中甸弧雪鸡坪斑岩铜矿含矿斑岩锆石SHRIMP U-Pb年代学及Hf同位素组成

SHRIMP Geochronology and Hf Isotope Composition of Zircons from Xuejiping Porphyry Copper Deposit,Yunnan Province

长期以来,关于雪鸡坪斑岩铜矿的成岩成矿时代具有很大的争议。为了限定成矿作用开始的时限,本文选择代表成矿前岩浆岩的绢英岩化带内含矿斑岩进行锆石SHRIMP年代学测试,获得了215.2±1.9Ma的成岩年龄,说明雪鸡坪斑岩铜矿形成于215Ma之后。锆石Hf同位素测试结果显示岩浆主要来源于地幔源区,但是锆石Hf同位素分布不均匀,9颗锆石εHf(t)的结果分布于1.1～2.1,二阶段模式年龄平均值为1150Ma,两颗锆石εHf(t)值为7.4和6.0,对应的二阶段模式年龄分别为778Ma和869Ma,暗示存在两种不同的岩浆源区,可能发生过岩浆混合作用,但需进一步的研究证实。区域同位素年代学对比结果表明,215Ma左右的岩浆活动是中甸弧主要的控制斑岩铜矿成矿的热事件。

There are a lot of debates about the age of mineralization of Xuejiping porphyry copper deposit, Yunnan province. For determination of the time limit of beginning of the mineralization, the zireons from the porphyry of host ore in serieite-quartz alteration belt at Xuejiping porphyry eopper deposit was taken to do the SHRIMP U-Pb dating, and the result was 215.2±1.9 Ma, whieh indicated that the mineralization acurred after 215 Ma. Hf isotope composition of the zireons shows that the magma comes from mantle source. The distribution of the Hf isotope data is not homogeneous. εHf（t） of 9 zireons range from 1. 1 to 2. 1, and average of two stage model ages is 1150 Ma. But εHf（t） of 2 zircons are 7.4 and 6.0 respectively, and the corresponding two stage model ages are 778 Ma and 869 Ma. These data show the existence of two magmatic source, and magma mixing, which should be proved through farther study. Regional isotope chronology data indicated that the magmatism of 215 Ma was main heat event controlled the mineralization of porphyry copper deposits.