International Journal of Geosciences, 2012, 3, 960-971
http://dx.doi.org/10.4236/ijg.2012.325097 Published Online October 2012 (http://www.SciRP.org/journal/ijg)
Application of Electrical Resistivity and Chargeability
Data on a GIS Platform in Delineating Auriferous
Structures in a Deeply Weathered L ateritic Terrain,
Eastern Cameroon
Albert Nih Fon1*, Vivian Bih Che2, Cheo Emmanuel Suh1,2
1Economic Geology Unit, Department of Geology, Faculty of Science, University of Buea, Buea, Cameroon
2Remote Sensing Unit, Department of Geology, Faculty of Science, University of Buea, Buea, Cameroon
Received July 24, 2012; revised August 27, 2012; accepted September 26, 2012
ABSTRACT
Exploration for primary gold in tropical settings is often problematic because of deep weathering and the development
of a thick soil cover. In this paper we present the results of both chargeability and resistivity surveys carried out over the
Belikombone hill gold prospect (14˚00' - 14˚25'E, 5˚25' - 6˚00'N) in the Betare Oya area (eastern Cameroon), where
previous soil sampling had identified gold anomalies. The geophysical data were obtained using Syscal Junior 48 resis-
tivity meter and the Schlumberger configuration array for both the vertical electrical soundings (VES) and horizontal
profiling. These data were further built into a GIS framework and the continuity of favourable gold-bearing structures at
depth modeled using WINSEV, RED2INV and SURFER extensions softwares. IP (Induced Polarization)-chargeability
and resistivity data combined, have identified irregular anomalous zones trending NE-SW. This trend is consistent with
the attitude of most auriferous quartz veins exposed in artisanal pits and parallel to the regional shear zone system and
foliations. The high resistivity anomalies correspond to quartz veins while the relatively high IP anomalies correspond
to low sulphide ± gold concentrations in the quartz veins. Modeling IP-chargeability and resistivity data prepared as
contours and 3D maps, culminated to the development of an inferred, irregular and discontinuous mineralized body at
depths of up to 95 m. The size and shape of this mineralized body can only later be tested by drilling to ascertain the
resource.
Keywords: Gold Exploration; Tropical Settings; Deep Weathering; IP-Chargeability and Resistivity; Betare Oya; 3D
Maps; Cameroon
1. Introduction
In many areas around the world, gold mineralization is
structurally controlled [1-3] and usually associated with
faults, fractures and shear zones. However, in humid
tropical settings, where weathering processes are intense
and the lateritic soil profiles deep, exploration efforts are
hampered by the paucity of outcrops, vegetation cover
and extensive alteration of truncated lateritic soil profiles.
Recent alteration and reworking of the soil profile by
surface processes, results in extensive modification and/
or complete obliteration of previous primary geochemi-
cal dispersion patterns and pedological features of sur-
face soils [4] further complicating the search for primary
ore bodies at depth. For these reasons, soil geochemistry
alone cannot be effectively used in locating deeply em-
bedded and hidden mineralized primary ore bodies (often
referred to as blind ore bodies). Geochemical exploration
in such areas therefore, is often supplemented by geo-
physical techniques including combined IP-chargeability
and resistivity surveys. In the Belikombone hill investi-
gated in this study, gold mineralization is associated with
metallic sulfides and oxides, which are excellent electri-
cal conductors, making it possible to target them using
geoelectrical exploration methods.
Such ground geophysical surveys, in which the resis-
tivity and chargeability of subsurface materials can be
measured, is capable of delineating zones of high
chargeability and low resistivity which may represent
potential areas of mineralization. Geophysical techniques
such as self potential (SP), gravity combined with in-
duced polarization (IP) and resistivity techniques have
been used in the investigation of huge hydrothermal sys-
tems, active volcanoes and large geological structures
*Corresponding author.
C
opyright © 2012 SciRes. IJG

