| 内蒙古西胡里吐盆地下白垩统大磨拐河组沉积相及砂岩型铀矿成矿作用 |
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| 引用本文： | 董文明,李子颖,郭庆银.内蒙古西胡里吐盆地下白垩统大磨拐河组沉积相及砂岩型铀矿成矿作用[J].古地理学报,2005,7(4):509-517. |
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| 作者姓名： | 董文明 李子颖 郭庆银 |
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| 作者单位： | 核工业北京地质研究院 北京 100029 |
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| 基金项目： | 国防科工委核能开发项目 |
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| 摘 要： | 西胡里吐盆地是一个早白垩世断陷盆地，盆地盖层由下白垩统大磨拐河组构成。受同沉积断裂作用的影响，盆地的古地理格局总体为南陡北缓，南部主要发育冲积扇相、扇三角洲相，盆地北部以河流相、三角洲相为主，仅上部层位发育冲积扇相，而盆地中部的广大区域则以巨厚的湖泊相沉积占优势。大磨拐河组可进一步划分为三个岩性段。第一段形成于盆地断陷发育的初始阶段，以冲积扇、河流、三角洲发育为特征；第二段形成于湖泊迅速扩张至最大时期，沉积了一套巨厚的湖相泥岩，构成盆地盖层的主体，在晚期有河流、三角洲等粗碎屑沉积；第三段以冲积扇的极大发育为特征，代表盆地进入萎缩阶段。三个段总体表现为一段、三段岩性粗、煤层少且薄，二段岩性细、泥岩厚、煤层发育多。从第一段到第三段，基本构成了盆地一次完整的沉积充填历史。主要含矿层位大磨拐河组的沉积特点不仅控制着盆地内铀矿化的空间展布，而且也控制着本区的铀矿化类型。“粗～细～粗”的地层结构特点决定了本区的铀成矿作用主要发生于湖泊最大扩张的上部地层，即第二段上部及第三段的粗碎屑沉积物中，主要矿化层位为该套地层内的冲积扇、辫状河与三角洲相沉积，含矿岩石主要为渗透性好、富含有机质的砂砾岩、砂岩；同时由于上部含矿层位具有“砂多泥少”的特点，决定了本区铀矿化类型主要为具垂直分带的潜水氧化带型，仅局部存在潜水转层间氧化带型。
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| 关 键 词： | 内蒙古 西胡里吐盆地 下白垩统 沉积相 砂岩型铀矿 潜水氧化带型 |
| 文章编号： | 1671-1505（2005）04-0509-09 |
| 收稿时间： | 2005-04-03 |
| 修稿时间： | 2005-05-25 |
Sedimentary facies and sandstone-type uranium mineralization of the Damoguaihe Formation of Lower Cretaceous in Xihulitu Basin, Inner Mongolia |
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| Dong Wenming,Li Ziying,Guo Qingyin.Sedimentary facies and sandstone-type uranium mineralization of the Damoguaihe Formation of Lower Cretaceous in Xihulitu Basin, Inner Mongolia[J].Journal of Palaeogeography,2005,7(4):509-517. |
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| Authors: | Dong Wenming Li Ziying Guo Qingyin |
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| Institution: | Beijing Research Institute of Uranium Geology, Beijing 100029, China |
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| Abstract: | Xihulitu Basin is an Early Cretaceous downfaulted basin and the Damoguaihe Formation of lower cretaceous is its depositional cover. Influencing by syndepositional fault in southern margin, the alluvial fan and fan delta facies are developed mainly in the southern part of the basin while the braided stream and delta facies are developed in its northern part, only alluvial fans developed in its upper strata. However, the very thick lacustrine sediments are dominant in the central part of the basin. Studies of sedimentology show that the Damoguaihe Formation can be further subdivided into three members. The first member is developed in the beginning of downfaulted period during which alluvial fan, stream and delta facies are mainly developed; and the second member, which is the main component of the depositional cover, is formed in the extensively enlarged period of the lacustrine basin with very thick lacustrine mudstone, while the stream and delta facies are dominant at the end of this period. However, the third member features with the large-scale alluvial fan facies, which shows that the basin enters the shrinking stage of its evolution. The above characteristics of the Damoguaihe Formation reveal that the sedimentary facies plays an important role in controlling both the distribution and the type of mineralization of the epigenetic sandstone-type uranium deposits in the region. The stratigraphic structure of “coarse - fine - coarse” in granularity from bottom to top of the cover determines that the uranium mineralization mainly occur in the upper of depositional cover, that is, in the coarse detrital sediments in the upper of the second member and in the third member; main ore-bearing beds are in the alluvial fan, braided stream and delta facies of the second and third members, and the U-bearing host rocks are mainly the glutinite and sandstone of granule-supported massive and crossbedding litho-facies, which is abundant in organic matter and good in infiltration. At the same time, due to lack of the mudstone layer, which usually acts as groundwater confining bed, the uranium mineralization in the region is typically a kind of phreatic oxidized mineralization with vertical zoning, while phreatic - interlayered oxidized mineralization is only developed locally. |
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| Keywords: | Inner Mongolia Xihulitu Basin Lower Cretaceous sedimentary facies sandstone-type uranium deposit phreatic oxidized mineralization |
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