Inference of domain structure at elevated temperature in fine particles of monoclinic pyrrhotite (Fe7S8).

The thermal variation of the number of domains (nd) for Fe7S8 particles (within the size range 1-30 mm and between 20 and 300°C), has been inferred from the room temperature analytic expression between nd and particle size (L), the temperature dependences of the anisotropy energy constant (K) and the spontaneous magnetization (Ms) and, an assumed expression for the domain wall energy (Ew). It is found that nd increases or decreases with temperature rise depending on whether the inferred K(T) dependence is based on many defects in a domain wall, controlled by the volume reduction effect or the magnetostatic effect respectively. In either case however, nd is very weakly dependent on T which therefore points to a fixed domain multiplicity in the Fe7S8 particles within the temperature range specified. Based on this conclusion, it is suggested that the nucleation or denucleation of domain walls may be difficult processes in the acquisition of thermoremanent magnetization (TRM) in Fe7S8 particles. JOURNAL OF THE GHANA SCIENCE ASSOCIATION Volume 1 Number 1, July (1998) pp. 118-12

The coercive force of fine particles of monoclinic pyrrhotite (Fe7S8), between 77 K and 600 K

The temperature dependence of coercive force (Hc) between 77 K and 600 K has been investigated for fine particles of monoclinic pyrrhotite (Fe7S8) of < 1 mm and 1- 30 mm particle sizes. The study has shown that Hc is strongly dependent on temperature, as temperature rises above room temperature (293 K) to near the Curie point (Tc = 593 K). On the other hand, Hc was observed to be weakly dependent on temperature, between liquid Nitrogen temperature (77 K) and room temperature. For the entire temperature range, the data can be expressed satisfactorily as a second order polynomial, Hc (T) = aT 2 + bT + g where a, b and g are numerical constants for a given particle size fraction. The form of this analytic expression is different from that obtained by the authors for the coercive force dependence on temperature which they plausibly expressed in the form Hc (T) µ (1 - T/Tc)q where q < 1, for the temperature range 293-573 K, but which breaks down below 293 K. By considering the variation of the coefficient g with particle size, within the size range 1 and 30 mm it is shown that g(L) = 75.6 L-0.33 kA m-1. JOURNAL OF THE GHANA SCIENCE ASSOCIATION Volume 1 Number 2, January (1999) pp. 90-9

Prospecting for groundwater using the electromagnetic method in the Voltaian Sedimentary Basin in the Northern region of Ghana – a case study of the Gushiegu-Karaga district

The Gushiegu-Karaga District is one of the most deprived areas in the Northern Region of Ghana in terms of water supply. Only about 15% of the population have access to potable water, and has a chronic water supply problem. In an attempt to improve the water supply situation the Ghana Rural Water Project (GRWP) of the World Vision initiated Conrad-Hilton Funded Borehole Water Project in Gushiegu-Karaga district, with the objective of drilling 100 wet boreholes. In this study a ground geophysical technique, the Electromagnetic (EM) method using the GEONICS EM 34-3 equipment has been used to delineate and locate water-bearing zones. The EM profiles of interest were analysed and interpreted qualitatively to locate suitable and potential sites to drill boreholes for groundwater abstraction. Drilling results and findings from drill logs show that the mean depths of productive and unproductive boreholes were 41.0 and 64.0 m respectively. The groundwater producing zones were found to be between 30.0 m and 60.0 m depths. A minimum yield of 10 litres per minute has been used as the basis for a borehole to be successful. However, 60% success rate was achieved out of 100 boreholes drilled. When compared with the success rate of drilling productive boreholes, the 60% success achieved was higher. It is recommended that the EM method, which is fast, efficient, less laborious and cost effective, be used to locate suitable borehole sites in programmes aimed at accelerated rural water supply to the rural communities in the district. Journal of Science and Technology Vol. 25(2) 2005: 53-6

Results of pre-drilling potential field measurements at the Bosumtwi crater

Gravity and magnetic measurements were carried out at the Bosumtwi crater to determine the geophysical signature of the crater. Land gravity data was acquired at 163 locations around the structure and on the shore of the lake. The separation between the gravity stations was 500 m for radial profiles, but 700-1000 m along roads and footpaths that ran parallel to the lakes shore. Additionally, a marine gravity survey was carried out along 14 north-south and 15 east-west profiles on the lake. Magnetic data was also acquired along 14 north-south profiles on the lake. In all marine surveys, the line spacing was 800 m, and navigation was provided by a Garmin 235 Echo Sounder/GPS. The gravity signature of the crater is characterized by a negative Bouguer anomaly with an amplitude of about 18 mgal. Using the seismic results as constraints, the gravity model obtained indicates the central uplift at a depth of 250 m. The negative anomaly is the contribution of the gravity deficiencies due to fractured and brecciated rocks in the rim area and below the crater floor, the impact breccias within the crater, and the sedimentary and water infilling of the lake. Magnetic modeling yielded a model for the causative body, which is located north of the central uplift: the model has a magnetic susceptibility of 0.03 S.I. and extends from a depth of 250 to 610 m. The causative bodies have been interpreted as impactites.The Meteoritics & Planetary Science archives are made available by the Meteoritical Society and the University of Arizona Libraries. Contact [email protected] for further information.Migrated from OJS platform February 202