A. N. FON ET AL. 961
[5-7]. Results from these geophysical techniques are of-
ten presented in diverse ways including chloropleth, den-
sity, contour maps, profiles and pseudosections. Tra-
ditionally these geophysical data are processed to obtain
depth profiles in 2D using various softwares. In this
study we explore extending these traditional interpreta-
tion techniques to compute the continuity of the mineral-
ized body at depth and develop a 3D model in a GIS en-
vironment, of the ore-bearing trends. This final 3D prod-
uct, built up progressively from combined GIS soft-
wares, is capable of displaying the inferred shape, struc-
ture and nature of the mineralized body as it varies with
depth and will be useful to better appreciate and under-
stand the nature and extent of the ore body over a wide
area.
2. Location and Geology
The Belikombone hill gold prospect (14˚00' - 14˚25'E,
5˚25' - 6˚00'N) is a hydrothermal vein system and it is
situated within the Lom Basin (Figure 1). The Lom Ba-
sin is a syn-depositional Neoproterozoic pull apart basin
[8] bordered by strike-slip faults known locally as the
Sanaga Fault (SF). The SF is a relay of the Central Cam-
eroon Shear Zone (CCSZ) System [8-12] which is a con-
tinental scale transcurrent fault and potentially a deep
tapping crustal fault that has focused gold-bearing fluids
into structures in the Lom Basin [13]. The Lom basin is
composed mainly of metasedimentary rocks, grouped
into two main structural and metamorphic units. These
units include a monocyclic unit which comprises of Lom
volcanoclastic series, orthogneiss, Mari quartzite and po-
lygenic conglomerate [14] metamorphosed under green
schist facies and associated with grabens. A polycyclic
unit consisting of staurolite micaschists, Lom bridge
gneisses, and staurolite-chloritoid mylonites, closely re-
lated to horst structures [8]. The mylonites are the main
identifying features for the presence of the SF [14].
These units are intruded by quartz veins and granitoids
(granite, monzonite and lamprophres) which show evi-
dence of sinistral deformation [8]. Structurally the schist
is well foliated with a general N70˚E orientation, related
to the shear zone system. Specifically, the Belikombone
hill prospect is predominantly composed of mica schist
and quartzites intruded by gold-bearing quartz veins that
vary in size from a few centimeters to 10 m wide within
artisanal gold pits and have a general NE-SW orientation
Figure 1. Location and geologic map of Betare Oya modified from [8,10].

A. N. FON ET AL. 962
and dips of 45˚ - 55˚SE. The quartz veins show variable
textures (ranging from hard massive and whitish quartz
at surface to progressively brecciated, sheared, vuggy,
sugary and brown to smoky quartz veins with iron oxide
staining). This pervasive variation in quartz vein textures
is associated to the different generations and recrystali-
zation events commonly exhibited by quartz crystals.
Hand specimen samples for some of these quartz veins
show visible gold associated with disseminated sulphides
and oxides. The quartzite show well preserved primary
sedimentary structures such as current marks, indicating
the flow direction, together with oblique cross stratifica-
tion, and load casts.
3. Methods
The Belikombone hill prospect was selected for this
study because of its gold potential that has been uncov-
ered through structural and soil geochemical surveys
from previous field campaigns. In the present study the
IP (Induce polarization)—chargeability and resistivity
surveys were carried out simultaneously along the same
grid as the previous soil geochemical survey. A Syscal
Junior 48 resistivity meter was used to measure both the
resistivity and chargeability of subsurface materials over
the Belikombone hill gold prospect. The Schlumberger
configuration array was used [15,16]. Vertical electrical
soundings (VES) and horizontal profiling methods were
adopted to obtain apparent resistivity and IP-charge-
ability data for 17 lines (Figure 2).
Measurements were done at fixed stations while sys-
tematically varying the electrode spacing, giving an ap-
proximate maximum penetration depth of 130 m. A total
of 10 km (17 lines) of IP lines were completed at 50 m ×
50 m intervals for both the survey positions and the line
spacing.
The IP-chargeability and resistivity data were gener-
ated and recorded automatically by the resistivity meter.
These data were later extracted and processed using
WINSEV 5, RED2INV softwares to convert the apparent
resistivity data to true resistivity by inversion. The resis-
tivity meter measures apparent resistivity from which
pseudosections were developed and subsequently in-
verted to true resistivity 2D sections (Figures 3(a)-(f)).
The surface elevations are included in the final model,
accounting for variations in measurement geometry due
Figure 2. Resistivity and IP-chargeability survey grid (50 m × 50 m) designed for the Belikombone hill gold prospect.

