Zinc Isotopes And Minor Elements In Sphalerite From Magmatic Hydrothermal Deposit In The Middle-southern Part Of Da Hinggan Mountains, China

The zinc stable isotope system has been successfully applied to many different fields. Zn isotopes have seen increased interest in recent years as a useful tracer for studying hydrothermal processes. In this study, we first present the zinc isotope results and trace element concentrations of sphalerite samples from Weilasituo-Bairendaba ore field and Linxi Bianjiadayuan magmatic hydrothermal deposits in Inner Mongolia:(1)Zn isotopic composition of sphalerite samples in the Bairendaba and Weilasituo deposits show the δ66Zn variation of +0.20‰~+0.29‰ and +0.23‰~+0.40‰ respectively relative to the Lyon JMC 3-0749 L zinc standard. The results reveal a trend of increasing δ66Zn values from west to east in the Bairendaba deposit and the highest δ66Zn values can be observed in the Weilasituo deposit. Distribution of values of sphalerites from Weilasituo-Bairendaba deposits exhibit a unimodal distribution pattern that is the salient feature of magmatic hydrothermal deposit.(2)Zn isotopic composition of sphalerite samples shows a δ66Zn variation of +0.23‰~+0.36‰ relative to the Lyon JMC 3-0749 L zinc standard and exhibits a unimodal distribution pattern that is the salient feature of magmatic hydrothermal deposit. The results reveal a trend of increasing δ66Zn values from west to east(porphyry type-cryptoexplosion breccia type-hydrothermal filling type), also the lower δ66Zn values can be observed at deeper levels and the higher δ66Zn values at upper levels from the same borehole. The spatial variation between deposits revealed by the zinc isotope data shows that the formation of Cryptoexplosion breccia in the Linxi Bianjiadayuan magmatic hydrothermal deposit was caused by the quartz porphyry intruded into the eastern slate strata, and the ore-bearing hydrothermal fluid be filled in the internal or external contact zone of the eastern diorite bodies, finally, the hydrothermal deposit formed.(3)The δ66Zn values are inversely correlated with sphalerite Fe/Mn ratio and also tend to be higher in low In, Cd sphalerite, consistent with precipitation of lower δ66Zn sphalerite closer to the principal hydrothermal fluid conduits. But the lowest Cd Leucocratic sphalerite(ZK0710) has the highest δ66Zn values, whereas highest In and Bi are also enriched in it. It suggests that Leucocratic sphalerite which in the Weilasituo deposit could be formed in independent In-Zn(Cu)-Pb-Ag mineralization, and the W-Sn-In-Bi mineralizations in the Weilasituo deposit might form in same place but might come from different metallogentic fluids source.(4)Zinc isotopes in the magmatic hydrothermal systems have a similar effect and isotopic fractionation in high-temperature silicate melts. We conclude that the primary control on isotopic variation is temperature gradient.