Browsing by Author "Mshiu, Elisante E."

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    Aerogeophysical, Geological and Geochemical Investigation of the Late Archaean Granitoids in the Musoma- Mara Greenstone Belt, NE Tanzania
    (2008) Mshiu, Elisante E.; Maboko, Makenya A. H.; Marobhe, I.
    The Musoma Mara Greenstone Belt (MMGB) is intruded with syn-to-post orogenic suites of granitoids which range in composition from Tonalite Trondhjemite Granodiorites (TTG) to granite. High resolution aerogeophysical data surveyed by GST in 2003 has provided aeromagnetic and radiometric data that were used in this study to classify various granitoids existing in MMGB. The individual radioactive element content of K, Th and U, ternary image and K: U: Th composite classification map have been used in data presentation and interpretation. In addition the radioactive element ratios were used to enhance the radiometric signals. Based on the analysis and interpretations made on airborne radiometric, magnetic data and previous geological maps, a geophysical interpretation map was obtained. This map broadly categorized the MMGB granitoids into two types, the first granitoid type is characterized by high contents of all the three elements (K, U and Th) and low magnetic intensity (< 33997 nT). The second granitoid type is characterized by high K relative to U and Th, and higher magnetic intensity (>33997 nT). The aerogeophysical interpretation map was used as a base map for ground follow-up whereby the granite types were sampled accordingly for geochemical analysis. Geochemical classification of the two granitoid types from geophysical data interpretations further subdivided them into three types i.e. biotite granite, calcic granite and TTG. The overall analysis showed high correlation between aerogeophysical and geochemical data whereby the voluminous biotite and calcic granite are the subdivisions from the first granite type and the less voluminous TTG precisely correlated to the second granite type. Their compositional similarity in geochemistry with the northern MMGB high-K and Na-rich granitoids (Manya et al. 2007a, b) suggested tectonic setting and petrogenetic analogy. Biotite and calcic granites are inferred to have been generated from partial melting of pre-existing materials including TTG, intermediate and felsic volcanic rocks whereby TTGs were generated from partial melting of hydrous basaltic crust that transformed into garnet amphibolites.
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    Geochemistry and Petrogenesis of the Late Archaean High-K Granites in the Southern Musoma-Mara Greenstone Belt: Their Influence in Evolution of Archaean Tanzania Craton
    (Elsevier, 2012) Mshiu, Elisante E.; Maboko, Makenya A. H.
    Musoma-Mara Greenstone Belt (MMGB) is abundantly occupied by the post-orogenic high-K granites which also they mark the end of magmatism in the area. The granites are characterized by high SiO2 and Al2O3 contents that average 74.42% and 13.08% by weight respectively. They have low Na2O content (mean = 3.36 wt.%) and high K2O contents (mean = 4.95 wt.%) which resulted to relatively high K2O/Na2O ratios (mean = 1.50). They also characterized by low Mg# (mean = 33) as well as low contents of transition elements such as Cr and Ni which are below detection limit (<20 ppm). Negative anomalies in Eu (Eu/Eu*, mean = 0.56), Nd, Ta and Ti elements as shown in the chondrite and primitive mantle normalized diagrams indicate MMGB high-K granites originated from a subduction related environments. These high-K granites also characterized by relative enrichment of the LREE compared to HREE as revealed by their high (La/Yb)CN ratio ranging from 8.71 to 50.93 (mean = 26.32). They have relatively flat HREE pattern with (Tb/Yb)CN ratio varying between 0.81 and 2.12 (mean = 1.55). Their linear trend in the variation diagrams of both major and trace elements indicate magmatic differentiation was also an important process during their formation. Conclusively, the geochemical characteristics as well as experimental evidences suggests MMGB high-K granites were formed from partial melting of pre-existing TTG rocks, under low pressure at 15 km depth or less and temperature around 950 °C in which plagioclase minerals were the stable phases in the melt.
