Late Neoproterozoic overprinting of the cassiterite and columbite-tantalite bearing pegmatites of the Gatumba area, Rwanda (Central Africa)

Dewaele, Stijn; Henjes‐Kunst, Friedhelm; Melcher, Frank; Sitnikova, Maria; Burgess, R.; Gerdes, Axel; Fernandez, Max; Clercq, Friso De; Muchez, Philippe; Lehmann, Bernd

doi:10.1016/j.jafrearsci.2011.04.004

Cited by 97 publications

(84 citation statements)

References 46 publications

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“…U, W, Au, Zn, Sn, Pb, and As are locally enriched, possibly in part due to mining activity and anthropogenic pollution. In spite of widespread Sn, W, Nb, and Ta mineralizations (Dewaele et al 2011), wolframite, columbite-tantalite, or cassiterite were never found in our samples.…”

Section: Volcanic Rift Provenance (Limited Weathering)contrasting

confidence: 70%

Weathering and Relative Durability of Detrital Minerals in Equatorial Climate: Sand Petrology and Geochemistry in the East African Rift

Garzanti

Padoan

Andó

et al. 2013

The Journal of Geology

133

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This article investigates how, where, and to what extent the mineralogical and chemical composition of sand-sized sediments is modified by extreme weathering in modern equatorial settings, with the ultimate goal of learning to read climate from the sedimentary record. To single out the weathering effect, we studied the compositional trends of fluvial sands along the western branch of the East African Rift between 5 degrees S and 5 degrees N. The relative durability of different detrital components, as well as potential hydraulic-sorting and grain-size effects, were assessed by comparing samples with similar provenances in different climatic and environmental conditions or of different size classes within the same sample. Sands of equatorial central Africa at the headwaters of the Congo and Nile basins display the full spectrum of petrologic suites characterizing rift-shoulder and volcanic rift provenances. Unlike in arid Arabia, quartz-ose sands are not restricted to areas where detritus is recycled from prerift sedimentary covers. In a hot humid climate, weathering can effectively obliterate the fingerprint of parent rock lithology and produce a nearly pure quartz residue even where midcrustal basement rocks are being actively uplifted and widely unroofed. In such settings garnet is destroyed faster than hornblende, and zircon faster than quartz. Weathering control on detrital modes is minor only in the rain shadow of the highest mountains or volcanoes, where amphibole-dominated quartzofelicdspathic metamorphiclastic sands (Rwenzori Province) or clinopyroxene-dominated feldspatholithic volcaniclastic sands (Virunga Province) are generated. Our detailed study of the Kagera basin emphasizes the importance of weathering in soils at the source rather than of progressive maturation in temporary storage sites during stepwise transport and shows that the transformation of diverse parent rocks into a quartzose "white sand" may be completed in one sedimentary cycle in hydromorphic soils of subequatorial lowlands. Micas and heavy minerals, which are less effectively diluted by recycling than main framework components, offer the best key to identify the original source-rock imprint. The different behavior of chemical indexes such as the CIA (a truer indicator of weathering) and the WIP (markedly affected by quartz dilution) helps us to distinguish strongly weathered first-cycle versus polycyclic quartz sands

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Section: Volcanic Rift Provenance (Limited Weathering)contrasting

confidence: 70%

Weathering and Relative Durability of Detrital Minerals in Equatorial Climate: Sand Petrology and Geochemistry in the East African Rift

Garzanti

Padoan

Andó

et al. 2013

The Journal of Geology

133

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“…This magmatic event was followed by the intrusion of the G4-granites (or "tin granites") at 986 ± 10 Ma (U-Pb SHRIMP on zircon; [16]). Cassiterite, columbite-tantalite (coltan) and wolframite mineralizations are related to this G4-granite generation, either forming pegmatites (Sn-Ta-Nb) or hydrothermal quartz veins (W-Sn) [23]. The present study focuses on the mineralogy, paragenesis and mineral chemistry of tungsten mineralization that occurs in the particular form of reinite in central Rwanda along the so-called north-northwest to south-southeast trending "tungsten belt", more specifically, in the Nyakabingo, Gifurwe and Bugarama mines (Figure 1).…”

Section: Geologic Setting Of Tungsten Mineralizationmentioning

confidence: 99%

“…The thick W-mineralized bedding-parallel quartz veins are also typically hosted by the carbonaceous shales, where they formed along bedding-parallel parting planes. These veins are interpreted to be related to the intrusion of the G4-granites, which were emplaced in the context of post-collisional relaxation [5,22,23]. Both types of bedding-parallel veins are often crosscut by subvertical veins, which are at a high angle to bedding.…”

Section: Geologic Setting Of Tungsten Mineralizationmentioning

confidence: 99%

Mineralogy and Trace Element Chemistry of Ferberite/Reinite from Tungsten Deposits in Central Rwanda

et al. 2013

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Tungsten mineralization in hydrothermal quartz veins from the Nyakabingo, Gifurwe and Bugarama deposits in central Rwanda occurs as the iron-rich endmember of the wolframite solid solution series (ferberite) and in the particular form of reinite, which represents a pseudomorph of ferberite after scheelite. Primary ferberite, reinite and late secondary ferberite are characterized by their trace element chemistry and rare earth element patterns. The replacement of scheelite by ferberite is also documented in the trace element composition. Primary ferberite shows high Mg, Zn, Sc, V, Nb, In and Sn concentrations, but very low Ca, Pb, Sr and Ba contents. Reinite and late secondary ferberite display an uncommon trace element composition containing high concentrations of Ca, Pb, Sr, Ba, As and Ga, but very low levels in Sn, Zr, Hf, In, Ti, Sc, Nb, Ta, Mg and Zn. Late secondary ferberite replacing primary ferberite is characterized by additional enrichments in Bi, Pb, As and Sb. The rare earth element patterns of reinite and secondary ferberite are also similar to hydrothermal scheelite. The formation of the tungsten deposits in central Rwanda is interpreted to be epigenetic in origin, and the hydrothermal mineralizing fluids are related to the intrusion of the G4-granites.

