Migmatite-gneiss Complex Research Articles

Geology and Petrography of the Basement Complex Rocks of Tsauni and Environs, North Central Nigeria

Detailed geological mapping and petrographic study of the rocks in Tsauni area and environs situated within Gwagwalada in Abuja Federal Capital Territory have been carried out to establish the geology relative to the rock types, texture, mineralogy, and mineralization. The area is part of the Basement Complex of North Central Nigeria and a newly discovered skarn environment with preserved basement metagranitoids of the migmatite-gneiss complex and lower grade metasedimentary schist belts. Major rock types identified include migmatite and various types of gneisses. Subordinate rocks include calc-silicate (skarn) rocks, ultramafic relicts and fine to medium grained granite all crosscut by younger Pan African granite, diorite, pegmatites, and quartzo-feldspathic veins. Two types of skarn; A and B were distinguished petrographically being the first mention of skarn occurrence in Nigeria. Petrographic study of selected rocks under plane and crossed polarized light alongside Back Scattered Electron (BSE) images from microprobe analysis showed the mineral suites to include quartz, feldspar (mostly plagioclase and subordinate alkali feldspar), biotite, minor amphibole, pyroxene, calcite and muscovite with accessory epidote, allanite, zircon, titanite, apatite and opaque minerals which selectively occur in both metagranitoids and skarn. Opaque minerals include magnetite, ilmenite± rutile, galena, pyrite sphalerite, and chalcopyrite. Structural features include foliation, joints, xenoliths and pendant (flame) textures, veins, and veinlets which are all aligned in the NE-SW, NW-SE, and minor N-S and E-W directions suggesting control from some deep-seated sources.

Petrological insights into connections between the S- and I-type magmatic associations in metamorphic core complexes: a case study of the Çataldağ metamorphic core complex (NW Turkey)

As one of the Cordilleran-type metamorphic core complexes in the western Anatolian extensional province and the broader Aegean region, the Çataldağ metamorphic core complex is composed of a granite-gneiss-migmatite complex and a synkinematic pluton, bounded by a detachment fault zone. The plutonic rocks within the footwall of the Çataldağ metamorphic core complex consist of Eo-Oligocene anatectic S-type leucogranites associated with gneiss-migmatite complex forming the core rocks and an I-type synkinematic pluton that emplaced into the core rocks in the Early Miocene. This paper presents the petrography, mineral chemistry, major-trace element geochemistry, and Sr-Nd-Pb isotope compositions of the Çataldağ I-type synkinematic pluton. It discusses the magma source evolution from the Eo-Oligocene to the Early Miocene and their relations to the Çataldağ metamorphic core complex formation by comparing two contrasting granitic associations from a petrological perspective. The Çataldağ I-type synkinematic pluton primarily comprises porphyritic granodiorite, granite, and peripheral rocks including evolved granite and pegmatite dikes. Thermobarometry calculations estimate crystallisation conditions of approximately 795 °C at 1–2 kbar (averaging 1.5 kbar), corresponding to a shallow crustal magma chamber (⁓5 km deep). The pluton is metaluminous to slightly peraluminous and of a high-K calc-alkaline character. The 87Sr/86Sr(i) and εNd values of the studied samples range from 0.70684 to 0.70772 and from −6.1 to −2.3, respectively. Pb isotopic compositions are 18.74–19.29 for 206Pb/204Pb, 15.69–15.78 for 207Pb/204Pb, and 38.89–39.39 for 208Pb/204Pb. Geochemical modelling shows that a large amount of metasomatised lithospheric mantle-derived melt component (up to 70%) and a minor crustal component (<50%) contributed to the source region of the magma. The combination of isotopic data and thermodynamic modelling suggests that the compositional variations within the pluton were primarily the result of open system processes, predominantly the assimilation of crustal rocks with a dominance of fractional crystallisation. The Sr-Nd-Pb isotopic signatures and trace element characteristics of I-type pluton, as well as their comparisons with those of S-type leucogranites within the Çataldağ core complex, indicate heterogeneous magma sources, evolving from crust-dominated to mantle-dominated magma from Eo-Oligocene to the early Miocene, reflecting mantle upwelling beneath NW Anatolia. We infer that the long-lived, mantle-driven Eocene plutonic activity that preceded the development of core complexes may have led to thermal weakening, melting, and crustal flow in the lower-middle crust beneath NW Anatolia, facilitating the formation of the granite-gneiss-migmatite complex during the incipient phase of extension in the Eo-Oligocene. Coinciding with the rapid exhumation of the S-type granite and migmatite complex, the formation and emplacement of I-type synkinematic pluton along the detachment fault zone of the Çataldağ core complex were developed as a result of asthenospheric upwelling driven by lithospheric removal processes. This inferred lithospheric removal was triggered by Hellenic slab rollback affecting the entire western Anatolia since the Oligocene. The transition from S- to I-type granites observed in the Çataldağ core complex and other Aegean massifs may indeed be a manifestation of the intensity or accumulation of this crustal extension.

