| 1. |
- Abdelnasser, Amr, et al.
(författare)
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REE geochemical characteristics and satellite-based mapping of hydrothermal alteration in Atud gold deposit, Egypt
- 2018
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Ingår i: Journal of African Earth Sciences. - : Elsevier. - 0899-5362 .- 1464-343X. ; 145, s. 317-330
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Tidskriftsartikel (refereegranskat)abstract
- New geochemical data of the hydrothermal alteration zones associated with gold-bearing quartz veins at Atud mine are used for better understanding the ore evolution and exploration vectoring. ASTER and Landsat 8 OLI data are used to elucidate the distribution of gold-associated alteration zones. Three alteration zones are defined; zone 1 (sericite-kaolinite-quartz-pyrite), zone 2 (quartz-sericite-albite-pyrite), and zone 3 (chlorite-carbonate-epidote ± pyrite). Sericite and hydrothermal quartz are confined to the mineralized quartz veins. Fe-OH and OH-bearing minerals are observed along NW- and NE-trending shear zones in the Main Atud mine. The association of gold-bearing quartz veins and sericite alteration is constrained by processing ASTER- and OLI-imagery data. The geochemical data of the ore-enveloping hydrothermally altered rocks are used to assess the behavior of the REEs during the mineralization process. Mild enrichment in LREE and significant enrichment in the HREE are associated with sericite in zones (1) and (2) alterations. Carbonate alteration (zone 3) is enriched in LREE and in immobile HREE. Moreover, LREE and Eu anomalies have negative correlated with the Alteration Index (A.I.) and K2O index (K.I.) in zones 1 and 2, suggesting high mobility of LREE in K-rich hydrothermal fluids. On the other hand, HREE anomalies with increasing MgO index (M.I.) in alteration zone 3 may imply low solubility of these elements in alkaline solutions. Au anomalies linked to sericite/silica alteration is a rather meaningful vector for further exploration in the area.
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| 2. |
- Arellano, Santiago, 1981, et al.
(författare)
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Long-term monitoring of SO2 quiescent degassing from Nyiragongo’s lava lake
- 2017
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Ingår i: Journal of African Earth Sciences. - : Elsevier BV. - 1879-1956 .- 1464-343X .- 0899-5362. ; 134, s. 866-873
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Tidskriftsartikel (refereegranskat)abstract
- The activity of open-vent volcanoes with an active lava-lake, such as Nyiragongo, is characterized by persistent degassing, thus continuous monitoring of the rate, volume and fate of their gas emissions is of great importance to understand their geophysical state and their potential impact. We report results of SO2 emission measurements from Nyiragongo conducted between 2004 and 2012 with a network of ground-based scanning-DOAS (Differential Optical Absorption Spectroscopy) remote sensors. The mean SO2 emission rate is found to be 13 ± 9 kg s−1, similar to that observed in 1959. Daily emission rate has a distribution close to log-normal and presents large inter-day variability, reflecting the dynamics of percolation of magma batches of heterogeneous size distribution and changes in the effective permeability of the lava lake. The degassed S content is found to be between 1000 and 2000 ppm from these measurements and the reported magma flow rates sustaining the lava lake. The inter-annual trend and plume height statistics indicate stability of a quiescently degassing lava lake during the period of study.
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| 3. |
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| 4. |
- Bagherlbandi, Mohammad, et al.
