内蒙古东胜铀矿区后生蚀变的稳定同位素特征及其地质意义
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摘要
近十几年来,在鄂尔多斯盆地北部伊盟隆起东胜及其以西杭锦旗一带,相继发现了东胜等系列大型-特大型砂岩铀矿,目前已成为中国砂岩铀矿发现潜力最大的地区。矿床的主要特征是矿体受直罗组砂岩绿色蚀变带控制;同时,在容矿层及其附近伴生有砂岩白色化、后生碳酸盐化及方解石脉、黄铁矿化等蚀变现象。通过后生蚀变的C、H、O、S等稳定同位素方面研究、示踪和探讨了蚀变的形成过程和成因及其与铀矿化的关系。镜下特征显示,铀矿石中存在的大颗粒结核状黄铁矿与铀矿物共生,两者为同时期的产物;该类样品S同位素表现为较大的负值,表明硫质来源的微生物作用特征明显;与盆地内可能提供硫源的直罗组煤屑、延安组煤层、延长组和延安组原油、上古生界煤系地层等有机S同位素对比,发现铀矿与上古生界煤系烃源岩的有机硫源关系密切。延安组顶部大规模白色化砂岩的高岭石H、O同位素表明,其成因与低温热液作用有关;容矿层后生方解石C、O同位素表明,其形成主要是有机质作用提供了碳源,且其碳质来源主要为上古生界气源岩,而与奥陶系及延长组油气的碳源无关。后生作用流体包裹体的测温及其H、O同位素组成表明,成矿流体以低温的大气降水为主,且与上古生界天然气一起形成低温热液的气-水混合流体;正是这一特点的流体作用形成了本区与铀矿化关系密切的上述各类后生蚀变现象。各类后生蚀变的稳定同位素特征表明,东胜铀矿床形成过程中存在后生低温热液和油气还原改造作用两大特点。本次研究结果为东胜铀矿区的成因认识提供了证据。
Some large to giant sandstone-type uranium deposits were discovered in Yimeng uplift area of the north Ordos basin, especially in Hanggin Banner-Dongsheng area, in recent decades, which suggests that this area is the most favorable potential area in search for sandstone-type uranium deposits. The main characteristics of these uranium deposits are under the control of green sandstone alteration zone in Zhiluo Formation, with some epigenetic alteration phenomena, such as the whitened sandstone, carbonation and calcite vein, and pyritization. In this paper, the authors studied and discussed systematically the formation process, genesis and the relationship with uranium mineralization by means of carbon, hydrogen, oxygen, sulfur stable isotope tracing. The microscopic observation shows that there are large particles of nodular iron pyrites in the uranium ore in association with uranium minerals, and both are products formed at the same time. The larger negative data of sulfur isotope in this type of pyritization shows that microbial effect on sulfur source quality is obvious. The sulfur isotope comparison with dispersed slack of Zhiluo Formation, coal seams of Yanan Formation, crude oil and coal-bearing Yanchang Formation and Yan'an Formation of the Upper Palaeozoic period shows that the sulfur is close to the Upper Palaeozoic coal organic sulfur. The hydrogen and oxygen isotopes of kaolinite from large white sandstone located at the top of Yan'an Formation show that the genesis was related to low temperature hydrothermal process. The carbon and oxygen isotope features of calcite from the ore-bearing bed indicate that the carbon sources were mainly provided by organic function,whereas the main carbon source was from gas source rocks of Upper Palaeozoic,with no relation to the Ordovician and Yanchang Formation oil and gas. The hydrogen and oxygen isotopic composition of the epigenetic fluid inclusions indicates that the ore-forming fluids were mainly composed of low temperature atmospheric precipitation, and formed the low temperature hydrothermal gas –water mixed solution together with gas of Upper Palaeozoic. This feature of fluid effect led to the formation of all kinds of epigenetic alteration in this area which was closely associated with uranium mineralization. In short, the kinds of epigenetic alteration of stable isotopes show that the Dongsheng uranium deposit is characterized by late epithermal solution and reformation of oil and gas. The results obtained by the authors provide evidence for the genesis of the Dongsheng uranium deposit.
