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International Journal of Basic & Applied Sciences IJBAS-IJENS Vol: 11 No: 04 57
118404-7676 IJBAS-IJENS © August 2011 IJENS I J E N S
Petrographic and Geochemical Evaluations of Rare –
Metal (Ta-Nb) Potentials of Precambrian Pegmatities
of AWO Area Southwestern, Nigeria.
1Akintola, A. I.,
1 Omosanya, K. O.,
1Ajibade O. M.,
2Okunlola, O. A &
1 Kehinde-Philips, O. O
1, Department of Earth Sciences, Olabisi Onabanjo University, Ago-Iwoye, Nigeria.
2 Department of Geology, University of Ibadan, Ibadan, Nigeria.
E-Mail: busayoakins@yahoo.com
Abstract-- The Petrographic and geochemical evaluations of
pegmatite bodies around Awo in Southwestern Nigeria were
carried out with a view to characterising them and determining
their genesis and rare metal potentials that may be related to Ta-
Nb mineralization.
Fifteen (15) whole rock pegmatite samples and five (5) muscovite
samples extracted from the pegmatites were analyzed for major
and trace elements using the Inductively Coupled Plasma
Emission Spectrometer (ICP-AES) analytical method.
The petrography revealed preponderance of Microcline and
albite with subordinate muscovite and anhedral quartz,
accessory minerals found include tourmaline, garnet, beryl, and
spodumene.
The whole rock pegmatites are highly siliceous having SiO2 mean
value to be (54.95%) while the muscovite extract has a mean
value of (44.61%); Al2O3 contents are fairly high in the muscovite
extracts than in the whole rock pegmatite samples with very low
mean values of MnO, MgO, CaO, Na2O, TiO2, and P2O5. Other
than these, the pegmatites are enriched in Rb, Cs, Zr, Ga, Ba, Be,
Y, W, and the rare metals Ta and Nb.
The variation diagram plot of Na2O/Al2O3 versus K2O/Al2O3
reveals igneous ancestry for the pegmatites with the Rb/Sr plot
suggesting a 30km crustal thickness during emplacement of this
pegmatite. There is low to moderately high albitisation,
progressive rare alkali fractionation, and controlled Ta-Nb
enrichment in the Awo fields with the sample plotting in the Rare
Metal Pegmatite Zone “RMP”. The recorded negative Ce
anomaly is an indication of oxidation due to the influence of fluid
– rock metasomatic processes in their genesis.
The enrichment pattern revealed by other geochemical variation
plots shows that the pegmatites have moderate to high Ta-Nb
mineralization.
Index Term-- Petrographic, Pegmatite, Metasomatic, Quartz,
Muscovite, Feldspars.
I. INTRODUCTION
The study area lies within longitude 4o 23
1 E
to 4
o 25
1 E
and
latitude 7o 45
1N to 7
o 47
1 N of Iwo Sheet 242 N.E. (Fig. 1). It
is accessible by complex road network of major and minor
roads as well as foot path linking one sampling point to the
other. In recent times there has been renewed interest in the
study of pegmatites globally because of its attractive
economic potentials. Earlier study of Pegmatites in Nigeria
include the work of Jacobs and Webb (1946) which identified
that the pegmatites are restricted within a confine of 400km
NE-SE trending belt. This point of view was refuted by the
work of Garba, (2003) and Okunlola, (2005). The occurrences
in the Southeastern part of the Nigeria, notably around Obudu
hills were presumed to extend into Northeast Brazil (Garba,
2003; Ekwueme, 2004). The Nigerian pegmatites evolved
during the time span of 600+530Ma, (Matheis and Caen
Vachete, 1983), which indicates formation (Orogeny) during
the periods of Pan African magmatism.
Precambrian pegmatites of Nigeria are known to host a variety
of rare metals, tantalum, niobium, tin, tungsten, columbite as
well as lithium which found use in the production of
microchips and microprocessors for computers and
electronics, aircraft construction, casting, galvanizing,
production of containers, metal wears. More importantly, the
tantalum and niobium contained in this specialty metals are
used for heat and corrosion resistant steels and alloys applied
in space ships and gas turbines. (Okunlola,1998., Adekoya et
al., 2003., Garba, 2003., Okunlola and Ogedengbe, 2003.,
Akintola, 2004., Okunlola, 2005., Okunlola and Jimba, 2006.,
Okunlola and Somorin, 2005., Okunlola and Akintola, 2007.,
Okunlola and Akintola, 2008 ).
Matheis, 1981, Matheis et al., 1982., Kuster, 1990., Garba,
2003, Okunlola, 2005 classified the metallogeny of the rare
metal Ta-Nb pegmatites of Nigeria, outlining 7 broad fields
namely Kabba - Isanlu, ljero - Aramoko, Keffi- Nasarrawa,
Lema -Ndeji, Oke Ogun, Ibadan -Osogbo and Kushaka -
B/Gwari. The Awo Pegmatites occurrence which is part of the
Precambrian pegmatites in Ibadan-Osogbo field was studied
with the aim of elucidating their petrography and geochemical
features and thus characterizing them, and understanding their
genesis and rare metal potentials.