On Some Accessory Minerals in Upper Paleozoic Granites of the Khrami Crystalline Massif

The Khrami crystalline massif is exposed within the Black Sea – Central Transcaucasian terrane (Georgia). The massif is built up of Preсambrian gneiss-migmatite complex, the packet of Middle Paleozoic (?) metasandstones and protrusions of mantle serpentinites; Paleozoic gabbroids; Middle-Upper Paleozoic granitoids and rocks of volcanogenic-sedimentary complexes and Upper Paleozoic quartz-porphyry - granite-porphyry formations. A number of scientists have studied the granitoids of the Khrami crystalline massif, but detailed investigations on some minerals using modern analytical facilities have not been conducted yet. The Late Variscan granitoids of the Khrami massif are represented by biotite-hornblende-allanite-, biotite-microcline- and biotite-garnet-bearing granites and aliaskites. We have studied in detail the accessory minerals - garnet and allanite in the Late Variscan granites of the massif. Their microprobe analysis has been performed. According to the microprobe analysis of the studied garnets, the centre of the crystal is homogeneous, while the peripheral part is zonal. The amount of FeO decreases slightly from the centre to the periphery, while the amount of CaO and MgO significantly decreases; a well-expressed increase in MnO content is recorded. The variation in almandine content is insignificant. The amount of pyrope and grossular drops sharply from the centre to the periphery while the number of spessartine increases. The amount of Al2O3 in all varieties of granitoids is similar. In our opinion, the garnet formation occurred in two stages: during the crystallization process of granitic magma and its subsequent post-magmatic stage. The core of the garnet was formed in the magmatic stage, but its periphery - was in the cooling stage of granitic magma. According to the results of the microprobe study of allanite, the same - two stages of their formation have been conducted: during the crystallization process of granitic magma and in its next post-magmatic stage. The genesis of allanite in the biotite-hornblende-allanite-bearing granites of the massif is due to the concentration of REE in the granitic magma and the introduction of calcium by hydrothermal solutions. These allanites belong to the cerium variety with high content of Ce2O3, La2O3 and Nd2O3.

Geologic mapping and basement\u2013sediment contact delineation along Profile X, Igarra\u2013Auchi area, Southern Nigeria using ground magnetic and electromagnetic methods

Outcrop mapping as well as electromagnetic and ground magnetic surveys was carried out within Auchi and Igarra localities in order to attempt an interpretation of the geology of the areas and to delineate the boundary between basement and sedimentary terrains. Geologic mapping was done by collecting samples of outcrops at five different locations within the areas. Three lithofacies were identified within Auchi area and they are the basal shale unit, tabular cross-bedded sandstone unit and ferruginized sandstone unit. The pebbly shale is greyish black in colour; the cross-bedded sandstone unit is greyish white, coarse-grained at the base and finer at the top with pockets of clay, while the ferruginized sandstone is dark red. Rocks of the Precambrian basement complex underlie Igarra area. The area is underlain by metasediments that have been intruded by igneous rocks. Results show the presence of three major groups of igneous and metamorphic rocks within the area, and they are the migmatite–gneiss complex, metasediments and porphyritic granites. The electromagnetic and ground magnetic data acquired along Profile X located along Auchi–Igarra–Ibillo road were processed using Microsoft Excel Software and the resulting plots delineated areas with lower electrical conductivities and higher magnetic susceptibilities, as well as areas with higher electrical conductivities and lower magnetic susceptibilities. The areas with lower electrical conductivities and higher magnetic susceptibilities are interpreted to be underlain by basement rocks, while the areas with higher electrical conductivities and lower magnetic susceptibilities are underlain by sedimentary rocks. The plots also delineated the most likely basement–sedimentary boundary in the area.

