Indicator mineralogy of the KL-01 and KL-22 kimberlites, Lake Timiskaming kimberlite field, Ontario

Kimberlite and till samples from the recently discovered KL-01 and KL-22 kimberlites in the Lake Timiskaming kimberlite field, northeastern Ontario, have been studied by the Geological Survey of Canada to determine their kimberlite indicator mineral signatures. These new results compliment earlier work published on the Lake Timiskaming kimberlites by the GSC. The KL-01 kimberlite is covered by only 1 to 4 m of till and thus is deeply weathered. The KL-22 kimberlite is covered by more than 10 m of glacial sediments and thus is fresh at its subcropping surface. Both kimberlites contain thousands of indicator minerals per 10 kg in the 0.25 to 0.5 mm fraction. The kimberlites, however, are characterized by different relative abundance of indicator mineral species. The 0.25 to 2.0 mm fraction of the KL-22 kimberlite is dominated by chromite, with lesser amounts of Cr-pyrope and Cr-diopside, very few Mg-ilmenite, scarce eclogitic garnets, and no olivine. The 0.25 to 2.0 mm fraction of the KL-01 kimberlite is dominated by Cr-pyrope, with lesser amounts of chromite, Mg-ilmenite and Cr-diospide, scarce eclogitic garnets, and no olivine. Till overlying the KL-22 kimberlite contains only a few tens of indicator mineral grains and does not contain much garnet, a relatively abundant indicator mineral in the KL-22 kimberlite. Thus this till likely reflects background concentrations in the area rather than incorporation of KL-22 kimberlite debris. Indicator mineral populations of the KL-01 and KL-22 kimberlites are dominated by chromite, Crpyrope, and Cr-diopside from fertile garnet lherzolite. Subcalcic garnets are abundant as well but they are only marginally Cr-rich with respect to diamond potential and magnesiochromites include some diamond inclusion and diamond intergrowth field. Garnet megacrysts are rare in both kimberlites, as are orange diamond sub-class eclogite garnets. Similar mineral compositions and age dates for the two kimberlites strongly suggest that KL-01 and KL-22 are genetically related.