Diamond bearing Neoarchean metaconglomerates are present in the Michipicoten greenstone belt, Wawa-Abitibi Subprovince, near Wawa, Ontario. They form a portion of the Dore Metasedimentary rocks in the Arliss Lake subbasin, and unconformably overlie a succession of mafic metabasalts. The conglomerates are transitional into argillite and are also overlain by argillite, which in turn is conformably overlain by metabasalts. The conglomeratic succession has a maximum thickness of 454 meters and is confined to what appears to be a deformed paleovalley at the base of the sedimentary succession.
Three lithofacies associations were recognized, and interpreted to indicate that the Leadbetter Conglomerate represents a high-energy, alluvial fan-delta succession. Lithofacies Association One is dominated by weakly sheared and highly viscous debris-flows and represents the upper reaches of the alluvial fan. Lithofacies Association Two is dominated by superimposed longitudinal bars that represent the transformation of the depositional environment to a mid-fan and lower-fan proximal braided system. Lithofacies Association Three is dominated by distributary channel mouth-bars, graded turbiditic density deposits and argillite facies, which represent a transgression and transition to a delta-front and subsequently pro-delta environment.
Whole rock geochemical studies of the Leadbetter Conglomerate indicated that the elements Co, Ni, Sc, TiO2, V, Al2O3, Y, Nb, Zr, Hf, Ta, Th and U are chemically immobile. The immobile elements were used to investigate possible source rock compositions. A mixture of source rocks (mafic, intermediate and felsic igneous rocks, lamprophyre, and possibly kimberlitic occurrences) contributed sediment to the depositional system of the Leadbetter Conglomerate. Of these mafic volcanic rocks and lamprophyres provided the majority of the sediment. Ratio plots used to investigate whether placer accumulation of the heavy minerals chromite and zircon were present indicated that significant placer accumulation had not occurred.
Possible source rocks for the diamonds include either diamond-bearing, ultramafic, lamprophyre dikes and breccias, which have been observed and described near the Leadbetter Conglomerate, or a more commonly diamond associated rock type, such as kimberlite, which have yet to be observed in the area. The presence of kimberlites could be investigated by a study of mineral chemistry, but that was beyond the scope of this thesis.
Corey is currently working as a geologist for North American Palladium, in December 2010 he will start work with Exxon in Houston.
For more details about this thesis contact Dr. Philip Fralick
A copy of the thesis can be downloaded here