Petrography and geochemistry of Neoproterozoic charnockite–granite association and metasedimentary rocks around Okpella, southwestern Nigeria

The Neoproterozoic charnockite–granite association of Okpella intrudes metasedimentary and migmatite-gneiss complex rocks in the eastern Igarra Schist Belt, southwestern Nigeria. In order to unravel the complex processes involved in the formation and tectonic evolution of the Igarra Schist Belt during the Neoproterozoic, detailed field, petrographic and whole-rock geochemical study of the charnockite–granite association and metasedimentary rocks around Okpella was conducted. Published data on the metasedimentary rocks and Pan-African granitoids in different sectors of the belt were also compiled for detailed interpretations. The charnockites and granites of Okpella show primary magmatic mineralogy and geochemical characteristics. They are silicic (> 63 wt% SiO2), metaluminous to peraluminous, high-K calc-alkaline, ferroan, post-collisional granitoids. The garnet-biotite schist, calc-silicate gneiss and quartzite in the area are low–medium grade metasedimentary rocks. The mineralogy and geochemistry of the charnockites suggest that the charnockitic melt was derived from mafic lower continental crust through partial melting and assimilation-fractionation processes. The granites probably originated from mixed melts derived from lower- to mid-crustal tonalites-trondhjemites-granodiorites and/or subducted metagreywackes and mantle-derived magmas (probably the charnockitic melt and/or its progenitor). The granites and charnockites are coeval and were presumably emplaced during the post-collisional stages of the Pan-African Orogeny. The garnet-biotite schist, calc-silicate gneiss and quartzite represent metamorphosed immature to slightly mature sedimentary rocks, probably greywacke, marl and subarkose, respectively, that were sourced from intermediate–acid rocks which underwent low–moderate chemical weathering with minor contribution from recycled sediment sources and deposited in active continental environments. The Neoproterozoic evolution of the Igarra Schist Belt, therefore, involved deposition and infolding of sediments in active continental margin during the early Pan-African followed by upwelling of basaltic magma from the mantle which underplated and crystallized in the lower continental crust and was subsequently partially melted to generate the charnockitic and granitic melts through mantle-crust interaction during the late Pan-African.

Generation and maturation of Mesoarchean continental crust in the Anshan Complex, North China Craton

The mechanisms underlying the generation of tonalite–trondhjemite–granodiorite suites and the transition to K-rich granitoids, which marks the most profound stage of Archean intracrustal differentiation, remain controversial. The Archean Anshan Complex (AAC) of the North China Craton (NCC) preserves diverse 3.8–2.5 Ga granitoids, providing an excellent opportunity to address these problems. We conducted a detailed field, petrological, geochemical, and zircon isotopic study on AAC units, demonstrating that: (1) the Li–Dong–Ying trondhjemite intrudes and encloses ca. 3.3 Ga gneiss–migmatite complex across the Anshan, and crystallized at ca. 3.14 Ga; and (2) the porphyritic and fine-grained Chentaigou monzogranites were emplaced contemporaneously with the trondhjemite, both at ca. 3.14 Ga.The Li–Dong–Ying trondhjemites show high SiO2, Na2O, low MgO, significant variations in Sr, Y, and Yb, REE fractionation (LaN/YbN = 9–140), and variable Eu anomalies (Eu/Eu* = 0.4–1.3). The magmatic zircons yield δ18O of +4.8 ± 0.2‰ to +6.9 ± 0.4‰ and initial εHf of −1.1 ± 0.7 to +4.4 ± 0.9, which translate to TDM ages of 3.6–3.3 Ga. The Chentaigou monzogranites have higher SiO2 and K2O, lower Na2O and CaO, similar δ18O of +5.1 ± 0.3‰ to +7.0 ± 0.3‰, and more negative Eu anomalies as compared with the trondhjemites. The Hf–O isotopes, geochemistry, particularly considerable variations in pressure-sensitive proxies of the trondhjemites, suggest that they were derived by melting of low-temperature altered basaltic rocks at 1.0–1.5 GPa and 900–950 °C, leaving a garnet amphibolite residue with variable amounts of plagioclase but no rutile; the most plausible source is ca. 3.3 Ga basaltic rocks. Polybaric melting of basaltic sources and fractionation of hornblende and plagioclase from trondhjemitic magmas account for the chemical variability of AAC granitoids, providing a mechanism for the coeval emplacement of diverse Archean granitoids. Secular compositional changes in AAC trondhjemites imply that the depth and interval of melting of basaltic sources increased from the Eoarchean to Mesoarchean. Changes in the nature of the source and melting depth characterized the early stage of Archean intracrustal differentiation in the NCC.

