下庄矿田“交点”型铀矿床成矿机理研究及勘查思路探讨

文章通过岩石学、主微量地球化学、岩脉定年和实际勘查成果的对比研究,表明下庄矿田的中基性岩脉对铀成矿的控制作用在岩性上没有专属性。通过对中基性岩脉进行U_Pb锆石同位素测年,发现"交点"型铀矿床成矿时代与中基性岩脉成岩时代存在着巨大的矿岩时差,岩脉成岩过程中不能为铀成矿提供热源及矿化剂CO_2。对流体作用敏感的U/Th、Pb/Ce、Ba/La、Cs/Rb比值和对流体作用不敏感元素Ce/Yb比值研究为"交点"型铀成矿存在地幔流体作用提供了佐证;通过Fe~(3+)、Fe~(2+)、K_2O、Na_2O和Al_2O_3等与SiO_2线性关系的研究表明,矿化与硅化和碱交代关系密切,与其他常量元素的关系不明显。研究结果显示,中基性岩脉对铀成矿的控制作用通过对构造裂隙的控制实现,所谓的"交点"控矿本质是硅化带型铀矿化通过"界面效应"控矿的特殊表现形式,其本质是由于不同岩浆岩的产状和机械强度有所不同所致。

A study of metallogenic mechanism of "intersection" type uranium deposit and exploration thinking of Xiazhuang orefield

A comparative study of petrology, major and trace element geochemistry, dike dating and practical exploration results show that the control effect of mafic dikes in the study area has no lithologic specificity for uranium mineralization. Zircon U-Pb isotopic chronology of mafic dikes show that the time lag is huge between mafic dikes and the deposit, and the mafic dikes could not provide heat source and mineralizer (CO₂) during the rock-forming process. U/Th, Pb/Ce, Ba/La and Cs/Rb ratios are sensitive to fluid, whereas Ce/Yb ratio is not sensitive to fluid. Researches on these rations can therefore provide evidence for the effect of fluids on mafic dikes. Research on the linear relationship of Fe³⁺, Fe²⁺, K₂O, Na₂O or Al₂O₃ to SiO₂ indicate that silicification and alkali metasomatism are important for mineralization, but the contribution of other major elements is not obvious. The results show that, in the control effect of mafic dikes on uranium ore formation through the control role of tectonic fissures, the silicified zone type uranium mineralization by "the effect of interface" of mineralization is the essence of the so-called "intersection" controlling of mineralization.