II. GEOLOGICAL SETTING, FIELD DESCRIPTION
AND PETROGRAPHY OF ROCKS
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Nigeria is underlain by Precambrian basement complex rocks,
younger granites of Jurassic age and Cretaceous to Recent
sediments. The basement rocks occupy about half of the land
mass of the country, and is a part of the Pan-African mobile
belt lying between the West African and Congo cratons
(Black,1980). There are however contrasting documentation
of the evolution of the basement rocks. However loosely, the
basement is grouped into three major groups
lithostratigraphically viz: the Migmatite- Gneiss Quartzite
Complex: comprising biotite and biotite hornblende gneisses,
quartzites and quartz schist. Schist Belts, comprising
paraschists and meta igneous rocks, which include schists,
amphibolites, amphibole schists, talcose rocks, epidote rocks,
marble and calc-silicate rocks. They are mainly N-S to NNE-
SSW trending belts of low grade supracrustal (and minor
volcanic) assemblages. Other secondary rocks used in
delineating them are carbonates, calc gneiss and banded iron
formation (BIF) and Older granites, which include granite,
granodiorite, diorite charnockite, pegmatites and aplites.
The Awo study area is generally underlain by granite, banded
gneiss, quartzite and quartz schist, with pegmatite trending in
the NNW-SSE direction occurring as near vertical intrusions
into the older rocks. (Fig. 2)
The granite occurs mostly in the northwestern portion of the
map, the granites which are often coarse grained to porphyritic
in texture are mainly composed of biotite, microcline and
quartz.
The banded gneiss occurs as a massive rock consisting of
alternating bands of felsic minerals notably plagioclase
feldspars and quartz, and the dark bands consisting of biotite
and hornblende.
The quartzite samples are mostly white in color but some
ferruginized varieties display reddish bands. They consist
mainly of quartz which occurs as irregular fine to medium
grained crystals with interlocking grains of muscovite.
Fig. 1. The location map of Awo with the sampling points
The quartz schist occurs as low-lying outcrops, they are fine
to medium – grained, display incipient schistocity and contain
quartz, microcline, and muscovite with accessory haematite.
The pegmatites of Awo occur as near vertical intrusions
covering the study area, they are coarse grained rock with a
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general milky white appearance. The main mineral
assemblages are microcline, quarzt, biotite, and tourmaline
(black and green) while the secondary associated minerals
include kaolinite, tantalocolumbite and cassiterite.
Petrographical studies of the Awo pegmatite show that they
contain mainly plagioclase, muscovite, quartz, microcline,
biotite, and accessory opaque minerals such as garnet,
tourmaline, cassiterite and tantalocolumbite (Table I).
Plagioclase ranges from (15 - 60 %), it exhibits characteristic
albite twinning and it is well distributed in all the samples.
Muscovite occurs as tiny elongated plates with high relief and
perfect cleavage in one direction with strong birefringence, it
ranges between (5-20%)
Quartz ranges between (25-35%), it occurs as cloudy anhedral
grains with wavy extinction and characteristic weak
birefringence.
Microcline often intergrown graphically, they are sometimes
perthitic with albite occurring as patchy perthite. It however
displays characteristic cross hatch twinning it ranges between
(1-50%).
Biotite ranges from (1-5%), it however occurs as fine dark
brown platy grains. Figures:3a(i.),b(i),c(i),d(i)
&3a(ii),b(ii),c(ii),d(ii)
Fig. 2. Geological map of Awo area southwestern Nigeria.
III. METHODS
Systematic geological mapping followed by thin sectioning of
fresh whole rock samples was carried out. The whole rock and
muscovite extracts of the pegmatite samples were then
analyzed for major, minor, trace, and rare earth elements using
inductively-coupled plasma atomic emission
spectrophotometry (ICP-AES), at Activation Laboratories ltd.
(ACTLAB) Ancaster, Ontario Canada.
The geochemical analytical procedure involves addition of
5ml of Perchloric acid (HClO4), Trioxonitrate (V) HN03 and
15ml Hydrofluoric acid (Hf) to 0.5gm of sample.
The solution was stirred properly and allowed to evaporate to
dryness after it was warmed at a low temperature for some
hours. 4ml hydrochloric acid (HCl) was then added to the
cooled solution and warmed to dissolve the salts. The solution
was cooled; and then diluted to 50ml with distilled water. The
solution is then introduced into the ICP torch as aqueous -
GG
G
G
Bgn
Bgn
Bgn
Bgn
Bgn
Q
Q
Q
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aerosol. The emitted light by the ions in the ICP was
converted to an electrical signal by a photo multiplier in the
spectrometer, the intensity of the electrical signal produced by
emitted light from the ions were compared to a standard (a
previously measured intensity of a known concentration of the
elements) and the concentration then computed.
Table I
Average modal composition (%) of minerals in Awo pegmatites
Minerals P1 (%) P2 (%) P3 (%) P4 (%)
Plagioclase (PL) 45 15 50 60
Muscovite (Mu) 5 5 20 - Quartz (Q) 35 25 25 30 Biotite (B) 5 - - -
Garnet (G) 5 - - - Microcline (M) - 50 - - Accessories (A) 5 5 5 10
PI-P4 Represent Photomicrographs of Pegmatites from Awo study area
IV. RESULTS AND DISCUSSION
The geochemical data of major and trace element analysis
which are presented in (Table II) show that the Awo pegmatite
have SiO2 values ranges from 44.79-70.37% with a mean
value of 54.95% in the Awo whole rock pegmatite, while it
ranges from 44.27-44.89% with a mean value of 44.61% in
the muscovite extracts. The SiO2 values of the Awo whole
rock and muscovite extracts compares with the values of rare
metal Ta-Nb mineralized pegmatites across Nigeria
(Okunlola, 2005; Okunlola and Akintola, 2007; Akintola and
Adekeye, 2008). Al2O3 ranges from 14.70-33.51% with an
average of 25.77% in the Awo whole rock samples, while it
ranges from 33.20 to 34.20% with a mean value of 33.83% in
the muscovite extracts. There is a sharp contrast in the values
of some of the whole rock and muscovite extracts sample of
the alumina content in addition with other rare metal
characteristics for the pegmatites of this study area which
simply confirms the complexity of the Awo pegmatites. Fe2O3
ranges from 0.25-7.22% with an average of 2.44% in the
whole rock pegmatite, while the muscovite extract gives a
range of 4.36-4.52% with an average value of 4.46%. Mean
contents of major oxides MnO (1.61%, 0.12%), MgO (0.06%,
0.36%), CaO (0.30%, 0.01%), Na2O (1.28%, 0.58%), K2O
(3.74%, 10.05%),TiO2 ( 0.06%, 0.07%), P2O5 (0.14%, 0.03%),
for the whole rock and muscovite extract samples of Awo
pegmatites respectively, compare favourably with the rare
metal bearing pegmatites of Lema-Ndeji, Igbeti and Isanlu-
Egbe areas (Okunlola, 2005 ; Okunlola and Akintola, 2008 ;
Okunlola and Oyedokun, 2009).
