Hydrogeochemical characteristics and quality assessment of surface and groundwater around Adudu-Abuni lead-zinc minefields, Northcentral Nigeria

ABSTRACT This study aims to evaluate the effects of contaminants on the surface and groundwater resources in the mining communities of Adudu-Abuni, Central-Nigeria. Thirty-one (31) water samples including 21 surface (streams) and 10 groundwater were analyzed for physicochemical parameters (major cations, anions, and heavy metals) using the APHA (2011) and (ICP-MS) standard methods. Physicochemical analysis showed that the concentration of heavy metal for both surface and groundwater of the area in the following order of abundance Fe>Pb>Zn>Cu>Cr>Cd>As and Fe>Zn>Pb>Cu>Cr>Cd>As, respectively. High concentrations of the heavy metals in the surface and groundwater are attributed to anthropogenic activities; improper channeling of mine effluents into the environments, these effluents reacted via oxidation and dissolution process, making solutions (contaminants) infiltrate into the aquifer system. Results showed for both surface (67%) and groundwater (70%) waterfall within the rock weathering dominance for both anions and cations, with few exceptions who fall into the precipitation dominance, suggesting that rock–water interface is the primary influencer for both surface and groundwater chemistry. This deduced that rock weathering and precipitations are the principal factors controlling the water chemistry in the study areas. WQI analysis for groundwater shows that the northern axis of the area depicts poor water quality while the southern regions are good for drinking. Whereas surface water source from the southern zones is unsuitable for drinking, while those in the northern region are good. This is attributed to the proximity of Pb-Zn mines to the southern region because streams within this zone serve as repositories for mine effluents.


Introduction
The role of mineral resources in the economic growth and development of nations and regions of the world cannot be overemphasized.Solid mineral resources have, over the years, defined the civilization and urbanization of many states and regions in Nigeria, starting with coal mining in Enugu in 1903, Tin, Columbite, and lead in Jos Plateau, and recently gold mines in Zamfara State.As a result of mineral extraction, jobs are created, foreign exchange earnings are generated, domestic production and consumption are increased, revenue is generated, the economy is diversified, industrialization occurs, and energy is generated.Water resources on their own part are an essential commodity for life, it is required for human, plant and animal growth and development.It also promotes the stability and functionality of our ecosystem.Poor exploitation and management of these resources have led to water pollution and the degradation of our environment, thereby posing significant health challenges to the inhabitants of their host communities (Adamu, Nganje, & Edet, 2015).
The study area is a predominant lead and zinc mining community where solid mineral mining has generated mine effluents, wastes, tailings, and rock fragments that are dumped in landfills, farmlands, ponds, and flowing streams thereby degrading the water quality, reducing its suitability for use at home and in the workplace as well as human and agricultural purposes (Egbueri, 2019a;Mgbenu and;Egbueri, 2019b).The sitting of these mine spoils is selected for ease and nearness to the mining province instead of environmental, geological, or engineering considerations (Ezeigbo & Ezeanyim, 1993).Researchers have shown that the provision of excellent water quality has declined mostly in developing regions, this is often attributed to human (anthropogenic) and natural (geogenic) factors (Adimalla, Vasa, & Li, 2018;Egbueri & Unigwe, 2019;Ezugwu, Onwuka, Egbueri, Unigwe, & Ayejoto, 2019).
Globally, mining activities continue to pollute the environment and impact negatively to health and economic development (Adamu, 2000).A significant environmental issue is water and soil pollution caused by acid mine drainage (AMD) in many parts of the world, particularly in underdeveloped and developing countries, where mines are usually located close to human habitats (Lee, Chon, & Kim, 2005).
Researchers have, over the years, employed different techniques in the study of the degradation and contamination of water and other environmental media in the vicinity of mining and agricultural dominant communities.Numerical models such as Water Quality Index (WQI) have been developed and employed for the assessment of the quality of surface and groundwater in different parts of the universe.This model has been very effective in the quantification of waters into suitable and unsuitable for consumption, since they reflect the composite levels of contamination and pollutions (Batabyal & Chakraborty, 2015;Zakir, Sharmin, Akter, & Rahman, 2020).
Water quality assessment in the vicinity of leadzinc mine communities has become the major focus of many researchers around the world.For example, Obasi and Akudinobi (2020) posited that the exposed mine spoils which are composed of fragments of barite, lead and the host rocks in the Enyimba district of the lower Benue trough, Nigeria, are associated with myriads of environmental hazards.
The inhabitants of Adudu-Abuni minefields use water from different sources, especially from streams, ponds, and hand-dug wells for drinking and domestic purpose.Given the over-dependency on surface water (streams and ponds) due to insufficient deep boreholes in area, it is pertinent to examine the level of contamination and enrichment of water resources in the study area by lead-zinc mining activities.It is, therefore, the aim of this paper to evaluate the hydrogeochemistry and the impacts of lead-zinc mining activities on the water quality with respect to drinking and human health risk using WQI, and to identify the possible sources of contaminations and to create awareness of the impending hazards related to the continuous intake of untreated water resources in the study area.

