Genesis of the Binh Do Pb-Zn Deposit in Northern Vietnam: Evidence from H-O-S-Pb Isotope Geochemistry

The Binh Do Pb-Zn deposit in the Phu Luong region (Thai Nguyen Province, northern Vietnam) is located on the southern margin of the South China Block. The fault-controlled Pb-Zn orebodies are mainly hosted in Upper Paleozoic carbonate formations. In order to reveal the mineralization type and metallogenesis of this deposit, multi-isotopic (S, Pb, H and O) analyses on typical ore and gangue minerals were conducted. The average ore sulfide δ34SΣS value is 4.3‰, suggestive of magmatic sulfur. The ore sulfide Pb isotope compositions are homogeneous, with the 206Pb/204Pb, 207Pb/204Pb and 208Pb/204Pb values of 18 501 to 18 673 15.707 to 15 798, and 38 911 to 39.428, respectively. Lead isotope model ages of the ore sulfides (240-220 Ma) are consistent with the timing of regional Triassic S-type granite emplacement (250-220 Ma), suggesting that the metals may have been granite-derived. The quartz δDV-SMOW (-82.4‰ to -70.5‰) and δ18OH2O (-0.4‰ to +6.4‰) values suggest that the ore-forming fluids were composed of mixed magmatic and meteoric waters. Combined with the geological features of the Pb-Zn deposit in the region, we propose that the Pb-Zn deposits belong to magmatic-hydrothermal type, rather than MVT-type as previously suggested. The Triassic granites may have contributed the ore-forming material and heat that drove the hydro-thermal system. The ore-forming fluids may have migrated into interlayer faults and fractures of the carbonate strata, diluted by subsurface meteoric water and deposited successively the vein-type and stratiform-type Pb-Zn ores.