Browsing by Author "Manu, J."

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Establishing the Kojina Gold Deposit as Aviable Mining Venture for Sameva Ltd, Ghana
(University of Ghana, 2014-10) Mensah, E. K. A.; Manu, J.; Afenu, R.; University of Ghana College of Basic and Applied Sciences, School of Physical and Mathematical Sciences, Department of Earth Science
Assessment of viability of an ore deposit depends on the accurate estimation of the quantity and quality of the commodity, which is a function of the sample data quality. SAMEVA Limited, a fully owned Ghanaian company, wants to acquire Kojina Gold deposit as an investment opportunity in the gold industry of Ghana. The decision to invest in the mining industry comes with huge capital requirement and the associated risks are very high. The major objectives with regards to evaluating the viability of the deposit are; to define appropriate mineralized zone based on available drill core data, use an appropriate estimation method to create a model that accurately predicts grade and tonnes and finally use a suitable financial model to establish the viability or otherwise of the Kojina project. An Ordinary krigged geostatistical model was used to estimate the quantity and quality of gold within the deposit based primarily on diamond drill holes. The Net Present Value (discounted cash flow) method of financial analysis was used to arrive at the investment decision on the Kojina deposit. Capital and Operating Costs estimates used were based on benchmarking of adjacent mine operations within the catchment area of Kojina. Using appropriately planned drilling and representative sampling as well as predominant use of diamond core gives more accurate information with no contamination and has structural orientation which allows for better geologic and structural mapping therefore helping define the mineralization zones more accurately. The mineralization zone defined based on reverse circulation holes gave 37,413,998 tonnes at 1.47g/t whereas that based on the diamond holes gave 26,674,888 tonnes at 1.57g/t. Again, based on the more accurate deductions from diamond holes, the Net- Present value of the project was estimated at USD 187,796,325 with a payback period of three years.
Evaluation Of Kobada North Gold Resource, Mali, Using Two Different Drill Directions
(University of Ghana, 2013-11) Nkansah, J.Y.; Manu, J.; Yidana, S.M.; University of Ghana, College of Basic and Applied Sciences, School of Physical and Mathematical Sciences, Department of Earth Science
The 22.5 km2 Kobada project which is located in the Kangaba Cercle of the Koulikouro region of Mali, is owned and operated by African Gold Group Inc. (AGG), a Canadian junior exploration company (Fig. 1.1 shows perimeter for 22.5 km2; fig. 1.9 shows perimeter for consolidated permit of 215 km2). Notably the permit hosts a soil anomaly greater than 500 ppm arsenic that extends over 12 km of strike length and one kilometre of width, which is offset to the west of extensive artisanal surface saprolite and placer gold mining activity. Most importantly just about two kilometres of this strike length host the Kobada gold zone referred to as “Kobada Zone 1” which has over 1.6 million oz (oxide) gold in 59.1 million tonnes grading 0.87 g/t at the 0.3 g/t cut-off and still expanding in both directions along strike and at depth. Historically, the major drilling direction in the Kobada zone 1 have been on azimuth 290⁰. However recent structural investigations indicate that whilst the Kobada Shear Zone exhibits a N20E (easterly dipping) strike, the mineralisation most actually occurs in quartz vein swarms with an average strike orientation that is E-W (azimuth 190⁰-200⁰), confined within the boundaries of the Kobada Shear Zone. There is an area in the northern most 400m of the current resource where it is covered with drill information of both orientations by which the project sets out to test which drilling direction will yield the most gold resource. Gold mineralisation has been constrained by the development of wireframes modeled at a 0.2 g/t Au lower cut-off grade at an average dip of 74o respectively for both drilling directions. For subsequent analysis and estimation, two geostatistical domains, the saprolite (modelled at an average dip of 74o ) and the duricrust domain (a roughly flat lying horizontal hard pan on top of the saprolite) have been used. Variography was completed on the 2m composite for the duricrust and saprolite domains for each drilling direction. Using the ordinary kriging methodology, drilling to the west is relatively continuous and hence more viable than drilling south, with the west yielding in excess of 15,000 ounces more in the various respective grade cut offs. Geological and structural models have been recommended as well as closing in the drill spacing to help establish more confidence in the resource estimate.
