Indicator Mineral Chemistry of P-17 Kimberlite, Wajrakarur Field, Eastern Dharwar Craton, Southern India: Implications for Diamond Prospectivity

ABSTRACT Indicator mineral chemistry is a well-known prospecting tool in diamond exploration due to the unique association between indicator minerals such as pyrope garnets, chrome diopsides and Mg-ilmenites with kimberlites as well as diamonds. The Penna Ahobilam Pipe-17 kimberlite in the well-known Wajrakarur kimberlite field, Eastern Dharwar Craton, southern India, is one of the latest discoveries by the Geological Survey of India and very little information is available as to its diamond prospectivity visà-vis indicator mineral composition. Indicator mineral chemistry (IMC) indicates that majority of the Pipe-17 pyrope garnets belong to the G-4 and G-5 clusters of the pyroxenitic group, with a small population displaying affinity to the G-10 cluster of the peridotitic group. Ilmenites exhibit high MgO values, consistent with those reported from the kimberlitic ilmenites, and their low Fe3+/Fe2+ ratios indicate reducing conditions favourable for diamond formation. In contrast, the ilmenites have high Fe2O3 values with respect to MgO contents and imply an intermediate to marginal preservation with significant diamond resorption. The apple-green chrome diopsides are characterized by distinct high Cr2O3 and Na2O contents and are indistinguishable from those reported from worldwide diamondiferous kimberlites of deeper mantle origin. The indicator minerals recovered from the Pipe-17 kimberlite highlight that it has a lower diamond potential which is also confirmed by the poor recovery of diamonds by testing.