[H-RE11] Earth Resource Science

[HRE11-P05] Mineralogical and Geochemical Characterization of Gold Deposits of the Neoarchean Tati and Vumba Greenstone Belts of NE Botswana

*Kelebogile Phili¹, Ryohei Takahashi¹, Andrea Agangi¹, Pearlyn Cabarubias Manalo¹, Hinako Sato¹, Lebogang Mokane¹, Thierry Bineli Betsi², Tebogo Kelepile², Zibisani Biza Bagai³ (1.Akita Univ., 2.BIUST, 3.UB)

Keywords:Tati greenstone belt, Vumba greenstone belt, native gold, arsenopyrite

The Tati greenstone belt (TGB) and the Vumba greenstone belt (VGB) are gold-bearing Neoarchean terrains located in the northeastern part of Botswana within the southwestern margin of the Zimbabwe craton. These greenstone belts are surrounded by granitoids and consist of supracrustal rocks that are dominated by mafic and ultramafic meta-volcanic rocks. There are numerous gold deposits in both greenstone belts. Minor Ni-Cu-PGE sulfide deposits are also present in the TGB. Despite early gold discoveries in the 1800s, limited research has been done with regards to the fluid evolution and genesis of gold mineralization in either the TGB or VGB. This study, therefore, aims to constrain the genesis of gold mineralization and to compare the mineralization in the TGB and VGB using the mineralogy, geochemistry, and alteration patterns. This study focuses on the Mupane, Golden Eagle and Map Nora gold deposits of the TGB and the White Pidgeon and Somerset gold deposits of the VGB. Preliminary petrographic observation of mineralized samples collected from outcrops and stockpiles have revealed that gold-bearing sulfide mineralization in the TGB and VGB is primarily hosted within quartz veins and extensively altered schists and amphibolites. The TGB host rocks comprise of mostly quartz, calcite, graphite, mica and chlorite dominated schists that are commonly silicified. Sulfide bearing amphibolites are also present. The quartz veins include vuggy, brecciated, and milky quartz veins that host pyrrhotite and pyrite disseminations as well as massive pyrrhotite. In comparison the VGB host rocks are dominated by quartz, calcite and mica rich schists that are crosscut by sulfide rich milky quartz veins. Sulfide bearing amphibolites comprising of amphibole, clinopyroxene, epidote, plagioclase and garnet are also present. Gold mineralization in the TGB mainly occurs as inclusions within sulfides, primarily arsenopyrite but also pyrite and sphalerite. In contrast, native gold in the VGB has not yet been observed. However, ICP-MS analysis from VGB samples have revealed a gold content of at least 0.71 ppm, and at least 3.78 ppm for samples from the TGB. δ³⁴S values from pyrrhotite, arsenopyrite and pyrite (n=20) from the TGB and VGB range from -0.7 to +4.0 ‰. The range of δ³⁴S is narrow despite measurements on sulfides from different deposits and host rocks within the TGB and VGB. Recent studies in the TGB specifically the Tau deposit of the Mupane deposits also reported a restricted range of δ³⁴S values in gold bearing sulfides, thereby suggesting dominant reduced hydrothermal conditions during gold mineralization in the TGB.