江西宜春花岗岩型稀有金属矿床的岩浆分异机制及成矿模型  

The magmatic differentiation mechanism and metallogenic model of the Yichun granite-type rare metal deposit in Jiangxi Province

作　　者：凡秀君 刘杨 丁沛勋 钟春荣 陈莉 于成涛 FAN XiuJun;LIU Yang;DING PeiXun;ZHONG ChunRong;CHEN Li;YU ChengTao(Basic Geological Survey Institute of Jiangxi Geological Survey and Exploration Institute,Nanchang 330030,China;Jiangxi Nonferrous Geological Mineral Exploration and Development Institute,Nanchang 330030,China)

机构地区：[1]江西省地质调查勘查院基础地质调查所,南昌330030 [2]江西有色地质矿产勘查开发院,南昌330030

出　　处：《岩石学报》2024年第9期2803-2818,共16页Acta Petrologica Sinica

基　　金：中国地质调查局项目(DD2023028、DD20243484)资助.

摘　　要：江西宜春是我国华南地区重要的稀有金属矿产地之一,分布有全国最大的锂和钽矿生产基地,而雅山复式岩体是华南地区著名的稀有金属花岗岩。本文通过对前人岩石地球化学和岩石矿物学数据的梳理,发现锂及其他稀有元素在黄玉锂云母花岗岩中高度富集,具有以下规律:黑磷云母-白云母花岗岩→锂云母钠长花岗岩→黄玉锂云母花岗岩,岩浆分异程度逐步增加且逐渐从熔体过渡到熔体-流体共存体系,全岩SiO_(2)含量、Nb/Ta和Zr/Hf比值、A/CNK和δEu值发生规律性变化;Ta、Nb等稀有矿物在矿床中呈浸染状均匀分布而不是流体成因的脉状或网脉状,且被主要造岩矿物所包裹,并见有雪球结构;各阶段的云母具有岩浆结晶作用形成的特征,如呈片状产出,边界平直,有锯齿状、裂片等。综合分析,我们认为:(1)在经过壳幔岩浆组合的过程中使得华南变质基底部分熔融形成初始岩浆,初始岩浆经历了原地高度结晶分异演化过程;(2)富含稀有金属的岩浆热液经过高度结晶分异过程,使得锂、铌、钽等稀有金属元素愈来愈富集于残余熔体中,最终形成稀有金属花岗岩;(3)伟晶岩壳构成岩浆房与外界的隔绝屏障,使F、B、Li、P、H_(2)O等易挥发组分无法逃逸。由于上覆伟晶岩壳形成的封闭体系和下伏幔源岩浆提供的充足热量,使得岩浆房在热驱动机制下长期保持原地分异状态,最终形成雅山锂铌钽矿床。Yichun deposit in Jiangxi Province is one of the most important rare metal deposits in South China,which is the largest production base for lithium and tantalum in China,while the Yashan composite rock pluton is a famous rare metal granite in South China.In this paper,based on the previous geochemical data and lithological minerals,it is found that lithium and other rare elements are highly enriched in the topaz lithium mica granites of the pluton.The magmatic differentiation of the deposit gradually increases from melts to melt-fluid coexistence systems.The whole rock SiO_(2) content,Nb/Ta and Zr/Hf ratios,A/CNK andδEu values of the granites change regularly.Rare metal elements such as Ta and Nb are distributed uniformly in the deposit in the form of disseminated rather than fluid-derived veins or network veins,and are wrapped by the main rock-forming minerals with snowball structures.Mica in each stage has the characteristics of magmatic crystallization,such as flake output,flat boundary,serrated and lobed.It can be concluded that:(1)In the process of crust-mantle magma combination,the metamorphic basement of South China is partially melted to form the initial magma which experienced the evolution process of in-situ high crystallization differentiation;(2)The magmatic hydrothermal fluid rich in rare metals is highly crystallized and differentiated,which makes rare metal elements such as lithium,niobium and tantalum getting more and more enriched in the residual melt,and finally formed the rare metal granites;(3)Each pegmatite crust constitutes an isolated barrier between the magma chamber and the outside wall rocks,making F,B,Li,P,H_(2)O and other volatile components unable to escape.Due to the closed system formed by the overlying pegmatite crust and the sufficient heat provided by the underlying mantle-derived magma,the magma chamber maintained a long-term in-situ differentiation state under the thermal driving mechanism,and finally formed the Yashan lithium-niobium-tantalum deposit.

关 键 词：稀有金属 成矿模型 高分异花岗岩 岩浆演化 江西宜春 

分 类 号：P588.121[天文地球—岩石学] P618.7[天文地球—地质学]