投稿时间：2017-07-06
修订日期：2018-06-11
网络发布日期：2018-11-03
中文摘要:四川冕宁-德昌稀土元素成矿带长约270 km，宽15 km，该成矿带包括牦牛坪超大型、大陆槽大型、木落寨中型和里庄小型稀土元素矿床及一系列矿点和矿化点。里庄稀土元素矿床作为矿带中唯一矿化特征以细脉浸染状为主的矿床，该矿床细脉浸染状矿化特征的成因和围岩蚀变特征尚未得到详细研究。文章将通过详细野外调查和室内研究，总结矿石类型和碳酸岩、正长岩蚀变特征，揭示细脉浸染状矿化特征的成因。研究表明，里庄矿床矿石类型以细脉浸染状为主，兼有少量角砾状。细脉浸染状矿石呈致密块状，矿物共生组合主要为氟碳铈矿+方解石+萤石+天青石+金云母，大规模的氟碳铈矿形成于热液阶段晚期并叠加在早期方解石、萤石和天青石等脉石矿物之上。细脉浸染状矿石全岩稀土元素配分显示LREE富集（33430×10-6~46530×10-6），HREE亏损（160×10-6~192×10-6），稀土元素总量高（33620×10-6~46690×10-6），全岩稀土元素配分特征与碳酸岩和正长岩相似，但后两者稀土元素总量较低。与牦牛坪发育脉状矿化系统、大陆槽角砾岩筒系统相比，里庄矿化特征以细脉浸染状为主，其可能是由于张性裂隙不发育造成的。区内正长岩-碳酸岩杂岩体广泛发育强烈的蚀变作用。正长岩发育典型霓长岩化，这种蚀变以钾长石被钠长石交代为特征，并形成次生鳞片状黑云母，少量半自形氟碳铈矿叠加在钠长石和黑云母之上。碳酸岩广泛发育红化，其原生表面洁净的方解石被流体交代，大量氟碳铈矿叠加在蚀变方解石之上。矿区矿体赋存在正长岩-碳酸岩杂岩体中，BSE图像及显微镜观察显示氟碳铈矿叠加在蚀变碳酸岩-正长岩之上，结合已有数据发现矿石及部分脉石矿物与碳酸岩-正长岩在微量元素和Sr-Nd-Pb同位素组成特征的一致，表明碳酸岩-正长岩杂岩体提供了本矿床稀土元素矿化的物质来源。此次研究中发现，在里庄矿床中大量发育与氟碳铈矿密切共生的金云母。文章对该金云母进行了Ar-Ar同位素测年，获得金云母形成年龄为（26.0±1.1）Ma，误差范围内与已报道的氟碳铈矿SIMS Th-Pb年龄和正长岩的锆石SHRIMP U-Pb年龄一致，进一步说明REE成矿与正长岩-碳酸岩在成因上具有一致性。
Abstract:The Mianning-Decahng REE belt of Sichuan is 270 km long and 15 km wide, and includes superlarge Mao-niuping deposit, large Dalucao deposit, middle Muluozhai deposit, small Lizhuang deposit and a series of mineralized spots. In the whole REE belt, the Lizhuang deposit is the the only one with stringer-disseminated characteristics. The causes of mineralization characteristics and main features of altered carbonatite and syenite have not been studied in detail. Based on field geological investigation and indoor study, the authors have emphatically summarized ore types and features of altered carbonatite and syenite and revealed stringer-disseminated ore genesis.It is found that the main ore types in the Lizhuang deposit are stringer-disseminated type and minor breccia type. Stringer-disseminated ore is massive and has stable mineral assemblage, mainly consisting of bastnaesite, calcite, fluorite, celestite and phlogopite. Large scale bastnaesite formed in the late hydrothermal stage and overlies the early calcite, fluorite and celestite. The rare earth elements distribution curves of stringer-disseminated ore show LREE enrichment (33430×10-6~46530×10-6), HREE loss (160×10-6~192×10-6), and high rare earth content (33620×10-6~46690×10-6). The characteristics of rare earth elements distribution ofstringer-disseminated ore is consistent with those of carbonatite and syenite, but the last two are lower in total amounts of rare earth elements. Compared withMaoniuping with developed vein mineralization system and Dalucao with breccia pipe, the mineralization characteristics of Lizhuang mainly are stringer-disseminated type, and the reason may be due to the undeveloped extension fracture. The syenite-carbonate complex in the area shows strong alteration. The syenite with typical fenitization is characterized by the replacement of K-feldspar by albite, with secondary scaly biotite. Minor bastnaesite is superimposed on the albite and biotite. The carbonatite widely develops reddening alteration. The primary calcite with clean surface was altered by fluid, and a large amount of bastnaesite is superimposed on the altered calcite. Orebodies are present in the syenite and carbonate rocks, BSE images and microscopic observations show that the bastnaesite is superimposed on the altered carbonatite-syenite. In combination with the available data, the authors found that features of ore and some gangue minerals are consistent with the characteristics of trace elements and Sr-Nd-Pb isotopic compositions of carbonatite-syenite, indicating that the carbonate-syenite complex provided the source of REE mineralization. In addition, there were lots of metallogenic ages in the previous studies.However, there exist obvious differences between these ages; there is no good consistency due to different testing techniques and different test minerals. The systematic field geological mapping,microscopic observation and electron microprobe analysis show that the phlogopite is closely associated with bastnasite in the Lizhuang deposit. The phlogopite Ar-Ar plateau age is (26.0±1.1) Ma,which is very close to the previously reported zircon SHRIMP U-Pb age of syenite and SIMS Th-Pb age of bastnaesite within the error range, andthis further explain genetic consistency between REE mineralization and syenite-carbonatite.
keywords:geochemistry ore types and genesis alteration material source 40Ar/39Ar age Lizhuang deposit
文章编号：
中图分类号：P618.7
文献标志码：
基金项目:本文得到中国地质科学院基本科研业务费（编号：YYWF201509、YYWF201705）、中国地质调查项目（编号：1212011020000150011-03）和国家自然科学基金面上项目（编号：41772044）联合资助
引用文本：
李德良,刘琰,郭东旭,舒小超,姜恒,陈超,欧阳怀,郑旭,李自静.2018.四川冕宁里庄稀土元素矿床矿石类型及金云母Ar-Ar年龄[J].矿床地质,37(5):1001~1017LI DeLiang,LIU Yan,GUO DongXu,SHU XiaoChao,JIANG Heng,CHEN Chao,OUYANG Huai,ZHENG Xu,LI ZiJing.2018.Ore types and phlogopite Ar-Ar age in Lizhuang REE deposit, Mianning County, Sichuan Province[J].Mineral Deposits37(5):1001~1017
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