Some large to giant sandstone-type uranium deposits were discovered in Yimeng uplift area of the north Ordos basin, especially in Hanggin Banner-Dongsheng area, in recent decades, which suggests that this area is the most favorable potential area in search for sandstone-type uranium deposits. The main characteristics of these uranium deposits are under the control of green sandstone alteration zone in Zhiluo Formation, with some epigenetic alteration phenomena, such as the whitened sandstone, carbonation and calcite vein, and pyritization. In this paper, the authors studied and discussed systematically the formation process, genesis and the relationship with uranium mineralization by means of carbon, hydrogen, oxygen, sulfur stable isotope tracing. The microscopic observation shows that there are large particles of nodular iron pyrites in the uranium ore in association with uranium minerals, and both are products formed at the same time. The larger negative data of sulfur isotope in this type of pyritization shows that microbial effect on sulfur source quality is obvious. The sulfur isotope comparison with dispersed slack of Zhiluo Formation, coal seams of Yanan Formation, crude oil and coal-bearing Yanchang Formation and Yan'an Formation of the Upper Palaeozoic period shows that the sulfur is close to the Upper Palaeozoic coal organic sulfur. The hydrogen and oxygen isotopes of kaolinite from large white sandstone located at the top of Yan'an Formation show that the genesis was related to low temperature hydrothermal process. The carbon and oxygen isotope features of calcite from the ore-bearing bed indicate that the carbon sources were mainly provided by organic function,whereas the main carbon source was from gas source rocks of Upper Palaeozoic,with no relation to the Ordovician and Yanchang Formation oil and gas. The hydrogen and oxygen isotopic composition of the epigenetic fluid inclusions indicates that the ore-forming fluids were mainly composed of low temperature atmospheric precipitation, and formed the low temperature hydrothermal gas –water mixed solution together with gas of Upper Palaeozoic. This feature of fluid effect led to the formation of all kinds of epigenetic alteration in this area which was closely associated with uranium mineralization. In short, the kinds of epigenetic alteration of stable isotopes show that the Dongsheng uranium deposit is characterized by late epithermal solution and reformation of oil and gas. The results obtained by the authors provide evidence for the genesis of the Dongsheng uranium deposit.
引文
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(1)赵建社,蔡义各,梁玲玲,等.煤、气、油在铀成矿过程中作用的实验模拟.国家973项目“多种能源矿产同盆共存、成藏(矿)机理与赋存条件的实验-模拟研究”专题报告.西北大学,2008.
[2]彭云彪,陈安平,李子颖,等.东胜砂岩型铀矿床特殊性讨论[J].矿床地质,2006,25(S1):249-252.
[3]向伟东,方锡珩,李田港,等.鄂尔多斯盆地东胜铀矿床成矿特征与成矿模式[J].铀矿地质,2006,22(5):257-266.
[4]李子颖,方锡珩,陈安平,等.鄂尔多斯盆地北部砂岩型铀矿目标层灰绿色砂岩成因和找矿意义[J].中国科学(D辑),2007,37(增刊Ⅰ):139-146.
[5]肖新建,李子颖,方锡珩,等.东胜砂岩型铀矿床低温热液流体的证据及意义[J].矿物岩石地球化学通报,2004,23(4):301-304.
[6]李子颖,方锡珩,陈安平,等.鄂尔多斯盆地东北部砂岩型铀矿叠合成矿模式[J].铀矿地质,2009,25(2):65-70.
[7]吴柏林,王建强,刘池阳,等.东胜砂岩型铀矿形成中天然气地质作用的地球化学特征[J].石油与天然气地质,2006,27(2):225-232.
[8]吴柏林,邱欣卫.论东胜矿床油气逸散蚀变的地质地球化学特点及其意义[J].中国地质,2007,34(3):455-462.
[9]吴柏林,魏安军,胡亮,等.油气耗散作用及其成岩成矿效应:进展、认识与展望[J].地质论评,2014,60(6):1-13.
[10]刘汉彬,夏毓亮,田时丰.东胜地区砂岩型铀矿成矿年代学及成矿铀源研究[J].铀矿地质,2007,23(1):23-29.
[11]焦养泉,陈安平,王敏芳,等.鄂尔多斯盆地东北部直罗组底部砂体成因分析--砂岩型铀矿床预测的空间定位基础[J].沉积学报,2005,23(3):371-379.
[12]刘池洋,马艳萍,吴柏林,等.油气耗散-油气地质研究和资源评价的弱点和难点[J].石油与天然气地质,2008,29(4):517-526.
