云南香格里拉盖吉夏含矿石英二长闪长玢岩年代学、地球化学、锆石Hf同位素特征及其地质意义

Geochronology,geochemistry,and zircon Hf isotope characteristics and their geological significances of the Gaijixia ore-bearing intrusive rocks in the Shangri-La region,NW Yunnan,SW China

盖吉夏铜多金属矿床位于香格里拉地区格咱斑岩带红山-普朗铜多金属成矿亚带北段,铜多金属矿化与石英二长闪长玢岩紧密相关。石英二长闪长玢岩LA-ICP-MS锆石U-Pb年龄为216.6±2.3Ma(MSWD=1.9),与区域上普朗、松诺、地苏嘎、雪鸡坪、春都等含矿斑岩体年龄一致。锆石εHf(t)值分布范围为-1.55~3.27,平均为1.57,分布较集中;单阶段Hf模式年龄(tDM1)变化范围为733~918Ma,平均为795Ma,二阶段Hf模式年龄(tDM2)为923~1178Ma,平均为1015Ma,揭示其源区可能为亏损地幔或新生壳源物质。岩石SiO2为61.08%~69.55%,Na2O+K2O为7.22%~7.82%,Na2O/K2O为0.87~1.87,具高钾钙碱性准铝质-弱过铝质(A/CNK=0.75-1.34)特征,岩石富集轻稀土元素[(La/Yb)N=13.35-24.85]和大离子亲石元素(Rb、Ba、Pb等),相对亏损重稀土元素和高场强元素(Ti、Nb、P等),且具有高Sr(>400×10-6),低Y(<18×10-6)、Yb(<1.9×10-6)及高Sr/Y、La/Nb等特点,显示出正常弧岩浆系列钙碱性岩石特征,说明含矿石英二长闪长玢岩与岛弧环境密切相关。这种特征的花岗岩可能为盖吉夏的Cu成矿作用提供了重要的物质来源。

The Gaijixia Cu polymetallic mining area is located in the northern segment of the Hongshan-Pulang Cu polymetallic metallogenic sub-belt in the Geza porphyry belt.The Cu polymetallic mineralization at Gaijixia is closely related to the quartz monzodiorite porphyrite,zircons from which yield an average LA-ICP-MS U-Pb age of 216.6±2.3 Ma CMSWD=1.9 D,consistent with the forming ages of Pulang,Songnuo,Disuga,Xuejiping and C.hundu ore-bearing intrusive rocks nearby.The concentrated εHf CtD values of these zircon grains range from-1.55 to 3.27 Caverage of 1.57 D,with corresponding Hf model ages of tDM1 and tDM2 of 733~918 Ma Caveraged at 795 MaD and 923~1178 Ma Caveraged at 1015 MaD,respectively,indicating contributions from depleted mantle or neonatal crust-derived materials.The intrusive rocks are lithologically high-K alkaline CSiO2=61.08%~69.55%,Na2 O+K2 O=7.22%~7.82%,Na2 O/K2 O=0.87~1.87 D,metaluminous-weakly peraluminous CA/CNK=0.75~1.34,Al2 O3=14.82%~17.07% D,enriched in LREEs [CLa/YbDN=13.35~24.85] and LILEs Ce.g.,Rb,Ba,and PbD,depleted in HREEs and HFSEs Ce.g.,Ti,Nb,and PD,with a high content of Sr C>400×10-6 D,low contents of Y C<18 × 10-6 D and Yb C<1.9 × 10-6 D,and high Sr/Y,La/Nb ratios.The geochemical characteristics of them coincide with those of the calc-alkaline rocks of normal arc magma series,suggesting a close correlation with island arc environment.Such type of granites could have provided a significant amount of material sources to the Gaijixia Cu mineralization.