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Fig. 3a(i). Photomicrograph of Pegmatite in transmitted light showing Plagioclase (PL),Biotite (B), Muscovite (MU), Quartz (Q) and Garnet (G). b(i):
Photomicrograph of Pegmatite in transmitted light showing Microcline (M), Plagioclase (PL) Muscovite (MU) and Quartz (Q). c(i): Photomicrograph of Pegmatite in transmitted light showing Plagioclase (PL), Quartz (Q) and Muscovite (MU). d(i): Photomicrograph of Pegmatite in transmitted light showing
Plagioclase (PL) and Quartz (Q).a(ii), b(ii), c(ii) and d(ii)Modal distributions of estimated minerals in Awo pegmatites.
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Fig. 4(a). Plot of K/Rb vs Cs for Awo Pegmatite (After Cerny, 1982);( b) K/Rb vs Rb distribution pattern in the Muscovite extracts of Awo Pegmatites; Arrow
indicate normal differentiation trend after Staurov et al., (1969); (c) K/Rb vs Rb distribution pattern in the whole rock Pegmatites of Awo study; Area, arrow
indicate normal differentiation trend after Staurov et al., (1969);(d) Plot of Na2O/Al2O3 vs K2O/Al2O3 (Wt%) showing variation diagram for the Field Of Igneous
and Meta sedimentary rocks of Awo Pegmatites. (After Garrels and Mackenzie, 1971); (e) Plot of Ta vs Cs for the pegmatites of Awo study area; (After Moller and Morteani, 1987); (f) Plot of Ta vs Rb for the pegmatites of Awo study area; (After Moller and Morteani, 1987); (g) Plot of Ta vs Cs+Rb for the pegmatites
of Awo study area. (After Gaupp et al., 1984);(h) Plot of Ta vs Nb for the pegmatites of Awo study area.(i.) Plot of Ta vs K/Cs ratio for the pegmatites of Awo
study area. (After Gordiyenko, 1971 and Beus, 1966 ). (j): Plot of Ta/W ratio vs. Cs for the pegmatites of Awo study area.The Ta/W ratio increases with increasing elements fractionation as indicated by Cs. (After Moller and Morteani, 1987);(k): Rb vs (Y+Nb) discriminant diagram for the whole rock sample
pegmatites of Awo=AO compared to those of Olode = OD, Komu= IK, and Ago-Iwoye AOI (After Pearce et al., 1984). VAG- VOLCANIC ARC GRANITE;
ORG- OCEANIC RIDGE GRANITE; WPG- WITHIN-PLATE GRANITE; SCG- SYN-COLLISIONAL GRANITE ;(l): Zr-Sio2 Plots of the pegmatites of Awo= AO compared to those of Olode=OD, Komu=Ik, and Ago-Iwoye =AOI pegmatites; (m): Sr-Rb Plots of the Awo =AO compared to those of Olode=OD,
Komu=Ik,and Ago-Iwoye =AOI pegmatites.(n): Plot of Rb-Sr for the pegmatites of Awo study area. (After Condie, 1976). (o) Plot of Ta/(Ta+Nb) vs Mn/(Mn+Fe) variation plots of the Awo Pegmatites
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Trace and rare earth element data (Table III) show that the
pegmatites are enriched in rare metals with moderately high
values of Cs, Nb, Sn, Rb, and Ta. With Cesium ranging from
(2.5-526ppm; 160.2-210.8ppm), Niobium (4-390ppm; 370.5-
383.1ppm), Tin (2-244ppm; 1050-1104ppm), Rubidium (58.0-
1000ppm; 2936-3136ppm) and Tantalum (1.0-365ppm; 35.3-
41.9ppm), for the whole rock and muscovite extracts samples
of Awo pegmatites respectively. The Ta and Nb values in the
whole rock and mica extracts in the same vein with the Komu
pegmatites are comparable with those of the richer Nasarawa-
Keffi and Kushaka Ta-Nb fields of Nigeria respectively
(Okunlola, 2005). The mean values of Be (34.2ppm,
24.80ppm), Ga (54.52ppm, 257.32ppm), W (4.79ppm,
9.18ppm), Sr (45.93ppm, 0.58ppm), Zr (49.04ppm, 7.36ppm),
Ba (79.67ppm, 1.4ppm) and Y (5.16ppm, 0.2ppm) are as
shown for the Awo whole rock and muscovite extract
pegmatite samples respectively. These values compare
favourably with the mineralized pegmatites of Noumas South
Africa, Silver leaf, Canada and Homestead Canada. (Moller
and Morteani, 1987). However the level of mineralization in
Awo pegmatites is lower than that of the highly mineralized
Tanco Ta-Nb (Cerny, 1982; Moller and Morteani, 1987).
Average elemental ratio Rb/Sr is expectedly high compared
with most of the other rare metal pegmatites Of Nigeria.
