Characterisation and geodynamic setting of the 1 Ga granitoids of the Karagwe-Ankole belt (KAB), Rwanda

Clercq, Shana De; Chew, David; O’Sullivan, Gary; Putter, Thierry De; Grave, Johan De; Dewaele, Stijn

doi:10.1016/j.precamres.2021.106124

Cited by 8 publications

(7 citation statements)

References 46 publications

(115 reference statements)

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“…The precipitation of CGM and some cassiterite has been suggested to pre-date the albitization event, with CGM crystals providing U-Pb ages of 936 ± 14 Ma (upper Discordia intercept), while the main cassiterite mineralization is associated with greisenization pockets (Dewaele et al 2011). The CGM ages are slightly younger than ages obtained in the surrounding granites, ~1020-950 Ma by zircon U-Pb dating (Tack et al 2010;De Clercq et al 2021;Nambaje et al 2021), but are within the age range of 975 ± 29 Ma to 940 ± 28 Ma obtained in the pegmatite dikes by muscovite Rb-Sr dating (Monteyne-Poulaert et al 1963). Recent studies of the mineralization in the Gitarama-Gatumba field point to a more complex mineralization history, with at least three generations of cassiterite formed from a water-saturated melt system, and triggered initially by local disequilibrium around the fast-growing pegmatitic minerals or lately by metasomatic fluid-rock interactions (Hulsbosch and Muchez 2020).…”

Section: Buranga Pegmatitementioning

confidence: 59%

Paragenesis and precipitation stages of Nb-Ta-oxide minerals in phosphorus-rich rare-element pegmatites (Buranga dike, Rwanda)

Araujo

Hulsbosch

Muchez

2023

American Mineralogist

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Nb-Ta-oxide minerals (NTO) are commonly associated with rare-element pegmatites where they are interpreted to precipitate at magmatic up to magmatic-hydrothermal conditions. Although high-temperature experiments show that phosphorus and other fluxing elements (e.g., Li, B, F) can affect the saturation of NTO in pegmatitic systems, it is still uncertain how NTO saturation occurs in natural, flux-rich pegmatitic melts and whether crystallization occurs at multiple stages during magmatic or subsolidus conditions. The LCT family P-rich Buranga granitic pegmatite (western Rwanda) is used as a type locality to address this question. NTO mineralization in the Buranga dike occurs in two mineralogical units: in mineralogically complex phosphatic nodules, and in albitized parts. In the phosphatic nodules, Fe-Nb-Ta-rich rutile and columbite-group minerals (CGM) are observed, while in the albitized parts, only CGM is found. Fe-Nb-Tarich rutile precipitates at the magmatic stage along with early primary phosphates (i.e., F-rich montebrasite, wyllieite, and fluorapatite). Conversely, CGM mineralization occurs at the magmatic-hydrothermal stage in association with replacement phosphates like bertossaite, after primary minerals (i.e., rutile, wyllieite, rosemaryite, and trolleite) are destabilized due to crystal-melt-fluid interactions. NTO textures and chemical zoning show uneven evolution from core to rim and are related to localized alteration phenomena of the surrounding minerals. This indicates that local processes and element transfers are more important than dikescale fractionation processes for NTO mineralization in P-rich granitic pegmatites. The restricted availability of Fe and Mn in the system, which is related to the competition between phosphate and oxide minerals, is identified as the main control on the CGM mineralization in the Buranga dike. CGM precipitation is only This is the peer-reviewed, final accepted version for American Mineralogist, published by the Mineralogical Society of America.The published version is subject to change. Cite as Authors (Year) Title. American Mineralogist, in press.

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Section: Buranga Pegmatitementioning

confidence: 59%

Paragenesis and precipitation stages of Nb-Ta-oxide minerals in phosphorus-rich rare-element pegmatites (Buranga dike, Rwanda)

Araujo

Hulsbosch

Muchez

2023

American Mineralogist

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“…Finally, the metamorphic conditions are also not well studied. The results of [59] suggest a metamorphic origin in a compression context. However, such environmental studies have not been conducted in the Kivu area.…”

Section: Granitoid Intrusions and Metamorphic Eventsmentioning

confidence: 81%

“…These mineralogic associations and the spatial relationships between the G2 and G3 batholiths suggest a G4 thermo-metamorphism giving way to crustal feeding. Recent investigations [59] in the ca. 1 Ga G4 granitoids of Rwanda show the inheritance of zircon from the G1 granites in the G4 occurrences and thus favoring an intra-continental geodynamic context and an anatectic origin of melts.…”

Section: Granitoid Intrusions and Metamorphic Eventsmentioning

confidence: 99%

“…N. Varlamoff expanded his fieldwork to Rwanda and Burundi between 1960 and 1969 in order to study similar mineralizations. Since 1960, the investigations on the origin of minerals deposits have mainly focused on the KAB, and numerous papers have been published [4,[48][49][50][51][52][53][54][55][56][57][58][59]. The best studied occurrence is the Gatumba mine in Central Rwanda [4,54,57].…”

