扬子地块周边C、P硅岩建造中硒的富集机理对比研究-以渔塘坝、紫阳富硒区为例

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	扬子地块周边C、P硅岩建造中硒的富集机理对比研究-以渔塘坝、紫阳富硒区为例
其他题名	The Enriching-mechanism of Selenium of Cambrian and Permian Silicalite Formation in the Peripheral margins of Yangtze Block-Taking Yutangba and Ziyang Selenium-rich areas as an Example
	冯彩霞
	2004
学位授予单位	中国科学院地球化学研究所
学位授予地点	中国科学院地球化学研究所
学位名称	博士
学位专业	地球化学
关键词	扬子地块周边硅岩建造二叠纪和寒武纪富集机理渔塘坝紫阳
摘要	在自然界中存在一套由硅质岩、泥质岩／页岩或板岩、碳酸盐岩和粉砂岩组成的沉积建造，并以富含有机质和菌藻微生物等为特征，沉积厚度较大，岩石类型以硅岩为主，称之为“硅岩建造”。硅岩建造中的硅质岩不仅是许多重要矿种（如金、硒、铀、钒、磷、锰、铂族元素、重晶石和黄铁矿等）的赋存层和含矿岩系的重要岩类，而且由于它形成于特定的地球化学条件下，能够反映出某些沉积相带特殊的地质背景，另外，硅质岩本身就是一种生物岩，对探讨生物成岩、成矿作用有重要意义。所以对硅岩建造及其内硅质岩研究具有十分重要的理论意义和实用价值。因此，本论文选择扬子地块周边寒武系（南秦岭紫阳硒富集区）、二叠系（湖北恩施双河渔塘坝硒矿床）富硒硅岩建造为研究对象。通过岩石地球化学、同位素地球化学、矿物学以及流体包裹体等方法从含硒规律、岩石成因、沉积环境、成矿流体性质等方面，分别对对两个不同时代或不同层位的富硒硅岩建造开展了系统的地球化学对比研究；并从矿物学、包裹体成分及物理化学条件等方面对渔塘坝硒矿床的成因作了探讨。通过研究，取得了以下主要认识：1渔塘坝硒矿区和紫阳硒富集区富硒硅岩建造岩石以硅质岩为主，硅质岩中5102含量范围分别为64.2％-95.84％和63.62％-95.24％。同时包括部分碳质硅质岩丫碳质页岩和碳、硅板岩及含腐泥层的石煤；渔塘坝硒矿床硅质岩中Se含量大于80ug/g的样品均采自下二叠统茅口组的硅质岩段内，紫阳下寒武统硒富集体中硅质岩中硒的含量最高（可达278ppm）。2微量元素研究表明，两地区富硒硅质岩中均含有较高的Cu，Ni、V、As、Sb、Cr，且U／Th＞1。在U-Th、Zr-Cr和P2O5-Y相关图以及Fe-Mn-（Cu+Co+Ni）三角图上，两研究区内硅质岩样品点均落于热水沉积区。渔塘坝硒矿区硅质岩的REE总量较低，平均为38.9×10-6，紫阳硒富集区硅质岩REE总量除个别较高（达110×10-6以上）外，总体也较低（12.0-37.6）×l0-6；另外，从稀土元素配分模式看，两地区硅质岩均有较明显的Ce负异常，且Eu从无明显Eu异常到出现正Eu异常。都反映出热水沉积硅质岩的特征。从si和O同位素组成来看，两个地区硅质岩的δ3051和δ18O值也总体位于热水成因硅质岩区域内。根据隧石一水的氧同位素分馏方程计算得知，两研究区硅质岩的形成温度分别为46℃-72℃和78.6℃-126.20℃。地球化学特征表明，两地区富硒硅质岩均来自热水沉积作用。另外，渔塘坝硒矿区硅质岩中Cr含量较高，且存在腕足类生物化石；紫阳硒富集区硅质岩中Ba及有机质含量较高，且存在叶琳生物标志化合物。结合两地区碳同位素组成特征（渔塘坝地区δ13c为正值，可能和上扬子区早、晚二叠世之间多期次喷发的火山活动，造成地球史上二叠纪生物大灭绝有关；紫阳地区δ13C为负值，说明碳同位素来源于沉积有机物质），暗示两地区硅质岩的成因可能与火山沉积作用有关，且在成岩过程中有部分生物的参与。3渔塘坝赋矿硅质岩硫同位素组成具有较高的负值，表明矿床形成于缺氧的海盆内：紫阳硒富集区形成黄铁矿的硫主要来自海水硫酸盐。4系统研究了渔塘坝硒矿区硒的矿物学，显示硒以自然硒、独立矿物、类质同像及有机吸附四种形式赋存于矿床中。废弃石煤堆中的自然硒矿物，是自然因素和人为活动共同干预的结果，并非石煤的缓慢自燃的结果。5对研究区成矿流体中包裹体均一温度、盐度和密度进行了系统研究，结果显示：两地区的流体包裹体以原生包裹体为主，数量较多且形态复杂；研究区（渔塘坝硒矿和紫阳硒富集区）成矿流体处于中一低温（ 190-250）℃和（120-155）℃条件。渔塘坝硒矿区石英和方解石包裹体内的流体盐度分别为（5.9-10.l）B％和（3.9-4.5）WB％，紫阳硒富集区流体盐度为（1.2-2.8）WB％，后者流体盐度明显低于前者。流体密度经计算分别为0.79-0.79／cm3和0.69-0.969／cm3。重点对渔塘坝硒矿区的石英和方解石包裹体进行了拉曼光谱成分测试，结果显示：包裹体成分以H2O和N2为主，含少量 CH4、C2H4、C2H6、C3H5、C4H6、C4H4和C6H6等成分，说明成矿溶液介质主要为具有还原性质的水溶液，其成矿条件具还原性的特点。6渔塘坝硒矿区成矿物理化学条件的研究表明，即富硒成矿流体为中低温（190-250）℃、压力平均为60Mpa。成矿早期02、eZ相对较低，乃较高，且fS2/fSe2＞l，有利于硫化物沉淀在成矿主阶段，随着硫化物的沉淀，fS2和fSe2相应增大，且fO2较高。高的fO2阻止了硒进入硫化物，而有利于硒化物的形成。 7系统研究了富硒硅岩建造的沉积环境和构造环境特征，认为渔塘坝硒矿床中富硒硅质岩主要形成于浅海滞留的盆地沉积环境，紫阳下寒武统硅质岩沉积环境属于深水滞留沉积环境；渔塘坝硒矿床主要形成于拉张的断陷盆地中，紫阳硒富集体则形成于拉张的裂谷环境。
其他摘要	As a sediment formation, silicalite formation with a large sedimentary thickness is consist of siliceous rocks (cherts), mud stone/shale or callys, carbonatite and siltstone, and is charactered by enrichment in organic and bacterium-alga microbe. In addition, the cherts in siliclite formation, as an uppermost member, generally, possess many mineral products, such as Au, Se, U, V, P, Mn, PGE, barite and py etc). Thereupon, it is