武夷-云开造山带早古生代镁铁-超镁铁质岩富钪风化壳的首次发现及其意义  

Identification and significance of the Sc-rich regolith on Early Paleozoic mafic-ultramafic intrusions in the southeastern Wuyi-Yunkai Orogenic Belt,South China

作　　者：周美夫 赵文 周岱 杨胜标[1] 申宇 王振朝 漆亮 王敏[1] 陈伟 ZHOU Meifu;ZHAO Wen Winston;ZHOU Dai;YANG Shengbiao;SHEN Yu;WANG Zhenchao;QI Liang;WANG Min;CHEN Wei Terry(State Key Laboratory of Ore Deposit Geochemistry,Institute of Geochemistry,Chinese Academy of Sciences,Guiyang Guizhou 550081,China;School of Earth Resources,China University of Geosciences,Wuhan Hubei 430074,China;Wuhan Center,China Geological Survey,Wuhan Hubei 430205,China)

机构地区：[1]中国科学院地球化学研究所,贵州贵阳550081 [2]中国地质大学(武汉)资源学院,湖北武汉430074 [3]中国地质调查局武汉地质调查中心,湖北武汉430205

出　　处：《矿物学报》2024年第3期303-316,共14页Acta Mineralogica Sinica

基　　金：中国科学院战略性先导科技专项“低碳能源金属矿产(锂、稀土、钴、镍、铜)找矿增储与高效提取”(编号:XDA0430201);国家自然科学基金重大研究计划集成课题“关键金属元素超常富集机理集成研究”(编号:92162323);国家自然科学基金重大研究计划;重点项目“中国南方及邻区大规模风化壳稀土矿床成矿作用”(编号:91962216)。

摘　　要：本文首次报道华南古生代武夷-云开造山带东南缘的兰排镁铁-超镁铁质岩体富钪(Sc)风化壳,初步计算获得区域内钪的潜在资源为524~566 t,为一潜在大型风化壳型钪矿。兰排岩体呈小型岩株侵入到永和闪长质岩体内,主要由橄榄岩、辉石岩和辉长岩组成,辉石岩锆石^(206)Pb/^(238)U年龄为(428.3±2.0)Ma(MSWD=0.92)。镁铁-超镁铁质岩全岩w(TFe_(2)O_(3))为12.1%~18.7%,其中辉石岩钪含量为44×10^(–6)~97×10^(–6),总体高于橄榄岩(20×10^(–6)~89×10^(–6))和辉长岩(28×10^(–6)~48×10^(–6))。兰排这类富钪岩石组合与以往认为富钪的碳酸岩-碱性岩体和阿拉斯加型岩体都存在较大差异,可能代表了一种新的钪成矿母岩类型,推测碰撞后陆内伸展诱发富钪地幔源区熔融可能是富钪母岩浆形成的重要机制。镁铁-超镁铁质岩体上部发育完整的风化壳剖面,可分为全风化层和半风化层。全风化层的上部富集铁(氢)氧化物(磁铁矿、赤铁矿、针铁矿),而中下部以高岭石等黏土矿物为主。半风化层除了包含蒙脱石等黏土矿物,还包括铁钛氧化物及辉石等硅酸盐矿物或相关蚀变矿物。风化壳样品的Sc含量为21×10^(–6)~304×10^(–6),富集程度最高可达相应基岩的3倍以上。其中,钪含量最高的样品主要分布在铁氧化物最富集的全风化层上部,其钪含量多数超过100×10^(–6)。风化壳钪含量与红土化指数(IOL)呈明显的正相关性,表明红土化过程对风化壳钪的富集有显著影响。初步研究认为钪在风化壳红土化过程中经历了活化-迁移-沉淀的多阶段富集过程:1)风化早期钪以类质同象替换的形式赋存在蒙脱石等黏土矿物中;2)风化后期磁铁矿和蒙脱石溶解,钪赋存在以铁(氢)氧化物为主的矿物中,并达到最高程度的富集(Sc>100×10^(–6));3)风化晚期铁(氢)氧化物溶解,一部分钪向下迁移到特定层位。兰排镁铁-超镁铁质岩体富钪�This paper reports the discovery of scandium(Sc)-rich regolith of the Lanpai mafic-ultramafic intrusion in the southeastern Wuyi-Yunkai orogenic belt,South China.Preliminary estimates yield a potential Sc resource of 524 to 566 tonnes which makes the regolith a potentially large-size Sc deposit.The Early Paleozoic Lanpai mafic-ultramafic intrusion,which intruded into the Yonghe dioritic pluton,consists of peridotite,pyroxenite and gabbro.The pyroxenite has a zircon U-Pb age of 428.3±2.0 Ma(MSWD=0.92).Rocks from this intrusion have total w(Fe_(2)O_(3))contents ranging from 12.1%to 18.7%.Pyroxenites contain Sc contents varying from 44×10^(–6) to 97×10^(–6) which are generally higher than those of peridotites(20×10^(–6) to 89×10^(–6))and gabbro(28×10^(–6) to 48×10^(–6)).The Sc-rich rock association of the Lanpai intrusion differs significantly from carbonatite-alkaline rock complexes and Alaskan-type complexes which are thought to be rich in Sc.It may represent a new type of source rocks for the regolith-hosted Sc deposit.It is inferred that the Sc-rich Lanpai intrusion was formed by the magma produced from the partial melting of the Sc-enriched mantle source in a locally induced extensional part of the post-collisional setting.The well-developed weathering profile includes a pedolith zone and saprolith zone overlying on bedrocks of the mafic-ultramafic intrusion.The upper part of the pedolith is rich in iron(hydro)oxides(magnetite,hematite,and goethite),whereas the middle and lower parts of the pedolith are predominantly composed of clay minerals such as kaolinite.The saprolith is composed of major clay minerals including montmorillonite,with minor Fe-Ti-oxides and silicates including pyroxene or related alteration minerals.The regolith samples in the Lanpai area contain 21×10^(–6)-304×10^(–6) of Sc,which are 2 to 3-times higher than those of corresponding bedrocks.Especially,a sample containing the highest Sc concentration was collected from a layer,which is mostly enriched in Fe-oxides an

关 键 词：风化壳型钪矿床 武夷-云开造山带 镁铁-超镁铁质岩 红土化指数 

分 类 号：P61[天文地球—矿床学] P595[天文地球—地质学]