A. N. FON ET AL. 963
Figure 3. Inverted 2D sections for resistivity and IP-chargeability for six lines (12 to 17, Figure 2) obtained from VES data
using Schlumberger configuration over the Belikombone hill gold prospect a: for line 12; b: 13; c: 14; d: 15; e: 16; f: 17.
Anomalous zones for both resistivity and IP are represented by the deep-red to purple colouration on these sections.
to changing topography.
2D sections of the resistivity and IP-chargeability for
each line were developed to a maximum depth of 130 m
from the extracted data set.
3D contour maps and chloropleth maps of both resis-
tivity and IP-chargeability were developed using SURFER
9.0. for depths of 1.9 m, 3.8 m, 5.7 m, 9.5 m, 19 m, 28.5 m,
38 , 57 m, 76 m and 95 m (Figures 4(a)-(j) and Figure
5(a)-(j)). These 3D IP maps were further stacked together
to portray the nature of the mineralized body at depth.
4. Results and Synopsis
The geophysical data analyzed revealed a significant
resistivity (Figures 4 and 6) and IP-chargeability (Fig-
ures 5 and 7) anomalies. Individual chargeability values
within these anomalies range from 15 mV/V to 35 mV/V.
These anomalies occur within zones of elevated resistiv-
ity that may represent silicification and quartz veining.
This is confirmed by the location of quartz veins on areas
with very high resistivity values as observed in Figures 4
nd 6. a

A. N. FON ET AL. 964
Figure 4. Resistivity contour maps derived for different depths at the Belikombone hill gold prospect. a: map for depth of 1.9
m; b: 3.8 m; c: 5.7 m; d: 9.5 m; e: 19 m; f: 28.5 m; g: 38 m; h: 57 m; i: 76 m and j: 95 m. Red dots on the map indicate loca-
tion of quartz veins observed in artisanal pits and trenches. Zones of high resistivity anomalies are represented by the green
to red colouration. All other colours are zones of low resistivity anomalies.

A. N. FON ET AL. 965
Figure 5. IP-chargeability contour maps for different depths at the Belikombone hill gold prospect. a: map for depths of 1.9
m, b: 3.8; c: 5,7m; d: 9.5; e: 19 m; f: 28.5, g: 38 m, h: 57 m; i: 76 m and j: 95 m. Black dots on the map indicate the location of
quartz veins in artisanal pits and trenche s. Zones of high IP anomalies are highlighted by red colouration. All other colours
are zones of low IP anomalies.

A. N. FON ET AL. 966
Figure 6. 3D resistivity maps for different depths at the Belikombone hill prospect. a: map for depths of 1.9 m, b: 3.8 m; c: 5.7
m; d: 9.5 m; e: 19 m; f: 28.5 m; g: 38 m; h: 57 m; i: 76 m and j: 95 m. Red dots on the map indicate the location of quartz
veins in artisanal pits and trenches. Anomalous resistivity values are represented by green to red colouration at each depth
these high resistivity values represent quartz veins. Variation in the shape of the resistivity contour patterns with depth high-
lights the irregular nature of the quartz veins. Purple and blue colourations represent relatively low resistivity values.

A. N. FON ET AL. 967
Figure 7. 3D IP chargeability maps for different depths at the Belikombone hill prospect. a: map for depths of 1.9 m, b: 3.8; c:
5,7 m; d: 9.5; e: 19 m; f: 28.5, g: 38 m, h: 57 m; i: 76 m and j: 95 m. Black dots on the map indicate the location of quartz
veins. The anomalies defined by areas of high IP values (represented by the red colouration at each depth). The size and
shape of the red patches varies with depth highlighting the irregular nature of the ore body. All other colours represent lower
IP anomalies.