Section: Introductionmentioning

confidence: 99%

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A Review of the G4 “Tin Granites” and Associated Mineral Occurrences in the Kivu Belt (Eastern Democratic Republic of the Congo) and Their Relationships with the Last Kibaran Tectono-Thermal Events

et al. 2022

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The Mesoproterozoic Kibaran belts host large amounts of mineral resources such as cassiterite, wolframite, gold, and columbite-group minerals (“coltan”), all of them in high demand for new technologies and related industries. Most of these mineral occurrences are linked to the latest Mesoproterozoic to early Neoproterozoic G4 granitoid intrusions, also termed “tin(-bearing) granites”. Three main parts constitute the Kibaran belts: the Kibaride Belt (KIB) in the south, the Karagwe-Ankole Belt (KAB) in the east, and the Kivu Belt (KVB) in the west. Geological detail concerning the metallogeny of the KVB, which hosts large parts of these mineral resources, is very sparse. Previously, there was an assumed time gap of about 200 Ma between the formation of the last Kibaran terranes (1250 to 1200 Ma) and the emplacement of the G4 granites (ca. 1050 to 970 Ma), which generated the main mineralizations. Recent studies dated the last Kibaran tectono-thermal events younger than 1120 to 1110 Ma, which gave evidence for a drastic reduction in this time gap. Thus, the two newly recognized tectono-thermal events have likely contributed to the remobilization of older mineralized granites. These new data allow us to link the G4 granitoids and the associated mineralizations with the terminal Kibaran orogeny. However, the G4 emplacement and its relationships with older granites, with their host rocks and associated mineralizations, are not yet understood. Here, the main occurrences of the KVB are reviewed, and comparisons with similar mineralizations in the adjacent KAB are undertaken to improve our understanding on these complex relationships.

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“…A large bimodal magmatic event, the 'Kibaran' event, occurred in the early Mesoproterozoic, 1400-1370 Ma (Tack et al, 2010), which comprises peraluminous S-type granite intrusions, as well as subordinate (ultra-)mafic intrusive rocks. This main granite generation (G1-3 granites) was dated at 1381 ± 8 Ma by U-Pb SHRIMP zircon age dating (Tack et al, 2010;De Clercq et al, 2021;Nambaje et al, 2021). The mafic intrusive rocks constitute the Kabanga-Musongati (KM) alignment (Tack et al, 2010).…”

Section: Regional Geologymentioning

confidence: 99%

Current state of knowledge of the gold mineralization at Imonga-Saramabila, Maniema (DR Congo): a petrographic and mineralogical study of the mineralized vein system

DE GROOTE,

COOLS,

WOUTERS

et al. 2023

Geol. Belg.

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The Great Lakes area in Central Africa forms a large metallogenic province that hosts important deposits of gold mineralization. We present a petrographic, mineralogical and geochemical study of unique borehole samples from the Imonga-Saramabila gold deposit, a historical mine site located in the Maniema Province (DR Congo) in the Karagwe-Ankole belt (KAB) in the Great Lakes area and one of the only places in the Maniema province with accessible boreholes allowing to study the mineralization. The samples are metasedimentary rocks belonging to the Mesoproterozoic Kivu Supergroup, with bedding-parallel meta-igneous rocks. These rocks have undergone upper greenschist to lower amphibolite facies metamorphism, based on the presence of andalusite and chiastolite porphyroblasts, and are affected by hydrothermal alteration. The porphyroblasts formed during peak metamorphism and posterior to a first vein generation. Three additional vein generations were identified at Imonga based on crosscutting relationships, with the second and third events overprinting the porphyroblasts by intense chloritization, and associated with sulfide mineralization. The fourth vein generation is again barren. The first veining event formed pre-folding and the three subsequent generations postdate folding, as concluded based on the relationship of the veins with the cleavage. Only one important folding event is proposed based on the development of only one cleavage. Gold occurs as free gold or is included in pyrite in the second (and maybe third) vein generation. Based on the paragenesis, structural characteristics, and the link between veining and metamorphic minerals, the gold mineralization at Imonga is interpreted to be linked to the early Neoproterozoic (~980 Ma) compressional deformation event, associated with the amalgamation of the Rodinia supercontinent.

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Characterisation and geodynamic setting of the 1 Ga granitoids of the Karagwe-Ankole belt (KAB), Rwanda

Cited by 8 publications

References 46 publications

Paragenesis and precipitation stages of Nb-Ta-oxide minerals in phosphorus-rich rare-element pegmatites (Buranga dike, Rwanda)

Paragenesis and precipitation stages of Nb-Ta-oxide minerals in phosphorus-rich rare-element pegmatites (Buranga dike, Rwanda)

A Review of the G4 “Tin Granites” and Associated Mineral Occurrences in the Kivu Belt (Eastern Democratic Republic of the Congo) and Their Relationships with the Last Kibaran Tectono-Thermal Events

Current state of knowledge of the gold mineralization at Imonga-Saramabila, Maniema (DR Congo): a petrographic and mineralogical study of the mineralized vein system

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