Multiple Frustrated Total Internal Reflection IR Spectroscopy as a Way to Study the Typomorphism of Silica Minerals in Gold Deposits

A study was carried out on multiple frustrated total internal reflection (MFTIR) spectra of silica mineral aggregates containing various amounts of opal, chalcedony, and quartz from barren volcanics and also shallow gold-silver deposits as well as medium-depth gold-quartz and gold-sulfide-quartz aggregates. Clear differences in the MFTIR IR spectra of opal-chalcedony-quartz aggregates from the spectra for barren volcanics and the superore zone of shallow gold-silver deposits were revealed, consisting in the splitting of the K3 absorption band at 475-490 cm-1 into peaks at 470-484 and 492-500 cm-1 due to different ratios of opal, chalcedony, and quartz. A connection was found between the different ratios of the reflection band intensities in these spectra with the crystallinity index and depth of the mineral formation. The indicated features of silica mineral aggregates can be used for their typomorphic assignment to ore deposits of a shallow gold-silver formation and assessment of the erosional cut of such ore deposits.