CHARACTERISTICS OF KIMBERLITES OF GALANGE PIPE II (SOUTH-WESTERN ANGOLA)

Abstract

The purpose of the work is to study the petrographic and mineralogical composition of the kimberlites of the Galange II tube from the southwestern part of the Republic of Angola, which from the rocks selected within the Angolan Shield belong to brecciated porphyry and massive olivine kimberlites. Rocks were investigated by methods of visual diagnostics, petrographic study, X-ray structural and microprobe analyses. The study of kimberlite rocks of the Galange-II tube makes it possible to emphasize that they belong to porphyry brecciated kimberlites that have undergone secondary metasomatic changes. According to the petrographic study, porphyry outcrops of kimberlites are mainly represented by olivine, which is replaced by pseudomorphs of serpentine, sometimes carbonate. The rock matrix is characterized by a carbonate-smectite (saponite) aggregate. According to X-ray structural and microanalytical studies, carbonates (calcite, dolomite), smectites, phlogopite, pyroxene, barite are present in the matrix; ore minerals (titanite, perovskite, ilmenite). Established crystal chemical formulas of carbonates and smectites. The structural and textural features of the kimberlites of the Galange-II tube make it possible to note that their formation probably took place in at least two stages. At the first stage, porphyry outcrops crystallized in a magmatic environment at depths greater than 150 km; after that, there was a rapid uplift, a volcanic eruption with the formation of a diatreme. The porphyry structure of kimberlite rocks, the presence of a matrix represented by a carbonate-smectite (saponite) aggregate, and the detection of an increased content of perovskite belong to the typomorphic features of the Galange-II tube.