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. 2022 Dec 21;8(12):e12541. doi: 10.1016/j.heliyon.2022.e12541

Integrated geophysical investigation for lead and zinc mineralization in Wase, middle Benue Trough, Nigeria

Solomon Nehemiah Yusuf a,∗, Mubarak Umar Faruk a, Lucky Osaro Imagbe a, Ovye Musah Yohanna a, Ishaq Yusuf b, Abraham Onoshagbegbe c, Musa Kamal d, Timbee Terunga Jacob d
PMCID: PMC9803722  PMID: 36593845

Abstract

There is an increasing demand for solid industrial minerals worldwide, as countries seek to support their economic growth. Wase, situated in Plateau State, is notable for lead and zinc mineralisation due to tectonic and hydrothermal activities in the region. The study utilises geophysical surveys to map mineralised zones of lead-zinc occurrence. These include ground magnetic survey, very low frequency electromagnetic, electrical resistivity tomography, and induced polarisation (IP). The field data were acquired using a GEMSys Overhauser magnetometer with VLF option and ABEM LS 2 Terrameter. twenty-nine (29) magnetic profiles with 50m spacing and a total length of 24.0 km were obtained and fifteen (15) very low frequency electromagnetic (VLF-EM) profiles with 10 m spacing in the E-W direction. A total length of 12.5 km was acquired across target areas of the magnetic profiles. The multiple-gradient electrode array of the ERT/IP surveys was used for data acquisition, and RES2DINV software by Geotomo was used for the inversion of the acquired data. High chargeability values corresponding to low resistivity values characterised zones with suspected lead-zinc mineralisation. Following this preliminary finding, we advise that further trenching, pitting, or core drilling be carried out to ascertain ore grade, possible beneficiation, and estimate of the reserve.

Keywords: Lead, Zinc, Mineral, Resistivity, Tomography, Induced polarisation, Wase

Lead; Zinc, Mineral; Resistivity; Tomography; Induced polarisation; Wase

1. Introduction

Globally, over 50 per cent of lead-zinc mineralisation and occurrences are hosted by sedimentary deposits in veins and veinlets created by effects such as shale tectonism (Tikkanen, 1986; Adejuwon et al., 2021), steeply dipping cracks, and sheeted zones in sediments intruded by sills, as well as in stratiform or stratabound environments hosted by carbonates (Olade and Morton, 1985). Lead–Zinc mineralisation in Nigeria has been reported from the late Albian to the end of the Turonian (Farrington, 1952), primarily as epigenetic deposits within the Cretaceous layers of the Upper, Middle, and Lower Benue Troughs (Fatoye et al., 2014; Haruna, 2017).

The genesis of the lead-zinc mineralisation in Nigeria has remained controversial (Ogundipe, 2018). Olade and Morton (1985) discussed three hypotheses on the possible origin, which include (1) magmatic-hydrothermal (Farrington 1952; Nwachukwu, 1974) based on the epigenetic characteristics and the proximity of some of the lodes to mafic-intermediate igneous rocks (Olade and Morton, 1985); (2) circulating heated connate waters (brines) originating from the Asu River Group evaporitic shales deposited concurrently with or before the mineralisation processes (Haruna, 2017); intensive heat flow associated with mantle plume activity and continental rifting may have likely enhanced the leaching characteristics of the ore fluids and promoted active circulation through dilated fractures, according to fluid inclusion studies and the geologic settings of the Benue Valley lead-zinc deposits (Olade and Morton, 1985; Haruna, 2017); (3) mixing of juvenile and connate waters (Offodile &Reyment 1976), this might not be the sole likely source of mineralising fluids absent of a magmatic spatial relationship. But a magmatic intrusion may cause a shallow, local convective system (Olade and Morton, 1985). Fatoye et al. (2014) found that the mineralisation is connected to saline water intrusion or fractures and shear zones. Its genesis is thought to be hydrothermal, although their connection is re yet unclear.