A. N. FON ET AL. 968
These high chargeability anomalies may represent
disseminated sulphide ± gold mineralization in the quartz
veins. True resistivity and IP-chargeability sections were
developed for 17 lines, each to a maximum depth of 130
m. Only sections for lines 12 to 17 have been presented
here (Figur es 3( a)-(f)) as examples.
It is observed that both the resistivity and IP sections
show similar trends and consistent anomalies over zones
of low resistivity and high chargeability (Figures 3(a)-
(f)). Significantly high chargeability anomalies (>20
mV/V) are observed to the right of the 2D sections which
correspond to relatively low resistivity (<1200 Ohm-m)
anomalies (Figures 3(a)-f)). Extremely high resistivity
anomalies were observed for line 17 with values over
15000 Ωm. The almost homogeneous patterns and trends
defined by the anomalous zones suggest that the miner-
alization is structurally controlled and follows a NE-SW
orientation. This orientation is consistent with the local
shear zone system in the Lom basin.
Contour maps of resistivity and IP-chargeability were
computed for the total surface area concerned. The resis-
tivity and IP-chargeability contour maps reveal distinct
anomalous zones for the various depths (1.9 m, 3.8 m,
5.7 m, 9.5 m, 19 m, 28.5 m, 38 m, 57 m, 76 m and 95 m).
To avoid ambiguity the general trends will be discussed
rather than individual anomalies. The resistivity anoma-
lies are very high and limited to a narrow surface area for
depths of 1.9 m to 9.5 m, with values that range from
3000 Ωm to over 15000 Ωm (Figures 4(a) -(d)). Resistiv-
ity then decreases from 19 m to 57 m, (ranging from
1000 Ωm to 3000 Ωm, Figures 4(e)-(h)) covering a wid-
er surface area. It then rises again at 76 m to 95 m from
3000 Ωm to over 15000 Ωm (Figures 4(i) and (j)).
Maximum resistivity values were recorded at two depths
(1.9 m & 95 m). A distinct anomalous NE-SW trend is
consistent at various depths. All the quartz veins located
in artisanal pits and trenches fall on zones with high re-
sistivity anomalies (Figures 4(a)-(j)). Thus quartz veins
signatures are locally identified by high resistivity ano-
malies.
The IP anomalies are high and widespread at shallow
depths from 1.9 m to 9.5 m, ranging from 20 mV/V to
over 30 mV/V (Figures 5(a)-(d)). Optimum IP anoma-
lies were recorded at 19 m and 28.5 m (Figures 5(e) and
(f)) with values ranging from 20 mV/V to over 36 mV/V,
a well distinct NE-SW trend is discernable. Relatively
low IP was recorded at 38 m (Figure 5(g)) and it rises
again at 57 m to 95 m with a similar NE-SW trend as
above (Figures 5(h)-(j)). The high pervasive IP anoma-
lies at shallow depths have no specific trend and may
partly be related to prevalent clay minerals derived from
the weathering and alteration of the micaschist as well as
the massive sulphide-bearing quartz veins. The high IP
anomalies at depth with well defined patterns are related
to the mineralized sulphide ± goldbearing quartz veins
that are sub-parallel to the regional shear system with a
NE-SW orientation.
5. 3D Display of Resistivity and
IP-Chargeability Maps
For better appraisal of the auriferous structures associat-
ed with the mineralized quartz vein, a 3D stacked model
for IP-chargeability was developed for the various depths.
Similar trends and anomalies observed for the contour
maps above were consistent, though, now, with elevated
peaks for easy and better visualisation (Figures 6 and 7).
The resistivity and chargeability 3D maps were com-
pared to delineate the mineralized body. Furthermore,
due to the significance of IP in relation to gold ± sulphide
mineralization, the 3D IP maps were combined and
stacked together vertically according to their respective
depths (Figure 8). A composite 3D IP map was develop-
ed from which the mineralized structure and ore body
could be discerned down to a maximum depth of 95 m.
This final product and a model of the inferred ore body is
a function of the vertical variation of IP-chargeability
and resistivity over a defined area.
6. Discussion and Conclusions
Ground geophysical surveys of IP/chargeability and re-
sistivity are routinely used for a wide range of applica-
tions, ranging from environmental pollution studies (e.g.
oil spills), lithology variation, hydrology in locating
aquifers [17,18] to mineral exploration. However the
effectiveness of these geophysical techniques in explora-
tion are enhanced when integrated with geochemical and
geological data [19] which define the target of investi-
gation. Thus to enhance effective target recognition the
element whose physical signature is investigated must be
known. In this study, gold hosted by sulphide-bearing
quartz veins within schist was the target of interest and
the IP and resistivity were therefore efficient techniques
in identifying the mineralized body.
Hydrothermal fluids that result in mineralization often
cause changes in the adjacent rocks, a phenomenon often
referred to as wall rock alteration [1,20]. These changes
may be in the form of mineralogy (formation of neo-
minerals, notably silica, sulphides and oxides) which in
turn brings about extensive variation in physical pro-
perties of subsurface materials and they consequently
exhibit variable geophysical signatures [21]. The contrast
of these physical properties in rocks is revealed by the
significant low resistivity and high IP-chargeability ano-
malies in altered wall rocks, relative to the non-
mineralized and unaltered counterpart. It has been report-
ed that the production of certain clay minerals by hydro-
thermal alteration significantly increases the electrical

