La géologie et la minéralisation primaire de l'or de la Chaîne Kibarienne, nord-ouest du Burundi, Afrique Orientale

Meer over het boek

Gold mineralization in NW Burundi is found in a 60 by 10 km zone extending from Ntendezi/Rwanda to Ndora/Burundi, underlain by a 1300 Ma-old clastic sedimentary sequence with minor volcanic intercalations and granitic intrusions from the Kibaran (1265-1210 Ma) and post-Kibaran (970 Ma) periods. There are two types of gold mineralization linked to shear and fracture zones. Type 1 consists of mesothermal quartz-tourmaline-muscovite-(rutile) veins containing refractory microgold in pyrite and arsenopyrite, as well as visible gold from supergene enrichment. These hydrothermal veins overlap with granite-related rare metal pegmatite systems near Ruhembe and Ndora. Radiometric ages for Ta pegmatites and Au-bearing quartz veins suggest synchronous formation. Similar chemical features and fluid inclusion data indicate comparable physicochemical conditions for both tin and gold mineralization, suggesting a genetic link to post-Kibaran G4 granite magmatism. Type 2 features epithermal hematite/limonite breccia zones with visible gold, where Au occurs in aggregates associated with replaced pyrite cubes. These breccia bodies contain mesothermal hydrothermal quartz clasts, with a low-temperature and low-pressure siliceous matrix. Monazite from this matrix has a Panafrican U-Pb age of 535 +/-2 Ma, indicating a period of rapid uplift and high heat flow. This suggests a two-stage model for gold mineralization in NW Burundi: initial post-Kiba