Evolutionary Trends for the Auriferous Hydrothermal Fluids Inclusions: A Microstructural Study of the Emplacement of Banded Quartz Veins in the Birimian Rocks in Southern Ghana
(2012) Hayford, E.K.; Manu, J.; Nyarko Odei, F.
Using polarizing microscope, the Scanning Electron Microscope (SEM) and the LINKAM THM 600, techniques, genetic connections between opening of space, the filling with mobile hydrothermal fluid phase, of banded gold quartz veins from the Birimian rocks were studied. The internal structure and the filling along the vein-wall contact suggest a crack-seal mechanism of emplacement. Observations of inhomogeneous extinction of bands under crossed polars, show the opening direction across the vein. The ion content of the fluid inclusion that find their way into the interstice are controlled by low frequency and temperature. Microthermometric data on primary inclusions indicate that there are two main types of fluids: partly aqueous (CO2-rich ) fluid, and aqueous (H2O- rich,) fluid. The limited range of the degree of fill (0.5 to 0.7) for the CO2 – rich and H2O – rich inclusions indicates the original homogeneous fluid. The CO2-rich fluids homogenize at a higher temperatures (350 – 400°C) than the H2O-rich fluids (310 – 370°C) and had salinity ≈5 wt % NaCl equiv. while H2O-rich fluid had salinity ≈16 wt % equiv. Dominant trace gases in both fluids are CH4 and N2. Observations suggest that the geometric peculiarities of macroscopic growth mechanism may account for capillary effects. Based on this consideration, a simple quantitative model of quartz vein formation is proposed. This model provides a possible origin for the enhancement and maintenance of a diffusional mass transfer from the matrix to the position of the crack. The study of the development of such veins and dikes with discontinuities, is a vital tool to the discovery of hydrothermal gold and other economic minerals. It can also helps to understand crystal growth in localized weak planes within massive blocks of quartz, which in time and space may preferentially accommodate further brittle deformation; a phenomena which often affects long term sustainability of engineering projects such as hydro-dams and tunnels.
Geochemical and Sm-Nd isotopic evidence for the composition of the Palaeoproterozoic crust of the West African Craton in Ghana
(Geological Journal, 2018-11) Sakyi, P.A.; Manu, J.; Su, B.X.; Kwayisi, D.; Nude, P.M.; Dampare, S.B.
The metasedimentary rocks of the Sefwi and Lawra volcanic belts in Ghana respectively were analysed for their major and trace elements and Sr‐Nd isotopic compositions to constrain the provenance, palaeo‐weathering conditions, and tectonic setting of the rocks. Geochemical characteristics of the metasedimentary rocks show low to moderate chemical weathering in their source regions and the rocks are interpreted to have been derived from mixture of mafic and felsic rock components. The LREE show much enrichment in relation to the HREE (LaN/LuN, 4.67‐11.66). The εNd (2.1 Ga) values of −0.12 to +3.72 strongly suggest that the source of the sedimentary rocks was derived from a depleted mantle source and that they were most likely produced in an almost entirely oceanic environment with minor influence from the continental crust. The Nd model ages ranging from +2.05 to 2.41 Ga suggest possible contributions of a pre‐Birimian crustal material (or Archaean?) in the source material of the volcanic rocks. The rock types that contributed as detritus to the Birimian metasedimentary rocks were mainly pyroclastics and basalts, and their REE patterns suggest that the contribution to the phyllites can be modelled after 20% basalt, 13% andesite, and 67% dacite. Similarly, the schists can be modelled as a mixture of 16% basalt, 34% andesite, and 50% dacite. The Nd isotopic modeling implies that the bulk of the sedimentary detritus was supplied by the Palaeoproterozoic volcanic arc with contributions of less than 10% from the pre‐Birimian crust (Archaean?).
Geochemistry and Alteration Mapping of the Paboase Deposit at Chirano Gold Mines, Ghana
(University of Ghana, 2014-06) Afloe, A.B.; Manu, J.
