新疆东准噶尔坝西早石炭世石英闪长岩及其对斑岩铜矿的指示意义  

Early Carboniferous quartz diorite in the Baxi copper deposit,East Junggar:Insight into potential for porphyry copper deposits

作　　者：张铭鸿 姚勇 程志国[1] 张招崇[1] ZHANG Ming-hong;YAO Yong;CHENG Zhi-guo;ZHANG Zhao-chong(State Key Laboratory of Geological Processes and Mineral Resources,China University of Geosciences,Beijing 100083,China)

机构地区：[1]中国地质大学(北京)地质过程与矿产资源国家重点实验室,北京100083

出　　处：《岩石矿物学杂志》2021年第1期153-168,共16页Acta Petrologica et Mineralogica

基　　金：国家自然科学基金资助项目(41390442,41772057)。

摘　　要：新疆东准噶尔琼河坝地区位于中亚成矿域中段,虽然该地区近年来相继发现了一系列的古生代斑岩铜(钼)矿床,但矿床规模均较小,其成矿潜力有待进一步评价。坝西铜矿床是其中的一个代表性斑岩铜矿。与斑岩铜矿矿化密切相关的是石英闪长岩和石英二长闪长岩,获得其中石英闪长岩的锆石U-Pb加权平均年龄为345.7±3.0Ma,说明其形成于早石炭世。石英闪长岩和石英二长闪长岩的斜长石并不是通常的中长石,而是更加富钙的拉长石。全岩地球化学分析结果表明,它们为准铝质-弱过铝质的钙碱性Ⅰ型花岗岩类,微量元素原始地幔标准化曲线展示出大离子亲石元素相对富集、高场强元素相对亏损并有明显的Nb、Ta和Ti的负异常,显示出典型的岛弧岩浆岩的特征。岩石中具有暗色微细粒镁铁质包体、正的εHf(t)值(+13.66~+15.56)和岩体中的富钙斜长石暗示了其形成于幔源基性岩浆与新生地壳部分熔融的酸性岩浆的混合。基于角闪石成分计算结果,其压力为28.6~166.9 MPa,相当于大约0.6~3.1 km,温度673~908℃,水含量约3.18%~4.64%,氧逸度为ΔNNO-0.22~ΔNNO+3.27。结合其产出的构造背景以及矿区地球物理异常,岩浆高的水含量与高的氧逸度条件说明该区具有很好的斑岩铜矿找矿潜力。The Qiongheba area in the East Junggar terrain is located in the middle section of the Central Asian metallogenic domain. Although many Paleozoic porphyry copper( molybdenum) deposits have been discovered in this area in recent years,these deposits are all small in scale and the metallogenic potential requires further evaluation.The Baxi copper deposit is one of the typical and representative porphyry copper deposits. The quartz diorite and quartz monzodiorite are closely related to porphyry copper mineralization. The zircon mean U-Pb weighted average age of quartz diorite is 345.7±3.0 Ma,indicating that it was formed in the Early Carboniferous. The plagioclase in quartz diorite and quartz monzonite is not andesine that is common in intermediate rocks,but calcium-richer labradorite. The bulk-rock geochemical characteristics show that they have meta-aluminum-weak peraluminum calc-alkaline I-type geochemical signatures. The primitive mantle normalized incompatible element patterns show the enrichment of large ion lithophile elements relative to high field strength elements as well as significantly negative Nb,Ta and Ti anomalies,suggesting a typical island arc-like geochemical feature. The mafic microgranular enclaves( MMEs),positive εHf( t) values( +13.66~ +15.56) and the calcium-rich plagioclase in the rocks suggest that the magma originated from the mantle-derived basic magma mixed with felsic magma derived from juvenile crust. Based on the amphibole compositions,the authors calculated the pressure( 28. 6 ~ 166. 9 MPa,equivalent to 0. 6 ~3.1 km),temperature( 673 ~ 908℃),water content( 3. 18% ~ 4. 64%),and oxygen fugacity( ΔNNO-0. 22 ~ΔNNO+ 3. 27). Combined with the tectonic setting and geophysical anomaly of the mining area,the high water content and oxygen fugacity of magmas indicate that the area has good prospecting potential for porphyry copper deposits.

关 键 词：石英闪长岩 岩浆源区 物理化学条件 成矿潜力 坝西铜矿 

分 类 号：P618.41[天文地球—矿床学] P588.122[天文地球—地质学]