Geochronology, geochemistry and petrogenesis of two-stage Indosinian granites from the Xiajiang uranium ore deposit, Jiangxi Province: Implication for Indosinian tectonics and genesis of uranium-bearing granites in South China

The Xiajiang uranium ore deposit in Jiangxi Province is one of the granite-hosted uranium ore deposits in South China. The uranium orebodies are hosted by the Jintan granitic batholith in the Jiangxi Province. Field geological survey and zircon U-Pb dating indicated that the Jintan batholith is composed of two stage Indosinian granites. The U-bearing two-mica granite was emplaced at 239 +/- 1Ma, and the porphyritic biotite granite was emplaced at 226 +/- 2Ma. The two-mica granite has high SiO2 contents (74. 09% similar to 74. 53%) and low TiO2, CaO and MgO contents. A/CNK values of the granites vary from 1. 20 to 1. 46, which is consisted with that the granite contains muscovite and garnet. The two-mica granite belongs to typical strongly peraluminous S type granite. However, the porphyritic biotite granite shows different geochemical characteristics. It has relatively higher HFSE and REE contents, lower Rb/Sr ratios and less pronounced negative Eu anomalies. A/CNK values of the porphyritic biotite granite vary from 1. 05 to 1. 13. Both of the granites have low epsilon(Nd) (t) values (-9. 0 to -8.8 for the two-mica granite and -9.8 to -9.4 for the porphyritic biotite granite) with Paleo-proterozoic model ages (1. 73 similar to 1. 75Ga for the two-mica granite and 1. 77 similar to 1. 80Ga for the porphyritic biotite granite) Geochemical and isotopic characteristics indicate that both the two-mica granite and the porphyritic biotite granite belong to S-type granite. However, the two-mica granite should be derived from anatexis of clay-rich pelitic rocks and the porphyritic biotite granite from partial melting of clay-poor psammitic rocks. We suggested that the two-mica granite formed earlier from dehydrate-melting of crust at syn-collisional compressional environment and the porphyritic biotite granite formed later at the post-collisional extensitional environment. The two-mica granite contains higher U contents, and its mineralogical and geochemical characteristics are similar to those of typical U-bearing granites in South China. Comparative studies indicate that Indosinian U-bearing granites in South China are likely formed from anatexis of pelitic rocks during syn-collisional compressional tectonic regime.