新疆阿舍勒铜锌矿区(潜)火山岩LA-MC-ICP-MS锆石U-Pb年龄及其地质意义

LA-MC-ICP-MS U-Pb dating of zircons from volcanic rocks and subvolcanic intrusions in Ashele Cu-Zn ore district,Xinjiang,and its geological implications

阿舍勒铜锌矿床是中国阿尔泰南缘典型的VMS型矿床,赋存于阿舍勒盆地阿舍勒组一套海相火山-沉积岩系中。Ⅰ号主矿体呈层状位于凝灰岩与玄武岩之间,矿化呈（致密）块状、条带状、层纹状、稠密浸染状、细脉状。在潜英安岩中也伴有热液蚀变及矿化。前人对该矿床进行了大量的研究,但对容矿火山岩、潜火山岩及成矿时代还缺乏年代学资料。文章应用LA-MC-ICP-MS锆石U-Pb定年法对矿体的直接围岩凝灰岩、玄武岩、潜英安岩和石英闪长岩进行了研究。获得年龄：凝灰岩为（387.0±4.2）Ma,玄武岩为（388.2±3.3）Ma,潜英安岩为（379.4±0.8）Ma,石英闪长岩为（378.5±0.9）Ma,限定阿舍勒组时代为早-中泥盆世。阿舍勒铜锌矿为同生沉积矿床,Ⅰ号主矿体产于玄武岩和凝灰岩之间,限定了Ⅰ号主矿体喷流沉积期形成于早泥盆世末期（388-387 Ma）;潜英安岩的U-Pb年龄为（379.4±0.8）Ma,表明与潜火山岩有关的岩浆热液期矿化形成于中泥盆世。获得玄武岩、凝灰岩、潜英安岩和石英闪长岩中古老锆石U-Pb年龄变化于743-2505 Ma,暗示了阿尔泰造山带存在前寒武纪结晶基底。

The Ashele Cu-Zn deposit is representative volcanogenic massive sulfide（VMS）deposit in China＇s Altay region.The deposit occurs in the marine volcano-sedimentary sequence of the Ashele Formation in the Ashele Basin.No.Ⅰmain ore body occurs in the stratiform form between tuff and basalt,and mineralization occurs in massive,densely massive,banded,laminated,densely disseminated and veinlet forms.The hydrothermal alteration and mineralization also occur in the sub-dacite.Lots of research work has been carried out in the Ashele deposit,but the ages of its ore-hosting volcanic rock,subvolcanic rock and mineralization have not yet been clearly determined.In this paper,LA-MC-ICP-MS zircon U-Pb dating was used for studying the tuff and basalt from the direct host rocks of the ore bodies,sub-dacite and quartz diorite in the Asele Cu-Zn district.The U-Pb ages are（387.0±4.2）Ma,（388.2±3.3）Ma,（379.4±0.8）Ma,（378.5±0.9）Ma for tuff,basalt, sub-dacite and quartz diorite,respectively,suggesting that the Ashele Formation is Early-Middle Devonian in age.The Ashele Cu-Zn deposit is an syngenetic deposit,and No.Ⅰmain ore body occurs between tuff and basalt.The ages of the tuff and basalt suggest that the mineralization in the sedimentary exhalative period occurred in the late Early Devonian（388-387 Ma）.The U-Pb age of the sub-dacite is（379.4±0.8）Ma,imrplying that the magmatic hydrothermal mineralization took place in the Middle Devonian.The U-Pb ages of the older zircons from tuff,basalt,sub-dacite and quartz diorite range from 743 to 2505 Ma,which represent the forming age of the Precambrian crystalline basement in Altay region.