Coupled uranium mineralisation and bacterial sulphate reduction for the genesis of the Baxingtu sandstone-hosted U deposit, SW Songliao Basin, NE China
Coupled uranium mineralisation and bacterial sulphate reduction for the genesis of the Baxingtu sandstone-hosted U deposit, SW Songliao Basin, NE China
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DOI：
10.1016/j.oregeorev.2016.11.013
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发表时间：
2017-04-01
影响因子：
3.3
通讯作者：
Cai, Jiangfang
中科院分区：
文献类型：
--
作者：
Bonnetti, Christophe;Liu, Xiaodong;Cai, Jiangfang
吉林图铀存款是一个典型的氧化还原前缘板状铀存款矿床，产于松辽盆地后裂谷期辫状河环境下的晚白垩世姚家组砂岩中。本研究提出了第一个成矿模式的Xingtu存款，并提供了新的数据，通过岩相学观察，全岩地球化学，地球化学和/或矿物学研究的二硫化铁，铀矿物，铁钛氧化物（EPMA，LA-ICP-MS），和有机质（REP）的砂岩型矿床的铀矿化的成因过程。用西姆斯原位测量了不同世代的硫化亚铁的δ S-34值。在区域原生还原砂岩中，（全岩U平均值= 7.6 ppm）在蚀变铁-钛氧化物上被识别，沿着在有机质上有少量浓度（分别占全岩铀含量的26.3%及1.3%），两者共同代表矿化的重要铀源。另外的矿石前铀浓度也可能与粘土矿物有关。岩相学观察和REP数据表明，宿主砂岩中存在的有机质主要继承自陆地植物，对应于III型或IV型干酪根。矿石阶段的二硫化铁主要以草莓状体和有机质的替代物或以半自形到自形胶结物和晶体的形式出现。在framboids内检测到的微量元素特征可能指示主要来自单一事件的形成。替代有机质的硫同位素δ S-34值为-72.0 ~-6.2ppm，表明硫来源于细菌硫酸盐还原作用，这主要是（1）从Fe-Ti氧化物和有机质中释放U，（2）生成矿石阶段的二硫化铁，（3）铀的生物还原作用;（4）次生富H_2S还原屏障的产生也参与了铀的还原作用。铀酰和硫酸根离子通过主机砂岩运输低温含氧地下水和U（IV）沉淀在氧化还原界面的纳米到微晶的沥青铀矿和coffinite，主要与细菌基质和共生与生物成因的二硫化铁或直接与有机质和残留的Ti-Fe氧化物。铀矿化并没有取代矿石阶段的二硫化铁。因此，结合矿物学、地球化学和同位素特征的乌宁图板状铀存款主要是生物过程的铀矿化的成因，（C）2016 Elsevier B. V.保留所有权利。
The Baxingtu deposit is a typical redox front tabular-shaped uranium deposit hosted in sandstones of the Late Cretaceous Yaojia Formation deposited within a braided river environment during the post-rift stage of the Songliao Basin, in northeast China. This study proposes the first metallogenic model for the Baxingtu deposit and provides new data on genetic processes involved in the uranium mineralisation of sandstone-type deposits that were characterised through petrographic observations, whole-rock geochemistry, and geochemical and/or mineralogical study of iron disulphide, uranium minerals, Fe-Ti oxides (EPMA, LA-ICP-MS), and organic matter (REP). The delta S-34 value has been measured in situ by SIMS on the different generations of iron disulphide.Within regional primary reduced sandstones, pre-ore uranium enrichment (U-mean = 7.6 ppm in whole rock) was identified on altered Fe-Ti oxides along with minor concentrations on organic matter (respectively 26.3% and 1.3% of the whole-rock U content), which together represent a significant source of uranium for the mineralisation. Additional pre-ore uranium concentrations may also be associated with clay minerals. Petrographic observations and REP data indicate that organic matter occurring in the host sandstone is mainly inherited from land plants and corresponds to type III or type IV kerogens. Ore stage iron disulphides largely occur as framboids and in replacement of organic matter or also as subidiomorphic to idiomorphic cement and crystal. Trace element signatures detected within framboids are likely indicative of formation mainly from a single event. Framboids and iron disulphide in replacement of organic matter have a light sulphur isotope signature characterised by delta S-34 values from -72.0 to -6.2 parts per thousand, suggesting that sulphur originated from bacterial sulphate reduction, which was mainly responsible for (1) the liberation of U from Fe-Ti oxides and organic matter, (2) the generation of ore-stage iron disulphides, (3) the bioreduction of uranium and (4) the production of a secondary H2S-rich reducing barrier also involved in uranium reduction. Uranyl and sulphate ions were transported through the host sandstone by low-temperature oxygenated groundwater and U(IV) was precipitated at the redox interface as nano to microcrystals of pitchblende and coffinite, dominantly associated with bacterial substrate and as intergrowth with biogenic iron disulphide or directly associated with organic matter and residual Ti-Fe oxides. The uranium mineralisation does not replace ore-stage iron disulphides. Therefore, the combined mineralogical, geochemical, and isotopic characteristics of the Baxingtu tabular uranium deposit characterise dominantly biogenic processes for the genesis of the uranium mineralisation, (C) 2016 Elsevier B.V. All rights reserved.