However, average K/Rb values are low and this value suggest
and indicate late stage progressive fractionational
crystallisation and probable mineralization (Kuster, 1990).
Ratios of K/Cs, K/Ba, and Th/U are also low, typical of rare
metal mineralization (Garba, 2003). Following after the
classification criteria of pegmatites based on bulk chemistry
signatures (Cerny, 1991a; 1991b), and the Ta/ (Ta+Nb) versus
Mn/ (Mn+Fe) plot (Fig. 4(o.)). The Awo pegmatites are of the
rare element class, complex pegmatite. They are of the LCT
petrogenetic family (Li, Rb, Cs, Be, Ga, Sn, Ta < > N (BPF)
and of the Beryl sub type. The pegmatites are of per
aluminous bulk composition {A/CNK>1} (where A: Al2O3,
CNK: CaO+ Na2O+K2O). Cerny, (1992) has observed that the
LCT family has a mild to extremely Per aluminous parent
granitic composition. Using the K/Rb versus Cs plots, the
pegmatites in Awo area are also rare metal bearing because all
the samples plot in the field of rare metal pegmatite “RMP”.
(Fig.4a).
The low values of Mg, Ti, Ba and Zr with attendant high Rb,
and Cs composition indicate high fractionation of the
pegmatites, while the moderately high Cs values of the Awo
pegmatites indicate moderately high alkali metal fractionation.
(Cerny, 1982a; 1982b; 1989). There is a clear enrichment of
Nb, Ta, Rb, Sn, Cs, Rb and depletion of Sc, Co which also
suggest mineralization of the rare metal columbo-tantalite
(Moller and Morteani, 1987). The samples are also relatively
higher In Ta content in the whole rock samples than in the
mica extracts showing that the pegmatites in Awo area are
adequately enriched in Tantalite.
The Ta-Nb mineralization potential trend as shown from plots
of K/Rb versus Cs (Fig.4a), and K/Rb versus Rb (Fig4(b) &
(c)) revealed a consistent trend as all the samples plot in the
mineralized field which is similar to those of Noumas deposits
in South Africa (Moller and Morteani, 1987). Some samples
also plot close to those of the highly evolved Tanco
pegmatites (Cerny, 1989).
The degree of albitization is revealed by the Triangular Ti-Sn-
(Nb+Ta) discriminant plot in the zone of albitization (Fig. 5)
for the Awo pegmatites. This plot also reveals a high degree
of albitization and it indicates a significant difference between
the mineralized and unmineralized pegmatite samples
(Matheis and Emofurieta, 1990; Okunlola and King, 2003;
Okunlola and Somorin, 2005; De Kun, 1965; Jacobson and
Webb, 1946). However these values are still low when
compared to those of the economically viable bodies like
Tanco Canada (Moller and Morteani, 1987), but they compare
favourably with those of other richer mineralized pegmatite
areas like Lema-Ndeji Central Nigeria, Egbe and Igbeti areas
southwestern Nigeria (Okunlola and Akintola, 2008; Matheis,
1987; Okunlola and Oyedokun, 2009). This is also indicative
of the degree of fractionation. In addition, the variation plots
of Ta versus Cs (Fig.4(e)), Ta versus Rb (Fig.4(f)), Ta versus
Cs + Rb (Fig.(g)), Ta versus Nb (Fig.4(h)), Ta versus K/Cs
(Fig.4(i)) and Ta/W versus Cs (Fig.4(j)) confirm their rare
metal mineralization potentials. These plots also show the
Awo pegmatite samples occurring over the mineralized lines
of Beus, (1966) and Gordiyenko, (1971).
The variation diagram plot (Fig.4(d.)) of Na2O/Al2O3 versus
K2O/Al2O3 reveals the igneous ancestry of the pegmatite
which plot in the granite-igneous field of Garrells and
Mackenzie, thus indicating and suggesting a granitic-igneous
ancestry for the Awo pegmatites. Samples also plot in the field
of volcanic arc granites on the Rb versus Y+Nb diagram
(Fig.4(k)), while crustal thickness during emplacement of
these pegmatite bodies (Fig.4(n)) reached about 30km as
shown from the Rb/Sr plot of Condie, (1976).
The plots of Zr/SiO2 (Fig.4(l)) and Sr/Rb plots (Fig.4(m)),
reveals their mixed ancestry with some samples plotting
completely out of the magmatic “M” field, in the after
magmatic field “AM” hence suggesting Awo pegmatites to be
a mixed basement plus supracrustal protoliths having
homogenous chemistry.
In the pegmatites of this study area; Rare earth elements
(REE) abundance as presented in (Table III) reveals the
chondrite normalized plot (Fig.6) which shows high light
(REE) LREE (La, Ce, Pr) values and lower heavy (REE)
HREE (Er, Lu, Yb) values. There is a negative Europium (Eu)
anomaly which according to Taylor et al., (1986) suggests
fractionation and indicates a late metasomatic effect. The
weak negative Ce anomaly observed in Awo pegmatites may
also suggest their rare metal mineralization. However, Taylor
et al., (1986) had suggested earlier that where there is a weak
negative Ce anomaly and a negative Eu anomaly as in this
case of Awo pegmatite samples it is an evidence of
considerable fractionation and metasomatism. Similarly,
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Piper, (1974) and Garba, (2003) believe that Negative Ce
anomaly of rare metal pegmatite is taken to indicate oxidizing
condition during mineralization and interaction between, melt
fluids and host rocks sometimes over long distance.
Fig. 5. Triangular Ti-Sn-(Nb+Ta) Plot for Awo Pegmatite’s (After Kuster, 1990)
REE Chondrite normalized plots
Fig. 6. Chondrite normalized plots of Awo Pegmatite.