Geographic setting
The study area is situated between latitude 8° 10 1 50 11 and 8° 18 1 12 11 N and longitude 8° 58 1 38 11 to 9° 1 1 18 11 E. The area is characterized by gently undulating lowlands (Igwe, Una, Abu, & Adepehin, 2017), except for the fact that high concentrations of mine heaps and tailings which are densely distributed in the farmlands and stream channels within the mining provenience have altered the topography of the area to a somewhat undulating, mountain-like environment (Figure 1).The elevation ranges between 116 and 268 m.The study area falls within the tropical rainy climate with distinctive dry and wet seasons.The rainy season spans 7 months from April to October with an annual rainfall of about 1200-2000 m and an average temperature of 25 to 275°C while the dry season commences in November and terminates in March (Akaama, Onoja, & Nwakonobi, 2014).Here is location for Figure 1.

Geology and Hydrogeology
The area consists of two out of the six reorganized geologic formations in the Middle Benue Troughs.They include the Awgu and Ezeaku Formations (Obaje, 2004).Figure 2  of units of weathered, light brown, fissile, and carbonaceous shales of about 1.8 m thick which is overlain by another distinct pale gray, slightly indurated, and carbonaceous shale which is overlain by another gray, fissile, carbonaceous, and horizontally laminated shale of about 5 m thick and then finally capped with overburden mixture of weathered sand and siltstones with plant rootlets of about 1.2 m thick (Figure 3) which is typical of Ezeaku  formation.Another logged outcrop along stream channel in Abuni reveals a light gray, fissile, highly weathered shale of 2 m thick with horizontal laminations, it is overlain by another distinct dark gray, fissile, carbonaceous, highly weathered shale of about 4 m thick with horizontal laminations which in turn covered by an overburden of weathered silt and sandstones of 0.8 m thick with plant rootlets (Figure 4).Here is location for Figures 2, 3 ,  and 4.
The study area has varying hydrogeological characteristics; the Asu River group consists of folded shales and siltstones that are sometimes highly fractured, with appreciable quantity of water (Obaje, 2004).The sandstone of Awgu Formation is known to be a water-bearing member which may be confined and gives pressure water (Patrick, Fadele, & Adegoke, 2013).The coal-bearing measures are highly fractured with coal shales which are associated with continuous groundwater flow.The Awe Formation is water bearing although the water is saline in nature, thus making it a poor aquifer.The saline groundwater associated with the formation results from brines which are known to emanate from the formation (Offodile, 1992).Akaama, Onoja, and Nwakonobi (2014) have recently shown that three aquiferous units in the Adudu axis of the study area.The inferred lithologies of the aquifers are mainly clayey sand, shales, shally sandstone, and silty clayey whose thickness varies between 17 and 20 m.

