红石泉伟晶状白岗岩型铀矿床蚀变特征及意义

发布时间：2018-05-26 17:16

本文选题：伟晶状白岗岩 + 热液蚀变　；参考：《东华理工大学》2015年硕士论文

【摘要】：红石泉伟晶状白岗岩型铀矿床地处甘肃省山丹县境内,是我国最为典型的白岗岩型铀矿床。本区研究工作主要完成于上世纪八十年代及之前,对与铀矿化关系密切的蚀变矿物的研究较为薄弱。本文通过对红石泉伟晶状白岗岩型铀矿床蚀变岩开展系统研究,在厘定其特征基础上,探讨热液蚀变的形成环境、物质来源及与铀成矿的关系。研究发现,该区铀矿主要赋存在伟晶状白岗岩与围岩交界附近的蚀变带中。铀矿化类型可归纳为两种,一为黑色富含绿泥石化黑云母的黑化矿石;另一种为红色与钠长石化、赤铁矿化关系密切的红化矿石。两者叠加存在,一般在富铀矿体中心,绿泥石化发育最强,赤铁矿化、钠长石化、钾长石化次之,绢云母化最次。相较于正常伟晶状白岗岩,主量元素方面,蚀变岩的Si、K组分减少,TFe、Mg、Mn、Ti组分增多,且Fe价态发生了变化。微量元素方面,蚀变岩的U、Th、Pb、Mo、Li、Ti明显偏高,尤其是U、Mo增高数倍;Th*均值为5.84,增加明显,而Sr*均值为0.83,降低明显;微量元素蛛网图总体上呈“W”分布模式,大离子亲石元素Rb、Th、U、Pb相对富集及高场强元素Ti、P、Cr相对亏损,与正常岩石一致。稀土元素方面,蚀变岩的ΣREE含量(均值为88.412)增加明显,尤其HREE,在稀土元素分配模式上表现为蚀变岩更趋于水平,负δEu(均值为0.856)异常稍弱些,而δCe值十分接近1,呈较弱的负异常与正常岩性基本一致。成矿元素方面,蚀变岩的U含量增加明显,Th变化不大。研究表明,本区热液蚀变形成于中低温度、低氧逸度、低PH值及富含铁镁质组分环境。蚀变作用一方面能够改变岩石的物理性质,形成有利于铀成矿的空间条件,另一方面又能够促进铀的活化转移与沉淀。蚀变可分成三个阶段,第一阶段发生在伟晶状白岗岩成岩晚期,以黑云母绿泥石化为主,部分晶质铀矿析出分布在蚀变矿物的边缘或裂隙中,铀初步富集;第二阶段主要表现为碱交代,蚀变以钠长石化、钾长石化为特征,铀进一步富集成贫矿石;第三阶段为酸交代,绿泥石化蚀变强烈,赤铁矿化蚀变中等,铀富集成富矿石,是红石泉铀矿化主成矿期。绿泥石化、钠交代、赤铁矿化等热液蚀变可作为该区重要找矿标志。
[Abstract]:The Shi Quan pegmatite Baigang type uranium deposit is located in Shandan County Gansu Province and is the most typical Baigangyan type uranium deposit in China. The research work in this area was mainly completed in the 1980s and before, but the study of altered minerals which are closely related to uranium mineralization is relatively weak. Based on the systematic study of altered rocks in the Shi Quan pegmatite Baigangyan type uranium deposit, the forming environment, material source and the relationship between hydrothermal alteration and uranium mineralization are discussed on the basis of the determination of its characteristics. It is found that the uranium deposits in this area are mainly located in the altered zone near the boundary between pegmatite and surrounding rock. The uranium mineralization types can be divided into two types, one is black rich in chlorite biotite, the other is red and albite, the red ore is closely related to hematitization. They are superimposed, generally in the center of the uranium rich body, with the strongest development of green mud fossilization, hematitization, albite, potassium feldspar, sericite, and sericite. Compared with the normal pegmatite, the Si-K component of the altered rock decreases and the Fe valence state changes as compared with the normal pegmatite. In respect of trace elements, the Uttrium, PbPbPbMoMoLiOTi in altered rocks is obviously higher, especially the average value of Th* is 5.84, the average value of Sr* is 0.83, and the distribution pattern of trace element cobwebs is "W" pattern in general, the average value of Th* is 5.84, and the average value of Sr* is 0.83.The trace element cobweb pattern shows a "W" distribution pattern in general. The relative enrichment of the heavy ion lithophile element RbBX and the relative depletion of the high field strength element TiOPU Cr are consistent with that of the normal rocks. For rare earth elements, the 危 REE content (mean value is 88.412) of altered rocks increases obviously, especially HREE, which shows that the REE distribution model shows that the altered rocks tend to be more horizontal, and the negative EU 未 (mean 0.856) anomaly is slightly weaker. The 未 ce value is very close to 1, and the weak negative anomaly is basically consistent with the normal lithology. In terms of ore-forming elements, the increase of U content in altered rocks has little change in Th. The results show that the hydrothermal corrosion in this area is formed in the environment of low temperature, low oxygen fugacity, low PH value and rich in ferromagnesia components. On the one hand, alteration can change the physical properties of rocks and form the space conditions conducive to uranium mineralization, on the other hand, it can promote the activation, transfer and precipitation of uranium. The alteration can be divided into three stages. The first stage occurs in the late diagenetic period of pegmatite bhagite, mainly in biotite greenstone, and some of the uraniferous uranium deposits are precipitated and distributed in the edge or fissures of altered minerals, and the uranium is initially enriched. The second stage is mainly characterized by alkali metasomatism, albite and potassium feldspar, and uranium is further enriched and integrated into poor ore, while in the third stage, acid metasomatism, strong alteration of green-mud petrifaction, moderate alteration of hematite and uranium rich ore are the main features. It is the main metallogenic period of red Shi Quan uranium mineralization. The hydrothermal alteration, such as green mud fossilization, sodium metasomatism and hematitization, can be used as an important prospecting marker in this area.
【学位授予单位】：东华理工大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：P619.14

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