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Kabanga |
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Tanzania |
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Ni Cu
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Super Porphyry Cu and Au
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IOCG Deposits - 70 papers
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All papers now Open Access.
Available as Full Text for direct download or on request. |
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The Kabanga sulphide nickel deposit is located in far north-western Tanzania, approximately 120 km south-west of Lake Victoria and within a few kilometres of the Burundi border.
The deposit is hosted by one of a series of mafic-ultramafic intrusions that is known as the Kabanga-
Musongati belt which extends for at least 500 km from northwestern Tanzania to the Kapalagulu
intrusion located on the eastern shore of Lake Tanganyika. These intrusions are hosted by the 1.4 to 1.0 Ga Kibaran orogenic belt that extends in a SW-NE direction for around 1500 km, from Zambia through the Democratic Republic of Congo (DRC), Burundi, Rwanda, and Tanzania to Uganda. The Kibaran orogenic belt is interpreted to have been formed during of the collision of the Tanzania craton and the Bangweulu block in the east, with the Congo-Kasai craton in the west.
The Kibaran fold belt is predominantly composed of a sequence of alternating arenaceous and pelitic meta-sedimentary rocks (shallow water, closed basin quartzite, schist, greywacke and conglomerate), grouped into the Burundi Supergroup in Burundi and the equivalent Karagwe-Ankolean Supergroup in Tanzania. Rhyodacitic flows, that have been dated at 1.35 ±0.05 Ga, are found in the lower portion of the Burundi Supergroup which reaches a thickness of between 2500 and 5000 m in Rwanda. The
lower and middle sections of the Burundi Supergroup are taken to represent an early rifting phase of the intracratonic Kibaran basin, while the upper series, which is only locally developed, contains immature clastic sedimentary rocks at the base, overlain by chert-bearing siltstones and shales, interpreted to represent a saline lake depositional environment.
Weakly deformed Meso- to Neoproterozoic sediments (conglomerates, quartzites, dolomitic carbonates, calcareous schists and phyllites that were deposited in isolated sedimentary basins) are found along the Burundi-Tanzania border, represented by the Malagarazi Supergroup in Burundi and the equivalent Bukoba Supergroup in Tanzania, the latter hosting the Kapalagulu intrusion. The ages of these supergroups are poorly defined. They unconformably overlie both the Tanzanian craton and Ubendian domain, while some of the sequence is cut by 1.28 to 1.39 Ga intrusions.
The Proterozoic successions are intruded by:
i). the mafic-ultramafic intrusions of the Kabanga-Musongati belt;
ii). S-type granitoids, possibly representing partial melts of crust formed by the ponding of basic magmas at the base of the lithosphere; and
iii). minor bodies of A-type granitoids.
These successions unconformably overlie the Congo craton in the west and the Tanzania craton to the east. The Tanzanian craton in Burundi and Tanzania is largely composed of granitic, granodioritic and tonalitic gneiss, and migmatite. These rocks have been dated at around 2.5 Ga in Burundi, while the Ubendian basement in the Kapalagulu area to the south is composed of hornblende and biotite-oligoclase gneisses believed to be older than ca. 1.8 Ga.
Age dating suggest that the Kabanga-Musongati intrusions formed during a Kibaran-wide 1.4 to 1.37 Ga igneous event while the postorogenic A-type granites and minor mafic intrusions were emplaced in shear zones at around 1.205 Ga. Recent dating of the Kabanga North intrusion has yieded and age of 1403 ± 14 Ma.
The intruded country rock in the Kabanga district comprises a sequence of steeply dipping andalusite-muscovite-staurolite schists and banded metapelites that locally contain abundant lenses and disseminations of pyrrhotite and minor pyrite. These are cut by several mafic-ultramafic intrusions of variable shape and size, all of which are broadly concordant with the sedimentary layering and occur a sills or tubes that have thicknesses from a few tens of centimetres to more than 1000 m.
The Kabanga North intrusion which hosts the bulk of the nickel sulphide ores has of a tubular shape, several tens to as much as 250 m in both width and height, and extends for several hundreds
of metres in length. The base of the body is defined by a fine-grained, sulphide-poor, pyroxenite
or melanorite which is up to several tens of cm thick, overlain by up to several metres of massive sulphides. The sulphides commonly occur as decimetre - to metre-thick veins which were injected into the underlying pyroxenite-melanorite and the sedimentary footwall rocks. The massive sulphides are in turn overlain by several metres of medium-grained pyroxenites and olivine pyroxenites that contain up to as much as 20% by volume disseminated sulphides. These rocks have either progressively or sharp contacts intovpoikilitic harzburgites with variable sulphide contents that may reach a thickness of several tens of metres. Where the contacts between the pyroxenites and harzburgites are sharp, the latter tend to be fine grained at the base, becoming progressively more medium grained upwards. In the upper portion of the intrusion, the harzburgites grade into sulphidic olivine pyroxenites and pyroxenites. At the top of the intrusion, sulphide-poor gabbronorites may be developed.
The Kabanga deposit has been stated as containing a resource of 26 Mt @ 2.6% Ni (Maier, et al., 2007), while Barrick (2007) quotes the following figures (after X-strata, Dec. 2006):
Total indicated resource - 9.7 Mt @ 2.37% Ni, 0.32% Cu, 0.19% Co, 0.04 g/t Au, 0.07 g/t Pt, 0.09 g/t Pd, 1.04 g/t Ag;
Total inferred resource - 36.3 Mt @ 2.8% Ni, 0.4% Cu, 0.2% Co, 0.1 g/t Au, 0.3 g/t Pt, 0.3 g/t Pd, 1.5 g/t Ag;
The most recent source geological information used to prepare this decription was dated: 2007.
This description is a summary from published sources, the chief of which are listed below.
© Copyright Porter GeoConsultancy Pty Ltd. Unauthorised copying, reproduction, storage or dissemination prohibited.
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Begg, G.C., Hronsky, J.A.M., Arndt, N.T., Griffin, W.L., O Reilly, S.Y. and Hayward, N., 2010 - Lithospheric, Cratonic, and Geodynamic Setting of Ni-Cu-PGE Sulfide Deposits: in Econ. Geol. v.105, pp. 1057-1070.
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Maier W D and Barnes S-J 2010 - The Kabanga Ni sulfide deposits, Tanzania: II. Chalcophile and siderophile element geochemistry: in Mineralium Deposita v.45 pp. 443-460
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Maier W D, Barnes S-J, Sarkar A, Ripley E, Li C and Livesey T, 2010 - The Kabanga Ni sulfide deposit, Tanzania: I. Geology, petrography, silicate rock geochemistry, and sulfur and oxygen isotopes: in Mineralium Deposita v.45 pp. 419-441
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Maier W D, Peltonen P and Livesey T, 2007 - The Ages of the Kabanga North and Kapalagulu Intrusions, Western Tanzania: A Reconnaissance Study: in Econ. Geol. v102 pp 147-154
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Porter GeoConsultancy Pty Ltd (PorterGeo) provides access to this database at no charge. It is largely based on scientific papers and reports in the public domain, and was current when the sources consulted were published. While PorterGeo endeavour to ensure the information was accurate at the time of compilation and subsequent updating, PorterGeo, its employees and servants: i). do not warrant, or make any representation regarding the use, or results of the use of the information contained herein as to its correctness, accuracy, currency, or otherwise; and ii). expressly disclaim all liability or responsibility to any person using the information or conclusions contained herein.
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