In the past decades, several iron ore occurrences have been discovered in the Precambrian Belt of southern Cameroon, with focus on their economic potential, and little attention on the deposit type. However, few studies have been geared towards understanding the different deposit types within this region. This paper seeks to provide new insight on the different styles of iron ore mineralisation of two potential, yet least studied iron ore deposits in this region in addition to enhancing exploration efforts within the different prospects. Petrology and geochemistry of rock samples from the Binga and Djadom iron prospects in southern Cameroon are investigated. The structural disposition of the prospects was mapped and cores described, sampled and subsequently analysed to enhance the understanding of the alteration mineralogy, ore mineralogy and textural features of the iron-bearing lithologies. Polished thin sections were studied by standard microscopy while the bulk rock geochemistry was determined by X-ray fluorescence (XRF) for major and trace elements. At Binga, the main rock types are magnetite gneisses, amphibolites, quartz-biotite gneisses, and mafic intrusions, while the main rocks encountered at Djadom are magnetite gneisses, amphibolitic BIFs, quartz-biotite gneisses, amphibolites and fault rocks. At both prospects, the target lithology for iron ore is the magnetite gneiss. The magnetite gneisses at the Binga prospect are weakly to moderately foliated, but strongly foliated at Djadom, and both contain fractures that are healed by irregular magnetite. Magnetite is anhedral to euhedral in outline and it is closely associated with amphibole, garnet and pyroxene. Iron content of the magnetite gneisses ranges from 17.44 - 33.40 wt% (at Binga) and 27.73 - 43.39 wt% (at Djadom) and the ore enrichment process involved progressive loss of silica and aluminium. Trace element concentrations show high contents of Ba, Zn, Cu and V but lower abundances of Sr and Zr, as well as low values for Ti in both prospects. At the Binga iron ore prospect, TiO 2 and Al 2 O 3 display a linear co-variation with Zr, while in the Djadom prospect, TiO 2 , Al 2 O 3 and MgO display a negative co-variation with Zr. The origin of the former could be linked to a magmatic fluid-related process, while the genesis of the later is tied to both skarn formation and hydrothermal enrichment.
With the high demand for steel worldwide, partly driven as a result of global economic growth, exploration for new iron deposits is experiencing a boom, particularly in nonproducing countries such as Cameroon [
According to [
This study seeks to provide new insight on iron ore mineralization within the Precambrian Belt of southern Cameroon (northern extension of the Congo Craton) and contribute to exploration efforts of Compagnie Minière du Cameroun, currently exploring for iron ore in this region.
The Djadom and Binga iron ore prospects are located in southern Cameroon, at the northern edge of the Congo craton (
The Ntem Complex constitutes the Archean cratonic basement of southern Cameroon and lies at the north western coner of the Congo Craton in central Africa [
The Paleoproterozoic Nyong Series is defined as the reactivated NW corner of the Archean Congo craton [
The Binga and Djadom iron ore prospects are located in the Precambrian Belt of southern Cameroon, and form part of what is locally termed the Central African Iron Ore Emerging Province, which is known to host several world class deposits, such as; Mballam, Nkout, Ntem, Ngovayang and the Mamelles in southern Cameroon, and Boka Boka, Belinga, Badongo, Nabeba, Minkebe, Avima, in Congo and Gabon.
Core samples for this study were collected from six different diamond drill holes, three from each iron ore prospect. The core samples were carefully selected to represent the span of possible Fe-rich chemistry within both prospects, also taking into consideration the distance between drilled holes (holes that were selected were widely spaced) and drill depth which was on average 100 meters. These cores comprise mainly of magnetite gneisses, amphibolitic BIFs, amphibolites, mafic intrusions and fault rocks (dominated quartz with stains of goethite). Samples BCS08, BCS09, BCS013, were selected for Binga and DCS04, DCS05, and DCS020 for Djadom (
Only fresh samples were selected for this study, as thin sections could not be prepared on weathered samples. The author was part of the drilling team and after. The cores obtained were laid out in numbered sample boxes, and after determination of the sample depth the cores were subsequently quartered using a diamond saw (
The core samples, once selected were carefully described and placed in pre-labelled samples bags.
After sampling, the cores were sent to Alex Steward (ALS) laboratory facility in Mvan Yaoundé, where they were dried in an electric oven at a temperature of about 1200˚C or more, depending on their moisture content. This makes the samples friable so as to ease to the subsequent procedures.
