Browsing by Author "Mnali, Saidi Rashidi"

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    Palaeoproterozoic felsic magmatism and associated gold-quartz vein mineralization in the western part of the Lupa gold field, south-western Tanzania.
    (University of Dar es Salaam, 1999) Mnali, Saidi Rashidi
    Detailed geological mapping, petrographic study, whole-rock geochemical investigation and isotopic dating of the granitoid samples as well as ore mineralogy study of the gold-quartz veins were used to establish the geology and styles of gold mineralization in the western part of the Lupa Gold Field, south-west Tanzania. The study area contains two contrasting types of coeval granitoids: the Saza-Chunya granodiorite and the Ilunga granite and associated volcanic rocks, which were emplaced between 1920 and 1960 Ma ago. The Saza-Chunya granodiorite is a peraluminous to slightly metaluminous, I-type granodiorite. It has LREE-enriched pattern with Eu/Eu* ratio varying from 0.66 to 1.31. The REE pattern resembles that of the country rock granitic gneiss, suggesting a genetic relationship between the two rocks. The geochemical data suggest that the Saza-Chunya granodiorite is a volcanic arc granitoid (VAG). The Ilunga granite and associated volcanic rocks are peraluminous to slightly metaluminous, A-type felsic rocks. They are characterized by a falt REE patterns with a large negative Eu anomaly. The Eu/Eu* ratio ranges between 0.26 and 0.27 for the volcanic rocks and 0.32 to 0.42 for the granite. The Ilunga granite is a withinplate granite (WPG) and the volcanic rocks are within-plate rhyolites (WPR). The gold-quartz veins in which gold occurs in the free state, as electrum and occasionally as sulphide- and telluride-hosted, were emplaced in shear zones, faults, small fractures as well as along the contact between felsic and mafic rocks. The general paragenetic sequence in the early, main-phase veins is: quartz-pyritechalcopyrite- galena-tellurides-gold+/-silver, and in the late-phase veins is: quartz-pyrite-gold+/-silver-molybdenite/sphalerite/pentlandite.