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V. CONCLUSION
Results of this study show that the Precambrian pegmatites of
Awo which intruded the granite, banded gneiss, quartzite and
quartz schist, are rare-metal pegmatites. Average length of
each body is about 650m with variable width but usually not
less than 7 m. They are usually complex albitized pegmatites.
Microcline and albite are the dominant feldspars with
subordinate muscovites and quartz. Following after the
classification criteria of pegmatites based on bulk chemistry
signatures (Cerny, 1991a; 1991b), and Ta/ (Ta+Nb) versus
Mn/ (Mn+Fe) plot for the Awo whole rocks and muscovite
extracts pegmatites respectively, the Awo pegmatites are of
the rare element class, complex pegmatite type. They are of
the LCT petrogenetic family (Rb, Cs, Be, Li, Ga, Sn, Ta < > N
(BPF) and of the Beryl sub type. The pegmatites are of per
aluminous bulk composition {A/CNK>1} (where A: Al2O3,
CNK: CaO+ Na2O+K2O). Cerny (1992) has observed that this
LCT family has a mild, to extremely Peraluminous parent
granitic composition.
This field is clearly enriched in Ta-Nb rare – metal
mineralization. The lower K/Rb ratio, lower K/Cs, K/Ba,
Th/U ratios and higher Rb/Sr ratio for the Awo Ta-Nb rare-
metal pegmatites suggest that these pegmatites have benefited
from fluids that have been derived from late but highly
differentiation processes suggesting probable mineralization.
The rare-metal content Ta, Nb is moderately high when
compared with other mineralized pegmatites of Nigeria.
K/Rb versus Rb and plots of Ta versus Cs, Ta versus Rb also
confirm the moderate-high level of Ta-Nb mineralization
potentials comparable with other pegmatites across the world
such as those of Noumas (South Africa), Silver Leaf and Odd
West (Canada).
Acknowledgement
The authors acknowledged Dr Oshin O.O, Mr R.O Egbeyemi,
Mr Oyebolu Olalekan of Earth Sciences Department Olabisi
Onabanjo University Ago-Iwoye, Ogun State, Nigeria for their
considerable support. Mrs Akintola Omolara Olufunke was
exceptionally supportive.
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[28] Okunlola, O.A and Oyedokun, M.O. (2009). Compositional trends and rare metal (Ta-Nb) mineralization potential of pegmatite and
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ABOUT THE AUTHORS
Akintola, A.I., MSc Mineral Exploration with option in Economic and Mining Geology (Ibadan) and BSc Geology (Ogun). He is a Lecturer in the
Department of Earth Sciences Olabisi Onabanjo University. His research
interests include Mineral exploration and environmental geology. He is a specialist in the study of granitic intrusions especially pegmatites.
Omosanya, K.O., MSc Structural Geology with Geophysics (Leeds), BSc Geology (Ogun). He is a Lecturer in the Department of Earth Sciences Olabisi
Onabanjo University. His research interests include Basin analysis, Seismic
interpretation, Structural geology and Environmental Geophysics.
Ajibade, O.M., M.sc. Applied Geochemistry (Ibada), B.Tech Applied
Geology (FUTA). He is a Lecturer in the Department of Earth Sciences Olabisi Onabanjo University. His research interest covers Petrology and
Environmental Geochemistry.
Okunlola,O.A., B.Sc (Ilorin), M.Sc (Zaria), PhD, (Ibadan). A senior lecturer
with the Department of Geology University of Ibadan. His research interest
covers mineral exploration and environmental Geology. He is a specialist in the study of petrology, Geochemistry and granitic intrusions especially
pegmatites.
Kehinde-Phillips, O.O., B.Sc (Ibadan), M.Sc (Laurentian Canada), Ph.D (Ibadan). A Professor of Economic Geology and Environmental
Geochemistry. Presently the Head of Department of Earth Sciences Olabisi
Onabanjo University.
International Journal of Basic & Applied Sciences IJBAS-IJENS Vol: 11 No: 04 67
118404-7676 IJBAS-IJENS © August 2011 IJENS I J E N S
Appendix Table II
Major element oxide composition of Awo Pegmatites (Wt %).
Oxides 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20
SiO2 49.73 54 51.5 49.64 46.76 49.9 52.38 45.32 44.79 53.53 60.69 59.53 67.64 68.46 70.37 44.27 44.89 44.42 44.89 44.6
Al2O3 32.19 29.14 28.94 31.67 32.88 28.56 29.5 33.15 33.51 28.96 16.1 16.46 15.89 14.91 14.7 34.2 33.2 34.1 34.08 33.56
Fe2O3 1.24 0.57 1.58 0.88 1.32 2.23 1.32 2.73 2.69 0.25 7.22 6.17 2.43 3.94 2.1 4.42 4.51 4.36 4.48 4.52
MnO 0.026 0.024 0.03 0.042 0.032 0.041 0.025 0.05 0.052 0.008 8.41 7.67 2.44 3.87 1.44 0.12 0.12 0.1 0.12 0.12
MgO 0.09 0.03 0.06 0.04 0.07 0.1 0.06 0.08 0.08 0.14 0.02 <0.01 <0.01 0.06 0.05 0.32 0.37 0.44 0.32 0.36
CaO 0.06 0.03 0.05 0.04 0.05 0.05 0.05 0.09 0.09 0.4 1.74 0.23 0.48 0.63 0.47 <0.01 <0.01 <0.01 <0.01 <0.01
Na2O 0.11 0.25 0.11 0.19 0.1 0.09 0.12 0.16 0.19 0.3 2.93 2.01 4.02 4.82 3.76 0.57 0.58 0.57 0.58 0.58
K2O 1.47 6.05 1.55 4.46 1.89 1.5 2.15 3.18 3.24 5.82 2.05 6.95 6.52 2.96 6.34 9.85 10.17 10.02 10.05 10.18
TiO2 0.062 0.027 0.089 0.035 0.079 0.072 0.08 0.199 0.194 0.017 0.04 0.02 <0.01 0.02 0.01 0.07 0.07 0.07 0.06 0.07
P2O5 0.05 0.11 0.05 0.08 0.05 0.05 0.07 0.06 0.06 0.016 0.34 0.41 0.31 0.19 0.27 0.02 0.03 0.03 0.03 0.03
LOI 14.05 9.7 15.55 12.3 15.9 17.29 14.51 13.69 14.51 10.48 0.3 0.5 0.2 0.1 0.4 6 5.9 5.8 5.3 5.9
Total 99.07 99.94 99.51 99.38 99.13 99.89 100.3 98.72 99.38 100.1 99.87 99.96 99.96 99.97 99.95 99.88 99.89 99.9 99.88 99.89
The numbers 1, 2, 3,….20 represent sample numbers.
