Diamond formation in Earth's mantle

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***Diamond exploration and mining is the principal economic driving force in Canada's remote North. However, current levels of production will be unsustainable unless new deposits are discovered within the next few years. To help develop more efficient exploration strategies, we will geochemically fingerprint the conditions deep in the Earth's mantle that enhanced or prevented diamond formation in the distant past.*******The investigations outlined below are expected to produce not only ground-breaking basic research but also new and better methods for diamond exploration.*******1. Processes of diamond formation****The layered internal structure of diamond can be compared to tree rings in that both can reveal complex and extended growth histories. I direct a multi-collector ion microprobe facility, which will enable us to obtain profiles of carbon and nitrogen isotopic compositions and nitrogen contents at high spatial resolution across diamond growth zones. These profiles allow us to deduce the chemical character of the original diamond-forming fluids or melts and reveal if they were methane- or carbonate-bearing. By studying diamonds with known ages of crystallization, we will be able to follow variations in the preferred modes of diamond precipitation through time.*******2. Unconventional diamond deposits****Archean cratons are large, stable blocks of the Earth's crust that are older than 2.5 billion years. The lithospheric mantle beneath such cratons is the source of >99% of current diamond production, and the rock type harzburgite is its key diamond substrate. However, younger areas of the crust can also host world-class diamond deposits. The rock type eclogite is a key diamond substrate in such unconventional deposits, but our preliminary results suggest that lherzolite may also be important. We will investigate two such diamond-bearing areas beneath the Canadian Shield (sampled by kimberlite volcanoes at Fort à la Corne and the Victor Mine) that were strongly affected by tectonic/thermal events less than two billion years ago. By studying the diamonds, their inclusions, and the associated mantle rocks, we aim to determine the diamond-forming conditions in the lithospheric mantles of these areas through time.*******3. New Canadian diamond deposits****Diamonds from two new deposits will be used to probe the mantle roots of little-studied deep sections of the Canadian Shield:****(1) The Chidliak kimberlite field (Baffin Island). This area is underlain by a small cratonic fragment of unclear origin, and its diamond source rocks have not yet been investigated.****(2) The Gahcho Kue diamond mine. This mine provides unique access to an exceptionally thick section of lithospheric mantle in the southern Slave Craton.*******The knowledge gained in all three study themes will be crucial to future exploration for new diamond deposits in Canada.*******