鄂尔多斯盆地北部直罗组沉积特征及其与铀成矿关系
发布时间：2018-10-09 21:34
【摘要】：鄂尔多斯盆地北部是我国重要的砂岩型铀矿床分布区,已先后发现东胜、大营、纳岭沟等多个大型铀矿床。勘查和研究表明,这些铀矿床的储层均为侏罗系直罗组下段砂岩,其形成和分布受控于储集砂体的沉积特征。因此,开展铀矿床储集层沉积特征的研究,对于指导砂岩型铀矿的勘查开发和资源预测具有重要意义。本文以鄂尔多斯盆地北部为研究区,重点对直罗组下段地层的分布、划分对比、沉积相类型及其与铀成矿关系开展详细研究,以期为盆地北部砂岩型铀矿床的勘查和开发工作提供沉积学方面的依据。通过露头实测、测井资料统计分析,认为直罗组地层整体连片分布于鄂尔多斯盆地内,总体呈西部厚东部薄的变化趋势;垂向上直罗组可划分出2个明显的由粗变细的沉积旋回,进而可以分为下、上2段,并进一步将直罗组下段划分为两个亚段。其中下段下亚段和上亚段的地层厚度、砂岩厚度均呈西北部厚东南部薄的变化趋势;上段地层厚度呈西南部厚东北部薄的变化趋势,砂岩厚度呈西南、东北部厚、东南部薄的变化趋势。通过典型井、野外露头剖面和岩心资料沉积相分析,在直罗组中识别出河流相(砾质辫状河、砂质辫状河、曲流河)和辫状河三角洲相沉积。结合野外古水流测量统计和岩样薄片观察分析,推测盆地北部直罗组存在北部,西北和西部三个物源。物源主要来自盆地以北阴山—大青山—狼山一带的前寒武变质岩和岩浆岩系,并有晚古生代中酸性岩浆岩的加入。物源方向总体为由北西指向南东方向。通过对直罗组砂岩厚度、砂地比值平面展布特征的分析,认为直罗组下段下亚段主要发育砾质、砂质辫状河沉积,盆地东北部边缘地区发育辫状河三角洲沉积;下段上亚段靠近物源区的地区主要发育砂质辫状河沉积,远离物源区演化为流河沉积;上段以曲流河沉积为主,仅在杭锦旗以北地区发育砂质辫状河沉积。分析认为直罗组沉积期经历了初始发育、扩张、鼎盛及萎缩4个演化阶段,气候环境由湿润还原转变为干旱氧化环境。运用经验公式对东胜和杭锦旗地区铀储层骨架砂体的规模进行定量恢复,认为沉积体系对于铀矿床的分布有着重要的控制作用。其中辫状河沉积体系下的单砂体厚度在2m～10m之间,砂体宽度约380m～3800m,宽厚比介于150～400,具大规模、高宽厚比、泛连通等特点,可以为含矿流体的运移和储集提供有利空间,且砂体富含黄铁矿、炭屑等有机质,是铀矿床的最佳储集层。结合勘查实际,认为盆地西缘有较大的铀矿勘查潜力。
[Abstract]:The northern part of Ordos Basin is an important distribution area of sandstone-type uranium deposits in China. Many large uranium deposits such as Dongsheng, Daying and Naling Gou have been discovered successively. The exploration and study show that the reservoirs of these uranium deposits are all sandstone of the lower Jurassic Zhiluo formation and their formation and distribution are controlled by the sedimentary characteristics of the reservoir sand bodies. Therefore, it is of great significance to study the sedimentary characteristics of uranium deposits in order to guide the exploration and development of sandstone-type uranium deposits and the prediction of their resources. Taking the northern part of Ordos Basin as the study area, this paper focuses on the stratigraphic distribution, classification and correlation, sedimentary facies types and their relationship with uranium mineralization in the lower member of Zhiluo formation. It is expected to provide sedimentological basis for the exploration and development of sandstone-type uranium deposits in the northern part of the basin. Through outcrop measurement and statistical analysis of logging data, it is considered that the whole formation of Zhiluo formation is distributed in the Ordos basin, and the overall trend is thin and thick in the western part of the basin. The vertical Zhiluo formation can be divided into two distinct sedimentary cycles from coarse to fine, and then can be divided into lower and upper two sections, and the lower part of Zhiluo formation can be further divided into two subsections. The formation thickness of the lower and upper submember of the lower part of the formation and the sandstone thickness of the lower and upper submember are both thin and thick in the northwest and southeast, and the formation thickness in the upper section is thin in the southwest and the northeast, and the sandstone thickness is in the southwest and the northeast, and the thickness of the sandstone is in the southwest and the northeast. A thin trend in the southeast. The fluvial facies (gravel braided river, sandy braided river, meandering river) and braided river delta facies were identified in Zhiluo formation by analyzing the sedimentary facies of typical wells, outcrop profiles and core data. Based on the statistics of paleocurrent measurement and the observation and analysis of rock samples, it is inferred that there are three provenances in the northern part of the basin, namely, the north, the northwest and the west. The provenance mainly comes from the Precambrian metamorphic rocks and magmatic rocks in the area of Yinshan Daqingshan and Langshan north of the basin with the addition of late Paleozoic intermediate-acid magmatic rocks. The source direction is from north to west to south to east. Based on the analysis of the sandstone thickness and the distribution characteristics of sandstones in the lower part of the Zhiluo formation, it is concluded that the lower submember of the Zhiluo formation is mainly composed of gravelly, sandy braided river deposits and braided river delta deposits in the northeastern margin of the basin. Sand braided river deposits are mainly developed in the upper submember of the lower member near the provenance area, which evolved into fluvial river deposits far from the source area, and the upper member is dominated by meandering stream sediments, only developed in the area north of Hangzhou Jinqi, where sandy braided river deposits are developed. It is concluded that the sedimentary period of Zhiluo formation has experienced four stages of initial development, expansion, peak and atrophy, and the climate environment has changed from wet reduction to dry oxidation environment. The scale of uranium reservoir skeleton sand body in Dongsheng and Hangzhou Jinqi areas is quantitatively restored by empirical formula. It is considered that sedimentary system plays an important role in controlling the distribution of uranium deposits. The thickness of single sand body in braided river sedimentary system is between 2m~10m, the width of sand body is about 380 m ~ 3 800 m, the ratio of width to thickness is between 150 ~ 400, it has the characteristics of large scale, high ratio of width to thickness and pan-connectivity, which can provide favorable space for the migration and reservoir of ore-bearing fluid. The sand body is rich in organic matter such as pyrite and carbon debris, and is the best reservoir of uranium deposit. Combined with the exploration practice, it is considered that the western margin of the basin has a great potential for uranium exploration.
