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中元古代昆阳群Fe-Cu-REE矿床地球化学研究-以武定迤纳厂矿床为例
其他题名Study on Geochemistry of Fe-Cu-REE Deposit in Kunyang Group in Mid-Proterozoic
杨耀民
学位类型博士
导师胡瑞忠
2003
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
关键词火山喷流-沉积成矿 地球化学 碱性火山岩 Sm-nd年代学 迤纳厂矿床
摘要稀土元素成矿与地壳的构造运动密切相关,稀土在中元古代具有大规模暴发性成矿特征。云南武定迤纳厂稀土铁铜矿床为昆阳群因民组出现稀土富集成矿的典型代表。本论文选择迤纳厂矿床为主要研究对象,系统研究矿床不同类型岩(矿)石和矿物的稀土元素地球化学特征,探讨富稀土的成矿流体、成矿物质来源和稀土元素成矿时代,揭示昆阳裂谷初期因民组稀土元素富集的地球化学机制。主要认识如下:1、迤纳厂矿床产于昆阳裂谷初期形成的禄丰一武定火山断陷盆地中。早中元古界昆阳群分布于绿汁江岩石圈断裂和小江一易门断裂的夹持地带,呈狭长状展布。迤纳厂矿床赋矿地层为昆阳群因民组上段的硅质白云岩和碱性火山岩(粗面安山岩)。矿体产出形态和矿石的结构构造等均显示矿体与赋矿地层同沉积特征;出现独立矿物氟碳饰矿、独居石及褐帘石,磷灰石、萤石、菱铁矿等矿物中也含有一定量的稀土,沿矿体走向和垂向稀土元素变化不大。2、矿体顶、底板围岩(石榴石黑云母片岩、钠长黑云母片岩等)的原岩为碱性火山岩(粗面安山岩),相对富集大离子亲石元素Ba、Cs、Rb、K、LRE日及贫Zr、Sr、Ti、Hf、HEE,为早元古代末期一中元古代早期交代富集地慢低程度部分熔融所形成的碱性火山岩。矿石稀土总量高(645-4443)×10-6,强烈富集轻稀土((La/Tb)N=17.3-81.1),稀土元素分布特征明显不同于矿区正常沉积的硅质白云岩和后期侵入的钠长石英斑岩及火山角砾岩,而与矿体顶、底板碱性火山岩中稀土元素配分特征基本一致,暗示稀土成矿物质来源与碱性火山岩有密切的关系;3、矿石中微量元素组合及变化特征与现代海底正在喷出的热液和热液沉积物中元素组合有较大的可比性,明显不同与火成碳酸岩型稀土矿床中的特征元素组合;在微量元素判别图解(Al-Fe-Mn、Fe/Ti-Al/(Al+Fe+Mn)、U-Th、Y-P2O5等)中,逸纳厂矿石均投影在热水沉积区,矿石的Y/Ho值与黑烟囱值接近,表明成矿流体为高温、还原性质,稀土成矿可能以热水沉积作用方式为主;4、对矿石中主要矿物萤石、菱铁矿、磁铁矿、石英、方解石的稀土元素特征研究表明,矿石沉积时不同矿物中稀土元素分布特征基本相同,主要受成矿流体中稀土分布特征制约。而后期变质作用形成的矿物,其稀土元素分布主要受矿物晶体结构控制。同期成矿流体从早期到晚期(块状矿石→条带状矿石),轻重稀土分异变小,稀土总量增加,条带状矿石中稀土含量最高;矿石黄铜矿6345值变化在一任3%0到2g%。范围,显示慢源硫特征;菱铁矿6r3C(8%-9.1%)、δ18O(-11.17%-15.37)‰指示成矿流体具岩浆来源和有机质的脱梭酸分解作用参与;成矿流体中稀土元素可能主要以(RE(CO3)3F)4-、(既(CO3)3F2)、(RE(F,Cl万等形式迁移,当温度降低时沉淀出氟碳饰矿等稀土矿物;5、矿石和萤石单矿物 Sm-Nd等时线年龄分别为1621士110Ma和15:38士43Ma,与矿区碱性火山岩错石的U-Pb年龄1676Ma、因民组顶部石英正长斑岩的错石U-P1。年龄1685Ma基本一致,也与因民组地层年龄1765M。较为接近,反映成矿时代为早元古代晚期和中元古代早期:这一时间也与一早元古代晚期一中元古代早期昆阳裂谷初始裂陷阶段,大量来自于地幔的碱性火山岩喷发事件相吻合。矿石。Nd(t):-2.87-3.60,萤石单矿物εNd(t):-3.93-5.90,变化范围较窄并全为负值,接近0,指示源区为富集地幔。同时结合矿床形成的构造一地质环境及矿体产出的地质形态,认为逛纳厂稀土铁铜矿床可能是在昆阳裂谷初期,在碱性火山岩浆喷发的间歇期,来自地幔富稀土、挥发份的成矿流体由火山喷流一同生沉积方式形成的矿床。6、昆阳群因民组地层中出现的稀土富集、成矿与我国的白云鄂博稀土REE-Fe-Nb超大型矿一床和澳大利亚的olympic Dam Cu-U-Au-Ag-REE超大型矿床,在成矿时代、产出大地构造背景、成矿物质来源等方面具有较大的相似性,均体现成矿受控于中元古代1.5Ga超大陆聚合前或随后裂解初始阶段伴随的非造山型碱性岩浆或热液作用,稀土来源于超大陆拼合前因板块俯冲交代而形成的富集地幔。
其他摘要The ore-forming process of REE deposits is closely related to the evolution of the crust, tectonic movement and magmatism. The REE mineralization suddenly occurred and largely distributed on the Earth in Middle Proterozoic metallogenetic epoch in the evolution of the Earth. The Yinachang Fe-Cu-REE deposit is one of typical deposits and mainly occurs in Yinmin Formation of Kunyang Group of Middle Proterozoic epoch. This paper mainly reports the results of investigation on the REE geochemistry of various rocks and minerals, the sources of ore -forming materials and the age of mineralization. The Preliminary mechanism of sudden REE enrichment and mineralization in Middle Proterozoic has been interpreted. In this paper, the main conclusion have been put forword as following: Yinachang Fe-Cu-REE deposit occurred in Wuding -Lufeng volcanic fault deporssion during the initial stage of Kunyang rift. The Kunyang Group is distributed in the marrow and long belt constrained by the Luzhijiang lithospheric fault and the Xiaojiang-Yimeng fault. The wall rock of ore-bodies is the siliceous dolostone and alkaline volcanic rock (trachy andesite) in the Yinachang deposit. Based on the shape of ore-bodies and the structure and texture of ores, the deposit was identificed as synsedimentary with wall rocks. There occurred REE minerals, such as bastnaesite , monazite and allanite., associated with apatite and fluorite with REE contents to a certain extent. Both The hanging wall and the footwall rock of ore bodies are garnet biotite schist, protoliths are alkaline volcanic rocks (tracyh andesite). According to characteristics of trace elements assemblages and the setting of tectonics, these alkaline volcanic rocks were derived from the lower degree melting of metasomatic and enriched mantle (EMI) in the initial stage of Middle Proterozoic epoch, they strongly enriched in Large Ion