Search

The Bin Yauri-Libata polymetallic ore district is a Sn and Au ore-bearing district in the Zuru schist belt, Northwestern Nigeria. The Libata Sn ore field is characterized by a set of cassiterite-bearing hydrothermal veins associated with Neoproterozoic Pan-African granites affected by deformation and low-grade metamorphism. The hydrothermal alteration associated with cassiterite-bearing quartz veins in the Libata deposit includes silicification, albitization, chloritization, and potassic alteration. In this study, geochemical and geochronological data from tourmalines and zircons from Sn-bearing lodes, unmineralized and altered granites is applied to reveal the timing, fluid composition, and source of ore-forming materials for tin mineralization in the Libata ore field. Zircon trace element and Hf isotopes [εHf(t) = +4.37 to +10.85] reveal a mantle-derived source with some crustal contribution for the melts forming the Libata Sn-bearing granites. LA-ICP-MS zircon U-Pb dating constrains the magmatic and hydrothermal ages to 650–646 and 649–646 Ma for the Libata granites. Overlapping zircon εHf(t) and 176Hf/177Hf but distinct 176Lu/177Hf and 176Yb/177Hf ratios from magmatic and hydrothermally altered zircons reveal a magmatic source for the hydrothermal fluids which triggered cassiterite deposition in the Libata ore field. Major element chemistry constrain tourmalines from the Libata ore field as schorls that show high alkalis, low-Ca contents, and moderate □ values (where □ is x-site vacancy). High Li, Zn, and Sn concentrations in tourmaline as well as Li/Sr and Ca-Fe-Mg ratios demonstrate that the tourmaline formed from granite-sourced fluid likely derived from the host Libata granites. Measured δ11B values from the Libata tourmaline range from –15.7‰ to –14.1‰. The δ11B of the mineralizing fluid is estimated to be –13.1 to –11.9‰ for the Libata tourmalines at 400–500 °C and overlaps with averages from fractionated granites worldwide. Therefore, our data show that tourmaline and zircon are useful tracers of magmatic-hydrothermal evolution in rare-metal-bearing granite systems. [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]

High-K granites dominate the rock units in the Bakoshi and Gadanya areas located in the northwestern Nigerian subshield, part of the Trans-Saharan Belt, West Africa. In this contribution, the LA-ICP-MS zircon trace element revealed the fertility of magma responsible for the high-K granites that hosts the Bakoshi–Gadanya gold mineralization. Two likely metallogenic granites types are 1) Gadanya alkali granite, with high Ce4+/Ce3+ (mean 1485) and limited range of Eu anomalies may likely be associated with the gold mineralization, and 2) Bakoshi porphyritic granite, Jaulere biotite granite, Shanono coarse-grained granite, and Yettiti granite, all have low Ce4+/Ce3+ ratios (mean < 100, except second Bakoshi granite D2-1) with wider ranges of Eu/Eu* values, thus are considered reduced granites. These reduced granites have oxygen fugacity values and Eu anomalies comparable to reduced granites associated with tin belts in Myanmar and Zaaiplaats granites in Bushveld Complex, South Africa. Ti-in-Zircon thermometric study revealed two thermal regimes during the crystallization of the Bakoshi–Gadanya granites: the high temperature (746–724 °C): Shanono coarse-grained granite, Bakoshi granite D2-1, and Jaulere biotite granite; and relatively low temperature (705–653 °C): Bakoshi porphyritic granite D1-1, Yettiti medium-grained granite, and Gadanya alkali granite. Zircon trace elements including U, Yb, Y, Nb, and Sc ratios constraint the magma source of Bakoshi–Gadanya granites to an enriched mantle metasomatized during the subduction process before its melting. Except for Gadanya alkali granite, fractionation of titanite and apatite dominate the magma evolution with limited amphibole fractionation. Melt that crystallized Gadanya alkali granite is rather saturated in zircon without accessory titanite or apatite. [ABSTRACT FROM AUTHOR]

