新疆东准噶尔老鸦泉碱性岩及相关锡矿的岩石地球化学特征

Rock geochemistry of Laoyaquan alkaline granites and related tin deposits in eastern Junggar,Xinjiang

老鸦泉富碱花岗岩杂岩体与侵入其中的富碱花岗斑岩岩体及云英岩型锡矿体、石英脉型锡矿体等REE配分曲线类似,均具有强烈的Eu亏损,它们的微量元素蛛网图等岩石地球化学特征也类似,是同源岩浆结晶分异演化的结果。锡矿体是老鸦泉富碱岩浆分异演化及以钠质为主的强烈碱交代自变质作用的最终产物。侵入于老鸦泉岩体内的花岗斑岩为锡矿体的直接围岩,它是岩浆结晶分异更晚期混入了更多地壳组分,并向酸性方向演化的产物,该花岗斑岩经自变质热液蚀变作用造成锡的富集并成矿。因此,碱性岩浆结晶分异晚期混有地壳组分,岩浆向酸性演化可能是碱性花岗岩形成锡矿的重要条件之一。

Laoyaquan alkali granite complex and such bodies as alkali-rich small granite porphyry pluton,greisen-type tin ore body and quartzite tin ore body that have intruded the alkali granite possess similar REE distribution patterns.They all show strong depletion of Eu,and their trace element spidergrams and other geochemical characteristics are similar too.Moreover,they are the final products of the fractional crystallization of homologous magmatic evolution.Tin ore body is the final product of Laoyaquan alkaline magmatic differentiation and strong alkali-metasomatic autometamorphism.The granite porphyry pluton which intruded Laoyaquan alkali granite pluton was the direct wall rock of the tin ore body and was the product of late magmatic differentiation in which more crustal constituents contaminated the melts,leading to evolve in the acidic direction.The autometamorphic hydrothermal alteration caused the mineralization of tin in granite porphyry.Therefore,the phenomena that crustal constituents contaminated alkaline magma at the late stage of the fractional crystallization and the magma evolved in the acidic direction might have constituted one of the important prerequisite for alkali granite mineralization in the tin deposit.