International Journal of Geosciences, 2012, 3, 365-372
http://dx.doi.org/10.4236/ijg.2012.32040 Published Online May 2012 (http://www.SciRP.org/journal/ijg)
An Integration of Self Potential, Electr o magnetic and
Resistivity Profiling Methods in the Search for Sulfide
Deposits in Gwoza, Borno State, Nigeria
Okwong Tom Nkereuwem, Solomon Nehemiah Yusuf, Manaja Uba Mijinyawa
Department of Geology, University of Maiduguri, Maiduguri, Nigeria
Email: okwong_holiness@yahoo.com
Received November 11, 2011; revised December 16, 2011; accepted January 31, 2012
ABSTRACT
The combination of Self Potential (SP), Electromagnetic (EM) and Resistivity profiling methods in Gwoza has resulted
in the delineation of conductive zones suspected to be sulfide mineralization in the area. Mineralization potentials of
–201 mV on the profile AA’, –250.2 mV on the profile BB’ and –203 mV on the profile CC’ respectively have been
observed. Correspondingly, both the vertical coil and the horizontal coil readings of the EM anomalies on the profiles
AA’, BB’ and CC’ also show significant negative anomalies across the delineated conductive zones. Three resistivity
profiles DD’, EE’ and KK’ have also shown very low resistivity values across the said conductive zones. These conduc-
tive zones have been established as sulfide mineralization within faults in this work. The recovery of chalcopyrite sam-
ples from a hand-dug well close to the delineated conductive zone of the profile BB’ tends to lend credence to the inter-
pretation in this study.
Keywords: Conductive Zones; Mineralization Potentials; Faults; Sulfides; Chalcopyrite and Delineation
1. Introduction
For several decades, the economy of Nigeria has been
closely associated with the sale of crude oil, but in the
face of dwindling oil prices, recourse is being made to
the solid mineral sector. The country is abundantly en-
dowed with a variety of solid minerals (Gold, Silver, Tin,
Zinc and massive sulphides etc.) scattered all over the
thirty six states of the federation. The pivot role of solid
minerals in our national economy is attributable to their
widespread utilization as foreign exchange earners. The
need to further develop this sector through intensive geo-
logical/geophysical exploration, drilling and mining can-
not be over emphasized.
A detailed study/exploration for industrial rocks and
minerals in the northern part of Mandara Hills (Figure 1)
[1], revealed extensive pegmatization and hydrothermal
activity. The study also observed that the dissolution of
feldspar within the zone is a positive indication of the
presence of hot fluid circulation in the area. Mineraliza-
tion of manganese in association with quarts chlorite in
feldspar and mica were also detected in the area. From a
detailed study of some trace elements and elemental ratio
of the alkali feldspar from rocks of Liga Hill, [2] was
able to establish a tentative order of emplacement of the
rocks of the area.
According to Perkins [3] chalcopyrite is widespread
and common. It is present in most sulfide deposits, but
the most significant ores are formed by hydrothermal
veins or by replacement. Common associated minerals
include pyrite, sphalerite, bornite, galena and chalcocite
[3]. Several researchers [4-6] have carried out self poten-
tial investigations in various parts of Gwoza and obtained
mineralization potentials ranging from –210 to –230 mV
in places within the Gwoza sheet. These observed ano-
malies are clearly indicative of the presence of sulfide
mineralization in the area.
The present study is premised on the assumption that
the hydrothermal activity widely reported by [1] might
have resulted in the occurrence of some sulfide minerili-
zation in the area. The present study is much more el-
aborate, employing both SP and EM methods on much
longer profiles, to confirm the existence or otherwise of
mineralisation potentials widely reported by previous
workers in the area.
2. Geology of Gwoza Area
The geological map of Gwoza area is presented in Fig-
ure 2, while the rocks identified are tentatively presented
in the following chronological order (Table 1).
The migmatites, gneisses, schists and quartzites out-
crop mainly at the margins of the granite batholith or as
Xenoliths within them. Their modes of occurrence and
C
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O. T. NKEREUWEM ET AL.
366
Figure 1. Location map of Gwoza.
Figure 2. Geological map of Gwoza area (Geological survey of Nigeria sheet 114).
field relationship with the other rock types suggest that
they belong to the ancient units into which the Pan-Afri-
can granites were intruded. Their foliations, which com-
monly trend N-S, appear to have influenced the form of
the bulk of the Pan-African granites during emplacement.
