Improving the usefulness of eclogitic garnet as a diamond indicator mineral

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Because of the extremely low abundance of diamond even in deposits with economic grades (less than 1 parts per million), more abundant "indicator minerals" are used very successfully to guide exploration to new finds. For peridotite, the most abundant source rock of diamond in Earth's mantle, this methodology is so advanced that robust predictions about yet undiscovered deposits can be derived from a small number of indicator mineral grains recovered, e.g., during sampling of glacial till. For eclogite, the second most important source of diamond in Earth's mantle, indicator mineral assessment is much less reliable. The principal indicator mineral, eclogitic garnet, currently does not allow us to predict an origin from depths where diamond would be stable nor are there established chemical signatures that would indicate an association of such garnets with carbon (diamond). In addition, difficulties persist during indicator mineral assessment to separate garnet grains of interest (mantle eclogites) from crustal background without any diamond association. In this project we will use a large number of eclogitic mineral samples (ca. 2600 grains) and determine major and trace element chemical compositions. This will not only allow for improved garnet classification during exploration, but is also expected to yield more reliable, trace element-based signatures for a high pressure (diamond stable) origin and an association with diamond.