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The Geological Survey of Canada investigated four kimberlite pipes in the Kirkland Lake area, northeastern Ontario to document indicator signatures in glacial sediments. This report focuses on results from the C14 kimberlite in Clifford Township. The kimberlite has been eroded down by preglacial and glacial weathering to a level approximately 20 to 30 m below the surrounding bedrock. The subcropping surface consists of heterolithic tuffisitic kimberlite breccia. Kimberlite indicator minerals of the C14 pipe are dominated by Cr pyrope and chromite (± Cr-diopside) derived from lherzolitic xenoliths with only a minor proportion from harzburgite and dunite sources. No evidence of eclogitic xenoliths in the C14 kimberlite were found in this study. The low numbers of Cr-poor pyrope, diopside and Mg-ilmenite point to a low contribution from the Cr-poor megacryst suite which can be dominant in other kimberlites in the Kirkland Lake kimberlite field. The presence of subcalcic garnet and Cr-rich and (magnesio-) chromite suggests a moderate diamond potential for the Cl4 pipe. The relative abundance of indicator minerals in the C14 kimberlite, listed in decreasing order of abundance, is: pyrope > Cr-diopside > chromite > Mg-ilmenite. These relative abundances are mimicked in till overlying and just down-ice of the kimberlite. Indicator mineral chemistry for grains recovered from the glacial sediments around the C14 kimberlite are also similar to that for the kimberlite. Kimberlite samples from the C14 pipe contain tens of thousands of indicator mineral grains in 10-kg. Incorporation of kimberlite into the till is obvious overlying the Cl 4 kimberlite and just down-ice and is reflected in all size fractions of till. The non-ferromagnetic heavy mineral fraction (coarse to fine sand) of till contains anomalous concentrations of indicator minerals (tens to thousands of grains) and displays elevated concentrations of Cr, Sr, Ta, La, Ce, and Eu. The |