Next the dried samples were then crushed to fractions of about 2 mm using a jaw crusher. This reduced the bulk sample into mille-able sizes, which was then introduced directly into the milling bowl. The main objective of milling the sample is to increase the surface area of the sample, thus exposing the target minerals for reaction with reagents during subsequent chemical attack. After milling, the samples were split into sub samples using a riffle splitter, thus homogenizing the samples into representative sub-samples.
This overall exercise also reduces the weight, while preserving the homogeneity of the sample thereby reducing the cost incurred for shipment.
The milled samples were shipped to the ALS laboratory in Cape Town South Africa, where they were analyzed for major and trace elements by use of X-Ray Florescence (XRF) technique after lithium metaborate fusion. The advantage of this method is that there is relatively low flux to sample ratio, which offers good sensitivity for the majority of elements and creates a matrix which is not subject to particle size effect.
With very low spectral interferences and high instrument sensibility, the XRF method delivers highly accurate and precise results across the full range of iron oxide ore types.
For more on the analytical technique please visit [
Subsamples of the uncrushed core material were taken to “Laboratoire de Traitement des Minerais (LTM) de Nkol-Bisson” in Yaounde, where thin sections for petrographic analysis were prepared. These were subsequently studied under an ore microscope at the Department of Geology, University of Buea.
Geochemical data were computed and plotted with the aid of the Geochemical Data Toolkit (GCD kit) software package, while the maps were produced by the couple use of Surfer9, and ArcGIS 10 software systems.
The main rock types at the Binga iron ore prospect are magnetite gneisses, amphibolites, gneisses, and mafic intrusions, while the main rocks encountered at the Djadom iron ore prospect are magnetite gneisses, amphibolitic BIFs (an intercalation of Banded Iron Formations and amphibolite), gneisses, amphibolites and fault rocks.
The magnetite gneisses at Binga (samples BD.9.50, BD.9.67, BD.9.86, BD.13.19, BD.13.28, and BD.13.38) are generally granoblastic and porphyroblastic with a dominance of magnetite over quartz and other gangue minerals. Mineralogically, they are dominated by magnetite, amphibole, quartz, garnet, and a few crystals of pyroxene and biotite. The magnetite grains are occasionally stretched defining a weak mineral lineation of magnetite stringers that accentuates the foliation in the rock (
In the highly deformed samples, quartz exhibits wavy extinction and contains micro-fractures healed by sericite (
The amphibolites in Binga are generally granoblastic (samples BD.8.50, BD.8.52, BD.8.54). Magnetite occasionally appears as an opaque core with serrated margins enclosed within altered amphibole (
Kyanite occurs as a lenticular crystal, with inclusions of magnetite within its matrix (
The Djadom magnetite gneisses (samples DD.4.80 and DD.5.70) generally show weak banding with alternating magnetite-rich and quartz-rich bands. Mineralogically, they are dominated by magnetite, amphibole, quartz and a few crystals of pyroxene (
The Djadom amphibolitic BIF samples (samples DD.4.70, DD.5.57, DD.20.70, and DD.20.80) are generally strongly foliated with distinct magnetite-rich bands alternating with quartz-dominated bands. The magnetite bands are more conspicuous and continuous (