The Paboase deposit located in the Chirano gold district is hosted in Paleoproterozoic rocks within the Sefwi-Bibiani volcanic belt of the Birimian, which has been regionally metamorphosed to greenschist facies. Gold mineralization at Paboase is largely hosted by albite-pyrite-carbonate altered mafic and porphyry intrusive rocks rather than Birimian sedimentary rocks and graphitic shear zones which are well known style of mineralization in southwest Ghana. Multi-element geochemistry shows a quite weak fractionation trend among the mafic rocks, despite the doleritic and gabbroic textures. One different exotic mafic dyke signature can be recognised. Amongst the porphyries, two different compositional groups were recognized. There is a small scale intermixing of felsic dykes within mafic volcanics.The dominant alteration signature is intense albitisation along with ferroan dolomite and pyrite. There is about 150 m wide zone where the Analytical Spectral Device (ASD) maps strong carbonate alteration. The proximal alteration is carbobonate-albite-pyrite. This is surrounded by a distal halo of sericite-chlorite. Within the porphyries, the mineralogy is sericite-rich. Sericite-chlorite alteration is very widespread in the mafic rocks. Paboase has a Tungsten-Molybdenum-Bismuth-Terrarium (W-Mo-Bi-Te) signature. The Mo, Bi and Te have a strongly skewed distribution, and they are highly correlated with gold, so their usefulness as pathfinders is limited. The tungsten is remarkably uniformly distributed in the albite-dolomite rocks, and has a halo extending far beyond the footprint of the gold. Tungsten is therefore the best pathfinder for gold at Paboase. The host rocks for the anomalous W are essentially just albite-pyrite-dolomite rocks. Arsenic is clearly depleted in the proximal parts of the system compared to the pelitic sedimentary hosted graphitic shear zones of the Ashanti and Bogoso deposits in Ghana. It is suggested that the depletion of arsenic is as a result of flushing the rocks with an oxidized fluid early in the history of the system.
Geochemistry of Paleoproterozoic metasedimentary rocks from the Birim diamondiferous field, southern Ghana: Implications for provenance and crustal evolution at the Archean-Proterozoic boundary
(Geochemical Journal, 2004-01) Asiedu, D.K.; Dampare, S.B.; Sakyi, P.A.; Banoeng-Yakubo, B.; Osae, S.; Nyarko, B.J.B.; Manu, J.
Metagraywackes and metapelites from the Paleoproterozoic Birimian Supergroup in the Birim diamondiferous field, southern Ghana, were analyzed for their major and trace element contents. Compared to early Proterozoic crust, the metasedimentary rocks are enriched in ferromagnesian elements but depleted in rare earth elements (REE), high field strength elements (HFSE) (with exception of Zr), and Th. They show REE patterns similar to their Archean counterparts. The chemical data indicate that the sediments were derived from a local source of mixed felsic-mafic composition, with the latter dominating. The source rocks were the basaltic to dacitic volcanic rocks and granitoids within the Birimian greenstone belts. The chemical data further suggest their deposition in a tectonic setting comparable to modern island arcs, and that minimal old upper crust (i.e., pre-Birimian sources) was involved in their formation. The analyzed metasedimentary rocks have Eu-anomalies and GdN/YbN, Sm/Nd, Th/Sc, Cr/Sc and Cr/Th ratios that closely resemble those of their Archean counterparts, and therefore inconsistent with models suggesting abrupt compositional changes in upper crust at the Archean-Proterozoic boundary. © 2004 by The Geochemical Society of Japan.
Hydrologic fluxes in the Volta River watershed : A paleo-terrestrial environment in West Africa
(2010) Hayford, E.K.; Manu, J.; Asiedu, D.
The hydrologic cycle plays an important role in carbon cycling, due to the coupling of vapour release and CO2 uptake during photosynthesis. This coupling, expressed as water use efficiency of transpiration ratio, can provide an inexpensive alternative for estimating the Net Primary Productivity (NPP) of terrestrial ecosystem. Stable isotopes of hydrogen and oxygen and long-term hydrologic and meteorological data together with stoichiometric relations of water and carbon are used to constrain water and carbon balances for the Volta River watershed. Soils annually respire 0.199 Pg C, and the balance of these fluxes or Net Ecosystem Productivity (NEP) is +0.029 Pg C Yr-1, implying an annual flux of CO2 to the atmosphere. Annually, the Volta river watershed receives about 380 km3 of rainfall. Approximately 50% of this volume of water is returned to the atmosphere through plant transpiration. Associated with annual transpiration flux is a carbon flux of 0.170 × 1015 g C yr-1 or 428 g C m-2 yr-1 from the terrestrial ecosystem. Modeled estimates of heterotrophic soil respiration exceed slightly the NPP estimate, implying that carbon flux to and from the Volta river watershed is close to being in balance or the watershed is a small annual source of carbon dioxide to the atmosphere. In addition to terrestrial carbon flux, the balance of photosynthesis and respiration in Volta Lake is also examined. The lake was found to release carbon dioxide to the atmosphere, although the magnitude of the flux is smaller than that of the terrestrial ecosystem.
