甘肃龙首山地区碱交代型铀钍矿床地质及成矿流体研究

发布时间：2018-07-06 09:32

  本文选题：龙首山地区 + 碱交代型铀钍矿化　； 参考：《中国地质大学(北京)》2017年硕士论文

【摘要】：龙首山地区是我国重要的花岗岩型铀钍成矿带,至少包括新水井、芨岭、革命沟、红石泉、金边寺等5个铀矿床/点。本文重点对芨岭与新水井两个典型碱交代型铀(钍)矿床开展了详细研究,试图查明矿床地质特征及成矿流体性质以及流体来源。区内主要赋矿岩石为加里东期中粗粒似斑状花岗岩(芨岭岩体),花岗岩地球化学特征表明其为是华北陆块南缘上地壳熔融的产物,形成于加里东晚期,北祁连洋壳板块与其北侧华北板块碰撞后挤压向伸展转变的构造背景之下。该期花岗岩普遍具有较高铀、钍含量,是本地区合适的铀源和钍源。芨岭和新水井矿床为典型的碱交代热液型铀(钍)矿床,热液蚀变发育广泛,由早至晚包括:矿化前期钾长石化;矿化期钠长石化、方解石化、赤铁矿化、绿泥石化、高岭石化、硅化;矿后期褐铁矿化等。矿化期蚀变可划分两期:即早期强碱性钠交代期,该期特征是花岗岩完全钠长石化,并伴随蚀变矿物系列有碳酸盐化、绿泥石化和微量的锐钛矿、赤铁矿和黄铁矿形成。在矿床碱交代早期、交代岩铀含量有所增加。矿床晚期围岩蚀变属于钙、镁交代期,此时热液碱度明显减弱,向弱酸性转变,交代矿物组合是方解石(碳酸盐化)、铁绿泥石、赤铁矿、胶状磷灰石和钙蒙脱石等,矿床铀、钍矿化在该期产生。通过系统流体包裹体研究,获得芨岭和新水井矿床成矿流体温度为130℃~150℃。包裹体主要为水溶液包裹体和CO2-H2O溶液包裹体,激光拉曼检测到包裹体气相普遍发育CO2及H2等气体,暗示铀、钍可能主要以挥发份络合物形式搬运(如铀酰碳酸离子等)为主。流体包裹体均一温度-盐度分布表明中低温低盐度流体与中低温中盐度流体混合可能为本区重要的矿质沉淀机制。通过C-O同位素的研究,认为铀钍矿化的成矿流体应为大气降水与岩浆水混合而成。推测该地区铀矿化主要受碱交代岩、构造破碎带、岩性接触带控制,区内广泛发育的碱交代作用完成了铀的初步预富集,后期酸性含铀热液与大气降水汇合,发生减压沸腾作用,在构造有利部位及岩性接触界面附近发生铀的沉淀、富集成矿。
[Abstract]:Longshoushan area is an important granitic uranium-thorium metallogenic belt in China, including at least five uranium deposits / sites, such as Xinshui well, Jiling, Chuanggou, Red Shi Quan and Phnom Pensi. In this paper, two typical alkaline metasomatic uranium (thorium) deposits in Jiling and Xinshui are studied in detail, and the geological characteristics, ore-forming fluid properties and fluid sources of the deposits are attempted to be ascertained. The main ore-bearing rocks in the area are Caledonian coarse-grained porphyry granites (Jieling granite). The geochemical characteristics of the granites indicate that they are the product of the melting of the upper crust in the southern margin of the North China continental block and formed in the late Caledonian period. The northern Qilian oceanic crust plate collided with the North China plate in the tectonic setting of compressional to extensional transition. The granites in this period generally have high uranium and thorium contents, which are suitable uranium and thorium sources in this area. The Jiling and Xinshui deposits are typical alkali-metasomatic hydrothermal uranium (thorium) deposits with extensive hydrothermal alteration and development, including: early to late mineralization of potassium feldspar; mineralization of albite, calcite, hematitization, green-mud fossilization. Kaoling Petrochemical, silicification, late ore limonitization, etc. The mineralization period can be divided into two periods: the early strongly alkaline sodium metasomatism period, which is characterized by the complete albite of granite, accompanied by carbonation of altered mineral series, green mud petrifaction and trace anatase, hematite and pyrite formation. During the early alkali metasomatism, the uranium content of metasomorphic rocks increased. The late metamorphism of the surrounding rock belongs to calcium and magnesium metasomatism, at which the hydrothermal basicity is obviously weakened and the metasomatic mineral assemblage is calcite (carbonation), iron chlorite, hematite, colloidal apatite and calcium montmorillonite. Thorium mineralization occurred during this period. Through systematic fluid inclusion study, the ore-forming fluid temperature of Jiling and Xinshui deposits is 130 鈩，

本文编号：2102349