Emmanuel Arhin

Significance of regolith mapping and its implication for gold exploration in northern Ghana: a case study at Tinga and Kunche

ABSTRACT 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.

Trace elements distributions at Datoko-Shega artisanal mining site, northern Ghana

AbstractEnvironmental geochemistry classifies elements into essential, non-essential and toxic elements in relationship to human health. To assess the environmental impact of mining at Datoko-Shega area, the distributions and concentrations of trace elements in stream sediments and soil samples were carried out. X-ray fluorescence analytical technique was used to measure the major and trace element concentrations in sediments and modified fire assay absorption spectrometry in soils. The results showed general depletion of major elements except titanium oxide (TiO2) compared to the average crustal concentrations. The retention of TiO2 at the near surface environment probably was due to the intense tropical weathering accompanied by the removal of fine sediments and soil fractions during the harmattan season by the dry north-east trade winds and sheet wash deposits formed after flash floods. The results also showed extreme contamination of selenium (Se), cadmium (Cd) and mercury (Hg), plus strong contaminations of arsenic (As) and chromium (Cr) in addition to moderate contamination of lead (Pb) in the trace element samples relative to crustal averages in the upper continental crust. However Hg, Pb and Cd concentrations tend to be high around the artisanal workings. It was recognised from the analysis of the results that the artisanal mining activity harnessed and introduces some potentially toxic elements such as Hg, Cd and Pb mostly in the artisan mine sites. But the interpretation of the trace element data thus invalidates the elevation of As concentrations to be from the mine operations. It consequently noticed As values in the mine-impacted areas to be similar or sometimes lower than As values in areas outside the mine sites from the stream sediment results.

Use of termitaria in surficial geochemical surveys: evidence for >125-μm size fractions as the appropriate media for gold exploration in northern Ghana

ABSTRACT 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.

Geochemical Background of Some Potentially Toxic and Essential Trace Elements in Soils at the Nadowli District of the Upper West Region of Ghana

Introduction: Use of universal baseline values, such as continental crustal averages, to assess health issues from trace elements in environmental soils may be fraught with challenges because the method only considers unmineralized rocks and soils in the determination of average crustal abundances or background values. Legislated guideline values are also for specific geographic locations in the environments. None of these take into account the human activities at a particular local community as the environmental conditions have dire influence on trace element mobility, concentrations, and storage in the surface soils. Aim: The aim of this article therefore is to evaluate site-specific geochemical background concentrations of some potentially toxic trace elements in the artisanal mine area and farmland soils of Nadowli District. Materials and Methods: The method involved collection of 29 samples of trace element from soils up to the depth of 20 cm. These samples were analyzed using inductively coupled plasma-mass spectrometry (ICP-MS) analytical technique. Results: The results of the trace element concentrations were statistically and graphically analyzed to isolate sets of background values that are better suited locally to identify and assess areas contaminated and depleted by trace elements. Local background values of 15.00 ppm was estimated for arsenic (As), 0.02 ppm for cadmium (Cd), 0.01 ppm for mercury (Hg), 35.0 ppm for zinc (Zn), 20.0 ppm for copper (Cu), and 0.40 ppm for selenium (Se). The study found that estimated local backgrounds for essential elements were in the range of the legislated guideline values and should be used to assess the environmental quality and health as well as develop environmental policies for environmental monitoring. The potentially toxic elements contrastingly have higher local background values for As and Cd and lower local background for Hg when compared with the legislated soil guideline values. Conclusion: In conclusion, for cleanup goals in environmental legislation and for the assessment of the impacts of trace elements on health in Nadowli District, these background values should be used.

Economic Importance of Termites and Termitaria in Mineral Exploration

Shelter comes to mind for staying alive. However the well-decorated buildings lose their beauty when termites feed on the wood members of the house. While they destroy the wood members of our shelters, they contribute also to human developments. Termites while transporting the inorganic and organic matters into their shelter, the nest in the termitaria, enriched the surrounding soils. Furthermore, the burrowing activities into the subsoils contribute to the development of soil profiles which help in agricultural production. The economic importance of termites extends to mineral exploration, particularly in regolith-dominated terrain, where mineral deposit haloes have been masked by exotic and redistributed weathered materials. Termitaria formed from deep-seated burrowed subsoil materials were able to show the real geochemical anomalies in such complex terrains. Termite mounds sampled and analysed for their element contents using XRF technique for multi-elements and fire assay (FA-AAS) for gold portrayed another economic significance of termites in the delineation of hidden mineral deposits. The case study revealed that the mounds are made up of several size fractions in which gold (Au) is enriched in a particular fraction. Additional economic advantage of termites realised from the study was that the complex regolith rendering determination of pathfinder elements from surface soils was possible from mounds formed from subsurface soils, brought to surface by them. Considering the declining trends especially in gold discoveries, often attributed to the complex regolith, pathfinder elements and gold anomalies concealed by the regolith can be determined and defined by sampling termitaria. It also concludes the suitability of termitaria as a sample medium, to support soil samples typically in areas under cover. It is further recognised that the <125 μm size portions of the termitaria are the most appropriate fraction that host gold signatures in the study area. We finally realised that the hidden gold anomalies in the thick complex regolith overburden were detectable using As and Zn identified as pathfinder elements in the termitaria samples.

Inherent Errors in Using Continental Crustal Averages and Legislated Accepted Values in the Determination of Enrichment Factors (EFs): A Case Study in Northern Ghana in Developing Environmental Policies

Health problems related to geological and environmental processes often have been assessed using enrichment factors derived from global and legislated accepted values. The petrological studies and the analysis of soils in this study reveals elements storage and concentrations in the environment exposed to life depends on several factors which are not incorporated using the example the continental crustal averages and the accepted legislated values. The results from the study suggest the establishment of local background values particularly from more large-scale surveys where quality and statistically significant environmental data had been collected for local background value estimation for enrichment factors. The continental crustal averages and legislated values either overestimate or underestimate the enrichment or depletion factors hence making policies developed from them unreal. General name granite can be given to a suite of rocks but their mineralogical and modal compositions will vary. Same continental crustal average can be used for them whilst disregarding the local environmental activities. The study concludes from the results in the petrological studies of rocks in Bongo and environmental soil studies at Nadowli that EFs calculated from the local background values can be used appropriately to propagate the true environmental policy to clean up the environment against the related health issues connected with the geogenic and anthropogenic processes than continental crustal averages as well as the legislated accepted values that may have no relationship with the study environment.