The migmatites are infact the result of migmatizing ef-
fects from the Pan-African Magmatism on the gneisses
and schists. Scholars of petrology in Nigeria have em-
phasized the need to distinguish these Pan-African mig-
matites from the Pre-Pan-African ones. This was done by
the [7].
The migmatites, gneisses and schists are of significant
occurrence, located mostly to the east of the batholith.
The gneisses include the augen gneisses and granite gnei-
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O. T. NKEREUWEM ET AL. 367
Table 1. Chronological presentation of Gwoza rocks.
AGE (MILLIONS YEARS) ROCK TYPES
Tertiary (50 - 30 my) Syenite Rhyolite porphyry Rhyolite
Pan-African Older granite
suite (750 - 450 my)
Late pegmatites (muscovite-free),
quartz veins and graphic granites.
Dolorite dykes
fine grained biotite granites and
cataclastic biotite granites and
early pegmatites (muscovite-bearing)
coarse porphyritic biotite granite (two
generations).
Medium and medium-coarse grained bio-
tite granites.
Liberian-Eburnean
(2800 - 1900 my) Migmatite, gneisses, schists, quartzites
sses while the schists are predominatly micaceous with a
few hornblendic ones. Quartzites are found as cobbles
and pebbles gernetiferous.
The medium grained granites, which outcrop in the
northeast and central part of the hills, are also found in
close association with the migmatites in the eastern part
(Gavva and Chikide areas).
The coarse grained granites are, from all appearances
of two generations; one is found almost always weath-
ered while the other is fresh. One minor faulting episode
which affected the weathered type has not been observed
in the fresh variety. They are, however, mineralogically
and texturally similar.
The coarse porphyritic granite, which is the most do-
minant rock type in this area, is believed to be the main
phase of the older Granite (Pan-African) suite in Nigeria.
On the basis of the Feldspar content (phenocrysts), two
varieties are recognised. The Pink—feldspar variety and
the white-feldspar variety. The latter is characterized by
pockets of mafic concentrates. These two types of grani-
tes are seen to grade into one another in Lufu and Gwoza.
The cataclastic biotite granites and mylonites out-crop
mainly in Liga, Limankara, Takaskara and Ngoshe. These
sheared rocks are believed to have been emplaced syn-
chroneously with a faulting episode towards the closure
of the Pan-African Orogency. The degree of the shearing
in the southern part of the mapped area seems to be most
intense in Limankara/Takaskara Hills and dies out to-
wards liga Hills.
The fault zone which trends approximately N-S is
however traced from Pulka in the north to Limankara in
the south and further. The zone measures between 50 M
(in the North) to 3 KM (in the south).
The pegmatites occurring in the area are of two gene-
rations, the early pegmatites are characterized by the ap-
pearance of muscovite in them while the later one is
muscovite-free. Field observation has shown that the
muscovite—free pegmatites are of more economic signi-
ficance.
Rhyolites are of minor occurrence but widely distri-
buted within the basement rocks. It has been established
that such extrusives, in addition to fracturing and uplifts,
mark the final close-up of the Pan-African Orogenic ac-
tivities. The rhyolites outcropping in Kirawa are of Ter-
tiary age and have no apparent genetic relationship with
the basement rhyolites. Two generations of the Tertiary
rhyolites have been identified west of Kirawa. The early
one is pink or grey equigranular rhyolite, while the later
one is a porphyry type which is characterized by abun-
dant Xenoliths of early phase.
Syenite which occurs adjacent to the rhyolite bodies at
kirawa is believed to have been emplaced in the late Ter-
tiary period.
3. Materials and Methods
3.1. Field Procedure
The methods, used in this investigation were selected on
the basis of availability of equipment and their relative
ease of interpretation.
The techniques of SP, EM and Resistivity profiling
field measurements are well described in standard text-
books [8-11]. The EM 34-3 field equipment with a fixed
transimitter—receiver separation of 40 m was used for
the acquisition of EM data, while the ABEM terrameter
SAS 300C using two nonpolarizable electrodes, was used
in the acquisition of SP data. Similarly, the ABEM ter-
rameter SAS 300C using steel electrodes, was used to
acquire resistivity profiling data. The station spacing for
the SP survey was 30 m, while the wenner array with a
fixed electrode separation of 10 m was adopted for the
resistivity traversing.
