新疆阿尔泰南缘克因布拉克铜锌矿区黑云母二长花岗岩地球化学特征及意义

Geochemical Characteristics and Its Significance of Biotite Monzogranite in the Keyinbulake Copper-Zinc Deposit at the Southern Margin of Altay,Xinjiang

新疆阿尔泰南缘克因布拉克铜锌矿区出露大面积花岗岩，岩性主要为二长花岗岩、钾长花岗岩、黑云母花岗岩和英云闪长岩，矿体赋存于二长花岗岩与上志留统—下泥盆统康布铁堡组外接触带中。室内显微镜下鉴定二长花岗岩发育二云母二长花岗岩和黑云母二长花岗岩2种岩相。黑云母二长花岗岩具有高硅、高碱、贫钠富钾、准铝质—过铝质的特点；微量元素特征表现为Rb、Th、K、Ce、Nd、Tb富集，Ba、Nb、Sr、Ti强烈亏损；稀土元素配分模式为轻稀土相对富集的右倾型，具有稀土总量中等及中等负铕异常的特点。这些特征表明该花岗岩属于高钾钙碱性准铝质—过铝质S型。岩石的ISr（t）值为0.703 039-0.705 729，εNd（t）值相对较低，多数为近于0的负值，T2DM两阶段模式年龄集中在1.145-1.194 Ga。岩石可能由中元古界富含黑云母的变质砂岩或正变质岩和少量幔源物质在较低压力条件下熔融形成，源区有斜长石的残留。地球化学特征表明该区花岗岩具有良好的含矿性，其矿床形成于后碰撞的伸展环境，成矿作用与二长花岗岩的岩浆期后热液有关。

Granites at the southern margin of Altay, Xinjiang crop out widely in the Keyinbulake copper-zinc deposit, including monzogranite, moyite, biotite granite and tonalite, where ore bodies occur in the exocontact zones between Permian monzogranite and the Upper Silurian-Lower Devonian Kangbutiebao Formation. The monzogranite has two lithofacies of two-mica monzogranite and biotite monzogranite under the microscope. The biotite monzogranites are characterized by enrichment of silica, total alkali, low Na/K value, and metaluminous-prealuminous. Trace elements show characteristics of noticeable positive anomaly of Rb, Th, K, Ce, Nd, Tb and negative anomaly of Ba,Nb,Sr,Ti. The REE patterns show richness of LREE, moderate total REE contents and Eu negative anomaly. The characteristics indicate that the biotite monzogranites are high K-low Ca-metaluminous-peraluminous S-type granites. These rocks have near-zero or negative εNd（t） values and high Sr isotopic compositions, with corresponding to Nd model ages of 1.145 to 1.194 Ga. The granites were probably formed by melting of the middle Proterozoic biotitebearing metamorphic sandstone or orthometamorphite and limited mantle material, with residual of plagioclase in the melting source. Geochemical characteristics showed favorable mineralization potentiality of monzogranite. The deposit was formed in post-collision extension setting, and metallogenesis is related to the hydrothermal from monzogranite magma.