[13]马艳萍,刘池洋,赵俊峰,等.鄂尔多斯盆地东北部中生界漂白砂岩的特征及其与天然气逸散的关系[J].中国科学(D辑),2007,37(增刊Ⅰ):127-138.
[14]Moulton G F.Some features of red bed bleaching[J].American Association of Petroleum Geologists Bulletin,1922,10:304-311.
[15]Reeves F.Geology of the Cement oil field,Caddo County Oklahoma[J].US.Geol.Surv.Bull.,1922,726:41-85.
[16]Levandowski D W,Kaley M E,Silverman S R,et al.Cementation in Lyons sandstone Colorado[J].American Association of Petroleum Geologists Bulletin,1973,57:2217-2244.
[17]Segal D B,Ruth M D,Merin I S.Remote detection of anomalous mineralogy associated with hydrocarbon production,Lisbon Valley,Utah[J].The Mountain Geologist,1986,23:51-62.
[18]Kirkland D W,Denison R E,Rooney M A.Diagenetic alteration of Permian strata at oil fields of south central Oklahoma,USA[J].Marine and Petroleum Geology,1995,12(6):629-644.
[19]Chan M A,Parry W T,Bowman J R.Diagenetic hematite and manganese oxides and fault-related fluid flow in Jurassic sandstones,Southeastern Utah[J].AAPG Bulletin,2000,84(9):1281-1310.
[20]Beitler B,Chan M A,Parry W T.Bleaching of Jurassic Navajo sandstone on Colorado Plateau Laramide highs:Evidence of exhumed hydrocarbon supergiants[J].Geology,2003,31(12):1041-1044.
[21]李细根,王乐民.层间氧化带中褪色带的成因及其找矿意义[J].铀矿地质,2004,20(3):151-155.
[22]黄以.塔里木盆地中新生代红层的次生还原作用与铀矿化[J].新疆地质,1997,15(1):84-89.
[23]Fu B H,Zheng G D,Ninomiya Y,et al.Mapping hydrocarboninduced ineralogical alteration in the northern Tian Shan using AS-TER multispectral data[J].Terra Nova,2007,19(4):225-231.
[24]杨晓勇,罗贤冬,凌明星.鄂尔多斯盆地含铀砂岩碳酸盐胶结物C-O同位素研究及地质意义[J].中国核科学技术大学学报,2007,37(8):979-985.
[25]冯乔,张小莉,王云鹏,等.鄂尔多斯盆地北部上古生界油气运聚特征及其铀成矿意义[J].地质学报,2006,80(5):748-752.
[26]刘友民.陕甘宁盆地北缘乌兰格尔地区白垩系油苗成因及意义[J].石油勘探与开发,1982,3:39-42.
[27]妥进才,张明峰,王先.鄂尔多斯盆地北部东胜铀矿区沉积有机质中脂肪酸甲酯的检出及意义[J].沉积学报,2006,24(3):432-439.
[28]朱西养,彭新建,汪云亮,等.新疆十红滩层间氧化带型砂岩铀矿同位素地球化学研究[J].地球化学,2004,23(4):443-451.
[29]Wu B L,Liu C Y,Wang J Q.Basical Characteristics of Fluid Geologic process of Interlayer Oxidation Zone Sandstone-type Uranium Deposit[J].Science in China(Series D)2007,50(Supp.Ⅱ):185-194.
[30]Wu B L,Xu G W,Liu C Y,et al.Alteration Effects of Hydrocarbon Dissipation in the Dongsheng Uranium Deposit,Ordos Basin--Explanation for Green Alteration and Bleaching Phenomenon[J].Energy Exploration&Exploitation,2009,27(3):181-199
[31]Wu B L,Zheng G,Zhang A J,et al.The different characteristics and geological significance of reduction alteration of sandstonetype uranium deposits in Northwest Region of China[J].Energy Exploration&Exploitation,2009,27(4):261-275.
[32]刘德长,叶发旺,张静波.东胜铀成矿区断隆成矿观点的提出及其地质意义[J].铀矿地质,2007,(1):38-42.
[33]刘池洋,赵红格,桂小军,等.鄂尔多斯盆地演化--改造的时空坐标及其成藏(矿)响应[J].地质学报[J].2006,80(5):617-638.
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