High-Grade Metamorphism and Anatexis in the Teletskoe–Chulyshman Belt (Gorny Altai): U–Pb Geochronology, P–T Estimates, and Thermal Tectonic Model

Abstract —A model of the formation of the Teletskoe–Chulyshman metamorphic belt (TCMB) in Gorny Altai has been elaborated. The estimated pressure (not exceeding 3–4 kbar) and temperature (about 740 °C) indicate an increased regional crustal thermal gradient equal to 60–90 °C/km during the formation of the metamorphic belt. The age of migmatites of the Chulyshman complex has been evaluated at 483.9 ± 5.7 Ma (Early Ordovician) by U/Pb (SHRIMP) zircon dating. The paleogeodynamic setting of the TCMB formation and the protolith nature are identified based on the geochemical and petrochemical parameters of the metamorphic rocks. Structural parameters and numerical modeling show that the Chulyshman migmatite–gneiss complex is an apical part of the thermal-dome structure formed under the thermal impact of a magmatic basic heat source in the base of the crust and displaced to the relevant depths via thrusts and crustal extrusion during the Early Ordovician accretion–collision event. Matching the metamorphism parameters and the numerical-modeling results for the crustal thermal regime, we determined the rate of the anatectic front displacement along the thrust to be at least 6 cm/yr.

Geochemical and organic petrological study of bituminous sediments from Dahomey Basin, SW Nigeria

Abstract The Dahomey Basin, SW Nigeria, hosts a 3000-m-thick sedimentary succession of Cretaceous and Cenozoic age, of which the Turonian-Maastrichtian Afowo Formation includes sandstones, arkoses, shales, shelly limestones, unconsolidated sand, clay and most importantly, bituminous (tar) sand strata. Eighteen samples were picked up from outcrops exposed by streams and channels, and were examined applying sedimentological, mineralogical, petrographical, geochemical (inorganic and organic) and radiological techniques with the aim of assessing the origin and the thermal maturity of the organic facies. The samples represent mostly coarse-grained sands and subordinately shales, referred usually as ‘tar sands’; they consist of mainly quartz and kaolinite, with variable amounts of mixed clay layers of illite-montmorillonite, mica and pyrite, probably derived from weathering of the Migmatite Gneiss Complex exposed to the north of the basin; this can also explain the relative enrichment in the natural radionuclides 40K, 238U, 226Ra and 232Th for some samples, although the radioactivity falls within the range for world values for soils. The clastic material of Afowo Formation was deposited in a rather oxic shallow marine environment. The particulate organic matter of the bituminous sediments comprises solid hydrocarbons, coalified (huminite) and partially oxidized (inertinite) remnants of terrestrial plants, and minor amounts of both terrestrial and marine liptinite macerals. The random reflectance values of the indigenous huminite population ranges between 0.40 and 0.45% pointing to an immature stage for oil generation. The respective reflectance of the migrabitumens ranges from 0.49 to 0.59% corresponding to vitrinite equivalent reflectance values of 0.70–0.76% falling well within the oil window. This study concludes that the hydrocarbons contained in the Afowo Formation are upwards migrating from parts of the basin where Afowo Formation has subsided at depths corresponding well within the oil window; the source rock corresponds to the middle shale horizon, whereas the sandy horizons act as migration paths and/or reservoirs.

Cooling and deformation history of the Çataldağ Metamorphic Core Complex (NW Turkey)

