Gold Mining Activities and Impact on Osun River Basin in Southwestern Nigeria

Abstract

This chapter examines the environmental and socioeconomic impacts of gold mining activities in the Osun River Basin, Southwestern Nigeria.
Gold is highly sought after for its physical and chemical properties and occurs naturally in low concentrations globally, often in alluvial and eluvial deposits.
The Osun River Basin covers approximately 1942 $km^2$ and supports around 200,000 people, experiencing a humid tropical rainforest climate with significant rainfall between April and November.
Gold mining has been associated with significant environmental degradation, including water contamination and land degradation.
Sediment samples from the Osun River at mining locations have shown high concentrations of potentially toxic metals exceeding World Health Organization (WHO) limits such as cadmium, arsenic, copper, zinc, chromium, and manganese.
The use of mercury and cyanide in artisanal mining exacerbates pollution, impacting water quality and posing severe health risks to local communities.
Pollutants disrupt aquatic ecosystems, leading to habitat destruction and biodiversity loss.
Economically, gold mining has contributed to unequal wealth distribution and social tensions, supporting the resource curse theory which posits that resource-rich countries often experience negative economic outcomes like corruption, political instability, and economic disparities.
Despite its economic potential, gold mining in the Osun River Basin has not equitably benefited local populations but has led to environmental harm and socioeconomic challenges.
The chapter underscores the importance of conducting comprehensive environmental impact assessments before initiating mining activities.
Sustainable mining practices and regulatory frameworks are essential to minimize the adverse effects on both the environment and the socioeconomic well-being of local communities.
Recommendations include stricter enforcement of environmental regulations, adoption of cleaner mining technologies, and community engagement in decision-making processes.
The study highlights the complex interplay between gold mining activities and their environmental and socioeconomic impacts, emphasizing the need for balanced and sustainable approaches to resource extraction.

Introduction

Gold: symbolized by Au, atomic number 79 ( $Z = 79$ ), and atomic weight 196.97 (atomic mass = $196.97$ ), with Gold-197 as its only naturally occurring isotope.
Gold is a dense, precious, non-readily reactive transition metal of Period 6 and Group 11 of the periodic table.
Qualities include attractive color, brightness, durability, high malleability, and occurrence in comparatively pure form.
Gold occurs in low concentrations, about 0.0005 ppm, across the globe.
It largely occurs in its native state and rarely in a combined state with other minerals, except selenium, bismuth, and tellurium.
Gold generally occurs in alluvial, eluvial placers, and primary veins from several parts of supracrustal (shale) belts including Nigeria.
Alluvial gold deposits occur at different times along a river channel, while eluvial gold deposits form on the flanks of actively rising antiformal mountain ranges.
Both alluvial and eluvial deposits are the most common and richest types of placer gold, containing pieces of gold washed away from the deposit by the force of water and deposited in sediments in or near watercourses or former watercourses.
Gold belts include the Proterozoic schist belts of Nigeria with north-south trending features restricted to the western half.
Specific areas in Nigeria with hydrothermal gold mineralization include Maru, Anka, Malele, Tsohon Birnin Gwari-Kwaga, Gurmana, Bin Yauri, Okolom Dogondaji, and Iperindo.
Africa is richly endowed with mineral reserves, accounting for:
- 59% of the world’s platinum.
- 62% of its aluminum silicate.
- More than 50% of all vanadiumites and vermiculites.
- More than 50% of diamonds, palladia, and chromite.
- More than 20% of gold, uranium, cobalt, and manganese.
Over the past five decades, most of the foreign direct investment to Africa has gone to the mining sector.
Nigeria was a major source of exports before the oil boom in the 1970s, but the fortune of mining declined from the 1980s, before increasing again in the 2000s.
Mining activities in Nigeria have been largely poorly controlled, with most operators unlicensed.
Many African countries have undertaken mineral extraction through tax revenues, job creation, technology transfer, and foreign exchange acquisition.
Mining is of research interest to physical geographers and other earth scientists because of the unique types of excavated and accumulated landforms and landscapes that are produced during the process, their impact, and the vulnerability of society to geomorphic hazards.
Mining landscapes tend to create more sediments than the combination of paved road construction, house construction, and agricultural activities.
Small-scale mining is a subsistence activity generally mechanized and carried out by poor people.
Surface mining involves the clearing of large tracts of forest and agricultural land, resulting in serious land and forest degradation.
Mining activities also cause frequent destruction of farm lands without adequate compensation being paid to the affected farmers.
Rising demand for primary commodities from fast-growing and emerging countries has added to the persistent high level of mineral demand in developed countries, stimulating an investment surge in mineral exploration and production in developing countries.
Nations were either reviewing or reforming their policies to liberalize the mining sector that would encourage the inflow of foreign capital for investment, causing growing competition between nations to capture investments.
Minerals policy, legal frameworks, and institutions were reformed to encourage foreign and local investments in the extractive sector and to optimize the contribution of mining to the national economy.
The objective of this study is to review existing studies and fieldworks on the impact of gold mining activities at a gold mining part in southwestern Nigeria.
The aim is to provide information on the sustainability of gold mining activities in the region, as it will likely be for similar part of the continent, following similar pattern of exploration approach.

