The economic implications of kimberlite emplacement

The economic potential of kimberlite bodies is defined by the volume and diamond content of all their internal units which are summarised in three dimensional geological models. Canadian geological models reveal distinct types of kimberlite bodies characterised by fundamentally different emplacement processes and products. Data for representative samples of Canadian kimberlites are used to show that qualitative and quantitative macroscopic petrography (olivines and xenoliths) are powerful and practical techniques in assessing the economic implications of emplacement within individual phases of kimberlite. Kimberlite bodies result from the near-surface emplacement of multiple discrete batches of mantle-derived magmas, each carrying different diamond populations and, in some instances, subsequent resedimentation processes. Magmas containing ~ 25 modal % of olivine macrocrysts, the average maximum load of solids that can be carried to surface by a kimberlite magma, have the greatest potential to be significantly diamondiferous. Modifications to the abundance and size distribution of the olivine macrocrysts in each batch of magma commonly occur during emplacement. The modifications to the olivine macrocrysts, which vary with different emplacement processes and products, are mirrored in the macrodiamond content. Dilution by xenoliths is important in predicting diamond contents but it is also reflected in reduced olivine contents. Thus, olivine macrocrysts can act as a proxy for macrodiamonds. The abundance and size distribution data for olivine can improve the prediction of diamond grade and distribution within, and between, kimberlite units. Summary geological models and macroscopic petrography, together, improve the evaluation of newly discovered bodies resulting in enhanced resource estimates and increased degrees of confidence.