Spinel and Ti-rich schorlomite from the Wajrakarur kimberlites, southern India: implications for metasomatism, diamond potential and orangeite lineage

Abstract Mesoproterozoic kimberlite pipes designated as Kl-4 and P-5, along with several other well-known diamondiferous (ca. 1110 Ma) kimberlites in the Wajrakarur kimberlite field (WKF) intruded into the cratonic roots of Eastern Dharwar craton (EDC) in southern India. The groundmass minerals of the kimberlites exhibit inequigranular texture with spinel showing straddle between MUM and Mag trend, Ti-rich schorlomite garnet, two generations of olivine (macrocrysts and groundmass microphenocrysts), phlogopite, perovskite, clinopyroxene (diopside), ilmenite (low Mn) and rare apatite. We identified three distinct spinel associations in Kl-4 and P-5: (i) finer-grained ( 500 μm). The schorlomite garnet in both P-5 and Kl-4 represents solid solution of schorlomite-pyrope-almandine-grossular. Additionally, Kl-4 contains another Cr-rich schorlomite-pyrope-almandine-uvarovite solid solution. Macrocrystic spinel exhibits distinct composition of chromium (Cr2O3 up to 59.62 wt%), and TiO2-poor (