Study Area

The Osun River Basin occupies an area of about 1942 $km^2$ and is home to a population of around 200,000 people.
It is a major drainage system in Southwest Nigeria with a rise in the Okemesi ridge (~5 km north of Efon-Alaye) from where it flows through Itawure, westward through Osogbo and Ede and then southward to enter Lagos Lagoon.
The Inter-Tropical Convergence Zone (ITCZ) has a significant impact on the climate of the basin.
The rainy season normally starts in March and lasts until late October or early November.
The basin has a humid tropical rainforest climate, similar to that of Koppen Aw.
Average annual rainfall in the area is between 150 cm and 180 cm, with the rainy season lasting roughly 8 months (April– November) and double maxima rainfall occurring in July and September/October.
Average monthly air temperature varies between 27 °C and 30 °C.
The northern portion of the basin is the source of many of the basin’s rivers, most notably the major Osun River.
The majority of the land surface in the basin is undulating, with high altitudes in the northern and low altitudes in the southern regions.
The basin has a dendritic drainage pattern.
The northern portion is characterized by many domed hills and sporadic flat-topped ridges.
The more notable hills in this area are located at Ilesa, Igbajo, Okemesi, Elu, and Oba.
There are 14 different water supply schemes, including the Esa Odo Water Scheme, Ilesa Water Works, Ede Booster Station, Mokuro Water Works, Ifewara Water Works, Ikeji Ile, and Iwo.
The Ede-Osogbo water project provides potable water to more than half of the drainage basin.
Major river systems in the area, including the Osun, Erinle, Otin, and Ayiba Rivers, have dams.
There are also weirs at Inisa, Okuku, and Oyan, around Epe, and Ibeju Lekki at the basin’s mouth.
The topography varies from 50 m at the basin’s mouth to about 700 m at Effon-Alaye in the basin’s northeast.
The source generally exists on a gradual slope, as evidenced by the relief ratio of 3.04 and the overall basin relief of 650 m.
The geology of the basin is composed of two types of rocks: sedimentary basins, especially Neogene-mesozole and Basement Complex rocks including granite, gneiss, and migmatite.
Sedimentary basins are found in the southern portion of the basin, whereas basement complex rocks cover the majority of the basin.
The newer sedimentary layers cover a total of 667.72 $km^2$ , while the basement complex rocks cover 9258.5 $km^2$ .
The Precambrian Basement Complex’s metamorphic rocks, which have outcrops in different places, underlie the basin.
The Basement Complex’s crystalline rocks are part of the older intrusive series and are primarily folded gneiss, schist, and quartzite complexes.
The vast majority of these Basement rocks are extremely old and exhibit wide differences in grain size and mineral content.
The southern parts of the Osun basin contain sedimentary rocks from the Cretaceous and subsequent periods.
Secondary forest covers the basin, with the derived Savanna mosaic predominating in the northern portion.
Due to years of human habitation, the lowland tropical rainforest vegetation that once covered almost the whole basin has given place to secondary forest regeneration.
The area’s vegetation can be defined as a derived savanna, with tall grasses and sporadic perennials alternating with a gallery of woodland along stream banks.
The drainage basin’s land use pattern consists of land used for farming, urban areas, bare rock and soil surfaces, residential and settlement areas, vegetation, and water bodies.
The area’s thick, humid forest cover is typically associated with deep soils; the sandier hill wash soils on lower slopes and low, smooth hillcrests, and deep, clayey soils.
The Osun River, within the basin, has grown to be a popular worldwide tourism destination and is an internationally approved UNESCO World Heritage site due to its significance for biodiversity and cultural property.
Along the river courses, farming and fishing are examples of agricultural pursuits.
The water is used by numerous farms as an irrigation source, as well as by humans for other purposes including abattoirs.
Most of the densely populated communities surrounding the Osun River Basin like Arimoro and the Isale General areas of Ilesa towns engage in artisanal gold mining, while sparsely populated rural communities like Obokun, Iloko Ijesa, and Atakunmosa East and West have essentially been overtaken by illegal miners who excavate soil for gold mines which has a detrimental effect on the water in nearby streams and rivers.

Impact of Gold Mining Activities

Vegetation

Gold mining in Africa has been linked to significant environmental damage, including deforestation and habitat destruction.
The need for land to mine gold has led to widespread deforestation, which in turn has had a devastating impact on local ecosystems and wildlife.
The loss of habitat has also resulted in the displacement of indigenous/ local communities, further exacerbating the environmental impact of gold mining.
Deforestation and habitat destruction are not only detrimental to the environment but also have long-term consequences for the local communities that depend on these natural resources.
A study carried out a species identification of plants in four plots of 25 m × 25 m using random sampling techniques.
In each sample plot, plant species were identified and those of unknown identity were collected.
Girth and height of woody plant species were determined, and species richness, diversity with dominance were estimated using appropriate ecological methods.
The study showed varied plant species diversity, evenness, family, species, habit, and relative abundance of the plant species under active and abandoned gold mine plots, farmlands, and relatively undisturbed forest.
While species diversity was 3.47 at the forest, it was least (2.88) at the abandoned mine site.
The least numbers of plant family and trees at abandoned mine sites is an indicator number of what will befall the active sites in the area.
Gold mining activities in the area led to the reduction of trees and plant families in the area.
The number of shrub and climbers were also more at the mine sites.
The ecosystems of the study area are experiencing disturbances of various magnitudes, mostly due to gold mining activities.