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.
Origin and tectonic significance of the metavolcanic rocks and mafic enclaves from the Palaeoproterozoic Birimian Terrane, SE West African Craton, Ghana
(Geological Magazine, 2020-03-12) Sakyi, P.A.; Su, B-X.; Manu, J.; Kwayisi, D.; Anani, C.Y.; Alemayehu, M.; Malaviarachchi, S.P.K.; Nude, P.M.; Su, B-C.
The Palaeoproterozoic Birimian Supergroup of the West African Craton (WAC) consists of volcanic belts composed predominantly of basaltic and andesitic rocks and intervening sedimentary basins composed predominantly of wackes and argillites. Mafic metavolcanic rocks and granitoid-hosted enclaves from the Palaeoproterozoic Lawra Belt of Ghana were analysed for geochemical and Sr–Nd isotopic data to constrain the geological evolution of the southeastern part of the WAC. The metavolcanic rocks display mainly tholeiitic signatures, whereas the enclaves show calc-alkaline signatures. The high SiO2 contents (48.6–68.9 wt%) of the enclaves are suggestive of their evolved character. The high Th/Yb values of the samples relative to that of the mantle array may indicate derivation of their respective magmas from subduction-modified source(s). The rocks show positive εNd values of þ0.79 to þ2.86 (metavolcanic rocks) and þ0.79 to þ1.82 (enclaves). These signatures and their Nd model ages (TDM2) of 2.31–2.47 Ga (metavolcanic rocks) and 2.39–2.47 Ga (enclaves) suggest they were probably derived from juvenile mantle-derived protoliths, with possible input of subducted pre-Birimian (Archean?) rocks in their source(s). Their positive Ba–Th and negative Nb– Ta, Zr–Hf and Ti anomalies may indicate their formation through subduction-related magmatism consistent with an arc setting. We propose that the metavolcanic rocks and enclaves from the Lawra Belt formed in a similar island-arc setting. We infer that the granitoids developed through variable degrees of mixing/mingling between basic magma and granitic melt during subduction, when blobs of basic to intermediate parental magma became trapped in the granitic magma to form the enclaves.
Preserved Sm-Nd Isotopic composition as useful provenance indicators in Neoproterozoic sandstones in the Voltaian basin, Ghana
(2012) Anani, C.; Asiedu, D.; Manu, J.; Nude, P.; Kutu, J.; Asamoah-Sakyi, P.
The provenance of sandstones derived from the Lower Voltaian Kwahu-Morago Group and the Middle Voltaian Oti- Pendjari Group of the Neoproterozoic Voltaian Basin are discriminated by their Sm-Nd Isotopic compositions. Plots from the Sm-Nd data suggested provenance of the Kwahu-Morago Group to be from the Birimian metasediments and associated “basin type” granitoids. The Sm-Nd studies have further revealed an average TDM model age of whole rock samples in the Kwahu-Morago Group to be 2.2 Ga which shows that this portion of the Voltaian Supergroup represents eroded remnants of “basin type” granitoids. Sm-Nd data from the Oti-Pendjari Group suggested provenance from the Birimian volcanic rocks and probably with contribution from the Pan African rocks. Its average TDM model age of whole rock samples was 2.0 Ga, which generally falls in the range of the model ages for the basement Birimian vol-canic rocks as well as the model ages for the granitoid rocks and thus suggests the major source rock of the Oti-Pendjari Group as coming from the volcanic belts. The model ages for both groups seem to indicate clastic supply from an early Proterozoic crustal provenance. This study shows that whole rock isotopic analyses can also be complementary in pro-viding an insight into the origin and development of sedimentary successions.