Kevin Dumoulin Honours Thesis Abstract

The Dickenson-Campbell diorite (DCD) is a lithological unit that is exposed at surface on and around the Red Lake Gold Mines (RLGM) near the town of Red Lake, Ontario.  The DCD has had an uncertain past with geologists using a variety of naming schemes for these rocks since their initial description in the 1940’s.  The goal of this thesis was to properly classify the DCD using modern geochemical methods combined with mapping and petrography.  Mapping was undertaken on all exposed DCD within Balmertown where structure and lithology were noted in detail.  Samples of the outcrop, as well as near-surface intersections of drill core were taken for geochemistry and petrography.  Analysis of the data that was obtained showed that the DCD is not an intermediate intrusive lithology.  Petrographic analysis revealed an abundance of glass and / or very fine-grained silica and carbonate mineralogy.  Not only was the very fine grain size an indicator of petrogenesis but the resemblance to the regional and underground basalts also helped refute the diorite theory.  Major and trace element geochemistry showed that all DCD outcrop and drill core samples were tholeiitic basalts and basaltic-andesites, with MORB-like signatures.  Mapping of the area provided an idea as to the stratigraphic relationship between the pillowed basalts and the DCD exposed at surface on the mine site.  Only one unit had well preserved pillows these showed evidence of south-western topping direction (towards the DCD).  The presence of narrow shear zones and conjugate fractures led to the conclusion that there has been an effect of pure shear on these rocks, likely due to regional scale deformation.  Samples taken from various areas in the Balmertown area revealed that there is a variation in the degree of alteration affecting the DCD.  The alteration is the most extreme near the base of the unit, where it is in contact with the underlying basalts.  The black ilmenitic flecks, commonly used as an identifier for the DCD, are the coarsest and most obvious where carbonatization and silicification of the rocks is the strongest.  This has led to the conclusion that the DCD is a rock type that is contiguous with the underlying Balmar assemblage basalts.