Alteration Mineralogy of Alberta Kimberlites: PIMA Infrared Spectroscopic Analysis

This report contains data collected with the PIMA portable infrared spectrometer from a sample suite of kimberlite and ultramafic cores from Alberta, Canada, including 14 core samples from the Buffalo Head Hills kimberlite field, one core sample from the Mountain Lake diatreme, and one hand sample from the Black butte minette. The suite was supplied by the AGS.

There were a number of objectives for the work. These include, to generally demonstrating the operation of the PIMA portable Short Wave Infrared (SWIR) spectrometer, to evaluate the applicability of the SWIR analytical method to kimberlite alteration minerals, and to show the usefulness of PIMA for logging core. This was accomplished using core samples and one hand sample.

A brief overview of reflectance spectroscopy and how it relates to alteration mineralogy and zoning is provided as background.

The infrared active minerals observed in the samples are summarized using reference spectra from SPECMIN, to represent 'ideal' examples of the spectra of these alteration minerals.

This report illustrates how PIMA is a convincing tool for the identification and evaluation of alteration minerals found in kimberlites. The Short Wave Infrared (SWIR) technique is extremely sensitive to alteration minerals such as clays, carbonates and selected sulfates, and phyllosilicates such as serpentines and amphiboles. It can track elemental substitution and changes in order or crystallinity in the minerals. In hydrothermal deposits, this is often an indicator of temperature changes in the alteration halo. It is also useful for examining weathered surfaces, and weathering profiles. In kimberlites it appears to be able to discriminate between the two alteration types common to those complex rocks: deuteric alteration, and weathering from meteoric and/or ground water activity.