Browsing by Author "Tadesse, Solomon (Professor)"

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    Analysis of Mine Call Factor at Meli Gold Mine (Ezana): Implementing an Ore Reconciliation System Considering Key Performance Indicators
    (Addis Ababa University, 2020-06-03) Medhane, Tesfaye; Tadesse, Solomon (Professor)
    The study area is located in the promising geological region, the ANS, where the first gold mining started in human history which also hosts the VMS deposit that yields multiple metals from single ore like Au, Cu, and Zn. Mining helps for sustainable development, however, involves high levels of complexity and uncertainty which require huge capital investment and risk. The most profitable way to exploit a mineral deposit requires continuous evaluation and planning. One practical method is to compare what was planned and what is achieved using MCF. It is the ratio, expressed as a percentage, of the gold called for to the gold accounted for. If everything went well, the comparison of what the mine delivered to the plant and what the plant received and processed must be as close as possible equal or an MCF of approximately 100%, a situation that is impossible in practice, hence an MCF of 85% was considered reasonable for shortfalls as per different practices in different mining operation. Using additional data and study, this case study will help to draw a national standard in the MCF acceptable values. The design capacity of the plant is 35 tonnes per hour. Considering the designed plant schedule, the crusher has a capacity of 12,500 tonnes per month crushing. The actual total crushed tonne is 175,742, with an average of 5,325 tonnes per month. Considering the crusher plant design capacity plan, the achievement is 42.6%. The total reconciled total mined and hauled ore were 281,246 tonnes with an average monthly of 8,523 tonnes, indicating that the shortfall is not due to ore supply; instead, it linked to the process plant related to various factors, mainly frequent and extended shutdown of the mill due to many reasons which are not the scope of this research. With the assumption of a metal recovery of 90.6%, the assumed metal recovered is 25,565 ounces which contributes to an MCF of 85.9%. Though the operation is within the acceptable range of MCF values, it requires studying and addressing the shortfalls. The MCF suggests that gold losses averaged at 14.1%, which implies a 14.1% of the expected revenue was not realized and this translates into negative financial underperformance. Total ore reserve is estimated at 515,837t@4.81 Au g/t contained 79,748.38 Oz of gold; with the design 92% recovery, the expected gold recovered is 73,368.51 Oz. As at March 2020, the mine extracted 55% (281,246t) of the reserve mass, indicating a 45% (234,591t) tonnes still remain on the ground. The plant processed 62.5% of the tonnes hauled from ROM stockpile, which is only 34% of the total reserve in terms of tonnes.
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    Assessment of the Loss of Gold to the Tailing Dam: A Case Study on Meli Gold Plant, Northwestern Tigray, Ethiopia.
    (Addis Ababa University, 2020-09-08) Kifle, Liyou; Tadesse, Solomon (Professor)
    This study is designed to evaluate and calculate a possible gold loss by metallurgic operation of meli gold plant which is located in northwestern Tigray region, northern Ethiopia. To understand the problem systematic samples has been carried out from tailing dam. Geochemical analysis in support with secondary data review has been done. From geochemical data analysis of samples, concentration of gold in the tailing dam was found to be significant amount. The gold grade in the tailing dam falls within the range of 1.14 to 0.34g/t with an average grade of 0.61g/t. This indicates loss of gold in the tailing dam. As evidenced from the geochemical results, there exists a clear gold grade decrement as it moves from outlet to inlet. One of the possible cause for gold loss to the tailing dam is the presence of base metals (Cu, Ni, Zn..). They affect the rate of gold dissolution because they consume both cyanide and the dissolved oxygen and forming stable complexes with cyanide and retarding gold cyanidation. In addition to these the lime proportion and pH regulation problems affect the gold recovery and leads to loss of gold. For mitigating gold loss for ore containing soluble copper, multi stage leaching, Ammonia-cyanide mixtures, treating by non-cyanide leaches such as thiorea leaching can be employed. Moreover, EMD needs to use 60-75% of particle size percentage range. In addition to these proper maintenance of the lime feeder should have to be done.
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    Environmental and Socio Economic Impact of Artisanal and Small Scale Placer Gold Mining at Dima Gambella Ethiopia
    (Addis Ababa University, 2021-06-30) Tariku, Selam; Tadesse, Solomon (Professor)
    Gold mining plays a significant economic role in the vicinity of Akobo River, Gambella, South-Western Ethiopia; yet the rudimentary nature of artisanal and small scale gold mining activities often caused extensive degradation and shocking environmental as well as social-conditions. The aim of this study is to emphasize the methods of production existing in artisanal and small-scale placer gold mining of the study area and examine environmental and socioeconomic impacts generated by these activities. The study adopted a multi-method approach that involved assessed the variability of physicochemical parameters in water along the Akobo River; collected data using a semi structured questionnaire, group discussions and one-to-one interviews; inspected the rate, extent and distribution of various land use and cover changes(LULC) in Dima district from 2000 to 2020 on the basis of Landsat 7 ETM satellite images downloaded in raw format from the USGS website (https://earthexplorer.usgs.gov/) and fieldwork. Facing a rapid expansion of artisanal and small-scale gold mining, governments, academia, green economy competitiveness, inter-institutional and multidisciplinary collaborations are urgently needed to overcome environmental and socio-economic challenges drawn from this sector in the study area.