Evaluation of Aquifer Characteristics of Voltaian Sedimentary Rocks in the Brong Ahafo Region of Ghana

Groundwater potential of the sedimentary formation in the Brong Ahafo Region of Ghana has been evaluated using computed transmissivity and specific capacity values. Data on multiple step and constant-discharge tests on twenty (20) boreholes were analyzed. The Cooper-Jacob’s straight line analytical approach was used to determine the aquifer characteristics. Computed transmissiv-ity coefficients of the underlying aquifer ranged widely from 0.82 – 61.27 m2d-1. The specific ca-pacity values obtained varied between 0.59 and 75.20 m3d-1m-1. Total head loses of the boreholes ranged generally between 5.49 and 99.2%. Hydrogeologically, the aquifer systems can be described as fairly heterogeneous in accordance with Krasny’s transmissivity classification model. Ground-water potential of the sedimentary aquifer system could be classified as high to intermediate to yield substantial groundwater resource for domestic and industrial water supply. To secure sub-stantial quantity of water for sustainable water supply in areas underlain by this sedimentary aqui-fer system in Ghana, integrated geophysical approach including 2D-Continuous Vertical Electrical Resistivity (CVES) survey, and other related tools such as Remote Sensing (RS) and Geographical Information Systems (GIS) should be used to enhance the delineation of deeper aquifer zones of high groundwater potentialKeywords: Ghana, Brong Ahafo, groundwater, sedimentary rocks, transmissivity, aquifer, sustainable, specific capacit

Prospecting for Groundwater in the Bawku West District of the Upper East Region of Ghana Using the Electromagnetic and Vertical Electrical Sounding Methods

An integrated approach involving the Electromagnetic (EM) and Vertical electrical sounding (VES) survey methods, has been used to locate potential drilling sites to find groundwater for twenty (20) rural communities in the Bawku West District of the Upper East Region of Ghana. The EM method involved the use of the Geonics EM 34-3 equipment to obtain traversing data for the horizontal dipole (HD) and vertical dipole (VD) modes at station intervals of 10 m for a 20 m coil separation. The EM survey provided subsurface information relating to positions of high electrical conductivity anomalies which presumably pointed to locations for groundwater structures. As a follow up, the VES was carried out with respect to the anomalous positions, using the dipole-dipole configuration with the McOhm-EL resistivity meter. The VES enabled the estimation of the depth of the weathered layer to the bed rock. The results of the VES data were interpreted quantitatively by modeling using IX1D V.3 software. The study identified prospective sites for drilling of bore-holes to provide potable water for the communities. Results for the VES suggested that the aquifer zones in the area under study are mainly deeply weathered and fractured. The lithology for some of the recommended drilled points correlated well with the results obtained from the EM and VES investigations. The aquifer depth was found to be between 10 and 40 m with an average value of 21.5 m. The depth of the basement rock from the surface was 21.4 m. The estimated yield of the boreholes drilled within the area was between 10 and 500 litres/min with an average value of 136.8 lit/min. the success rate was found to be about 95%. The integrated use of EM and VES surveys has been found to be very successful in locating groundwater resources for the rural communities with the area studied

Spectral time-domain induced polarisation and magnetic surveying - An efficient tool for characterisation of solid waste deposits in developing countries

Time-domain induced polarisation and magnetic data were acquired to map and characterise the decommissioned and un-engineered municipal solid waste disposal site of the Kwame Nkrumah University of Science and Technology, located in the Kumasi Metropolis of Ghana. In this survey. 13 induced polarisation profiles 500-800 m long and 26 magnetic profiles 400-800 m long were acquired. In addition, two boreholes were drilled to help in the interpretation of the geophysical data. The study was carried out with the aim of determining the risk posed by the waste deposit to the quality of the soil and the ground water system, which is the main potable water supply for the Secondary School, the University Teaching Hospital and the Veterinary School, situated within the catchment area of the site. Full-decay 2-D time-domain induced polarisation inversions in terms of Cole-Cole parameters were used for interpreting the induced polarisation data. The chargeability, resistivity and normalised chargeability distributions, together with the magnetic results, aided in a full characterisation of the site geology, the waste and the associated pollution plume. In particular, clear contrasts in resistivity and the polarisation parameters were found between the saprolite layer and the granitic bedrock, which are the main lithological units of the area. Furthermore, it was found that the Kwame Nkrumah University of Science and Technology waste deposit is characterised by a low-chargeability and low-resistivity signature and that the low-resistivity area spreads out from the waste deposit into the permeable saprolite layer, indicating the presence of a leachate plume. A fracture zone in the granitic bedrock beneath the waste deposit, which is a potential conduit for leachate contamination of the ground water system, was also identified. The study thus provides the information needed for assessing the future impact of the waste on the water quality in the area and for designing risk-mitigation actions