| 云南武定迤纳厂Fe-Cu-REE矿床年代学及矿床成因研究 |
| 叶现韬
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| 导师 | 朱维光
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| 2013
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| 学位授予单位 | 中国科学院研究生院
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| 学位授予地点 | 北京
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| 学位名称 | 硕士
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| 学位专业 | 地球化学
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| 关键词 | 铁-铜-稀土矿床
锆石u-pb定年
黄铜矿re-os定年
成矿物质来源
成矿流体
迤纳厂
云南
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| 摘要 | 云南武定迤纳厂Fe-Cu-REE矿床位于扬子地块西南缘，康滇地轴云南段中部。该矿床中的矿体赋存于早-中元古代下昆阳群迤纳厂组中。迤纳厂矿床是康滇地区典型的铁-铜-稀土矿床之一。因为其特殊的矿物组合（磁铁矿与黄铜矿共生）以及富含稀土矿物，这类矿床一直是矿床学家研究的热点。然而由于其围岩遭受不同程度的变质和蚀变作用，因此这类矿床的成矿时代一直存在争议，而且对矿床的成矿物质和成矿流体来源的认识也存在一定争论。本文通过对迤纳厂组中层状凝灰岩和火山角砾岩中的锆石进行LA-ICP-MS U-Pb定年来揭示迤纳厂组的最大沉积年龄。大多数锆石具有明显的震荡环带和较高的Th/U比值（＞0.4）表明它们均是岩浆锆石，近200粒碎屑锆石的207Pb/206Pb年龄大致可以分为四组：最年轻的锆石年龄在1750 Ma左右。这一定年结果反映了迤纳厂组的沉积时代的上限年龄大约为1.7 Ga。本文还通过对矿石矿物黄铜矿的Re-Os同位素定年测试，直接限定了矿床的成矿时代。6个黄铜矿样品的Re-Os同位素等时线年龄为1690 ± 99 Ma（MSWD = 9.0），模式年龄的加权平均值为1685 ± 37 Ma（MSWD = 3.0），表明该矿床形成于距今约1.7 Ga。上述年代学研究结果显示矿床与地层几乎是同时形成的。迤纳厂矿床中硫化物的δ34S值变化范围较窄，分为两个区间，主要集中在-0.3~+3.2‰之间，平均值为+2.1‰；少部分在+4.0~+9.6‰之间，平均值为+7.3‰。表明硫化物硫源主要来源于岩浆作用，后期形成的硫化物可能有海水硫酸盐的硫源加入。对方解石的碳、氧同位素，石英的氢、氧同位素以及包裹体研究表明，围岩中的方解石的δ13C(PDB)值为-5.6~-4.3‰，δ18O(SMOW)值为+13.2~+14.5‰，表明碳来源于地幔。流体在演化过程中发生了的去CO2作用和流体的混合作用，使方解石中碳、氧同位素发生变化。这与方解石的稀土元素特征以及石英的氢、氧同位素组成都是一致的。通过石英的氧同位素和流体包裹体的均一温度，计算出流体中δ18O值的范围为+7.1~+13.9‰。另外，主要类型矿石具显著的正铕异常和轻稀土富集的特点，与现代海底热液极其相似。年代学研究结果显示矿床的形成时代和地层的沉积时代大致相同，而REE揭示的流体特征反映其成矿作用与海底热液活动有关。这些结果暗示了该矿床为海底火山喷发-同生沉积形成。近来的较多研究表明，康滇地区存在1.7Ga左右较大范围的岩浆活动和较多同期铁-铜矿床，表明该期岩浆活动可能是制约该区铁-铜矿床形成的关键因素，且岩浆活动可能与约1.7 Ga的Columbia超大陆的裂解事件有关。 |
| 其他摘要 | The Yinachang Fe-Cu-REE ore deposit in Yunnan Province is located in the southwestern margin of the Yangtze Block, SW China. The ore bodies are hosted in the Paleoproterozoic Yinachang Formation of the lower Kunyang Group in the Kangdian iron-copper metallogenic province,. The main minerals in the Yinachang ore bodies consist of chalcopyrite, magnetite, quartz and calcite. Meanwhile, the host rocks of the deposit had experienced intensively alternation and metamorphism. Therefore, the source of minerals, the ore-forming fluid, the age and origin of the Yinachang deposit are still a matter of hot debate. U-Pb ages of detrital zircons from the volcanic tuff and breccia in the Yinachang Formation have been used to identify the provenance and evaluate the age of the Yinachang Formation of the lower Kunyang Group. Most analyzed zircon grains show oscillatory zoning and have high Th/U ratios (>0.4), suggesting that they were mainly derived from igneous rocks. A total amounts of about 200 detrital zircons exhibit the youngest age of ca. 1750 Ma. The dating results provide a maximum deposition age of ca. 1.7 Ga for the Yinachang Formation. Rhenium-osmium dating for six chalcopyrite samples from the Yinachang Fe-Cu-REE deposit was conducted to constrain the timing of sulfide mineralization. Direct Re-Os dating for chalcopyrite of ore minerals yields an isochron age of 1690 ± 99 Ma (MSWD = 9.0) and a weighted mean of 1685 ± 37 Ma (MSWD = 3.0), respectively, indicating the main ore-forming age of about 1.7Ga. The zircon U-Pb geochronology thus suggests that the ore-forming age of the deposit is nearly contemporaneous with the deposition timing of the Yinachang Formation.The study on the sulfur isotope of sulfide indicates that the δ34S range is narrow and can be divided into two parts: mainly in -0.3~+3.2‰ and average of +2.1‰; less in +4.0~+9.6‰ with average of +7.3‰. It is suggested that the sulfur of early-stage sulfide may be derived from the magma and the late-stage sulfide may be derived from the sulfate of seawater.The study on the carbon and oxygen isotope of calcite, hydrogen and oxygen isotope of quartz and fluid inclusion indicate that the calcite in the wall-rock reveal δ13C from -5.6‰ to -4.3‰(PDB) and δ18O composition from +13.2‰ to +14.5‰(SMOW), indicative of the fluids are dominantly of magmatic origin. The CO2 degassing and fluids mixing in the evolution of ore-forming fluids may lead to the range of carbon and oxygen isotope. It is consistent with the composition of hydrogen and oxygen isotope of quartz. The δ18O values of the ore-forming fluids are +7.1~+13.9‰ according to the value of δD and δ18O of quartz and the homogenization temperature of fluid inclusions in quartz. In addition, the major ore types exhibit significantly positive Eu anomaly and LREE enrichment, similar to those of modern submarine hydrothermal fluids. The REE characteristics of the ore-forming fluids indicate that the ore formation was related to submarine hydrothermal fluids activity. It is therefore suggested that the Yinachang Fe-Cu-REE deposit is a volcanic exhalation-hydrothermal sedimentary deposit. Several recent studies showed the occurrence of relatively widespread magmatism at ca. 1.7 Ga and large numbers of synchronous Fe-Cu deposits, suggesting that the magmatism is probably the crucial factor for the formation of deposits in this region. Furthermore, the Fe-Cu deposits in the Kangdian region may be related to the break-up of the Columbia supercontinent at about 1.7 Ga. |
| 学科领域 | 矿床地球化学
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| 语种 | 中文
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| 文献类型 | 学位论文
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| 条目标识符 | http://ir.gyig.ac.cn/handle/352002/5865
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| 专题 | 研究生_研究生_学位论文
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推荐引用方式
GB/T 7714 |
叶现韬. 云南武定迤纳厂Fe-Cu-REE矿床年代学及矿床成因研究[D]. 北京. 中国科学院研究生院,2013.
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