Geology and U–Pb geochronology of the Amani Region, southwestern Tanzania

Abstract Large geographic regions of the Paleoproterozoic Ubendian Belt in southwestern Tanzania remain relatively understudied, hindering mineral exploration efforts in these remote areas. One example of such an understudied area is the Amani Region, a ∼48 km2 remote location in the Upangwa terrane which is characterized by significant alluvial gold endowment. Here, we present the first geochemical and petrographical characterization of lithologies encountered within the Amani Region. We propose original nomenclature for these lithologies and document the occurrence of four distinct lithological groups (Kabelege Group, Ulembo Suite, Rafiki Group and Amani Group). Lithostratigraphic correlations are made between the Kabelege Group and the Ubendian Supergroup. This study also documents a hitherto unrecognised package of greenschist facies metasediments (Amani Group), which seem to be lithologically and temporally equivalent to the Txitonga Group in NW Mozambique. New U–Pb zircon and rutile data collected from metasediments in the Amani Region are presented, which constrain the maximum depositional age of their sedimentary protoliths, thereby providing new time constraints on the tectonic evolution of the SE Ubendian Belt. The U–Pb zircon data substantiate a ∼1080-990 Ma regional metamorphic event in the bedrock sources that provided detritus to the Upangwa terrane, likely associated with the Kibaran-Irumide orogeny during the Mesoproterozoic. Our U–Pb rutile and zircon data from the Amani Group metasediments that host auriferous quartz veins, suggest that hydrothermal gold mineralization (responsible for the alluvial gold occurrence) in the Amani Region is younger than ∼944 Ma.