Archaean gold mineralization in an extensional setting: the structural history of the Kukuluma and Matandani deposits, Geita Greenstone Belt, Tanzania

Kwelwa, Shimba D., Dirks, Paul H.G.M., Sanislav, Ioan V., Blenkinsop, Thomas, and Kolling, Sergio L. (2018) Archaean gold mineralization in an extensional setting: the structural history of the Kukuluma and Matandani deposits, Geita Greenstone Belt, Tanzania. Minerals, 8 (4).

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Abstract

Three major gold deposits, Matandani, Kukuluma, and Area 3, host several million ouncez (Moz) of gold, along a ~5 km long, WNW trend in the E part of the Geita Greenstone Belt, NW Tanzania. The deposits are hosted in Archaean volcanoclastic sediment and intrusive diorite. The geological evolution of the deposits involved three separate stages: (1) an early stage of syn-sedimentary extensional deformation (D1) around 2715 Ma; (2) a second stage involving overprinting ductile folding (D2–4) and shearing (D5–6) events during N-S compression between 2700 and 2665 Ma, coeval with the emplacement of the Kukuluma Intrusive Complex; and (3) a final stage of extensional deformation (D7) accommodated by minor, broadly east-trending normal faults, preceded by the intrusion of felsic porphyritic dykes at ~2650 Ma. The geometry of the ore bodies at Kukuluma and Matandani is controlled by the distribution of magnetite-rich meta-ironstone, near the margins of monzonite-diorite bodies of the Kukuluma Intrusive Complex. The lithological contacts acted as redox boundaries, where high-grade mineralization was enhanced in damage zones with higher permeability, including syn-D3 hydrothermal breccia, D2–D3 fold hinges, and D6 shears. The actual mineralizing event was syn-D7, and occurred in an extensional setting that facilitated the infiltration of mineralizing fluids. Thus, whilst gold mineralization is late-tectonic, ore zone geometries are linked to older structures and lithological boundaries that formed before gold was introduced. The deformation-intrusive history of the Kukuluma and Matandani deposits is near identical to the geological history of the world-class Nyankanga and Geita Hill deposits in the central part of the Geita Greenstone Belt. This similarity suggests that the geological history of much of the greenstone belt is similar. All major gold deposits in the Geita Greenstone Belt lack close proximity to crustal-scale shear zones; they are associated with intrusive complexes and volcanics that formed in an oceanic plateau rather than subduction setting, and formed late-tectonically during an extensional phase. They are not characteristic of typical orogenic gold deposits.

Item ID: 53283
Item Type: Article (Refereed Research - C1)
Keywords: Archaean gold; Tanzania; structural controls; deformation; Kukuluma; Geita; orogenic gold
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© 2018 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (http://creativecommons.org/licenses/by/4.0/)

ISSN: 2075-163X
Date Deposited: 03 May 2018 03:56
FoR Codes: 04 EARTH SCIENCES > 0403 Geology > 040312 Structural Geology @ 50%
04 EARTH SCIENCES > 0403 Geology > 040313 Tectonics @ 30%
04 EARTH SCIENCES > 0403 Geology > 040307 Ore Deposit Petrology @ 20%
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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