鄂尔多斯盆地东胜地区直罗组砂体铀的预富集与铀成矿

Pre-enrichment and metallogeny of uranium in Zhiluo Formation sand bodies of Dongsheng area, Ordos Basin

通过岩石样品U-Pb同位素反演研究了鄂尔多斯盆地东胜地区直罗组砂体的原始铀质量分数(铀含量)，其平均值达21．95×10^(-6)，具有明显的铀预富集特征；低铀质量分数样品U-Pb等时线年龄为(177±16)Ma，它是直罗组沉积时就有铀预富集强有力的证据。计算表明，岩石样品铀的近代变化系数平均为-69．4％，呈现强烈铀丢失现象，推测近矿地段砂体能为铀成矿提供丰富的铀源。为此，提出在沉积盆地寻找砂岩型铀矿应强调砂体原始铀质量分数(U_0)和铀的变化系数(△U)的研究。

Through studying U-Pb isotopes of rock samples by reversal derivation method, this paper expounds the initial uranium mass fraction in Zhiluo Formation sand bodies of Dongsheng area, Ordos Basin. The average initial uranium mass fraction is 21.95 × 10^-6, it shows that the sandstone has an obvious characteristic of uranium pre-enrichment. The U-Pb isochron age of low uranium concentration samples is（177 ±16）Ma, it is also the evidence that the sandstone had uranium pre-enrichment phenomena. The results indicate that the modern average uranium variation coefficient is -69.4 % and the uranium in the sandstone is strongly lost. It is inferred that the sandstone near ore body provided the rich uranium source for metallogeny. So the study on the initial uranium mass fraction（U0） and the uranium variation coefficient（△U） should be emphasized in searching for sandstone-type uranium deposit in basins.