四极质谱流体包裹体气体成分测定技术

Quadrupole Mass Spectrometer Method in Analysis of the Gas Compositions of Fluid Inclusions

将四极质谱、分子泵和超高真空流体包裹体击碎装置联机,利用冷阱与外置液氮去除部分水蒸气和杂气,建立分阶段提取不同世代流体包裹体并测定其气体成分的实验平台。以锡田钨锡多金属矿床中石英脉型钨锡矿矿石为研究对象,分阶段提取不同世代流体包裹体并测定其气体成分,对比分析矿石中共生石英–黑钨矿矿物对不同阶段释气成分、气体百分含量特征。研究表明初始阶段和后期阶段提取的流体成分一致,以N_2、CO_2和CH_4为主,含少量^(40)Ar、C_2H_6和~4He;但初始阶段N_2、CO_2和^(40)Ar气体浓度高于后期阶段,而CH_4、C_2H_6和~4He气体浓度低于后期阶段,指示初始阶段和后期阶段提取出不同期次的流体包裹体,即初始阶段提取的主要是次生包裹体,后期阶段提取的主要是原生包裹体,而中间阶段是两者的混合,表明四极质谱和超高真空流体包裹体提取装置联用能够实现分阶段提取不同世代流体包裹体且测定其气体成分。其中,次生包裹体富N_2、CO_2和^(40)Ar,而原生包裹体富CH_4、C_2H_6和~4He。

Stepwise crush can be used to distinguish the secondary and primary fluid inclusions,and therefore can be used in 40Ar/39Ar dating of quartz,sphalerite,cassiterite,and wolframite.Secondary and primary fluid inclusions will mainly be released during the initial and the final crushing steps respectively,while a mixture of the two endmembers will be released in between the above mentioned steps.The quadrupole mass spectrometer has been applied to gas composition analysis of fluid inclusions since the early 1990s.However,the research has mainly focused on the compositions of bulk fluid inclusion by one-step crushing or heating.In this paper,we try to use the RGA200 quadrupole mass spectrometer connected to a crusher to extract fluid inclusions for gas composition analysis.The fluid inclusions were extracted by stepwise crushing of the paragenetic mineral pairs of quartz and wolframite.The results showed that fluid inclusions are similar in gas compositions,but they are different in gases proportion at different stages.In the initial crush steps,there are mainly secondary fluid inclusions with higher contents of N2,CO2 and 40Ar,while primary fluid inclusions are dominated in the final crush steps with higher contents of CH4,C2H6 and 4He.