云南中甸红牛-红山大型夕卡岩铜矿床石榴子石U-Pb年代学、元素地球化学及地质意义

The U-Pb chronology,element geochemistry and geological significance of garnets from the Hongniu-Hongshan large skarn copper deposit,Zhongdian,Yunnan,China

为厘定云南中甸红牛-红山大型夕卡岩铜矿床赋存矿体的夕卡岩的形成年龄,对矿区产出的石榴子石开展了U-Pb定年,并结合石榴子石的元素地球化学特征探讨矿床成因。结果显示,矿区不同矿段(红牛、红山)均发育早(GrtⅠ)、晚(GrtⅡ)两个世代的石榴子石,其成分均为钙铝-钙铁榴石固溶体(红牛为And_(27.02~62.53)Gro_(36.74~71.64),红山为And_(42.51~99.94)Gro_(0.00~56.37))。不同矿段、不同世代石榴子石的稀土元素配分模式特征迥异,表现为左倾型、负Eu异常和右倾型、正Eu异常两种配分模式;两个矿段石榴子石的稀土总含量相差较大(红牛为5.29×10^(-6)~102×10^(-6),红山为19.8×10^(-6)~206×10^(-6))。研究表明,石榴子石的稀土配分模式主要受钙铝榴石-钙铁榴石端元组分控制;更高的稀土元素含量可能与富氯流体的加入及流体运移距离较短有关。红牛-红山矿床石榴子石U-Pb年龄为(79.7±3.4)Ma,代表了夕卡岩化的形成年龄,指示该矿床形成于晚白垩世。

In order to determine the formation age of skarn in the Hongniu-Hongshan large skarn copper deposit in the Zhongdian area,Yunnan Province,the U-Pb dating of garnets from the deposit has been carried out and the genesis of the deposit has been discussed in combination with the elemental geochemical significances of the garnets.The results show that two generations of garnets[the early one(GrtⅠ)and the late one(GrtⅡ)]were developed in different oreblocks(the Hongniu and Hongshan oreblocks)in the deposit,with their components of the grossularite-andradite solid solution(And_(27.02-62.53)Gro_(36.74-71.64)at Hongniu,And_(42.51-99.94)Gro_(0.00-56.37)at Hongshan).The distribution patterns of rare earth elements in various generations of garnets from different oreblocks are quite different,manifested as two types of distribution patterns including the left-declined pattern with negative Eu anomaly and right-declined one with positive Eu anomaly;There are significant differences among the total REE contents of garnets from two oreblocks(5.29×10^(-6)~102×10^(-6)at Hongniu,19.8×10^(-6)~206×10^(-6)at Hongshan).The results show that the REE distribution patterns of garnets were mainly controlled by the end components of the grossularite-andradite;The relatively high contents of REE may be related to the addition of chlorine-rich fluids and the relatively short distance of fluid migration.The U-Pb age of the garnet from the Hongniu-Hongshan deposit is(79.7±3.4)Ma,representing the age of skarnization and indicating that the deposit was formed in the Late Cretaceous period.