陕西小花岔铀矿床地质地球化学特征与矿床成因

发布时间：2018-07-02 07:11

  本文选题：小花岔铀矿床 + 花岗伟晶岩　； 参考：《中国地质大学(北京)》2017年硕士论文

【摘要】：陕西小花岔铀矿床是一个典型的伟晶岩型铀矿床,位于北秦岭丹凤铀矿成矿区的东北部,是近年来新发现的一个铀矿床类型。本文在详细野外地质基础上,通过对矿床野外地质特征、矿区花岗质岩石岩相学特征、岩浆岩年代学、岩石地球化学特征和同位素地球化学的综合研究获得以下认识:矿床赋存于古元古界秦岭群地层中,其矿体产生在黑云母花岗伟晶岩和黑云斜长片麻岩的接触带同化混染区。铀的赋存形式主要以晶质铀矿为主,晶质铀矿主要以分散状或浸染状分布于产铀花岗伟晶岩中,位于黑云母包晶、斜长石、更长石和黄铁矿的粒间,并与锆石、磷灰石、独居石等副矿物共生,其周围常常有金红石和钛铁矿等金属氧化物产生,少量的晶质铀矿生长在矿物中心。矿区出露的花岗质岩石如花岗闪长岩、二长花岗岩等均属于钙碱性系列;弱过铝质-过铝质的中酸性岩浆岩;矿区岩浆岩均投点于花岗岩类;在岩浆岩分类中投点于I型花岗岩区域中。本文对区内出露的花岗岩、花岗伟晶岩进行了LA-ICP-MS锆石U-Pb定年,结果表明:灰池子花岗岩的形成年龄为444±4.0Ma;高山沟花岗岩的形成年龄为422±0.82Ma;产铀黑云母花岗伟晶岩的形成年龄为417±2.6Ma;非矿黑云母花岗伟晶岩形成年龄为413±1.8Ma。花岗质岩石的Lu-Hf同位素二阶段模式年龄平均为1.4Ga,花岗岩和花岗伟晶岩具有相似的Hf同位素特征(εHf(t)值分别为-0.48与-0.40),表现有明显的同源性。产铀黑云母花岗伟晶岩由于同化混染作用和围岩的元素交换等原因,其基性组分(Fe、Mg)和挥发分(F)含量较高,并且富集大离子亲石元素LILE(Rb、Ba、K),亏损高场强元素HFSE(Nb、Ta)。在伟晶岩-片麻岩的接触带发生化学组分的元素交换,使得岩浆中U-F络合物发生分解,并且在良好的成矿条件下(围岩的铀含量较高、较好的构造环境)使得U饱和沉淀形成现有的铀矿物如晶质铀矿等。小花岔铀矿床的形成受到了伟晶岩、围岩成分、岩浆热液中的挥发分共同的作用,最终导致了铀矿床的形成。
[Abstract]:Xiaohuacha uranium deposit in Shaanxi Province is a typical pegmatite type uranium deposit located in the northeast of Danfeng uranium deposit in North Qinling Mountains. It is a newly discovered uranium deposit type in recent years. On the basis of detailed field geology, this paper analyzes the field geological characteristics of ore deposits, the petrographic characteristics of granitic rocks, the geochronology of magmatic rocks. A comprehensive study of petrogeochemical characteristics and isotopic geochemistry shows that the deposit occurred in the Paleoproterozoic Qinling Group and its orebody occurred in the contact zone of biotite granitic pegmatite and biotite obliquity gneiss. The main forms of uranium occurrence are crystalline uranium deposits, which are mainly dispersed or disseminated in uranium-producing granitic pegmatite, located in the intergranular areas of biotite peritectic, plagioclase, more feldspar and pyrite, and associated with zircon, apatite, zircon, apatite. The secondary minerals such as monazite are symbiotic, and there are some metallic oxides such as rutile and ilmenite around them, and a small amount of uranite grows in the mineral center. The granitic rocks, such as granodiorite and monzogranite, all belong to calc-alkaline series, weakly peraluminous and peraluminous intermediate-acid magmatic rocks, magmatic rocks of mining area are all located in granites; In the classification of magmatic rocks, the input point is in the I type granite area. LA-ICP-MS zircon U-Pb dating of granitic pegmatite and granitic pegmatite has been performed in this paper. The results show that the age of formation of Liqizi granite is 444 卤4.0 Ma, that of Gaosanggou granite is 422 卤0.82Ma, that of uranium-producing biotite granitic pegmatite is 417 卤2.6 Ma, and that of non-mineral biotite granitic pegmatite is 413 卤1.8 Ma. The average age of Lu-Hf isotopic two-stage model of granitic rocks is 1.4Ga.The granite and granitic pegmatite have similar HF isotopic characteristics (蔚 HF (t) = -0.48 and -0.40, respectively), showing obvious homology. The uranium biotite granitic pegmatite is characterized by assimilation mixing and element exchange of surrounding rock, which results in higher content of basic component (Feo mg) and volatile fraction (F), and enrichment of large ion lithophile element Lile (RbPe BaK) and depletion of high field strength element HFSE (NbTa). In the contact zone between pegmatite and gneiss, element exchange of chemical components occurs, which results in the decomposition of U-F complex in magma and the higher uranium content in the surrounding rock under good metallogenic conditions. The better tectonic environment causes U saturation precipitation to form existing uranium minerals such as crystalline uranium deposits and so on. The formation of Xiaohuacha uranium deposit was influenced by pegmatite, composition of surrounding rock and volatile matter in magmatic hydrothermal solution, which resulted in the formation of uranium deposit.
【学位授予单位】：中国地质大学(北京)
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：P619.14
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本文编号：2089334