赣中乐安与钨锡多金属矿化有关的山心岩体地质地球化学特征、锆石LA-ICP-MS年龄及其成矿意义

摘要

Shanxin granite intrusion is located in the Majizhang area,Le'an,Central Jiangxi Province, where Mo-W-Sn poly-metallic mineralization occurs.Through precise LA-ICP-MS U-Pb dating of zircon from Shanxin fine two-mica alkali-feldspar granite,the crystallization age of the intrusion was determined to be 152.5±1.3Ma,corresponding to Late Jurassic era.The results of mineral chemistry indicate that micas are muscovite and ferrimuscovite,feldspars are albite and orthoclase.The and feladspars are all alkali feldspar.The granties are characterized by high in silicon,Na2 O+K2 O aluminum,low in calcium and magnesium,slightly to strongly peraluminous.The granites also show strong depletion of Sr,Ba,Ti, P and Eu,enrichment of Rb,Th,Ta and LREE,high Ga/Al and strong negative Eu anomaly.The chondrite-normalized patterns of rare earth elements are in seagull forms.The characteristics of the Shanxin granite are similar to that of aluminous A-type granite of the Nanling area.The Shanxin fine-granited granite is of A-type.The characteristics of high Rb/Sr and Rb/Ba ratios,low Nb/Ta,Zr/Hf and K/Rb ratios indicate that the magma experienced a strong fractional crystallization process and fluid process.ItsεNd (t)value is -8.9 and the calculated two-stage modle age of Nd isotope is 1662Ma, suggesting that the magma derived from the partial melting of old continental crust rocks.Combined with the previous research results, the granites of Shanxin unit might form in post-orogenic tectonic environment that is the transition from collision orogenic to intraplate extension.The development of abundant faults and felsic dykes and the W-bearing granite suggest that there may be a large concealed rock which might have good potential for tungsten—tin mineralization.%赣中乐安麻鸡嶂地区产出了一些与钨、锡多金属矿化有关的细粒二云母碱长花岗岩侵入体，统称为山心单元。本文通过对山心单元进行锆石LA-ICP-MS U-Pb 测年，获得其成岩年龄为152．5±1．3 Ma，属晚侏罗世岩浆活动的产物。矿物化学分析表明，山心单元中的云母属铁白云母（褐黑色云母）和白云母，长石为钠长石和正长石。山心单元花岗岩富硅富碱过铝，贫钙、镁，富集 Rb、Th、Ta 等，Ga／Al 值较高，亏损 Sr、Ba、Ti、P、Eu 等元素，稀土配分曲线为＂海鸥型＂，εNd（t）值为－8．9，T2DM＝1662 Ma，地球化学特征与南岭地区铝质A 型花岗岩相似，可能是高分异的铝质A型花岗岩。其高的Rb／Sr、Rb／Ba值，低的Nb／Ta、Zr／Hf、K／Rb 值暗示了岩浆演化过程中有挥发分流体参与，并经历了强烈的分异作用，是岩浆演化后期的产物。该岩体可能形成于后造山拉张构造背景下，主要来源于地壳物质的部分熔融，可能有少量地幔物质的参与。山心花岗岩的含钨特性及其与钨锡成矿时代的一致性，显示其与钨锡成矿有关，而山心花岗岩的高分异属性及大量伟晶岩、石英脉和云英岩脉的发育，暗示深部可能存在大的隐伏岩体，具有良好的钨锡成矿潜力。