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“…Melcher et al [45] have characterized some local to regional differences in the mineralogy and geochemistry of the Ta-Nb-Sn bearing phases. Rare-metal granite (RMG) and pegmatite-bearing rare-element are described in several districts (Figure 1), from Archean to Mesozoic provinces [45][46][47][48][49][50][51][52][53][54][55][56][57]. Each of these periods of Ta-Nb-Sn ore formation is characterized by peculiar mineralogical and geochemical features that, when combined with geochronological constraints, allow for associating these provinces with magmatic episodes and a geodynamic environment: syn-to late-orogenic (e.g., West African Craton, Zimbabwe Craton), post-orogenic (Kibara Belt, Damara Belt, Older Granites of Nigeria, Adola Belt of Ethiopia) and anorogenic (Younger Granites of Nigeria) ( [45]; Figure 1).…”

Section: Introductionmentioning

confidence: 99%

Evidence for Nb-Ta Occurrences in the Syn-Tectonic Pan-African Mayo Salah Leucogranite (Northern Cameroon): Constraints from Nb-Ta Oxide Mineralogy, Geochemistry and U-Pb LA-ICP-MS Geochronology on Columbite and Monazite

et al. 2018

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The Mayo Salah pluton, which is located in the North-Cameroon domain of Central African Bold Belt (CAFB), is emplaced as a laccolith in volcano-sedimentary schists of Poli series, and displays features of Rare-metal Granite (RMG). It is made of two main rock groups: (1) the metaluminous barren muscovite granite (MsG) and (2) the Nb-Ta bearing peraluminous leucogranite (MsL) which expresses four subtypes. The evolved Rare-element MsL is subalkaline, slightly peraluminous (ASI = 1.01-1.21), and it displays flat REE chondrite-normalized patterns with a strong negative Eu anomaly (Eu/Eu* = 0.02-0.20). It belongs to the peraluminous low phosphorus Rare-element Granites and L-type igneous rocks, as shown by the relatively low Zr/Hf (4.8-14) and Nb/Ta (1.4-9.0) ratios and the positive slope of the Zr-Hf-Nb-Ta profile in spider diagrams. The rare-element-bearing mineral is represented by columbite-group minerals (CGM) and other Nb-Ta-oxides (Nb-rutile and pyrochlore supergroup minerals). The CGM is classified as Mn-columbite, with Ta# and Mn# ratios increasing from core to rim. Two stages of mineralization are identified; the earliest stage (CGM-I) consists in scattered tabular or prismatic euhedral grains that were related to magmatic fractionation. The latest stage (CGM-II) is expressed as a Ta-rich Mn hydrothermal CGM episode represented as rims and/overgrowths around and/or as veinlet crosscutting CGM-I or in cleavage planes of muscovite. The U-Pb dating of columbite and monazite of the Mayo Salah leucogranite indicates a late-Neoproterozoic magmatic-hydrothermal mineralization event from 603.2 ± 5.3 to 581.6 ± 7.2 Ma, as consistent with both late D 2 to D 3 events that were recorded in the CAFB in Cameroon, and the associated continental collision environment. The Nb-Ta mineralization of the Mayo Salah pluton provides evidence for the presence of RMG in Northern Cameroon of CAFB, and its temporal association with the youngest period of metallogenic epoch of Nb-Ta-ore formation in Africa associated to Pan-African times. This paper presents an original geological description of the Mayo Salah leucogranite from the Poli region, North Cameroon ( Figure 2). It provides evidence for the first rare-metal bearing granite that is described in this area through field observations, whole-rock geochemistry, textural features, and Minerals 2018, 8, 188 5 of 36 mineralogy of Nb-Ta oxides-bearing minerals. Combining the geochemical and mineralogical features of the Mayo Salah leucogranite with U-Pb geochronological constraints on associated columbite and monazite minerals will allow for discussing the granite emplacement within the current knowledge of the geodynamic environment in this area during Pan-African times. Geological ContextThe Poli region belongs to the Northern Cameroon domain (NCD) of the Central Africa Fold Belt (CAFB) in Cameroon (Figure 2; [62 -64,67-70,79]). This domain results from the collision between the Sahara metacraton [80,81] and the Adamawa-Yadé domain (AYD). Precambrian terrains of the NCD are made of t...

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Late Neoproterozoic overprinting of the cassiterite and columbite-tantalite bearing pegmatites of the Gatumba area, Rwanda (Central Africa)

Cited by 97 publications

References 46 publications

Weathering and Relative Durability of Detrital Minerals in Equatorial Climate: Sand Petrology and Geochemistry in the East African Rift

Weathering and Relative Durability of Detrital Minerals in Equatorial Climate: Sand Petrology and Geochemistry in the East African Rift

Mineralogy and Trace Element Chemistry of Ferberite/Reinite from Tungsten Deposits in Central Rwanda

Evidence for Nb-Ta Occurrences in the Syn-Tectonic Pan-African Mayo Salah Leucogranite (Northern Cameroon): Constraints from Nb-Ta Oxide Mineralogy, Geochemistry and U-Pb LA-ICP-MS Geochronology on Columbite and Monazite

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