Browsing by Author "Desta, Zerihun (PhD)"

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    Assessing the Quality, Mining and Processing Techniques of Bombawuha Kaolin Deposit, Southern Ethiopia
    (Addis Ababa University, 2018-06-02) W/Maryam, Tilahun; Getaneh, Worash (PhD); Desta, Zerihun (PhD)
    Bombawuha kaolin deposit is a residual type deposit formed by weathering and hydrothermal alteration of granite and pegmatite units. The present study was designed to assess the quality, mining and processing techniques of Bombawuha kaolin deposit by physical observations of the site and different analytical methods. For this purpose, samples of the source rock, kaolin deposit, run of mine, and processed kaolin were collected for analyses. Chemical, and mineralogical (thin section) analyses were applied to examine the source rock of the deposit. For kaolin deposit, and processed kaolin chemical, mineralogical (XRD), and physical properties were investigated. A chemical analysis was also carried out to investigate the composition of run of mine. The result of the study revealed that the source rock of the deposit is composed of higher SiO2 (72.1%), coloring impurities (1.88% Fe2O3, and 0.13% TiO2), fluxes (5.765 alkalies, and 0.38% alkali earth oxides), and lower Al2O3 (16.3%) and loss on ignition (3.85%) values compared to its altered product. It is composed of quartz, k-feldspar, plagioclase, biotite, muscovite, and opaque minerals. The kaolin deposit has light gray to white color, higher grits (79.9-96.7%>63μm), pH (6.27-6.37), lower plasticity (<10%), linear shrinkage (0-3), and specific gravity (2.53-2.60) values. The deposit is constituted by higher SiO2 (51.5-70.5%), and lower Al2O3 (18.1-33.4%) comparing to ideal pure kaolin 46.6 and 39.5% respectively. It also has higher Fe2O3 (1.09-1.92%), and lower TiO2 (0.03-0.17%). The XRD result revealed that kaolinite and quartz are the major minerals of the deposit with minor k-feldspars and illite. Specifically, kaolinized granite and kaolinized pegmatite have different physical and chemical characteristics. The kaolinized granite has higher grits, lower plasticity, and linear shrinkage values. It also has higher SiO2 (68%), Fe2O3 (1.65%) and TiO2 (0.13%), and lower Al2O3 (20.19%) and LOI (7.84%) values compared to the kaolinized pegmatite. Mineralogically, it is composed of kaolinite, halloysite, quartz, and k-feldspar. Kaolinized pegmatite contains quartz, mica (illite), and kaolinite minerals. Although these two units have different characteristics, they are mined together by simple open pit mining method. A run of mine having higher SiO2 (71.2%), Fe2O3 (1.88%), and lower Al2O3 (17.95%) is produced for processing. The wet processing method enhanced the quality of kaolin product by producing higher Al2O3 (35.5%), lower SiO2 (45.8%), and Fe2O3 (0.99%). It reduced SiO2 and Fe2O3, and increased Al2O3 by 36%, 47% and 98% respectively from its crude state. The processed kaolin contains major kaolinite, and minor orthoclase and muscovite minerals. Based on findings of this study, it is concluded that Bombawuha kaolin product can be used in ceramics (bricks, pottery, floor and wall tiles), plastics, paint and rubber filer productions after processing.
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    Geology, geochemistry and genesis of tantalite deposit of the primary ore zone of Kenticha rare metal pegmatite field, Adola Belt, Southern Ethiopia
    (Addis Ababa Universty, 2016-05) Seid, Mohammed; Desta, Zerihun (PhD)
    Tantalum is the most important valuable raw-material in electronic, medical and chemical industries.The Kenticha rare-element granite pegmatite in the Neoproterozoic Adola Belt of southern Ethiopia, is a subhorizontal sheet-like structurally controlled intrusive body, is an important source of tantalite, niobite and beryl where tantalite is currently mined and exported globally. A little is known about the mineralogy, content of trace elements, ore forming and interplay processes, and mechanisms leading to tantalite-columbite mineralization in granite pegmatites. The aim of this work is to evaluate the geology and geochemistry of tantalite deposit in the primary ore zone of the Kenticha granite pegmatite to further elucidate the genesis of the tantalite deposit. An integrated approach of geological field work, rock and ore petrography, and whole-rock analysis by ICP-MS and ICP-AES using drill core data was used to achieve this aim. The Kenticha rare metal pegmatite deposit is controlled by major deep-seated normal faults striking in a N–S direction that allow the emplacement of the deposit bounded by the serpentinite to the hangingwall and granite to the footwall. The Kenticha peraluminous pegmatite deposit show zonal variations in mineralogical assemblage, tantalite concentration, and trace and rare earth elements content. Six distinct mineral assemblages and three main zones: border, intermediate and core zones were identified from literature analysis,field observation, petrographic study and whole-rock analysis. The tantalum and niobium concentration increase towards the core zone while the niobium concentration increase to border zone. The columbite group minerals (CGM) variation diagram shows progressive fractionation from ferroniobite to manganotantalite of primary magmatic fractionation with later hydrothermal-metasomatic alteration. It is strongly differentiated granitepegmatite enriched with Rb,Be, Nb, Ta and Csand depleted in V, Ba and Sr contents for whole–rock analyses of the Kenticha drill core samples. The rare earth element (REE) patterns of the primary ore zone shows slight enrichment in LREE with strong negative Eu-anomaly. From mineralogical assemblage, tectonic setting and geochemical signatures the genesis of Kenticha tantalite deposit is by partial melting of metasedimentary rocks predated the granite and pegmatite with later hydrothermal-metasomatic enrichment of tantalite in the area. Its formation and emplacement is related to the collision and felsic magmatism during post-Gondwana assembly
