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The Ririwai anorogenic alkaline complex harbours extensive rare metal (Nb-Zr-Sn-Zn) mineralization. However, uncertainty still surrounds their origin and magmatic-hydrothermal processes responsible for their rare metal mineralization. The complex is composed of peralkaline arfvedsonite ± albite-bearing granites, mildly peralkaline fayalite-bearing granite porphyries, and weakly peraluminous biotite-bearing granites, all of which show diagnostic A1-type characteristics. Zircon U-Pb dating reveals emplacement ages between 181.4 ± 0.81 and 188.6 ± 7 Ma for the three rock units. Sm-Nd and Pb isotopes (εNd (t) = –0.6 to −5.4, 206Pb/204Pb = 17.68–17.93) constrained the Ririwai A-type granites to represent highly fractionated products of enriched mantle-derived magmas. Mass-balance modelling suggests that magma evolution was fuelled by extensive fractional crystallization of 50 ~ 60 vol.% K-feldspar, 30 ~ 35 vol% fayalite, 5 ~ 10 vol.% amphibole, and ~ 5 vol.% apatite under reduced and water-undersaturated (ΔFMQ = –1.55; logfo2 = –18.63; H2O = <2.0 wt.%) conditions and assimilation of ~ 50 vol.% crust. Whole rock and amphibole compositions revealed an increasing degree of fractionation from the fayalite-bearing granite porphyries through biotite-bearing granites to the arfvedsonite ± albite-bearing granites. This extended fractionation at the late stage of magma differentiation, facilitated by fluorine dissolution and concentration of excess HFSE and REE as alkali-fluorocomplexes in the fluorine-rich silicate melt, allowed the accumulation of economic rare metal pyrochlore and columbite mineralizations in the highly fractionated arfvedsonite± albite- and biotite-bearing granites, respectively. Nonetheless, the metasomatic reaction rim textures around the magmatic pyrochlore, coupled with the M-type lanthanide tetrad effect (TE1,3 >1.10) indicate the subsequent effect of hydrothermal processes. Tectonically, reactivated shear fractures and transcurrent faults following lithospheric stresses in a transtensional regime allowed magma uprising and emplacement of A-type granites in the Ririwai complex. [ABSTRACT FROM AUTHOR]

Accurately determining the timing and mechanism of metallogenesis of ore deposits is essential for developing a robust genetic model for their exploration. In this paper, we analyze the formation conditions of cassiterite in five major deposits of southern Hunan Province, one of the most important tungsten-tin (W-Sn) provinces in South China, using a combination of cathodoluminescence imaging, in situ U-Pb geochronology, and trace-element concentration data. In situ cassiterite U-Pb geochronology constrains the main period of Sn mineralization to between 155.4 and 142.0 Ma, demonstrating a temporal and genetic relationship to silicic intrusive magmatism in the same area. Three stages of magmatic activity and metallogenic evolution are recognized: (1) Early Paleozoic and Triassic: the initial enrichment stage of tungsten and tin; (2) Jurassic: the metasomatic mineralization stage; and (3) Cretaceous: the magmatic-hydrothermal superposition stage. The cassiterite in these deposits takes four forms, i.e., quartz vein-type, greisen-skarn-type, greisen-type, and granite-type, representing a progression characterized by the increasing content and decreasing range of variation of high field strength elements (HFSEs), and reflecting a general increase in the degree of evolution of the associated granites. Rare earth element (REE) concentrations suggest that precipitation of cassiterite was insensitive to the redox state of the fluid and that precipitation of cassiterite in the southern Hunan Sn deposits did not require a high-fO2 environment. These findings provide new insights into tin mineralization processes and exploration strategies. [ABSTRACT FROM AUTHOR]

Zircon holds crucial information for deciphering the origin of granitic rocks, enabling robust scrutiny of their magmatic evolution. Herein, we report an integrated whole‐rock and zircon U–Pb and Lu–Hf isotope chemistry of Ropp alkaline granites in north‐central Nigeria. The rock units include riebeckite‐biotite granite porphyries (161.1 ± 1.7 Ma), aegirine‐biotite granites (162.4 ± 1.6 Ma), biotite granites (162.3 ± 5.1 Ma), and albite riebeckite granites. They show diagnostic characteristics of ferroan alkaline granites such as high FeOt/(FeOt + MgO), low Y/Nb (<1.2), and high Nb/Y (>1.0). Their zircon Hf isotopic compositions (εHf(t) = −8.08 to −4.38; 176Hf/177Hf = 0.282492–0.282543), major and trace element compositions such as high SiO2 >70% and incompatible trace elements (e.g., Rb, Ba, and La), low ratios of whole rock Th/U, Hf/Ta. Ni/Co and Th/Ta = 2.82, and zircon U/Yb, Gd/Yb, and Th/Yb ratios as well as oxygen fugacity (logfO2 = −26.09 to −12.32) reflect protracted fractional crystallization of a highly reduced mantle‐derived oceanic island basalt (OIB) magma from EM2 with considerable crustal involvement. Magma evolution was fuelled by fractionation of calcic‐pyroxene, calcic‐amphibole, Mg‐olivines, feldspars, titanite, and apatite, as corroborated by the marked depletions of CaO, MgO, TiO2, and P2O5. Intense crustal assimilation, particularly in the biotite granite masked their enriched mantle (EM) ancestry. This is attested by the presence of inherited Pan‐African (ca. 582 Ma) zircon, elevated crustal‐like zircon U/Yb, low zircon Gd/Yb, and Th/Yb ratios as well as high whole‐rock Rb/Nb ratios and relatively low estimated temperatures, which mimic crustal‐derived granites. Reactivation of pre‐existing megashear zones of weaknesses and opening of related transcurrent faults following periodic plate movements generated intense stress field which invoked the release of pressure and hot metasomatic fluids that partially melted the lower EM, giving rise to the Ropp OIB magmas. [ABSTRACT FROM AUTHOR]

