黑龙江金厂金矿田岩浆和成矿作用的LA-ICPMS锆石定年

黑龙江金厂金矿床为中亚造山带东段大型的浆控热液成矿系统,但成矿及其相关岩浆活动的时间研究薄弱.为厘定金厂金矿的形成时间和构造背景,本文利用单颗粒锆石激光探针LA-ICP-MS定年技术获得了赋矿花岗岩围岩和成矿闪长岩的锆石U-Pb年龄.结果表明,锆石韵律性环带结构发育,Th/U比值集中于0.5～1.5之间,具有岩浆锆石特征.两组锆石~(205)Pb/~(238)U谐和年龄分别为202.1±3.0Ma和111.5±1.2Ma,代表了两期岩浆.流体活动的时间;一组谐和性较差的蚀变花岗岩锆石~(206)Pb/~(208)U加权平均年龄为198.0±3.9Ma,指示赋矿花岗岩受到后期热液作用的影响而年龄偏小.据此认为,不同期次的岩浆-流体成矿事件在同一空间叠加复合是金厂大型金矿系统形成的重要原因;202Ma左右的岩浆一流体成矿事件缘于古亚洲洋闭合后大陆碰撞体制的岩浆作用,而111Ma左右的岩浆一流体成矿事件则缘于太平洋板块俯冲诱发的岩浆弧或弧后大陆伸展体制的岩浆活动.

LA-ICPMS zircon U-Pb dating of magmatism and mineralization in the Jinchang gold ore-field, Heilongjiang province

The Jinchang gold deposit,Heilongjiang province,is a large intrusion-related hydrothermal ore-system developed in the eastern end of the huge Central Asia orogenic belt.The ages of metallogenesis and related magmatism have not been well constrained yet.To bracket the mineralization time and to understand tectonic setting of the Jinchang gold deposit,precise isotope ages of orehosting granite and ore-forming diorite intrusions are obtained using single zircon-grain LA-ICPMS U-Pb dating method in this paper.All zircon grains have natural growth-zoning texture,with the Th/U ratio ranging mainly from 0.5 to 1.5,showing the nature of zircon grains of magmatic origin.The weighted average ~(206) Pb/~(238) U ages of zircon grains from granite and diorite are 202.1±3.0Ma and 111.5 ±1.2Ma,respectively,representing the times of two magmatic-hydrothermal mineralization events.The age of 198.0±3.9Ma for the altered ore-hosting granite in northern Banjiegou circular structure system possibly reflects a late hydrothermal modification event which causes the 202Ma granite yields younger age.Hence it is the overprinting and combination of two magmatic-hydrothermal mineralization events in the same position resulted in formation of the Jinchang large gold deposit.The earlier event at about 202Ma originated from granite magmatism occurred in continental collision regime after the closure of Paleo-Asia Ocean.The later magmatic-hydrothermal event at about 111Ma occurred in magmatic arc or back-arc extensional setting related to northwestward subduction of paleo-Pacific oceanic plate.