Browsing by Author "Kazimoto, Emmanuel O."
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Item The Age of Au–Cu–Pb-bearing Veins in the Poly-orogenic Ubendian Belt (Tanzania): U–Th–total Pb Dating of Hydrothermally Altered Monazite(Springer, 2015) Kazimoto, Emmanuel O.; Schenk, Volker; Appel, PeterThe age of gold–copper–lead mineralization in the Katuma Block of the Ubendian Belt remains controversial because of the lack of radiometric ages that correlate with the age of tectonothermal events of this polyorogenic belt. Previous studies reported whole rock and mineral Pb–Pb ages ranging between 1,660 and 720 Ma. In this study, we report U–Th–total Pb ages of monazite from hydrothermally altered metapelites that host the Au–Cu– Pb-bearing veins. Three types of chemically and texturally distinct types of monazite grains or zones of grains were identified: monazite cores, which yielded a metamorphic age of 1,938 ± 11 Ma (n = 40), corresponding to known ages of a regional metamorphic event, deformation and granitic plutonism in the belt; metamorphic overgrowths that date a subsequent metamorphic event at 1,827 ± 10 Ma (n = 44) that postdates known eclogite metamorphism (at ca. 1,880 Ma) in the belt; hydrothermally altered poikilitic monazite, formed by dissolution–precipitation processes, representing the third type of monazite, constrain the age of a hydrothermal alteration event at 1,171 ± 17 Ma (n = 19). This Mesoproterozoic age of the hydrothermal alteration coincides with the first amphibolite grade metamorphism of metasediments in the Wakole Block, which adjoins with a tectonic contact the vein-bearing Katuma Block to the southwest. The obtained distinct monazite ages not only constrain the ages of metamorphic events in the Ubendian Belt, but also provide a link between the metamorphism of the Wakole metasediments and the generation of the hydrothermal fluids responsible for the formation of the gold– copper–lead veins in the Katuma Block.Item The Age of Au–Cu–Pb-bearing Veins in the Poly-orogenic Ubendian Belt (Tanzania): U–Th–total Pb Dating of Hydrothermally Altered Monazite(Springer, 2015) Kazimoto, Emmanuel O.; Schenk, Volker; Appel, PeterThe age of gold–copper–lead mineralization in the Katuma Block of the Ubendian Belt remains controversial because of the lack of radiometric ages that correlate with the age of tectonothermal events of this polyorogenic belt. Previous studies reported whole rock and mineral Pb–Pb ages ranging between 1,660 and 720 Ma. In this study, we report U–Th–total Pb ages of monazite from hydrothermally altered metapelites that host the Au–Cu– Pb-bearing veins. Three types of chemically and texturally distinct types of monazite grains or zones of grains were identified: monazite cores, which yielded a metamorphic age of 1,938 ± 11 Ma (n = 40), corresponding to known ages of a regional metamorphic event, deformation and granitic plutonism in the belt; metamorphic overgrowths that date a subsequent metamorphic event at 1,827 ± 10 Ma (n = 44) that postdates known eclogite metamorphism (at ca. 1,880 Ma) in the belt; hydrothermally altered poikilitic monazite, formed by dissolution–precipitation processes, representing the third type of monazite, constrain the age of a hydrothermal alteration event at 1,171 ± 17 Ma (n = 19). This Mesoproterozoic age of the hydrothermal alteration coincides with the first amphibolite grade metamorphismof metasediments in the Wakole Block, which adjoins with a tectonic contact the vein-bearing Katuma Block to the southwest. The obtained distinct monazite ages not only constrain the ages of metamorphic events in the Ubendian Belt, but also provide a link between the metamorphism of the Wakole metasediments and the generation of the hydrothermal fluids responsible for the formation of the gold– copper–lead veins in the Katuma Block.Item Application of Infra-Red Spectral and Multi-Element Analyses in the Gold Exploration in North Mara Mines, Tanzania(2008) Kazimoto, Emmanuel O.; Ikingura, Justinian R.; Halley, S.A combination of Short Wavelength Infra red (SWIR) spectral and multielement analyses was used to characterize certain hydrothermal alteration, pathfinder elements and their distribution within gold deposits in the