The Çataldağ Metamorphic Core Complex (ÇMCC) consists of the Latest Eocene-Early Oligocene (34–32 Ma) Turfaldag gneiss-migmatite complex (TGMC) and an Early Miocene (21 Ma) Çataldağ synkinematic pluton (ÇSP) which were exhumed as a dome-shaped core complex in the footwall of the Çataldağ Detachment Fault Zone (ÇDFZ) in the Early Miocene. Microstructural features of the Çataldağ Metamorphic Core Complex (ÇMCC) and a two-feldspar geothermometry were studied to understand the cooling and deformation mechanisms. Microtectonic analyses of the TGMC and ÇSP show that the quartz, feldspar, and mica minerals underwent continuous deformation from ductile to brittle conditions during cooling of the ÇMCC. Two main deformation zones were determined according to temperature and strain intensity: a ductile deformation zone (DZ) within the central zones of the TGMC and ÇSP, and a mylonitic zone (MZ) within the peripheral zones of the TGMC and ÇSP (close to the ÇDFZ). Within the ductile zone, K-feldspar displays microcline twinning, myrmekite along the K-feldspar megacryst and flame-shaped perthite, and quartz displays chessboard extinction, grain boundary migration, and sub-grain rotation recrystallisation. These microstructures indicate that deformation temperature reached about 600 °C. Under high strain intensity along the ÇDFZ, the DZ microstructures turn to MZ microstructures. In the MZ, protomylonitic gneiss and mylonitic schists show distinct foliation and their K-feldspar and micas display C-S structures. The feldspars show bulging recrystallisation, a feldspar-fish structure, and domino-type microfractures, while the quartz displays ribbon structures, indicating ductile-to-brittle deformation with temperatures ranging from 500 °C to <250 °C. Two-feldspar geothermometry yields deformation temperatures in the DZ of 501–588 °C (an average of 544 °C for the ÇSP and an average of 517 °C for the TGMC) consistent with the temperature estimated by the microstructural analysis. The mylonitic zone has lower deformation temperature values of 430–557 °C (an average of 484 °C for ÇSP and an average of 436 °C for TGMC). Thermochronology data display TGMC was cooled slowly (<50 °C/my) throughout the Eo-Oligocene and rapidly (>500 °C/my) along the ÇDFZ in the Early Miocene (21 Ma). The shear zone-controlled ÇSP was emplaced into shallow levels of the Anatolian extending crust, deformed progressively (ductile-to-brittle) along the ÇDFZ, and cooled rapidly (>500 °C/my) in the Early Miocene (21 Ma). Together, the microstructure, two-feldspar geothermometry and thermochronology data indicate that the TGMC and ÇSP, which were emplaced into different crustal levels and in different periods, suffered continuous ductile-to-brittle deformation and were exhumed together along the ÇDFZ during the Early Miocene under the N-S extensional regime in western Anatolia.

Hydrogeophysical study of parts of charnockite terrain of Akure Southwestern Nigeria

Hydrogeophysical study of parts of Charnockite terrain of Akure, southwestern Nigeria was carried out using the electrical resistivity method. The study involved one hundred and fifty two (152) Schlumberger geoelectric soundings (with seven (7) of them parametric)) alongside static water level measurements in 102 hand-dug wells. The Precambrian Crystalline Basement Complex rocks underlying the area consist largely of Charnockite with some granite and migmatite-gneiss bodies. The interpreted results enabled the determination of overburden thickness, longitudinal unit conductance (S) and coefficient of anisotropy (λ). The static water level measurements were used to determine the vadose zone thickness and groundwater flow direction. The overburden thickness in the study area ranges between 2.0 and 66.9 m; bedrock resistivity range between 748 and ∞ Ω-m while the vadose zone thickness ranges between 0.5 and 11.3 m. The groundwater potential of the area was classified based on the overburden thickness (h) and resistivity values (ρ). Thus, areas characterized by 100 ≤ ρ ≤ 800 Ω-m with h ≥ 45 m are classified as high, while areas presenting 15 ≤ h ≤ 45 m are classified as medium and areas of h ≤ 15 m are classified as low. A modified geologic classification of the study area using λ values was undertaken with λ ≤ 1.2 areas classified as Charnockite while areas with λ &gt; 1.2 classified as granite and migmatite-gneiss complex. A correlation of the field geological map with the λ map presents a good correlation especially within areas underlain by Charnockite.Keywords: Charnockite, resistivity, groundwater, overburden thickness, longitudinal unit conductance and coefficient of anisotropy

Composition and genesis of garnet in the rocks of Paleoproterozoic gneiss-migmatite complex (Sharyzhalgai uplift, southwestern Siberian craton)

We present the results of study of garnet-bearing paragneisses, migmatites, and vein granites of migmatite-gneiss complex of the Irkut terrane (Sharyzhalgai uplift, southwestern Siberian craton), major- and trace-element zoning of the garnet, and the age and trace-element composition of zircon. The migmatite-gneiss complex of the Irkut terrane formed in the Paleoproterozoic, at 1.85-1.86 Ga. The maximum temperatures of metamorphism and partial melting evaluated with the Ti-in-zircon and Zr-in-rutile thermometers are 790-830 and 830-860 °C, respectively. Three generations of garnet have been recognized according to texture and zoning: metamorphic, peritectic, and magmatic. Metamorphic generation forms the core of garnet in paragneisses and migmatites, contains numerous fine inclusions, and has the highest contents of grossular (Grs) component, HREE, and Y decreasing from core to rim, which agrees with the Rayleigh fractionation of compatible components. Peritectic garnet with large inclusions of quartz and feldspar is predominant in diatexites and in gneisses in contact with leucosome. It has almost constant low contents of Grs, HREE, and Y slightly increasing in the rim. Garnet in vein melanocratic granites is similar in composition zoning to garnet in diatexites. Magmatic garnet in leucocratic granites is characterized by a decrease in the contents of Grs, HREE, and Y from core to rim and by a strong negative Eu anomaly. It seems to have resulted from the dissolution/precipitation of peritectic garnet in the melt. According to mineral and chemical compositions, the gneisses and migmatites are subdivided into high- and medium-alumina series produced through the metamorphism and melting of two source rocks, pelitic and graywacke, which is confirmed by their different REE patterns. The FeO and MgO enrichment of the granites relative to the melts experimentally produced of pelites and graywackes, the inherited contents of HREE in the diatexites and granites from paragneisses, and the presence of peritectic garnet in melanocratic granites evidence that the formation of granite was not accompanied by the effective segregation of garnet from the melt.