important to undertake study on the silicalite formation and cherts. This dissertation mainly focuses on two selenium-rich "silicalite formation" from Yutangba Selenium Deposit in Shuanghe(in Permian) and Ziyang Selenium-rich area in Southern Qinling(in the early Cambrian), respectively. Based on the petrochemistry, isotopic geochemistry, mineralogy and fluid inclusion, the Ph.D dissertation mainly focused on mineralization law, petrogenesis, sedimentary environment and fluid type of two areas, respectively, in addition, discussed the mineralogy, the composition of inclusions and physical chemistry characteristics of the selenium deposit in Yutangba, Hubei province. By studying, the main conclusions have been put forward as follows: The SiO2 content is 64.2%~95.84% and 63.62%-95.24% of two areas. Se contents analysis for the representative samples shows that the enrichment of selenium is strictly sedimentary strata-bound. With the exception of the Maokou Formation limestones, the samples with the Se contents higher than 80ug/g were all collected from the Lower Permian Maokou Formation siliceous rocks. The highest selenium's content is 278ppm of the siliceous rocks in Ziyang. For the trace elements, both of two areas have high Cu, Ni, V, As, Sb, Cr and U/Th (>1). Along with the projection in AI-Fe-(Cu+Co+Ni) ternary diagram, in U-Th, Zr-Cr and P2O5-Y relative diagram, both of two study areas' silicalite samples fall into the hydrothermal field. In Yutangba selenium deposit, the REE content of siliceous rocks is Iow(38.9 * 10-6), and enriched in LREE. In Ziyang selenium-rich area, it is from (12.0-37.6) - 10-6, In both of two areas, there exist Ce negative anomaly and Eu positive anomaly. They both show the character of hydrothermal genesis, the silicon and oxygen isotope composes are similar with the hydrothermal origin. Based on the Oxygen isotope fractionation equation of chert and water, the petrogenetic temperatures of the silicalites in two study areas are (46-72)°C and (78.6-126.20) ℃. Geochemistrical characteristics of the selenium-rich cherts from Yutangba and Ziyang suggest that the silicalite resulted from hydrothermal sediment. In addition, the high Cr content, the brachiopodous biology fossil existing in Yutangba cherts, and the high Ba contents, the organic matter in Ziyang samples, together with the positive 513C for the cherts of Yutangba, and negative513C for the cherts of Ziyang, all imply that the petrogenesis of the cherts is related with volcanism, however, during diagenetic process, biology may be an important role. The negative Sulfur isotope compositions of the pyrite in the cherts of Yutangba indicate that the selenium deposit was formed in an anoxic oceanic basin. However, the selenium of the cherts from Ziyang resulted from sea water due to the sulfur isotopic compositions. The study on the mineralogy suggests