tion sub parallel to the dominant foliation. However the rocks are highly deformed as quartz and garnet appear as lenticular crystals, sometimes occurring within a folded finer-grained matrix.
The fault rocks in the area are represented by samples DD.4.49, DD.5.37, and DD.20.51. These rocks show a clear mylonitic fabric with stains of goethite, and are more deformed than the magnetite gneiss and amphibolitic BIF (
The samples are generally strongly foliated with well aligned goethite/limonite-rich bands alternating with quartz-dominated bands (
The concentration of major and trace elements for eighteen core samples (nine from Binga and another nine from Djadom) are presented in
BD.8.50 | BD.8.52 | BD.8.54 | BD.9.50 | BD.9.67 | BD.9.86 | BD.13.19 | BD.13.28 | BD.13.38 | |
---|---|---|---|---|---|---|---|---|---|
Major elements (wt%) | |||||||||
SiO2 | 48.3 | 49.0 | 46.5 | 52.0 | 55.5 | 44.8 | 46.3 | 54.4 | 55.6 |
Al2O3 | 8.1 | 7.6 | 9.7 | 12.5 | 7.5 | 5.8 | 7.4 | 14.5 | 11.3 |
Fe2O3 | 32.8 | 30.6 | 32.6 | 21.2 | 29.7 | 40.8 | 33.4 | 17.4 | 22.0 |
MgO | 3.9 | 4.4 | 4.1 | 4.1 | 2.2 | 3.5 | 4.2 | 4.0 | 2.9 |
CaO | 3.8 | 2.4 | 3.1 | 6.3 | 2.6 | 3.1 | 4.6 | 3.5 | 3.6 |
Na2O | 1.9 | 1.6 | 1.2 | 3.5 | 1.8 | 1.30 | 1.7 | 3.7 | 2.7 |
K2O | 0.9 | 1.1 | 1.5 | 1.5 | 1.6 | 0.5 | 0.3 | 1.9 | 1.4 |
TiO2 | 0.6 | 0.5 | 0.6 | 0.5 | 0.2 | 0.3 | 0.6 | 0.8 | 0.4 |
MnO | 0.2 | 0.2 | 0.2 | 0.2 | 0.2 | 0.2 | 0.2 | 0.1 | 0.1 |
LOI | −0.4 | −0.5 | −0.2 | −0.3 | −0.4 | −1.1 | −0.8 | −0.2 | −0.3 |
Sum | 99.04 | 99.4 | 100.42 | 100.4 | 100.8 | 99.0 | 100.2 | 99.9 | 100.0 |
Trace elements (ppm) | |||||||||
As | 10 | 20 | 10 | 10 | 10 | 10 | 10 | 10 | 10 |
Ba | 630 | 600 | 730 | 820 | 640 | 240 | 360 | 600 | 730 |
Cl | 220 | 220 | 300 | 190 | 90 | 170 | 90 | 140 | 200 |
Co | 20 | 10 | 20 | 20 | 20 | 10 | 10 | 40 | 20 |
Cr | 111 | 118 | 106 | 57 | 12 | 54 | 136 | 500 | 161 |
Cu | 170 | 80 | 90 | 30 | 100 | 70 | 40 | 140 | 100 |
Ni | 60 | 80 | 60 | 30 | 50 | 30 | 40 | 110 | 190 |
P | 1020 | 920 | 930 | 800 | 530 | 810 | 1120 | 650 | 890 |
Pb | 50 | 10 | 10 | 10 | 40 | 10 | 10 | 30 | 10 |
S | 298 | 237 | 221 | 61 | 184 | 313 | 154 | 321 | 138 |
Sn | 10 | 10 | 10 | 20 | 30 | 10 | 10 | 20 | 10 |
Sr | 410 | 350 | 460 | 640 | 390 | 250 | 410 | 630 | 530 |
V | 100 | 60 | 90 | 130 | 50 | 70 | 150 | 250 | 70 |
Zn | 140 | 100 | 100 | 80 | 40 | 70 | 100 | 210 | 100 |
Zr | 140 | 130 | 150 | 140 | 150 | 70 | 70 | 150 | 200 |
Footnote 1: magnetite gneiss samples (BD.9.50, BD.9.67, BD.9.86, BD.13.19, BD.13.28, and BD.13.38) and amphibolite samples (BD.8.50, BD.8.52, BD.8.54).
DD.4.49 | DD.4.70 | DD.4.80 | DD.5.37 | DD.5.57 | DD.5.70 | DD.20.51 | DD.20.70 | DD.20.80 | |
---|---|---|---|---|---|---|---|---|---|
Major elements (wt%) | |||||||||
SiO2 | 45.9 | 49.8 | 47.1 | 56.9 | 49.1 | 51.0 | 66.5 | 45.3 | 42.9 |
Al2O3 | 10.2 | 2.9 | 2.8 | 0.3 | 0.1 | 8.0 | 0.1 | 2.1 | 1.8 |
Fe2O3 | 33.5 | 37.5 | 43.4 | 37.1 | 47.6 | 27.7 | 28.1 | 48.3 | 51.2 |
MgO | 3.1 | 2.6 | 2.2 | 0.7 | 4.1 | 4.1 | 0.4 | 3.5 | 3.8 |
CaO | 0.7 | 4.8 | 3.1 | 0.6 | 0.9 | 4.3 | 0.5 | 1.0 | 1.0 |
Na2O | 0.0 | 0.2 | 0.5 | 0.0 | 0.0 | 1.6 | 0.0 | 0.1 | 0.1 |
K2O | 0.9 | 0.4 | 0.4 | 0.0 | 0.0 | 0.5 | 0.0 | 0.1 | 0.0 |
TiO2 | 0.3 | 0.1 | 0.1 | 0.0 | 0.0 | 0.4 | 0.0 | 0.1 | 0.1 |
MnO | 0.2 | 0.1 | 0.1 | 0.4 | 0.4 | 0.2 | 0.0 | 0.5 | 0.7 |
LOI | 0.4 | 1.1 | 0.8 | 4.5 | −1.4 | 1.1 | 4.4 | −1.0 | −1.5 |
Sum | 100.1 | 97.1 | 99.9 | 101.5 | 101.1 | 99.4 | 100.0 | 100.2 | 100.1 |
Trace elements (ppm) | |||||||||
As | 10 | 5 | 20 | 10 | 20 | 10 | 5 | 10 | 10 |
