School of Physical and Mathematical Sciences
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Item Pathfnder elements and indicator minerals of Au from the Kubi Gold ore deposits in Ghana(Environmental Earth Sciences, 2023) Nzulu, G.K.; Högberg, H.; Eklund, P.; Hultman, L.; Nude, P.M.; Yaya, A.; Magnuson, M.The Au mineralization in the Kubi Gold Mining Area in the Birimian of Ghana is associated with garnet (about 85 vol.%), magnetite, pyrrhotite, arsenopyrite, and sulfde minerals, as well as quartz with gold and calcite. These minerals and the included elements can act as indicator minerals or pathfnder elements. For the present work, we collected samples from drill holes at diferent depths, from the alluvial zone (0–45 m) to the ore zone (75–100 m). The distributions of minerals and elements in the rocks that act as indicator minerals and pathfnder elements in the concession area were investigated along the drill hole cross sections. X-ray difraction shows that the samples contain garnet, pyrite, periclase, and quartz as the main indicator minerals. By energy-dispersive X-ray spectroscopy, Fe, Mg, Al, S, O, Mn, Na, Cu, Si, and K are identifed as corresponding pathfnder elements. The results indicate that the Au mineralization in the Kubi Mine area correlates mostly with the occurrence of garnet, pyrite, goethite, and kaolinite in the host rocks, which show towards the surface increasingly hematitic and limonitic alteration in form of Fe(oxy-)hydroxides.Item Impact of artisanal small-scale (gold and diamond) mining activities on the Offin, Oda and Pra rivers in Southern Ghana, West Africa: A scientific response to public concern(Heliyon, 2022) Nunoo, S.; Manu, J.; Owusu-Akyaw, F.K.B.; Nyame, F.K.The surface water systems of Ghana serve as a major source of drinking water, besides other multi-purpose benefit of hydro-electrical power generation and transportation. Thus, the dependence and benefits from such resources are of national interest. For instance, the Pra river of the South-Western surface water system of Ghana was a major consideration for a projected 5 billion m3 water demand in the year 2020 and “African Water Vision 2025”. In recent times, the colour state of the Pra river and similar surface water bodies of the Offin and Oda rivers has attracted intense public discussion. The prime issue relates to incessant illegal artisanal gold/diamond mining on or along these rivers. In order to assess the state of these rivers, water samples were taken, and analysed at the Council of Scientific and Industrial Research Laboratory (CSIR, Accra-Ghana) to investigate their physicochemical quality. The research objective was to assess the extent of their water pollution by measuring physico-chemical parameters of turbidity, colour, pH and content of selected metals. A total of 18 preserved bottled samples [(5 from Offin river and 2 boreholes), 5 from Oda river and 5 from Pra river and 1 borehole)] were analysed, and results compared with portable water standards as defined by the WHO and CSIR (GS-175-1) of Ghana. Results on turbidity, colour, mercury and iron from the river and water samples generally exceed WHO or GS 175-1 limit. The Pra river recorded the most alarming result; range for turbidity (2,010 to 2,745 NTU), colour (3,000 to 4,500 Hz), total suspended solutes (2,240 to 2,570 mg/L) and total dissolved solutes (97.80–99.60 mg/ L, excluding 319.00 to 25,440 mg/L). The Oda river shows lowest parameter values among the three rivers, as the areas have been dormant from illegal gold mining for 5 years. Current data suggests polluted river bodies and boreholes, and that none of these water resources meets the portable water consumption criteria unless treated prior to usage. As the current state of the water bodies may incur higher cost of water treatment or purification, an integrated water governance under Ghana's Ministry of Water Resource, Work and Housing, and the Minerals Commission and Environmental Protection Agency are recommended for the management of these valuable water resources.Item Characterisation and quality assessment of surface and groundwater in and around Lake Bosumtwi impact craton (Ghana)(Sustainable Water Resources Management, 2021) Loh, Y.S.A.; Addai, M.O.; Fynn, O.F.; Manu, E.Conventional graphical methods have been used to classify water in Lake Bosumtwi and groundwater around the lake. The study also assessed the suitability of these water resources for agricultural use. Results indicate slightly acidic, moderately hard to very hard groundwater with alkaline earth concentrations exceeding alkali metals. In contrast, the lake water is alkaline, showing alkalis in excess over alkaline earth metals. Weak acids exceed strong acids in both lake/groundwater. Rock weathering largely controls groundwater and lake water chemical compositions, resulting mainly in Ca–Mg–HCO3 groundwater and Na–HCO3 lake water types. Thus, suggesting that there is no apparent incipient relationship, which benefts the primary aquifer system in terms of recharge. Water quality indices