【摘要】：鄂爾多斯盆地北部是我國重要的砂巖型鈾礦床分布區(qū),已先后發(fā)現(xiàn)東勝、大營、納嶺溝等多個(gè)大型鈾礦床�？辈楹脱芯勘砻�,這些鈾礦床的儲(chǔ)層均為侏羅系直羅組下段砂巖,其形成和分布受控于儲(chǔ)集砂體的沉積特征。因此,開展鈾礦床儲(chǔ)集層沉積特征的研究,對于指導(dǎo)砂巖型鈾礦的勘查開發(fā)和資源預(yù)測具有重要意義。本文以鄂爾多斯盆地北部為研究區(qū),重點(diǎn)對直羅組下段地層的分布、劃分對比、沉積相類型及其與鈾成礦關(guān)系開展詳細(xì)研究,以期為盆地北部砂巖型鈾礦床的勘查和開發(fā)工作提供沉積學(xué)方面的依據(jù)。通過露頭實(shí)測、測井資料統(tǒng)計(jì)分析,認(rèn)為直羅組地層整體連片分布于鄂爾多斯盆地內(nèi),總體呈西部厚東部薄的變化趨勢;垂向上直羅組可劃分出2個(gè)明顯的由粗變細(xì)的沉積旋回,進(jìn)而可以分為下、上2段,并進(jìn)一步將直羅組下段劃分為兩個(gè)亞段。其中下段下亞段和上亞段的地層厚度、砂巖厚度均呈西北部厚東南部薄的變化趨勢;上段地層厚度呈西南部厚東北部薄的變化趨勢,砂巖厚度呈西南、東北部厚、東南部薄的變化趨勢。通過典型井、野外露頭剖面和巖心資料沉積相分析,在直羅組中識(shí)別出河流相(礫質(zhì)辮狀河、砂質(zhì)辮狀河、曲流河)和辮狀河三角洲相沉積。結(jié)合野外古水流測量統(tǒng)計(jì)和巖樣薄片觀察分析,推測盆地北部直羅組存在北部,西北和西部三個(gè)物源。物源主要來自盆地以北陰山—大青山—狼山一帶的前寒武變質(zhì)巖和巖漿巖系,并有晚古生代中酸性巖漿巖的加入。物源方向總體為由北西指向南東方向。通過對直羅組砂巖厚度、砂地比值平面展布特征的分析,認(rèn)為直羅組下段下亞段主要發(fā)育礫質(zhì)、砂質(zhì)辮狀河沉積,盆地東北部邊緣地區(qū)發(fā)育辮狀河三角洲沉積;下段上亞段靠近物源區(qū)的地區(qū)主要發(fā)育砂質(zhì)辮狀河沉積,遠(yuǎn)離物源區(qū)演化為流河沉積;上段以曲流河沉積為主,僅在杭錦旗以北地區(qū)發(fā)育砂質(zhì)辮狀河沉積。分析認(rèn)為直羅組沉積期經(jīng)歷了初始發(fā)育、擴(kuò)張、鼎盛及萎縮4個(gè)演化階段,氣候環(huán)境由濕潤還原轉(zhuǎn)變?yōu)楦珊笛趸h(huán)境。運(yùn)用經(jīng)驗(yàn)公式對東勝和杭錦旗地區(qū)鈾儲(chǔ)層骨架砂體的規(guī)模進(jìn)行定量恢復(fù),認(rèn)為沉積體系對于鈾礦床的分布有著重要的控制作用。其中辮狀河沉積體系下的單砂體厚度在2m～10m之間,砂體寬度約380m～3800m,寬厚比介于150～400,具大規(guī)模、高寬厚比、泛連通等特點(diǎn),可以為含礦流體的運(yùn)移和儲(chǔ)集提供有利空間,且砂體富含黃鐵礦、炭屑等有機(jī)質(zhì),是鈾礦床的最佳儲(chǔ)集層。結(jié)合勘查實(shí)際,認(rèn)為盆地西緣有較大的鈾礦勘查潛力。
[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.
【學(xué)位授予單位】：西北大學(xué)
【學(xué)位級(jí)別】：碩士
【學(xué)位授予年份】：2017
【分類號(hào)】：P619.14
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本文編號(hào)：2260865