Kimberlite indicator mineral chemistry of the Bucke and Gravel kimberlites and associated indicator minerals in till, Lake Timiskaming, Ontario

Abstract

A well documented glacial dispersal fan of kimberlite indicator minerals extends southward from the region of the Late Jurassic Bucke and Gravel kimberlites in the Lake Timiskaming kimberlite field of northeastern Ontario. The Geological Survey of Canada collected and analyzed a sample of kimberlite from both pipes and re-examined and analyzed indicator minerals from archived heavy mineral concentrates of till samples from the dispersal fan. The Bucke kimberlite contains more than 30,000 indicator mineral grains per 10 kg sample in the 0.25 to 0.5 mm fraction, which consists of, in decreasing order of abundance, Crpyrope>> Mg-ilmenite>chromite>Cr-diopside. The Gravel kimberlite is three times as indicator mineral rich, containing more than 100,000 grains per 10 kg sample in the 0.25 to 0.5 mm fraction, which consist of Mg-ilmenite>>Cr-pyrope>chromite>Cr-diopside. No olivine was recovered from either sample. Till samples within the fan contain 100s to 1000s of indicator minerals per 10 kg sample, mostly Mg-ilmenite, with Cr-pyrope and chromite, and lesser amounts of Cr-diopside and minor olivine. Indicator minerals are most abundant to the southwest to southeast of the two kimberlites and form a fan-shaped dispersal pattern that extends at least 6 km, and potentially 30 km down-ice. The results presented here demonstrate how ice-flow mapping can be combined with indicator mineral abundance, mineral chemistry, and relative abundance data to define dispersal patterns from kimberlite.