Archean Musoma- Mara greenstone belt in Tanzania. The aim was to fingerprint hydrothermal systems responsible for the formation of major gold deposits in the belt. The SWIR spectra of white mica and chlorite from the samples revealed compositional zoning which reflects pH changes associated with hydrothermal fluid- rock interaction during mineralization. White mica crystallinity is variable in the deposits reflecting thermal gradient during hydrothermal alteration. On the other hand, gold pathfinder elements distribution showed extension of pathfinder element signature beyond a distance of 600 m width from the ore zone with either As and Sb association or Ag and Bi association. This suggests that different redox conditions have affected the deposits. This study confirms that a combination of SWIR spectral and multielement data is a cost-effective method in generating mineralization targets and can be applicable in areas with similar styles of mineralization.Item Characterization of Hydrothermal Alteration Mineralogy and Pathfinder Elements in the Exploration for gold in North Mara mines,Tanzania(2015) Kazimoto, Emmanuel O.; Ikingura, Justinian R.; Halley, ScottA combination of mineralogical and multielement analyses was used to characterize the hydrothermal alteration,pathfinder elements and their distribution within the gold deposits in North Mara mines,the Archean Musoma-Mara greenstone belt,Tanzania. The aim was to evaluate the suitability of alteration mineral assemblages and composition as an effective exploration marker for fingerprinting hydrothermalItem Crustal Evolution and Hydrothermal Gold Mineralization in the Katuma Block of the Paleoproterozoic Ubendian Belt, Tanzania(2014) Kazimoto, Emmanuel O.Orogenic belts are regions of the Earth’s continental crust, in which regional metamorphic rocks occur that may have formed in the deep crust of an orogen. Studies of metamorphic belts are thus important to an understanding of processes that are taking place in roots of mountain belts. In order to determine the formation and crustal evolution of the linear Paleoproterozoic Ubendian Belt in Tanzania and the age and origin of its precious base metal deposits, the rocks in the Katuma Block of the northwestern Ubendian Belt were geochemically and petrologically investigated and their U-Pb zircon and U-Th-total Pb monazite ages determined using Laser Ablation Inductively Coupled Plasma Mass Spectrometer and an Electron Probe Micro Analyser, respectively. Internal textures of the zircon grains in combination with their U-Pb ages indicate that the magmatic formation of the protoliths of the orthogneisses and metabasites of the Katuma Block occurred mostly in the Neoarchean (ca. 2.71-2.64 Ga) but also during the Paleoproterozoic (2.05-1.94 Ga). These two periods are separated for about 600 Ma and are interpreted as active continental margin stages at the border of the Tanzania Craton, as deduced by the calc alkaline nature and trace element geochemistry of the metabasites and orthogneisses. The granulite facies corona assemblages in metabasites consisting of garnet, clinopyroxene, quartz and hornblende replacing magmatic orthopyroxene and plagioclase indicate that the magmatic protoliths experienced a near isobaric cooling after their intrusion into the deep crust during a tectonically quite period (< 2.64 Ga). The detrital zircon grains from the metasediments of the Katuma Block gave ages ranging between 2.64 and 2.05 Ga, similar to the magmatic formation ages of rocks of the Katuma Block, suggesting that the Katuma Block itself was most likely the source for the detritus. The time interval of sedimentation is constrained by the oldest age of the detrital zircon at about 2680 Ma and the age of the first metamorphism of the sediments at about 1960 Ma. This event is documented by the age of metamorphic zircon rims and that of monazite cores. The stage of sedimentation and the near isobaric cooling of the metabasites in the deep crust is ascribed to a passive continental margin stage of the Tanzania Craton between 2.65 and 2.05 Ga. In contrast to the post magmatic cooling nature of the Archean metamorphism of the metabasites, the common occurrence of sillimanite pseudomorphs after cm sized