However, Obaje’s (2009) suggestion that chemical interaction between the upwelling ore-bearing hydrothermal fluids with the host rock in the saliferous or evaporitic zone may have resulted in the deposition of lead-zinc mineralisation remains a valid possibility. The influence of structural control on the mineralisation processes suggests contributions by hydrothermal fluids under mesothermal conditions. They were also documented in Farrington (1952), Obaje (2009), Fatoye et al. (2014), and Ogundipe (2018). Despite these uncertainties associated with the genesis of the mineralisation, we intend to investigate the occurrence of lead-zinc mineralisation in the study area by integrating ground magnetic, very low frequency electromagnetic (VLF-EM), electrical resistivity tomography (ERT), and induced polarisation (IP) methods for this study.

VLF-EM has restricted probing depth capabilities, depending on the resistivity of the rocks and how they react to shallow bodies (Watson et al., 2001; Zou et al., 2022). Considering this, the magnetic method was used to make up for the VLF-limitations, as EM are easily affected by cultural noise. The magnetic approach can search for minerals as deep as 0 km–1 km (Lasheen et al., 2022). ERT is limited in delineating rocks with similar porosity values and the cumber some’s nature of data collection (Gourdol et al., 2018). Due to a lack of knowledge of the physical and chemical mechanisms regulating the IP response, near-surface research has had difficulty using IP. Also limiting constraints included inadequate instruments and software for interpretation (Slater, 2007).

Integrated geophysical methods are applied to detect contrast in various dimensions with the host rock in terms of the physical properties of the earth (Martínez-Moreno et al., 2014). Further, they help overcome the limitations/ambiguities and complement different methods (Cardarelli and Filippo, 2014). Integrating geophysical data can fill the gap between localised and regional anomalies, thereby leading to more reliable interpretation and results for mineral exploration. Preliminary studies are done to minimise cost and enhance proper planning in mineral exploration.

In order to find subsurface magnetic elements for potential exploration, the ground magnetic survey is a crucial geophysical technique to apply in mapping the unusual magnetisation, which might be linked to nearby mineralisation that is valuable commercially (Joshua et al., 2017). A well-known method for identifying subsurface structures is the magnetic survey which has been widely applied in various regions of the world (Danzalski, 1966).

The VLF-EM method is a practical and affordable geophysical technique for identifying blind orebodies underground (Zhang et al., 2007). The fractures may be quickly identified using the VLF-EM geophysical survey method, and the high conductivity of these fractured zones suggests that they may be mineralisation zones (Benson et al., 1997).

The electrical resistivity method involving electrical resistivity tomography (ERT) has been successfully applied in different mineral exploration projects (Alile et al., 2017; Arwech et al., 2020; Horo et al., 2020; Olenchenko and Osipova, 2022) and environmental studies (Pierwoła, 2015; Benyassine et al., 2017; Gabarron et al., 2020; Olenchenko et al., 2020).

The induced polarisation (IP) method measures changes in the chargeability of earth materials (Sumner, 2012; Zhdanov, 2018; Dusabemariya et al., 2020). This method has wide applications in mineral exploration (Dembicki, 2016; Evrard et al., 2018; Prakash et al., 2018; Zhdanov, 2018; Dusabemariya et al., 2020).

2. Location, accessibility, and climate of the study area

The research location is in the Wase local government area of Plateau State (Wase NE Sheet 191; and Bashar NW, Sheet 192) and lies between Latitudes 08°59'00" N and 09°21'00" N, and longitudes 09°58'00"E and 10°38'00"E. The license area is approximately about 1.08 square kilometres and is located about 40 km southeast of Bashar, 44 km southeast of Wase, and 32 km southwest of Zurak (Figure 1). The area is mainly accessible from Dengi through Bashar – Gajin Bashar – Safiyo – Dogon Ruwa to Tapga settlement or from Wase through the Wase – Mavo – Gimbi Road to Tapga. Since the area is relatively flat, it is accessible through footpaths and cattle-rearing paths. Its climate is Northern Guinea Savannah, with an average annual rainfall of 1,941 mm. The average annual temperature is 26.5 degrees Celsius, with a relative humidity of 23 per cent (NIMET, 2015; Adedeye et al., 2019).

Figure 1.

Figure 1

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Location and accessibility map of Wase and environs.

