| 滇西新生代富碱火成岩及其与金成矿关系研究-以北衙金矿为例 | |
| Alternative Title | The Cenozoic Alkali-rich Igneous Rocks, Western Yunnan and Their Relation with Metallogenesis of Gold |
| 吴开兴 | |
| Subtype | 博士 |
| 2005 | |
| Degree Grantor | 中国科学院地球化学研究所 |
| Place of Conferral | 中国科学院地球化学研究所 |
| Degree Name | 博士 |
| Degree Discipline | 地球化学 |
| Keyword | 滇西 富碱火成岩 富碱侵入岩 北衙金矿床 元素地球化学 同位素 地球化学 流体包裹体地球化学 |
| Abstract | 本论文在前人数据资料和研究成果的基础上，以北衙金矿床及其相关的富碱侵入岩作为主要研究对象，以探讨滇西新生代富碱火成岩成岩过程及富碱岩浆上升演化过程中的流体分异，北衙金矿床的成因，最终揭示北衙金矿床与相关的富碱侵入岩之间的关系为主要研究目的，通过主、微量（包括稀土）元素地球化学，Pb、Sr、Nd、C、O、S及He-Ar等同位素地球化学，以及流体包裹体地球化学等方面的研究获得以下主要认识：-1．滇西新生代富碱火成岩来源于EM-II型富集地慢，源区的交代富集过程与古特提斯洋壳的俯冲有关，俯冲板片的含水流体对上覆上慢楔的交代是滇西富碱侵入岩（相当于A型花岗岩）含水的原因，这次富碱岩浆活动是一次滞后的弧岩浆活动；富碱中、酸性岩浆由碱性玄武质岩浆混染约20％的主要来自变质基底的地壳物质演化而来；滇西新生代富碱岩浆具备岛弧岩浆的氧化条件（即fogfo2＞FMQ＋2，FMQ代表铁橄榄石一磁铁矿一石英氧缓冲），并在其上升演化过程中分异出大量的流体相，具有较大的An、Cu成矿潜力。2．北衙金矿的矿化时代33.0±1.5Ma与相关的富碱侵入岩的成岩时代（32-34Ma）一致。3，成矿早期流体或初始流体具有富碱岩浆在变质基底内分异的流体的Nd和sr同位素组成（Isr≈0.722390，ε Nd（t）≈-2.8）、矿区及外围富碱斑岩的平均Pb同位素组成（206Pb／204Pb＝18.590，207Pb／204Pb=15.606，208Pb／204Pb＝38.770）、与相关富碱斑岩一致的稀土配分模式、岩浆热液的C、O同位素组成（δ13C≈-5％0，61、尧11％0）、以及壳一慢混合He－Ar同位素组成（3He尸He；1 ．80-1．94 Ra，3He／3 6Ar＝1 ．19 * 10-3-3．93火10·3）并显示明显的He-Ar分异（4oAr*/He＝0．34-0．75），且以高温、高压、高盐度、富c02为特征，说明初始流体主要在变质基底内由富碱岩浆分异而来；初始流体在上升过程中由于温度、压力降低发生富co2相和盐水相的分离，成矿元素优先分配进入富COZ相，逐步演化为成矿阶段流体；成矿阶段流体在去气或与大气降水混合过程中释放出其中的成矿元素。4．约80％的成矿金属来自富碱岩浆，其余部分主要通过岩浆流体从变质基底摄取。结论：北衙金矿与相关的富碱侵入岩具有密切的成因关系。 |
| Other Abstract | In this dissertation, based on the data and fruits of previous studies, we take Beiya gold deposit and associated alkali-rich intrusions as main studying objects, aim to discuss the formation processes of the Cenozoic alkali-rich igneous rocks, the differentiation process of fluids from the alkali-rich magma during its uprising and evolution, and genesis of the Beiya gold deposit, and consequently discover the relationship between the Beiya gold deposit and associated alkali-rich intrusions. By studies of major and trace element (include REE) geochemistry, isotope (e.g. Pb, Sr, Nd, C, O, S and He-Ar) geochemistry and fluid inclusion geochemistry we have acquired the following principal cognitions: The Cenozoic alkali-rich intrusive rocks in western Yunnan are derived from enriched metasomatized mantle (EM- II), and the metasomatizing processes of mantle area were related to the subduction of the Palaeo-Tethyan oceanic crust. The metasomatism of hanging mantle wedge by aqueous fluids from subducted slab is accounted for the aqueousness of the alkali-rich intrusive rocks in western Yunnan which are equivalent to A-type granite. Thus the alkali-rich magmatism is considered to be a delayed arc magmatism. The intermediate-felsic alkali-rich magma is evolved from alkaline basaltic magma by assimilation of ca.20% of crustal materials that mainly from metamorphosed basement. The alkali-rich magma has relatively high-oxygen-fugacity (logfo2>FMQ+2, FMQ represents fayalite-magnetite-quartz buffer) as convergent margin magmas and has differentiated large amounts of fluids during its uprising and evolution process, and thus is of Cu-Au high mineralization potential. The mineralization age of Beiya gold deposit is dated as 33 ± 1.5Ma, which is consistent with the age of associated alkali-rich intrusions (32~34Ma). The primary fluid or early stage ore-forming fluid related to Beiya gold deposit has a Nd and Sr isotopic composition (i.e. Isr≈0.722390, ε Nd（t）≈-2.8) identical to that of the fluid differentiated from alkali-rich magma within the metamorphosed basement, a Pb isotopic composition (i.e. 206Pb/204Pb= 18.590, 207pb/204pb= 15 6Q6 f 208pb/204pb = 38 770) identical to the average of alkali-rich intrusions within the district or in the periphery of Beiya gold deposit, a mimic chondrite-normalized REEpattern of associated alkali-rich intrusions, and aC O isotopic composition (i.e. δ13C≈-5‰，δ18O≈11％0) peculiar to magmatic hydrothermal fluids, as well as a crust-mantle mixing He-Ar isotopic composition (i.e. 3He/4He= 1.80-1.94 Ra, 3He/36Ar =1.19 * l0-3～3.93 * 10-3) that also shows remarkable He-Ar differentiation (40Ar*/4He=0.34～0.75). In addition, it is characterized by high-temperature-pressure, high-salty and CCh-rich, The above signatures indicate that primary fluid is principally differentiated from alkali-rich magma within the metamorphosed basement. The mineralizing fluids were gradually evolved from the primary fluid by separation of CC^-rich and H2O-NaCl phases with the decrease of temperature and pressure and preferential partition of ore-forming metals into the, CO2-rich phases, and released the ore-forming metals by processes of gas loss or mixing with meteoric water. 4. About 80% of ore-forming metals are from the alkali-rich magma and the other fractions might be mainly scavenged by the magrnatic fluid from metamorphosed basement. Conclusion: the Beiya gold deposit has a close genetic relationship with associated alkali-rich intrusions. |
| Pages | 118 |
| Language | 中文 |
| Document Type | 学位论文 |
| Identifier | http://ir.gyig.ac.cn/handle/352002/3710 |
| Collection | 研究生_研究生_学位论文 |
| Recommended Citation GB/T 7714 | 吴开兴. 滇西新生代富碱火成岩及其与金成矿关系研究-以北衙金矿为例[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,2005. |
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