Katanga, Dem. Rep. Congo
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The Sase (also known as Lupoto) copper-cobalt deposit is located ~24 km south of the Kipoi Central deposit and ~52 km NW of Lubumbashi, in Katanga Province of the Democratic Republic of Congo
(#Location: 11° 26' 30"S, 27° 6' 10"E).
No significant mineralisation was known in the vicinity of the Sase deposit prior to its discovery, apart from minor abandoned artisanal workings and exploratory pits found at three sites in the surrounding district. The deposit was discovered as a result of follow-up by Tiger Resources of a geochemical soil anomaly. These anomalies were obtained from sampling undertaken in 2006-07, focussed on an area of structural complexity. The structural target was highlighted by east-west trending structural discontinuities which displace magnetically stratified sedimentary units that otherwise follow the general NW-SE structural grain of the area. Drilling from 2007 to 2010 resulted in a maiden resource being released in 2011. The deposit is planned to be mined as a satellite to the Kipoi operation.
The Sase deposit is located on the inner, southwestern margin of the central Congolese section of the Central African Copperbelt.
The deposits of the Central African Copperbelt, in both Zambia and the DRC, are hosted within the Neoproterozoic Katanga Supergroup of the Lufilian Arc, a Pan-African orogenic belt.
In the DRC, the 5 to 10 km thick Katanga Supergroup is composed of:
• R.A.T. Subgroup - >200 m of purple/lilac coloured dolomitic and chloritic brecciated siltstone and dolostone, interpreted to represent the insoluble residue of a much thicker evaporite package that has undergone dissolution and diapiric remobilisation. With other tectonic breccias, it is part of what is collectively referred to as 'breche heterogene'.
• Mines Subgroup - an up to 350 m thick transgressive sequence of interbedded, finely bedded to massive dolostones and dolomitic sedimentary rocks, the lower sections of which are variably silicified and dolomitised, and carbonaceous. The majority of the Cu-Co deposits of the Congolese Copperbelt are hosted within the lower sections of this subgroup.
• Dipeta Subgroup - comprising an initial regression and overlying transgression, resulting in an ~600 m thick succession similar to the R.A.T. and Mines subgroups.
• Mwashya Subgroup - a 200 to 250 m thick sequence comprising a lower unit of irregularly bedded dolomitic shales to siltstones, overlain by a sequence of finely bedded, grey to dark grey or black, pyritic carbonaceous shales, capped by a thinner unit of pink to green feldspathic sandstones with variable amounts of shale or siltite.
Nguba Group, that is up to more than 2000 m thick, commencing with the <30 to >1200 m thick, Sturtian 740 Ma Grand Conglomérat (Mwale Formation) diamictite unit, overlain by shales and the calcareous sedimentary rocks and dolostones of the Kakontwe Formation and an up to 1000 m thick suite of dolomitic sandstones and siltstones.
Kundelungu Group, commencing with the 40 to 60 m thick diamictites of the ~630 Ma Marinoan Petit Conglomérat (Kyandamu Formation), overlain by up to 3000 m of dolomitic sandstones, siltstones and argillites.
In the DRC, the Lufilian arc is characterised by linear outcrops of Roan Group sedimentary rocks, occurring as megabreccias in the cores of a series of tight, disjointed, sheared, NE vergent anticlines. These anticlines are separated by kilometre-scale synclines, cored by Nguba Group sedimentary rock successions made up of diamictites, carbonaceous mudstone, siltstone and carbonates, and locally, overlying Kundelungu Group sedimentary rocks.
In the Sase area, these folds and associated shears generally strike NW-SE. Late east-west and WNW-ESE fault zones trending at high angles to these fold-axes have displaced strata and led to the formation of zones of fracturing and tectonic brecciation.
For details of the regional setting, stratigraphy and metallogeny of the Central African Copperbelt and the Sase deposit, see the separate Central African Copperbelt - Congolese/Katangan Copperbelt record.
Within the Congolese Copperbelt, the bulk of the significant stratabound Cu-Co deposits are hosted by the lower Mines Subgroup (e.g., Tenke Fungurume), with lesser in the upper Dipeta Subgroup (e.g., Mutanda) and the Grand Conglomérat of the Nguba Group (e.g., Kamoa). Structurally controlled transgressive to stratabound mineralisation occurs in the same units, but also in the Mwashya Subgroup (e.g., Kipoi Central), and higher in the Nguba Group (e.g., Sase) and the Kundelungu Group (e.g., Dikulushi).
The Sase deposit occurs in a zone of anastomosing and overlapping fault structures that form a broad east-west trending and laterally extensive structural corridor that can be traced over an interval of >15 km. The imbricate overlap of these structures within the corridor can be more than a kilometre in width. The individual structures are recognised as discontinuities displacing magnetically stratified sedimentary units. The apparent cumulative lateral displacement on the structures that make up the Sase corridor is in the order of 400 m.
