北方盆地大规模铀成矿作用:地层篇
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1.中国地质调查局天津地质调查中心(华北地质科技创新中心);2.中国地质调查局铀矿地质重点实验室;3.法国洛林大学资源学院;4.俄罗斯科学院矿床地质、岩石学、矿物学和地球化学研究所

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P588.125; P618.2

基金项目:

国家重点研发计划项目(2023YFC2906700, 2018YFC0604200)、国家自然科学基金重点支持项目(92162212)、自然资源部青年人才项目(自然资科技函[2022]129号)、国家重点基础研究发展计划(973计划2015CB453000)、国际地球科学计划(IGCP675)、中国地质调查局地质调查工程、项目(0108, DD20230027, DD20221678, DD20190813等)联合资助.


The strata constraint on large scale sandstone-type uranium mineralization in Meso-Cenozoic basins, Northern China
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1.Tianjin Center, China Geological Survey (North China Center for Geoscience Innovation);2.Université3.de Lorraine, Gé4.oRessources;5.Institute of Geology of Ore Deposits, Petrography, Mineralogy, and Geochemistry, Russian Academy of Sciences

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    摘要:

    “红黑”耦合沉积建造是中国北方中、新生代盆地(简称北方盆地)砂岩型铀矿的重要控矿要素之一,在勘查实践中得到了广泛证实和应用,指导发现找矿靶区和矿产地300余处,在成矿理论方面取得重要进展。本文系统总结了北方产铀盆地的60万余米铀矿岩心钻探成果,通过典型矿床赋矿层沉积学、地球化学等对比研究,系统分析了北方盆地侏罗系、白垩系、新近系等赋矿层形成的沉积环境、物质组成等,进一步明确了制约成矿流体运移、铀矿物沉淀的储层条件。结果显示:(1)北方盆地侏罗纪以来,发育了I中侏罗世—晚侏罗世早期(Bathonian-Oxfordian),II早白垩世早期(Valanginian),III早白垩世晚期(Aptian),IV晚白垩世早期(Cenomanian),V晚白垩世晚期—早古近纪(Campanian-Thanetian)、VI早新近纪(Aquitanian-Burdigalian)和VII晚新近纪(Zanclean-Piacenzian)7套红层,与下伏富还原性组分的黑色层构成了典型的对偶沉积建造,为北方盆地大规模成矿奠定了储层基础;(2)地球化学指标显示:红层中Fe2+/Fe3+比值介于0.29~1.47,平均值为0.79,中位数为0.75(n=78),黑层Fe2+/Fe3+比值介于0.57~53.96,平均值为4.29,中位数为2.82(n=223),赋矿层Fe2+/Fe3+比值介于1.00~26.45,平均值为7.01,中位数为4.62(n=52)。赋矿层、黑层Fe2+/Fe3+比值一般大于1,以发育黄铁矿、碳屑、油斑为特征,为相对较还原的环境。红层Fe2+/Fe3+比值一般小于1,以发育钙质结核为特征,为相对较强氧化的环境。(3)有机地球化学总有机碳含量显示红层为0~0.16,平均0.046,中位数0.041(n=107),含矿层为0.01~2.65,平均值为0.32,中位数为0.14(n=137),黑层为0.01~2.66,平均值为0.36,中位数为0.18(n=339),含矿层略低于黑层总有总机碳含量,与铀矿的富集沉淀有密切关系。(4)砂岩型铀矿体呈“板状”或“楔状”产出于黑层顶部的灰色、灰绿色砂岩和细砂岩,甚至泥岩,红层为含氧含铀流体的运移通道,黑层为含氧含铀流体的富集沉淀的化学屏障。因此,北方盆地红层和黑层对偶沉积、旋回充填是大规模铀成矿必要的地层条件,这些认识打破常规思维,“红黑”旋回叠加导致了北方盆地多层成矿的现象,矿体一般呈板状就位于红层和黑层的过渡带,这对深入理解砂岩型铀矿成矿环境、成矿规律及成矿机理等工作和勘查工作部署具有重要实践意义。

