滇西北中甸地区普上含矿斑岩锆石U-Pb年代学和地球化学特征及其地质意义

Geochronological and Geochemical Characteristics of the Pushang Ore-bearing Porphyry in the Zhongdian Area of the Northwestern Yunnan and Its Geological Significances

滇西北格咱地区是我国重要的斑岩型铜矿田和勘查开发基地,近期在烂泥塘-雪鸡坪铜多金属成矿带北段的普上中酸性复式斑岩体中发现了石英闪长玢岩和石英二长闪长玢岩,为探讨该岩体成因、构造动力学背景及其与铜矿化的关系,对其进行了U-Pb年代学、Hf同位素和元素地球化学分析。结果显示,石英闪长玢岩发生全岩铜矿化,视厚35 m,刻槽取样铜品位为0.13%~4.66%,伴生金为0.24~0.78 g/t,有成为大型斑岩型铜多金属矿床的潜力;普上含矿斑岩体2件锆石U-Pb年龄为215.9~217.6 Ma,表明其为晚三叠世岩浆活动的产物。综合岩石学、地球化学及锆石Hf同位素等特征,认为普上含矿斑岩形成于印支期甘孜-理塘洋壳向西俯冲的构造背景,其源区为俯冲流体交代的岩石圈地幔,岩浆上升过程经历了壳源沉积物质混染。

In recent years,the Geza area in the northwestern Yunnan has gradually become an important porphyry copper orefield and copper resources exploration and development base in China.Quartz diorite porphyrite and quartz monzonitic diorite emplaced within the quartz diorite porphyrite have recently been recognized in the Pushang intermediate-acid porphyry complex in the northern part of Lannitang-Xuejiping Cu polymetallic metallogenic belt.In order to explore diagenetic mechanism and tectonic dynamic background of the Pushang complex and the relationship between the complex and the copper mineralization,the U-Pb chronology,Hf isotopes,and geochemical characteristics of the complex have been studied in this paper.The results show that the copper mineralization was developed in the whole quartz diorite porphyrite,with apparent thickness of 35 m,Cu grades of 0.13%-4.66%,andu grades of 0.24-0.78 g/t for samples collected by using the channel sampling,indicating that the Pushang deposit has the potential to become another large porphyry Cu polymetallic deposit in the southern part of the Yidun arc.The U-Pb ages of(215.9±1.4)Ma and(217.6±1.4)Ma for zircons of two ore-bearing porphyry samples indicate that the ore-bearing porphyries are products ofthe Late Triassic magmatism.Combined with petrological,geochemical,and zircon Hf isotopic characteristics of the porphyry complex,it is believed that the Pushang ore-bearing porphyry was mainly formed by the magma derived from the partial melting of metasomatized lithospheric mantle by subducted fluid under the tectonic setting of the westward subduction of the Ganzi-Litang oceanic crust in the Late Triassic,with contamination of crust-derived sediments in the process of magma ascent.