Mine site description and mining methods
There are three mining complexes within the study area, namely, the Adudu mine tunnel, Yuguda open cast, and the China Mine pits.The Adudu mine tunnel is an underground mine tunnel that gently steps downward from the entrance to a point where three underground mine tributaries were developed following mineralization veins.Each tributary extends to about 50 to 150 m with respect to the mineralization veins.Mining in this tunnel has been ongoing for at least 40 years.Artisanry miners in this tunnel use cutlass, digger, hammer, shovel, and hoe in removing the overburden materials before extracting the minerals.Miners here are faced with the challenges of dewatering the ponds created inside the tunnel (Figure 5a).The Yuguda mine complex practices an open caste system where tractors and excavators are used to remove the overburden (Figure 5b), and mining in this complex has been ongoing for the past 20 years.Figure 5c shows some lead samples mined out in the study area.The China mine pit deploys modern technological tools with highly skilled workers to advance their operations.The lead-zinc here occurs as veins and bedded deposits.The technique used here is the underground vertical pit that extends deep down to about 250 m with a diameter of 10-12 m.As observed in the field, the enormous volume of saline water is pumped out of the pit and channeled into the adjoining Bakebu stream, thereby making the entire stream taste salty along the flow direction.Mining in this complex has been ongoing for the past 15 years.Here is location for Figure 5a, b, and c.

Materials and method
Thirty-one (31) water samples including 21 surface water (streams and ponds) and 10 groundwater samples were collected in 45cl neatly washed and well- sterilized containers.At every sampling point, three samples were collected (each for the anion, cations, and heavy metal analyses).After collecting the samples, nitric acid was immediately added in order to prevent the degradation of elements.The samples were tightly cocked, neatly labeled, and transferred in an ice-cold cooler so as to avoid biodegradation of elements.Temperature was measured in the field using a mercury thermometer, and the total dissolved solids (TDS), electrical conductivity (EC), total hardness (TH), bicarbonate (HCO 3 − ), acidity/alkalinity (pH), nitrate (NO 3 ), phosphate (PO 4 ), and chloride (Cl − ) were analyzed in the laboratory following the American Public Health Association (APHA, 2011) standards.The inductively coupled plasma mass spectrometry (ICP-MS) PG-990 model was used to analyze the cations and heavy metals: K, Mg, Na, Fe, Ca, Zn, Cr, Cu, Cd, and As.

Water quality index (WQI) for drinking purposes
A WQI is a rating that takes into account the cumulative effects of various water quality parameters on water quality.In other to obtain a comprehensive insight into the overall quality of ground and surface water for consumption purposes, a WQI evaluation model used by Batabyal and Chakraborty (2015) was adopted and a standard specified by the WHO (2017) was also used.The WQI was computed through three steps.First, each of the 14 parameters (EC, TDS, pH, TA, HCO 3 Cl − , NO 3, SO 4 , K, Na, Ca, Zn, Fe, and Mg) used in this case was assigned a weight (w i ) according to its relative significance in the whole quality of water for drinking purposes (Table 1).The maximum weight of 5 was allotted to nitrate because of its key importance in water quality assessment; a minimum weight of 1 was assigned to zinc because of its insignificant role.Others were allocated weights between 1 and 5 based on their relative significance in the water quality evaluation.Second, the relative weight (W i ) of the chemical parameters was computed using the following Equation (1).
where W i is the relative weight, w i is the weight of each parameter, and n is the number of parameters Table 1 shows the calculated relative weight (W i ) values of each parameter.In the third step, a quality rating scale (q i ) for each parameter was calculated by dividing the absorption of that parameter in each water sample by its respective standard as demonstrated by (Batabyal & Chakraborty, 2015;WHO, 2017) and the result is multiplied by 100, as shown in Equation (2).where q i = the quality rating, C i =the concentration of each chemical parameter in each water sample in (mg/L), and S i = the WHO (2017) drinking water standard for each chemical parameter in (mg/L).
To compute WQI, the subindex (SI) is first determined for each chemical parameter, as given in Equations ( 3) and (4).
where SI is the subindex of ith parameter; W i is relative weight of ith parameter; q i is the rating based on the concentration of ith parameter, and n is the number of chemical parameters.Batabyal and Chakraborty (2015) have also classified WQI into five categories: excellent, good, poor, very poor, and unsuitable water for drinking (Table 2).
Here is location for Tables 1 and 2.

