桂西三合铝土矿演化过程中的矿物转化与元素迁移

发布时间：2018-05-13 22:14

本文选题：三合铝土矿 + 矿物转化　；参考：《中国地质大学(北京)》2015年硕士论文

【摘要】：桂西地区是我国铝土矿的重要产地。三合铝土矿区位于桂西的西南部,与周边德保、那坡一带的铝土矿组成特大型铝土矿田。桂西铝土矿为典型的喀斯特型,包括二叠系沉积型铝土矿和第四系堆积型铝土矿两种亚类。其中堆积型铝土矿品位高、储量大、易开采加工,是目前开发的主要对象。堆积型铝土矿是沉积型铝土矿经抬升、破碎、风化,最后堆积于喀斯特洼地中形成。本文运用多种实验测试和数据统计方法在矿物和元素尺度上详细研究铝土矿的演化过程。通过X射线衍射、电子探针对矿石的矿物组成和成分进行分析,结果显示三合铝土矿矿石的主要矿物组成为硬水铝石、鲕绿泥石、锐钛矿、黄铁矿、钛铁矿、针铁矿、高岭石等。铝土矿中矿物形态各异,各矿物组成呈混杂共生的状态。在表生条件下,铝土矿中的矿物都具有风化蚀变的特征,大多矿物都存在元素的混入或代换现象,矿物成分混杂。地球化学组分分析显示三合铝土矿的主要化学成分为Al2O3、Si O2、Fe2O3、Fe O、Ti O2、Mg O和H2O+。其它成分含量不足1%,铝土矿的成熟度高。微量元素中Zr和Cr的含量很高。平均含量分别为867.93×10-6和792.16×10-6。除此之外,铝土矿中元素Li、Ba、F、Nb、S、Sr、Zn和V的含量也较高,平均含量在100×10-6~40×10-6之间。其余元素Cs、Cu、Ga、Hf、Ni、Sc、Th和U的平均含量均在10×10-6~100×10-6之间。矿石中稀土总量较大,整体富集轻稀土。在原生的沉积型矿石在演化的过程中,首先受到水系对其淋滤的影响,此时矿石主要仍处于还原环境。裂隙经过处的一些矿物首先遭受风化溶蚀,在矿物内部形成溶蚀洞,一些元素被流水带走,一些元素在矿石内部发生各种交代替换。随着氧化作用向矿石内部的深入,赋存与基质和鲕粒中的鲕绿泥石大量风化溶解,Al、Si、Fe、Mg等元素随之迁移。其中的Fe2+氧化为Fe3+形成针铁矿及赤铁矿的集合体,将矿石“染成”红褐色。在这个过程中,赋存于硬水铝石中的元素Al没有明显迁移,较稳定。因此在堆积型铝土矿中,Al相对富集。铝土矿中微量元素的迁移随着矿物的溶解与结晶进行。在铝土矿演化过程中,元素Cr与Ti具有较一致的变化规律。铝土矿中稀土元素Ce的迁移变化与其它稀土元素的变化存在明显不一致,说明Ce很可能赋存于稀土矿物氟碳钙铈矿当中,其迁移与稀土矿物的风化溶解有关。铝土矿中LREE的含量高,但在风化的过程中更易迁移,在铝土矿演化过程中HREE有相对富集的趋势。
[Abstract]:Guanxi area is an important place of production of bauxite in China. Sanhe bauxite area is located in the southwest of western Guangxi, and the surrounding Debao, Napo bauxite constitutes a very large bauxite field. Guanxi bauxite is a typical karst type, including Permian sedimentary bauxite and Quaternary accumulative bauxite. Among them, accumulative bauxite has high grade, large reserves and is easy to be mined and processed, so it is the main object of development at present. Accumulative bauxite is sedimentary bauxite, which is uplifted, broken, weathered and finally deposited in karst depressions. In this paper, the evolution process of bauxite is studied in detail on the scale of minerals and elements by means of various experimental tests and data statistics. The mineral composition and composition of the ore are analyzed by X-ray diffraction and electron probe. The results show that the main mineral composition of the bauxite is hard boehmite, oolitic chlorite, anatase, pyrite, ilmenite, goethite. Kaolinite, etc The minerals in bauxite are of different shapes, and the mineral composition of bauxite is mixed and symbiotic. Under supergene conditions, the minerals in bauxite are weathered and altered, and most minerals are mixed or replaced by elements, and the mineral composition is mixed. The geochemical composition analysis shows that the main chemical compositions of the Sanhe bauxite are Al _ 2O _ 3H _ 2O _ 2 Fe _ 2O _ 3H _ 2O _ 3 Fe O _ 2O _ 2 O _ 2O _ 2O _ 2O and Al _ 2O _ 3H _ 2O. Other composition content is less than 1%, bauxite maturity is high. The contents of Zr and Cr in trace elements are very high. The average contents were 867.93 脳 10 ~ (-6) and 792.16 脳 10 ~ (-6), respectively. In addition, the contents of Zn and V in the bauxite are also higher, with an average content of 100 脳 10 ~ (-6) ~ 40 脳 10 ~ (-6). The average contents of Th and U of the other elements are in the range of 10 脳 10 ~ (-6) ~ 100 脳 10 ~ (-6). The total amount of rare earth in the ore is large and the light rare earth is enriched as a whole. During the evolution of the primary sedimentary ore, it was first influenced by the leaching of the primary sedimentary ore by the water system, and the ore was still mainly in the reduction environment. At first, some minerals passing through the fissure are weathered and dissolved, some elements are taken away by flowing water, and some elements are replaced by various metasomatism in the ore. Along with the oxidation into the ore interior, a large number of weathered and dissolved elements, such as AlAlSiSiFePg-mg in the matrix and oolitic particles, are transported. The Fe2 is oxidized to Fe3 to form an aggregate of goethite and hematite, and the ore is "dyed" reddish brown. In this process, the element Al in hard boehmite has no obvious migration and is relatively stable. Therefore, Al is relatively enriched in accumulative bauxite. The migration of trace elements in bauxite occurs with the dissolution and crystallization of minerals. During the evolution of bauxite, the variation of Cr and Ti is consistent. The migration change of rare earth element ce in bauxite is obviously inconsistent with that of other rare earth elements, which indicates that ce probably exists in the rare earth mineral, fluorocarbon-calcium cerium ore, and its migration is related to the weathering and dissolution of rare earth minerals. The content of LREE in bauxite is high, but it is easier to migrate during weathering, and HREE is relatively enriched during the evolution of bauxite.
【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】：2015
【分类号】：P618.45

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