Imaging the chemical environments of individual fluid Inclusions using Synchrotron Fourier Transform Infrared microscopy

Abstract

Fluid inclusions provide a record of the physical and chemical composition of fluids that form hydrothermal orebodies in the Earth’s crust. Microthermometry and in situ techniques such as laser ablation inductively coupled plasma mass spectrometry can provide important constraints on the temperature, apparent salinity and element concentrations of individual fluid inclusions and can be used to calculate inferred pressure conditions and formation depths. Here, we describe a novel use of synchrotron Fourier Transform Infrared (FTIR) microscopy to map three parameters in individual fluid inclusions: (1) very low levels of CO2, (2) variations of the state of CO2 and (3) variations in water structure. The intensity of the Synchrotron light source allows mapping of individual fluid inclusions, which provides high-resolution images of the distribution of different CO2 and H2O species within individual inclusions. High resolution spectra of the CO2, recorded here for the first time in fluid inclusions, show the rotational lines of CO2 gas. The results reveal predicted as well as unexpected distributions of CO2 gas in the inclusions.