Comparative Analysis Of Mineral Chemistry Of Two Tsabong Kimberlite Pipes And Charecteristics Of Sub-Continental Mantle Within The Tsabong Kimeberlite Cluster, Kgalagadi District, Botswana

Abstract

The aim of the project is to conduct a comprehensive comparative analysis of two kimberlites pipes of the Tsabong kimberlite field based on their mineral chemistry and characterise the mantle they sampled. Kimberlites world-wide receive a lot of attention despite their small volumetric significance mainly due to the diamonds they host. Much detailed study, including of emplacement, mantle sources and nomenclature, has been based on the Southern parts of Africa, particularly South Africa, and in Botswana. The main objectives of the project are to study the mineral chemistry (major elements; garnets and clinopyroxenes) of the kimberlite xenocryst to analyse the characteristics that associates them with diamonds in the mantle and to determine the depths from which the kimberlitic suites and mantle xenoliths have been derived. Finally, to establish the temperature and pressure conditions under which xenocrysts were derived from the mantle.

The study area is located approximately 35 km southwest of Tsabong village. The area is within Kalahari basin at the western edge of the Kaapvaal craton. The Kalahari region's geology is challenging to study and understand due to the scarcity of outcrops. The geology of Tsabong is predominantly composed of a basement complex consisting of ancient crystalline rocks.

Analysis of data and mineral chemistry including the Clinopyroxene Thermobarometry has been performed to meet the objectives. The evaluation of mineral compositions in the Tsabong kimberlite cluster suggests a potentially lower diamond potential. The garnet Cr-Ca plots indicate the predominance of lherzolitic pyrope garnets (G9) at exceptionally low chrome contents. Lherzolitic pyrope garnets signals the entrainment of very fertile mantle at shallow depths for these kimberlites hence the lower diamond potential. For future studies, sample size should be increased by expanding the number of boreholes sampled.