High-gradient metamorphism and anatexis in the Teletsk–Chulyshman metamorphic belt (Gornyi Altai): New data on the age and estimate of P–T parameters

Estimates of the P–T parameters of metamorphism, the first results of U–Pb dating of zircons from migmatites of the Teletsk–Chulyshman metamorphic belt, are reported. The age of migmatites from the southern block of the Teletsk–Chulyshman belt is 483.9 ± 5.7 Ma. As is evident from the pressure estimate (≤3–4 kbar), the Chulyshman migmatite–gneiss complex could be an apical part of the thermal–dome structure formed during the Early Ordovician thermal impact of a shallow magmatic basic thermal source, later displaced to the appropriate depth along the thrust at the collisional stage.

Geology and environmental impact of artisanal gold mining around kataeregi area, North-Central Nigeria

Geology and effect of artisanal gold mining was investigated in Kataeregi and environ, North-central Nigeria with the aim of determining its host rock and assessing the impact of such activity on the surrounding. Geological field mapping show the area comprise of the Migmatite-Gneiss complex, Schist, Granite and Sandstone lithologies. The geochemical analysis of the representative rock samples indicates probable Au, Ag and Hg mineralization (0.16ppm, 2.53ppm and 0.21ppm respectively on the average). Au is hosted by auriferous quartz veins within the Schist rock. Geochemistry of the sediment samples revealed the sediments are enriched with elements such as Au (0.23ppm), Ag (2.59ppm), Hg (0.21ppm) and Mo (1.14ppm). The water is earth-alkaline fresh water with high alkaline content, and mostly sulphate type. The average concentration of these elements in rocks and sediments were compared with published average crustal abundances of the elements in upper continental crust and the water compared with Nigerian Standard for Drinking Water Quality and World Health Organization Standards. Mining activity has impacted the environment with land degradation, loss of vegetation and erosion of soils. Trace elements like Hg in rocks and sediments, and Pb in water from the study area are potential toxic elements that can render water unfit, causes slow growth rate in plant and reproductive disorder in man. Keywords: Geology, Artisanal Gold Mining, Sediment Geochemistry, Water Quality, Kataeregi, North-central Nigeria

Geochemical Investigation and Physical Impact Assessment of Artisanal Gold Mining, Kataeregi, North-Central Nigeria

The geochemistry of mine products and stream sediments from Kataeregi area in North-central Nigeria was studied with the objective of environmental hazards assessment that is caused by artisanal gold mining activities through field work and laboratory analyses. The field work involves the observation of physical impact of mining on the environment and collection of representative samples along the streams, mined site and tailings within the location of study. The sediment samples were analyzed using X-ray fluorescence spectrometry. The result obtained from laboratory analysis was compared with the ideal average crustal concentration of the elements in upper continental crust. Field observation revealed that mining activity has impacted on the environment with land destruction, loss of vegetation and erosion of soils. Geological field mapping show the area is underlain with Migmatite-Gneiss complex, Mica Schist, Granite and Sandstone lithologies. Results from geochemical analysis revealed that sediments are enriched with elements such as Au (0.23ppm), Ag (2.59ppm), Hg (0.21ppm) and Mo (1.14ppm). The presence of Hg in sediments can get consumed directly or indirectly through food chain and passed on to human.

The migmatite–gneiss complex of the Chuya–Kendyktas sialic massif (Southern Kazakhstan): Structure and age

A migmatite–gneiss complex made up of paraand orthogneisses and crystalline schists with bodies of ultrametagenic tonalites is distinguished in the basement of the northwestern part of the Chuya–Kendyktas Massif. ID-TIMS dating of accessory zircon from orthogneisses and ultrametagenic tonalites in combination with LA-ICP-MS analyses of detrital zircons from garnet–biotite paragneisses showed that the migmatite–gneiss complex was formed after protoliths with an age within 800–770 Ma and completed its evolution in the first half of the Neoproterozoic.