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    Identification of Hydrothermal Paleofluid Pathways, the Pathfinders in the Exploration of Mineral Deposits: A Case Study from the Sukumaland Greenstone Belt, Lake Victoria Gold Field, Tanzania
    (Elsevier, 2015) Mshiu, Elisante E.; Cornelia, Glaesser; Borg, Gregor
    Hydrothermal fluids play a key role in the process of metalliferous mineralization such as gold deposits. The modern exploration indicators for such deposits are tectonic structures and characteristic alteration minerals observed as detectable halos adjacent to mineral deposits. Tectonic fractures are the conduits to these hydrothermal fluids and thus control the spatial locations for the formation of mineral deposits. Along crustal structures, hydrothermal fluids commonly induce mineral alteration in the adjacent wall rocks depending on the physical–chemical conditions. These alteration patterns, which are the pathfinders for the proxies in the modern mineral exploration, can be detected by innovative application of combined remote sensing techniques. The study area has experienced intense tectonic deformations, which resulted to two major sets of structures, the NW–SE and NE–SW-trending structures. The knowledge-based analysis applied to SRTM data was useful in identifying crustal lineaments, which the above two set of structures, truncating lithological units of the Sukumaland Greenstone Belt were identified. The Feature Oriented Principal Component Selection (FPCS) together with the GIS functions applied to Landsat 7 ETM+ data, were useful to enhance signals from hydrothermal alteration minerals. Results have revealed that the Sukumaland Greenstone Belt is intensively fractured, in a systematic pattern, and has apparently been “injected” with large volumes of hydrothermal fluids. Both processes together have resulted in the systematic and structurally controlled hydrothermal alteration patterns. In this study linear alteration patches are interpreted to represent the hydrothermal paleofluid pathways. Alteration patches coincide spatially with regional and local tectonic structures and are consistent with major gold occurrences and gold mines. This study indicate that careful analysis of SRTM and Landsat ETM+ data can identify crustal lineaments, the likely hydrothermal paleofluid conduits, which may lead to the discovery of potential ore deposits.
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    Landsat Remote Sensing Data as an Alternative Approach for Geological Mapping in Tanzania: A Case Study in the Rungwe Volcanic Province, South-Western Tanzania
    (2011) Mshiu, Elisante E.
    Rungwe Volcanic Province (RVP) is mostly covered by extrusive rocks that overlain the Precambrian basement. The use of Landsat data in this area has revealed the need of effective use of these data in geological mapping programs in Tanzania. Landsat band ratios 5/1, 3/7, 5/7 and 5/4 as well as R: G: B composite images 7:4:1, 7:5:4, 1/3:5/7:3/5 and 4/5:6/7:4/6 played an important role in identifying different rock types in the study area. Ratio images managed clearly to distinguish between mafic and felsic rocks whereby two lithological blocks were identified, Block 1 covers a combination of intrusive and metamorphic rocks while Block 2 is dominated by extrusive rocks. Composite images went further to the discrimination of individual lithological units in which different rock types were identified, example phonolitic trachytes, basalts, tephrites and granitoids. Vegetation overlap problem was cleared up by results from classification in which the thick vegetated areas were discriminated. Hence, results from Landsat data analyses showed clear lithological correlation between Landsat images and the available geological map in the study area. Apart from these data to show that they are effective in geological mapping, the performance showed by Landsat data suggests they can substitute geophysical data which are relatively very expensive.
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    Rock Phosphate and Lime for Small-Scale Farming in Tanzania, East Africa
    (2012) Kalvig, Per; Fold, Niels; Jønsson, Jesper B.; Mshiu, Elisante E.
    Poor soils are a major cause of poverty in sub-Saharan Africa, and thus restoration of soil fertility is a significant challenge for sustainable agriculture. Some of the main resources required, e.g. phosphate and lime, are present in many African countries and can be used by smallholder farmers in a relatively unprocessed form instead of expensive commercial fertilisers. Here we present a small study of the Mbeya region in Tanzania, which locally has both phosphate and lime. Most soils in sub-Saharan Africa are losing nutrients necessary for sustainable agriculture. This is mainly due to intensive farming and the fact that the nutrients are not replaced adequately. Further reasons for nutrient losses are leaching, soil erosion and fixation by iron and aluminium oxides. Vast areas experience moderate to acute phosphorus deficiency (Vanlauwe & Giller 2006). The Mbeya region in south-western Tanzania (Fig. 1) is characterised by intensive smallholder plots along with several local sources of phosphate-bearing rocks and limestone. The former were examined in the 1980s (Chesworth et al. 1988, 1989), but have never been utilised (Kalvig et al. 2010).