1-15: Whole rock Pegmatite samples from Awo
16-20: Muscovite extracts from Awo Pegmatites.
International Journal of Basic & Applied Sciences IJBAS-IJENS Vol: 11 No: 04 68
118404-7676 IJBAS-IJENS © August 2011 IJENS I J E N S
Table III
Trace and Rare earth element data of Awo Pegmatites (ppm).
Elements 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20
Ta 42.4 113 113 308 96.2 365 101 80.6 53.2 1 27.5 31 15.7 23.3 14.3 41.9 41.9 35.3 43.9 41.4
Cs 149 267 106 219 138 197 215 165 169 526 2.5 18.1 15.4 8.6 15.6 208.5 199.2 160.2 210.8 207.4
Rb 216 1000 267 1000 319 272 748 1000 1000 1000 58 531.9 482.3 177.7 430.4 3316 3295 2936 3304 3265
Sn 17 19 168 28 115 24 129 86 125 2 165 228 84 207 244 1096 1104 1050 1100 1099
Nb 47 80 102 390 121 139 110 95 87 4 20.2 35.4 42.8 70.2 41.7 378.5 383.1 375.4 375.3 370.5
Sr 28 29 31 24 30 29 30 25 22 43 278.9 33.7 35.4 24.5 26.2 0.9 0.5 0.5 0.5 0.5
Y 4 5 10 4 10 4 10 7 6 2 2 1 3.2 6.4 2.8 0.8 0.2 0.2 0.1 0.1
Ba 47 29 60 29 51 46 55 52 47 49 442 76 91 37 84 2 2 1 1 1
Hf 5.4 4.8 8.2 6.3 7.2 3.9 6.6 8.4 8.2 0.2 6.7 3.5 8.1 2.5 2.3 2.5 0.5 0.6 0.5 0.6
Th 4.1 2.9 12.9 1.5 8.6 3.9 11 4.8 3.9 0.2 2.8 0.5 1.5 2.2 2.1 0.4 0.5 0.2 0.2 0.2
W 1 1 1 3 8 1 1 1 1 3 0.5 0.6 1.3 1.4 1.1 8.8 9 9.9 9 9.2
Be 19 28 35 17 37 42 32 49 82 4 2 37 14 38 80 23 26 25 25 25
Zr 29 26 54 39 48 25 44 100 101 4 152.2 20.8 45.8 27.8 19 22.5 4.4 4.8 2.6 2.5
Ga 62 54 51 66 59 60 53 99 117 37 33 35.2 30.6 32.5 28.5 263.6 257.6 253 259.7 252.7
Zn 30 50 30 50 30 40 30 160 210 30 88 96 45 44 63 32 36 29 24 37
U 4.9 2 6.3 5 4.7 4.6 4.6 2.8 2.5 0.5 6.5 10.5 11.5 24.4 12.8 0.6 0.2 0.1 0.1 0.1
Ti 1.4 22.2 1.9 11.5 2.4 2.4 9.3 4.6 6.6 22.6 0.1 0.1 0.1 0.1 0.1 1.2 1.5 1.2 0.9 1.4
Cu 30 10 30 20 30 20 20 20 20 10 17.9 8.3 5.9 3.9 9.7 0.7 0.3 0.1 0.1 0.2
Li 188.3 199.5 22.2 203.6 158.3 191.5 198.7 201.9 202.7 205.8 45.6 145.2 122.5 112.1 123.2 665.3 336.7 399.5 646.2 583.1
Elements 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20
Co 1 1 1 1 1 1 1 3 3 1 1.2 0.8 0.3 0.9 0.7 0.2 0.2 0.4 0.2 0.2
V 8 5 15 5 14 12 12 29 30 5 19 8 8 8
8 8 8 8 8
Ni 20 20 20 20 20 20 20 30 20 20 7.7 3.8 3.5 4.3 4 0.6 0.6 0.3 0.3 0.3
Sc 7 3 6 3 7 8 6 6 6 2 1 1 1 2 1 7 8 13 7 8
Pb 14 29 21 19 24 23 35 9 10 39 26.1 24.6 26.8 7.2 21.5 0.8 0.6 0.6 0.3 0.5
Mo 2 2 2 2 2 2 2 2 2 2 1.7 1.6 1 1.2 1 0.2 0.2 0.1 0.1 0.1
La 15.4 6.1 18.5 6.8 17.3 20.8 18.9 21.1 19.7 47.8 4.9 0.3 1 1.3 0.9 0.7 0.3 0.2 0.1 0.1
Ce 27.6 11.5 33.7 12.5 31.6 35.9 34.7 36 31.8 76 8.5 1.2 2.2 3.3 1.8 1.6 1 0.9 0.5 0.4
Pr 4.33 2.09 4.82 2.16 4.53 5.59 5.18 5.34 4.98 13.7 0.99 0.13 0.24 0.4 0.24 0.2 0.1 0.09 0.05 0.05
Nd 15.8 9.3 18.7 9 16.6 20.4 17.4 17.7 16.6 46.2 3.7 0.6 0.4 1.4 0.7 0.8 0.4 0.3 0.4 0.3
Sm 4 2.7 4.7 2.5 4.2 4.9 4.6 3.2 3 7.1 0.72 0.14 0.35 0.54 0.42 0.19 0.11 0.11 0.1 0.09
