摘要
皖东蚌埠—五河地区位于华北克拉通东南缘,区内主要出露古老结晶基底五河杂岩。小红山重晶石石英脉呈近顺层状产出于五河杂岩地层内,脉中组成矿物以石英和重晶石为主,另有厘米级长柱状金红石以及少量的金属硫化物和黑云母,重晶石石英脉的上下围岩均发生不同程度的热液蚀变。显微镜下,金红石内部发育环带结构和核边结构,是脉体中早期晶出的矿物,可分为2种类型:黑色金红石和褐色金红石,其中前者为早阶段形成。金红石进行的EMPA和LA-ICP-MS分析测试结果显示,金红石W含量较低,且具有显著高的Nb/Ta、Zr/Hf比值,指示其变质流体成因。其高Nb低Cr、低Mg、Al、Si的特点,表现出壳源长英质(泥质)金红石的特点。金红石Zr温度t=(504.18±79.60)℃,位于角闪岩相变质区间,黑色金红石的形成温度较红褐色金红石更高。(Fe+Cr+V)含量与(Nb+Ta+W)含量的关系说明金红石中的V为V^(4+),元素置换方式在黑色金红石中为Fe^(2+)+2R^(5+)→3Ti^(4+),而在红褐色金红石中为Fe^(3+)+R^(5+)→2Ti^(4+),说明金红石结晶阶段热液沿着温度降低和氧逸度升高的方向在演化。极高的Nb/Ta和Zr/Hf比,Nb/Ta-Ta的强烈负相关和Zr/Hf-Hf的弱负相关,说明金红石重晶石石英脉为变质热液成因。
The Bengbu-Wuhe area,eastern part of Anhui Province,is located in the southeastern margin of the North China Craton.There is mainly outcropped ancient crystalline basement of the Wuhe complex.The barite-quartz veins in the Xiaohongshan deposit occurred nearly bedded in the Wuhe complex formation,and consist of major quartz and barite,with minor centimeter long columnar rutile and a small amount of metal sulfides and biotite.The surrounding rocks of barite-quartz veins were hydrothermally altered in different degrees.Under the microscope,rutile crystals have zonal and core-rim structures.The rutile was formed in the early stage of the barite-quartz vein.Two types of rutile,including the black rutile which was formed in the early stage and reddish-brown rutile,have been identified.The EMPA and LA-ICP-MS analytical results show that rutiles contain relatively low W contents,with obviously high ratios of Nb/Ta and Zr/Hf,indicating the origin of metamorphic fluid.They are characterized with high Nb and low Cr,Mg,Al and Si contents,showing the feature of crust-derived felsic (pelitic) rutile.The rutile has Zr-themometre calculated temperature of (504.18±79.60)℃,which is plotted in the metamorphic interval of amphibolite facies.The formation temperature of black rutile is higher than that of reddish-brown rutile.The relation between (Fe+Cr+V)contents and (Nb+Ta+W) contents shows that V is existed in form of V^(4+)in rutile,and the elemental substitution modes are Fe^(2+)+2R^(5+)→3Ti^(4+)for black rutile and Fe^(3+)+R^(5+)→2Ti^(4+)for reddish brown rutile,respectively.These indicate that the hydrothermal fluid had evolved into the one along the direction of decreasing temperature and increasing oxygen fugacity during the rutile crystallization stage.The extremely high Nb/Ta and Zr/Hf ratios,the strongly negative correlation of Nb/Ta ratios and Ta contents,and the weakly negative correlation of Zr/Hf ratios and Hf contents indicate that the rutile-bearing barite-quartz veins were originated from the metamorphic hydrothermal fluid.
作者
陶克勤
闫峻
李超
刘丹阳
徐琳玉
TAO Ke-qin;YAN Jun;LI Chao;LIU Dan-yang;XU Lin-yu(School of Resource and Environmental Engineering,Hefei University of Technology,Hefei 230009,China)
出处
《矿物学报》
CAS
CSCD
北大核心
2023年第2期201-214,共14页
Acta Mineralogica Sinica
基金
国家自然科学基金项目(批准号:42030801)
中国博士后科学基金资助项目(批准号:2022M710994)
关键词
蚌埠隆起
金红石
流体演化
Zr温度计
变质热液
Bengbu uplift
rutile
fluid evolution
Zr-in-rutile thermometer
metamorphic hydrothermal fluid
