江西金山金矿成矿时代探讨--来自石英流体包裹体Rb-Sr年龄的证据

Discussion on the Mineralogenetic Epoch of the Jinshan Gold Deposit,Jiangxi Province——Based on the Quartz Fluids Inclusion Rb-Sr Dating

本文测定了金山金矿含金石英脉型矿石的石英流体包裹体Rb-Sr年龄,试图弄清金山金矿的成矿时代。结果显示,含金石英脉型矿体的形成年龄为379±49Ma,所得Sr同位素初始比(87Sr/86Sr)i=0.7138±0.0011。根据笔者先前所测蚀变岩型矿体含金黄铁矿的黄铁矿Rb-Sr年龄及前人的定年工作,可以推测金山金矿的成矿作用是多期次的,并且在各期内部还有可能是多次脉动式成矿。但金山金矿主要的成矿时代是在晋宁期和海西期,其中晋宁期是蚀变岩型金矿体形成的主要时期,而海西期则是含金石英脉型金矿体形成的主要时期。石英流体包裹体所得的Sr同位素初始比,明显高于玄武岩的值(0.704),而比陆源硅酸盐的值(0.720)偏低,表明成矿物质为壳源物质,并有深源物质的混染。

Rb-Sr age dating of fluid inclusions in the Au-bearing quartz veins from the Jinshan gold deposit is applied to make clear the metallogenic time of the deposit. Experiment results revealed that the age of the quartz vein type ore bodies in Jinshan is about 379±49Ma, belonging to the Hercynian Period, and the initial 87Sr/86Sr value of the ore fluid is 0. 7138±0. 0011. Based on the age data of this work and many previous studies, the authors consider that the mineralization of the Jinshan gold deposit is a product of multi-staged mineralization, which may include the Jinning, Caledonia, Hercynian, and Yanshanian Periods. However, the most important ore-forming periods of the Jinshan gold deposit is the Jinning Period and the Hercynian Period. The Jinning Period is the main period for the formation of alteration-type Au ore bodies, while the Hercynian period was the main time for that of Au-bearing quartz veins-type ore. The value of the （87 Sr/86 Sr） i of the quartz fluid inclusion is obviously higher than that of the basalts （0. 704）, but lower than that of the terrigenous silicates （0. 720）. This may indicate that the ore-forming materials is mainly crust in origin but but contaminated by deep-sourced materials.