The genesis and Rb mineralization of the Changlingjian granite porphyry, eastern Jiangnan Orogenic Belt. Acta Petrologica Sinica

作者：Zhang Fei; Zhang DaYu^*; Weng WangFei; Wei DaoZhong; Wang Jing; Jiang ZhongRen; Hou ShuYa; Zhou TaoFa

来源：ACTA PETROLOGICA SINICA, 2023, 39(6): 1649-1673.

DOI：10.18654/1000-0569/2023.06.05

• A -type granite
• Nd-Hf isotope
• Rb mineralized intrusion
• Eastern Jiangnan Orogenic Belt

In the eastern Jiangnan Orogenic Belt ( EJOB), the Changlingjian granite porphyry is characterized by high Rb concentration according to recent exploration result, which opened a window to understand the genesis of EJOB granitoids and their Rb mineralization mechanism. Based on the geological characteristics of the granite porphyry in Changlingjian W deposit, the LA-ICP-MS U-Pb zircon age of the granite porphyry is 122.7 +/- 1. 8Ma ( n =14, MSWD =1. 3), which is the known latest Yanshanian granitoid in EJOB district. The Changlingjian granite porphyry exhibits high Si02 ( 75. 67% similar to 76. 71%), alkaline ( Na2O + K2O= 7. 12% 7. 77%), Rb (471 x 10(-6) similar to 512 x 10(-6)) and Sigma REE ( 501.0 x 10(-6) similar to 563.2 x 10(-6)) concentrations, characterized with high differentiation index ( DI = 91.8 similar to 92. 8), high Rb/Sr ratios (12. 2 - 17. 4), and distinctly negative Eu abnormality ( delta Eu = 0. 07 O. 08), which are discriminated as high potassium calc-alkaline and peraluminous A2 type granite. Isotope geochemistry shows that the granite -porphyry has weakly negative epsilon(Nd)( t) values ( - 2. 3 similar to - 2. 1) and weakly negative to weakly negative positive epsilon(Hf) t) zircons values ( - 4. 8 similar to + 4. 5), with coherent two -stage Nd isotopes model ages (1107 similar to 1091Ma). The comprehensive comparison with Yanshanian granites in the EJOB shows that the Changlingjian granitic melt is the remelting product of residual F -rich granulite basement ( rich in biotite) affected by mantle mixing and heating, and undergone significant fractional crystallization during its emplacement. The favorable magmatic factors of Rb enrichment in Changlingjian granite porphyry can be summarized as: (1) remelting of biotite -rich residual F -rich granulite basement, (2) high F, ( 3) low H2O and (4) reduced magma. The late Yanshanian stage (135 -120Ma) EJOB granite intrusions with similar geochemical features with Changlingjian granite porphyry have Rb and related rare metal metallogenic potential.