宜春Ta-Nb与黄山Nb-Ta矿床成矿元素差异性富集的因素研究

Factors Controlling the Differential Enrichment of Ore-forming Elements in the Yichun Ta-Nb and Huangshan Nb-Ta Deposits

宜春、黄山地区均位于华南板块钦杭结合带上。宜春Ta-Nb矿床与雅山岩体密切相关,为富Ta的Ta-Nb矿床,赋矿矿物主要为钽锰矿和铌钽锰矿;黄山Nb-Ta矿床与黄山岩体密切相关,为富Nb的Nb-Ta矿床,赋矿矿物以铌铁矿和铌钽铁矿为主。目前,二者在成矿元素上差异性富集的原因尚不清楚。本文在详细的岩相学观察基础上,对雅山和黄山岩体多期岩相中的云母进行主量和微量元素分析,并结合前人研究,综合探讨控制成矿元素Nb、Ta差异性富集的关键因素。雅山岩体为强过铝质S型花岗岩,具有高Al低碱、P和Li含量较高的特征,岩浆源区以古老地壳物质为主且源区熔融温度相对较低。黄山岩体为准铝质‒过铝质花岗岩,具有相对低Al高碱、P和Li含量低的特征,Zr+Nb+Ce+Y值为345~876μg/g,是典型的A型花岗岩,成岩岩浆主要来源于古老地壳部分熔融,且有相对较多新生地壳或地幔物质的参与,源区熔融温度较高。雅山岩体稀土元素总量较低,具有强烈的Eu负异常和明显的四分组效应;Nb/Ta值(0.32~4.91)、Zr/Hf值(3.96~32.0)较低,Rb/Ba值(1.06~6500)和Rb/Sr值(6.08~22750)较高,显示极高分异的特征;云母中的Ⅳ(F)平均值为–0.17,Ⅳ(Cl)平均值为–2.39,F富集程度较高,Cl富集程度较低。与之对比,黄山岩体稀土元素总量较高,呈现较强的Eu负异常和四分组效应;Nb/Ta值(3.80~45.2)、Zr/Hf值(13.3~30.1)较高,Rb/Ba值(2.61~136)和Rb/Sr值(9.46~521)较低,显示分异程度较高,但低于雅山岩体;云母中Ⅳ(F)平均值为0.01,Ⅳ(Cl)平均值为–3.52,F富集程度相对较低,较富集Cl挥发分。综上,岩浆富Al贫碱,分异演化极高,富F、P、Li,是形成富Ta的Ta-Nb矿床的重要因素;而岩浆贫Al富碱,分异演化较高,较富F、Li,贫P,且有更高比例新生地壳或地幔物质的加入,则有利于形成富Nb的Nb-Ta矿床。本研究认为岩浆源区及熔融温度、构造背景、岩浆演化程度、岩浆成分综合控制了宜春和黄山矿床Nb、Ta成矿元素的差异性富集,对今后指导找矿勘查具有重要的指示意义。

The Yichun and Huangshan deposits are both located in the Qin-Hang metallogenic belt of the South China Block.The former is a Ta-rich Ta-Nb deposit closely related to the Yashan pluton.The ore minerals in this deposit are mainly tantalum-(Mn)and niobium-tantalum-(Mn).The latter is a Nb-rich Nb-Ta deposit closely related to the Huangshan pluton,with ore minerals mainly consisting of niobium-(Fe)and niobium-tantalite-(Fe).However,the factors controlling the differential enrichment of ore-forming elements in these two deposits remain unclear.Based on detailed petrographic observations,the major and trace element compositions of micas in the multistage lithofacies of the Yashan and Huangshan plutons were analyzed.Combining the previous whole-rock geochemical and mica chemical data,the key factors controlling the differential enrichment of niobium and tantalum in the two deposits are comprehensively discussed.The Yashan pluton,which is strong peraluminous with high Al,low alkali,and high P and Li contents,is S-type granite derived from partial melting of the old crust at a relatively low melting temperature.The Huangshan pluton is a typical A-type granite that is metaluminous to peraluminous,relatively low in Al,high in alkali,and low in P and Li,with Zr+Nb+Ce+Y values ranging from 345´10-6 to 876´10-6.This pluton originated from partial melting of the old crust with a higher proportion of juvenile crustal or mantle-derived materials at a relatively high melting temperature.The total rare earth contents of the Yashan pluton are low,with strong negative Eu anomalies and obvious tetrad effects.The low ratios of Nb/Ta(0.32-4.91)and Zr/Hf(3.96-32.0)and the high ratios of Rb/Ba(1.06-6500)and Rb/Sr(6.08-22750)indicate extremely high magmatic evolution.The average values ofⅣ(F)andⅣ(Cl)in micas are-0.17 and-2.39,respectively,indicating a high degree of F enrichment and a low extent of enrichment of Cl.In contrast,the Huangshan pluton has higher total rare earth element contents with strong Eu negative anomalies and moderate tetrad effects.The higher Nb/Ta(3.80-45.2)and Zr/Hf ratios(13.3-30.1),and lower Rb/Ba(2.61-136)and Rb/Sr ratios(9.46-521)suggest that the Huangshan pluton experienced high degree of magmatic evolution,but it is still lower than that of the Yashan pluton.The average values ofⅣ(F)andⅣ(Cl)in micas are 0.01 and-3.52,respectively,suggesting that the enrichment degree of F is relatively low and that Cl volatiles are more enriched in the Huangshan pluton.In summary,the magmas enriched in Al,depleted in alkali,highly differentiated,and rich in F,P,and Li are important factors controlling the formation of Ta-rich Ta-Nb deposits.In contrast,magmas characterized by low Al,high alkali,relatively highly differentiated,enriched F and poor P and Li,with a higher proportion of juvenile crustal or mantle-derived materials in the source rocks,are conducive to the formation of Nb-rich Nb-Ta deposits.This study suggests that the magmatic source,melting temperature,tectonic setting,evolution process,and magmatic composition control the differential enrichment of niobium and tantalum in the Yichun and Huangshan deposits,which is of great significance for future mineral deposit prospecting.