A. N. FON ET AL. 969
conductivity of the rock [22] and thus might be an in-
dication of mineralization. [21] suggested that epithermal
gold deposits are produced by permeating hydrothermal
fluids which are rich in ions, capable of reacting with the
rocks over which they passes resulting in extensive
alteration, and/or complete recrystallization. This is also
applicable to mesothermal orogenic gold deposits where
the deposits usually vary in their form, structures, size
and physico-chemical environment, which makes their
investigation obscure. Nevertheless employing ground
geophysical techniques of resistivity and IP has unrave-
led some of these concealed properties of subsurface
mineralization in the Belikombene hill gold prospect.
From this study the 3D body varies in shape due to the
heterogeneous nature of gold distribution or minera-
lization within the inferred ore body at different depths.
The high resistivity at shallow depths reflects the late
quartz generation resulting in barren and massive quartz
veins. Resistivity variations with depth also reflect
changes in quartz vein textures and crystallization regime
Figure 8. 3D composite IP-chargeability map for the Belikombone hill gold prospect displaying the variation in
IP-chargeability with depth. The inferred ore body is define d by areas of high IP values (represented by the red colouration
at each depth). The location of these red patches varies with depth highlighting the irregular nature of the ore body. All other
colours are considered less prospective zone for gold.

A. N. FON ET AL. 970
with depth. Since the resistivity survey markedly identi-
fied potential quartz veins its 3D and contour maps re-
present the actual nature and extent of the quartz veins.
The IP-chargeability variations indicate the extent and
strength of mineralization (gold ± sulphide concentration
in the various materials). The high resistivity could partly
be attributed to a fault sub-parallel to the regional struc-
ture with a NE-SW orientation.
The mineralized halo observed on the maps is estimat-
ed to be ca 300 - 400 m wide. This, therefore, suggests
that not only the quartz veins are mineralized but also the
altered adjacent wall rock to a lesser extent. However,
[19] suggested that pervasive clay minerals associated
with argillic-propylitic zones cause low-resistivity ano-
malies which are related to the reaction of the rocks with
acid, steam-heated waters. In addition, the precipitation
of quartz and adularia which commonly accompanies
gold-silver mineralization causes an increase in resisti-
vity with values locally exceeding 1000 Ωm [19]. The
high resistivity observed in this study is therefore attri-
buted to the presence of quartz veins, the relatively low
resistivity areas correlate with high chargeability zones
which are indicative of sulphides associated with the
auriferous quartz veins and disseminated in the wall rock.
The significant correlation of the Au-in-soil geochemical
anomalies in the Belikombone hill gold prospect (from
previous works) with the IP-chargeability and resistivity
anomalies identified in this study, together with the
consistent NE-SW trend associated with all the anoma-
lies suggest a unique structural and mineralized body.
These anomalies are therefore succinct drill targets for
subsequent exploration and research works.
7. Acknowledgements
This article is part of a Ph.D. thesis by ANF at the Uni-
versity of Buea within a framework of cooperation with
the Cameroon Mining Company (CAMINCO SA) initi-
ated in 2006 with CES as the project academic coordina-
tor. This contribution is within the research framework of
“The Precambrian Mineral Belt of Cameroon” in the
economic geology unit of University of Buea with other
participating institutions. The authors express apprecia-
tion to the anonymous reviewers whose comments im-
proved on the nature of the figures.
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