The Niukutou deposit is located in the southwestern margin of the Qaidam Basin and the central part of the Qimantag metallogenic belt,Qinghai Province,which is a typical skarn Pb-Zn polymetallic deposit.According to the relationship with mineralization,the Early-Middle Devonian magmatic rocks in this deposit are divided into ore-forming rock mass and non-ore-forming rock mass.This work aims to investigate the differences of geochemical characteristics between ore-forming and non-ore-forming rock masses,as well as the relationship between oxygen fugacity and Pb-Zn mineralization.Trace elements analysis of zircons and electron probe analysis of biotite show that the Ce4+/Ce3+values of zircons in the two samples of the ore-forming rock mass range from 9.94 to 227.72(27.24 on average)and 9.79 to 197.95(34.13 on average),respectively.In contrast,the Ce4+/Ce3+values of zircons in the two samples of the non-ore-forming rock mass lie in 10.08～39.13(25.41 on average)and 8.14～33.78(19.16 on average).The average Ce/Nd values of zircons in ore-forming rock samples are 8.42 and 9.87,while those for non ore-forming rock samples are 8.20 and 2.69.According to the calculated zircon crystallization temperature based on the Ti content of zircons,the zircon crystallization temperature of the ore-forming rock mass(averaging 700 and 696)is slightly higher than that of the non-ore-forming rock mass(averaging 685 and 682).The absolute calculated oxygen fugacity of zircons in the ore-forming rock mass is-17.57 and-14.99,which is also larger than that of the non-ore-forming rock mass(averaging-17.76 and-22.49).In addition,electron probe analysis of biotite suggests that the oxygen fugacity and volatile content of ore-forming rock mass are higher than those of non-forming rock mass.It is thus inferred that the increase in oxygen fugacity of the ore-forming rock mass may be more conducive to the formation of Pb-Zn skarn deposits.Compared with previous data,the oxygen fugacity of rocks related to Pb-Zn mineralization is lower than that of skarn-porphyry Cu-Mo deposits,and is similar to that of granitic rocks related to skarn W-Sn deposits.The oxygen fugacity of ore-forming rock mass has a significant limiting effect on the mineralization types(Cu-Mo,Pb-Zn,W-Sn),and the oxygen fugacity of zircons in rock mass may be related to the geological background and the contribution ratio of mantle source components to the magmatic source.
Pb-Zn mineralizationzircon trace elementsbiotite electron probeoxygen fugacityNiukutou depositQimantag areaQinghai Province
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