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    Geology and Genesis of Shear-Zone-Hosted Gold-Base Metals Mineralization in May Hibey in Tigray, Northern Ethiopia
    (Addis Ababa University, 2013-05-05) Araya, Ashenafi; Tadesse, Solomon (Professor)
    Gold-base metal deposit at the May Hibey in northern Tigray occur within the Greenstone Belt, consists of gold intergrown with quartz and/or sulphide mineral and iron oxides in deformed and structurally complicated rocks. The gold-base metal mineralization in the area is hosted almost exclusively within a series of disconnected bands and lenses of quartz veins. These units which are hosted by sequences of metasedimentary and metavolcanic rocks including sericite quartz schist, chlorite mica schist, gossaniferous quartzite, quartz feldspathic schists, quartz porphyry and basic volcanic. Two types of ores have been observed in the field: Primary ore and oxidized ore. Mineralogicaly, the primary ore is marked by gold and sulphides (pyrite, pyrrhotite, galena, sphalerite, pyrrhotite). The oxidized ore is dominated by gold and oxides (hematite, ilmenite, limonite and goethite) facies. The main alteration processes is represented by silicification, seritization, chloritization, epidotization and sulphidation. Sulphidation involved pyrite, pyrrhotite, galena, sphalerite and chalcopyrite. The ore bodies occur in the form of veins, vein-lets, intervening silicified rocks, stringers and stockworks. The mineralization is defined by a complex paragenesis of gold in association with Cu-Pb-Zn- Fe- sulphides and iron oxide minerals. Field geological observations and laboratory analyses shows that: (1) interbanding of ores of contrasted composition within the greenstone belts, (2) presence of cross-cuttings veins, (3) variation of ore mineralization with variation in meta-volcanic-sedimentary facies, (4) metamorphism of both the ores and the host rocks, (5) intense brittle-ductile shearing along the ore zone, and (6) wall rock alteration: Suggest that gold and base metals mineralization were deposited by reaction of hydrothermal fluids with iron oxides and sulphides in the host during deformation and metamorphism. Three recent discoveries of VMS-type Cu-Zn-Pb-Au-Ag at Terer, Terakimiti, Adi Bladie in northern Tigray, along with the May Hibey Au and base-metals discovery, indicate good potential for base and precious metal resources in northern Tigray region.
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    Geology, Geochemistry & Genesis of Gold Mineralization in Ashashire Prospect, Benishangul-Gumz Region, Western Ethiopian
    (Addis Ababa University, 2014-05-30) Bedassa, Abebe; Tadesse, Solomon (Professor); Kebede, Ayele (PhD)
    The study area, Ashashire prospect, is located, in Benishangul-Gumz region western Ethiopia, about 741 km west of Addis Ababa. Field observation and petrographic study shows that the prospect comprises various units that include granite, plagioclase-muscovite (sericite)-quartz schist, quartz vein, actinolite-quartzchlorite schist, carbonitized chlorite-sericite-quartz schist and metasediments. Based on the critical mineral assemblages, the majority of the units are metamorphosed to green schist facies. Field observation and thin section analysis also revealed that the study area experienced at least three phase of deformations that are manifested by various structures. Fourteen samples are analyzed for major and trace elements using XRF method. Among the variation diagrams, only the graphs of K2O vs. Al2O3 and K2O vs. CaO show positive correlation. On the other hand, K2O is negatively correlated with MgO, Na2O and SiO2. Chondrite normalized (wood et al.1979b) spider diagram shows the pattern of the trace elements, particularly the pattern of high field strength elements (HFSE) Zr, Ti & Y, are generally similar, that implies the rocks are genetically related i.e. they have similar source rock. The discrimination diagram (Ti vs. Zr) shows the majority of the rocks of Ashashire area have similar tectonic environment as rocks formed in island arc tholeiites, calc-alkali basalt and mid oceanic ridge basalt (MORB) zone. Statistical analysis of AAS results of gold from forty samples showed a range of gold concentration from < 0.02-48.5 ppm and mean value of 2.88ppm. The histogram indicates about 49 percent of the samples have shown anomalous Au value i.e greater than 0.5ppm. Correlation value and the scatter diagrams of Au with the multi elements (Ag, Cu, Pb, Zn, Ni, Co and Mn) showed that gold has stronger positive association with silver (Ag) only. Based on field observation and textural relationship of ore minerals the gangue minerals that constitute the host rock are formed in the earliest phase and followed by magnetite hematite, ilmenite, pyrite; chalcopyrite and gold are crystallized respectively. The geological and structural setting, host rock alteration and gangue mineralogy are suggestive for a shear-zone hosted orogenic-gold type deposit at Ashashire.