(författare)
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Modelling the density contrast and depth of the Moho discontinuity by seismic and gravimetric-isostatic methods with an application to Africa
- 2012
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Ingår i: Journal of African Earth Sciences. - : Elsevier BV. - 1464-343X .- 0899-5362. ; 68, s. 111-120
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Tidskriftsartikel (refereegranskat)abstract
- The crustal thickness (Moho depth) is of interest in several geosciences applications, such as geography, geophysics and geodesy. Usually the crustal depth and density variations are estimated by seismic survey data. As such data collection is very time-consuming and expensive an attractive option could be to use a gravimetric/isostatic model. In this case, realistic estimates for the crustal density and Moho density contrast (MDC) are important. In this study, we first use the seismic crustal thickness of CRUST2.0 model as a known parameter in combination with gravimetric data in estimating the crust-mantle density contrast by the isostatic model of Vening Meinesz-Moritz. We present different models to estimate the MDC and its impact on the modelling of the gravimetric-isostatic Moho depth. The theory is applied to estimate the Moho depth of the African continental crust by using different models for the MDC: (a) constant value (0.6 g/cm(3)), (b) Pratt-Hayford's model, (c) CRUST2.0 as input to three gravimetric/isostatic models based on Vening Meinesz-Moritz theory. The isostatic models agree by 5.8-7.1 km in the rms with the regional seismic model at a resolution of 2 degrees x 2 degrees, and the smallest rms difference at a resolution of 1 degrees x 1 degrees is of 7.2 km. For comparison, the rms differences of CRUST2.0 and the regional seismic model are 8.8 and 9.1 km at the resolutions of 2 degrees (interpolated) and 1 degrees, respectively. The result suggests that the gravimetric/isostatic Moho model can be used in densification of the CRUST2.0 Moho geometry, and to improve it in areas with poor data.
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| 5. |
- Dulanya, Zuze, et al.
(författare)
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Comparative study of the silica and cation geothermometry of the Malawi hot springs : Potential alternative energy source
- 2010
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Ingår i: Journal of African Earth Sciences. - : Elsevier BV. - 0899-5362 .- 1464-343X. ; 57:4, s. 321-327
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Tidskriftsartikel (refereegranskat)abstract
- Malawi is one of the poorest countries in the world and one of the most densely populated in south-eastern Africa. Its major power source is hydro-electricity. During the past few years, the power generation capacity has been reduced, which has impacted negatively on the socio-economic development of the country. The country holds an enormous potential to generate geothermal energy due to the country’s position within the Great African Rift valley. This could contribute to economic growth, poverty reduction and technological development in Malawi. The paper presents findings of research on comparisons between silica (quartz and chalcedony) and cation geothermometers (Na–K, Na–K–Ca and K–Mg) of hot springs in the Malawi Rift, in order to deduce the temperature at depth of selected hot springs. The saturation indices of most springs have a bearing on the geology of the areas where these hot springs are found. The Na–K geothermometers are, in general, higher than the Na–K–Ca geothermometer and the K–Mg geothermometer shows temperatures that are too low to be considered. The difference in the results between the different geothermometers may indicate shallow conditions of mixing with groundwater. Results also indicate that some hot springs have sufficient heat-generating capabilities and warrant further exploration work to assess their suitability for energy generation.
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| 6. |
- Kasedde, Hillary, et al.
(författare)
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Characterization of brines and evaporites of Lake Katwe, Uganda
- 2014
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Ingår i: Journal of African Earth Sciences. - : Elsevier BV. - 0899-5362 .- 1464-343X. ; 91, s. 55-65
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Tidskriftsartikel (refereegranskat)abstract
- Lake Katwe brines and evaporites were investigated to determine their chemical, mineralogical and morphological composition. 30 brine samples and 3 solid salt samples (evaporites) were collected from different locations of the lake deposit. Several analytical techniques were used to determine the chemical composition of the samples including Inductively Coupled Plasma-Atomic Emission Spectrometry (ICP-AES), Inductively Coupled Plasma-Sector Field Mass Spectrometry (ICP-SFMS), ion chromatography, and potentiometric titration. The mineralogical composition and morphology of the evaporites was determined using X-ray diffraction (XRD) and scanning electron microscopy (SEM), respectively. Physical parameters of the lake brines such as density, electrical conductivity, pH, and salinity were also studied. The results show that the lake brines are highly alkaline and rich in Na+, Cl-, CO32-, SO42-, and HCO3- with lesser amounts of K+, Mg2+, Ca2+, Br-, and F- ions. The brines show an intermediate transition between Na-Cl and Na-HCO3 water types. Among the trace metals, the lake brines were found to be enriched in B, I, Sr, Fe, Mo, Ba, and Mn. The solid salts are composed of halite mixed with other salts such as hanksite, burkeite and trona. It was also observed that the composition of the salts varies considerably even within the same grades.
