| 贵州遵义地区早寒武世黑色岩系中镍钼多金属富集层的矿物学和地球化学研究 | |
| Alternative Title | Mineralogy and Geochemistry of the Early Cambrian Black Shale-hosted Ni-Mo Poly-metallic Layer in Zunyi area, China |
| 畅斌 | |
| Subtype | 硕士 |
| 2007-05-31 | |
| Degree Grantor | 中国科学院地球化学研究所 |
| Place of Conferral | 地球化学研究所 |
| Degree Name | 硕士 |
| Keyword | 早寒武世 黑色岩系 镍钼富集层 矿物学 元素富集特征 同位素地球化学 海底喷流成因 |
| Abstract | 在新元古代-寒武纪交替阶段（~544Ma）的短短几百万年间，生物种类和数量剧增，这一事件被称之为“寒武纪生物大爆发”（Cambrian Exploration），同时在这一时期，也发生了全球的海洋缺氧事件（Ocean Anoxic Event，OAE）。这些事件造成了在世界范围内的寒武系底部普遍发育了一套富有机质的黑色岩系。在中国南方，从皖南、浙江经赣北、湘西北、贵州至云南一线，下寒武统黑色岩系的分布近2000公里。这些黑色岩系的发育程度在全球背景中很具特色，是全球背景中研究黑色岩系及其相关科学问题的理想场所。 我国南方大陆早寒武世黑色岩系广泛分布且层位稳定，并伴有Mo、Ni、Se、V、Ag、Au、PGE等多种元素富集层。由于其处在特殊的地球演化背景及地质条件，成为目前国内外研究的一个热点区域。基于此，本文在前人工作的基础上，以贵州遵义地区早寒武世黑色岩系中镍钼多金属富集层为研究对象，通过矿物学、元素地球化学、同位素地球化学等研究手段，探讨中国南方早寒武世黑色岩系中镍钼多金属富集层的成因机制。通过研究，取得以下几点认识： (1) 下寒武统镍钼多金属富集层中SiO2含量较低，MgO、Na2O、K2O、MnO、TiO2在炭质页岩和镍钼层中含量差别不大。镍钼多金属富集层中Fe、Ca、P的含量明显高于碳质页岩，这与镍钼层中硫化物、方解石和磷质的显著增加有关。 (2) 镍钼多金属富集层中微量元素Se、Mo、Cd、Ag、Tl、U、Ni，、Bi、Zn、Cu、V等均有较大富集，富集系数为n到n×103。其中尤以Se、Mo最为富集，两者的富集系数均超过30000，其中Mo元素的富集系数大于50000。 (3)通过多种地球化学指标判别，如Se在黑色岩系中超常赋存，U/Th比值远大于1，黑色页岩和镍钼多金属富集层的Ce具有负异常、Eu有微弱的正异常，多种成矿元素的相关关系等这些特征，都暗示了海底喷流热液和生物的共同作用。此外，黑色岩系中V/(V+Ni)的比值反映了它的沉积环境为缺氧环境。 (4)研究区下寒武统黑色岩系中镍钼多金属富集层的矿物组合以黄铁矿、白铁矿、针镍矿、辉砷镍矿、铁辉砷镍矿、紫硫镍矿、赫硫镍矿和碳硫钼矿为主。 矿物生成大多经历了两个成矿阶段：沉积－早期热液阶段和热液－生物阶段。 (5)根据电子探针分析，对于主要富集元素Ni、Mo而言，Ni以出现大量的镍矿物为特征。镍钼多金属富集层中Mo元素主要以“碳硫钼矿”（MoSC）的形式赋存。Se与As元素在硫化物中含量变化十分特征，如在黄铁矿中Se元素较少而As元素含量较高，在碳硫钼矿中情况相反，推测这是由于Se与As元素不同的地球化学性质以及上述两种矿物不同的形成期次造成的。 (6)同位素研究表明，镍钼多金属富集层的硒同位素的分布范围较窄，δ82/76Se范围为-1.56‰- +1.85‰,平均值+0.25‰。根据目前所测得的硒同位素数据，不支持从海水中还原金属元素沉积富集的机制。我们认为当硒通过海底喷流作用释放后，首先以类质同象的方式结合到硫化物相中，这一过程不会造成硒同位素的大的分馏。流体中剩余的少部分硒与海水混合，并且为藻类吸附而沉淀下来，这一过程会造成约1-2‰的硒同位素分馏。这一模式可较好的解释遵义地区下寒武统Ni-Mo-Se富集层的硒同位素组成特征和硒在不同物相中的分配形式。 (7) 镍钼多金属富集层和围岩的有机碳含量为1.75%～13.9%，平均9.16%，有机碳同位素组成为（δ13Corg）-30.6‰～-32.2‰,这一负偏移可能是由于寒武纪早期的海侵作用造成的。 |
| Other Abstract | Within a few million years from Neoproterozoic to Early Cambrian (~544Ma), the types and quantities of biological materials had explosively increased to a huge amount. This event is called as "Cambrian Exploration". Simultaneously, there also existed a global anoxic event, called as “Oceanic Anoxic Event (OAE)”. The geological events resulted in the worldwide distribution of black shales in the lower Cambrian. In Southern China, the distribution areas of lower Cambrian black shales include Anhui, Zhejiang, Jiangxi, Hunan, Guizhou and Yunan provinces with the approximate range of 2000 Km. The formation of these black shales can partly represent the geologic evolution under the global background. South China continent is marked by the Early Cambrian black shales which are characterized by abundant organic matter and various metals, such as Mo, Ni, Se, V, Ag, Au and PGE etc. Because its important scientific significance and potential value economically, these black shales are causing widespread interest by global geologists. Therefore, in this paper, the Early Cambrian black shales-hosted Ni-Mo poly-metallic layer in Zunyi area is selected to study in terms of mineralogy, major and trace element, C, Se, S stable isotopes etc. Some new conclusions are listed as following: ⑴ The Ni-Mo