suggest groundwater of good to excellent quality for human consumption and other domestic use. An evaluation of lake/groundwater based on salinity, sodicity and bicarbonate hazard reveals that the groundwater is generally suitable for irrigation whiles the lake water is not suitable for irrigation. However, the lake water may be used in generous amounts on highly permeable soils and salt-tolerant crops under special soil and water management practices.Item Geochemical constraints on provenance and source area weathering of metasedimentary rocks from the Paleoproterozoic (~2.1 Ga) Wa-Lawra Belt, southeastern margin of the West African Craton(Geodinamica Acta, 2019-09-27) Asiedu, D.K.; Agoe, M.; Amponsah, P.O.; Nude, P.M.; Anani, C.Y.The Wa-Lawra Belt which is situated in the northern part of Ghana consists of Paleoproterozoic Birimian fine metasedimentary rocks metamorphosed to greenschist facies, particularly, in the western part. A whole-rock geochemical study of these metasedimentary rocks was undertaken to unravel their source area weathering, provenance and tectonic setting. Geochemical characteristics of the studied shales show that they are immature in nature and first cycle in origin, with little or no recycled component. Compared to Post- Archaean Australian Shales (PAAS), the studied shales indicate reduction in Zr, Hf, La, Nb, Th and Ta being the high field strength elements and evidences of transition metal enrichments in V, Ni, Sc, Co, and Cr. Major element geochemistry indicates that the shales were subjected to slight potassium metasomatism after deposition. Pre-metasomatized Chemical Index of Alteration calculations indicates that weak to moderate degree of chemical weathering took place at the sediment source area. Co-Th-La-Sc systematics reveals a combination of mafic and felsic provenances for the shales. Eu/Eu* together with values of Th/U and some abundances of trace elements show that the shales were mainly derived from juvenile rocks. Average REE model calculations suggest that the source materials are composed of about 49% basalt, 16% TTG and 35% granite.Item Geochemical constraints on provenance and source area weathering of metasedimentary rocks from the Paleoproterozoic (~2.1 Ga) Wa-Lawra Belt, southeastern margin of the West African Craton(GEODINAMICA ACTA, 2019-09-27) Asiedu, D.K.; Agoe, M.; Amponsah, P.O.; Nude, P.M.; Anani, C.Y.The Wa-Lawra Belt which is situated in the northern part of Ghana consists of Paleoproterozoic Birimian fine metasedimentary rocks metamorphosed to greenschist facies, particularly, in the western part. A whole-rock geochemical study of these metasedimentary rocks was undertaken to unravel their source area weathering, provenance and tectonic setting. Geochemical characteristics of the studied shales show that they are immature in nature and first cycle in origin, with little or no recycled component. Compared to Post- Archaean Australian Shales (PAAS), the studied shales indicate reduction in Zr, Hf, La, Nb, Th and Ta being the high field strength elements and evidences of transition metal enrichments in V, Ni, Sc, Co, and Cr. Major element geochemistry indicates that the shales were subjected to slight potassium metasomatism after deposition. Pre-metasomatized Chemical Index of Alteration calculations indicates that weak to moderate degree of chemical weathering took place at the sediment source area. Co-Th-La-Sc systematics reveals a combination of mafic and felsic provenances for the shales. Eu/Eu* together with values of Th/U and some abundances of trace elements show that the shales were mainly derived from juvenile rocks. Average REE model calculations suggest that the source materials are composed of about 49% basalt, 16% TTG and 35% granite.Item Petrology and geochemistry of TTG and K-rich Paleoproterozoic Birimian granitoids of the West African Craton (Ghana): Petrogenesis and tectonic implications(Precambrian Research, 2019-10-14) Sakyi, P.A.; Addae, R.A.; Su, B.; Dampare, S.B.; Abitty, E.; Su, B-C.; Liu, B.; Asiedu, D.K.We conducted petrologic, geochemical and isotopic studies on Paleoproterozoic Birimian granitoids that intrude the Bole-Nangodi Belt in northern Ghana, in southeastern West African Craton (WAC), to constrain the geodynamic evolution of the Birimian Supergroup. The rocks are potassic (K)-rich granitoids (KRGs), tonalities, trondhjemites, granodiorites (TTGs), pegmatite and aplite. The K2O contents of the KRGs are up to 5 wt%, with generally high concentrations of Rb, Ba, Sr, Cr and Ni. They are highly fractionated calc-alkaline I-type granitoids, enriched in LILE and LREE relative to HREE and HFSE. Chondrite-normalized REE diagrams indicate fractionated LREE (average LaN/SmN=5.05) and HREE (GdN/YbN=4.56) patterns, with slight negative Eu anomalies (average Eu/Eu*=0.75). This may indicate an evolved magma source with varying degrees of plagioclase fractionation. The KRGs share similar geochemical characteristics with the TTGs into which they intrude. Both rock types are characterized by Ba and Th enrichment and