扬子陆块北缘毕机沟钒钛磁铁矿床成因及成矿潜力研究

发布时间：2018-04-27 21:44

本文选题：扬子陆块北缘 + 毕机沟钒钛磁铁矿　；参考：《长安大学》2015年硕士论文

【摘要】：毕机沟大型钒钛磁铁矿床位于扬子陆块北缘汉南-米仓山构造带最北部,从大地构造位置上看,位于扬子陆块北缘和南秦岭构造带相交接部位,有利于成矿元素富集。该构造带区域上呈NE-SW向展布有一条宽约60km、长约180km的岩浆岩带,其中前人将该岩浆岩带中分布于汉中南部的岩浆岩统称汉南杂岩,前人虽然对该杂岩带中典型岩体进行了大量研究,但对于扬子陆块北缘新元古代时期构造环境仍存在分歧。本文主要通过研究毕机沟堆晶杂岩体的野外产出特征及规模,岩相组合及分带特征,典型造岩矿物及金属矿物特征,全岩主微量及稀土元素地球化学,锆石U-Pb年代学及Hf同位素特征,查明了毕机沟岩矿体岩浆演化特征、成矿时代、矿床成因以及岩浆源区特征。通过毕机沟钒钛磁铁矿床成岩成矿构造背景的研究对扬子陆块北缘新元古代构造演化提供约束,并在该岩浆岩带中寻找类似于毕机沟钒钛磁铁矿的岩体进行成矿潜力分析。主要取得了一下几点成果和认识:(1)毕机沟岩体主要由下部斜长橄榄岩相带;中下部辉长岩相带、中上部异剥辉长岩相带;上部闪长岩相带三个岩相带组成。岩石类型有橄榄岩、斜长橄榄岩、橄长岩、橄榄辉长岩、辉长岩、辉长闪长岩、闪长岩等。主要造岩矿物有橄榄石、斜方辉石、单斜辉石、斜长石和角闪石。矿石矿物主要以磁铁矿和钛铁矿为主,赋矿层位主要分布于中上部异剥辉长岩相带。(2)地球化学研究表明:毕机沟辉长岩具有拉斑玄武岩系列特征,贫Si,富Al、Ca,中等的Fe和Mg,低K、Na,在稀土元素球粒陨石标准化曲线显示出“右倾型”的平缓形式,Eu正异常,轻稀土略富集重稀土相对亏损;微量元素蛛网图中显示出富集大离子亲石元素(LILE),亏损Nb、Ta、Zr、Hf等高场强元素(HFSE),Th、U负异常以及Sr正异常特征。说明该岩体在岩浆演化过程中经历了明显的结晶分异作用,显示出了大陆边缘弧的地球化学特征。(3)对毕机沟岩体的主要岩石类型辉长岩、围岩花岗岩进行了锆石U-Pb测年,获得了辉长岩成岩年龄为766.9±4.5Ma;围岩花岗岩形成时代分别为784.2±3.6Ma和788.6±4.3Ma;同时获得穿插于良心河含钛磁铁矿基性岩体内部花岗脉岩年龄为760.2±2.9Ma。从而厘定了毕机沟地区在新元古代存在三期岩浆事件活动,毕机沟基性岩体中锆石Hf同位素研究表明岩浆源区为亏损地幔且经过地壳物质混染。
[Abstract]:Bijigou large scale vanadium titanomagnetite deposit is located in the northern margin of Yangtze block Hannan-Micangshan tectonic belt. From the geotectonic position, it is located at the junction of the northern margin of Yangtze block and the southern Qinling tectonic belt, which is favorable for the enrichment of metallogenic elements. There is a magmatic belt with a width of about 60km and a length of about 180km in the NE-SW direction. The magmatic rocks distributed in the zone in the southern part of Hanzhong are called Hannan complex by their predecessors. Although many researches have been done on the typical rock mass in the complex, there are still differences on the Neoproterozoic tectonic environment in the northern margin of the Yangtze block. In this paper, the characteristics of field production and scale, lithofacies assemblage and zoning, typical rock-forming minerals and metal minerals, main trace and REE geochemistry of the whole rock are studied. Zircon U-Pb chronology and HF isotopic characteristics have been used to identify the characteristics of magma evolution, metallogenic epoch, ore genesis and magmatic source area of the Bijingou ore body. Based on the study of diagenetic and metallogenic tectonic setting of the Bijigou vanadium titanomagnetite deposit, the Neoproterozoic tectonic evolution of the northern margin of the Yangtze block is constrained, and the ore-forming potential of the rock body similar to that of the Bijigou vanadium titanomagnetite is analyzed in this magmatic belt. The Bijigou rock body is mainly composed of three lithofacies zones: lower oblique peridotite facies belt, middle and lower gabbro facies belt, middle and upper heteropyroxene facies belt, and upper diorite facies belt. Rock types include peridotite, peridotite, olivine gabbro, gabbro, pyrodiorite, diorite, etc. The main rock-forming minerals are olivine, clinopyroxene, clinopyroxene, plagioclase and amphibole. The ore minerals are mainly magnetite and ilmenite, and the ore-bearing strata are mainly distributed in the middle and upper heteropyroxene facies belt. The geochemical study shows that the Bijigou gabbro has the characteristics of tholeiite series. Si-poor, Al-Ca-rich, medium Fe and Mg-rich, low Ka-Na. The normalized curves of chondrites show a positive anomaly of EU in the "right-dip" flat form, and a slight enrichment of heavy rare earths. The trace element cobweb shows the negative anomalies and the positive Sr anomalies of high field strength elements such as high field strength, such as the enrichment of large ion lithophile element Lilei, and the depletion of high field strength elements, such as NbBX, Tazo-ZrHf, and so on. The results show that the rock mass has undergone obvious crystallization differentiation during magmatic evolution, showing the geochemical characteristics of continental margin arc. The zircon U-Pb dating of the main rock types of the Bijigou rock body, gabbro and surrounding rock granites, has been carried out. The diagenetic age of gabbro is 766.9 卤4.5 Ma, the age of formation of surrounding rock granites is 784.2 卤3.6Ma and 788.6 卤4.3 Ma.The age of granitic dikes interspersed in the basic rocks of ilmenite bearing ilmenite is 760.2 卤2.9 Ma. It is concluded that there are three magmatic events in the Neoproterozoic in the Bijigou area. The HF isotopic study of zircon in the Bijigou basic rock body shows that the magmatic source area is a depleted mantle and is contaminated by crustal materials.
【学位授予单位】：长安大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：P618.2

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