The Bakoshi-Gadanya area, with widespread Neoproterozoic granites, is located within the Pan-African Trans-Sahara Belt, sandwiched between the West African and the Sahara metacraton. The whole-rock geochemistry, Sr-Nd isotope systematics and LA-(MC)-ICP-MS U-Pb-Hf isotopes of zircon were analysed to shed light on the age and genesis of the Bakoshi-Gadanya granites in the Precambrian basement of the northern western Nigeria shield. The granites are silicic (SiO2: 72.8–77.2 wt.%), ferroan, high-K, calc-alkalic to alkali-calcic in composition, with A-type granite affinities. The ferroan calc-alkalic types range in age from 706.6 ± 1 Ma to 638.4 ± 1 Ma, and the alkali-calcic type is dated at 710 ± 1 Ma. Whole-rock Sr-Nd and zircon Hf isotope systematics have constrained the ferroan calc-alkalic granites to an enriched mantle lithospheric magma source, contaminated by Archaean-Palaeoproterozoic crustal components. On the other hand, the magma that crystallized the alkali-calcic Gadanya granite originated from an enriched mantle source, triggered by reactivation of the lithosphere-scale Kalangai fault during the post 750 Ma major collision between West African Craton and the Saharan metacraton. Both alkali-calcic and calc-alkalic ferroan granites were formed contemporaneously with the last major Pan-African syn-metamorphic deformation in northern western Nigerian shield; thus, they are syn-kinematic granites. Neoproterozoic magmatism at Bakoshi-Gadanya area is related to easterly dipping subduction at the margin of microcontinental blocks in northern western Nigeria shield. Zircon U-Pb-Hf data envisaged both early Neoproterozoic and Cryogenian juvenile magmatic additions in this part of western Nigeria shield. [ABSTRACT FROM AUTHOR]

The Dutsen Wai and Ropp complexes are parts of the over 50 within-plate alkaline ring complexes in north-central Nigeria. These complexes consist mainly of A-type granites that were emplaced between 175 Ma (in Dutsen Wai) and 149 Ma (in Ropp). They are characterized by moderately negative zircon ԑHf(t) values (–9.8 to – 5.86) with Paleoproterozoic (1597–1884 Ma) crustal model ages (TDMc), suggesting the mantle-derived parental magmas have been substantially modified by assimilation of crustal materials. The granites exhibit elevated HFSEs (e.g., Nb and Zr) and LILE (e.g., Rb and REE) concentrations, with higher values in the peralkaline than in the aluminous granites, but are depleted in compatible elements (e.g., CaO, MgO, Ba and Sr). This is typical of highly differentiated granites associated with rare metal mineralization. The peralkaline plutons show REE patterns with strong negative Eu anomalies, significant M-type lanthanide tetrad effect (TE1,3 = 1.16–1.32), and non-CHarge and Radius Controlled (CHARAC) behaviour of some HFSEs. The positive correlation of Na2O vs. Nb (r2 = 0.92) and Nb vs. TE1,3 (r2 = 0.7), increasing degree of albitization and shift in eutectics of granite minimum towards Ab-Qtz sideline indicate that Na-rich fluid plays an important role in the complexation between F and other incompatible elements in open system processes. Fluorine also favoured the retention of these crucial metals in the peralkaline melt until late magmatic-stage during which the breakdown of the F-HFSEs and F-REE complexes was accompanied by crystallization of pyrochlore and REE-bearing accessory minerals. We proposed that the emplacement of these A-type granites was probably linked to the prevailing transtension regime before the fragmentation of Gondwana during the Mesozoic period which reactivated some deep-seated Pan-African transcurrent faults. This, in turn, caused pressure release and channelled fluid, which triggered partial melting of the lower part of the lithospheric mantle. [ABSTRACT FROM AUTHOR]

Late Cryogenian to Ediacaran magmatism of the East-Eastern Nigerian Terrane (E-ENT) in the Pan-African mobile belt provides a critical geological record that is important for unravelling regional tectonic and geodynamic setting. A detailed study that utilizes whole-rock elemental, in-situ zircon U-Pb and Lu-Hf isotopic geochemistry are conducted on the post-collisional granitoids from the Hawal Massif in the E-ENT. These granitoids are metaluminous to slightly peraluminous, alkali-calcic to calc-alkalic and ferroan in composition. U-Pb zircon ages suggest two granitic plutons were emplaced at 627 ± 4 Ma and ca. 580 Ma. Typically, these rocks are characterized by ƐHf(t) values ranging from +3 to -9.03 and TCDM ages range from 1.3 to 2.1 Ga, suggesting mixing of juvenile mafic melts with the older continental crust at different stages of the Pan-African Orogeny. Slab break-off most likely induced upwelling of the asthenosphere which in turn cause partial melting of the sub-continental lithospheric mantle (SCLM) and the lower crust at the early stage of Late-orogenic to generate 627 ± 4 Ma granites. The magmatism at ca. 580 Ma may have resulted from vertical planar lithosphere delamination as a consequence of transpressive movement along lithospheric scale shear zones which triggered asthenosphere upwelling that facilitated significant crustal melting at the waning stage of the Pan-African orogeny. The presence of post-collisional granite at 627 Ma and distinct isotopic signatures of the E-ENT granitoids compared to those from the NW-Cameroon and Mayo Kebbi domain suggest that E-ENT may have undergone different Pan-African evolution. [ABSTRACT FROM AUTHOR]