depletion in Nb‐Ta, Zr‐Hf, and Ti, which are typical characteristics of subduction-related magmas. The pegmatite-aplite association is slightly geochemically different and may have formed at a time later than the KRGs. The ԐNd(2.1 Ga) values range from+0.90 to+1.24 and −0.86 to+1.37 respectively for the TTGs and KRGs, with TDM1 ages of 2.34–2.38 Ga and 2.36–2.53 Ga and TDM2 ages of 2.21–2.24 Ga and 2.22–2.39 Ga respectively. These indicate their juvenile character, possibly a depleted mantle source with minor contributions from a pre-Birimian (or Archean?) crustal material in their source material(s). The TTGs and KRGs are volcanic arc granites (VAG) and syn-collisional (Syn-COLG) granites, with formation temperatures and pressures of ~640–750 °C and ~2–6 kbar respectively. Based on the high temperatures, I-type signature, calc-alkaline nature and other geochemical characteristics, we infer that the TTGs, KRGs and pegmatite-aplite association developed under high oxygen fugacity conditions in an orogenic tectonic setting related to subduction. Thus, our geochemical and isotopic results are consistent with an island arc tectonic setting arising from subduction–accretion processes, which are typical for the Paleoproterozoic terranes of the WAC. These processes may have contributed to the amalgamation of the Columbia (Nuna) supercontinent during the Paleoproterozoic (2.1–1.8 Ga) orogeny.Item Ultramafic–mafic and granitoids supra‐subduction magmatism in the southern Ashanti volcanic belt, Ghana: Evidence from geochemistry and Nd isotopes(Geological Journal, 2019-05) Dampare, S.B.; Shibata, T.; Asiedu, D.K.; Okano, O.; Osae, S.K.D.; Atta-Peters, D.; Sakyi, P.A.Geochemical and Nd isotope data are presented for Palaeoproterozoic ultramafic to mafic rocks and granitoids which are associated with volcanic rocks in the southern part of the Ashanti greenstone belts of Ghana. The Prince's Town granitoids display subduction‐zone geochemical features, with some showing signatures similar to high‐SiO2 adakites (HSA). Their initial εNd (2.1 Ga) values range from −1.01 to +2.92, and they have TDM2 of 2.17–2.51 Ga. The gabbros show slightly LREE‐depleted and ‐enriched patterns, Th–U troughs, negative Nb, Zr–Hf and Ti anomalies, spikes in Sr and Pb, have εNd (2.1 Ga) values ranging from −1.23 to +5.23, and TDM2 values from 2.08 to 2.57 Ga. The Ahama ultramafic body is characterized by two groups of pyroxenites. Both groups show LREE enrichment patterns, display Th–U and Nb–Ta troughs, minor or pronounced negative Zr–Hf and Ti anomalies. However, the Group I pyroxenites exhibit minor Ce anomalies and lower total REE contents (28.1–32.8 ppm) whereas Group II pyroxenites show significant negative Ce anomalies and relatively higher total REE contents of 57.1–124 ppm. The pyroxenites show negative initial εNd (2.1 Ga) values (−0.58 to −5.68) and have TDM2 values of 2.52 to 2.75 Ga. The pyroxenitic and gabbroic rocks were most likely originated from a subduction‐related lithospheric mantle. The Aketakyi ultramafic–mafic complex is made up of mainly cumulate dunite, harzburgite, pyroxenites, and gabbro. The rocks display LREE‐depleted to flat patterns with low total REE contents (1.71 to 22.3 ppm) and demonstrate a supra‐subduction affinity. They show high positive initial εNd (2.1 Ga) values (+3.69 to +4.93), and TDM2 values of 1.99 to 2.04 Ga, which suggest that they were derived from depleted mantle magmas and were juvenile at their time of formation. The Nd isotopic data provides evidence for a possible contamination of the juvenile Birimian crust of the southern Ashanti belt by some amount of a pre‐Birimian (or Archaean?) crustal material. The trace element and isotopic signatures as well as the field relations of the studied granitoids and mafic–ultramafic rocks show they were derived through supra‐subduction‐related magmatism during the Palaeoproterozoic.Item Use of termitaria in surficial geochemical surveys: Evidence for >125-μm size fractions as the appropriate media for gold exploration in northern Ghana(Geochemistry Exploration Environment Analysis, 2010-11) Arhin, E.; Nude, P.M.Extensive lateritization and widespread sheet wash and alluvial deposits characterize the thick regolith in the savannah regions of northern Ghana. As often is the case in these areas, the presence of these cover materials mask geochemical gold (Au) response in soils during surficial gold exploration. Anomaly detection thus becomes very difficult perhaps due to gold grain encrustation during lateritization and anomaly dilution by sheet wash deposits. Termite mound samples collected from areas of thick regolith, transported overburden and laterite cap in gold bearing areas of northern Ghana which were analyzed for gold defined anomalous zones. Gold contents were determined from size fractions consisting of -125 μm, +125-250 μm, +250-500 μm and +500 μm. The gold contents show relatively insignificant changes in concentration and in repeat samples in the - 125 μm and +125-250 μm size fractions, but there were significant differences when