In Situ Study of Geological Fluid Inclusions Using 23Na Nuclear Magnetic Resonance Spectroscopy
Abstract
23Na Magic Angle Spinning Solid State Nuclear Magnetic Resonance (MAS SS NMR) spectroscopy has been used to study natural geological samples of halite, fluorite, and quartz to evaluate the efficacy of NMR spectroscopy for in situ fluid inclusion analysis. NaCl calibration standards yielded a strong linear correlation (R2=0.9919) for salinity, albeit only over a ~1 ppm breadth of chemical shift. Fluid inclusions were successfully identified in all three types of minerals studied using MAS NMR. Chemical analysis with Inductively Coupled Plasma -- Mass Spectrometry (ICP-MS) was employed to quantify elemental contaminants in halite samples. Powder X-Ray Diffraction (pXRD) analysis was used to verify the mineral identity of the samples and identify any contaminant mineral phases. This research was successful in producing reasonable estimates for fluid salinity within halite samples. Quartz and fluorite samples showed evidence of further influence beyond salinity affecting the chemical shift of fluid peaks. This research was successful as a proof of concept for NMR analysis of fluid inclusions, however, further study is needed to understand the effects of pressure and fluid composition on fluid inclusion behaviour in order for NMR to be a useful technique to identify formation conditions of geological samples.