四川木里梭罗沟金矿床成因讨论:来自年代学和硫、铅同位素的约束

Discussion on the genesis of the Suoluogou gold deposit,Muli,Sichuan Province:Constraints from geochronology,and S and Pb isotopes

四川木里县梭罗沟金矿床是甘孜-理塘金矿带上目前已查明资源储量最大的金矿床,但是其矿床成因研究薄弱,制约了深部找矿勘探工作。本次研究对其赋矿岩石和含金矿脉的锆石U-Pb年代学、载金矿物黄铁矿和毒砂的硫、铅同位素开展了研究。结果表明,梭罗沟金矿床赋矿岩石的锆石U-Pb年龄为(252.8±2.3)Ma(MSWD=0.4,n=18),指示赋矿岩石为晚三叠世曲嘎寺组碎屑岩基质中的晚二叠世玄武岩岩块。含金矿脉碎屑锆石U-Pb年龄具有4个较明显的峰值,分别为119 Ma、255 Ma、526 Ma和962 Ma。最年轻的碎屑锆石年龄为(119±1.7)Ma(MSWD=0.2,n=13),指示梭罗沟矿床深部可能有隐伏的早白垩世花岗岩,并且金成矿时代晚于119 Ma。金成矿热液期的黄铁矿和毒砂的δ^(34)S值范围为4.8‰~7.79‰(平均值为6.2‰),与造山型金矿床的硫同位素相似。黄铁矿的(206)^Pb/(204)^Pb平均值为18.47、(207)^Pb/(204)^Pb平均值为15.63和(208)^Pb/(204)^Pb平均值为37.74,与造山带铅同位素演化一致。结合矿床地质特征,梭罗沟金矿床受晚白垩世-古近纪的韧性剪切带和走滑断裂控制,其成矿时代为119~27 Ma之间,其矿床类型为造山型金矿床。

The Suoluogou gold deposit,the largest gold deposit in the Ganzi-Litang gold belt,is located in Muli County,Sichuan Province.However,there has been little research on the ore genesis of this deposit,which has inhibited exploration.This study analyzes the U-Pb geochronology of zircons,as well as S and Pb isotopes of pyrites and arsenopyrites,from the Suoluogou gold deposit.The ore-bearing basaltic rocks formed in the late period of the Late Permian,based on the zircon U-Pb age of(252.8±2.3)Ma(MSWD=0.4,n=18).Zircon U-Pb ages of gold-bearing quartz veins present four distinct peaks of 962,526,255,and 119 Ma.The youngest zircon age is(119±1.7)Ma(MSWD=0.2,n=13),indicating that concealed Early Cretaceous granites may exist deep in the Suoluogou deposit.However,the age of Au mineralization is younger than 119 Ma.The average δ^(34)S values for pyrite and arsenopyrite from the ore-forming hydrothermal period,vary from 4.8 to 7.79‰(average=6.2‰),similar to that of metamorphic fluid.The average values of (206)^Pb/(204)^Pb,(207)^Pb/(204)^Pb,and (208)^Pb/(204)^Pb(18.47,15.63,and 37.74,respectively)are comparable to lead isotopic evolution curve of orogenic.Combined with the geological and geochemical evidence,it is inferred that the Suoluogou gold deposit was controlled by a Late Cretaceous to Paleogene ductile shear zone and strike-slip fault(119-27 Ma).The deposit is therefore characterized as an orogenic type gold deposit.