Research on Metallogenic Epoch of Xiangyangping Deposit in Miaoershan Uranium Ore Field, Guangxi

In-situ analyses are important techniques in earth science researches. However, these techniques are rarely used in hydrothermal uranium deposits in South China. The lack of highprecision age of uranium minerals restrains the understanding of the metallogenies of hydrothermal uranium deposits. The typical uranium deposit including the Shazijiang, Shuanghuajiang, Menggongjie, Zhangjia uranium deposits, et al. Xiangyangping uranium deposit is the latest mediumsized deposit in the middle of Miaoershan in recent years. All uranium orebodies are veintype in shape. The uranium minerals are mainly pitchblende, uramphite, coffinite, and the gangue minerals are mainly quartz, pyrite, calcite and fluorite. The characteristics of uranium mineralization in the field show that the deposit may be the products of the multistage mineralization. Pitchblende is not only ideal sample to date uranium mineralization directly but good mineral for measurement of UPb isotope testing as well. Based on the detailed mineralogical research, the pitchblende LA-ICP-MS U-Pb isotopic analysis and electron probe element surface scanning were carried out. The uranium metallogenic chronology and ore fluid properties of the Xiangyangping deposit were revealed. The results of 41 LAICPMS analysis spots of pitchblende show that the 206Pb/238U weighted average ages can be divided into (57.4±1.1) Ma and (43.1±2.1) Ma two groups, which are consistent with the main metallogenic epoch of the Miaoershan ore field, which indicating that there is an early uranium metallogenic event of about 100 Ma in Xiangyangping uranium deposit. The results of LAICPMS show that the pitchblende is characterized by low total amount of rare earth elements, but the chondritenormalized patterns of rare earth elements are rich in lightREE, with obvious negative Eu anomalies. It is indicated that the uranium source rocks may be the Douzhashan wall rock granite. This study suggests that the early hydrothermal fluid is rich in U, Fe, S, and the local reducing environment caused by pyrite crystallization forms early pitchblende. The late fluid is relatively rich in REE, Ca and Si. The pyrite and early pitchblende are altered by the late fluid, which results in the uranium activation and migration, and precipitation of the second phase pitchblende that rich in REE, Ca and Si. The comprehensive analysis suggests that the mineralization of the Xiangyangping uranium deposit may be controlled by the late Yanshanian subduction dynamic system between Ancient Pacific plate and Eastern Asia, and exists polyphase mineralization.