湘东北连云山地区上伏矿床伟晶岩地球化学特征、流体包裹体特征及其对矿床成因的约束

Pegmatites of Shangfu deposits, Lianyunshan, northeastern Hunan: Geochemical characteristics, fluid inclusions, and genetic constraints

湘东北连云山岩体上伏地区新发现铌钽矿化较富的3号伟晶岩脉,显示该区具有良好的找矿前景。本文选取上伏矿床伟晶岩为研究对象,开展伟晶岩地球化学、流体包裹体研究,探讨矿床成因,以丰富区域稀有金属成矿机制研究。研究表明:上伏矿床伟晶岩具硅含量较高(w(SiO_(2))为65.05%~79.15%)、高铝(w(Al_(2)O_(3))为11.38%~19.64%)、低钙镁铁、相对富碱(w(Na_(2)O+K_(2)O)为5.62%~9.87%)、(中钾)钙碱性及过铝质特征;微量元素总体富集Nb、Ta、Zr、Hf、U等高场强元素(HFSE),相对亏损Ba、Sr等大离子亲石元素(LILE);稀土元素总量(ΣREE含量)为(11.74~29.40)×10^(-6),轻稀土元素富集,重稀土元素亏损,具壳源特征。包裹体类型为气液两相的盐水溶液包裹体,均一温度为159~443℃,盐水溶液盐度为3.06%~6.74%,包裹体捕获压力均值约为190 MPa,成矿流体为中高温低盐度流体,C、H、O同位素测试结果显示成矿流体与深部岩浆活动有关,可能混入少量建造水。稀有金属成矿受岩浆的分异演化控制,区内二云母二长花岗岩与伟晶岩具有相同的物质来源,为铌钽成矿提供成矿物质和成矿流体来源。

The recent discovery of the Nb/Ta-rich,No.3 pegmatite vein in Shangfu area,Lianyunshan intrusion,northeastern Hunan,shows a good prospect for rare-metal deposits in this area.In this paper,the geochemistry of the Shangfu pegmatite and fluid inclusions in host minerals are studied,and the genesis of the pegmatite deposit is discussed to enrich the understanding of rare-metal mineralization in the region.The Shangfu pegmatite is characterized by high silicon(w(SiO_(2)),65.05%79.15%),high aluminum(w(Al_(2)O_(3)),11.38%19.64%)and low Ca,Mg,Fe contents,and is relatively rich in alkali(w(Na_(2)O+K_(2)O),5.62%9.87%),(medium potassium)calc alkaline and peraluminous.The pegmatite is distinctively enriched in Nb,Ta,Zr,Hf and U,and relatively depleted in Ba and Sr;∑REE ranges between(11.7429.40)×10^(-6),with enriched LREE and depleted HREE,consistent with a crustal origin.The fluid inclusion type is gas-liquid two-phase brine solution;the homogenization temperature of the fluid inclusions is between 159443℃;the salinity of brine solution is 3.06%-6.74%;and the average trapping pressure of the fluid inclusions is 190 MPa.The ore-forming fluid is characterized by medium-high temperature and low salinity;and C,H,O isotopic analysis shows that the ore-forming fluid is related to deep magmatic activity and may be mixed with a small amount of formation water.The rare-metal mineralization is controlled by magmatic differentiation and evolution.The mica monzonitic granite and pegmatite in the area have the same material source which provides the source material and ore-forming fluid responsible for Nb/Ta mineralization.