High-Resolution Physical Properties, Geochemistry, and Alteration Mineralogy for the Host Rocks of the Archean Lemoine Auriferous Volcanogenic Massive Sulfide Deposit, Canada

Abstract

Multiparameter data on drill cores have a range of useful applications for ore deposit modeling and mineral exploration. Density, magnetic susceptibility, eight major elements, seven trace elements (portable X-ray fluorescence [pXRF]), five mineral groups (near-infrared spectrometry), and average visible light reflectance were determined on rock cores from several drill holes. These are located near the Archean Lemoine auriferous volcanogenic massive sulfide (VMS) deposit in the Chibougamau mining district, Abitibi subprovince, Quebec, Canada. This case study focuses on one particular drill hole that has been recently characterized in detail by conventional methods (laboratory geochemistry, petrography, and stable isotopes); this provides validation for the multisensor dataset. The best variables and immobile element ratios to distinguish between different lithological units in the multiparameter data are density, magnetic susceptibility, Ti/Zr, Al/Zr, and Zr/Y. Downhole profiles of these parameters allow the four different felsic units in LEM-37, many of which are visually similar, to be distinguished, and geologic contacts to be positioned precisely. Such methods would be even more useful in environments where recognition of primary characteristics is strongly hampered by intense hydrothermal alteration and superimposed deformation or metamorphism. Volcanic and intrusive rocks can be placed on classic diagrams to assign them names and magmatic affinities based on the corrected pXRF data. Downhole profiles of major and trace elements, combined with infrared mineralogy, allow hydrothermal alteration to be characterized, yielding results comparable to those of conventional techniques for the same drill hole, but with a much tighter spacing and within potentially shorter time frames.