Eu 0.47 0.66 0.48 0.55 0.44 0.57 0.55 0.62 0.6 1.24 0.45 0.03 0.03 0.03 0.02 0.02 0.02 0.02 0.02 0.02
Gd 3.2 3.1 4.2 2.5 3.7 3.7 3.9 2.4 2.1 3.5 0.58 0.16 0.36 0.57 0.41 0.12 0.06 0.05 0.05 0.05
Tb 0.6 0.5 0.8 0.4 0.7 0.7 0.9 0.4 0.3 0.4 0.08 0.04 0.09 0.17 0.1 0.02 0.01 0.01 0.01 0.01
Dy 2.1 2.3 3.8 1.9 3.3 2.6 3.4 2.1 1.7 1.3 0.36 0.2 0.5 0.98 0.51 0.09 0.05 0.05 0.05 0.05
Ho 0.2 0.3 0.4 0.2 0.4 0.2 0.4 0.3 0.3 0.1 0.06 0.03 0.08 0.15 0.08 0.02 0.02 0.02 0.02 0.02
Er 0.5 0.7 1 0.6 0.9 0.5 0.9 0.9 0.7 0.3 0.2 0.05 0.21 0.49 0.16 0.04 0.03 0.03 0.03 0.03
Tm 0.06 0.08 0.13 0.07 0.12 0.07 0.11 0.12 0.1 0.05 0.04 0.02 0.05 0.1 0.04 0.01 0.01 0.01 0.01 0.01
Yb 0.4 0.5 0.9 0.5 0.8 0.4 0.8 0.8 0.6 0.2 0.26 0.11 0.46 1.01 0.29 0.05 0.05 0.05 0.05 0.05
Lu 0.05 0.06 0.11 0.07 0.11 0.06 0.11 0.11 0.09 0.04 0.05 0.01 0.07 0.16 0.05 0.01 0.01 0.01 0.01 0.01
The numbers 1, 2, 3,….20 represent sample numbers. 1-15: Whole rock Pegmatite samples from Awo
16-20: Muscovite extracts from Awo Pegmatites.
International Journal of Basic & Applied Sciences IJBAS-IJENS Vol: 11 No: 04 69
118404-7676 IJBAS-IJENS © August 2011 IJENS I J E N S
Table Iva
Range and average values of major elements in the whole rock and muscovite extracts of Awo pegmatites in mass fraction (Wt %).
Awo Sample
Whole Rock Muscovite Extracts
Pegmatite
N = 15 N = 5
Range Avr
(%)
Range Avr (%)
Si2O 44.79 - 70.37 54.95 44.27 - 44.89 44.61
Al2O3 14.70 - 33.51 25.77 33.20 - 34.20 33.83
Fe2O3 0.25 - 7.22 2.44 4.36 - 4.52 4.46
MnO 0.008 - 8.41 1.61 0.10 - 0.12 0.12
Mgo 0.01 - 0.14 0.06 0.32 - 0.44 0.36
CaO 0.03 - 1.74 0.30 0.01 - 0.01 0.01
Na2O 0.09 - 4.82 1.28 0.57 - 0.58 0.58
K2O 1.47 - 6.95 3.74 9.85 -10.18 10.05
TiO2 0.01 - 0.199 0.06 0.06 - 0.07 0.07
P2O5 0.016 - 0.41 0.14 0.02 - 0.03 0.03
Table IVb
Range and averages of some of the trace elements in the whole rock and muscovite extracts of Awo pegmatites (ppm).
Awo Sample
Whole Rock Muscovite Extracts
Pegmatite
N = 15 N = 5
Range(ppm)
Avr ppm Range(ppm) Avr ppm
Ta 1.0-365 92.35 35.3-41.9 40.88
Cs 2.5-526 147.41 160.2-210.8 197.22
Rb 58.0-1000 566.82 2936-3136 3223.20
Sn 2-244 109.4 1050-1104 1089.80
Nb 4-390 117.02 370.5-383.1 376.56
Sr 22-278.9 45.93 0.5-0.9 0.58
Y 1.0-10 5.16 0.1-0.4 0.2
Ba 29-442 79.67 1-2 1.4
Hf 0.2-8.4 5.49 0.5-2.5 0.94
Th 0.2-12.9 4.19 0.2-0.5 0.3
W 0.5-8 4.79 8.8-9.9 9.18
Be 2-82 34.2 23-26 24.80
Zr 4-152.2 49.04 2.5-22.5 7.36
Ga 28.5-117 54.52 252.7-263.6 257.32
Zn 30-210 64.13 24-37 31.6
Ti 0.1-22.6 5.69 0.9-1.5 1.24
International Journal of Basic & Applied Sciences IJBAS-IJENS Vol: 11 No: 04 70
118404-7676 IJBAS-IJENS © August 2011 IJENS I J E N S
Table V
Elemental ratios of selected major and trace elements of Pegmatites from Awo study area.
