赣西北狮子岭花岗岩型锂矿床成因:来自岩石地球化学和锆石U-Pb年代学的约束

Petrogenesis and rare metal mineralization of Shiziling granite-type lithium deposit in northwestern Jiangxi Province:Constraints from petrogeochemistry and zircon U-Pb geochronology

赣西北矿集区是中国重要的花岗岩型锂矿资源基地,以发育多期次多阶段岩浆作用和大规模锂等稀有金属矿床著称。区内花岗质岩浆与稀有金属成矿关系密切,为进一步研究该地区花岗质岩浆演化特征及其与稀有金属成矿的联系,确定相关花岗岩成岩时代及成因类型,查明稀有金属成矿机制,笔者选择九岭地区狮子岭花岗岩作为研究对象,对其开展了岩相学、锆石U-Pb年代学及岩石地球化学分析。结果显示,狮子岭花岗岩属高钾钙碱性系列,具有高Si,富P,贫Ca、Mg、Fe,富集U、Hf等高场强元素,亏损Ba、Sr等大离子亲石元素,稀土元素总量较低(ΣREE=2.12×10^(-6)~146.24×10^(-6)),轻稀土元素相对富集(LREE/HREE=3.5~16.53),弱Eu负异常(δEu=0.23~0.59)的特征。整体上具有S型花岗岩的地球化学特征。锆石U-Pb定年显示,黑云母二长花岗岩成岩年龄为(141.02±0.59)Ma,锂(白)云母碱长花岗岩成岩年龄为(113.96±0.72)Ma。锂(白)云母碱长花岗岩成岩过程中形成磷锂铝石及锂云母等含锂矿物,其成岩年龄可视为锂等稀有金属成矿年龄。该区稀有金属矿化受燕山晚期岩浆结晶分异作用及后期热液交代作用共同影响,岩浆结晶分异作用是Li、Nb、Ta成矿的决定性因素,后期热液交代作用为Li等成矿元素的二次富集提供条件。

The ore cluster in northwestern Jiangxi Province is a significant granite-type lithium mineral resource base which is characterized by multi-stage magmatism and large-scale mineralization of rare metals like lithium.The granitic magma and rare-metal mineralization are intimately connected,then we further study the evolution characteristics of granitic magma in this area and its relationship with rare metal mineralization,define the petrogenic age and genetic types of related granites,and find out the mechanism of rare metal mineralization.In this study,the Shiziling granites in Jiuling area were selected as the research object,petrography,zircon U-Pb geochronology and petrogeochemistry analysis of the granites were carried out.Results show that the Shiziling gra-nites are high-K calc-alkaline series,and rich in Si and P,deplete in Ca,Mg,and Fe.Moreover,these rocks enrich in the high field strength elements(HFSE,e.g.,U,Hf),and deplete in the large-ion lithophile elements(LILE,e.g.,Ba,Sr).The rocks have lower total rare earth elements(REE),range from 2.12 × 10~(-6) to 146.24 × 10~(-6).The ratio of LREE/HREE is relatively high(3.5~16.53).The rocks show weak negative Eu anomalies(δEu=0.23~0.59).Overall,the Shiziling granites have geochemical characteristics of S-type granite.The zircon U-Pb dating results show that the petrogenic age of biotite monzogranite is(141.02 ± 0.59) Ma,and the lepidolite(muscovite) alkali feldspar granite is(113.96±0.72) Ma.Amblygonite and lepidolite minerals formed in the petrogenic process of lepidolite(muscovite) alkali feldspar granite,so the petrogenic age of alkali feldspar granite could be regarded as the metallogenetic age of rare metals.Rare metal mineralization was influenced by the Early stage of Yanshanian magmatic crystallization differentiation and the late hydrothermal metasomatism,magmatic crystallization differentiation is the determinants for the mineralization of Li,Nb,and Ta mineralization,hydrothermal alteration in the late stage provides the conditions for the secondary enrichment of Li.