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    The Kilkile Emerald; Genesis, Mineralogy, Chemistry and Mining; Kilkile, Shakiso- Southern Ethiopia
    (Addis Ababa University, 2019-09-04) Abera, Girma; Desta, Zerihun (PhD); Getaneh, Worash (PhD)
    This study provides quantitative geochemical, petrological, and mineralogical data on major rock types and emeralds of the kilkile area. The meta-basic rocks containing 740ppm Cr provided the amount necessary for emerald mineralization. Emeraldhosting biotite schist is confined to the contacts of quartz- feldspar- muscovite pegmatite dykes/veins with meta-basics. The pegmatite dykes are genetically related to a fertile granite pluton within the Adola district. The formation of biotite schist from meta-basic rocks is associated with the introduction of pegmatitic components in to the meta-basics, causing enrichment with the pegmatitic composition. Quartz-feldsparmuscovite pegmatites of the kilkile area belongs to the rare-element pegmatites of the LCT family with common beryllium enrichment (12ppm). These pegmatite dykes/veins intruded the N-S orienting regional structures. The emeralds have higher MgO (0.26-4.08 wt. %), Fe2O3 (1.39-2.18 wt. %), Al2O3 (17.7- 20.1 wt. %), CaO (1.25- 3.85 wt. %), K2O (0.07-1.7 wt. %), P2O5 (0.02-1.88) and Be (527-1000 ppm) and lower Cr2O3 (0.01-0.09 wt. %) and SiO2 (59.13-61.79 wt. %) contents. The relatively higher value of iron and magnesium in the kilkile emerald might attribute for the ferromagnesian nature of the meta-basic rocks or aggressiveness of the brine solution in liberating Mg and Fe from meta-basic rocks. The low chromium content in the metabasic rocks contribute for chromium deficiency in the emerald. The high value of Fe2O3 depresses the green colour in addition to low Cr2O3. Compared to the Zambian, the meta-basic rocks in the case of Ethiopia have low magnesium and iron content. However, the relatively higher value of iron and magnesium in Ethiopian emerald might contribute for relative competency of magnesium and iron in occupying the aluminium site in the crystal structure of beryl. The higher value of K2O in the Ethiopian emeralds than in Zambian might suggest the role of potassium metasomatism at the pegmatite and meta-basic contact. The genesis of Ethiopian emerald holds the classical model for emerald mineralization, the condition in which pegmatites interact with the surrounding meta-basic rocks. The current mining activity at kilkile area requires vertical to horizontal ratio chances due to the overlapping of mining progress with direction with the dipping of the host rock units. Therefore, low vertical to horizontal ratio is recommended for the western berms of the mining pits.
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    Rare Metals Mineralization in the Kilkile Area of Kenticha Greenstone Belt, Adola Area, Southern Ethiopia
    (Addis Ababa University, 2018-06-06) Ayele, Mezmur; Desta, Zerihun (PhD); Alene, Mulugeta (PhD)
    Rare metal bearing pegmatite of Kilkile contains a number of economically important minerals which attract economic interest by offering rare metals (Ta, Nb, Cs, Li and others), gemstones (emerald, aquamarine, tourmaline, beryl and Others) and industrial mineral (quartz and feldspar). The present study area is located in Adola area, southern part of Kenticha belt (southern part of Ethiopia). The main objective of the study is to evaluate the geology and geochemistry and characterize the rare metal bearing pegmatite of Kilkile area. To achieve the objective, field work and laboratory studies (thin and polished section) and geochemical analysis (ICP-MS and ICP- AES) have been conducted for whole rock and muscovite chemistry. Description of the geological structures and correlation with other rare metal bearing pegmatites have also been conducted for further examination of the genesis of the Kilkile rare metals. Based on field observation the Kilkile area predominantly consists of chromite, amphibolite gneiss and schist, biotite gneiss, serpentinite, chlorite-talc-tremolite schist, granites associated with barren & rare metal bearing pegmatites. Most of the pegmatite bodies of the area are striking nearly N-S direction, not more than a km long and have less than 200m width. Fractionatiion incerases from south to north therefore rare metals like Rb, Li, Ga, Cs, and Ta concentration also increase towards north, while the Nb, Zn and Ba concentration decrease. Highly fractionated Kilkile I pegmatite plots in the zone of Ta-mineralization whereas Kilkile II and III plots in zone of Ta-prospect. REE chondrite normalized diagram shows all sample have enrichment in light rare earth element (LREE) contents relative to heavy rare earth elements (HREE) and shows negative Eu-anomaly. Kilkile rear metal bearing peraluminous granitic pegmatite is formed by partial melting of pre-existing metasedimentary rocks probably during post-Gondwana assembly, followed by hydrothermal-metasomatic enrichment of rare metals deposit. Muscovite chemistry, using Rb versus Tl and Rb versus K/Tl correlations, infers a cogenetic formation of Kilkile (I, II and III), Kenticha, Shuni and Bupo pegmatites and they are derived form same magma source most probably from Kilta Shumbela granite located on South of Kilkile III.