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 (Figure 5(a)). Magnetite also occurs as anhedral inclusions in garnet and amphibole. Quartz shows a granoblastic texture forming the matrix in the rocks. The rocks at Binga are highly deformed as quartz, pyroxene, and garnet are fractured and curviplanar fractures in quartz are more conspicuous. In most cases the fractures are filled with magnetite (Figure 5(b) & Figure 5(c)).

In the highly deformed samples, quartz exhibits wavy extinction and contains micro-fractures healed by sericite (Figure 5(c)), while plagioclase is altered resulting in vacuolization (Figure 5(d)), thus forming a lock-and- key structure.

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 (Figure 6(a)). Magnetite is closely associated with amphiboles, and the latter commonly occurs as green hornblende, mostly lenticular in shape (Figure 6(b) & Figure 6 (c)).

Kyanite occurs as a lenticular crystal, with inclusions of magnetite within its matrix (Figure 7(a)), while chlorite occurs as a secondary mineral possibly resulting from the alteration of biotite (Figure 7(b)).

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 (Figure 8(a)). This rock displays a variety of textures: foliated, porphyroblastic and granoblastic textures. Quartz crystals are generally less than 0.1 mm. Pyroxene grains commonly line the foliation.

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 (Figure 9(a)) in contrast to those of the magnetite gneiss. Mineralogically, the rock is dominated by magnetite, amphiboles (tremolite and actinolite), quartz (Figure 9(b)) and pyroxene. The quartz grains are elongated to sub-rounded and generally less than 0.1 mm in size. The rock also displays a variety of textures including foliated and porphyroblastic textures. Magnetite is closely associated with amphiboles (Figure 9(a)) and pyroxenes, possibly resulting from recrystallization of the amphiboles and/ or pyroxene. Magnetite crystals are subhedral to cubic porphyroblasts and range in size from <0.1 mm to about 0.5 m. These magnetite crystals also occur as disseminations within garnet and/or pyroxene (Figure 9(d)). Tremolite and actinolite occur mostly in the more altered samples. These minerals define a strong mineral linea-

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 (Figure 10 and Figure 11). The mineral assemblage is predominantly quartz with little amounts of, magnetite, garnet, and subordinate limonite/goethite.

The samples are generally strongly foliated with well aligned goethite/limonite-rich bands alternating with quartz-dominated bands (Figure 11(a)). Garnet and magnetite occur as deformed lenses or pods (possibly relic porphyroclasts) embedded within a folded, fine-grained matrix of mainly goethite/limonite (Figure 11(b)).

The chemistry of the magnetite gneiss (Table 1) shows a high Fe₂O₃ content (17.44 - 33.40 wt%), with a slightly higher value for sample BD.9.86 which has an Fe₂O₃ content of 40.87 wt%, while the amphibolite shows Fe₂O₃ values in the range of (30.62 - 32.80 wt%). SiO₂ concentration (46.50 - 49.00 wt%) is slightly lower in the amphibolite compared to its concentration (44.80 - 55.60 wt%) in the magnetite gneiss. Aluminium oxide content is low (7.61 - 9.71 wt% and 7.45 - 14.55 wt%) in both the amphibolite and the magnetite gneiss, respectively. Both the magnetite gneiss and the amphibolite are also characterized by a low TiO₂ content (0.16 - 0.8 wt% and 0.55 - 0.57 wt%, respectively).

The chemistry of the magnetite gneiss (Table 2) shows a slightly higher Fe₂O₃ content (27.73 - 43.39 wt%), than that of the fault rocks Fe₂O₃ content (37.12 - 33.56 wt%), while that of the amphibolitic BIF (major oxides, Table 4.2) shows a slightly higher Fe₂O₃ content (37.45 - 51.23 wt%). SiO₂ concentration is low for the magnetite gneiss (47.1 - 51 wt%) and fault rocks (45.9 - 56.9 wt%), but slightly lower in the amphibolitic BIF (42.9 - 49.8 wt%). The Al₂O₃ content in the amphibolitic BIF (0.09 - 2.89 wt%) is low as compared to the magnetite gneiss (2.8 - 8.03 wt%) and fault rocks (0.29 - 10.2 wt%). The magnetite gneiss, amphibolitic BIF and fault rocks are characterized by low TiO₂ content.

In both prospects, trace element concentrations (Table 1 and Table 2) show high contents of Ba, Zn, Cu and V but lower abundances of Sr and Zr.

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.

Figure 4.10 shows binary plots for some selected major elements (K₂O, Al₂O₃, TiO₂ and MgO) and selected trace elements (Ba, Ni, Sr, and Zr) for Binga, Djadom, Akom II and Bergslagen.

In both the Binga and Djadom prospects SiO₂ decreases with increasing Fe₂O₃ (Figure 12(a)). The same pattern is observed for Al₂O₃, and Na₂O (Figure 12(c) and Figure 12(f) respectively). This suggests that the iron enrichment process requires progressive loss of silicon and aluminium.

In both the Binga and Djadom prospects Ba, Co, Cr, Cu, and Ni are negatively correlated with Fe₂O₃ (Figure 13(a₁), Figure 13(b₁), Figure 13(c₁), Figure 13(g₁), Figure 13(h₁)).

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 (Figure 13(d₁) & Figure 13(e₁)).

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 (Figure 14(a₁), Figure 14(c₁), Figure 14(d₁) & Figure 14(e₁)), whilst in the Djadom iron ore prospect, plots of Ba and K₂O with the exception of Sr do not show any linear trend with Zr (Figure 14(a₁), Figure 14(c₁), Figure 14(d₁) & Figure 14(e₁)).

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 (Figure 4.3(B)), which might have resulted from chloritisation of biotite and/or hornblende. This could suggest retrograde metamorphism although kyanite, which is characteristic of middle amphibolite facies at a temperature of ~600˚C appears in the mode of some samples (Figure 7(a)).

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 (Figure 6(b)).

Most of the samples from Djadom show fine-scale banding and strong foliations defined by magnetite and quartzo-feldspathic minerals (Figure 9(a) and Figure 9(b)), occasionally with increasing amounts of actinolite, tremolite, and chlorite within the light-green bands. This scenario is similar to that of the Hainan Province, south China, and could have resulted from late-stage hydrothermal alteration as reported by [16] . Other samples show discontinuous, probably relict banding of magnetite within fine-grained quartz dominated matrix. Alteration halos are also present, which could be as a result of hydrothermal overprint (Figure 8(c) & Figure 8(d)).

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 (Figure 10(a) and Figure 10(b)). Magnetite is closely associated with amphiboles, garnets and pyroxenes, occurring either as disseminated inclusions, along micro-fractures and/or grain boundaries of these minerals. This suggests that amphiboles, garnets and pyroxenes in these samples are often replaced (either partially or completely) by medium- to coarse-grained magnetite.

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 [17] - [19] . Highly deformed samples show elongated lens- shaped garnets that have been folded and emplaced parallel to the deformation fabric (Figure 9(c)) and occur along with deformed quartz crystals (Figure 11(a)).

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 [20] , as the former consist of bands dominated mainly by two types of amphiboles (tremolite and actinolite) alternating with bands of iron oxides. The texture and mineralogy of these amphibolitic BIF’s is similar to those reported for amphibolitic itabirite by [16] for the Hainan Province in south China, as well [21] for the Cauê Formation in Quadrilátero Ferrífero, Minas Gerais, Brazil.