At the deposit scale, these structural discontinuities have been interpreted to represent a set of tear-faults that formed at a high angle to the NW-SE trend of regional fold axes.
The Sase deposit is located near the northern bounding structure of the Sase structural corridor. The host sequence dips at a moderate to steep angle to the SW and strikes NW-SE, and is interpreted to be located on the north-eastern limb of a NW plunging regional syncline. It is interpreted to belong to the Nguba Group and is as follows, from the base:
• Medium to fine-grained, massive and poorly textured, slightly graphitic quartz sandstone, comprising well rounded quartz grains set in a clayey calcareous matrix;
• Massive stromatolithic, recrystallised and weakly graphitic dolostone;
• Fine, laminated, carbonaceous sandy siltstone with disseminated stratabound pyrite, made up of cyclical, graded, upwardly fining Bouma-type turbidite beds, showing abundant evidence of soft-sediment deformation including flame-structures and ball-and-pillow textures.
The two lower units, the sandstones and dolomite, are found to the south east, and are separated by a fault, which controlled the introduction of an upward thinning wedge of 'breche heterogene', an allochthonous rock mass composed of hetrolithic rock fragments set in a soft talcose clayey matrix.
All rock types are deeply oxidised obliterating the protolith textures, and are not distinguishable near surface.
Copper mineralisation is both primary and secondary, with the highest grades resulting from the secondary enrichment and oxidation of hypogene sulphides in the weathering zone of the regolith profile.
Mineralisation is principally associated with dolostones and siliciclastic rocks that are carbonaceous, although structure appears to be the predominant overall control on mineralisation, which is hosted in locations of brittle and brittle-ductile deformation. Rock competence and rheological contrast influence the response of different lithologies to stress and the generation of structural porosity, consistent with the concentration of structures in the competent, carbonaceous dolomitic rock types, in contrast to the more ductile silty and clay-rich rocks.
In drill core from below the base of oxidation, mineralisation is commonly associated with breccia forming, cross cutting and bedding parallel veins. It occurs in the matrix of crackle and mosaic breccias, and as fragments and crystals in the matrix of tectonic rubble breccias. Copper-bearing veins and breccias in the primary zone contain chalcopyrite and pyrite, with an associated quartz-calcite gangue and local traces of barite and tourmaline. Petrographic work also indicates an earlier phase of pyrite occurring as diagenetic disseminated pyrite.
The hypogene mineralisation has been subjected to deep weathering, oxidation and supergene remobilisation of copper. The dominant copper minerals in the supergene zone are malachite with minor chalcocite, native copper and traces of bornite
and azurite. Oxide mineralisation occurs partly as in situ replacement of copper sulphides as well as being the product of dissolution, transport and reprecipitation on bedding, cleavage and joint surfaces, and as minor cavity infill. As a result, mineralisation is dispersed through a larger rock volume than the original primary sulphides.
The bulk of the mineralisation identified occurs in the oxide zone between 15 and 120 m below the surface. The mineralisation delineated from drilling has been interpreted to occur in three moderately NNE dipping lenses that, when projected to the surface, define an elongated, WNW-trending tear-shaped lens, with a combined strike extent of >600 m, varying in width from 50 to >200 m. These lenses are developed at a high angle to bedding.
Mineral resources at Sase Central, as at 31 December, 2013 (Tiger Resources website, 2016; 0.5% Cu cut-off), were:
Oxide ore - 2.1 Mt @ 1.49% Cu, 0.08% Co;
Transitional ore - 3.9 Mt @ 1.49% Cu, 0.04% Co;
Sulphide ore - 3.6 Mt @ 1.24% Cu, 0.04% Co;
TOTAL - 9.6 Mt @ 1.39% Cu, 0.05% Co.
Oxide ore - 0.2 Mt @ 1.47% Cu, 0.05% Co;
Transitional ore - 0.7 Mt @ 1.53% Cu, 0.04% Co;
Sulphide ore - 1.9 Mt @ 1.09% Cu, 0.03% Co;
TOTAL - 2.8 Mt @ 1.21% Cu, 0.03% Co;
Geological plans and sections yet to be drawn and inserted - to be completed soon
The information in this summary is drawn from: "Zammit. M. and Dorling, S., 2011 - Sase Project, Democratic Republic Of Congo, Independent technical report; prepared for Tiger Resources Ltd., by Cube Consulting Pty Ltd., 191p."
The most recent source geological information used to prepare this summary was dated: 2011.
This description is a summary from published sources, the chief of which are listed below.
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