kyanite crystals in migmatitic metapelites provides evidence for two stages of prograde metamorphism associated with Paleoproterozoic crustal thickening events. An early stage of metamorphism took place in the kyanite stability field whereas the subsequent peak metamorphism is characterised by the stability of the mineral assemblage sillimanite-garnet/cordierite-K-feldspar. Pseudosection modelling of the XMg ratios for garnet in combination with GASP barometry revealed that the formation of the compositionally homogenous cores of garnet porphyroblasts formed at conditions of about 7 kbar and 770 ̊C. The formation of late stage plagioclase coronas around garnet in metapelites and the decrease of XMg and of the spessartine component in rims of garnet porphyroblasts point to a near isothermal uplift after peak metamorphism and thus to a crustal thickening event that preceded the peak metamorphism. The U-Th-total Pb monazite ages suggest that during the Paleoproterozoic time the Katuma metapelites experienced two separate metamorphic events at about 1.96 Ga and 1.84 Ga. As the two ages of monazite growth zones (cores and rims) are found in monazite grains of the rock matrix and in inclusions in garnet porphyroblasts, the garnet growth must have occurred during or after the second metamorphic event at 1840 Ma. This interpretation is in agreement with the increasing depletion of HREE and Y in the monazite rims indicating concurrent growth of the monazite rims and the garnet porphyroblasts. The second, high-grade event at ca. 1840 Ma is correlated with the formation of the Ubendian Belt during the collision between the Tanzania Craton and the Bangwelu Block. The first metamorphic event at ca. 1960 Ma that preceded the collision for about 120 Ma is attributed to the kyanite grade metamorphism during accretionary processes and associated calc alkaline magmatism (2.05-1.94 Ga) along the active continental margin of the Tanzania Craton. U-Th-total Pb dating of hydrothermally altered monazite grains from hydrothermally altered metapelites hosting the Au-Cu-Pb bearing veins of the Mpanda Mineral Field in the Katuma Block yielded a Mesoproterozoic age (1171 ± 17 Ma). This age coincides with the first, amphibolite grade metamorphism of metasediments in the Wakole Block adjoining the Katuma Block to the southwest. The obtained age provides a link between the metamorphism of the Wakole metasediments and the generation of hydrothermal fluids responsible for the formation of the gold copper lead bearing veins in the Katuma Block.Item Granulite-facies Metamorphic Events in the Northwestern Ubendian Belt of Tanzania: Implications for the Neoarchean to Paleoproterozoic Crustal Evolution(Elsevier, 2015) Kazimoto, Emmanuel O.; Schenk, Volker; Appel, PeterWe present a geological evolution model for the Paleoproterozoic Ubendian Belt. This model is deduced from the metamorphic histories of metasediments and metamafites combined with previously obtained crust formation and metamorphic ages obtained from different rock types of the Katuma Block in the NW Ubendian Belt. Geothermobarometry and pseudosection modelling of metabasites indicate that the granulite-facies coronas containing garnet–clinopyroxene–quartz–hornblende formed at about 8.9–6.6 kbar and 790–700 °C. The formation of the corona textures is attributed to the post magmatic cooling history in the deep crust following their intrusion at about 2.65 Ga. This period correlates with the age of deposition of sediments in the Katuma Block, as deduced from the age of detrital zircon grains. The metamorphic P–T path of these sediments contrasts with that of the Archean mafic rocks. The common occurrence of sillimanite pseudomorphs after cm-sized kyanite crystals in migmatitic metapelites provides evidence that an early stage of metamorphism took place in the kyanite stability field whereas the subsequent peak metamorphism was characterised by the stability of the mineral assemblage sillimanite-garnet/cordierite-K-feldspar. Modelling of the XMg ratios of compositionally homogenous cores of garnet porphyroblasts together with GASP barometry suggest peak P-T conditions of about 7 kbar and 770 °C. The formation of plagioclase coronas around garnet in metapelites, the