The genesis and timing of molybdenum (Mo) mineralization in the Mada Ring Complex, north-central Nigeria, have been constrained using a combination of whole-rock elemental geochemistry, Nd-Sr isotopes, zircon U-Pb-Hf isotopes, and molybdenite Re-Os geochronological data. The Mada Ring Complex is one of fifty-three within-plate alkaline ring complexes with economically significant Sn and Nb production from largely alluvial placer deposits in north-central Nigeria. Molybdenum mineralization in the ring complex is dominantly disseminated with minor stockwork veins hosted within biotite granite. Integrated zircon U-Pb and molybdenite Re-Os geochronology constrain initial magma emplacement to between 152 and 151 (± 1) Ma and the Mo-mineralization event to ≤ 150 (± 1) Ma. The granites associated with Mo mineralization are highly silicic and display elevated whole-rock concentrations of Nb, Zr, Y, and REE (except Eu), as well as high 87Rb/86Sr ratios, but low concentrations of Sr, Ba, CaO, MgO, and TiO2, consistent with highly differentiated A-type granites. They yield moderately negative whole-rock εNd(t) (− 5.87 to − 5.47) and zircon εHf(t) (− 4.97 to − 10.06), suggesting that their parental magmas were largely derived from the lower crust with a contribution from the upper mantle. Magmatic oxygen fugacity (ƒO2) of the A-type granites (log FMQ = +1.16), constrained from zircon compositions, is lower than values reported from typical within-plate porphyry molybdenum deposits (log FMQ = +2 to + 3). However, compared to regional Sn ± Nb-mineralized A-type granites, the Mada A-type granites have higher ƒO2 and Ce4+/Ce3+, but are less differentiated. [ABSTRACT FROM AUTHOR]

Tourmaline and gold mineralization form an association in the Bakoshi-Gadanya (BAG) Goldfield on the northern West Nigerian Subshield, located in the southern Trans-Saharan Orogenic Belt of West Africa, although the cogenicity of this association remains untested. In this study, we report the results of an integrated study of the boron isotopic and major- and trace-elemental compositions of BAG tourmalines, from which we infer the nature and origin of the hydrothermal parent fluids and their role in the associated gold mineralization. Tourmalines in the BAG Goldfield are of four types: altered granite-related (Tur I), wallrock-hosted (Tur II), Gadanya Tourmalinite (Tur III) and Shanono Tourmalinite (Tur IV). The tourmalines mainly belong to the alkali group with dravite (i.e., Mg-rich) compositions. The MgFe −1 and □Al(NaR) −1 exchange vectors are the dominant substitution mechanisms for all BAG tourmalines with contributions from deprotonation AlO[R(OH)] −1 substitutions. Except for Tur I, which is enriched in Rb (0.02–21.9 ppm) and Cs (0.01–0.63 ppm), due to high fluid-rock reaction, the BAG tourmalines are enriched in Cr (2.0–3908 ppm), Ni (5.0–222 ppm), Co (0.05–27.4 ppm), Sr (41.8–3031 ppm), Sc (1.6–281 ppm), V (32.0–701 ppm), Al (0.01–0.35 apfu), Fe (0.59–1.47 apfu), and Mg (0.67–2.43 apfu), suggesting metasedimentary-derived components. Boron isotopes display bimodal populations from −16.8 to −12.0 ‰ (Tur II to IV) and from −23.0 to −19.0 ‰ (Tur I). We propose that greenschist to amphibolite facies metamorphism during the Pan-African Orogeny devolatilized country-rock metapelites and produced a metamorphic-hydrothermal fluid responsible for BAG tourmalinization. These metamorphic-derived Tourmalines show no relationship to the magmatic-hydrothermal fluid derived BAG gold ore. Our results show that the BAG tourmalines may not serve as indicator minerals in exploration for gold mineralization in the BAG Goldfield in northern West Nigerian Subshield. • Tourmalines from the Bakoshi-Gadanya area mainly alkali type and dravitic compositions • Metamorphic fluids led to tourmalinization • Tourmalines elemental composition contrast the gold fluid chemistry [ABSTRACT FROM AUTHOR]

We report a combined study of whole-rock major- and trace-element geochemistry, Sm Nd isotope composition, zircon U/Pb dating, and Lu Hf systematics of peralkaline and aluminous A-type granites from the Ririwai Ring Complex in north-central Nigeria. The Ririwai peralkaline and aluminous A-type granites are strongly ferroan, alkalic to alkali-calcic, and enriched in Hf, Zr, Ga, Rb, Y and REEs. They were emplaced between 176 ± 2.3 Ma and 169.6 ± 0.75 Ma. The peralkaline granites yield relatively higher ɛNd(t) (−2.3 to −1.2) and zircon ɛHf(t) values (−5.8 to −1.7) than the aluminous granites (ɛNd(t) = −3.6 to −3.3; zircon ɛHf(t) = −7.8 to −2.4). In addition, inherited zircons in the aluminous granites yield Pan-African (~590 Ma) ages and low ɛHf(t) values (−14.0). Taken together, these data suggest that the granites formed from extensive fractional crystallization of a transitional basaltic melt derived from an enriched OIB mantle source. The depletions of MgO, CaO, Ti 2 O, Sr and Ba in the granites indicate that Mg-rich olivine, calcic pyroxene, calcic amphibole, feldspars and Fe Ti oxides were the major fractionated phases during magma evolution. In addition, several types of evidence, e.g., moderately negative ɛNd(t) and ɛHf(t) values, and the presence of inherited zircons, imply that the parental melt was modified by assimilation of Pan-African upper crust into which the granites were emplaced. A transtensional regime generated prior to late Jurassic breakup of Gondwana, which led to reactivation of shear zones and opening of associated transcurrent faults, paved the way for emplacement of the A-type suite. The Sn–Nb–Zn mineralization of the Ririwai A-type suite was probably linked to complex magmatic evolutionary processes involving extensive fractional crystallization coupled with crustal assimilation and late-stage hydrothermal fluid activity. • The Ririwai granites show geochemical characteristics typical of A-type granite. • The A-type granite suites were emplaced between (176 ± 2.3 to 169.6 ± 0.75 Ma). • The granites formed from differentiation of magmas derived from enriched mantle. • Inherited zircon obtained from the granite suggests crustal contamination. • The Sn-Nb-Zn mineralization was linked to assimilation-fractional crystallization. [ABSTRACT FROM AUTHOR]

