湘南宝山铜铅锌多金属矿床石榴子石原位成分及其地质意义  

In-situ compositional analyses of garnets from the Baoshan Cu-Pb-Zn polymetallic deposit in the southern Hunan and their geological significances

作　　者：祝干 吴鹏[1] 韩润生[1] 杨航 ZHU Gan;WU Peng;HAN Runsheng;YANG Hang(Faculty of Land Resources Engineering,Kunming University of Science and Technology,Kunming Yunnan 650093,China)

机构地区：[1]昆明理工大学国土资源工程学院,云南昆明650093

出　　处：《矿物学报》2024年第2期211-225,共15页Acta Mineralogica Sinica

基　　金：国家重点研发计划项目(2018YFC0603902);云南省矿产资源预测评价工程实验室(2010);云南省地质过程与矿产资源创新团队(2012)。

摘　　要：宝山铜铅锌多金属矿床位于湘南钨锡多金属矿集区中西部,大地构造位置处于扬子地块与华夏地块两大构造单元的碰撞拼接地带。矿床中主要发育两类石榴子石,Ⅰ类石榴子石(Grt-Ⅰ)呈灰-灰绿色,具明显的韵律环带,Ⅱ类石榴子石(Grt-Ⅱ)呈棕红色或浅红色,环带不发育,较为破碎,呈脉状产出。本文利用激光剥蚀电感耦合等离子体质谱仪(LA-ICP-MS)分析了两类石榴子石成分,结果表明,Grt-Ⅰ主要富Fe,属于钙铁榴石(And_(91-93)Gro_(5-8)Spe+Pyr+Alm_(0.71-0.79));Grt-Ⅱ较Grt-ⅠFe含量降低,Al含量增加,以钙铝榴石组分增加为主要特征,属于钙铁榴石-钙铝榴石固溶体系列(And_(52-66)Gro_(32-47)Spe+Pyr+Alm_(1.10-1.37))。石榴子石稀土元素总量偏低(42.60×10^(-6)~201.50×10^(-6),不包括Y),Grt-ⅠΣREE、LREE/HREE值、δEu值高于Grt-Ⅱ,前者具强烈的Eu正异常、稀土配分曲线向右陡倾,而后者中等Eu负异常、稀土配分曲线向左平缓倾。两类石榴子石亏损Rb、Ba、Sr等大离子亲石元素,富集Nb、Zr和Hf等高场强元素,Grt-Ⅰ富集程度整体低于Grt-Ⅱ。两类石榴子石不同的端员组分、Eu异常等特征,指示Grt-Ⅰ富含Fe,且形成高氧逸度、碱性环境,Grt-Ⅱ形成于弱氧化-弱还原、弱碱性的环境,说明由Grt-Ⅰ至Grt-Ⅱ氧逸度逐渐降低,由氧化转变为弱氧化-弱还原环境。金属成矿元素Cu、Zn、Mo、Pb等在两类石榴子石中的含量较低,Sn含量却高达地壳中Sn平均含量(2.00×10^(-6))的几十甚至上百倍,指示深部石榴子石矽卡岩有利于Sn的富集,具成矿潜力。The Baoshan Cu-Pb-Zn polymetallic deposit is located in the central-western part of the southern Hunan W-Sn polymetallic ore concentration area.It is tectonically located in the collisional contact zone between the Yangtze block and Cathaysian block.There are mainly two types of garnets developed in the deposit.The type-Ⅰ garnets(Grt-Ⅰ)are graygrayish green ones with obviously rhythmic rings.The type-Ⅱ garnets(Grt-Ⅱ)are brownish red or light red ones without ring.They are relatively broken and occurred in form of vein.In this study,laser ablation inductively coupled plasma mass spectrometry(LA-ICP-MS)was used to analyze compositions of two types of garnets.Our results show that the Grt-Ⅰ is mainly rich in Fe,belonging to andradite(And_(91-93)Gro_(5-8)Spe+Pyr+Alm_(0.71-0.79)).Compared with the Grt-Ⅰ,the Grt-Ⅱ has relatively low Fe content and relatively high Al content.It is mainly characterized by the increase of grossularite composition.It belongs to the andradite-grossularite solid solution series(And_(52-66)Gro_(32-47)Spe+Pyr+Alm_(1.10-1.37)).The total REE contents of garnets are relatively low(42.60-201.50 ppm,excluding Y).The Grt-Ⅰ garnets have relatively high values ofΣREE,LREE/HREE,andδEu comparing to the Grt-Ⅱ garnets.The Grt-Ⅰ garnets have strong Eu positive anomalies with steeply right-declined REE distribution patterns,while the Grt-Ⅱ garnets have medium Eu negative anomaly,with slightly left-declined REE distribution patterns.The two types of garnets are both depleted in the LILE including Rb,Ba,and Sr,but enriched in the HFSE including Nb,Zr and Hf.The enrichment degrees of the Grt-Ⅰ garnets are generally lower than those of the Grt-Ⅱ garnets The two types of garnets have different end member components,Eu anomalies and other characteristics,indicating that the Grt-Ⅱ garnets whic are rich in Fe were formed in an oxidized(high oxygen fugacity)and alkaline environment,while the Grt-Ⅱ garnets were formed in a weakly oxidized-weakly reduced and weakly alkaline environment.

关 键 词：石榴子石 原位成分 物理化学条件 宝山铜铅锌多金属矿床 湘南 

分 类 号：P595[天文地球—地球化学] P61[天文地球—地质学]