西准噶尔阔尔真阔腊金矿区玄武安山岩锆石U-Pb年龄及其地质意义

LA-ICP-MS U-Pb Zircon Age of Basaltic Andesite in the Kuoerzhenkuola Gold Deposit and Its Geological Significance

萨吾尔地区位于西准噶尔东北缘,广泛发育古生代岩浆岩,这些岩浆岩的年代学以及地球化学研究对于限制西准噶尔地区区域构造演化具有重要的意义.阔尔真阔腊金矿床是萨吾尔地区最重要的金矿床,矿区内主要出露玄武安山岩、安山岩、闪长玢岩和少量闪长岩,其中玄武安山岩和安山岩是直接赋矿围岩.玄武安山岩中锆石LA-ICP-MS U-Pb谐和年龄为339.4±4.8 Ma,表明其形成于早石炭世.矿区内玄武安山岩和安山岩属于高钾钙碱性系列,相对洋中脊玄武岩富集Sr、Ba、Th等大离子亲石元素,亏损Nb、Ti等高场强元素.玄武安山岩和安山岩具有较高的Th/Yb值（0.87～4.84）,较低的Th/Zr值（0.023～0.071）,这些特征与形成于岛弧环境中的火山岩相似,其原始岩浆可能为受俯冲板片析出流体交代的地幔部分熔融形成,板片熔体交代作用并不明显.同处于西准噶尔地区的哈图金矿床赋矿玄武岩具有岛弧玄武岩和N MORB的地球化学特征,受俯冲流体交代作用弱,可能形成于弧后盆地环境.在西准噶尔地区,岛弧和弧后盆地环境中都可以形成火山热液型金矿床.

The Sawuer region is located at the northeastern margin of the West Juggar,where the late Paleozoic volcanic and intrusive rocks are widespread.The geochronology and geochemistry of these magmatic rocks has great significance to constrain the regional tectonic evolution in West Juggar.The Kuoerzhenkuola gold deposit is the most important gold deposit in the Sawuer region.The exposed intermediate-acid rocks in the deposit contain basaltic andesite,andesite,dioritic porphytite and diorite.The analysis by LA-ICPMS shows that the zircon crystals from the basaltic andesite have the concordant U-Pb age of 339.4±4.8Ma,indicting that they were formed in early Carboniferous.The Geochemical analysis show that the basaltic andesite and andesite belong to calk-alkaline series,and are enriched in large ion lithophile elements（such as Sr,Ba,Th）and depleted in high field strength elements（such as Nb,Ta）.The basaltic andesite and andesite in the deposit have high Th/Yb ratio（0.87~4.84）and low Th/Zr ratio（0.023~0.071）.These features are similar to those of the volcanic rocks in the island-arc environment.The primitive magma of the rocks was possibly generated by partial melting of a metasomatic mantle source modified by the subducted slab-derived fluid rather than the slab-derived melt.Geochemical characteristics of the ore-hosted basalt from the Hatu gold deposit in the West Junggar are similar with those of island-arc basalt and N-MORB.The mantle metasomatism induced by the subduction fluid beneath the Hatu deposit is weaker than that beneath the Kuoerzhenkuola deposit.These features indicate the basalt in the Hatu deposit was formed in arc-back basin environment.The volcanogenic hydrothermal gold deposit in the West Junggar can be formed in the island-arc and the arc-back basin.