冲绳海槽现代海底热液沉积物的矿物学与地球化学研究

IOCAS-IR > 海洋环流与波动重点实验室

	冲绳海槽现代海底热液沉积物的矿物学与地球化学研究
	蒋富清
学位类型	博士
	1998
学位授予单位	中国科学院海洋研究所
学位授予地点	中国科学院海洋研究所
学位专业	海洋地质学
摘要	冲绳海槽是一个目前正在扩张的弧后盆地，海槽具有特殊的地形、地球物理特征，广泛发育的断裂构造和频繁的岩浆活动，因此多年来一直是中外学者关注的地区之一。特别是近年来在冲绳海槽断裂带附近发现了计多热液活动区，促使人们从新的角度去重新认识冲绳海槽。冲绳海槽的热液沉物中富含Zn、Pb、Cu、Fe、Au、Ag、Hg等多种有用的金属元素，其潜在的巨大经济价值以及对热液活动研究的理论意义也使得冲绳海槽现代海底热液活动的研究成为众人瞩目的焦点。本论文运用显徽镜、Ｘ－射线衍射分析、扫描电镜分析、仪器中子活化分析、同位素质谱分析等先进的技术手段和方法，对冲绳海槽现代海底热液沉积物矿物组成、形貌特征、结构构造、矿物生成顺序、成矿作用阶段、元素的赋存状态、元素地球化学特征、以及重要元素的同位素组成等进行了系统的分析与研究，探讨了冲绳海槽现代海底热液活动的规律及其成矿作用机制，工作中获得一些新的发现和较前人工作更加深入的认识。(１）根据主要矿物的不同，将本区的热液沉积物分为硫化物矿石、以重晶石为主的硫酸盐矿石和以硬石膏为主的硫酸盐矿石等三类。硫化物矿石主要由闪锌矿、方铅矿、黄铁矿和黄铜矿和黄铜矿组成，明显地分为疏松粗粒和致密细粒两部分，代表着两个成矿作用阶段；在以重晶石为主的硫酸盐矿石中重晶石和非晶质ＳiO_2成为主要矿物，亦明显地分为粗粒和细粒两部分；在以硬石膏为主的硫酸盐矿石中，无色透明的自形板状硬石膏占了85％左右，其次为黑色细粒的硫化物。（２）利用电子探针和仪器中子活化分析法对部分金属元素的赋存状态进行了研究。结果表明，Zn、Pb、Cu、Fe的主要载体矿物和富集矿物为相应的硫化物。在各类矿石的粗颗粒矿物中，闪锌矿中Ａu的含量最高，其它矿物Ａu的含量相对较低；Ａu在细粒的矿物集合体中含量明显高于粗粒矿物。在分析过程中，首次在以重晶石为主的硫酸盐矿石中发现了颗粒状的单质Ａg矿物，它是Ａg的主要存在形式。除了单质Ａg矿物外，Ａg还有另外两种富集成矿形式，一是存在于银矿物（如：硫砷银矿）之中，另一种是以类质同象或分散态存在于各种硫化物和硫酸盐矿物中。Ｈg的主要载体矿物为方铅矿，而富集矿物为辰砂。（３）在硫化物矿石中，Ｚn的含量较高，在30％以上，Pb、Fe次之，其含量均大于５％；硫酸盐矿石中Ba、Ca为主要组分，金属元素的含量普遍较低，多数含量在３％以下。在各类矿石中Au、Ag、Hg相对明显富集，Au含量可达9.8ppm，Ａg为6500ppm，Ｈg为77ppm。（４）地球化学研究结果表明，不同的元素其来源不尽相同，Ａu、Hg、Zn、Cu、Fe主要来自火成岩，Pb则主要来源于火山岩和沉积物，其中沉积物的影响可能更大。Ag可能来自地球深部的物质。（５）对不同类型矿石及单矿物的硫同位素研究表明，无论是硫化物集合体还是单矿物闪锌矿，δ~(３４)Ｓ值变化范围都不大，均在5.2-7.2‰之间，表现出一致的来源与演化过程，而与其它热液活动区相比δ~(34)S明显偏高。重晶石、硬石膏的δ~(34)S值与其它地区相差不大，其变化范围在23－23‰之间。以上结果说明在热液流体成矿的不同阶段，硫的来源不同。在早期阶段，硫可能主要来自海水与周围的岩石，此后因流体受岩将活动的影响，硫主要来自岩浆和地球深部物质，在热液流体成矿的后期阶段的硫化物沉淀过程中，海水又对硫的来源起到巨大的影响。
其他摘要	The Okinawa Trough is a spreading back arc basin located between the East China Sea and Ryukyu island arc. It has special morphological features, intensive fracture system and frequent magmatic activities. So it is typically an important area. During this years, many hydrothermal active fields have been discovered near the fracture zones of the Mid-Okinawa Trough, which urged people to understand it from other hands. The hydrothermal sediments in the Okinawa Trough rich in many useful metal elements, such as Zn, Pb, Cu, Fe, Au, Ag, Hg, etc. The study on hydrothermal activity in this area has become a focus because of its great value in economy and theory. In this paper, we researched systematically the hydrothermal sediments' mineral compositions, morphological features, formation and texture, crystallization sequence of minerals and oreforming phrase. In addition, we also analysed some important elements' modes of presence and geochemical features and isotopic compositions by using some advanced instruments and means, such as, X-ray diffraction analysis, scanning electron microscope, neutron activate analysis and isotopic analysis. (1) The hydrothermal sediments in this area can be classified into three types according to the difference of mineral compositions. One is massive sulfide consisting dominantly of zenic, pyrite, galena and so on. The second is sulfate ore in which are mainly composed of barite and followed by amorphous silica and pyrite. The third is also sulfate ore but in which is mainly composed of anhydrite