Whole rock and zircon geochemistry of the Tieshan pluton in Daye region, Eastern China: Implication for petrogenesis and Fe-Cu-Au-(Co) mineralization

Abstract

The Tieshan pluton is situated in the Daye region of the Middle-Lower Yangtze River Valley metallogenic belts. It consists mainly of quartz diorite and host abundant mafic microgranular enclaves (MMEs) and is associated with the renowned Daye Fe-Cu-Au-(Co) skarn deposit. The presence of disequilibrium textures in MMEs, including quenched margins, acicular apatite and elongated amphibole, provides evidence that the pluton underwent magma mixing involving mafic and felsic magma. In comparison with the Fe (4.20 wt% on average), Cu (28 ppm on average) and Co (10 ppm on average) concentrations in the quartz diorite, the Fe (7.26 wt% on average) and Cu (57 ppm on average) concentrations are doubled and Co (29 ppm on average) are tripled in MMEs. The recharge of mafic magma, therefore, likely adding significant amount of Fe, Cu and Co metals into the felsic magma, therefore enhancing the fertility of the Tieshan pluton.

Zircons from quartz diorite of the Tieshan pluton exhibit U-Pb ages of 138.2 ± 1.6 Ma and 136.9 ± 1.6 Ma, respectively. The zircon ε_Hf(t) values of the Tieshan quartz diorite (ranging from −17.6 to −16.1) closely match to those of the Cu-Fe-Au fertile granitoids in the Daye region. Zircons from the Tieshan quartz diorite display Eu/Eu* and Yb/Dy values ranging from 0.4 to 0.6 and 3.6 to 4.2, respectively. These ratios suggest substantial amphibole fractionation with minimal plagioclase fractionation and indicate high magmatic water contents. This is corroborated by the zircon oxybarometer-hygrometer analysis, which estimates the melt H₂O content to be between 8.3 and 10.3 wt%. The zircons from the Tieshan quartz diorite exhibit Ce⁴⁺/Ce³⁺ ratios of 67 to 201 and oxygen fugacity (logfO₂ values of ΔFMQ) from ΔFMQ+2.1 to ΔFMQ+2.8. The calculated zircon Ce⁴⁺/Ce³⁺ ratios and oxygen fugacity (logfO₂) for the quartz diorite from Tieshan pluton are comparable to the values of Tonglushan Cu-Fe-Au related fertile quartz diorite, indicating the similar oxygen fugacity of the Cu-Fe-Au ore-related magmas in Daye region. Our research demonstrates that the geochemistry of whole-rock and zircon is a powerful tool for identifying granitoids with potential for skarn Fe-Cu-Au-(Co) mineralization.