Platinum group element mineralization at Musongati (Burundi) : concentration and Pd-Rh distribution in pentlandite

The mafic-ultramafic intrusions of the Karagwe-Ankole belt in Burundi are considered as a new potential source for platinum group elements (PGE). The intrusions have mainly been studied for their PGE potential with regard to PGE concentration, but the mineralogical distribution of PGE has not been examined to the same level. This study focuses on the Pd and Rh distribution in pentlandite of ultramafic rocks of the Musongati layered intrusion. The results are based on whole rock and pentlandite analyses which were incorporated into a mass balance. Palladium proportions in pentlandite vary between 4 and 69%. Rhodium is present in proportions ranging from 1-39% in pentlandite. Other PGE distributions could not be determined in pentlandite due to concentrations below detection limits. The results from this study demonstrate that Pd and Rh are hosted by sulfides since sulfur saturation of the magma occurred early on, perhaps before or simultaneously with the precipitation of silicate minerals. Based on these findings, a preliminary model for the mineralization of PGE in the Musongati intrusion is proposed

Metamorphic and metasomatic evolution of the Western Domain of the Karagwe-Ankole Belt (Central Africa)

The tectonometamorphic evolution of the Western Domain of the Karagwe-Ankole Belt, containing widespread granite-related W-Nb-Ta-Sn mineralization in pegmatites and hydrothermal quartz veins of Early Neoproterozoic age, is largely unknown. This study aims to characterize the Meso- and Neoproterozoic metamorphism and metasomatism in the Karagwe-Ankole Belt, to reconstruct the temperature evolution and to investigate its temporal relation to deformation and the widespread granite magmatism and mineralization. A quantitative geothermometric study was conducted on metasiltstones and amphibolites, and applies thin section petrography, garnet-biotite and chlorite geothermometry on samples collected in the representative KibuyeGitarama-Gatumba area in West Rwanda. The presence of garnet, staurolite and kyanite in metasiltstones, and hornblende and andesine-labradorite feldspar in amphibolites indicates prograde Barrovian metamorphism up to syn-to post-deformational (D1 or D2) lower amphibolite facies (up to 630 degrees C). This peak metamorphism was followed by post-D2 greenschist facies metamorphism (c. 525 degrees C-440 degrees C; garnet, biotite, chlorite, muscovite in metasiltstone), probably related to the East African Orogeny as part of the Gondwana assembly. A geothermometric evolution with high temperature conditions ( > 500 degrees C) at least from the flare-up of Early Neoproterozoic tin granites and their metasomatic haloes onwards for most of the Neoproterozoic is proposed, in close correspondence with the geodynamic evolution of the neighboring terranes. Additionally, this high temperature regime is an important factor to be taken into account when interpreting thermal diffusion-sensitive geochronological data

Metal sources for the Katanga Copperbelt deposits (DRC) insights from Sr and Nd isotope ratios

The ore deposits of the Central African Copperbelt formed during a multiphase mineralisation process. The basement underlying the Neoproterozoic Katanga Supergroup that hosts the ore, demonstrates the largest potential as metal source. Various ore deposits that formed during different mineralisation phases are taken as case studies, i.e. Kamoto, Luiswishi, Kambove West, Dikulushi and Kipushi (Democratic Republic of Congo, DRC). The Sr and Nd isotopic compositions of gangue carbonates associated with these deposits is determined and compared with those of rocks from several basement units, bordering or underlying the Copperbelt, to infer the metal sources. The mineralising fluid of diagenetic stratiform Cu-Co mineralisation interacted with felsic basement rocks underlying the region. The Co from these deposits is most likely derived from mafic rocks, but this is not observed in the isotopic signatures. Syn-orogenic, stratabound Cu-Co mineralisation resulted mainly from remobilisation of diagenetic sulphides. A limited, renewed contribution of metals from felsic basement rocks might be indicated by the isotope ratios in the western part of the Copperbelt, where the metamorphic grade is the lowest. The mineralising fluid of syn- and post-orogenic, vein-type mineralisations interacted with local mafic rocks, and with felsic basement or siliciclastic host rocks

Rare earth element and yttrium characteristics of carbonates within the sediment-hosted Luiswishi and Kamoto Cu-Co deposits, Katanga Copperbelt (Democratic Republic of Congo - DRC)

The Neoproterozoic Central African Copperbelt is a world-class metallogenic province characterized by sediment-hosted stratiform Cu-Co ore deposits and polymetallic vein-type deposits. Two main mineralization phases have been recognized in the Katanga Copperbelt (Democratic Republic of Congo). The first phase occurred during early to intermediate diagenesis and the second during deep burial and the Lufilian orogeny. The Rare Earth Element and Yttrium (REY) concentrations of gangue dolomites associated with the second mineralization phase at the Kamoto and Luiswishi ore deposits were determined and compared to those of their respective host rocks. Kamoto samples exhibit convex Upper Continental Crust-normalized patterns with a pronounced light BEE depletion without significant Eu anomalies and with positive La anomalies. The Luiswishi samples exhibit either progressively increasing REY patterns or ramp-shaped patterns with minor mid BEE-heavy BEE fractionation, accompanied by pronounced negative Ce and Eu anomalies. These differences suggest that a more intense metamorphic overprint at Luiswishi contributed to the differences with the Kamoto deposit