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| 7. |
- Mapani, Benjamin, et al.
(författare)
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Geochronology and tectonic evolution of the Hohewarte Complex,central Namibia: New insights in Paleoproterozoic to Early Neoproterozoic crustal accretion processes
- 2014
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Ingår i: Journal of African Earth Sciences. - : Elsevier BV. - 0899-5362 .- 1464-343X. ; 99, s. 228-244
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Tidskriftsartikel (refereegranskat)abstract
- The Hohewarte Metamorphic Complex has been variously correlated with the Abbabis Complex, Kaman- jab Inlier and the Rehoboth inlier, which is better studied. The Hohewarte Metamorphic Complex is wholly surrounded by the Damara Sequence that experienced peak orogenesis at circa 550 Ma. The Dam- aran cover has been thrusted over the Hohewarte gneisses, producing subhorizontal fabrics. The Hohew- arte Metamorphic Complex was already accreted onto the Kalahari craton during Damaran peak orogenesis. The Hohewarte Metamorphic Complex is composed of a variety of gneisses, ranging from amphibolites, quartz-feldspathic gneiss, plagioclase-rich striped gneisses that enclose two varieties of augen gneiss; a felsic K-feldspar-augen gneiss and an augen gneiss with plagioclase and K-feldspar augens in a matrix of biotite and hornblende rich matrix, occurring mainly to the east of the complex. To the northeast in the Seeis inlier, occurs a medium-grained granitic gneiss with a weak foliation. To the west occurs the ubiquitous banded quartz-feldspar-biotite gneisses, that were intruded by megacry- stic granites that are now gneisses. The whole complex has been deformed with two deformations prior to the Damaran orogeny. The fabrics in the gneisses are vertical to subhorizontal, whereas the Damaran cover rocks show a distinct ENE trending fabrics with a consistent dip of 30–45 to the NW. Four samples were selected for single zircon U–Pb dating to establish the age relations; the amphibolite unit within the quartzo-feldspathic gneiss records an age of 1758 ± 10 Ma; the felsic augen gneiss yielded an age of 1290 ± 10 Ma. The megacrystic K-feldspar gneiss yielded an age of 1168 ± 38 Ma, whereas the granitic gneiss gave the youngest age of 1061 ± 10 Ma. e Hf model ages show that all the Hohewarte Metamorphic Complex gneisses plot close to the CHUR and posses very primitive crustal signatures and have not been recycled much in the crust. A depleted mantle source is suggested for their origin
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| 8. |
- Mattsson, Hannes, et al.
(författare)
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Magnetic mineralogy and rock magnetic properties of silicate and carbonatite rocks from Oldoinyo Lengai volcano (Tanzania)
- 2018
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Ingår i: Journal of African Earth Sciences. - : Elsevier BV. - 0899-5362 .- 1464-343X. ; 142, s. 193-206
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Tidskriftsartikel (refereegranskat)abstract
- Oldoinyo Lengai, a stratovolcano in northern Tanzania, is most famous for being the only currently active carbonatite volcano on Earth. The bulk of the volcanic edifice is dominated by eruptive products produced by silica-undersaturated, peralkaline, silicate magmas (effusive, explosive and/or as cumulates at depth). The recent (2007–2008) explosive eruption produced the first ever recorded pyroclastic flows at this volcano and the accidental lithics incorporated into the pyroclastic flows represent a broad variety of different rock types, comprising both extrusive and intrusive varieties, in addition to various types of cumulates. This mix of different accidental lithics provides a unique insight into the inner workings of the world's only active carbonatite volcano.Here, we focus on the magnetic mineralogy and the rock magnetic properties of a wide selection of samples spanning the spectrum of Oldoinyo Lengai rock types compositionally, as well from a textural point of view. Here we show that the magnetic properties of most extrusive silicate rocks are dominated by magnetite-ulvöspinel solid solutions, and that pyrrhotite plays a larger role in the magnetic properties of the intrusive silicate rocks. The natrocarbonatitic lavas, for which the volcano is best known for, show distinctly different magnetic properties in comparison with the silicate rocks. This discrepancy may be explained by abundant alabandite crystals/blebs in the groundmass of the natrocarbonatitic lavas.A detailed combination of petrological/mineralogical studies with geophysical investigations is an absolute necessity in order to understand, and to better constrain, the overall architecture and inner workings of the subvolcanic plumbing system. The results presented here may also have implications for the quest in order to explain the genesis of the uniquely natrocarbonatitic magmas characteristic of Oldoinyo Lengai.
