中亚造山带南缘天河石的成因与致色机理研究OA

The southern margin of the Central Asian Orogenic Belt(CAOB)represents one of the world's most important provinces of amazonite-bearing granites and associated rare-metal deposits.However,the genesis and coloration mechanism of amazonite remain insufficiently constrained,which limits a deeper understanding of the petrogenesis of amazonite granites and the related rare-metal mineralization(e.g.,Rb and Cs).In this study,amazonite samples were collected from five representative amazonite granite-type rare-metal deposits along the southern CAOB,namely Zhangbaoshan,Jiangjunshan,Yilanlik,Guobaoshan,and Shihuiyao.Detailed miner-alogical and spectroscopic investigations were conducted,including X-ray diffraction(XRD),Raman spec-troscopy,and UV-Vis spectroscopy,together with major-and trace-element analyses by LA-ICP-MS.The re-sults show that the mineralogical and spectral characteristics of amazonite are overall consistent with those of microcline,indicating that the primary crystal structure remains relatively stable.UV-Vis spectra generally dis-play absorption peaks at 248 nm and 382 nm and a broad absorption band between 620 and 740 nm,suggesting that color-center absorption is closely associated with the blue green hue.Trace-element data reveal systematic enrichment of Rb,Cs,and Pb in amazonite.Integrating these observations,we propose that the blue-green col-oration of amazonite is unlikely to be controlled by a single element;instead,it is more plausibly related to the coupled enrichment of Rb and Pb via isomorphous substitution for K in the feldspar lattice.Substitution of Rb+for K+induces subtle lattice adjustments,whereas substitution of Pb2+for K+,owing to charge imbalance,more readily generates localized defects that facilitate the formation of color centers,ultimately producing the charac-teristic blue green coloration.This interpretation is further supported by the UV-Vis responses linked to color-center absorption.Based on comparisons with previous studies,amazonite in the southern CAOB is inferred to have formed predominantly during the late stage of highly fractionated granitic magmatism,closely associated with the enrichment of rare metals(Rb\Cs)and the role of volatiles(e.g.,F).Amazonite is therefore suggested to be a useful indicator mineral for Rb-related rare-metal mineralization in granitic systems.