[Display omitted] • The Bakoshi-Kundila deposit is Au-rich and akin to an orogenic gold deposit. • Al3+ and Fe3+ were the main elements substituting Si4+ in the quartz structure. • Fluid-rock reaction and pH controlled the element incorporation into quartz. • Magmatic-derived hydrothermal fluid was responsible for Au formation. The Bakoshi-Kundila Au deposit is located in the Nigerian Shield in West Africa. In this deposit, Au-bearing pyrite contains inclusions of Au-rich hydrothermal quartz. Whether or not this co-precipitation relationship of quartz and pyrite is cogenetic and related to the gold fluid remains untested. The deposit's genetic affiliation is controversial. This study reports the results of textural and in situ chemical compositions of hydrothermal quartz, and sheds light on fluid composition, element substitutions into quartz structure, and inferred the deposit genetic type. We grouped the quartz into four generations: Qz1 and Qz2 (vein-type) and Qz3 and Qz4 (wallrock-type). The Qz2 is deformed, overprinted by late-stage fluid activity. The Qz1 is rich in Ga and Sr but poor in Al and Fe than Qz3 and Qz4: average Ga in ppm (Qz1 – 0.62, Qz3 – 0.08, Qz4 – 0.15), Sr (Qz1– 26.7, Qz3 – 4.59, Qz4 – 5.78), Al (Qz1– 16.7, Qz3 – 82.8, Qz4 – 136), Fe (Qz1– 131, Qz3 – 144, Qz4 – 133). However, the contents of low melting point chalcophile elements (LMCE) are higher and overlapped between Qz1 and Qz3 than those from Qz4: average Au in ppm (Qz1– 33.9, Qz3 – 38.2, Qz4 – 7.83), C u (Qz1 – 13.1, Qz3 – 14.8, Qz4 – 5.95), Bi (Qz1 – 3.48, Qz3 – 0.25, Qz4 – 0.51). The LMCE in Qz1 displayed covariant relationships with Au (but poorly defined in Qz3 and Qz4), suggesting the likely presence of Au-Ag-(±Te)-bearing phases like petzite and argentum. Aluminum is the main trivalent element substituting Si4+ in Q3 and Qz4, whereas Fe3+ in Qz1. The charge-balanced cations are Li+, Na+, and K+ in Qz3 and Qz4, whereas Sr2+ in Qz1. The Al and Ti contents (in ppm) are higher and more variable in Qz3 (Al: 5.97–374, avg 82.8; Ti: 2.69–12.5, avg 6.60) and Qz4 (Al: 8.13–792, avg 136; Ti: 7.64–72.0, avg 20.2), which may imply fluctuation in fluid pH. These element concentrations are lower and less variable in Qz1 (Al: 5.25–47.8, avg 16.7; Ti: 3.41–18.0, avg 5.43), suggesting a less acidic and probably stable pH condition during its precipitation. The Qz1 has a lower average content (in ppm) of compatible elements (K – 15.7, Fe – 13.1, Ti – 5.43) than Qz3 (K – 25.9, Fe – 144, Ti – 6.60) and Qz4 (K – 63.0 Fe – 133, Ti – 20.2), implying that Qz3 and Qz4 precipitated at a higher temperature than Qz1. However, the contents of the incompatible elements (e.g., P, Ge, Rb, and Li) are not enriched in the supposed lately-formed Qz1 over Qz3 and Qz4, which is inconsistent. The inconsistency is also true between the wallrock type, with lower contents in low-temperature Qz3 than in high-temperature Qz4. Thus, temperature is considered not a major controlling factor during the formation of Bakoshi-Kundila quartz; instead, the pH condition and fluid-rock reaction are favored. The Bakoshi-Kundila quartz has Al-Ti contents akin to quartz from orogenic Au deposits. [ABSTRACT FROM AUTHOR]