Atio 1 2 3 4 5 6 7 8 9 10
K/Rb 0.0056479 0.0050209 0.004817772 0.0037014 0.004917 0.0045767 0.0023854 0.0026391 0.0026889 0.00483
K/Ba 0.0259564 0.1731343 0.021439083 0.1276329 0.0307551 0.027062 0.0324415 0.0507516 0.0572101 0.0985718
Na/K 0.0668862 0.0369356 0.063433993 0.0380785 0.0472933 0.0536306 0.0498889 0.0449732 0.0524167 0.0460744
Rb/Sr 7.7142857 34.482759 8.612903226 41.666667 10.633333 9.3793103 24.933333 40 45.454545 23.255814
Ba/Rb 0.2175926 0.029 0.224719101 0.029 0.1598746 0.1691176 0.0735294 0.052 0.047 0.049
Zr/Hf 5.3703704 5.4166667 6.585365854 6.1904762 6.6666667 6.4102564 6.6666667 11.904762 12.317073 20
Sr/Rb 0.1296296 0.029 0.116104869 0.024 0.0940439 0.1066176 0.040107 0.025 0.022 0.043
Rb/Cs 1.4496644 3.7453184 2.518867925 4.56621 2.3115942 1.3807107 3.4790698 6.0606061 5.9171598 1.9011407
Ta/W 42.4 113 113 102.66667 12.025 365 101 80.6 53.2 0.3333333
K/Cs 0.0081876 0.0188049 0.01213533 0.0169012 0.011366 0.006319 0.008299 0.0159944 0.0159105 0.0091825
Zr/Zn 0.9666667 0.52 1.8 0.78 1.6 0.625 1.4666667 0.625 0.4809524 0.1333333
Th/U 0.0084699 0.0361632 0.00674185 0.0216682 0.0071038 0.0101105 0.0056584 0.0255911 0.0330813 0.0688691
Ta/Nb 0.9021277 1.4125 1.107843137 0.7897436 0.7950413 2.6258993 0.9181818 0.8484211 0.6114943 0.25
Nb/Ta 1.1084906 0.7079646 0.902654867 1.2662338 1.2577963 0.3808219 1.0891089 1.17866 1.6353383 4
K2O/Na2O 13.363636 24.2 14.09090909 23.473684 18.9 16.666667 17.916667 19.875 17.052632 19.4
Na2O/Al2O 0.0034172 0.0085793 0.003800968 0.0059994 0.0030414 0.0031513 0.0040678 0.0048265 0.0056699 0.0103591
K2O/Al2O3 0.0456664 0.2076184 0.053559088 0.1408273 0.0574818 0.052521 0.0728814 0.0959276 0.0966876 0.2009669
Ratio 11 12 13 14 15 16 17 18 19 20
K/Rb 0.0293327 0.0108438 0.0112191 0.0138239 0.0122248 0.0024652 0.0025615 0.0028323 0.0025244 0.0025876
K/Ba 0.0038491 0.0758922 0.059461 0.066392 0.0626377 4.0872575 4.2200415 8.315598 8.340495 8.448382
Na/K 1.2775409 0.258507 0.5511116 1.455514 0.5301023 0.0517249 0.0509763 0.0508473 0.0515849 0.0509262
Rb/Sr 0.2079598 15.783383 13.624294 7.2530612 16.427481 3684.4444 6590 5872 6608 6530
Ba/Rb 7.6206897 0.142884 0.1886792 0.2082161 0.1951673 0.0006031 0.000607 0.0003406 0.0003027 0.0003063
Zr/Hf 22.716418 5.9428571 5.654321 11.12 8.2608696 9 8.8 8 5.2 4.1666667
Sr/Rb 4.8086207 0.0633578 0.0733983 0.1378728 0.0608736 0.0002714 0.0001517 0.0001703 0.0001513 0.0001531
Rb/Cs 23.2 29.38674 31.318182 20.662791 27.589744 15.904077 16.541165 18.327091 15.673624 15.742527
Ta/W 55 51.666667 12.076923 16.642857 13 4.7613636 4.6555556 3.5656566 4.8777778 4.5
K/Cs 0.680518 0.3186633 0.3513603 0.28564 0.3372799 0.0392063 0.0423699 0.0519076 0.0395659 0.0407347
Zr/Zn 1.7295455 0.2166667 1.0177778 0.6318182 0.3015873 0.703125 0.1222222 0.1655172 0.1083333 0.0675676
Th/U 0.3934664 1.4707535 0.345223 0.4520921 1.118349 0.0557601 0.3466628 0.3136084 0.3652238 0.6028739
Ta/Nb 1.3613861 0.8757062 0.3668224 0.3319088 0.3429257 0.1107001 0.1093709 0.094033 0.1169731 0.1117409
Nb/Ta 0.7345455 1.1419355 2.7261146 3.0128755 2.9160839 9.0334129 9.1431981 10.634561 8.5489749 8.9492754
K2O/Na2O 0.6996587 3.4577114 1.6218905 0.6141079 1.6861702 17.280702 17.534483 17.578947 17.327586 17.551724
Na2O/Al2O 0.1819876 0.1221142 0.2529893 0.323273 0.2557823 0.0166667 0.0174699 0.0167155 0.0170188 0.0172825
K2O/Al2O3 0.1273292 0.4222357 0.410321 0.1985245 0.4312925 0.2880117 0.3063253 0.2938416 0.2948944 0.3033373
The numbers 1, 2, 3,…20 represent sample numbers.
1-15: Whole rock Pegmatite samples from Awo
16-20: Muscovite extracts from Awo Pegmatites