延边农坪富金斑岩铜矿床花岗闪长斑岩年代学、地球化学及其地质意义

农坪金铜矿床位于吉林省珲春市春化境内,是一座中型富金斑岩型矿床。文章采用LA-ICP-MS锆石U-Pb定年方法,对农坪含矿花岗闪长斑岩进行了锆石U-Pb分析,获得加权平均年龄为(95.6±1.6)Ma,表明花岗闪长斑岩形成于晚白垩世。地球化学分析显示,农坪含矿斑岩富碱(5.6%~6.7%),高Mg#(47~55)、富集LILE和LREE,亏损HFSE和HREE,高Sr/Y(32~57)、(La/Yb)N(10~21)比值,具有埃达克质岩石的特点,岩浆的形成可能存在壳幔混合及分离结晶作用。结合区域大地构造背景和同一构造带上其他矿床的形成时代和特征,笔者认为农坪矿床是晚白垩世古太平洋板块向欧亚大陆斜向俯冲背景下陆缘弧岩浆作用及热液活动的产物。

Geochronological and geochemical constraints on age and origin of granodiorite of Nongping Au-Cu porphyry deposit in Jilin Province, China

The Nongping Au-Cu deposit, located in Chunhua County of Hunchun City in Jilin Province, is a newly discovered medium-sized porphyry deposit. This paper reports the LA-ICP-MS zircon U-Pb age of the ore-bearing granodiorite-porphyry. The dating result shows that the granodiorite-porphyry was formed in the Late Cretaceous, with a weighted average age of (95.6±1.6) Ma. The granodiorite-porphyry is characterized by high alkali content (5.6%~6.7%), high Mg^#(47~55), enrichment of LILE and LREE but depletion of HFSE and HREE, with high Sr/Y(32~57) and (La/Yb)_N (10~21)ratios. These characteristics indicate that the host rocks are calc-alkaline adakites, probably formed by magma mixing and fractional crystallization. Considering the regional tectonic background and ages of deposits in the same metallogenic belt, the authors hold that the Nongping Au-Cu deposit was formed during the latest magmatic metallogenic peak stage (the late Early Cretaceous to Late Cretaceous) and represents the product of the continental arc magmatism and hydrothermal activities associated with the subduction of the Paleo-Pacific plate beneath the Eurasian continental margin.