内蒙元宝山侵入岩地球化学特征及其与成矿的关系

Geochemical characteristics of the Yuanbaoshan intrusive rocks and their relation to mineralization in Neimeng

元宝山矿区内侵入岩分布广泛。中侏罗世碱长花岗岩与二长花岗岩同源且属同一岩体,以高硅、高钾、富碱、低钙、准铝一弱过铝质为特征,具中等含量的稀土元素丰度值,轻稀土明显富集、重稀土相对平坦,负铕异常强烈,属A型花岗岩,是下地壳物质经部分熔融作用在造山后的伸展机制背景下形成的。晚侏罗世花岗斑岩与流纹斑岩S iO2含量稍低,A l2O3含量偏高且变化范围大,A/CNK显示其为过铝质花岗岩,具S型花岗岩的典型特征,是下地壳发生深融作用并混入少量地幔物质,形成于碰撞后的构造环境中。区内具铅锌矿化、银矿化、钼矿化,流纹斑岩体为其成矿母岩。

Intrusive rocks are widely distributed in the Yuanbaoshan deposit. The Middle Jurassic alkalifeldspar granite and adamellite have high silicon, high potassium, high alkaline, low calcium, metaluminous or weak-peraluminous. The REE patterns show medium REE contents, obvious enrichment of light rare earth elements, clear deficiency of heavy rare earth elements, and intense negative Eu anomalies. The all characteristics above suggest that the Middle Jurassic intrusive rocks have the same origin and are belonged to one pluton. They are the A-type granites and derived from partial melting of the lower crust in the setting of post-orogenic extension mechanism, The Late Jurassic granite-porphyry and rhyolite-porphyry are similar to S-type granites by their slightly lower silicon, slightly higher aluminum, and high A/CNK ratio, which has great varying range and indicates these rocks are peraluminous. They are products of crustal anatexis and little mantle material mixture during the post-collisional tectonic setting. There are Pb-Zn, Ag and Mo mineralization in the ore field. The rhyolite-porphyry is the mineralization mother rock of the deposit.