Heavy Mineral Identification and Quantification Using Fourier Transform Infrared Spectroscopy.

Abstract

We evaluated the application of Fourier transform infrared (FT-IR) microspectroscopy in the mid-IR region (1500-550 cm^-1) in reflectance mode as a semi-automated tool to quantify common heavy minerals (HM) found in natural sediments and sedimentary rocks. An in-house database of IR spectra for the main HM was acquired. Then, automated HM identification using FT-IR spectroscopy was tested on synthetic mixtures with known HM proportions. HM fractionation during sampling and mounting in epoxy is evaluated by testing several sample preparations techniques. Overall, HM are properly determined using FT-IR microspectroscopy. Most of the HM are found in proportions comparable to those documented in the synthetic mixtures. Main drawbacks to this method include: (i) the mid-IR region does not give access to the absorption bands of some HM, such as fluorite, pyrite, and cassiterite, compared to other methods such as Raman microspectroscopy, (ii) the failure to discriminate titanium dioxide (TiO₂) polymorphs, and (iii) large spectral variations in some mineral groups such as amphiboles. Beyond these limitations, mid-FT-IR microspectroscopy in reflectance mode can be used to accurately determine HM proportions and could be simpler, faster, and/or cheaper when compared to other methods such as optical microscopy or scanning electron microscopy.