Impact of mining activities on water resources in the vicinity of the Obuasi mine

Surface and groundwater samples within the catchment area of the Obuasi mine were analysed to assess the impact of mining activities on water resources. The concentration of Fe, Mn, Cu, Zn, Pb, Cd, Hg, As and selected major ions in water samples were analysed to assess their role in the contamination of both surface and ground water. The mineralogical composition of various mine spoil and rock samples was investigated by microprobe analysis to ascertain the possible sources of the metals in drainage and ground water. The hydrochemical analytical study, using standard methods, shows that streams in the study area have higher trace and major ions loading than ground water with iron and arsenic concentrations ranging from 0.025 mg/l to 17.19 mg/l and < 0.001 mg/l to 18.91 mg/l, respectively. Hydrochemical modeling of water types showed varied composition for both ground and surface water, but with strongindication of mixed waters from a variety of sources. The microprobe results showed that waste rocks and related mine spoil contain a variety of Fe, Cu, As, Sb, Zn and co-bearing sulphides with strong compositional variations, and account for the augmented levels of these metals in drainage proximal to mining and processing facilities. The proberesults did not show Hg in mine spoil, and very high Hg values observed in the vicinity of areas of intense illegal smallscale mining are attributed to the use of this chemical by miners in gold amalgamatio

ガーナ, ビルム・ダイヤモンド産地のアクァティア地域に分布する沖積層の重鉱物分析

Heavy mineral analysis was carried out on Pliocene to Recent alluvial sediments from the Birim diamondiferous field od Ghana. The main objective of the study was to examine the mineral composition of heavy fractions in order to identify : (1) the heavy mineral assenblage that occur in the sediments, (2) particular diamond indicator minerals associated with the diamonds, and (3) the provenance of the alluvial sediments. The heavy minerals are essentially composed of staurolite, ilmenite and magnetite in varying proportions, with trace amounts of leucoxene, rutile, garnet and zircon. The heavy mineral assenblage and chemical composition of ilmenite and gamet suggest their derivation from phyllites and schists which reflect directly the composition of the basement rocks developed in the study area. The absence of diamond indicatior minerals such as apatite, pyrope garmet, chromian spinel, and picroilmenite in the heavy fraction is unlikely to be due to their destruction during intense weathering and/or diagenesis but rarher their non-occurrence in the area

Hydrochemical Characterisation of Groundwater in Parts of the Volta Basin, Northern Ghana

Conventional graphical methods were applied to major ion concentrations and stable isotope data to determine the genesis and evolution of the hydrochemistry of groundwater from fractured aquifers in the northern parts of Ghana. The analyses suggest that groundwater hydrochemistry is controlled by the incongruent weathering of silicate minerals in the aquifers. Hierarchical cluster analysis confirms the results and shows that anthropogenic factors also contribute to the groundwater chemistry. Montmorrillonite, apparently resulting from the incongruent dissolution of calcium and sodium rich feldspars in the rock matrix is probably the most stable clay mineral phase in the system. Chloroalkaline indices (CAI) 1 and 2, calculated from the major ion data suggest reverse cation exchange activity between Na+ and K+ in the water and Ca2+ and Mg2+ in the rock matrix. This study finds that the groundwater in the area is classified into Ca-Mg-HCO3, mixed Ca-Mg-Na-HCO3 and Na-HCO3 water types, which are typical of groundwaters influenced by silicate mineral weathering and ion exchange. Stable isotopes of oxygen and hydrogen (&delta;18O and &delta;2H) show that groundwater originates from meteoric source, derived from rainfall which rapidly recharges the aquifers through the weathered overburden and ingresses such as joints and fracture systems. Silicate mineral weathering, which appears to be the main controlling process in the hydrochemistry, does not appear to influence the stable isotope data since a plot of &delta;18O against EC is a straight line of zero slope

Hydrogeochemical evolution of groundwater in a Quaternary sediment and Cretaceous sandstone unconfined aquifer in Northwestern China

A better understanding of the hydrogeochemical evolution of groundwater in vulnerable aquifers is important for the protection of water resources. To assess groundwater chemistry, groundwater sampling was performed from different representative aquifers in 2012–2013. A Piper trilinear diagram showed that the groundwater types can be classified into Na–SO4 and Na–Cl types. Only one groundwater sample was Na–HCO3 type. The dominant cations for all samples were Na+. However, the dominant anions varied from HCO3− to SO42−, and as well Cl−. The mean total dissolved solid (TDS) content of groundwater in the region was 1889 mg/L. Thus, only 20% of groundwater samples meet Chinese drinking water standards (< 1000 mg/L). Principal component analysis (PCA) combined with hierarchical cluster analysis (HCA) and self-organizing maps (SOM) were applied for the classification of the groundwater geochemistry. The three first principal components explained 58, 20, and 16% of the variance, respectively. The first component reflects sulfate minerals (gypsum, anhydrite) and halite dissolution, and/or evaporation in the shallow aquifer. The second and third components are interpreted as carbonate rock dissolution. The reason for two factors is that the different aquifers give rise to different degree of hydrogeochemical evolution (different travel distances and travel times). Identified clusters for evolution characteristic and influencing factors were confirmed by the PCA–HCA methods. Using information from eight ion components and SOM, formation mechanisms and influencing factors for the present groundwater quality were determined

Irrigation Water Resource Management for Sustainable Agriculture - the Ankobra Basin, Ghana

Two irrigation water assessment methods, the USDA classification scheme and the soil infiltration potential, were applied to water from three different locations (Ankwaso, Dominase, and Prestea) of the Ankobra River basin in Ghana, to evaluate its effectiveness as a sustainable water resource for irrigation. The study classifies water from all three locations into the low salinity, low sodicity zone with Prestea and Ankwaso having waters of the highest sodicity and salinity, respectively. A classification scheme based on effects of the water on the hydraulic properties of soils reveals that water from all locations of the basin has the potential to affect the infiltration properties of soils, especially when applied over a long period of time. Linear regression analysis indicates a strong relationship between electrical conductivity (EC) and sodium adsorption ratio (SAR) at R2 = 0.773 (n=30) for Prestea. This relationship is probably due to the fact that Na, Mg, and Ca, which are the major determinants of water SAR, are also the major contributors to the water EC at Prestea, and this is probably due to surface mining activities, which encourage the weathering of calcic and albitic feldspars. Time series analysis reveals that EC and SAR for Dominase and Prestea, respectively, have increased from 1989 to 1992. On the other hand, SAR and EC have been decreasing since 1989, for the two locations. Forecast data from the time series analyses agree well with observed data, at 0.01 level of significance. Projections were made at ten time steps ahead of 1992 using time series analysis