decrease in XMg and an increase of the spessartine fraction in rims of garnet porphyroblasts point to a near isothermal uplift after peak metamorphism. Texturally controlled in situ U–Th–total Pb microprobe dating of monazite in metapelites resulted in two ages for metamorphic events. The monazite of the two dated samples is mostly complex and patchy zoned. The cores record ages of 1957 ± 10 Ma and 1967 ± 16 Ma, whereas the rims give ages of 1837 ± 6 Ma and 1848 ± 16 Ma. As the two ages of monazite growth zones (core and rims) are found in monazite of the rock matrix and in monazite inclusions of garnet porphyroblasts, we conclude that garnet growth occurred during or after the second metamorphic event at 1840 Ma. This interpretation is in agreement with the depletion of HREE and Y in the monazite rims. We correlate the second, high-grade event with the collisional stage between the Tanzania Craton and the Bangweulu Block. The first event that preceded the collision for about 120 Ma is attributed to the kyanite grade metamorphism during accretionary processes and associated calc-alkaline magmatism along the continental margin of the Tanzania Craton. Combining our new data with those of previous studies on the geochemistry and zircon geochronology we develop a new evolutionary model for the Paleoproterozoic orogenic cycle. The geologic history in the Ubendian Belt began in the Neoarchean (2.7–2.6 Ga) with a magmatic crust formation phase in an active continental margin setting. In the following Neoarchean–Paleoproterozoic (2.65–2.05 Ga) stage of a tectonically inactive, passive continental margin the protoliths of metabasites cooled under near-isobaric conditions and sediments were deposited on the Neoarchean crust. Subsequently, there was a protracted period of subduction (2.05–1.84 Ga) at an active continental margin, which was associated with magmatic additions and metamorphic events during tectonic accretions, that led to kyanite-grade metamorphism in wedge sediments. The final collision at 1.84 Ga leading to garnet–sillimanite–cordierite grade metamorphism in metapelites most likely was responsible for the exhumation of the 1880–1860 Ma MORB-type eclogites in the Ubendian Belt.Item Granulite-Facies Metamorphic Events in the Northwestern Ubendian Belt of Tanzania: Implications for the Neoarchean to Paleoproterozoic Crustal Evolution(Elsevier, 2015) Kazimoto, Emmanuel O.; Schenk, Volker; Appel, PeterWe present a geological evolution model for the Paleoproterozoic Ubendian Belt. This model is deduced from the metamorphic histories of metasediments and metamafites combined with previously obtained crust formation and metamorphic ages obtained from different rock types of the Katuma Block in the NW Ubendian Belt. Geothermobarometry and pseudosection modelling of metabasites indicate that the granulite-facies coronas containing garnet–clinopyroxene–quartz–hornblende formed at about 8.9–6.6 kbar and 790–700 °C. The formation of the corona textures is attributed to the post magmatic cooling history in the deep crust following their intrusion at about 2.65 Ga. This period correlates with the age of deposition of sediments in the Katuma Block, as deduced from the age of detrital zircon grains. The metamorphic P–T path of these sediments contrasts with that of the Archean mafic rocks. The common occurrence of sillimanite pseudomorphs after cm-sized kyanite crystals in migmatitic metapelites provides evidence that an early stage of metamorphism took place in the kyanite stability field whereas the subsequent peak metamorphism was characterised by the stability of the mineral assemblage sillimanite-garnet/cordierite-K-feldspar. Modelling of the XMg ratios of compositionally homogenous cores of garnet porphyroblasts together with GASP barometry suggest peak P-T conditions of about 7 kbar and 770 °C. The formation of plagioclase coronas around garnet in metapelites, the decrease in XMg and an increase of the spessartine fraction in rims of garnet porphyroblasts point to a near isothermal uplift after peak metamorphism. Texturally controlled in situ U–Th–total Pb microprobe dating of monazite in metapelites resulted in two ages for metamorphic events. The monazite of the two dated samples is mostly