The Use of Chemistry of Garnets and Heavy Minerals Around Lalago Kimberlite Pipe in Deciphering Diamond and Non-Diamond Bearing Kimberlite Pipes in Tanzania

Abstract

More than three hundred kimberlite pipes have been reported in Tanzania. Only a few are diamond–bearing. A prospecting criteria to outline the diamond and non-diamond bearing kimberlites has been proposed. Bulk rock chemical analyses and chemistry of garnets and black minerals (picroilmenite, magnetite, rutile and titanite) collected around one kimberlite pipe in Tanzania were studied using Atomic Absorption Spectrophotometer (AAS) and Electron Microprobe (EMP). Although chromite and zircons occur in kimberlite pipes, they were not used in this study because they also characterize other surrounding rocks. Electron microprobe analysis of heavy minerals indicate that the ilmenites (picroilmenite) are poor in MgO contents (0.03 – 0.6 wt.%); but are rich in MnO (9.94 – 12.27wt.%). The garnets are poor in Cr2O3 with pronounced almandine content which has led to the conclusion of having a barren kimberlite source. It is suggested that combination of the chemistry of garnet and heavy minerals may be used as an exploration tool for deciphering diamond and non-diamond bearing kimberlites.

Keywords: Electron microprobe, black minerals, mineral and fluid inclusions, kimberlites, garnets.