湘黔新晃—天柱重晶石矿床形成环境和成矿作用

发布时间：2018-02-21 18:59

  本文关键词： 重晶石矿床 钡冰长石 微量元素 稀土元素 S同位素 有机地球化学 新晃 天柱　出处：《南京大学》2015年硕士论文　论文类型：学位论文

【摘要】：重晶石是一种重要的含钡矿物,在多个工业部门广泛应用,是人类社会不可缺少的一种重要的非金属矿产资源。目前重晶石的主要用途是用于石油天然气钻探的泥浆加重剂。我国扬子地台东南缘湘西-黔东交界处的新晃贡溪-天柱大河边地区的早寒武世重晶石矿床是世界上最大的沉积型重晶石成矿带,在世界范围内极具代表性,对其进行研究具有重要的科学意义。本文在查阅了大量相关文献的基础上,对新晃-大柱地区重晶石矿床进行了电子探针的矿物学研究以及矿床矿石与围岩的微量稀土元素对比研究、重晶石矿石的主量元素研究、硫同位素特征的分析研究和有机地球化学研究,讨论其形成环境和成矿过程,为该地区重晶石矿床的成矿理论提供一定的依据。主要得到了以下认识：(1)电子探针矿物分析中环带钡冰长石的发现表明了海底富钡热液流体对重晶石矿床的形成有较大贡献,而且是一个幕式、逐渐的过程；(2)微量元素V/Cr、U/Th等地球化学指标表明重晶石矿床形成时处于缺氧环境,稀土元素具有明显的Ce负异常,及较高的Y/Ho比值,重晶石矿石具有明显的Eu正异常,这些特征反映了成矿过程受到了较强的海底热液物质的影响,表明钡可能主要来自于海底热液喷流物质；(3)新晃-天柱重晶石矿石的主量元素分析n(SiO2)/n(Al2O3)、n(Al2O3)/n(Al2O3+Fe2O3)、n(Al)/n(Al+Fe+Mn)、n(Si)/n(Si+Al+Fe)值表明了重晶石矿石的形成环境为在大陆边缘并受到热水物质影响。(4)重晶石的δ34S值主要分布在+40‰～45‰,表现出重硫富集的特征,且重晶石硫同位素呈塔式分布,表明硫源来源单一,主要来自同期海水硫酸盐。黄铁矿634S值低于同期海水硫同位素组成,表明生物细菌对海水硫酸盐的还原起到了很大作用,并且反映了矿床形成于海水交换有限的滞留的海盆系统。(5)重晶石含矿岩系有机质的Ro值都大于2%,氯仿沥青“A”和有机转化率、Ts/(Ts+Tm)比值、C29TS/(C29H+C29TS)、甾烷的异构化指数等的结果也都表明了有机质达到了过成熟阶段,经历了较高的热演化阶段,热液可能对有机质的成熟起到了促进作用。正构烷烃和类异戊二烯的碳数分布、Pr/Ph比值、伽马蜡烷、C30*/C29Ts值等都表明了重晶石含矿岩系的有机质母质来源为海相低等的菌藻类等生物,并在还原环境下沉积形成。有机质为重晶石的形成提供了一定的能量,菌藻类生物对重晶石的形成起到了提供生成空间和加快晶体生长的作用。综合以上分析认为重晶石成矿时期为缺氧还原环境、海底热液活动频繁、封闭-半封闭的台地泻湖环境,生物-有机质对重晶石矿床的形成起到了重要的作用。
[Abstract]:Barite is an important barium bearing mineral, which is widely used in many industrial sectors. Barite is an indispensable nonmetallic mineral resource in human society. At present, the main use of barite is mud aggravation for oil and gas drilling. Xinhuang at the junction of west Hunan and east Guizhou on the southeast margin of Yangtze platform. The early Cambrian barite deposit in the Gongxi-Tianzhu River area is the largest sedimentary barite metallogenic belt in the world. It is of great scientific significance to study it on the basis of consulting a large number of relevant literature. The mineralogy of barite deposits in Xinhuang-Dazhu area is studied by electron probe, the trace rare earth elements of ore and surrounding rock are compared, and the principal elements of barite ores are studied. The characteristics of sulfur isotopes and organic geochemistry are analyzed, and the formation environment and metallogenic process are discussed. It provides a basis for the metallogenic theory of barite deposits in this area. The following conclusions are obtained: 1) the discovery of barium ice feldspar in Central Zone by electron probe mineral analysis shows that the hydrothermal fluid rich in barium on the sea floor has a great contribution to the formation of barite deposits. Moreover, it is a series and gradual process. The geochemical indexes such as trace element V / Cr ~ (2 +) / T _ h indicate that the barite deposit was formed in anoxic environment, the rare earth element has obvious negative ce anomaly, and the ratio of Y / Ho is relatively high. The barite ore has obvious positive EU anomaly, which reflects that the ore-forming process is influenced by strong submarine hydrothermal material. The main element analysis of Xinhuang-Tianzhu barite ore indicates that barium may mainly come from submarine hydrothermal jet. The main element analysis of Xinhuang-Tianzhu barite ore shows that the formation environment of barite ore is that the barite ore was formed on the continental margin and was influenced by hot water matter. The value of Al _ 2O _ 3 / Al _ 2O _ 3 / Al _ 2O _ 3 shows that the barite ore is formed in the continental margin and under the influence of hot water matter in the formation environment of the barite ore, which is composed of Al / Al _ 2O _ 3 / Al _ 2O _ 3 / Al _ 2O _ 3 / Al _ 2O _ 3 / Al _ 2O _ 3 / Al _ 2O _ 3. The 未 34s value of the barite is mainly distributed in 40 鈥，

本文编号：1522622