云南大坪金矿床赋矿闪长岩锆石SHRIMPU-Pb定年及其地质意义

SHRIMP U-Pb dating of zircons from diorite batholith hosting Daping gold deposit in Ailaoshan gold belt,Yunan Province,China

云南大坪金矿床是哀牢山金矿带中最重要的金矿之一,主要赋存在受到强烈剪切和水-岩反应的闪长岩中,是典型的喜马拉雅期造山型金矿。本文对大坪金矿床赋矿闪长岩中锆石进行了SHRIMPU-Pb定年,得出闪长岩围岩的年龄为773±12Ma,为晚元古代,显示该岩体为华南地区晋宁-澄江期大规模基性到酸性岩浆活动的产物,是Rodinia超大陆形成、裂解后冈瓦纳大陆形成过程的响应,而不是前人普遍认为的加里东期岩体。该岩体侵入年龄与大坪金矿脉石英流体包裹体40Ar-39Ar年龄测定给出的高温坪年龄(765.5±7.0Ma)基本一致,显示大坪金矿床具有多期成矿的特征,其主体形成于喜马拉雅期碰撞造山运动,但早在晋宁造山运动中就有金的初步富集。在闪长岩中还发现了年龄为33.7±1.1Ma的锆石,其时代与大坪金矿床含金石英脉中热液绢云母的40Ar-39Ar定年结果(33.76Ma)基本一致,显示它们很可能为该区强烈的韧性剪切和局部岩浆部分熔融作用的产物。

Being one of the largest gold deposits in Ailaoshan gold belt,the Daping gold deposit is hosted in a ductile deformed and alterated diorite batholith,and is believed to be a typical Cenozoic orogenic type gold deposit.In this study,SHRIMP U-Pb dating of zircon from the diorite batholith was performed,and the result is 773±12Ma,suggesting that the diorite was a Late Proterozoic batholith,but not a commonly recognized Caledonian rock body.The diorite batholith is a product of large-scale basic to acidic magmatism during the Jinning-Chengjiang epoch,and is corresponding to a period of Gondwana accretion after Rodinian dispersion.The forming age of the diorite is nearly the same as the high temperature 40Ar-39Ar plateau age（765.5±7.0Ma） of fluid inclusions in Daping auriferous quartz veins,suggesting that the Daping gold deposit was formed during multiple metallogenic epochs：the major ore body was formed during Cenozoic orogeny,while the gold mineralization was started during Jinning orogeny.Cenozoic epoch zircons are also recognized in the diorite,and the age 33.7±1.1Ma is nearly the same as the 40Ar-39Ar age（33.76Ma） of hydrothermal sericite from the Daping auriferous quartz veins,suggesting that the some of the zircons were probably formed during extensively ductile deformation and subsequent magmatic partial melting.