吉林延边五星山–五凤金矿床碱长花岗岩锆石U-Pb定年及其地质意义

五星山–五凤金矿床为一典型的浅成低温低硫型热液金矿床。矿体产于碱长花岗岩和金沟岭组火山岩地层之中,其产出受断裂、裂隙和次火山岩脉内外接触带构造控制。本文对五星山–五凤矿区岩浆岩开展了年代学及岩石地球化学研究,结果表明区内碱长花岗岩LA-ICP-MS锆石U-Pb年龄为189.2±1.7 Ma,成岩时代为早侏罗世;岩石地球化学结果表明,区内岩浆岩富SiO_2(74.75%~75.45%)、K_2O(3.73%~4.46%),贫Al_2O_3(12.09%~12.86%)、Ba(8.31×10~(–6)~281×10~(–6))、Sr(6.96×10~(–6)~61.3×10~(–6)),稀土元素配分曲线呈轻稀土富集型的右倾型,具明显Eu负异常(δEu=0.01~0.23),富集高场强元素Zr、Hf和大离子亲石元素Rb、U、Th,具有典型A2型造山后花岗岩地球化学特征,其形成的构造背景应为中亚造山带碰撞造山后陆壳伸展环境。而五星山–五凤金矿床成矿时代为晚白垩世,表明五星山碱长花岗岩早于金成矿时代,两者之间无成因联系,金矿化应形成于太平洋板块向欧亚大陆俯冲构造背景环境。

LA-ICP-MS Zircon U-Pb Dating of Alkali Granite in Wuxingshan-wufeng Gold Deposit in Yanbian area,Jilin Province and its Geological Significance

The Wuxingshan-wufen gold deposit is a low sulfur epithermal gold deposit.It occurs in the Wuxingshan alkali granite and the overlying Jingouling Group volcanic rocks.The ore bodies are controlled by faults,fissures and contacts of the dikes.Chronological and geochemical studies of the alkali granite in the Wuxingshan-wufeng mining area were carried out.LA-ICP-MS U-Pb dating of zircons showed that the alkali granite was formed in 189.2±1.7 Ma,i.e.,Early Jurassic.The granite is enriched in SiO2 (74.75％-75.45％),K2O (3.73％-4.46％),depleted in Al2O3 (12.09％-12.86％),Ba (8.31 × 10-6-281 × 10-6) and Sr (6.96× 10 6-61.3 × 10-6),and high concentrations of HFSEs (Zr,Hf) and LILEs (Rb,U,Th).REE patterns of the rocks are right-dipping lines with significant negative Eu anomalies (δEu=0.01-0.23).All these characteristics resemble the type A2 postorogenic granites.So the geological setting of formation of the Wuxingshan alkali granite is more likely the post orogenic extension environment in Central Asia Orogenic Belt.The Wuxingshan-wufeng gold deposit was formed in the Late Cretaceous,lagged far behind the Wuxingshan alkali granitic magmatism.So there is no direct relations between gold mineralization and Wuxingshan alkalite granites,and gold mineralization formed in an environment corresponded to the subduction of the Pacific Plate to the Eurasian Plate.