3. Regional geological setting

The origin, formation, and evolution of the Benue Trough (Figure 2) as part of the West and Central African Rift System (WCARS) resulted in a positive interplay of stratigraphic profiling and their tectonic juxtaposition. This combination led to rich deposits of economically viable minerals (Abubakar et al., 2014). Since the Benue Trough was formed as a rifted basin modified by strike-slip (transcurrent) faulting and subsequent inversion, multiple structures of varying styles are similar to those found in other WCARS basins with oil and gas reserves. The stratigraphic arrangement in the basin is similar to that of Sudan’s Muglad Basin and the Termit and Doba Basins of Chad and Niger. The Benue Trough in Nigeria is an intracratonic rift basin that stretches for 800 km north-northeast to south-southwest, is 90–150 km wide (Ogungbesan and Akaegbobi, 2011), and consists of a lower, middle, and upper section (Obaje, 2009).

Figure 2.

Figure 2

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Benue trough of Nigeria (modified from Nwachukwu et al., 2017).

The continental Bima Sandstone Group comprises the earliest sediments in the Upper Benue Trough, unconformably overlies the crystalline Basement Complex rocks, and forms part of the Upper Benue Trough’s stratigraphic succession (El-Nafaty, 2015). The transitional Yolde Formation is followed by the marine Pindiga Formation, the Gombe Formation, and the more recent Kerri-Kerri Formation. The Trough contains up to 6,000 m of Cretaceous-Tertiary sediments, some of which have been folded, faulted, and uplifted before the mid-Santonian period (Okiyi et al., 2021).

3.1. Local geology of the license area

Rock exposures are rare within the study area; however, exposures are still found within or around river channels, road cuts, erosional pathways, and stiff cliffs in the form of the Bima Sandstone of the Lower Albian age, composed of feldspathic, calcareous, and shelly sandstones, often highly indurated. Petrographically, the sandstone has colours varying from white, brownish, to pinkish (El-Nafaty, 2015). The colour is determined by the colours of the cementing material, weathering, or alteration. Sandstones are mostly observed around stream channels as outcrops, followed by the Pindiga Formation of the Turonian period.

The Pindiga Formation, which consists of shales and limestones, is attributed to the onset of marine incursion in the late Cenomanian period, followed by the Palaeocene Kerri-Kerri Formation in the form of recent sediments of sand grits and clays (Aminu et al., 2017; Ogundipe, 2018), exposed at stream channels as sub crops. In addition, abundant duricrust (ferricrete) is observed around the western parts of the area (Figure 3). They appear as ferruginous materials with no stratification, are filled with voids and pores, and contain a substantial quantity of iron in the form of red and yellow ochres. The development of these duricrusts is related to the climatic condition of the mapped area, which formed during periods of little or no tectonic activity and prolonged subaerial exposure in a contrasted hot and dry climate.

Figure 3.

Figure 3

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Geology of Wase and environs.

3:2. The Zurak - Wase deposits

The Zurak–Wase Lead–Zinc deposits are found in medium-grained arkosic sandstones with thin, distinctive cross-beddings interspersed throughout (Ogundipe, 2017). They are limonitic in some locations due to iron impregnation, probably caused by siderite dissolution.

A monoclonal structure has been created by the gentle folding of all the sediments (Ogundipe and Obasi, 2016). Although the dips may get steeper close to the mineralisation zones, they are typically mild, ranging between 5–150° E. The lead/zinc ores are well-defined veins which strike north to south and drop steeply to the east in fault and fracture zones. The veins’ strike lengths range from a few meters, and their thicknesses range from a few centimetres to two metres, according to a detailed fieldwork inspection.

4. Materials and methods

4.1. Ground magnetic

The basic operating principles of the ground magnetic method is based on detecting changes in the Earth's magnetic field caused by items that are magnetized and buried deep underground (Bevan, 2006). The entire process is passive because no field generation is required on the part of the instruments. Basic igneous rocks, specific types of mineralization, and a wide range of man-made materials and creations including metal pipes, reinforcement bars, electric cables, and different kinds of furnace ash are among the materials that have an impact on the Earth's magnetic field (Bickler et al., 2017; Escada, 2019; Cozzolino et al., 2018).

Any substance that is sensitive to magnetization or includes some sort of iron oxide (such as a ferromagnetic substance) records the strength of the Earth’s magnetic field at the spot where the substance becomes magnetized Tarling and Hrouda (1993), Sandgren and Snowball (2002), Evans and Heller (2003), Cullity & Graham, 2011 and Babker (2019). Detailed principles of the ground magnetic survey can be found in (Reford, 1980; Paterson and Reeves, 1985; Brodie, 2002).

