Reassessment of Controls on the Gold Mineralisation in the Nyankanga Deposit – Geita Gold Mines, North-Western Tanzania

摘要

The Geita gold mines in north-western Tanzania have produced 5 Moz of gold from an estimatedrnendowment of 15 Moz. They are generally classifi ed as typical Archaean orogenic banded ironrnformations (BIF)-hosted gold deposits in banded iron formations as described by Goldfarb,rnGroves and Gardoll (2001); Neall and Phillips (1987); Phillips and Powell (1993) and Neall (1987).rnThe controls on gold mineralisation have been reassessed to conclude that Nyankanga, and wernconclude that Nyankanga, the largest deposits within the group, developed during a dynamic andrnprotracted deformation history intimately associated with several stages of hydrothermal fl uidrnfl ow and alteration.rnThe fl uid-induced fractures associated with gold mineralisation are primarily manifested asrnsubmillimetre to metre-scale fractures and breccias developed preferentially in rocks that havernbeen previously deformed and altered by silicifi cation or seafl oor metasomatism. This realisationrndetracts from the exploration and mining strategies that would solely concentrate on fl uid pathwaysrnand associated wallrock alteration and veining solely within the BIFs as hosts for economic goldrnmineralisation.