lithophile elements (LILE), such as Ba, Cs, Rb, K and LREE, depleted Zr, Hf ,Ti, Sr and HREE. Comparative studies of REE geochemical characteristics of various geologic bodies in the deposit indicate that the various ores and alkaline volcanic rocks contain abundant REE, specially LREE (£REE=645 * 10-6~4443 * 10-6; (La/Yb)N=17.3~81.1), the chondrite-normalized patterns of both ores and alkaline volcanic rocks show a strong LREE enrichment and positive Eu anomaly, in contrasting with the dolostones which show slight LREE enrichment and moderately negative Eu anomaly. REE patterns of ores are similar to hydrothermal sediment core in the East Pacific Rise, whereas REE patterns of dolostones are similar to those of PA AS. 3. The composition of trace elements of ores are similar to those of hydrothermal sediment core in the East Pacific Rise, obviously distinguished from the composition of carbonatite-type REE deposits. In diagram (Al-Fe-Mn, Fe/Ti-Al/(A1+Fe+Mn), U-Th, and Y-P2O5). the element composition of ores exhibits hydrothermal sedimentary signification. The ratio of Y/Ho in ores approximates to the ratio of black chimney in TAG seafloor. The ore-forming fluids show high temperature and redox characteristics. In conjunction with the geological setting of the deposit, the primary ore-forming fluids might certain higher REE and higher volatile elements derived from the mantle degassing or the alkaline volcanic magmas. The genesis of Yinachang Fe-Cu-RE deposit might belong to volcanic exhalation-hydrothermal sedimentary. 4 REE geochemistry of fluorite, siderite, quartz, magnetite, calcite in ores mainly controlled by ore-forming fluids, in contrasting to those of the metamorphic minerals which controlled by crystal structure. The ore-forming fluids of initial stage show larger LREE/HREE fractionation than that of later stage. A narrow range of 5 14S valus for early stage chalcopyrite (-0.3%0 to 2.8%o) suggested that S originated from the mantle and the 8 13C and 5 18O valus of siderite range from -11.17%o to -15.37%o and from 8%0~9.1%o, respectively, it indicates that the C and O of ore-forming fluids were derived from the magma or organogenous sediment. The main REE complex in ore-forming fluids may be (RE(CO3)3F)δ (RE(CO3)3F2)5- RE(F,C1)- finally they deposited to form REE minerals such as bastnaesite when the temperature and press are droped. 5 Sm-Nd isochron ages of minerals (δ-points) and fluorite (δ-points) are 1621 + llOMa and 1538±43Ma, respectively, which are similar to zircon U-Pb age (1676Ma) of alkaline volcanic rock (trachy andesite) and the zircon U-Pb age (1685Ma) of quartz syenite porphyry in the Yinachang ore district, and approximating to Yinmin Formation strata age (1765Ma). The mineralization age is much the same as alkaline volcanic eruption events in early stage of Middle Proterozoic in Kunyang rift. The signatures of Nd(t) for: -2.87- -3.6 and for flourite f Nd(t): -3.93-5.49 indicated they have been derived from the enriched mantle. 6% There is strong similarity in REE mineralizaton among the Yinachang Fe-Cu-REE deposit, the Bayan Obo REE-Fe-Nb superlarge deposit and the Olympic Datn O. Au-U-Ag-REE superlarge deposit. The tectonic setting of mineralization are all in the marginal rift of the continents, the mineralizing events mainly took place in the Middle-Proterozoic epoch, and the REE are mainly generated the anorogenic magmatism which recorded the extensional tectonic activity that took place in the final stage of the formation of a 1.5Ga supercontinent and in the initial stages of its breakup, or derived from metacomatic enriched mantle.
语种中文
文献类型学位论文
条目标识符http://ir.gyig.ac.cn/handle/352002/3688
专题研究生_研究生_学位论文
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杨耀民. 中元古代昆阳群Fe-Cu-REE矿床地球化学研究-以武定迤纳厂矿床为例[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,2003.
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