The nature of kimberlitic and mantle fluid and diamond preservation

Kimberlites are the most deep-seated magmas (>150 km depth) that form primary deposits of diamonds. They fill carrot-shape pipes found only within continents. The origin of kimberlites is linked to processes in the deep mantle. Kimberlites transport diamonds from the Earth's mantle to the surface and partially dissolve them during the ascent. The dissolution impacts the commercial value of diamonds and the diamond grade of a kimberlite pipe. Volatile-rich nature of kimberlites plays an important role in diamond dissolution. It is not well known how much and what kind of volatiles kimberlites contain. Lack of such knowledge obscures our understanding of the origin of kimberlites. The proposed research investigates volatile content and fluid system of kimberlite magmas and the mantle fluid, and uses this information to put new constraints on the origin, primary melt composition and mantle source of kimberlites; to learn about conditions during emplacement and the mechanism of kimberlite eruption at the surface; and to understand what causes diamond destruction in the mantle. The program will use a new method based on the relationship between the fluid phase of kimberlite magma and the surface features on diamonds discovered in my recent experimental study to investigate fluid system of natural kimberlites. The results of my experiments show that the H2O/CO2 ratio on the fluid determines the type of dissolution features on diamonds. After experimental calibration of the new method, natural diamond parcels from Lac de Gras kimberlites (N.W.T., Canada) will be used to collect detailed data on the diamond surface features in order to determine composition and evolution of magmatic fluid in these kimberlites. The research will also use traditional analytical techniques to study mineralogy, geochemistry and petrography of the Lac de Gras kimberlites and kimberlite indicator minerals in order to find some geochemical fluid indicators and to understand the role of magmatic fluid in the crystallization and eruption of kimberlite magmas. The obtained data will provide better understanding of the origin of kimberlites, processes in subcratonic mantle, will help to predict preservation and quality of diamonds in a kimberlite pipe.