Mbalam - Mbarga, Metzimevin


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The Mbalam iron deposits are located close to the southern border of Cameroon with Congo (Brazzaville) approximately 450 km east of the Atlantic Ocean coast and 300 km ESE of the capital city, Yaounde (#Location: 2° 14' 9"N, 13° 57' 10"E).

Like the major Belinga deposit (see the Belinga record), 150 km to the SSE in Gabon, these deposits lie on the northwestern section of the Congo craton where a broad upwarp of the du Chaillu granite-greenstone terrane stretch across Gabon, extending into the Congo and into Cameroon to the north where it grades into the Ntem charnockite terrane.

The Gabon Orogenic Belt, within which these deposits lie, is a major Eburnian tectono-thermal event. The oldest rocks in the belt in Gabon and Congo are the 3.13 to 2.6 Ga, medium to high metamorphic grade, du Chaillu granite-gneiss and greenstone terrane. These old rocks are unconformably overlain by the thick Palaeoproterozoic (2.3 to 2.0 Ga) sandstones, conglomerates and shales of the Francevillian Supergroup, which is in turn overthrust on its western side by the Ogooue Metamorphics that are also considered to be of Palaeoproterozoic age. All of these rocks are concealed on the margins of the upwarp by Neoproterozoic and Mesozoic cover.

The du Chaillu granite-greenstone terrane is largely composed of two granitoid generations, all of which are overprinted by a north-south foliation. Both have been dates at around 2.7 Ga. The older granitoid is a grey granodioritic to quartz-dioritic biotite or biotite-amphibole gneiss. These are cut by veins of the younger granitoid, pink, mostly potassic migmatites.

Within the granitoids there are septa of older schists and greenstones which have not been completely granitised. Examples of the larger of these septa cover areas of the order of 20 x 5 and 30 x 25 km and contain steeply dipping banded iron formation (BIF), amphibolites, pyroxeno-amphibolites, biotite gneisses, amphibolite bearing quartzites, pyroxenites and in one case a small dunite mass.

To the north, in Cameroon, the du Chaillu granite-greenstone terrane grades into the high grade granulite facies charnockite terrane which was formed at about 2.9 Ga. It results from the intense metamorphism of highly evolved precursor rocks including dolerite dykes. These charnockitic products then suffered cataclasis, retrograde metamorphism as well as granitisation during the 2.7 Ga event that accompanied the introduction of granitoids into the du Chaillu terrane.

The probably Mesoarchaean iron formations of the du Chaillu schist-greenstone terrane host the iron mineralisaiton in the Mbalam deposits.

There are two main deposits at Mbalam, namely Mbarga and Metzimevin. These occurrences lie on a contorted and disrupted 35 km long magnetic iron formation and have been tested by the UNDF and the Canadian International Development Agency between 1976 and 1984.

Mineralisation at Mbarga was tested by surface trenching of laterite and scree covered massive hematite for an estimate of 184 Mt @ >60% Fe over a strike length of 2 km and average width of approximately 400 m, but up to 600 m wide in places.

At Metzimevin two 600 m long hematite outcrops were tested by 6 diamond drill holes which intersected thicknesses of 37 to 65 m of >64% Fe with 0.056% P, 0.67% Al2O3, with massive hematite persisting to a depth of 200 m at steep dips of 70 to 80° SW for an estimated 35 Mt @ >60% Fe.

On the basis of the UNDF testing, the two deposits have a combined resource of approximately 220 Mt @ >60% Fe, within a potential 800 Mt of mineralisation.

The deposits are supergene hematite (martite) enrichments of an Archaean banded iron formation (BIF) protore that has been recrystallised to form a ferruginous quartzite (itabirite). The mineralised unit has a strong magnetic reflection.

The supergene high grade ore forms a horizontal layer that is generally ~45 m in thickness, overlain by a 0 to 10 m thick surficial zone characterised by high alumina levels. The high grade supergene ore is underlain by a narrow 5 to 10 m thick transition zone containing high silica levels, passing down into the steeply dipping itabirite hypogene zone that is as much as 1200 m thick. The deposit generally occurs as a topographic highs as the capping to mesas.

Published JORC compliant resources in 2009 (Sundance Resources website) were:
      Indicated + inferred resource of high grade hematite ore: 215 Mt @ 60.2% Fe, 9.8% SiO
2, 2.3% Al2O3, 0.08% P,
      Indicated + inferred resource of "itabirite" hematite ore: 2.325 Gt @ 38.0% Fe, 44.4% SiO
2, 0.48% Al2O3, 0.04% P.

Published JORC compliant resources at Mbarga and Metzimevin in 2013 (Sundance Resources ASX release) were:
      Indicated + inferred resource of high grade hematite ore: 775.4 Mt @ 57.2% Fe, 9.4% SiO
2, 4.3% Al2O3, 0.04% P, 3.8% LOI
      Indicated + inferred resource of "itabirite" hematite ore: 2.325 Gt @ 38.0% Fe, 44.4% SiO
2, 0.48% Al2O3, 0.04% P, 0.4% LOI.
  These include resources at Metzimevin of:
      Inferred resource of high grade hematite ore: 15.2 Mt @ 59.5% Fe, 12.6% SiO
2, 4.1% Al2O3, 0.08% P, 2.0% LOI.
Published JORC compliant ore reserves at Mbarga and Mbarga South in May 2015 (Sundance Resources ASX release) were:
      Mbarga - Probable reserves of high grade hematite ore: 134 Mt @ 63.1% Fe, 4.98% SiO
2, 2.70% Al2O3, 0.08% P, 2.09% LOI.
      Mbarga South - Probable reserves of high grade hematite ore: 19.6 Mt @ 61.4% Fe, 6.39% SiO
2, 3.59% Al2O3, 0.06% P, 3.63% LOI.

The Nabeba deposit, ~45 km to the south in the Republic of Congo, is being investigated in conjunction with Mbalam, with the view of developing both as a combined operation. See the separate Nabeba record.

This record is a combination of information from a range of published sources, including Petters (1991), Regional Geology of Africa; Rundqvist, et al., (2006), Largest Mineral Deposits of the World; Sundance Resources website, 2013.

The most recent source geological information used to prepare this summary was dated: 2006.    
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.


  References & Additional Information

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 takes no responsibility what-so-ever for inaccurate or out of date data, information or interpretations.

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