| 其他摘要 | The East Qinling area is an important Mo-Au-Pb-Zn poly-metallogenic belt in China, where numerous Pb-Zn deposits and porphyry Mo deposits related to Mesozoic magmatism were found. The Houyaoyu Pb-Zn-Fe-Mo polymetallic deposit in this paper is one representative of this type of deposits, locating in the accretion zone in southern margin of the North China Block. This paper discusses major and trace element, Sr-Nd isotopic compositions, and zircon SIMS U-Pb dating for the intrusion associated with the formation of the Houyaoyu Pb-Zn-Fe-Mo polymetallic deposit. This paper also investigates geological characteristics of the deposit and the origin of ore-forming materials and fluids, and the major conclusions are summarizd as below: 1. The implacement of igneous rocks directly resulted in the formation of the Houyaoyu Pb-Zn-Fe-Mo polymetallic deposit, and zircon SIMS U-Pb dating results indicate that the crystallization age of the porphyry intrusion is 131±1.1Ma (Early Cretaceous). This age could also represent the ore-foming age of the Houyaoyu Pb-Zn-Fe-Mo polymetallic deposit. 2. The porphyry intrusion related to the formation of the Houyaoyu Pb-Zn-Fe-Mo polymetallic deposit is divided into Houyaoyu intrusion and Mo-bearing intrusion，and exhibits massive structure and porphyritic texture, and the phenocrysts are mainly composed of orthoclase and quartz (minor biotite). The porphyrys have high SiO2 (66.1%~76.1% wt) and high alkali (K2O+Na2O= 2.15%~9.42% wt), belonging to K-feldspar granite porphyry. 3. With the increasing SiO2 contents, the contents of Fe2O3, CaO, Na2O, P2O5 gradually decrease, implying that the parental magma experienced fractional crystallization of magnetite, plagioclase, and apatite during early evolution. The granite porphyry samples exhibit LREE/HREE of 11.8~22.2, (La/Yb)N of 16.9~55.2, and slightly negative Eu anomaly, suggesting that the granite porphyry experienced high degree of evolution and fractionation of minor plagioclase. The negative Nb-Ta anomalies in the primitive mantle normalized spider diagram might be related to the residual of ilmenite and rutile or the Nb and Ta depletion in the source region, and the slightly negative Ti and P be due to crystal fractionation of sphene and apatite. The (87Sr/86Sr)i ratios of granite porphyry samples range between 0.7083 and 0.7097 (with the exception of YY-22 and YY-56), lower than that of the crust of southern margin of North China Block, indicating that mantle material was possibly involved in the formation of the granite porphyry. The (87Sr/86Sr)i ratios of YY-22 and YY-56 are 0.7345 and 0.7475, and εNd values are between -2.91 and -13.1(with the exception of YY-22 and YY-56), implying that ancient continental crust of North China Block was involved in the formation of the granite porphyry. Sr-Nd isotopic compositions indicate that the granite porphyry might be predominantly derived from the remelting of lower crust in the southern margin of the North China Block. 4. The granite porphyry samples have high saturation temperature of zirconium (849 ℃~890 ℃). Geochemical characteristics and relatively low (87Sr/86Sr)i (0.7083-0.7164) suggest that the Houyaoyu intrusion belongs to I-type granite. 5. The contents of the ore-forming elements for the ores indicate Pb, Zn, Fe, Mo, Ag, and Cu mineralization in the Houyaoyu Pb-Zn-Fe-Mo polymetallic deposit, forming a metallogenic series. Geological characteristics of the deposit show that Pb-Zn polymetallic deposit is magmatic-related hydrothermal vein type, and the Mo deposit is porphyry Mo deposit. 6. The H isotopic compositions (δDV-SMOW) in quartz are between -68 ‰ and -139 ‰, and the O isotopic compositions (δ18OV-SMOW) in quartz range between 7.1‰ and 12.1‰, similar to those of the granites, implying that the ore-forming fluids were derived from the granitic magma, probably involved with minor meteoric water. The S isotopic compositions (δ34SV-CDT) in sulfides are between 1.57 and 5.31, similar to those of t |
修改评论