【作者】 赵晶；

【导师】 徐争启；

【作者基本信息】 成都理工大学 ， 地球化学， 2016， 硕士

【摘要】 375铀矿床是广西十万大山盆地发现的规模最大铀矿床,也是我国南方产铀盆地中发现的唯一产于侏罗系地层中且品位较高的砂岩型铀矿床。矿床含矿层位稳定,品位较高。对该矿床特征及矿床成因的研究,不仅对十万大山盆地铀矿资源调查和研究有十分重要的意义,而且对我国南方砂岩型铀矿的勘查有十分重要的理论和实践意义。本论文在收集前人资料基础上,通过野外地质调查和后期的资料整理和综合研究,对375铀矿床的地质地球化学特征进行了研究,揭示了矿床的成矿物质来源、流体来源,探讨了矿床成因。所得成果如下:（1）375铀矿床位于十万大山盆地北段东南侧,矿区内由南东向北西,依次岀露侏罗系（J）和下白垩统（K₂）地层。矿床内主要存在两个铀矿化层位:那荡组上段（J₂n³）和岽力组（J₃d）。含矿层位主要集中在侏罗系地层中的浅色岩系中,含矿浅色岩系的顶底板均为紫红色泥岩;矿体与浅色砂体的产状基本一致。在构造上位于矿区内“S”褶曲上段的轴部及其邻近的上、下翼,主要是上翼部。铀矿化在空间上与地层以及褶曲、断裂构造密切相关。（2）通过比对不同岩性样品的常量元素特征发现,各类样品中SiO₂含量占主导地位,Fe₂O₃/FeO数值指示当时形成环境偏氧化环境;通过元素的相关性分析,Fe₂O₃和MgO、TiO₂存在高度的正相关关系,在一定程度上指示物源与花岗岩有关。（3）通过微量元素分析,围岩和矿石以及贫矿石具有相同的变化趋势,不同样品的元素富集和亏损以及富集系数的变化指示,矿石在具有相同来源的同时伴随了后期的热液叠加改造作用。微量元素V/（V+Ni）比值分析,成矿环境为一个厌氧环境。通过稀土元素分析,富矿石的ΣREE低于围岩和矿化岩石,贫矿石的ΣREE几乎高于围岩的稀土含量,通过Sm-Nd和La/Yb-REE稀土元素地球化学判别图解,沉积碎屑物质可能来源于花岗岩。（4）对矿床方解石分析表明,矿区内至少存在三期方解石（分别是水平、垂直和倾斜产状）,反映至少有三次流体活动;方解石碳氧同位素特征投点图显示,方解石脉流体部分来自于深部,同时也有可能来自于海相沉积碳酸盐岩的溶解作用有关,表明了成矿流体的来源的多样性。通过硫同位素发现,硫同位素为生物成因,说明有机质对U成矿起着一定的作用。（5）综合前人资料,375铀矿床成矿年代分别是（113、61、51、38Ma）,说明该矿床是多次成矿,特别是与后期热液叠加作用有密切的关系。（6）建立了矿床成因模式。通过综合研究,认为375铀矿床是在干旱-半干旱环境的交替作用下形成了对U富集有利的砂泥互层岩性组合,在沉积成岩阶段预富集;后在后生作用阶段氧化还原作用下,富氧的大气降水将地层或富铀地质体中的铀淋滤进入砂体,在流体运移过程中六价铀不断被地层中的还原组分还原成为四价铀,在氧化还原过渡带形成层间氧化带型铀矿;在喜山期,受到构造-流体作用的影响,深部流体沿构造上移,在运移过程中不断萃取铀,叠加在先期矿体之上,形成高品位工业化铀矿床。更多还原

【Abstract】 375 Uranium deposit is the largest uranium deposit which were found in Shiwandashan basin of Guangxi,also is the only uranium deposits that founded in Jurassic formation of uranium-productive basin in southern China.The ore-bearing layers are stability,and the grade of ore are higher.The study to Characteristics of the ore deposit and genesis of mineral deposit,not only have a great significance to the investigation and research on uranium resource of Shiwandashan basin,but also has very important theoretical and practical significance to the exploration of sandstone type uranium deposit in south China.In this paper,by studying the geological and geochemical characteristics of 375 uranium deposit which based on the basis of predecessors’information collection,field geological survey and data compilation and comprehensive study,to reveal the source of ore-forming materials,fluid source of ore deposits,and discuss the genesis of ore deposit.the result is as follows:（1）375 Uranium deposit is located in southeast side of northern section in Shiwandashan basin,the mining area by the south east to north west emerges Jurassic（J）and the strata of lower cretaceous（K₂x）in turn.There are two main uranium mineralization horizon inside the Deposit:in the upper of the Nadang group（J₂n³）and Dongli group（J₃d）.The ore-bearing bed mainly existed in the rock series of Jurassic that the color is light,and the roof and floor of the rock series that the color is light are purple-red mudstone;the occurrence between Ore body and sand body with light color are basic accordance.Be located in the axis of the fold which is in the upper of the"S"and its nearby upper and lower limb on the structure,mainly on the upper wing.Uranium mineralization is closely related to the formation and fold and fault in space.（2）By comparing the characteristics of constant element samples with different lithologic,showed that SiO₂ content is dominate in all the kinds of sample,Fe₂O₃/FeO numerical indication environmental form is partial oxidation;Through the analysis of the correlation element,Fe₂O₃ and MgO,TiO₂ has highly positive correlation,to a certain extent indicate matter source related to the magmatic rocks.（3）Through the microelement analysis,surrounding rock,ore and lean ore with the same change trend,the change of the enrichment coefficient and element enrichment and loss of different samples instructed that ore with the same source accompany with the later hydrothermal superimposition reformation at the same time.V/（V+Ni）ratio analysis showed that metallogenic environment is anaerobic.Analyses of rare earth elements,ΣREE of rich ore is lower than the surrounding rock and mineralization rocks,andΣREE of the lean ore almost higher than the surrounding rock of the rare earth content,through Sm-Nd and La/Yb-REE geochemical discrimination diagram of rare earth elements,sedimentary clastic substance may be derived from granite.（4）The analysis of calcite shows that there are three periods of calcite（horizontal,vertical and inclined occurrence）at least,reflect the thermal fluid activity at least three times;the characteristics of carbon and oxygen isotope in calcite show that vein fluid of calcite part comes from the deep crust,also may come from the dissolution of carbonate rocks of marine sediment,shows that the diversity of the sources of ore-forming fluid.Through the sulfur isotope found that sulfur isotope is biogenic,and account for the organic matter plays a certain role to Uranium metallogenic.（5）Synthesize the former data,the metallogenic time of 375 uranium deposit respectively are 113,61,51,38Ma,indicated that the deposit is multi-stages mineralization,especially the later hydrothermal superimposition effect has important role.（6）Deposit genetic model is established.Through comprehensive study,considered that the ore-bearing stratum of 375 uranium deposit is sand mud interbedding lithologic combination that formed under the alternating effect of dry-semi-arid environment action,and enriched in the stages of sedimentary diagenesis;then under the action of redox in epigenesis stage,oxygen-enriched atmosphere precipitation leaching the uranium in stratum or rich uranium geological body into the sand body,in the process of fluid migration,the hexavalent uranium has been restored tetravalent uranium by reduction of components in the stratum,formed the uranium deposit of oxidation zone type in the redox transitional zone;In Himalayan period,under the influence of structure and fluid effect,deep fluid along the tectonic up constantly,and in the process of migration continuously extract uranium and superimposed on early ore body,form the industrial uranium deposit with high grade of ore.更多还原