Search

The Muchang composite intrusion is located about 14 km southeast of the Fengwei town and south of the Baoshan-Zhenkang block. The rift-related intrusion consists of the early-stage riebeckite nordmarkite in the east and west sides and the discontinuous marginal zone, the late-stage main body of dominant riebeckite granite, and minor aegirine granite. Studies on petrological geochemistry and LA-ICP-MS zircon U-Pb dating of the late-stage riebeckite granite, origin and evolution of the Muchang alkali granite and the relationship between the granite and the associated skarn-type Luziyuan Pb-Zn deposit are discussed in this paper. The results show that the Muchang alkali granites belong to A-type granites, which are characterized by enrichment in Al2O3, SiO2, total alkali and Fe, depletion in MgO and CaO contents with high FeOT/MgO ratios. The REE concentrations are relatively high, exhibiting highly fractionated LREE patterns with significantly Eu negative anomaly. The Muchang granites are obviously enriched in lithophile elements (e.g., Rb, K, U and Th) and high field strength elements (e.g., Zr, Hf, Nb, Y and Ga) with high 10000×Ga/Al ratios and depleted in Sr, Ba, Ti, Cr and Ni, which are similar to those of the A-type granites and quite different from those of S-type and I-type granites. The LA-ICP-MS zircon dating results of the Muchang granite gave a weighted mean age of 266.2±5.4 Ma (2σ), suggesting that they were formed in the stage of extension at the end of post-collision at Middle Permian and the consumption of Paleo-Tethys ocean took place before 266 Ma. It is suggested that the unexposed intermediate-acid intrusive rocks in the Luziyuan ore district, which is the 'sister' rocks material of the Muchang granites and related closely to Luziyuan Pb-Zn mineralization, were the product of Middle Permian. [ABSTRACT FROM AUTHOR]