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Tulawaka East |
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Tanzania |
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Au
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Super Porphyry Cu and Au
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IOCG Deposits - 70 papers
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The Tulawaka East gold deposit is located in the western part of the Rwamagaza Greenstone Belt of the Lake Victoria Gold Belt in the Late Archaean Tanzanian Craton of northern Tanzania. It is 1000 km from Dar es Salaam and 120 km west of the Bulyanhula mine.
The southern part of the Lake Victoria Gold Belt lies within the Sukumaland greenstones which are represented by two concentric belts of greenstone, separated by granite. The inner or Rwamagaza belt, which trends east-west, comprises a generally vertically dipping sequence of mainly mafic volcanics of the lower Nyanzian System with scattered remnants of BIF. Tulawaka area straddles the western contact between the 'inner' and 'outer' greenstone belts.
The Nyanzian System in the Tulawaka area has undergone upper greenschist facies, high-pressure metamorphism as indicated by the various chlorite sericite schists. This contrasts with most of the Nyanzian to the east that has only undergone metamorphism to lower greenschist facies. This is a regional effect, the result of deeper burial possibly under thickened Bukoban package rocks.
The Rwamagaza Greenstone Belt is known for its artisanal laterite workings with Matabi (6.25 tonnes of Au) being the largest. A set of parallel regional shear structures, referred to as the Muhama Dislocation crosscut the belt in the Tulawaka area. This set of dislocations, which can be traced from the Golden Pride Mine in the Nzega Belt to Tulawaka are spatially related to a number of gold occurrences, including Golden Pride, Chocolate Reef, Miyabi, Nyakafuru and Tuluwaka with gold mineralisation typically located at the intersection of parallel second order structures and structures with a different orientation (often N-S).
The Tulawaka East gold deposit is hosted in a complex terrain of upper greenschist to amphibolite facies metamorphic rocks composed of metasediments and metavolcanics, including a minor component of metasilicate-iron formation. The central sector of the greenstone belt is occasionally invaded by NE trending metagabbro dykes or sills of probable Neoproterozoic age. The local stratigraphy has been folded into a large-scale 'Z-shaped' fold that plunges to the south. The anticline portion of the fold has been truncated by a thrust fault sub-parallel to the south-dipping fold axial plane. Thrust faulting has provided the dilation required for the injection of gold bearing quartz veins and associated quartz-feldspar porphyry intrusions.
The principal lithologies of the host greenstone belt in the Tulawaka area includes:
Schist - At least three types of schist are recorded, varying from quartz-biotite to chlorite sericite schist. They are usually very fine-grained, and felsic in composition, comprising varying amounts of quartz, sericite and chlorite, representing original felsic intrusives and extrusives.
Phyllite - A very fine-grained, finely laminated, silver-grey to greenish coloured strongly foliated and crenulated rock with a distinct silky lustre, composed predominantly of sericite and quartz ±chlorite.
Basalt - A very fine- to fine-grained, massive, dark grey coloured rock composed of pyroxene, plagioclase and quartz ±amphibole with accessory ilmenite and/or magnetite. Structurally this unit is highly fractured and weakly to strongly foliated. Iron staining, epidote and occasionally dendretic psilomelane are common along fracture planes. Silicification and chloritisation are common and tend to be pervasive where the basalt is strongly foliated. Patchy localized bleaching, carbonitisation and biotite alteration are also evident. Minor amounts of coarse disseminated to euhedral pyrite cubes are occasionally obvious.
Andesite - Andesites predominate in the eastern portion of the area and are distinguished from the basalts to the west by their more leucocratic green colour, suggesting a change in facies from W to E.
Intermediate Tuff - A very fine-grained, massive to weakly laminated, intermediate rock of probable dacitic composition that is light grey in colour which has been moderately to strongly silicified and displays minor chlorite alteration. Its mineral assemblage includes plagioclase, quartz and amphibole. Trace amounts of finely disseminated euhedral cubic pyrite are present.
Banded Iron Formation/Chert - BIF occurs as sub-crop and gravel rubble within the overburden profile. The sub-crop occurs as very fine-grained oxide to silicate facies BIF interbedded with grey chert and possible volcanics. The BIF occurs as well-rounded, well-sorted, fragments of thinly laminated (2 to 5 mm) sulphide facies BIF interbedded with quartz veins and chert. Disseminated to euhedral cubic pyrite is comparatively abundant. All of the BIF is strongly silicified and ferruginised.
The weathering profile at Tulawaka East is extensive, with saprolite extending to depths of as much as 46 m. The mafic and intermediate host rocks generally have a deeper saprolite profile than the felsic saprolites. As a result, the weathering profile at the property shallows to the north. Kaolinite is the dominant secondary mineral with minor amounts of hematite and/or limonite and K-feldspar.
Gold occurs dominantly as free gold within quartz veins or stockworks, often associated with felsic intrusives. Pyrite and arsenopyrite occur in minor quantities but do not contain significant gold. The mineralisation is hosted in sediments metamorphosed to greenschist and amphibolite facies schists. Mineralisation is contained in saprolite, which is itself overlain by a discontinuous laterite zone that also contains detrital or chemically remobilized gold. At least five gold-bearing quartz vein systems occur within the Tulawaka area. Among these, the East Zone system contains the most economically significant gold mineralisation identified to date. The East Zone mineralisation has a northwesterly strike distance of approximately 1 km and dips at angles of 40 to 65° to the northeast. The gold bearing quartz vein in the East Zone ranges in thickness from 60 cm to 4 m.
In 2004 the deposit included:
Proven + Probable reserves of 1.08 Mt @ 10.9 g/t Au for 11.75 t of Au
Mineral resources of 0.58 Mt @ 2 g/t Au for 1.06 t of Au.
The most recent source geological information used to prepare this decription was dated: 2005.
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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Selected References:
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Cloutier J, Stevenson R K and Bardoux M, 2005 - Nd isotopic, petrologic and geochemical investigation of the Tulawaka East gold deposit, Tanzanian Craton: in Precambrian Research v139 pp 147-163
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Henckel, J., Poulsen, K.H., Sharp, T. and Spora, P., 2016 - Lake Victoria Goldfields: in Episodes, v.39, pp. 135-154
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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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