Provenance of Tertiary volcanoclastic sediment in NW Thrace (Bulgaria): Evidence from detrital amphibole and pyroxene geochemistry

Detrital heavy mineral and bulk rock geochemistry and a review of sandstone petrographic data have been used to investigate the post-collisional effusive magmatism that followed the closure of the Vardar Ocean and the generation of volcanic sediments in a complex and compositionally variable volcanic region. Available petrographic data gives evidence of contributions from three key source areas corresponding to the three main tectonic units: the structurally lower Gneiss–Migmatite Complex (Byala Reka-Kechros and Kesebir-Kardamos domes) and the upper Variegated (Kimi) Complex, both fringed by the low-to-medium-grade Mesozoic rocks of the Circum-Rhodope Belt. Besides the deposition of siliciclastic material, volcanic contributions from both, intermediate and acid products represent an important source of sediment in the area. Despite dominant intermediate to acid volcanic products, volcanic lithic fragments in sandstones (microlithic, lathwork and brown vitric textures) indicate main inputs from intermediate and basic-intermediate products generating questions on the interpretation of volcanic detritus in reconstruction of provenance. Detrital amphibole and pyroxene chemistry is used to characterise the supply of volcanic material as well as the dispersal mechanisms and understand the role played by each of the volcanic centers present in the area in the infill of the north-western Thrace basin. Amphibole chemistry reveals high compositional heterogeneity according to both compositional variability of the numerous volcanic centres active at the time of deposition and presence of metamorphic amphibole. 4Al and AlT apfu values indicate that most of the amphiboles from the NERZ are not of volcanic origin and their presence can only be attributed to the numerous amphibolite facies metamorphic rocks abundantly documented in the area. Detrital amphibole compositions from the ZKVS indicate major contributions from the Iran Tepe and Zvedzel volcanoes. Analysed detrital clinopyroxenes from the NERZ are mostly diopside–augite, with no hedenbergite or Fe–augite detected. The 4Al/6Al ratio is comparable with compositions of volcanic pyroxenes from the Momchilgrad–Arda (ZKVS) region and products from the pre-caldera phase of the Borovitza.

Geochemistry and U-Pb zircon geochronology of the pegmatites in Ede area, southwestern Nigeria: A newly discovered oldest Pan African rock in southwestern Nigeria

Field and petrographic studies, whole rock geochemistry and in-situ LA-ICP-MS geochemical and isotopic U-Pb measurements on zircons have been performed on granitic pegmatites of Ede area, southwestern Nigeria with a view to characterize them, determining their mineralization potentials, petrogenetic attributes and emplacement age. The pegmatites are hosted by migmatite gneiss complex, biotite-muscovite schist and associated quartzite. The textural and mineralogical characteristics of these pegmatites indicate the occurrence of two main varieties, namely, muscovite pegmatite and garnet pegmatite. Of less importance are inclusions and pods of graphic granite, quartz-microcline aplitic and pegmatitic bodies. At the present level of erosion, the parent igneous rocks of the pegmatites are not exposed. The two dominant pegmatite varieties show slightly different chemical peculiarities but similar peraluminous character. The average K/Rb ratios of 165 and 163, respectively, for muscovite and garnet pegmatites combined with other trace element compositions are indicative of affinity to muscovite class of pegmatite which are generally not promising for rare elements mineralization. However, the unusually high concentration of bismuth in the zircons indicates Bi mineralization in the area which can either be in the pegmatites or host rocks.The Nb/Ta ratios for both muscovite and garnet pegmatites range from 0.7 to 15.2 and 1.0 to 14.8, respectively. These Nb/Ta ratios and Eu anomalies are statistically similar for both pegmatites. These probably indicate the pegmatites crystallized from a common source but separated into crystallization paths that produced different pegmatite varieties through liquid-liquid immiscibity mechanism. In-situ measurements of REE, P, Y, Nb, Hf, Ta, Bi, Th and U of individual zircon grains show the existence of two chemically and texturally different domains which are indicative of alteration that may be due to interface-coupled dissolution-precipitation promoted by microfractures induced by metamictization. Notwithstanding, the (Sm/La)N vs. La plot for zircon, weak positive Ce and variable europium anomaly (Eu*) are suggestive of pegmatites of hydrothermal origin. The pegmatites yielded a discordant U-Pb zircon age with upper concordia intercept of 709 +27/−19 (at 2σ, MSWD = 1.5) Ma which can be attributed to their emplacement. This age represents the oldest Pan African magmatic event reported so far in southwestern Nigeria.