Correlation analysis
In order to establish the relationships between parameters, correlation coefficients are used and can be helpful in knowing the relationship between one parameter and the other (Ezugwu, Onwuka, Egbueri, Unigwe, & Ayejoto, 2019).Coefficients are employed to evaluate the correlation among two or more variables if the dependent (x) is influenced only by the independent variable (y) and vice versa (Batabyal & Chakraborty, 2015).Hence, correlation matrix of 19 parameters for each of ground and surface water was calculated with the aid of SPSS software version (V.22).The degree of a linear association between any two parameters is measured by simple correlation coefficient (r).Equation 5expresses the linear regression method for the calculation of coefficient (r).
ffi ffi ffi ffi ffi ffi ffi ffi ffi ffi ffi ffi ffi ffi ffi ffi ffi ffi ffi ffi ffi ffi ffi ffi ffi ffi ffi ffi ffi ffi ffi ffi ffi ffi ffi ffi ffi ffi ffi ffi ffi ffi ffi ffi ffi ffi ffi ffi ffi ffi ffi ffi ffi ffi ffi ffi ffi ffi ffi ffi ffi ffi ffi ffi ffi ffi ffi ffi ffi ffi ffi ffi ffi ffi ffi ffi ffi ffi ffi ffi ffi ffi ffi ffi ffi ffi ffi ffi where x and y are the variables, n is the number of sample parameters

Physicochemical and heavy metal analyses of the groundwater
The physical, chemical, and heavy metal contents of the groundwater were compared to the World Health Organization (2017) standard for drinking, and domestic purposes and the results are presented in Table 3. pH is an indicator of the basic or acidic nature of water (Arshad & Shakoor, 2017).The pH value ranges from 6.8 in LC25 to 7.6 in LC30, although the pH values of the entire pore water samples fall within the World Health Organization (2017)acceptable limits for drinking, LC23, LC25, and LC28 tend to be acidic given that they fall below 7, the midpoint between acidity and alkalinity; LC14, LC24, and LC27 are basic while LC31 and LC26 are neutral.EC is the measure of the ability of water to conduct electric current, it is also an indicator of salt content in water which is a function of TDS.The TDS ranges from 80 mg/l in LC31 to 540 mg/l in LC 27 and 29 while EC ranges from 350 mg/L in LC31 to 1080 mg/L in LC27 and LC29.With the exception of LC23, LC27,  and LC29 for both EC and TDS, all other sampled points showed values within the acceptable limits (Table 3).The TDS is classified as fresh, if it is less than 1000 mg/L; brackish, if it ranges from 1000 and 10,000 mg/L; it is considered saline, if it falls between 10,000 and 100,000 mg/L; and brine, if it is more than 100,000 mg/L (Todd & Mays, 2004); therefore, all the groundwater of the study area are classified as fresh.
Although the groundwater of the area studied is classified as fresh based on its TDS contents, certain locations show variations above the World Health Organization (2017) standard for drinking.The variations in LC23, LC27, and LC29 are thought to have been influenced by the dissolution of host rocks in the aquifers, infiltration into the water table by surface run off, use of fertilizers and chemicals in farmlands, and domestic wastes in the study area as demonstrated (Mbaka, Mwangi, & Kiptum, 2017).Here is location for Table 3.
The major cations in the other of decreasing concentrations as revealed by the groundwater sample analyses are Na + >K + > Ca 2+ > Mg 2+ (Figure 6).The concentration of Na + ranges from 10.40 at LC 31 to 30.32 mg/l at LC27, Mg 2+ ranges from 2 mg/l in LC31 and 8.38 mg/l in LC26, K + ranges from 4.89 mg/l in LC30 and 26.31 mg/l in LC 26 while Ca 2+ ranges from 3.92 mg/l in LC 30 to 27.06 mg/l in LC 23.Although the absorptions of Na + and Mg 2+ fall within the acceptable limits for drinking, the high contribution of Na + and Ca 2+ to the total cations is due to ion exchange and precipitation of CaCO 3. LC23, LC24, LC25, LC26, LC27, LC28, LC29, and LC31 which constitute 80% of the groundwater samples has high concentration of potassium while 20% (LC22, LC30) are within the World Health Organization (2017) acceptable limits.High concentrations of Ca 2+ and K + in the groundwater samples of the area studied are probably caused by the application of fertilizers in farmlands of the study area (Rao, 2018).Bicarbonate, chloride, and nitrate are the prevailing anions in the groundwater of the study area, they're in order of abundance: HCO 3 − >Cl − >NO 3 − >CL − >SO 4 (Figure 7).The mean concentration of SO 4 2-and CL − are 9.0 and 73.56 mg/L, respectively (Table 3).The mean concentration of HCO 3 − is 256 mg/l, it ranges from 55 in LC31 to 383 at LC23. 70% of the sampled locations (LC22, LC23, LC25, LC27, LC28, LC29, LC30) are above the maximum permissible limit for drinking water.The high concentration of HCO 3 − in water signifies the dominance of mineral dissolution (Umar, Igwe, & Idris, 2019), it has direct link to the reactions of CO 2 with the calcareous and carbonates rocks: limestone, coal, and shales which dominate the tailings in the area (Arshad & Shakoor, 2017;Rao, 2018).Average concentration of NO 3 − is 63.49 mg/l, it ranges from 1.9 mg/l at LC30 to 164 mg/l at LC23.The concentrations of NO 3 − at LC23, LC25, LC26, and LC29 which constitute about 40% of the groundwater sampled locations are above the World Health Organization (2017) permissible limit.Here is location for Figures 6 and 7.
The heavy metal concentration in the water within pore spaces or voids of the area studied is in the following order of abundance Fe>Zn>Pb>Cu>Cr>Cd>As. reveals that 70% of the sampled groundwater locations (LC22, LC23, LC24, LC26, LC27, LC28, and LC29) shows slight contamination as the values were slightly above the maximum permissible limit, 20% of the sampled locations (LC28, LC29) shows concentrations of Cd above the permissible limit, 80% (LC23, LC24, LC26, LC27, LC28, LC29, LC30, and LC31) reveals Cr values higher than that prescribed by World Health Organization (2017).The concentrations of Zn and As for all the sampled ground water locations fall within the acceptable limits, whereas the concentrations of Fe and Cu for all the ground water locations revealed values slightly above the World Health Organization (2017) acceptable limit for drinking purposes.Absorption of heavy metals in ground and surface water system is an indication of anthropogenic activities as proved by (Igwe, Una, Abu, & Adepehin, 2017;Jabłońska-Czapla, Nocoń, Szopa, & Łyko, 2016).