that there are four type forms for selenium existing in the deposits, such as native selenium, independent selenium minerals, isomorphism and organic adsorption. Native selenium minerals from the abandoned coal pile are the results of natural factors and anthropologic activities, instead of the slow combustion of the coal. Systematic studies on many multiform fluid inclusions including temperature, salinity and density have been conducted for the quartzes and calcites of Yutangba selenium deposit and Ziyang selenium-rich area, and the results show that most of fluid inclusions from two study areas are primary. The homogenization temperatures of the fluid inclusions from two study areas (Yutanba and Ziyang) are changeable from 190 ℃ to 250 ℃, and from 120 ℃ to 155 ℃, respectively, in addition, some may reach to 300 ℃ or even higher, In the histogram of temperature vs. number of samples, it is obvious that the quartzes and calcites are the results of mediate-low temperature hydrothermal. The salinities in the fluid inclusions of quartzes and calcites from Yutangba selenium deposit are 5.9-10.1 WB%, and 3.9-4.5WB%, while the salinities for the fluid inclusions in barite, witherite and quartz from Ziyang are low, distribute between 1.2WB% and 2.8WB%. In addition, by calculating, the density of the fluid inclusions from two areas (Yutangba and Ziyang) distribute between 0.79 g/cm3 and 0.92 g/cm3, and between 0.69 g/cm3 and 0.96 g/cm3. The fluids in Yutangba selenium deposit are dominated by H2O and N2, by the way, other compositions, such as CHUN C2H C2He> C3H8s C4H6 and CeHie also appear in fluids. Indicating that the aqueous solution is reducing, and the ore-forming conditions are characterized by reducing environment. 6 Evidence from physical and chemical show that the metallogenetic fluids are formed environment with low-mediate temperature (19Q-250 ℃) and low pressure (average in 60 Mpa). Before mineralization period, the fO2 and fSe2 of the metallogenetic fluids are low, while the fS2 and fS2/fSe2(>1) is high, which are favored for the precipitation of sulfur, then fS2, fSe2an6 fO2 increases, and the high fO2 is useful for the formation of selenides. 7 By studying the sedimentary environment and the tectonic setting, some conclusions have been achieved as follows: the selenium-rich siliceous rocks in Yutangba resulted from epicontinental environment, while the siliceous rocks from lower Cambrian in Ziyang are formed in the deep-water environment. The Yutangba selenium deposit and Ziyang selenium-rich area both are formed in extensional setting, difference is classified by broken basin and rift.
页数	107
语种	中文
文献类型	学位论文
条目标识符	http://ir.gyig.ac.cn/handle/352002/3706
专题	研究生_研究生_学位论文矿床地球化学国家重点实验室
推荐引用方式 GB/T 7714	冯彩霞. 扬子地块周边C、P硅岩建造中硒的富集机理对比研究-以渔塘坝、紫阳富硒区为例[D]. 中国科学院地球化学研究所. 中国科学院地球化学研究所,2004.

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