川西甲基卡烧碳沟地区伟晶岩脉地球化学特征

通过对烧碳沟地区伟晶岩的岩石学特征及地球化学特征进行分析,探讨了其成矿构造背景及物质来源等成矿地质条件.结果表明:烧碳沟一带伟晶岩的SiO2含量为73.46%~75.96%,全碱含量为4.71%~7.36%,里特曼指数为0.70~1.84,反映了伟晶岩的钙碱性特征;铝饱和指数A/CNK 为1.54~2.49,全部大于1.1,反映了强过铝质S 型花岗岩的特征.伟晶岩的主量、微量和稀土元素特征表明,其源岩以黏土沉积物为主,与甲基卡二云母花岗岩相比,两者具有高度相似的微量、稀土元素配分模式,以及近似的Nb/Ta 比值,表明两者具有同源性,且属于分异程度较高的钙碱性花岗伟晶岩脉.构造背景分析显示伟晶岩属于同碰撞花岗岩,在印支运动末期相对稳定的环境中,甲基卡一带的穹状构造为稀有金属伟晶岩矿床提供了良好的成矿环境.

Geochemical characteristics of the pegmatite veins in Shaotangou area,Jiajika of Western Sichuan Province

Based on petrological and geochemical investigations of the pegmatite veins in Shaotangou area, this paper discusses their origin and tectonic setting. The results show that SiO₂ content of the pegmatite veins in Shaotangou ranges from 73.46% to 75.96%, and the total alkaline content ranges from 4.71% to 7.36%, with Rittman index of 0.7 to 1.84, which indicates that the rocks have calc-alkaline characteristics. The aluminum saturation index (A/CNK) of the pegmatite veins is over 1.1 (1.54 to 2.49), indicating that these rocks belong to peraluminous S-type granite. The major, trace and rare earth elements data of the pegmatite veins indicate that they are mainly sourced from clay sediments. They have similar trace and rare earth elements distribution and Nb/Ta ratio, compared with Jiajika two-mica granite. And these two pegmatite veins are cogenetic and belong to highly differentiated granite. The tectonic setting analysis shows that the pegmatite veins are classified as syn-collision granite, and that the dome structure in Jiajika area provides a favorable structural environment for the formation of the rare metal pegmatite veins during the relative stable late stage of Indo-China movement.