Physicochemical and heavy metals analyses of the surface water
The surface water pH values vary from 6.2 to 7.8 with a mean value of 7. Based on the values of physicochemical parameters (Table 4), the pH shows slight acidity to alkalinity.The EC values of the surface water ranged from 72 to 1367 mg/l.43% of the sampled points (LC3, LC4, LC5, LC6, LC7, LC8, LC13, LC17, and LC18) showed EC values above the World Health Organization (2017) permissible standard for drinking and domestic uses.High EC values imply that there is high rate of mineralization, dissolution of host rocks, mine spoils, and contamination of the stream water regime by mined effluents.Just like the EC, the TSS revealed that 43% of the total surface water sampled locations, LC3, LC4, LC5, LC6, LC7, LC8, LC13, LC17, and LC18 were above the standard limits for drinking.
The mean concentration of salinity is 4406 mg/l, it ranges from 6.22 to 12,610.30mg/L.Sample locations (LC3, LC4, LC5, LC6, LC7, LC8, LC13, and LC17) which constitute 40% of the analyzed surface water showed salinity concentrations above the World Health Organization (2017) permissible limit.High salinity in the surface water is traceable to LC3, a point source of stream contamination, where intense pumping out of saline water from the Chinese mining complex pits (Figure 10d) discharges into the Bekebu stream resulting in high salinity of the downstream water.Salt has a wide range of economic importance in food processing industries, human health, and agriculture.Hypertension and cardiovascular diseases, however, can be caused by excessive salt consumption as demonstrated (Elias, Laranjo, Agulheiro-Santos, & Potes, 2020).Contaminants from mines entering streams, coupled with acidic pH, may cause plants and people to absorb heavy metals, thus posing a high health risk to those who consume contaminated agricultural products as verified (Boularbah et al., 2006).
The dominant cations in surface water of the study area in the order of increasing dominance are Ca 2 + >Na + >K + >Mg 2+ (Figure 8) while that of anions are CL − >HCO 3 >SO 4 >NO 3 − >PO 4 (Table 4).SO 4 2-, Na + and Mg 2+ show concentrations within the acceptable and safe limit for drinking with respect to World Health Organization (2017) standards.The mean concentrations of Ca 2+ and K + are 36.34mg/l and 13.73 mg/l, respectively.Ca 2+ ranged from 0.27 to 112.14 mg/l while K + ranged from 3.52 mg/l to 24.62 mg/l.The concentrations of Ca 2+ and K + in sample location (LC3, LC4, LC5, LC6, LC7, LC8, LC16, LC17, and LC18) exceeds the World Health Organization (2017) permissible limits for drinking.The mean concentration of HCO 3 is 141.56 mg/l, it ranges from 15.30 mg/l to 325 mg/l.10% of the surface water samples (LC13 and LC18) showed HCO 3 − concentration above the permissible limits for drinking.This is primary due to dissolution of carbonate rocks in the study area.Cl − ranged from 2.50 at LC20 to 7643 at LC3, the mean concentration of chloride is 2558 mg/l.38% of the surface water samples (LC3, LC4, LC5, LC6, LC7 LC, LC8, LC13, and LC17) expresses chloride concentration above the permissible limit for drinking purpose.Here is location for Table 4.
The heavy metals' concentration of the surface water in the order of increasing dominance is Fe>Pb>Zn>Cu>Cr>Cd>As (Figure 9).The mean values of Zn and As are 0.86 mg/l and 0.03 mg/l, respectively.The concentration of Zn varies from 0.24 mg/l at LC6 to 2.05 mg/l at LC18 while the concentration of As varies from 0 to 0.03 mg/l in sample LC9.
The concentrations of Zn and As are within the approved limit for drinking.The mean concentration of Cr is 0.31 mg/l, it varies from 0.03 (LC13) to 0.065 mg/l (LC3).80% of the surface water sampled locations shows Cr concentration above 0.05 mg/l prescribed by World Health Organization (2017) for drinking.The mean concentration of Cd is 0.05 mg/l.33% of sampled locations (LC1, LC2, LC3, LC4, LC5, and LC10) revealed Cd concentration above permissible limit.The concentration of Cu in the study area ranged from 0.01 to 0.33 mg/l.57% of the sampled locations (LC6, LC7, LC8, LC9, LC10, LC11, LC16, LC17, LC18, LC19, LC20, and LC21) showed Cu content of the surface water above the World Health Organization (2017) limits for consumption.Here is location for Figures 8 and 9.The concentration of Fe and Pb varies from 0.48 mg/l to 30.71 mg/l and 0.05 mg/l to 2.07 mg/l, respectively (Figure 9).Apart from LC21 that showed Pb concentration within the permissible limit, other surface water sampled locations were above the acceptable limits for consumption and domestic uses.High concentrations of the heavy metals in the ground and surface waters in the study area are attributed to both geogenic and anthropogenic activities such as improper dispositions of mine tailings, channeling of mine effluents into the farmlands, streams, and rivers (Figure 10) emanating from the mining complex (Obasi & Akudinobi, 2020), these mine effluents reacts with water via oxidation and dissolutions mechanisms, and the solutions eventually infiltrate into the water table through the rock pores and fractures which serves as excellent conduits for contaminants introduction into the aquifers.
Pb and Zn occurrences are associated with iron and sulfide minerals.It is possible that pollution in water is caused by pyrite (FeS 2 ) and other sulfide minerals in adjacent lithologies, which are exposed and oxidized, thereby releasing iron and sulfate into the water as verified (Obiadi, Obiadi, Akudinobi, Maduewesi, & Ezim, 2016).Ca, Mg, SO 4, and HCO 3 , which are weathering products of carbonate minerals, were found in high abundance in the rock units of the Study Area, suggesting significant influence of geology and lithology.As a result, surface water has been more adversely affected than shallow groundwater.Here is location for Figure 10.