Ba | 70 | 20 | 20 | 5 | 5 | 40 | 5 | 5 | 5 |
Cl | 280 | 200 | 190 | 10 | 250 | 150 | 10 | 50 | 110 |
Co | 5 | 5 | 5 | 5 | 10 | 20 | 5 | 5 | 10 |
Cr | 174 | 180 | 173 | 239 | 231 | 248 | 176 | 20 | 16 |
Cu | 30 | 20 | 30 | 40 | 20 | 80 | 20 | 20 | 40 |
N | 20 | 10 | 20 | 20 | 20 | 40 | 10 | 5 | 5 |
P | 710 | 630 | 690 | 580 | 700 | 450 | 650 | 770 | 800 |
Pb | 5 | 5 | 20 | 20 | 40 | 5 | 20 | 60 | 50 |
S | 873 | 172 | 695 | 779 | 72 | 105 | 84 | 18 | 495 |
Sn | 5 | 5 | 5 | 5 | 5 | 5 | 5 | 10 | 20 |
Sr | 5 | 40 | 30 | 30 | 30 | 70 | 110 | 100 | 100 |
V | 50 | 20 | 20 | 5 | 5 | 100 | 10 | 20 | 10 |
Zn | 60 | 20 | 40 | 30 | 20 | 40 | 30 | 40 | 50 |
Zr | 100 | 50 | 40 | 40 | 60 | 70 | 240 | 180 | 180 |
Footnote 2: magnetite gneiss (samples DD.4.80 and DD.5.70), amphibolitic BIF (samples DD.4.70, DD.5.57, DD.20.70, and DD.20.80), fault rocks (sample DD.4.49, DD.5.37, DD.20.51).
The chemistry of the magnetite gneiss (
The chemistry of the magnetite gneiss (
In both prospects, trace element concentrations (
In depicting the relationship between the various major oxides and trace elements in the Binga and Djadom iron ore prospects, binary plots were done for major oxides and some selected trace elements. In an attempt to understand these trends, geochemical data for two known magmatic-related iron ore occurrences (Akom II, Cameroon) and (Bergslagen, Sweden) were incorporated and plotted alongside those from the Binga and Djadom iron ore prospects. The results are presented in Figures 12-14. Figures 12(a)-(h) shows binary plots for Fe2O3 versus other major oxides (SiO2, TiO2, Al203, MgO, CaO, Na2O, K2O, and MnO), while Figures 13(a1)-(h1) shows binary plots of Fe2O3 versus trace elements (Ba, Cr, Ni, Sr, Zr, V, Cu, and Co) for Binga, Djadom and Akom II, and (A to H) for Bergslagen.
In both the Binga and Djadom prospects SiO2 decreases with increasing Fe2O3 (
In both the Binga and Djadom prospects Ba, Co, Cr, Cu, and Ni are negatively correlated with Fe2O3 (
Sr and Zr show a strong negative correlation with Fe2O3 in the Binga prospect, while in the Djadom prospect Sr and Zr show a weak positive correlation with Fe2O3 (
In the Binga iron ore prospect, binary plots for large ion lithophile (LIL) elements Ba and Sr together with K2O and Al2O3 display a strong linear co-variation with zirconium (
Most samples within the Binga prospect show a close association of magnetite with amphibole and pyroxene. This suggests that amphiboles and/or pyroxenes in these samples are often replaced (either partially or com-
pletely) by magnetite. Replacement of amphiboles/pyroxenes by magnetite may be hydrothermal and/or metamorphic in origin. The Binga amphibolites show some chlorite alteration (
Rocks in the Binga prospect possibly underwent an intensive high-temperature recrystallization which gave rise to small new grains of hornblende, plagioclase, and pyroxene, all of which are rimmed by late garnet overgrowths.
Furthermore, metamorphic overprint in these rocks is represented by rims of biotite around oxides, and rims of secondary amphibole around primary amphibole and pyroxene (
Most of the samples from Djadom show fine-scale banding and strong foliations defined by magnetite and quartzo-feldspathic minerals (
In the altered samples, leucocratic bands and magnetite crystals are crosscut by micro-fractures, while microfolds are occasionally observed. The highly altered samples show deformed porphyroclasts of garnet crystals that have survived ductile deformation lying within a fine-grained iron oxide matrix.
