Diffusion profiles of OH towards melt inclusions in garnets in lherzolite xenoliths from the Victor diamond mine, South Africa

In diamond exploration it is important to understand the mechanism of the kimberlite eruption and dynamics of kimberlites in terms of the composition of the kimberlitic melt. Water is found as OH in nominally water free minerals (NAMS) caused by mantle metasomatism. The water has a higher solubility in the kimberlitic melt and thus is removed from the NAMS. The decrease of OH content in NAMS can thus be measured and used to find the composition of the kimberlitic melt. We present for the first time high resolution FT-IR based synchrotron measurements of OH concentrations towards melt inclusions in lherzolitic garnets from the Victor Diamond Mine in South Africa. We measured hydrogen profiles towards totally embedded microcracks and melt inclusions in these garnet crystals. The measurements show a strong variation in OH-concentrations and demonstrate that the amount of water stored in diamond bearing layers has been underestimated for a long time due to the loss of water during the uplift of the kimberlite.