Chemistry of water and hydrologic processes
According to Egbueri (2018), Gibbs diagrams help identify the relationship between chemistry of water and various hydrologic processes and lithology of an aquifer.The natural mechanisms controlling groundwater chemistry, such as rainfall dominance, rock weathering dominance, evaporation, and precipitation dominance, were illustrated by Gibbs (1970) using TDS versus Na+/Na+ + Ca2+ for cations, and TDS versus for anions.In accordance with the Gibbs diagram, the plotted groundwater samples fall into the rock weathering dominance group for both anions and cations, except LC31 whose cation falls into the precipitation dominance, suggesting that rock-water interactions in this area, may have been influential on the groundwater chemistry (Figure 11).67% of the surface water sampled locations (LC1, LC2, LC3, LC4, LC5, LC6, LC7, LC8, LC9, LC10, LC13, LC16, LC17, LC18, and LC19) for both anions and cations fall within the rock weathering class, implying that rock-water interface is the primary influencer of the surface water chemistry, while 30% of the samples (LC11, LC12, LC14, LC15, LC20, and LC21) falls within the precipitation dominance class implying that rainfall is also a contributory factor to the surface water chemistry (Figure 11).
Generally, it can be deduced that precipitation and rock weathering are the principal factors controlling the water chemistry in the study areas and may have been caused by weathering and dissolutions of rocks and sediments as demonstrated (Mbaka, Mwangi, & Kiptum, 2017).The mean correlation score of ≥ 0.5 (or +) and ≥ 0.4 (-or +) was applied for ground and surface water, respectively.In both cases, strong positive correlation exists between EC, TDS, Cl − , K, Ca, Pb, Fe, HCO 3 , and SO 4 , (Tables 5 and 6) indicating that there is intense ion dissolution of parameters and oxidation-reduction reaction within the water system as proved (Batabyal & Chakraborty, 2015).This also accounts to the TH of water in the study area.Pb correlates positively with Fe, Zn, SO 4 , EC, Cl − , salinity, K, and Ca TDS.
The correlation observed among the heavy metals suggests that they have commonality of origin sourced from the mining operation in the study area (Egbueri, 2019b;Ezugwu, Onwuka, Egbueri, Unigwe, & Ayejoto, 2019); however, the positive correlation that exists between, Pb, Zn, and Nacl, EC and TDS are an indication of the occurrence of salt water intrusion (Adimalla, Marsetty, & Xu, 2019).K has strong positive correlation with EC, TDS, Salinity, SO 4 , PO 4 , Mg, and NO 3 for both ground and surface water and could be attributed to agricultural waste enrichment by fertilizers and other agrochemicals used in the farmlands of the study area.TH has strong positive correlation with EC, Salinity, PO 4 , Mg, (Table 5) Fe, Na, Ca, and K (Table 6) which indicate that the dissolution of host and carbonate rocks in the study area may have influenced the water hardness, it is also an indication of domestic waste, Pb-Zn mines, and geogenic contaminations (Obialo & Kenneth, 2019).Arsenic has positive correlation with Fe and Zn, indicating that they are likely from the same sources (Mama, Nnaji, Emenike, & Chibueze, 2020).Here is location for Tables 5 and 6.