The magnetic data was acquired using a portable GEMSys Overhauser magnetometer. The rover unit had a GPS built into it, and it digitally recorded the coordinates, total magnetic field intensity, and time of each measurement taken. The magnetic readings were obtained at intervals of 1 s. Outside the survey region, a fixed base magnetometer was also installed, and it was used to track the daily variations in the earth's magnetic field throughout the whole survey.

A low/negative magnetic intensity peak value surrounded by highs shows common abnormal signatures in low latitude magnetic latitudes, particularly around the equator, which is where Nigeria is located (Toyin, 2021; Apeh et al., 2022). Magnetic contours are useful for charting structural trends since their lineation typically corresponds to the local geology, which may include faults and structural patterns (Stewart and Boyd 1983; Gattacceca et al., 2004; Rowland et al., 2021). Oasis Montaj was used for processing, filtering, and data analysis, the total magnetic intensity data (TMI) is presented in Figure 4, and the reduction to the equator in Figure 5.

Figure 4.

Figure 4

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Total Magnetic Intensity (TMI) Data over the area of interest.

Figure 5.

Figure 5

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Reduced to the Equator over the area of interest.

4.2. Very low-frequency electromagnetic (VLF-EM)

The response of the ground to the propagation of electromagnetic fields, which are made up of an alternating electric intensity and magnetizing force, is used in electromagnetic (EM) surveying techniques. The electromagnetic field that penetrates the ground when there is a conducting body causes alternating currents, which create their secondary electromagnetic field (Haldar, 2013). The receiver then reacts to the resultant of the incoming primary and secondary fields in a manner distinct from the primary field alone in terms of both phase and amplitude. These variations show the conductor's presence and inform us of its shape and electrical characteristics. The VLF (Very Low Frequency) technique makes use of electromagnetic radiation produced at low frequencies between 15 and 30 kHz.

A trio-electric circuit system connected by electromagnetic induction is a good analogy for an EM field arrangement. The three circuits consist of the subsurface conductor, a Receiver (Rx) part, and a Transmitter (Tx) part. Through the passage of a primary a. c. current (ip) through a coil, the transmitter creates the primary field (Hp). In the subsurface conductor, the primary field (Hp) causes an eddy or vortex current (or secondary current). The secondary field (Hs), which is detected at the receiver (Rx) site, is subsequently induced in the subsurface conductor by the eddy current (is). The instrument simultaneously measures the primary (in-phase) and secondary (quadrature) fields. The "tilt angle" and the "ellipticity" of the magnetic field are the two components of the magnetic field that are measured by all VLF sensors.

The rover unit had a GPS built into it, and it digitally recorded the coordinates, total magnetic field intensity, and time of each measurement taken. The magnetic readings were obtained at intervals of 1 s. Outside the survey region, a fixed base magnetometer was also installed, and it was used to track the daily variations in the earth's magnetic field throughout the whole survey.

The VLF survey utilized three adjustable frequencies between 16.4 kHz, 19.6 kHz, 22.2 kHz, 23.4 kHz, and 24.0 kHz. Selected profiles were acquired with in-phase and out-of-phase measurements at a 10 m station-to-station distance.

Twenty-nine (29) magnetic profiles of 50m spacing with an approximate total length of 24.0 km were carried out in the E-W direction, and fifteen (15) Very low frequency electromagnetic (VLF) profiles of 10 m spacing with an approximate total length of 12.5 km line were surveyed across some target areas of the magnetic profiles. The magnetic data were acquired using a portable GEMSys Overhauser magnetometer, and VLF data were also acquired using the GEMSys Overhauser magnetometer with the VLF option. The magnetic readings were taken at intervals of 1s; the rover unit incorporated a GPS and digitally recorded the coordinate, total magnetic field intensity, and time of each measurement. A stationary base magnetometer was also set up outside the survey area, which was used to monitor the daily changes in the earth's magnetic field for the entire survey. The data were grided, filtered, and transformed into the appropriate grids for interpretation using the Oasis Monjaj software and its many extensions. The results were then displayed as stacked VLF profile plots and magnetic contour maps. VLF-EM Frazier Filtered In-phase grid is presented in Figure 6.

