The Seed and Triple B kimberlites and associated glacial sediments, Lake Timiskaming, Ontario

Abstract

In 200 l and 2002, shallow trenches were excavated by the Geological Survey of Canada into the Seed and Triple B kimberlites, ill the northeast part of Firstbrook Township, near Lake Timiskaming, Ontario. The Triple B kimberlite was discovered by the Geological Survey of Canada in 2001. The purposes of studying these two kimberlites are to docu�ment kimberlite mineralogy as well as glacial dispersal patterns associated with the kimberlites The Triple B kimberlite is intrusive into Paleoproterozoic argillites (Firstbrook Member of the Gowganda Formation) but may also be, in part, intrusive into Nippising diabase. The Seed kimberlite subcrop, excavated by GSC in 2001, is a pelletal textured kimberlite breccia (>15% clasts larger than 4 nun), with the clasts dominantly argillite and limestone, with minor diabase. It's radiometric age of 153.7± 1.8 Ma suggests the Seed kimberlite is amongst the oldest of the eight Lake Timiskaming field kimberlites dated so far, which vary from 155.4 ±1.5 Ma to 133.9±1.5 Ma in age. At the northern contact of the main Triple B kimberlite body with Firstbrook argillite, is hypabyssal aphanitic kimberlite. This aphanitic kimberlite grades into 'normal' looking olivine macrocrystic hypabyssal kimberlite. Approximately 13 m from the north contact is diatreme kimberlite microbreccia which is altered in its southernmost part. A narrow hypabyssal phlogopite spinel calcite kimbernite dyke trending approximately 310o subcrops west of the main kimberlite body. Based on caustic fusion results of small samples, the diamond potential of the Seed and Triple B kimberlites is suggested to be low. Airborne and ground magnetic surveys clearly show the negative magnetic anomalies associated with the Seed and Triple B kimberlites, as well as two untested negative magnetic anomalies nearby. The relative abundance of kimberlite indicator minerals in the Seed kimberlite is Mg-ilmenite >>Cr-pyrope >Cr-diopside > chromite > olivine. The relative abundance of kimberlite indicator minerals in the Triple B kimberlite is Mg-ihnenite >> Cr-diopside > Cr�pyrope > olivine > chromite. These relative abundances are different from other kimberlites in the Lake Timiskaming field and can be used to distinguish then· dispersal trains from dispersal trains derived from other nearby kimberlites.