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    Geology, Mineral Paragenesis, and Sequence Study of Bikilal Iron Mineralization in West Wollega; Western Ethiopia: Implication to Genesis.
    (Addis Ababa University, 2013-12-12) Rebso, Solomon; Tadesse, Solomon (Professor); Asrat, Asfawossen (PhD)
    Bikilal iron ore deposit is a Kiruna-type magnetite – ilmenite deposit in West Wollega Western Ethiopia. It is formed within syn-post tectonic intrusive gabbroic complex that intrudes the Precambrian gneiss. Bikilal gabbroic intrusion comprises olivine gabbro in the center, hornblende gabbro and hornblendite as dominant rock at the periphery of the intrusive as well as pegmatite, granite, migmatite, and anorthosite found as a minor lithology. Generally all lithological units are dipping SW with dip angles ranging from 350 ─ 750. The major structural trends in the study area are NW – SE following the regional lineament. Drill hole data shows that the rocks have layering. Hornblende gabbro and hornblendites with anorthosite are characterized by magnetite- ilmenite and apatite mineralization. Identification of different minerals and their textural relationships have been studied using ore and transmitted light microscope at the School of Earth Sciences, Addis Ababa University. The iron ore bearing hornblendite is classified into upper zone in the northern, middle zone in the north- eastern, and lower zone in the southern part of the study area. Bikilal iron deposit consists of magnetite, ilmenite, hematite, sulphides, apatite and gold. The principal ore minerals are magnetite and ilmenite. Apatite is the second most abundant mineral in association with magnetite and ilmenite. The sulfide minerals present are pyrite, chalcopyrite, pyrrhotite and pentlandite. Gold grains are found as isolated free grain in association with other sulphide minerals but commonly it is found as hatched inclusion inside chalcopyrite. The paragenetic sequence of mineralization was classified into four phases based on the microscopic study and existing geochemical data from previous works: Phase I = Silicates (olivine + pyroxene+ feldspar); Phase II =magnetite + massive- veinlet ilmenite + pyrite + pentlandite+ free gold; Phase III =exsolved ilmenite + hematite + pyrrhotite + gold; and Phase IV=chalcopyrite + geothite. In this work mineral association and paragenesis of Fe-Ti oxide-Py-Cu-Pyr-Ni-Au were identified and studied.
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    Gis-Based Geostatistical Analysis of the Kenticha Tantalum Deposit and Impact of the Mining on the Environment Adola, Southern Ethiopia
    (Addis Ababa Universty, 2007-07) Girma, Arsema; Tadesse, Solomon (Professor)
    The developing mineral industry of Ethiopia brings a considerable and irreplaceable input fro the country’s economy. Mining at present is concentrated in the southern part of the country within a relatively small area, where gold and tantalite ores are being mined by open pit methods and processed. The main target of the mineral development are (i) Adola gold field with its primary gold (Lega Dembi and Shakiso) and numerous rich placer gold and (ii) the Kenticha province of rare metal bearing pegmatite. The present study is concerned with the latter. The Kenticha area in southern Ethiopia is located in the Neoproterozoic metamorphosed volcano-sedimentary succession of greenschist to amphibolite facies metamorphism. In the studied area, the rock sequences consist of serpentinite, talc, talc-chlorite-tremolite schist, and granite-pegmatite units. In order to make prognosis on the possible presence of undiscovered ore-shoots in unexplored and under-explored parts of the Kenticha tantalite deposit, Adola Belt, GISbased geomathematical techniques where tested. Analytical sample data generated from thirty bore holes formed the basis for computing the studies. The studies consisted of processing the Kenticha mine sample data- width, Ta-Nb-grade, and accumulation from borehole data’s to discern patterns and asses the environmental impact associated with the mining activity in the region. The techniques adopted were frequency distribution, trend analysis, auto-grade correlation, variogram analysis and spatial variation and land use and land cover analysis. The frequency studies show positively skewed distributions for grade and accumulation. Trend analysis indicates certain clear patters of value distribution. Variogram show high ‘nugget’ (random) component, anisotropy and nested structure for grade at the Kenticha tantalite deposit. From an integration of the results of the above different kinds of studies, certain parts of the mine were identified for selective mining of the deposit and to further investigations and exploration in other rare-metal-bearing pegmatite-granite districts of the rare-metal field. The importance of appreciation of geological factors in interpreting the geomathematical models is stressed. The impact of the mineral industry on the environment at Kenticha area is considerable. Therefore, the most effective least expensive and quickest means must be identified and urgently implemented to preserve the environment or at least to minimize the undesirable damage to it within the region.