Figure 6.

Figure 6

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VLF-EM Survey, Frazier Filtered In-phase over the area of interest.

4.3. Electrical resistivity tomography and induced polarization (IP)

Electrical resistivity tomography (ERT) is a widely utilized geophysical subsurface imaging technology that is frequently used in archaeological mapping, hydrological exploration, environmental research, and civil engineering (Daily et al., 2004; Zhou and Kanl, 2018; Ducut et al., 2022). The conventional DC resistivity investigation was transformed into a computerized tomography technique, which makes use of multielectrode hardware or systems to automatically collect a lot of data and then uses software to recreate the subsurface resistivity structure using the observed data (Loke, 1999, 2004).

The ABEM LS2 Terrameter was used for the ERT and IP measurements. A global positioning system (GPS) was used for field mapping and georeferencing profile lines. Logging sheets were used for recording observations of the rocks and measurements. The Geotomo RES2DINV software was used to invert the ERT and IP data. ERT was used to image the subsurface through currents and potential electrodes (Uhlemann et al., 2018; Louvaris et al., 2021). By supplying direct continuous current through current electrodes and recording the potential difference between pairs of potential electrodes, variation in ground resistivity due to variation in geological materials is measured (Al-Fares, 2014; Nabi et al., 2020). This technique provided 2D and 3D imaging from which accurate subsurface geological models were generated (Gourdol et al., 2021; Hasan et al., 2021). The most common electrodes configuration used in ERT surveys are Wenner, Dipole-Dipole, Wenner-Schlumberger, Pole-Dipole, and Pole-Pole (Moreira et al., 2016; Uhlemann et al., 2018).

A multiple gradient array was used for the data acquisition with the transmitted current in the range of 0.1 mA and 500 mA as the maximum output current. A dipole M-N was moving between two fixed current electrodes, A and B, to measure the potential difference using a multiple-gradient array. The electrical field produced by the two fixed current electrodes is mapped using the array. (s + 2)a, where a is the smallest electrode spacing, is the distance between current electrodes (Dahlin and Zhou, 2006). The separation factor (s, an integer) is the largest possible number of measurements. With a multichannel resistivity system, the multiple-gradient array is simple since you can perform several measurements using various potential electrode pairs at various locations.

Additionally, it enables several sets of multiple gradient measurements to be taken using the current electrodes at various locations. One of these unconventional arrays is the multiple-gradient array, which Dahlin and Zhou proposed in 2006.

A current-stimulated electrical phenomenon known as induced polarization (IP) is observed in earth materials as a delayed voltage response (Shi et al., 1998; Sumner, 2012). It is useful as a technique for searching the subsurface for hidden mineral resources (Nguyen et al., 2020). Up to a saturation potential of 1.2 V, the potential produced is a linear function of the potential drop across the body in the energizing field. The main factors that affect how quickly the polarization potential grows or decays are ion diffusion and chemical reaction. Only at the borders of electrically conducting minerals does polarization occur (Bleil, 1953; Sumner, 2012). The term ”induced polarization” describes an electrical or resistive blocking effect in earth materials, with the process being most pronounced in pores that are fluid-filled adjacent to metallic minerals (Revil et al., 2015). Therefore, it is noted that the IP effect is strongest close to rocks that contain metallic luster minerals. In areas with dispersed mineralization, where conventional geophysical exploration techniques are significantly less efficient, induced polarization is a helpful tool (Shah et al., 2013).

Tthirteen (13) ERT/IP profiles in zone A, B, C, and D were collected as presented in Figure 7 with electrode spread of 2 × 21, and 10 m spacing was used for multiple gradient array with the number of stackings of 1–30 with error limit of 1%, the delay time was 0.7s and acquisition Time of 0.3s. The IP survey used a pair of non-polarising electrodes to pass current into the subsurface (Clement, 2021). When the current was abruptly turned off, the primary voltage (v) between another pair of non-polarising potential electrodes did not return to zero but dropped to a secondary voltage (Vs) that decayed over time, thus producing an IP effect in the time domain. The effect is apparent chargeability (Binley, 2015; Clement, 2021). The ERT/IP profiles were conducted in an E-W direction cutting across the general trends of the veins extracted using the magnetic and VLF-EM data.

