热液体系氩同位素示踪研究

AN INVESTIGATION ON ARGON ISOTOPE TRACE IN HYDROTHERMAL SYSTEM

采用分阶段加热爆裂法测定了不同成因热液矿床脉石英流体包裹体的氩同位素，计算出各温度段内大气氩的相对含量，从而，总结出大气降水热液矿床、再平衡岩浆水热液矿床等成矿流体的氩同位素组成特征及其演化规律。典型的大气降水热液矿床，其成矿流体以具有高大气Ａｒ组分（约９５％－１００％）为特征；再平衡岩浆水热液矿床成矿流体的Ａｒ同位素组成特征取决于与其有成因关系的初始岩浆水的Ａｒ同位素组成及矿源层和围岩的性质，产于古老变质岩中的，一般以具有低大气Ａｒ组分（约６％－２０％）为特征，其它的再平衡岩浆水热液矿床在主成矿温度范围内一般为５０％－６０％左右。

Using the decrepitation technique by step heating,Argon isotope composition of fluid inclusions in quartz from various hydrothermal deposits in different geological conditions was systematically determined and contents of atmospheric Argon constituent (wArA/%) in each heating steps were calculated.Accoridingly,Argon istotope composition characteristics and evolution rule of ore forming fluid in the hydrothermal deposits with different genesis were summarised.The ore forming fluid in typical meteoric hydrothermal deposits has high atmostheric Argon constituent (95%-100%);Argon isotope property of ore forming fluid in re equilibrated magmatic hydrothermal deposits is related to the property of the Argon isotope composition of initial magmatic water and source bed and wall rocks.It is low in atmospheric Argon constitutent (about 6%-20%) for the hydrothermal deposits in ancient metamorphic rock while it is 50%-60% of atmospheric Argon constituent in other re equilibrated magmatic hydrothermal deposits when they are within ore forming temperature. It is shown that in hydrothermal system the Argon isotope composition is closely related to Oxygen isotope composition.Meteoric hydrothermal generally has high and stable atmospheric Argon constitutent and low and variable Oxygen isotope composition.For example,wArA values are 100% in nearly all of the ore forming fluid in the Lianghe Au deposit,the Erentaolegai Ag deposit and the Bainaimiao Au deposit,but the δ18OOH2O values are -2.2‰,-13.9‰ and -8.5‰ respectively.Re equilibrated magmatic hydrothermal generally has high and stable δ18OOH2O values and low and variable wArA values.For example,δOH2O values are about 5.0‰-6.9‰ in the ore forming fluid in the Jinguanding Au deposit,the Majiayao Au deposit,the Linglong Au deposit,the Xihuashan W deposit and the Piaotang W Sn deposit,but the wArA values are about 6%-62%.