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| 9. |
- Stendal, Henrik, et al.
(författare)
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Gold potential of the Mpanda Mineral Field, SW Tanzania : Evaluation based on geological, lead isotopic and aeromagnetic data
- 2004
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Ingår i: Journal of African Earth Sciences. - : Elsevier. - 0899-5362 .- 1464-343X. ; 38:5, s. 437-447
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Tidskriftsartikel (refereegranskat)abstract
- Gold and base metals of the Mpanda Mineral Field (MMF) is the focus of this paper. Gold veins and gold-bearing base metal occurrences are structurally controlled by conjugate sets of NW-SE and E-W trending faults and/or shear zones that crosscut high-grade metamorphic rocks and post-kinematic intrusions. It was anticipated that Palaeoproterozic country rocks could have been potential host rocks for the gold mineralisation in this area. This argumentation was based on Pb model ages of various deposits from the MMF. Recent fieldwork and Pb isotopic results presented herein indicate that epigenetic gold and base metal vein-type mineralisation in the MMF is post-Palaeoproterozoic. Our Pb isotope study concentrates on constraining the sources of metals in gold-bearing quartz reefs and base metal occurrences. Pb isotopes of whole rocks and minerals indicate that mineralisation was emplaced during the Neoproterozoic, contemporaneous with the intrusion of alkaline granites and carbonatite complexes (e.g., Sangu-Ikola carbonatite complex) at ∼720 Ma. The source of Pb in the mineral occurrences is compatible with that characteristic of the Palaeoproterozoic host rocks. Aeromagnetic data suggest that the gold-bearing, NNW-SSE trending area continues to the north beyond Mpanda town. Pb isotope results and aeromagnetic data have significant implications for future exploration programs within the region, in that the search should potentially focus on the defined geophysical borders and trendlines, and on Neoproterozoic, rather than Palaeoproterozoic vein systems
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| 10. |
- Werdelin, Lars, et al.
(författare)
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Carnivora from the Kanapoi hominin site, northern Kenya
- 2012
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Ingår i: Journal of African Earth Sciences. - : Elsevier BV. - 0899-5362 .- 1464-343X. ; 64, s. 1-8
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Tidskriftsartikel (refereegranskat)abstract
- The assemblage from Kanapoi represents the most diverse early Pliocene carnivore assemblage from sub- Saharan Africa. Carnivora from Kanapoi were originally described by Werdelin (2003a), but continuing field work has brought to light significant new material from the site, shedding new light on the earliest post-Miocene radiation of Carnivora in Africa. Most importantly, a second species of Enhydriodon has been recovered from the site, including the first specimen to include a large part of the neurocranium. This makes Kanapoi the first site to include two species of this genus. This addition to the fauna will be of prime significance to understanding the ecology and evolutionary radiation of these giant, extinct otters. Other significant new finds include additional material of a wildcat-sized felid. Finds of this group are rare, and the new Kanapoi material adds significantly to our knowledge of the stem lineage of the genus Felis, which is widespread in Africa today.
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