| 白云鄂博含矿碱性火山岩建造及其地球化学 |
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| 引用本文： | 肖荣阁,费红彩,王安建,杨帆,颜开.白云鄂博含矿碱性火山岩建造及其地球化学[J].地质学报,2012,86(5):735-752. |
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| 作者姓名： | 肖荣阁 费红彩 王安建 杨帆 颜开 |
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| 作者单位： | 1. 中国地质大学地球科学与资源学院,北京,100083
2. 中国地质科学院,北京,100037 |
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| 基金项目： | 本文为国家自然科学基金项目（编号40073013）和国土资源部国际合作与科技司自由探索项目（编号2000440）资助成果。 |
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| 摘 要： | 白云鄂博矿床历经几十年的研究,主要集中在矿区H8岩性段矿化白云岩成因的认识,许多研究显示含矿白云岩是岩浆碳酸岩,本文主要从岩石学和地球化学方面进一步分析其属于火山喷发环境形成的火山碳酸熔岩。H8含矿白云岩段和H9板岩段作为一套含矿岩系主要由含矿白云岩、霓闪钠长岩、钾长板岩3类岩石组成,白云岩和霓闪钠长岩都具有的碎屑结构及角砾状构造、条带构造,显示为火山熔岩和火山碎屑岩特征,而钾长板岩则主要显示致密微晶火山熔岩特征。工业矿物主要是磁铁矿、赤铁矿、稀土矿物和铌铁矿物,其重要特征是出现大量原生赤铁矿,反映岩石氧化系数高,与火山喷发环境一致。霓闪钠长岩、钾长板岩岩石化学显示碱性特征,稀土元素与CaO、F相关系数在0.7以上,并与Fe2O3高氧化物相关,而与硅酸盐矿物组分反相关,表示碳酸岩与稀土成矿密切相关,并显示为表生氧化环境形成。稀土地球化学特征显示白云岩∑REE最高,钾长板岩∑REE最低,相应的岩脉∑REE低于喷发岩。各种岩石均表现为明显的轻重稀土分异,但是以白云岩LREE/HREE比值最大,霓闪钠长岩LREE/HREE比值最小,而纯钠长石岩脉和含稀土磁铁矿LREE/HREE明显高于其他岩石。白云岩和霓闪钠长岩均表现出不同的铕、铈负异常,但是碳酸岩脉和钾长板岩则显示弱正铈异常,霓闪钠长岩和钾长板岩铕异常不明显。矿化白云岩和碳酸岩脉的δ18O、δ13C值介于沉积灰岩与已知碳酸岩的δ18O、δ13C值之间,碳酸岩中白云石的δ18O低于方解石的δ18O,而δ13C高于方解石的δ13C,稀土矿物的δ13C、δ18O与碳酸岩脉δ13C、δ18O接近。归纳这些特征,含矿白云岩与霓闪钠长岩、钾长板岩是碱性火山岩组合,与一系列同期的碳酸岩、霓闪钠长岩碱性岩脉一起,构成一套完整碱性火山岩系。
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| 关 键 词： | 碱性火山岩 岩石化学 微量元素 稀土元素 白云鄂博 |
| 收稿时间： | 2011/9/14 0:00:00 |
| 修稿时间： | 2012/1/12 0:00:00 |
Formation and Geochemistry of the Ore-Bearing Alkaline Volcanic Rocks in the Bayan Obo REE-Nb-Fe Deposit, Inner Mongolia, China |
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| XIAO Rongge,FEI Hongcai,WANG Anjian,YANG Fan and YAN Kai.Formation and Geochemistry of the Ore-Bearing Alkaline Volcanic Rocks in the Bayan Obo REE-Nb-Fe Deposit, Inner Mongolia, China[J].Acta Geologica Sinica,2012,86(5):735-752. |
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| Authors: | XIAO Rongge FEI Hongcai WANG Anjian YANG Fan and YAN Kai |
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| Institution: | China University of Geosciences, School of the Earth Sciences and Resources, Beijing, 100083;Chinese Academy of Geological Sciences, Beijing, 100037;Chinese Academy of Geological Sciences, Beijing, 100037;China University of Geosciences, School of the Earth Sciences and Resources, Beijing, 100083;China University of Geosciences, School of the Earth Sciences and Resources, Beijing, 100083 |
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| Abstract: | Several decades of research on the Bayan Obo REE-Nb-Fe deposit have been focusing on genesis of ore-bearing dolomitic rock in the H8 lithological section of the mining area.A large volume of study suggests that the ore-bearing dolomitic rock is originally magmatic carbonatic rock.This study,from the lithological and geochemical viewpoint,re-analyzed the eruptive carbonatic lava and its geological settings.H8 ore-bearing dolomite section and H9 slate section,both of which have long been regarded as ore-bearing rocks,consist of ore-bearing dolomitic rock,aegirine-diorite-albitite,and K-feldspar slate.The former two are all characterized by clastic texture,breccia and banded structures,reflecting the features of volcanic lava and clastic rock,whereas the K-feldspar slate is characteristic of compact micrite volcanic lava.Economic minerals mainly contain magnetite,hematite,REE-bearing minerals,as well as Nb-Fe-bearing minerals.Presence of voluminous primary hematite indicates a high oxidation coefficient,which is in accordance with eruptive geological background.Aegirine-diorite-albitite and K-feldspar slate are lithochemically characterized with alkali.Coefficient factor of REEs and CaO and F is above 0.7,and is associated with Fe2O3,but in negative relation with compositions of silicate minerals,indicating that carbonatite has close relation with REE mineralization and likely formed in a supergenetic oxidizing environment.REE geochemical analysis shows that dolomitite contains highest ∑REE and K-feldspar slate contains least,and the dykes of both rocks contain less ∑REE than eruptive rocks.Rocks of various types in the mining area show a strong differentiation between LREE and HREE,with a highest ratio of LREE to HREE in dolomitite and a lowest ratio in Aegirine-diorite-albitite,but the ratios of LREE to HREE in albitite dykes and REE-bearing magnetite are distinctly higher than those in other rocks.In addition,dolomitic rock and aegirine-diorite-albitite show varied negative Eu and Ce anomalies,carbonatite dykes and K-feldspar slate show weak positive Ce anomaly,but aegirine-diorite-albitite and K-feldspar slate have no distinct Eu anomolies.Mineralized dolomitic rock and carbonatitic dykes have δ 18O and δ 13C values between those of sedimentary limestone and known carbonatite.Dolomitic rock hosted in carbonatite has lower δ 18O value than that in calcite,but higher δ 13C than that in calcite.REE-bearing minerals have similar δ 13C and δ 18O values as carbonatite dykes.To sum up,ore-bearing dolomitic rock,aegirine-diorite-albitite and K-feldspar slate are an assemblage of alkaline volcanic rocks,and they,along with a series of contemporaneous carbonatite,aegirine-diorite-albitite and alkaline dykes,constitutes one complete group of alkaline volcanic rocks series. |
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| Keywords: | alkaline volcanic rocks lithochemisty trace elements rare earth elements Bayan Obo |
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