Geochronology, Geochemistry And Petrogenesis Of The Jintan Granites From The Xiajiang Uranium Ore District, Jiangxi

The Xiajiang uranium ore district is one of the most important granite-hosted uranium ore producers in South China and lies in western Xinyu Country in central Jiangxi Province. The orebodies were hosted by the Jintan granites. The Jintan granites are mainly composed of two-mica granite and the porphyritic biotite monzonite granite. Most orebodies are hosted by the two-mica granite.LA-ICPMS U-Pb dating results of zircons imply that the two-mica granite was emplaced at 239±1Ma and was an Indosinian granite. The two-mica granite has high SiO2 contents (74.09%～74.53%) and Al2O3 contents (13.54～14.27%). The A/CNK values of the two-mica granite vary from 1.20 to 1.46. Thus, the two-mica granite belongs to strongly peraluminous S-type granite. The two-mica granite is enriched in Rb, Th, U, and depleted in Ba, Sr, Eu and Ti. The two-mica granite contains low contents of rare earth elements.LA-ICPMS U-Pb dating results of zircons imply that the porphyritic biotite monzonite granite was emplaced at 226±2Ma. The biotite monzonite granite is also an Indosinian granite, but it was emplaced later than the two-mica granite. Geochemical characteristics of the porphyritic biotite monzonite granite are different from those of the two-mica granite. The porphytitic granite has lower SiO2 contents (69.14～73.77%), but higher TiO2, CaO and MgO contents than the two-mica granite. The A/CNK values of the porphyritic biotite monzonite granite vary from 1.05 to 1.13. The porphyritic biotite monzonite granite belongs to weakly peraluminous to strongly peraluminous granites. The porphyritic biotite monzonite granite is more enriched in HFSE and REE contents. It has lower Rb/Sr ratios and little negative Eu anomalies.Both the two granites have relatively lowεNd(t) values. The two-mica granite has slightly higherεNd(t) values (-9.0-8.8) than the porphyritic biotite monzonite granite (-9.8～-9.4). The two granites have paleoproterozoic model ages (the two-mica granite: 1.73～1.75Ga, the porphyritic biotite monzonite granite:1.77～1.80Ga).εHf(t) values of zircons from the two-mica granite vary from -7.8 to -4.8, with an average value of-6.0. The Hf isotopic model ages vary from 1.57 to 1.76Ga. The porphyritic biotite monzonite granite has slightly lower zirconεHf(t) values, varying from -8.3 to -4.8, with an average value of -6.6. The Hf isotopic model ages vary from 1.56 to 1.78Ga.Geochemical and isotopic characteristics imply that both the two granite belongs to S-type granites. However, the differences of geochemistry and isotopic compositions imply that the two granties formed from different crustal sources with different depths. The two-mica granite might form from partial melting of clay-rich pelitic sedimentary rocks, but the porphyritic biotite monzonite granite might from from partial melting of clay-poor psammitic rocks. Difference in the sources may reflect differences in depths for partial melting. The two-mica granite might form at the syn-collisional environment of the Indosinian Orogen, but the porphyritic biotite monzonite granite might from at the post-collisional extensional environment.The two-mica granite contains higher U contents than the porphyritic biotite monzonite granite. Combined with studies of other uranium-bearing granites in South China, it is induced that the Indosinian uranium-bearing granites in South China might be probably formed at syn-collisional environment and from partial melting of clay-rich pelitic sedimentary sources.