当前位置: X-MOL 学术Petrology › 论文详情
Our official English website, www.x-mol.net, welcomes your feedback! (Note: you will need to create a separate account there.)
Behavior of the 238 U, 235 U, and 234 U Isotopes at Weathering of Volcanic Rocks with U Mineralization: A Case Study at the Tulukuevskoe Deposit, Eastern Transbaikalia
Petrology ( IF 1.5 ) Pub Date : 2019-08-08 , DOI: 10.1134/s0869591119040027
I. V. Chernyshev , V. N. Golubev , A. V. Chugaev , G. V. Mandzhieva , B. I. Gareev

Abstract

The trend fractionation of the 238U and 235U isotopes and the extent of this process at the oxidative weathering of uranium minerals were evaluated by studying the variations in the U isotope composition of rocks, minerals, and fracture waters sampled in the quarry of the broadly known Tulukuevskoe uranium deposit in the Streltsovskoe ore field, eastern Transbaikalia. In the rock block in question, fine uranium minerals disseminated in the rocks were weathered under the effect of oxidizing fracture waters. Uranium isotope composition was measured in 22 water samples, eleven samples of the mineralized rocks, and eight uranium minerals. High-precision (±0.07‰, 2SD) measurements of the 238U/235U were carried out by MC-ICP-MS, using a 233U–236U double spike. The results involve the 238U/235U and 234U/238U ratios and the overall range of the δ238U variations determined in the rocks and waters (from –0.13 to –1.0‰ and from –0.22 to –0.59‰, respectively). Interaction between the waters and rocks induces U(IV) → U(VI) oxidation, U(VI) transfer into the aqueous phase, and 0.15–0.28‰ enrichment of U dissolved in the water in the 235U isotope. When the pitchblende is replaced by U(VI) minerals, the 238U and 235U isotopes also fractionate with ~0.3‰ enrichment of the younger U(VI) mineral phases in the light 235U isotope. The 238U/235U and 234U/238U ratios are proved to correlate, and hence, the fractionation of the 238U and 235U isotopes and the enrichment of the aqueous phase in the light 235U isotope proceed simultaneously with the well known shift in equilibrium the 238U–234U system with the accumulation of excess amounts of the 234U in the aqueous phase. Uranium leaching from uranium minerals, which is associated with the enrichment of the aqueous phase in excess amounts of the 234U isotope, can be viewed as a process that controls isotope fractionation in the 238U–235U system. This should be taken into account in describing the fractionation mechanism of the 238U and 235U isotopes at U(IV) → U(VI) oxidation. The fractionation of the 238U and 235U isotopes, which results in the isotopic “lightening” of U in the aqueous phase, largely controlled the complicated distribution pattern of the 238U/235U ratio in the quarry. In addition to isotope fractionation, this distribution was likely also affected by isotope exchange between uranium dissolved in the water and uranium in the finely dispersed minerals. The isotopically light uranium of the water could participate in forming U(VI) minerals at lower levels of the quarry.


中文翻译:

238 U,235 U和234 U同位素在具有U矿化作用的火山岩风化中的行为:以东贝贝卡利亚东部Tulukuevskoe矿床为例

摘要

通过研究广泛采石场采样的岩石,矿物和压裂水的U同位素组成变化,评估了238 U和235 U同位素的趋势分馏以及铀矿物氧化风化过程中该过程的程度。 Transbaikalia东部Streltsovskoe矿田中的已知Tulukuevskoe铀矿床。在所讨论的岩石块中,散布在岩石中的细铀矿在氧化裂隙水的作用下被风化。在22个水样品,11个矿化岩石样品和8个铀矿物中测量了铀同位素组成。238 U / 235 U的高精度(±0.07‰,2SD)测量通过MC-ICP-MS使用233 U– 236 U双尖峰。结果涉及238 U / 235 U和234 U / 238 U的比率以及在岩石和水域中确定的δ238 U变化的总范围(分别从–0.13至–1.0‰和从–0.22至–0.59‰)。 )。水和岩石之间的相互作用导致U(IV)→U(VI)氧化,U(VI)转移到水相中,并且235 U同位素中溶解在水中的U富集0.15-0.28‰ 。当沥青藻被U(VI)矿物替代时,238 U和235 U同位素也会随着轻235中年轻的U(VI)矿物相的〜0.3‰富集而分馏。铀同位素 的238 U / 235 U和234 U / 238 U比值被证实相关,并且因此,分馏238 U和235 ü同位素和在光水相中的富集235 ù同位素与公知的同时进行238 U– 234 U系统的平衡发生了变化,水相中过量的234 U积累。从铀矿中浸出铀,这与过量234的水相富集有关U同位素可以看作是控制238 U– 235 U系统中同位素分级的过程。在描述U(IV)→U(VI)氧化作用下238 U和235 U同位素的分馏机理时应考虑到这一点。238 U和235 U同位素的分馏导致水相中U的同位素“变轻”,很大程度上控制了238 U / 235的复杂分布模式采石场中的U比率。除了同位素分级分离外,这种分布还可能受到溶解在水中的铀与细分散的矿物中铀之间的同位素交换的影响。水的同位素轻铀可能参与在较低采石场形成U(VI)矿物。
更新日期:2019-08-08
down
wechat
bug