Figure 7.

Figure 7

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Grey Scale Tilt derivative map showing magnetic lineaments.

5. Results

5.1. Processed results of ground magnetic data and very low-frequency electromagnetics (VLF-EM)

The tilt derivative was applied to the reduced-to-equator grid of the ground magnetic data to produce a structural map of the area of interest. The linear structural maps extracted from ground magnetic and VLF-EM data are presented in Figures 7 and 8, respectively. The tilt derivative is very useful in mapping structures significant in mineral exploration (Miller & Singh, 1994; Verduzco et al., 2004; Salem et al., 2008), and the dominant linear structures over the area of interest are predominantly in the N–S direction.

Figure 8.

Figure 8

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Resistivity/induced polarization data acquisition map over linear structures extracted from ground magnetics and VLF-EM data.

5.2. Processed ERT and IP of zone A

Zone A contained four continuous profile lines: L1, L2, L3, and L4 (Figures 9, 10, 11, and 12, respectively). Line L1 revealed a major chargeable body (A) with chargeability >420 mV/V and resistivity values ranging from 8.99 to 1,074 Ωm. Meanwhile, L2 is characterised by medium to low chargeability anomalous bodies (B and C) of 200 mV/V at about 30 m and corresponding low resistivity values of 8.05–17.6 Ωm, whereas L3 revealed the highest chargeability (D) of 630 mV/V at 40–70 m deep. Last, L4 showed anomaly (E) with low resistivity values ranging from 5.04 to 17.5 Ωm and chargeability of >280 mV/V.

Figure 9.

Figure 9

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Electrical resistivity and induced polarization line L1.

Figure 10.

Figure 10

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Electrical resistivity and induced polarization line L2.

Figure 11.

Figure 11

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Electrical resistivity and induced polarization line L3.

Figure 12.

Figure 12

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Electrical resistivity and induced polarization line L4.

5.3. Processed ERT and IP of zone B

Zone B contained three profile lines (Figures 13, 14, and 15). Line L5 (Figure 13) is characterised by two anomalies, F and G, having high chargeability values of 560 mV/V and corresponding to a resistivity value of 9.65 Ωm. Line 6 (Figure 14) showed pockets of anomalous bodies (H, I, J, K, and L) at about 30–60 m deep, with resistivity anomalies ranging from 6.12 to 47.3 Ωm. L7 (Figure 15) has anomaly M with low resistivity values ranging from 3.23 Ωm, which is not reflected in the IP result. Pockets of high chargeability were recorded with values of 400–560 mV/V.

Figure 13.

Figure 13

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Electrical resistivity and induced polarization line L5.

Figure 14.

Figure 14

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Electrical resistivity and induced polarization line L6.

Figure 15.

Figure 15

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Electrical resistivity and induced polarization line L7.

5.3. Processed ERT and IP of zone C

Numerous chargeable structures were mapped across Zone C (Figures 16, 17, and 18). One anomalous body (N) was delineated in L8 (Figure 16) with medium chargeability values ranging from 28 to 56 mV/V. The variation in resistivity values ranges from 5.51 to 111 Ωm. L9 (Figure 17) showed wide chargeability anomalies O, P, and Q ranging from 84 to 98 mV/V, corresponding to medium to low resistivity values. L10 in Figure 18 revealed a medium chargeability anomaly (R) with values ranging from 80 to 280 mV/V with other minor anomalies corresponding to relatively low resistivity values.

Figure 16.

Figure 16

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Electrical resistivity and induced polarization line L8.

Figure 17.

Figure 17

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Electrical resistivity and induced polarization line L9.

Figure 18.

Figure 18

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Electrical resistivity and induced polarization line L10.

5.3. Processed ERT and IP of zone D

Zone D comprises L11, L12, and L13, corresponding to Figures 19, 20, and 21. L11 revealed a relatively large chargeability anomaly (S) toward the centre of the profile with values ranging from 300 to 420 mV/V. L12 showed a high chargeability anomaly (T) with 340 to >476 mV/V values in the centre of the profile, corresponding to low resistivity values at shallow depths. L13 (Figure 21) revealed a medium chargeability anomaly (U, V, and W) and a relatively high chargeability anomaly body in (X) 20–50 m deep.

