Improving the usefulness of eclogitic garnet as a diamond indicator mineral

由于钻石丰度极低，即使是在经济品位(不到百万分之一)的矿床中，更丰富的“指示矿物”被非常成功地用于指导勘探寻找新的发现。橄榄岩是地球地幔中最丰富的钻石源岩，这种方法是如此先进，以至于可以从采集到的少量指示矿物颗粒中得出关于尚未发现的矿床的可靠预测，例如在冰川取样期间。榴辉岩是地球地幔中钻石的第二大来源，指示矿物评估的可靠性要低得多。目前，主要指示矿物榴辉石榴石不能让我们预测钻石的稳定来源，也没有确定的化学特征表明这种石榴石与碳(钻石)有关。此外，在指示性矿物评估期间，将感兴趣的石榴石颗粒(地幔榴辉岩)从地壳背景中分离出来仍然存在困难，没有任何钻石伴生。在这个项目中，我们将使用大量榴辉岩矿物样品(约2600粒)，并测定主要元素和微量元素的化学成分。这不仅可以改进勘探过程中的石榴石分类，还有望为高压(钻石稳定)成因和与钻石的联系产生更可靠的基于微量元素的特征。

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.