The geology of the giant Nyankanga gold deposit, Geita Greenstone Belt, Tanzania

Sanislav, Ioan V., Kolling, Sergio L., Brayshaw, Mathew, Cook, Yvonne A., Dirks, Paul H.G.M., Blenkinsop, Thomas G., Mturi, Marwa I., and Ruhega, Roger (2015) The geology of the giant Nyankanga gold deposit, Geita Greenstone Belt, Tanzania. Ore Geology Reviews, 69. pp. 1-16.

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Abstract

Nyankanga is the largest gold deposit in the Geita Greenstone Belt of the northern Tanzania Craton. The deposit is hosted within an Archean volcano-sedimentary package dominated by ironstones and intruded by a large diorite complex, the Nyankanga Intrusive Complex. The supracrustal package is now included within the intrusive complex as roof pendants. The ironstone fragments contain evidence of multiple folding events that occurred prior to intrusion. The supracrustal package and Nyankanga Intrusive Complex are cut by a series of NE–SW trending, moderately NW dipping fault zones with a dominant reverse component of movement but showing multiple reactivation events with both oblique and normal movement components. The deposit is cut by a series of NW trending strike slip faults and ~ E–W trending late normal faults. The Nyankanga Fault Zone is a major NW dipping deformation zone developed mainly along the ironstone–diorite contacts that is mineralised over its entire length. The gold mineralization is hosted within the damage zone associated with Nyankanga Fault Zone by both diorite and ironstone with higher grades typically occurring in ironstone. Ore shoots dip more steeply than the Nyankanga Fault Zone. The mineralization is associated with sulfidation fronts and replacement textures in ironstones and is mostly contained as disseminated sulphides in diorite. The close spatial relationship between gold mineralization and the ironstone/diorite contact suggests that the reaction between the mineralising fluid and iron rich lithotypes played an important role in precipitating gold. Intense brecciation and veining, mainly in the footwall of Nyankanga Fault Zone, indicates that the fault zone increased permeability and allowed the access of mineralising fluids. The steeper dip of the ore shoots is consistent with mineralization during normal reactivation of the Nyankanga Fault Zone.

Item ID: 37323
Item Type: Article (Refereed Research - C1)
Keywords: gold deposits; Archean; Tanzania Craton; Nyankanga gold deposit; roof pendants
ISSN: 1872-7360
Funders: Geita Gold Mine, Anglogold Ashanti
Date Deposited: 16 Jun 2015 23:53
FoR Codes: 04 EARTH SCIENCES > 0403 Geology > 040312 Structural Geology @ 70%
04 EARTH SCIENCES > 0403 Geology > 040307 Ore Deposit Petrology @ 30%
SEO Codes: 84 MINERAL RESOURCES (excl. Energy Resources) > 8401 Mineral Exploration > 840105 Precious (Noble) Metal Ore Exploration @ 50%
97 EXPANDING KNOWLEDGE > 970104 Expanding Knowledge in the Earth Sciences @ 50%
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