| Abstract:The Ruanjiawan W-Cu-Mo deposit, situated in the eastern part of the Maopu-Liangjianqiao East-West fault zone in the Edong district, is the largest W-Cu-Mo deposit in this region. The granodiorite closely associated with Ruanjiawan W-Cu-Mo deposit. This study investigates the whole rock geochemistry, zircon U-Pb geochronology, zircon trace elements, and Hf isotopic compositions of the Ruanjiawan granodiorite to constrain its age and petrogenesis, as well as to elucidate the indicative significance of zircon for W-Cu-Mo mineralization in Edong district. Zircon U-Pb geochronology results show that the emplacement age of the Ruanjiawan granodiorite is 143.00 ± 0.74 Ma, corresponding to the late Mesozoic magmatism and metallogeny in Edong district. The Ruanjiawan granodiorite has relatively uniform Hf isotopic compositions (εHf(t) = -5.4 to -2.2), similar to the zircon Hf isotopic compositions of the Tongshankou granodiorite, Tonglushan quartz diorite, and Longjiaoshan granodiorite, indicating that these rocks mainly derived from an enriched lithospheric mantle, with minor crustal contamination during magma evolution. Zircons from the Ruanjiawan granodiorite exhibit high Eu/Eu* (>0.4) and low Dy/Yb (<0.3) values, suggesting that the magma f was relatively hydrous. This hydrous characteristic is consistent with the water content values (6.85%~8.45%) obtained from the whole-rock and composition. Based on trace element analysis of zircons from the Ruanjiawan granodiorite, the calculated magma oxygen fugacity values range from ΔFMQ + 1.07 to ΔFMQ + 2.88, indicating relatively oxidized conditions. In addition, the Ce4+/Ce3+ ratios in zircon range from 93 to 190, slightly lower than those in the Tongshankou granodiorite and Tonglushan quartz diorite, suggesting a relative decrease in the oxidation state of the metallogenic magma from the Tongshankou Cu-Mo deposit to the Tonglushan Cu-Fe-Au deposit, and finally to the Ruanjiawan W-Cu-Mo deposit. The Hf content in zircon is negatively correlated with the Ti-in-zircon temperatures, reflecting the fractional crystallization during magma evolution and cooling. The Ti-in-zircon temperatures for the Ruanjiawan granodiorite range from 660°C to 727°C, similar to the crystallization temperatures of zircon in the regional Tongshankou granodiorite and Tonglushan quartz diorite. This study demonstrates that the trace element compositions of zircon, such as Eu/Eu*, Dy/Yb, and Ce4+/Ce3+ ratios, are effective indicators of magmatic differentiation, oxygen fugacity, and water content characteristics. Zircon thus serves as a powerful tool for identifying granitoids with potential for skarn mineralization. |