The Benue Trough of Nigeria is an intracratonic rift basin hosting several vein-type base metal deposits. The Akiri Cu ± (Ag) deposit represents a distinct sub-class of sediment-hosted Pb-Zn-Cu-Ba mineralization found throughout the Benue Trough. The deposit is hosted in bleached red beds of the Keana Formation and in shale-siltstones and carbonates of the Ezeaku Formation in the Middle Benue Trough, North-Central Nigeria. Mineralization at the Akiri deposit occurs as vein in-fillings in a series of N E -SW and E-W trending faults and fractures in the Early- to Late-Turonian Keana and Eze-Aku sedimentary rocks. To better constrain the sources of ore minerals and structural controls on the formation of this sediment-hosted Cu ± (Ag) mineralization, we report combined geologic, geochemical, mineralogical, and stable isotopic data for the Akiri Cu ± (Ag) deposit. Major ore-stage sulfides at Akiri are chalcopyrite and pyrite, which were accompanied by several types of alteration, including silicification, hematization, limited pyritization, and bleaching of mineralized sandstone bodies. In-situ trace element and sulfur isotopic data distinguishes early-stage pyrite (Py1) from late-stage pyrite (Py2). The late-stage Py2 co-exists with chalcopyrite suggesting coeval precipitation. Early-stage pyrite (Py1) contains lower Ag (avg. 0.04 ppm) but higher Au (avg. 3.03 ppm) than the late-stage pyrite (Py2) (avg. Ag = 2.78 ppm; Au = 0.424 ppm). The δ34S values of the early-stage sulfide (Py1) vary from 19.07‰ to 25.99‰ (avg. 22.20‰), suggesting that sulfur was largely derived from thermochemical reduction (TSR) of seawater sulfate. The δ34S values for co-existing Py2 and chalcopyrite range from 9.83‰ to 11.24‰ (avg. 10.32‰) and from 7.37‰ to 10.69‰ (avg. 8.96‰), respectively, suggesting a derivation of sulfur from TSR of seawater sulfate with contributions from magmatic sulfur. Based on structural features and ore textures, we propose that sulfide precipitation at Akiri was facilitated by sulfur-rich fluids circulating through pre-existing structures (fractures and faults) under fairly high (>200 °C) to moderate (<170 °C) temperature conditions. Geological, mineralogical, geochemical and isotopic data from this study support the classification of the Akiri Cu (+Ag) deposit as an epigenetic sandstone-hosted copper deposit. [ABSTRACT FROM AUTHOR]

The Ningi-Burra Pb−Zn mineralization forms part of the Nigerian Sn-Nb ± (Pb-Zn-Mo)-rich anorogenic alkaline province, also known as the Nigerian Younger Granite Complexes. Six distinct E -W trending magmatic centres have been identified in the Ningi-Burra complex, but the Pb−Zn mineralization is confined to highly evolved biotite granite in Koluki (centre 6). In this paper, a combination of geochronological and geochemical data of magmatic and hydrothermally-altered zircon from the Ningi-Burra complex are used to constrain magmatic and hydrothermal processes that facilitated the formation of Pb−Zn mineralization. Zircon trace element and Hf isotopes (εHf(t) = −5.3 to −10.3) indicate that the parental magma of these ore-bearing granites were largely derived from lower crustal sources with contributions from the upper mantle. The hydrothermal alteration that accompanied the Pb−Zn mineralization include silicification, chloritization and limited sodic metasomatism. Zircon U/Pb dating reveal that magma emplacement and subsequent hydrothermal process in Ningi-Burra complex occurred at (~192 Ma) and (<191 Ma), respectively. Zircon grains from unmineralized and hydrothermally altered rock suites have similar 176Hf/177Hf but distinct 176Lu/177Hf and 176Yb/177Hf ratios which suggest a magmatic source for the hydrothermal fluids responsible for the formation of the mineralization. This study highlights the application of zircon trace element and U-Th-Hf isotopes as robust tools for constraining magmatic and mineralization process that facilitate the formation of economically significant mineralization in highly differentiated granites. • Zircon can track magma origin and evolution in highly differentiated granites. • Slightly reduced trace-element rich fluids are favored for Pb−Zn mineralization. • The main magmatic-hydrothermal episodes appear to have peaked at 191–189 Ma. • Rock-forming magmas are likely of crustal origin with contributions from the mantle. [ABSTRACT FROM AUTHOR]