Water quality index (WQI) for drinking
Despite several other pathways through which heavy metals are exposed to humans (air, food), its intakes through drinking water, especially in the vicinity of lead-zinc mining constitutes the greater proportion as verified (Sawyer, MWood, & World Health Organization., 2001).It is on this basis that the overall WQI for drinking was calculated for ground and surface water.The WQI values and its corresponding water type are presented in Table 7.
In the case of groundwater, location (LC22 and LC30) which constitutes 20% of the sampled groundwater shows excellent drinking water, LC25, LC28, and LC31 which constitute 30% of the sampled groundwater are good for drinking while LC23, LC24, LC26, LC27, and LC29 which constitute 50% depicts poor water quality for drinking.It is worthy to note that the two groundwater sampled locations (LC22 and LC30) in (Figure 12) depicted as excellent water for drinking are the only two deep boreholes that were sampled as groundwater in the     in the southern regions (LC 22, LC 30) are good for drinking (Figure 12).Also, the WQI spatial distribution map of the surface water sourced from the southern zones of the study area is unsuitable for drinking (Figure 13) while those in the northern region are of relatively good quality.The near proximity of Pb-Zn mining activities to the surface water in the southern zone of the area is believed to have had negative impacts on the water quality because the streams and ponds situated in this region act as repositories for mined effluents as can be seen in Figure 10.Here is location for Figures 11, 12 , and 13.