The early Precambrian history of rock metamorphism in the Urals segment of crust

Early Precambrian rock units in the Urals are present in several polymetamorphic complexes, which are exposed in the Urals in the form of small (<1500 km2) tectonic blocks. Their ages are Archaean (as old as 3.5 Ga) and Palaeoproterozoic. During the formation of these complexes in the early Precambrian, two stages of ultra-high-temperature (granulite) metamorphism occurred. The maximum age of the early Neoarchaean stage of metamorphism is 2.79 Ga. Evidence of this metamorphic event includes the dating of the Taratash gneiss-granulite complex of the South Urals. Gneiss-migmatite complexes, which dominate the lower Precambrian section of the Urals, were formed in the Palaeoproterozoic during the sequential appearance of granulite facies metamorphism followed by amphibolite facies metamorphism and accompanying granitization. The maximum age of the Palaeoproterozoic stage of granulite metamorphism in the Alexandrov gneiss-migmatite complex, the most well-studied complex in the South Urals, is 2.08 Ga.

Geology and Geochemistry of Zungeru Amphibolites, North Central Nigeria

Basement rocks of Zungeru area consist of gneisses, schists, migmatites and intercalations of amphibolites and quartzites .This work involves detailed geological and geochemical investigation of Zungeru amphibolites so as to reveal their possible protolith. Field investigations show two petrographic types of the amphibolites on the basis of their textures, structures and mineralogy. They include the banded and massive types. The banded type is medium grained, strongly foliated and dark coloured rock while the massive type is fine to medium grained, dark-grey to black coloured with very weak foliations. Both types have been fractured due to deformation resulting in the development of joints and faults. Twelve representative samples of the amphibolites in the study area were collected and analyzed for major and trace elements using the Energy Dispersive X-Ray Fluorescence (EDX-RF) Spectrometer, Model: Minipal 4 at the laboratory of the National Geological Agency, Kaduna. However, only the major elements data was used for determination of the protolith of the amphibolites. The analytical results show that the Zungeru amphibolites contain on average 50.15% SiO2,12% Al2O3, 0.39% Na2O, 0.02% K2O, 9.41% CaO, 9.90% MgO, 0.02% MnO, 12.24% Fe2O3, 4.89% FeO, 0.5% TiO2, 0.10% P2O5 and 0.78% H2O. Various bivariate plots indicate that the precursors of the amphibolites are sedimentary. They are inferred to have been formed from metamorphism of decarbonated mixtures of pelitic sediments and calcite or dolomite. The occurrence of the amphibolites in association with quartzites further strengthened the fact that their origin is sedimentary and therefore referred to as para-amphibolites. African (600 ma) granitic series commonly called older granite suites. The most pervasive tectonic fabric of igneous reactivation of this suite is attributed to Pan-African event. This Precambrian crystalline basement complex covers nearly 60% of land surface of Nigeria and extends to neighboring countries. The migmatite-gneiss complex makes up about 60% of surface area of Nigeria basement. These rocks recorded at least four major tectonic cycles of deformation, metamorphism and remobilization in the Liberian, Eburnean, Kibarian and Pan-Africa, thus, confirming Russ's view of age of determination from various part of the Nigeria basement. The migmatite-gneiss complex rocks are believed to be basement rocks in real sense.

Phanerozoic continental crust evolution of the Inner Caucasian Microplate: The Dzirula massif

In the Pre-Alpine Dzirula massif of the Inner Caucasian Microplate is coded a wide spectrum of the geodynamic and magmatic events taking place in the region and that's why it represents important and major structure for general geological interpretations. In the given work, on the example of the mentioned crystalline massif evolution are considered processes of the continental crust in Phanerozoic collisional orogens. We consider, that in Variscan consolidation Dzirula massif formations of the Neoproterozoic Pan-African tectonicthermal events are observed, that are organically involved in the evolution processes of the Caucasian Phanerozoic collisional orogen and their role in these processes are probably caused by the migration of lithospheric residues to the north, that are formed as a result of Gondwana northern edge Late Ordovician destruction and opening of Palaeo-Tethys. Within the Dzirula massif, a Gondwana-derived Neoproterozoic gneiss-migmatite complex is situated obductively on ensialic island arc. In this Variscan collision-accretion structure, the crustal thickening and released water caused partial melting of the ensialic island arc, thus generating the granitoid melt, which intruded the overlying gneiss-migmatite complex. By the end of this process, the Dzirula massif resembled typical Phanerozoic continental crust.