complex and patchy zoned. The cores record ages of 1957 ± 10 Ma and 1967 ± 16 Ma, whereas the rims give ages of 1837 ± 6 Ma and 1848 ± 16 Ma. As the two ages of monazite growth zones (core and rims) are found in monazite of the rock matrix and in monazite inclusions of garnet porphyroblasts, we conclude that garnet growth occurred during or after the second metamorphic event at 1840 Ma. This interpretation is in agreement with the depletion of HREE and Y in the monazite rims. We correlate the second, high-grade event with the collisional stage between the Tanzania Craton and the Bangweulu Block. The first event that preceded the collision for about 120 Ma is attributed to the kyanite grade metamorphism during accretionary processes and associated calc-alkaline magmatism along the continental margin of the Tanzania Craton. Combining our new data with those of previous studies on the geochemistry and zircon geochronology we develop a new evolutionary model for the Paleoproterozoic orogenic cycle. The geologic history in the Ubendian Belt began in the Neoarchean (2.7–2.6 Ga) with a magmatic crust formation phase in an active continental margin setting. In the following Neoarchean–Paleoproterozoic (2.65–2.05 Ga) stage of a tectonically inactive, passive continental margin the protoliths of metabasites cooled under near-isobaric conditions and sediments were deposited on the Neoarchean crust. Subsequently, there was a protracted period of subduction (2.05–1.84 Ga) at an active continental margin, which was associated with magmatic additions and metamorphic events during tectonic accretions, that led to kyanite-grade metamorphism in wedge sediments. The final collision at 1.84 Ga leading to garnet–sillimanite–cordierite grade metamorphism in metapelites most likely was responsible for the exhumation of the 1880–1860 Ma MORB-type eclogites in the Ubendian Belt.Item Neoarchean and Paleoproterozoic Crust Formation in the Ubendian Belt of Tanzania: Insights from Zircon Geochronology and Geochemistry(Elsevier, 2014) Kazimoto, Emmanuel O.; Schenk, Volker; Berndt, JasperLA-ICP-MS U–Pb zircon geochronological and geochemical data of meta-igneous and metasedimentary rock types of the Katuma Block of the Paleoproterozoic Ubendian Belt in Tanzania are used to unravel the crustal evolution of this metalliferous terrain. The protoliths of the metabasites and orthogneisses previously considered to be Paleoproterozoic are in fact mostly Neoarchean in age (2713 ± 11 Ma to 2638 ± 5 Ma), from which the oldest rocks experienced their first metamorphism during the same Neoarchean orogenic cycle at ca. 2650 Ma. A second event of mafic magmatism (2021 ± 11 Ma) was concomitant with the migmatization of the Neoarchean orthogneisses and was succeeded by granitic intrusions at 1990–1940 Ma. All rocks of the Katuma Block experienced their main metamorphic reworking during several Paleoproterozoic orogenic events, which were recognized by dating of various metamorphic zircon growth zones and the age of magmatic events dated at ca. 2050, 1960 and 1880 Ma. The detritus of the high-grade metasedimentary rocks derived from Neoarchean (Katuma Block or Tanzania Craton?) and Paleoproterozoic provenances and the minimum age for the deposition is constrained by its first metamorphism at ca. 1960 Ma. The Neoarchean and Paleoproterozoic metabasites, gabbronorites and orthogneisses are sub-alkaline in composition displaying a REE and trace element geochemistry akin to those of rocks formed in modern-arc settings. On the basis of the geochemical data, the presence of eclogites, deformation and metamorphic ages, we suggest that in Paleoproterozoic time the Katuma Block was again at an active continental margin, below which a Paleoproterozoic oceanic lithosphere was subducting.Item Neoarchean and Paleoproterozoic Crust Formation in the Ubendian Belt of Tanzania: Insights from Zircon Geochronology and Geochemistry(Elsevier, 2014) Kazimoto, Emmanuel O.; Schenk, Volker; Berndt, JasperLA-ICP-MS U–Pb zircon geochronological and geochemical data of meta-igneous and metasedimentary rock types of the Katuma Block of the Paleoproterozoic Ubendian Belt in Tanzania are used to unravel the crustal evolution of this metalliferous terrain. The