and a few fine-grained sulfide aggregate. The results suggest that the ore-forming processing is more than one phrase. The major minerals in types of roe, such as sphalerite, galena, barite and anhydrite etc., are mainly formed at the beginning of ore-forming procession, the others are formed later phrase. So it can be concluded that evolution of the hydrothermal sediments are multi-phrased. (2) Based on the electron probe and neutron activate analyses, part metal elements' modes of presence are analysed. Some metal elements, such as Zn, Pb, Cu, Fe present mainly as a part of corresponding sulfide respectively. Au is richer in the fine-grained mineral aggregates than in the coarse-grained minerals in all ore samples. In coarse-grained minerals, Au is relative rich in zenic. Silver exists in three types: natural silver, which is found in sulfate ores mainly composed of barite for the first time, is the main modes of presence. Part silver exist in sulfide and sulfate crystal as dispersion regime or isomorphism. In addition, part silver occur as asilver minerals. Hg's carrier mineral and richness mineral are galena and cinnabar respectively. (3) In the massive sulfide ores, Zn's content is the highest, which is more than 30%, Fe and Pb are relative lower than Zn, but still over 5%. Ba and Ca are the major compositions in sulfate ores, whereas, metal elements' content are relative lower, most of which are less than 3%. All the ore samples rich in Au, Ag and Hg, which are up to 9.8ppm, 6500ppm and 77ppm respectively. (4) Geochemistry researching results show that the sources of different elements are different. According to the results we can conclude that Zn, Cu, Fe, Au and Hg mainly come from igneous rock. Pb come partially from igneous, but mainly come from sediments. Ag perhaps comes from the earth's depth. (5) We analysis the sulfur isotope of different ore samples and part minerals. The results showed that the δ~(34)S value of sulfide have a narrow range from 5.2‰ to 7.2‰ in all the three types of ores. It shows a consistent source and development procession. But the δ~(34)S value is instinctive higher than other hydrothermal active fields. The δ~(34)S value of sulfate minerals, such as barite and anhydrite, has a consistent range with other fields, which are from 21 ‰ to 23‰. According to research results, the sulfur has a different source in the procession of fluids' development. At the nascent phrase, sulfur comes mainly from seawater and igneous rock. Igneous and mental contribute major sulfur when the fluids enter into the deep part of the crust. When the fluid uplift the surface of seafllor, seawater provide major sulfur. Fluid and complexion are the major medium and carrier respectively of those elements during the oreforming elements carrying. The elements' corresponding sulfide is the richness mechanism.
页数	57
语种	中文
文献类型	学位论文
条目标识符	http://ir.qdio.ac.cn/handle/337002/1373
专题	海洋环流与波动重点实验室
推荐引用方式 GB/T 7714	蒋富清. 冲绳海槽现代海底热液沉积物的矿物学与地球化学研究[D]. 中国科学院海洋研究所. 中国科学院海洋研究所,1998.

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