Sulfur and lead isotope compositions of sulfides in the Cho Dien Pb- Zn deposit,northeast Vietnam, and their geological implications

The Cho Dien Pb-Zn deposit in northwest Cho Don of Bac thai Province, northeast Vietnam, is located in the north Vietnam uplift of the South China fold system. In order to explore the ore-forming material sources of the Cho Dien Pb-Zn deposit and acquire an overall understanding of the metallogenic mechanism, the authors collected ore samples from the orebody to analyze the sulfur and lead isotope composition. The results achieved show that δ34S values of eleven metal sulfides (sphalerite, galena, pyrrhotite) vary from 4.1‰ to 6.8‰, with an average value of 5.51‰ and the range of 2.7‰, indicating that the sulfur isotope composition is stable. Through the calculation, δ34S value of the hydrothermal solution is about 7‰, showing that the source of sulfur was mainly strata sulfur, with some mixture of magmatic sulfur. 206Pb/204Pb, 207Pb/204Pb and 208Pb/204Pb ratios of the eleven metal sulfides (sphalerite, galena, pyrrhotite) vary in the range of 18.451~18.682, 15.685~15.878, 38.909~39.636, with the average value being 18.59855, 15.78227 and 39.30773, respectively. Calculations also show that the sulfides have a relatively high μ values (9.36~9.98), ω values (39.04~42.63) and Th/U (3.92~4.13), with the average value being 9.8, 40.79 and 4.03, respectively. These lead compositions indicate that the ore-forming materials not only had features of the upper crust but also had characteristics of the mantle. The metal sulfide isotope compositions show that the sulfur of the Cho Dien Pb-Zn deposit was mainly from sedimentary rock, with some from the Phia Bioc pluton of Triassic, while the lead of the Cho Dien Pb-Zn deposit was mainly from the upper crust, with some from the Phia Bioc pluton. The present data, combined with previously published results, indicate that the ore deposit was formed due to collision between Indochina and South China Blocks in the Early Triassic period. The Phia Bioc pluton resulted from the collision process and it provided the ore-forming material for the Cho Dien Pb-Zn deposit, which genetically belongs to hydrothermal deposit.