protoliths of the metabasites and orthogneisses previously considered to be Paleoproterozoic are in fact mostly Neoarchean in age (2713 ± 11 Ma to 2638 ± 5 Ma), from which the oldest rocks experienced their first metamorphism during the same Neoarchean orogenic cycle at ca. 2650 Ma. A second event of mafic magmatism (2021 ± 11 Ma) was concomitant with the migmatization of the Neoarchean orthogneisses and was succeeded by granitic intrusions at 1990–1940 Ma. All rocks of the Katuma Block experienced their main metamorphic reworking during several Paleoproterozoic orogenic events, which were recognized by dating of various metamorphic zircon growth zones and the age of magmatic events dated at ca. 2050, 1960 and 1880 Ma. The detritus of the high-grade metasedimentary rocks derived from Neoarchean (Katuma Block or Tanzania Craton?) and Paleoproterozoic provenances and the minimum age for the deposition is constrained by its first metamorphism at ca. 1960 Ma. The Neoarchean and Paleoproterozoic metabasites, gabbronorites and orthogneisses are sub-alkaline in composition displaying a REE and trace element geochemistry akin to those of rocks formed in modern-arc settings. On the basis of the geochemical data, the presence of eclogites, deformation and metamorphic ages, we suggest that in Paleoproterozoic time the Katuma Block was again at an active continental margin, below which a Paleoproterozoic oceanic lithosphere was subducting.Item Trace Element Geochemistry and Petrogenesis of the Granitoids and High-K Andesite Hosting Gold Mineralisation in the Archean Musoma-Mara Greenstone Belt, Tanzania(Elsevier, 2014) Kazimoto, Emmanuel O.; Ikingura, Justinian R.Modern and ancient active continental margins are well known for their potential for hosting important gold deposits. The Neoarchean Musoma-Mara Greenstone Belt of the Tanzania Craton is also known for hosting several important gold deposits. Previous geochemical studies of the belt demonstrated that the rocks formed along Neoarchean convergent margins. The host rocks of the three important deposits in this belt had not yet been geochemically investigated. Therefore, we studied the host rocks of the Gokona, Nyabigena and Nyabirama gold deposits in the Neoarchean Musoma-Mara Greenstone Belt of the Tanzania Craton to determine the tectonic setting of their formation and constrain their petrogenesis. The host rocks of the Gokona and Nyabigena deposits are classified as high-K andesite, whereas the host rocks of the Nyabirama deposit are classified primarily as trondhjemite and granite and minor granodiorite (TGG). The high-K andesite and TGG were formed in an active continental margin similar to that of other Neoarchean volcanic rocks found in the Musoma-Mara Greenstone Belt. The host rocks contain low Ni and Cr concentrations and are characterised by negative Eu anomalies (Eu/Eu* = 0.67-0.72 and 0.17-0.6). The chondrite-normalised rare earth element (REE) patterns of the rocks display strong enrichment in light REEs over heavy REEs (high-K andesite (La/Yb)N = 21.7-35.6, and TGG (La/Yb)N = 2.4-94.4). Moreover, the primitive normalised diagrams show enrichment in large-ion lithophile elements (Ba, Rb, Th and K), negative Nb and Ta anomalies and depletion in heavy rare earth elements and high field-strength elements (Y and Ti). The high-K andesite has a Nb/Ta value close to that of depleted mantle (mean = 15.0), lower Zr/Sm values (19.4-30.6) and higher concentrations of REEs, large ion lithophile elements, Sr (607 ppm) and Y than in the TGG. The TGG has a low mean Nb/Ta value (13.2) and Sr concentration (283 ppm) and a lower amount of HREEs and higher values of Zr/Sm (32.5-91.0) compared to the high-K andesite. However, all of the rock types contain high Ta/Yb and Th/Yb values (high-K andesite and granitoids; mean = 5.9 and 0.8, 17 and 21.3). These characteristics are interpreted as an indication of the formation of the Gokona, Nyabigena and Nyabirama host rocks from the hydrous partial melting of mantle peridotite, similar to the evolution of classical island arc rocks. The primary melts subsequently underwent fractional crystallisation to form high-K andesite, dacite and TGG prior to their extrusion or emplacement in the continental crust.