东胜铀矿砂岩中方解石富集及铀矿成因

东胜铀矿区方解石富集特征、无机碳氧同位素以及邻近气藏包裹体捕获压力、有机碳同位素和~3He/~4He的相关研究表明,东胜铀成矿与深层天然气存在密切关系。方解石的δ~(13)C值-19.6‰~-1.11‰,δ~(18)O值-17.13‰~-9.00‰,δ~(13)C值的变化范围较宽,可能是地表水和深层天然气影响程度不同所致。鄂尔多斯盆地北部气藏储层包裹体捕获压力从深部向浅部和从盆地西南向东北方向逐渐降低的变化趋势表明,天然气为铀的转化提供了充足的还原剂,为大型东胜铀矿形成提供了必要条件。天然气中~3He/~4He比值证明东胜直罗组铀矿砂岩中没有有意义的幔源流体贡献。这些证据表明东胜铀矿砂岩中的方解石是地表水和深部天然气共同作用的结果,这暗示了东胜大型铀矿床是由低温混合成矿作用形成的。

Study on the Source of Ore-forming Fluid and Ore-forming Material of the 302 Uranium Deposit in Northern Guangdong Province :Evidence from H-O-Sr-Nd Isotope Geochemistry

The 302 uranium deposit, located at the eastern part of the Zhuguangshan granite composite in northern Guangdong province which is the most important large ore-concentrated area of granite-hosted uranium deposit in China, is a large-scale, deeply buried and largely vertical mineralized granite-hosted uranium deposit. Uranium ore bodies occur mainly as vein type, flat beanpod-like and lens-like, and are hosted within hydrothermally altered fault zones in the Indosinian Youdong granite and the early Yanshanian Changjiang granite. And the dominant uranium-bearing mineral is pitchblende. Despite intensive research over the past few decades, the source of ore-forming fluid and ore-forming material of this uranium deposit remains controversial. The results of hydrogen and oxygen isotopes in this article show that δDH2O and δDH2O values of ore-forming fluids range from -7.09‰ to 3.24‰ and from -105‰ to -63‰ , respectively, indicating that ore-forming fluids were mainly formed by deeply circulating meteoric water which have experienced water-rock interaction. The relatively low δDH2O value may be caused by hydrothermal boiling action of ore-forming fluids or mixing up with small amount of organic water ( δOH2O -90‰ to -250‰) in the process of deep circulation. The εNd(t) values (-11.9 to -11.4) and rare earth element distribution patterns of the fluorite of metallogenic period are similar to those of the Changjiang granite but obviously different from those of the Youdong granite. Fluorites are in or near the scope of Changjiang granite in Gd/Yb-Nb/Ta diagram, indicating that uranium source of the 302 deposit was mainly derived from the Changjiang granite.