Natural Ammonium Illites from Black Shales Hosting a Stratiform Base Metal Deposit, Delong Mountains, Northern Alaska

Abstract

Abstract Naturally occurring ammonium illites have been discovered in black shales surrounding a stratiform base metal deposit in the DeLong Mountains, northern Alaska. Infrared spectra of the samples exhibit pronounced absorption at 1430 cm −1 , the resonant-banding frequency for NH 4 + coordinated in the illite interlayer. X-ray powder diffraction characteristics of the ammonium illites include an expanded d(001) spacing, with values as large as 10.16 Å, and ratios for I 001 /I 003 and I 002 /I 005 of about 2. Infrared analyses of physical mixtures of NH 4 Cl with a standard illite, and comparisons with synthetic ammonium micas indicate significant substitution (>50%) of NH 4 + for K + in the illite interlayer position. Nitrogen determinations on two ammonium illites after removal of carbonaceous matter gave values of 1.48 wt. % NH 4 + and 1.44 wt. % NH 4 + . A survey of more than 150 different shale horizons indicates that the NH 4 + content of the illites increases in proximity to the stratiform base metal mineralization.