胶东旧店金矿床赋矿岩浆岩岩石成因及其地质意义

Petrogenesis of ore-hosting magmatic rocks from the Jiudian gold deposit in Jiaodong area,and its geological implications.

胶东地区是我国最重要、规模最大的金矿集区,其中晚侏罗世玲珑花岗岩分布较为广泛,是最主要的金赋矿围岩。旧店金矿床位于胶北隆起与胶莱盆地的交界处,是招平断裂带的重要组成部分,片麻状二长花岗岩为其主要的赋矿岩体,对其岩石成因进行研究,可以为探究金成矿作用提供线索和约束。本文对旧店金矿床周围两处的片麻状二长花岗岩开展LA-ICP-MS锆石U-Pb年代学以及Lu-Hf同位素研究。分析结果显示,锆石^(206)Pb/^(238)U年龄为160.1±1.1Ma、160.4±0.7Ma、161±0.4Ma和162.2±0.9Ma,表明旧店金矿床区域内在晚侏罗世存在较强的岩浆作用。ε_(Hf)(t)值为-31.9~-20.8,二阶段Hf模式年龄(t^(2)_(DM))为2996~2516Ma,表明其岩浆来源于下地壳物质部分熔融,同时二阶段Hf模式年龄(t^(2)_(DM))与地幔物质加入和新生地壳产生的岩浆热事件相对应,因此旧店金矿床的围岩可能由古老镁铁质下地壳物质的部分熔融产生。研究认为二长花岗岩的形成过程可能促使了前寒武纪变质基底中成矿物质活化,同时岩体发育广泛的断裂为矿床形成提供了良好的围岩条件。

Jiaodong Peninsula is the most important and largest gold concentration area in China,and the Jiaodong gold resource is widely hosted by Linglong suites.Jiudian gold deposit is located at the junction of Jiaobei uplift and Jiaolai basin,which is an important part of Zhaoping fault,gneissic monzogranite is the main ore-hosting rocks,the study of petrogenesis can provide clues and constraints for exploring gold mineralization.In this paper,we carried out LA-ICP-MS zircon U-Pb dating and Lu-Hf isotopes of gneissic monzogranites around the Jiudian gold deposit.The analysis results show that the zircon ^(206)Pb/^(238)U ages are 160.1±1.1Ma,160.37±0.7Ma,161.04±0.4Ma and 162.2±0.9Ma,indicating that the Jiudian gold deposit contains strong magmatism in the Late Jurassic.Theε_(Hf)(t)value in range of-31.9~-20.8,and the two-stage Hf ages(t^(2)_(DM))is 2996~2516Ma,indicating that the magma was sourced from partial melting of lower crust.The two-stage Hf age(t^(2)_(DM))is corresponding to the magmatic activity caused by the addition of mantle materials and the juvenile crust.Therefore,the surrounding rock of the Jiudian gold deposit being derived from the partial melting of ancient mafic lower crust.The study shows that the formation of gneissic monzogranite may promote the activation of ore-forming materials in the Precambrian metamorphic basement,and the developing faults in the rock mass provide fit surrounding rock conditions for the formation of the deposit.