    Abstract:

    The "red-black" coupling sedimentary architecture is one of the most important ore-control features of sandstone-type uranium deposits in the Middle and Cenozoic basins of the Northern China (referred to as the Northern Basins), which has been widely validated and applied in exploratory strategies. Simultaneously, more than 300 prospecting targets and orefields have been detected, and the the metallogenic theories have made considerable progress. The findings from more than 600,000 meters of boreholes in the Northern Basins are methodically summarized in this publication. Additionally, a comparative analysis of the sedimentology and geochemistry of typical deposits serves as the basis for a thorough assessment of the depositional conditions and material compositions of the Cenozoic, Cretaceous, and Jurassic reservoirs in the Northern Basins. This gave additional insight into the actual reservoir conditions that control metallogenic fluid flow and uranium mineral precipitation. The findings demonstrate the Northern Basin has developed seven sets of red beds since the Jurassic: (1) I. the Middle Jurassic-Early Late Jurassic (Bathonian-Oxfordian) red beds, II. Early Cretaceous (Valanginian) red beds, III. Late Early Cretaceous (Aptian) red beds, IV. Early Late Cretaceous (Cenomanian) red beds, V. Late Late Cretaceous-Early Palaeocene (Campanian-Thanetian) red beds, VI. Early Cenozoic (Aquitanian-Burdigalian) red beds, VII. Late Cenozoic, (Zanclean-Piacenzian) red beds. The red beds, along with the underlying black organic-rich strata, built upon the reservoir foundations for large-scale uranium mineralization in Northern Basins. (2) Geochemical indicators show that the Fe2+/Fe3+ ratio in the red strata range from 0.29 to 1.47, with an average value of 0.79 and a median of 0.75 (n=78), the Fe2+/Fe3+ ratio in the black strata range from 0.57 to 53.96, with an average value of 4.29 and a median of 2.82 (n=223), and the Fe2+/Fe3+ ratio in the orebodies range from 1.00 to 26.45, with a average value of 7.01 and a median of 4.62 (n=52). The growth of pyrite, carbon debris, and oil spots, which indicate the reduced environments, are characteristics of the orebodies and black strata with Fe2+/Fe3+ ratios that are typically more than 1. The red strata's Fe2+/Fe3+ ratio is typically less than 1, and they are distinguished by the formation of calcareous nodules that presenting strong oxidising environment. (3) As to the carbon content, the red strata range from 0 to 0.16, with an average of 0.046 and a median of 0.041 (n=107), the orebodies range from 0.01 to 2.65, with an average of 0.32 and a median of 0.14 (n=137), and the black strata range from 0.01 to 2.66, with an average of 0.36 and a median of 0.18 (n=339). Additionally, the enrichment and precipitation of uranium are intimately tied to the orebodies' carbon content that slightly less than the black strata. (4) Red beds, black strata, and sandstone-type uranium ore reside together closely in space. The uranium ore bodies usually occurred at the transitional zones between the red beds and black strata. The oxygenated uranium-bearing fluids migrate through the red beds, progressively eating away at the black strata' reducing medium and causing mineralization to occur. This process continues deep into the basin's interior. The ore bodies are mostly tabular-like and occur in gray, grayish green sandstone, fine sandstone, and even in mudstone. Large-scale uranium concentration and mineralization are not appropriate for regions with excessive oxidation or reduction. Large-scale uranium mineralization in the Northern Basins requires paired deposition and cyclic filling of the red and black strata. In the Northern Basins, the superposition of "red and black" strata results in multi-layer mineralization. This has significant practical implications for the deployment of exploration efforts as well as for a thorough understanding of the metallogenic environment, regularity of ore formation, and metallogenic mechanism.

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  • 收稿日期:2023-12-25
  • 最后修改日期:2024-03-23
  • 录用日期:2024-04-13
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