sub-samples were re-analysed in the coarser samples. Gold content repeatability was relatively better in the fine size fractions (- 125 μm) and decreased in the coarser size fractions. The study showed that termite mounds can be used as a geochemical sample medium to support conventional soil surveys especially in areas under thick regolith and transported cover, and the - 125 μm size fraction appears the most appropriate. © 2010 Geological Society of London.Item An assessment of the origin and variation of groundwater salinity in southeastern Ghana(Environmental Earth Sciences, 2010-09) Yidana, S.M.; Yidana, A.Groundwater from the major aquifers in southeastern part of Ghana was sampled to determine the main controls on groundwater salinity in the area. This paper uses multivariate statistical methods, conventional graphical methods and stable isotope data to determine spatial relationships among groundwaters from the different hydrogeologic units in the area on the basis of salinity. Q-mode hierarchical cluster analysis (HCA) was used to spatially classify the samples, whilst R-mode factor analysis was used to reduce the dataset into two major principal components representing the sources of variation in the hydrochemistry. Analysis of the major chemical parameters suggests that the principal component responsible for salinity increment in the area is the weathering of minerals in the aquifers. This factor is especially more significant in the upland areas away from the coast. The second factor responsible for salinity in the area is the combined effects of seawater intrusion, and anthropogenic activities. This study finds that four major spatial groundwater groups exist in the area: low salinity, acidic groundwaters which are mainly derived from the Birimian and Togo Series aquifers; low salinity, moderate to neutral pH groundwaters which are mainly from the Voltaian, Buem and Cape Coast granitoids; very high salinity waters which are not suitable for most domestic and irrigation purposes and are mainly from the Keta aquifers; and intermediate salinity groundwaters comprising groundwater from the Keta basin aquifers with minor contributions from the other major terrains. The major water type identified in this study is the Ca-Mg-HCO3 type, which degrades into predominantly Na-Cl-SO4 more saline groundwaters toward the coast. Stable isotope data analyses suggest that groundwater in the Voltaian aquifers is largely of recent meteoric origin. The Birimian and Togo aquifers receive a component of recharge from the tributaries of the Densu and Volta Rivers, after the waters have undergone evaporative enrichment of the heavier isotopes. In the Keta basin, recharge is mainly from precipitation but an observed enrichment of 2H and 18O isotopes is probably due to seawater and evaporative effects since the water table there is very shallow. An analysis of the irrigation quality of groundwater from the six aquifers in the study area using sodium adsorption ratio and electrical conductivity suggests that most of the aquifers supply groundwater of acceptable quality for irrigation. The only exception is the Keta Basin area, where extremely high salinities and SAR values render groundwater from this basin unsuitable for irrigation purposes. © 2010 Springer-Verlag.Item Significance of regolith mapping and its implication for gold exploration in northern Ghana: A case study at Tinga and Kunche(Geochemistry: Exploration, Environment, Analysis, 2009-01) Arhin, E.; Nude, P.M.The complex regolith in the savanna belts of northern Ghana is believed to be a major cause of the failure of gold exploration in the area. The present study highlights the integration of field regolith mapping, pitting and trenching in the classification of regolith and its significance to gold exploration at Tinga and Kunche in northern Ghana. These two areas are underlain by Birimian greenstones but have not seen any gold production apart from the reported gold occurrences known to be associated with the metavolcanic and metasedimentary rocks in the area. The importance of understanding the regolith, the landscape, and the sampling medium has not been seriously considered in past exploration programmes. The classification of the regolith regimes into ferruginous, relict, erosional and depositional regimes in the two study areas aided in determining the differences in the soil profiles, the source of the regolith materials and nature of weathering. For relict and erosional regimes, optimum depth of sampling was established to be between 0.2 and 0.4 m. However, for depositional regimes, because of the variable overburden thickness, the base of the transported materials was sampled. The pits and trenches dug also contributed in identifying the in-situ and transported regolith. The study shows that, in savanna areas of northern Ghana, relict regimes generally have preserved laterite profiles whereas the ferruginous, erosional and depositional regimes are associated with landscape modifications. © 2009 AAG/Geological Society of London.