Soil

The mine sites (active and abandoned) were characterized by soil composed of over 60% sandy, total N of about 0.03% and 0.4 mg $kg^{-1}$ of available P.
Mean total N and available P, respectively, at the farm site were 1.1% and 2.33 mg $kg^{-1}$ , while they were 1.2% and 3.93 mg $kg^{-1}$ at the forest site, respectively.
Organic C and the main ions (Ca2+, K+, Mg2+, and Na+) were significantly (p < 0.05) more at the farm and forest sites than at the mine sites.
The values of cation exchange capacity (CEC) at the farm and forest sites were 3.38 and 3.68 cmol $kg^{-1}$ , while at the mine sites, the CEC values were 1.47 cmol $kg^{-1}$ (at the active sites) and 1.29 cmol $kg^{-1}$ (at the abandoned site).
The mine sites were also acidic (about 3.8–4.6 units in terms of H2O and KCl).
The concentrations of trace or heavy metals (Zn, Cu, Mg, Fe, Pb, Cd and Hg) were significantly higher at the mine sites (p < 0.05) than the farm and forest sites.
Whereas significant differences occurred in the physical and chemical properties in the soil at either the active or abandoned mine sites and either the forest or farm site, there were no significant differences in the properties between either the active or abandoned site on the one hand, and between the farm site and the forest site on the other.
When assessed with Nemerow pollution index (Ps), the Ps scale showed the mine (abandoned and active) sites as “heavily polluted” with above 3.0 index, with the selected heavy metals, except Mn and Fe.
The farm site was also classified as “slightly polluted” with an overall Ps index of about 1.3.
All the investigated heavy metals were indexed in the “slightly polluted” Ps index, except Pb (Ps =0.9) that was still in the precautionary state at the farm site.

Micro-Climate

Daytime changes in thermal conditions along N-S and W-E directions were computed values of heat index and dew point temperature.
The mine sites were warmer than outside them, and so were the mean heat index and dew point temperature.
Active mine sites generally exhibited averagely warmer air temperature, greater heat index, and dew temperature values than the dominant mine sites.
Since the heat index and air temperature exhibited a direct relationship the body temperature (as measured by the heat index) would increase as air temperature increases in the area, and this would result in people within the mining sites will likely feel more uncomfortable than other areas within the basin.
Land use within mine sites were formerly cultivated agricultural farmlands; especially with cassava and cocoa, but most of the farmlands have now been taken over for mining activities.
Lands that have not been cultivated are also being dug for mining purposes unless gold deposits are not detected or have been exhausted.
The mining activities causes consistent removal of vegetation, and thereby exposing the soil to direct impact of precipitation, and heat.
Mining activities within the mining area settlements have increased with increased population of immigrants and laborers in the area; the net incomes of land owners have apparently increased as well.
Vegetation was significantly removed and thermal discomfort was reported to have increased in the area as was reported in some other mining environments.

Waterbody

Sediment samples from the tributaries and distributaries of Osun River at mining locations were loaded with high concentrations of potentially toxic metals, especially Cd, As, Cu, Zn, Cr, and Mn, and that they were higher than the recommended limits by World Health Organization (WHO).
Loaded toxic metals can be released into the stream water to be absorbed by benthic organisms as evident in the low enrichment factors (<1) calculated for all the metals in the sediment samples by the authors.
Mercury and cyanide are widely used in artisanal mining to extract gold, and that the chemicals are highly toxic and pollute rivers when not disposed of properly.
The combined effect of these practices includes water contamination as mercury and cyanide levels in rivers like Osun be many times higher than safe limits.
This can cause serious health problems for people and animals who depend on the river water.
It can also result to damaged ecosystems which can cause pollution and disruption of the river bed destroy aquatic life and make it difficult for fish and other organisms to survive, as well as loss of livelihoods.
As rivers become polluted, they become unusable for fishing, farming, and other traditional activities.

Conclusion

Gold mining in the Osun River Basin, like in many parts of the region has been associated with unequal distribution of wealth and resources, leading to economic disparities and social tensions.
The resource curse theory suggests that countries with abundant natural resources, such as gold, often experience negative economic consequences, including corruption, political instability, and unequal distribution of wealth.
Gold mining in the Osun River Basin has significant implications for water quality, vegetation, and overall environmental health.
Efforts to mitigate these impacts are essential for the well-being of local communities and ecosystems.
To mitigate the negative impacts of gold mining, there is a need to consider the environmental impact assessment and alternatives before exploration is commenced.