Dizhi lixue xuebao (Dec 2023)
Geochronology and petrogeochemical characteristics of U-bearing granites in the Dongshang deposit, northwestern Jiangxi, China and its geological significance
Abstract
The Dongshang Uranium Deposit is situated in the southern section of the Ganfang Pluton in the Jiuling Orogenic Belt of northwestern Jiangxi Province. The U-bearing granites consist mainly of medium- to coarse-grained, porphyritic biotite(binary) granite. Through zircon and monazite U-Pb geochronology, petrology, and rock geochemistry studies, the U-bearing granites' age, source characteristics, and rock genesis were determined, and their uranium metallogenic potential was also discussed. The LA-ICP-MS analysis showed that the zircon U-Pb intercept and weighted average ages are both 152±1 Ma, and the monazite U-Pb intercept and weighted average ages are 151±1 Ma and 151±2 Ma, respectively, indicating the formation of the U-bearing granites during the early Yanshan period. The major elements exhibit the characteristic of high silica content (SiO2 ranging from 72.1% to 75.6%), high alkalis content (K2O+Na2O ranging from 7.26% to 8.43%), potassium-rich and sodium-poor (K2O/Na2O=1.07 to 1.42), high aluminum (A/CNK=1.12 to 1.29), low titanium content (TiO2 ranging from 0.07% to 0.17%), and iron-poor magnesium (FeOT ranging from 0.75% to 1.28%, MgO ranging from 0.19% to 0.31%), classifying the U-bearing granites as high potassium calcalkaline peraluminous granites. Trace elements Ba, Sr, Nb, and Ti are depleted, while Rb, U, Pb, and Ta are enriched, representing a typical low Ba, Sr granite. The total rare earth elements (ΣREE) are relatively low (∑REE=21.6×10−6 to 50.7×10−6), exhibiting a right-dipping light rare earth enrichment pattern with a prominent negative Eu anomaly, which belongs to S-type granites. Based on geochronology and rock geochemical features, it's suggested that the Dongshang U-bearing granites were formed during the syn-collision compressional setting, resulting from the partial melting of the muscovite-rich metapelites of the Anlelin Formation in the Neoproterozoic Shuangqiaoshan Group. High uranium content, high Rb/Sr ratios, Th/U ratios less than 3, and high zircon uranium contents indicate the potential for uranium ore-forming conditions within these granites.
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