layer is characterized by lower SiO2 compared to host rock-black shales. Their contents of MgO, Na2O, K2O, MnO and TiO2 are similar to these of carbonaceous shalet. In the Ni-Mo layer, Fe, Ca and P are significantly higher than the carbonaceous shale, which is related to the increase of calcite and phosphorus in the Ni-Mo layer. ⑵ The trace elements, such as Se, Mo, Cd, Ag, Tl, U, Ni, Bi, Zn, Cu, V are enriched in the Ni-Mo layer with the larger enrichment coefficient ranging from n to n×103. The enrichment coefficient of Se and Mo is beyond 30,000 with largest enrichment coefficient of 50,014 for Mo. ⑶ Some geochemical parameters, such as selenium variations in black shales, U/Th ratio, negative Ce anomaly, slightly positive Eu etc, indicated the mixing of submarine hydrothermal and biological effects. In addition, the ratio of V/ (V+Ni) in black shales also indicated the anoxic sedimentary environment. ⑷ Mineral assemblage in Ni-Mo layer mainly included pyrite, vaesite, gersdorffite, Fe-bearing gersdorffite, violarite, heazlewoodite and C-Mo-S mixed-layer phase (MoSC). Most minerals experienced two mineralization stages, namely sedimentary - hydrothermal early stage and hydrothermal-biological stage. ⑸By the EMPA analysis, Ni is mostly hosted in nickel minerals . Mo is occurred in MoSC. The variation of As and Se in different minerals is complicated. In pyrite Se is less while As got a higher content, however, in MoSC the situation is the opposite. It was believed that due to different geochemical behavior of Se and As in the hydrothermal system, so the two different mineral phases formed. ⑹ Se stable isotopic measurement showed that the Ni-Mo layer has a narrow isotopic fractionation as δ82/76Se ranging from -1.56‰ to +1.85‰ and with average of +0.25‰. This result does not support the mechanism that metals remove and deposit from water by redox reactions. Based on the Se isotopic variations in Ni-Mo layer, a model is built: when Se was released from hydrothermal fluid, Se was preferentially incorporated into sulfide phase. This process did not cause the larger isotope fractionation. The small residual portion of Se in fluid was mixed into seawater, and was adsorbed by plankton. This process will result in about 1-2% shift of Se isotopic ratio. The model is favor to explain Se isotopic variations in the Ni-Mo layer and Se occurrence in different phase. ⑺The organic carbon contents of Ni-Mo layer and host rock range from 1.75% to13.9%. Organic carbon isotopic composition (δ13Corg) varied from -30.6‰ to -32.2 ‰. The negative shift may be due to the early Cambrian transgression in these area. |
| Pages | 94 |
| Language | 中文 |
| Document Type | 学位论文 |
| Identifier | http://ir.gyig.ac.cn/handle/352002/3348 |
| Collection | 研究生_研究生_学位论文 |
| Recommended Citation GB/T 7714 | 畅斌. 贵州遵义地区早寒武世黑色岩系中镍钼多金属富集层的矿物学和地球化学研究[D]. 地球化学研究所. 中国科学院地球化学研究所,2007. |
| Files in This Item: | ||||||
| File Name/Size | DocType | Version | Access | License | ||
| 贵州遵义地区早寒武世黑色岩系中镍钼多金属（2738KB） | 学位论文 | 暂不开放 | CC BY-NC-SA | Application Full Text | ||
Items in the repository are protected by copyright, with all rights reserved, unless otherwise indicated.
Edit Comment