173.7 ± 7.4 Ma) and Rb–Sr (147 ± 3.2 Ma) isochron ages match three regional extensive seafloor volcanic events during synsedimentary period (220–130 Ma); the younger 206Pb/238U (62 ± 8.2 Ma) and older Re–Os (47.7 ± 7.9 Ma; 43.1 ± 2.5 Ma) ages are in accord with the formation age of regional orogenic Au–Sb deposits associated with metamorphic fluid system during syn-collision period (60–42 Ma); and the Ar–Ar (19.3 ± 1.1 Ma) and younger Re–Os (9.0 ± 1.9 Ma) isochron ages are consistent with the regional magmatic-hydrothermal mineralization event during post-collision period (25 Ma to now). We thus proposed that Zhaxikang deposit is a superimposed deposit that experienced three pulses of mineralization corresponding to three regional mineralization events: the first pulse of mineralization (stages 1 and 2) is related to multiple seafloor volcanic events during synsedimentary period with submarine hydrothermal sedimentation (metasomatism) genesis; the second pulse of mineralization (stages 3 and 4) is associated with metamorphic fluid system during syn-collision period that overprint the Pb–Zn mineralization; and the third pulse of mineralization (stages 5 and 6) relates to magmatic-hydrothermal activity during post-collision period and also overprints early mineralization. Furthermore, the complicated superimposed mineralization results in the discordance of different geochronological methods.