【学位授予单位】：西北大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：P619.14
，
本文编号：2260865
[Abstract]:The northern part of Ordos Basin is an important distribution area of sandstone-type uranium deposits in China. Many large uranium deposits such as Dongsheng, Daying and Naling Gou have been discovered successively. The exploration and study show that the reservoirs of these uranium deposits are all sandstone of the lower Jurassic Zhiluo formation and their formation and distribution are controlled by the sedimentary characteristics of the reservoir sand bodies. Therefore, it is of great significance to study the sedimentary characteristics of uranium deposits in order to guide the exploration and development of sandstone-type uranium deposits and the prediction of their resources. Taking the northern part of Ordos Basin as the study area, this paper focuses on the stratigraphic distribution, classification and correlation, sedimentary facies types and their relationship with uranium mineralization in the lower member of Zhiluo formation. It is expected to provide sedimentological basis for the exploration and development of sandstone-type uranium deposits in the northern part of the basin. Through outcrop measurement and statistical analysis of logging data, it is considered that the whole formation of Zhiluo formation is distributed in the Ordos basin, and the overall trend is thin and thick in the western part of the basin. The vertical Zhiluo formation can be divided into two distinct sedimentary cycles from coarse to fine, and then can be divided into lower and upper two sections, and the lower part of Zhiluo formation can be further divided into two subsections. The formation thickness of the lower and upper submember of the lower part of the formation and the sandstone thickness of the lower and upper submember are both thin and thick in the northwest and southeast, and the formation thickness in the upper section is thin in the southwest and the northeast, and the sandstone thickness is in the southwest and the northeast, and the thickness of the sandstone is in the southwest and the northeast. A thin trend in the southeast. The fluvial facies (gravel braided river, sandy braided river, meandering river) and braided river delta facies were identified in Zhiluo formation by analyzing the sedimentary facies of typical wells, outcrop profiles and core data. Based on the statistics of paleocurrent measurement and the observation and analysis of rock samples, it is inferred that there are three provenances in the northern part of the basin, namely, the north, the northwest and the west. The provenance mainly comes from the Precambrian metamorphic rocks and magmatic rocks in the area of Yinshan Daqingshan and Langshan north of the basin with the addition of late Paleozoic intermediate-acid magmatic rocks. The source direction is from north to west to south to east. Based on the analysis of the sandstone thickness and the distribution characteristics of sandstones in the lower part of the Zhiluo formation, it is concluded that the lower submember of the Zhiluo formation is mainly composed of gravelly, sandy braided river deposits and braided river delta deposits in the northeastern margin of the basin. Sand braided river deposits are mainly developed in the upper submember of the lower member near the provenance area, which evolved into fluvial river deposits far from the source area, and the upper member is dominated by meandering stream sediments, only developed in the area north of Hangzhou Jinqi, where sandy braided river deposits are developed. It is concluded that the sedimentary period of Zhiluo formation has experienced four stages of initial development, expansion, peak and atrophy, and the climate environment has changed from wet reduction to dry oxidation environment. The scale of uranium reservoir skeleton sand body in Dongsheng and Hangzhou Jinqi areas is quantitatively restored by empirical formula. It is considered that sedimentary system plays an important role in controlling the distribution of uranium deposits. The thickness of single sand body in braided river sedimentary system is between 2m~10m, the width of sand body is about 380 m ~ 3 800 m, the ratio of width to thickness is between 150 ~ 400, it has the characteristics of large scale, high ratio of width to thickness and pan-connectivity, which can provide favorable space for the migration and reservoir of ore-bearing fluid. The sand body is rich in organic matter such as pyrite and carbon debris, and is the best reservoir of uranium deposit. Combined with the exploration practice, it is considered that the western margin of the basin has a great potential for uranium exploration.
【学位授予单位】：西北大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：P619.14
，
本文编号：2260865
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