Tuffisitic Kimberlite (TK): A Canadian perspective on a distinctive textural variety of kimberlite

Abstract

Tuffisitic Kimberlite (TK) is a textural variety of kimberlite first described from a number of southern African kimberlite pipes. This particular variety of kimberlite is a specific type of Massive Volcaniclastic Kimberlite (MVK) and bodies infilled with TK are classified as Class 1 kimberlites. TKs are fragmental rocks which dominate the steep sided diatreme zones or conduits of kimberlite pipes and are less commonly encountered within more complex root zones and blind intrusions. This textural variety of kimberlite is characterised by a unique set of macroscopic and microscopic features which are distinctive compared to those present in fragmental rocks or MVKs found within Class 2 and Class 3 pipes. The distribution of olivine macrocrysts and phenocrysts within TKs is most similar to texturally unmodified kimberlites classified as hypabyssal kimberlites (HK). In addition, they are dominated by a restricted range of distinctive juvenile clasts. In contrast, MVKs from Class 2 and Class 3 pipes are often characterised by an olivine distribution and morphology that is unlike that encountered within texturally unmodified kimberlites or HKs. They are also characterised by more complex and highly variable juvenile clasts, consistent with higher degrees of textural modification. A number of the kimberlites discovered in Canada over the last two decades display geological features similar to those described from the Kimberley area of South Africa. The general geology of pipes infilled with TK from Canadian occurrences is summarized in this contribution. It is also presented as a schematic diagram which can be used as a guide for kimberlite evaluation as well as for emplacement models for Class 1 kimberlites. The geology represented in this generalized model summarises observations and interpretations of drill cores, thin sections, diamond distribution data, geophysics and a variety of other data sets from five different kimberlite clusters across Canada. All the pipes investigated have undergone evaluation work in order to determine their economic potential.