A lead isotope study of Archaean mineralized areas in Tanzania

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Abstract
Single-stage lead extracted from pyrite and galena collected from Nyanzian greenstone belts in the northern half of the Tanzanian Shield yields a recalculated model age of 2700 ± 150 m.y. for the gold mineralization, a date that is consistent with existing radiometric ages. Anomalous multi-stage lead has also been found in the Nyanzian sulphides, and is interpreted as indicating that radiogenic lead was added to the original lead during an event 900 ± 300 m.y. ago. This event is tentatively correlated with the Bukoban phase of basic dyke intrusion. Two mineralized areas in the adjacent Ubendian Orogenic Belt were also investigated. Lead from the Mpanda Mineral Field, also apparently single-stage, yields a model age of 1400 ±150 m.y. for the mineralization. Anomalous multi-stage leads from the Lupa Goldfield indicate that the area has experienced a complex history starting with a mineralizing event at least 2400 ±150 m.y. ago.