Figure 19.

Figure 19

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Electrical resistivity and induced polarization line L11.

Figure 20.

Figure 20

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Electrical resistivity and induced polarization line L12.

Figure 21.

Figure 21

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Electrical resistivity and induced polarization line L13.

6. Discussion

The interpreted results of ground magnetic and very low frequency electromagnetic in Figures 7 and 8, respectively, revealed structures that are predominantly trending in NS directions in agreement with the occurrence of lead-zinc in Benue Trough (Olade and Morton, 1985), the presence of these veins is possibly filled with lead-zinc mineralisation. The direction of the veins was used as a guide to run the ERT and IP profiles perpendicular to the general structural trend in the Wase area.

Zone A of the ERT/IP comprises L1, L2, L3, and L4. L1 revealed a vein with high chargeability values of 420 mV/V corresponding to low resistivity values of 5.99 Ωm. The vein is observed to continue in L2 with anomaly (C), indicating an increase in chargeability values of 200 mV/V, suggesting an increase in the quality of the lead-zinc mineralization in the area. A significant vein was interpreted at the beginning of profile L2 (B), showing an improvement in the quality of lead-zinc mineralisation due to the strength of the chargeability. Profile L3 shows that the veins revealed by L1 and L2 are smaller than anomaly (D) in L3, interpreted with a high chargeability value of 650 mV/V corresponding to low resistivity values of 6.35–141 Ωm. The IP profile on L4 did not reveal the continuation of veins in the southern direction, a small vein of lead-zinc was detected as an anomaly (E) in L4.

Profile L5 in zone B revealed two possible veins of lead-zinc identified as F and D, which correspond to low to medium resistivity values ranging from 9.65 to 28 Ωm on the ERT profile. Profile L6 revealed smaller lenses of high chargeability materials suggesting lead-zinc corresponding to low resistivity values of 6.12–47.3 Ωm on the ERT profile and at a shallower depth of 20 m. Profile L7 shows discontinuation of these small lenses of lead-zinc and a new anomaly detected as (M). Profile L8 in Zone C shows one weak anomaly (N) with very low chargeability values of 28 mV/V at a depth of 40m and a resistivity value of 13 Ωm. At the same time, Profile L9 suggests the continuation of the vein and a possible increase in size and quality of the lead-zinc mineralisation (O and P), which corresponds to relatively low resistivity values (5.06–25.5 Ωm) at a depth of 30–60m. The vein shows a decrease in size toward profile L10 with anomalies identified as (R), and the veins are shallower in the southern direction.

One large anomaly (S) was interpreted on profile L11 in zone D at a very shallow depth of 10–30m and corresponded to medium to low resistivity values (23.1 Ωm) on the ERT. Profile L12 revealed the continuation of the veins as anomaly S toward the southern part, which are bigger and deeper with a possible increase in quality. The veins that were picked on L13 show a decrease in size toward the southern part of the area of interest, with anomalies identified as U, V, W, and X. Anomaly X is shallower (Olade and Morton, 1985) and with an indication of an increase in quality of the lead-zinc mineralisation in this anomaly.D.

7. Conclusion

The interpretation of the integrated geophysical methods such as ground magnetics, VLF-EM, ERT, and IP data embodied in this work is essentially a geophysical appraisal for lead-zinc mineralisation in the area. Based on the interpretations, the tenement is considered economically viable for further investigation. Therefore, it is recommended that trenching, pitting, or core drilling should be carried out on the target points to ascertain the ore grade and ore reserve.

Declarations

Author contribution statement

Solomon Nehemiah Yusuf, Mubarak Umar Faruk, Lucky Osaro Imagbe, Ovye Musah Yohanna, Ishaq Yusuf, Abraham Onoshagbegbe, Musa Kamal & Timbee Terunga Jacob: Conceived and designed the experiments; Performed the experiments; Analyzed and interpreted the data; Contributed reagents, materials, analysis tools or data; Wrote the paper.

Funding statement

This research did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors.

Data availability statement

Data will be made available on request.

Declaration of interest’s statement

The authors declare no competing interests.

Additional information

No additional information is available for this paper.

Acknowledgements

The authors thank Matrix Fertilizer and Eureka Drills and Mines Ltd for fieldwork and data.

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