The different habits of magnetite from anhedral to euhedral could suggest a metamorphic or hydrothermal origin. Samples with cubic megacrystals suggest that magnetite occurs here as a result of hydrothermal overprint and this is strongly supported by foliated texture presented by the fault rocks (
Replacement of amphiboles, garnets/pyroxenes by magnetite may be hydrothermal and/or metmorphic in origin.
Biotite (annite) K-feldspar Magnetite
At low and medium grade conditions, garnet is much stronger than quartz and feldspar and does not deform when isolated in a quartzo-feldspathic matrix. At higher temperatures, the difference in strength decreases to an extent that all three minerals can deform together [
The sigmoidal shape of the garnet porphyroclasts attest to deformation, and suggests that differential stresses were high around the rims of these porphyroclasts, probably leading to dynamic recrystallization forming a core- and-mantle structure.
The amphibolitic BIF’s at the Djadom iron ore prospect are interbedded with magnetite-amphibole-pyroxene bearing gneisses, and are similar to amphibolitic itabirite as defined by [
Considering that all the amphibolites associated with BIF belong to the same genetic type then those elements which are incompatible in basaltic systems [
As a generalization, incompatible elements belonging to the LIL (Sr, K, and Ba) group are mobile, whereas High Field Strength (HFS) elements are immobile [
[
At the Binga iron ore prospect, TiO2 displays a linear co-variation with Zr, and Al2O3 displays a strong linear co-variation with Zr. This is supported by [
Whilst in the Djadom prospect, TiO2, Al2O3 and MgO display a negative co-variation with Zr. This could suggest that the rock suits at the Djadom iron ore prospect were overprinted by metamorphism, likely involving some hydrothermal fluids. This statement is supported by [
The results of this study suggest that the Binga iron ore prospect could be contemporaneous with magmatic intrusions, as most features of this prospect show evidence of magmatic fluid activity. This is however in line with studies carried out by several authors such as; [
Most of the samples from Djadom show foliated and granoblastic textures, which are characteristic of metamorphic rocks. Three metamorphic events are postulated; a high grade metamorphic event (which led to the development of garnets) followed by dynamo-metamorphism, which is represented by mylonitic and ductile deformation (
The depletion of LIL elements (K and Ba) coupled with the negative correlation between Al, Mg and HFS elements with Zr could suggest metamorphic over print on the Djadom prospect, which was accompanied by hydrothermal fluids. This is in line with studies carried out by [
Hydrothermal alteration could have been the most significant process contributing iron ore enrichment in this prospect, as evidence by the presence of; garnet, tremolite, actinolite, biotite, feldspar, quartz, and iron oxide (Figures 9(a)-(d)). Structurally, this is evidence by discontinuous pinch-and-swell boudinages and irregular folds in amphibolitic BIF’s and Fe-rich fault rocks, (
The Djadom iron ore prospect lies in the Ayena Series. Very little is known about this series. This area must have probably experienced complex deformation and metamorphism resulting in the development of folds, micro-fractures and possibly shear zones. The magnetite ore at Djadom is structurally-controlled and attest to the role of deformation and, possibly, hydrothermal alteration in the ore-forming process.
Several iron ore occurrences have been discovered in the Precambrian Belt of southern Cameroon, but much is not known about the Binga and Djadom iron ore occurrences. These iron ore occurrences are described here for the first time, and represent probably skarn-related deposits, as their nature and complexity are similar to those of other skarn-related deposits, as emphasized by several workers [
The Binga iron ore prospect probably represents an intrusive related iron skarn deposit which is associated with a shear zone and magmatism.
The genesis of the Djadom iron ore prospect is possibly tied to both skarn formation and hydrothermal enrichment.
By analysing for Rare Earth Elements (REE’s) and comparing their patterns to those of other known iron ore deposits in the world, new fingerprints could be developed, which could be taken into consideration during subsequent exploration activities in the different prospects.
This article is a part of the MSc. thesis of G. N. N, at the University of Buea under the supervision of C. E. S. This work is greatly supported by West African Minerals (represented by CMC in Cameroon), and G. N. N thanks the management of CMC especially Mr. Anton Mauve, Mr. Steve Makang and Mr. Duncan Bowker for their kind support and consideration.
Gilles Nyuyki Ngoran,Cheo Emmanuel Suh,Dunkan Bowker,Raymond Beri Verla,Godlove Tasin Bafon, (2016) Petrochemistry of Two Magnetite Bearing Systems in the Precambrian Belt of Southern Cameroon. International Journal of Geosciences,07,501-517. doi: 10.4236/ijg.2016.74038