EM and SP data, were acquired along the profiles AA’
(near Kirawa), BB’ (near Ngoshe) and CC’ (near Ham-
bagda). Each EM/SP profile was about 4 km long (Fig-
ure 1). The location of the three profiles was guided by
previous SP reports by various workers in Gwoza area
[12,13]. Three resistivity traverses DD’, EE’ and KK’,
each of which was about 1 km long, were laid parallel to
AA’, BB’ and CC’ respectively in portions where both
EM and SP anomalies indicated the presence of conduc-
tive bodies in the subsurface.
3.2. The Profiles AA’ and DD’
Approximately, about the middle of the profile AA’ both
SP and EM anomalies have clearly indicated the pres-
ence of a subsurface conductor (Figures 3 and 6). The
SP value of 201 mV on line AA’ within the said ob-
served interval is indicative of a mineralization potential.
The vertical and the horizontal coil EM anomalies also
possess negative values within the observed interval; thus
strengthening the believe that a conductive body exists in
the subsurface within the said interval. The middle sec-
tion of the resistivity profile, DD’ (Figure 9) which lies
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O. T. NKEREUWEM ET AL.
Copyright © 2012 SciRes. IJG
368
A
A
Distance (m)
Figure 3. SP profile along line A-A’.
BB’
Distance (m)
Figure 4. SP profile along line B-B’.
C C’
Distance (m)
Figure 5. SP profile along line C-C’.
O. T. NKEREUWEM ET AL. 369
A
A
H-Coil
V-Coil
Receiver Distance (m)
Figure 6. EM profile along line A-A’.
H-Coil
V-Coil
B B’
H-Coil
V-Coil
Series1
Receiver Distance (m)
Figure 7. EM profile along line B-B’.
CC’
H-Coil
V-Coil
Series1
Receiver Distance (m)
Figure 8. EM profile along line C-C’.
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O. T. NKEREUWEM ET AL.
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370
3.4. The Profiles CC’ and KK’
across the said suspected conductive zone, also displays
very low resistivity values thereby confirming the exis-
tence of a subsurface conductor within the anomalous
zones of the profiles AA’ and DD’. The negative picks of
the EM and SP anomalies along line AA’ correspond to
the point (Lat. 11˚11'N, Long. 13˚46'12"E), while the
conductive zone of the resistivity anomaly along the line
DD’ is located at the point (Lat. 11˚10'N, Long.
13˚46'12"E).
Towards the beginning of the profile CC’, both SP and
EM anomalies (Figures 5 and 8) clearly indicate the
presence of a conductive zone as shown in Figure 5. The
SP value of 203 mV within the said zone is suggestive
of a mineralization potential. The negative anomalies
displayed by both the vertical and the horizontal coil
readings of the EM anomalies across the said conductive
zone of the profile, strongly suggest the presence of a
subsurface conductor. The low resistivity zone along the
parallel resistivity profile KK’ (Figure 11) also corre-
sponds to the observed anomalous zone on the profile
CC’ as indicated in Figure 11. The negative picks of the
EM and SP anomalies along the line CC’ correspond to
the point (Lat. 11˚03'N, Long. 13˚39'E), while the con-
ductive zone of the resistivity anomaly along line KK’ is
located at the point (Lat. 11˚01'N, Long. 13˚39'E).
3.3. The Profiles BB’ and EE’
Towards the end of the profile BB’, both SP and EM
anomalies have revealed a zone of high conductivity
within the same interval of the said profile. The SP value
of 250.2 mV (Figure 4) within this anomalous zone is
suggestive of a mineralization potential. Both the vertical
and the horizontal coil readings of the EM anomalies
within the same interval of the profile are also negative.
Similarly, the portion of the resistivity profile EE’ (Fig-
ures 7 and 10) with the lowest resistivity values also
corresponds to the same anomalous zone revealed by SP
and EM anomalies. The negative picks of the EM and SP
anomalies along line BB’ correspond to the point (Lat.
11˚03'N, Long. 13˚46'12"E), while the conductive zone
of the resistivity anomaly along line DD’ is located at the
point (Lat. 11˚03'N, Long. 13˚46'12"E).
4. Findings
The applications of the SP, EM and resistivity traversing
methods in the quest for sulfide mineralization in Gwoza
and its environs, have resulted in the delineation of con-
ductive zones which are interpreted as sulfide minerali-
zation within faults in this study. This work has also de-
monstrated that the hydrothermal activity widely re-
ported by [6], might have resulted in the occurrence of
Figure 9. Resistivity profile along line D-D’.
O. T. NKEREUWEM ET AL. 371
Figure 10. Resistivity profile along line E-E’.
Figure 11. Resistivity profile along line K-K’.
some sulfide minerilization in the area.
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