Conclusion
The assessment of the physicochemical parameters and heavy metals in the surface and ground water of the study area was carried out.Result showed that the concentration of heavy metal for both surface and groundwater is high, which is attributed to anthropogenic activities such as inappropriate channeling of mine wastewater into the surroundings making polluted solutions permeate into the water resource system.This makes the water unfit for drinking due to increased concentration levels of some parameters that exceed the World Health Organization (2017) recommended permissible limits for drinking purposes.Rock-water interface (weathering) generally controls the groundwater chemistry while a combination of rock weathering, precipitation and ion exchange controls the surface water chemistry.The groundwater correlation scores revealed positive correlation between pH and temperature; EC, TDS, HCO 3 − , TH, CL, and SO 4 2-indicating that they are from same source and has direct relationship with TDS, EC, and TA.Phosphate has positive correlation with nitrate, Cl, and HCO 3 − indicating agricultural waste based on parameters association.pH correlated positively with Mg and Fe which can be attributed to geogenic enrichment based on parameter association.Pb has positive correlation with K, Ca, and Cu and can be attributed to galena and sphalerite mines in the study area.
The surface water exhibits the same correlation pattern with the groundwater, except that Na and Cl in the surface water samples correlate positively with Mg, temp, phosphate, and TDS and can be attributed to contamination by saline water in the study area.The overall WQI computed for drinking purposes revealed that approximately 61% were poor/unsuitable for drinking while 39% is good/excellent.However, treatment of this water will therefore be mandatory before it can be used for drinking purposed.Furthermore, groundwater in the study area seems relatively of better quality for human and animal consumption than its corresponding surface water.
This study, therefore, recommends the need for a strong and sustained awareness programme for the benefit of the inhabitants around the minefield.Such awareness creation would safeguard them from serious health issues that could arise from consumption of the untreated water.
Figure 1.A 3-D map showing the elevation and topography of the study area.

Figure 2 .
Figure 2. Geologic and sample location map of the study area.

Figure 3 .
Figure 3. Lithostratigraphic description of outcrop exposure along stream channel in Abuni.

Figure 6 .
Figure 6.Concentration of cations in groundwater.

Figure 7 .
Figure 7. Concentration of anions in groundwater.

Figure 8 .
Figure 8. Major cations concentrations in surface water.

Figure 9 .
Figure 9. Heavy metal concentrations in surface water.

Figure 10 .
Figure 10.(a) local miners washing mined Pb-Zn in the streams of the study area.(b) mines tailings deposited in the flowing stream.(c and d) mine effluents from the China mine complex discharging into Bakebu stream.

Figure 11 .
Figure 11.Gibbs (1970) diagram showing mechanism controlling water chemistry in the study area.
is significant at ≥ 0.5 (in bold).
is significant at ≥ 0.4 (in bold).

Table 3 .
Basic statistics, heavy metals, and physicochemical parameters of groundwater.
Note: Values above WHO permissible standards are denoted in bold, whereas all parameters except pH, Temp.( o C), and EC (µS/cm) are measured in mg/L.

Table 5 .
Pearson correlation scores for major physicochemical parameters and heavy metals of groundwater.

Table 6 .
Pearson correlation scores for major physicochemical parameters and heavy metals of surface water.