Felsic Source Research Articles

Paleoenvironmental changes during the Middle-Late Ordovician transition, Northwestern Tarim Basin, NW China and implications for the great Ordovician Biodiversification Event

• Black shales of Saergan Formation had a mainly felsic source region likely in an active continental margin. • The paleoenvironment exhibited a semiarid climate with high salinity and anoxic marine conditions during the Middle–Late Ordovician in the Awati Sag. • The Middle–Late Ordovician was a transition period which the paleoenvironment changed greatly. • The GOBE may be triggered by supergreenhouse climate. The changes in the geological environment during the Middle–Late Ordovician transition are well documented by geochemical evidence. We study the paleoenvironmental changes during the Middle–Late Ordovician and their effects on the Great Ordovician Biodiversification Event (GOBE) through the analysis and testing of the major elements, trace elements and rare earth elements (REEs) present in 21 samples from the Middle–Upper Ordovician Saergan Formation in the Awati Sag, Northwestern Tarim Basin, NW China. Compared with post-Archaean Australian Shale, the Saergan Formation is enriched in Ca, P, U and REEs. The total abundance of REEs ranges from 107.3 to 674.8 ppm, with obvious enrichment of light REEs and negative Eu anomalies, as well as Ce shows a weak negative anomaly. Furthermore, the parent rock of Saergan Formation is mainly felsic. Combined with the provenance attributes and tectonic background, the source area is considered to be mainly in an active continental margin tectonic environment. The black shales underwent moderate weathering and simple cyclical sorting, with an immature composition. Multiple geochemical indicators show that the Middle–Late Ordovician is a transition period and the paleoenvironment had semiarid climate and hypersaline anoxic marine conditions. The supergreenhouse climate may accelerate chemical weathering and increase nutrient inputs. In addition, the warm climate melting of the polar ice sheet which leads to the relative shallowness of the sea surface temperature gradient, sea level rise and expansion of marine habitats. The resultant environmental changes could have accelerated the diversification of benthos, which provides an ancient analogue for anthropogenic climate change.

Geochemical characterization of Egbetua stream sediments, southwestern Nigeria: implication for provenance and depositional conditions

The aim of this work is to determine the provenance, chemical index of alteration, elemental spatial distribution in the stream sediments, stream flow energy and the depositional conditions in the study area. The study area is located in Egbetua area in Akoko Edo Local Government Area of Edo State, Southwestern Nigeria. It is located on latitudes 07º 21’30’’N and 07º 22’N longitudes 06º 15’ 30” E and 06º 17’E and average elevation of 182 metres. Standard field and laboratory procedures were used in the study. Geochemical analysis was carried out using x-ray fluorescence method. Average concentrations of SiO2 (78.24 wt. %), Al2O3 (ca. 12.15 wt. %) and the chemical index of alteration (CIA) values of 68.90% indicate felsic granitic source rocks. Ce/Ce*, Eu/Eu* and (La/Yb)n ratios were used to deduce the prevailing reducing-oxidizing depositional environment of the sediments. Ce/Ce* (0.80) confirmed an oxidizing environment of deposition with low stream flow energy, while Eu/Eu* (0.07) corroborated an oxidizing environment with felsic source rock. (La/Yb)n (5.95) indicated an oxidizing environment in a low stream energy flow with coarse-grained and clay size sediment input.

Petrography and geochemistry of the Sanaga river sediments, central Cameroon: Constraints on weathering, provenance, and tectonic setting

The Sanaga River (SR), central Cameroon, flows predominantly over metasediments (2.1 Ga), Paleoproterozoic amphibolites and orthogneisses, granitoids from the Adamawa-Yade batholith (AYB), sedimentary clastic rocks of Cretaceous age, and Cenozoic rocks of the Cameroon Volcanic Line. To infer the origin of alluviums and tectonic setting of source rocks, the texture, heavy mineral, major, trace, and rare earth element concentrations of stream sediments were investigated. The very high SiO2/Al2O3 ratios and the ZTR (Zircon-Tourmaline-Rutile) index of SR sediments suggested a high maturity. This interpretation was additionally confirmed by the Th/Sc vs Zr/Sc plot. The Plagioclase- and Chemical Index of Alteration (PIA and CIA) values, the (A-K)-C-N and A–CN–K triangular plots show an intense degree of weathering in the source area. Numerous discrimination diagrams, based on trace elements, indicate that sediments were derived from felsic source rocks mainly granodiorites, granites, and biotite granitoids exposed in the SR watershed. This shows that the metamorphic and volcanic rocks do not significantly contribute to the stream sediments. Paleotectonic investigations using multi-element discrimination plots indicate passive and rift settings for the SR drainage basin. Rift settings were also inferred from downstream sediments of the SR. They are probably related to Proterozoic events including opening of large oceanic basins. The passive and rifted margin settings are supported by the occurrence of rare ophiolitic rocks, which indicate an old oceanic crust.

Geochemical characterization of altered rocks and element dispersion around an abandoned mining site in an arid zone: A case study of Fatira gold mine area, Eastern Desert, Egypt

Environmental impacts related to mining are widespread due to poor waste management. Fatira abandoned gold mine area in Egypt was studied for the geochemical/mineralogical properties of alterations haloes, mine tailings, stream sediments under dry conditions and impacts to nearby environment. Results of this study indicated that stream sediments and soil-tailings mixture were derived from felsic sources, while tailings, weathered and old tailings were obtained from intermediate-felsic sources. The Pb load was much higher in weathered rocks, soil-tailings mixture and old tailings, while metals like As, Co, Cr, Cu, Ni, V, and Zn show elevated values in weathered rocks nearby Fatira mine area and in downstream sediments. The tailings have high average concentrations of heavy elements, Sr (439), Zn (389), Cu (310), and Cr (50) (in mg/kg), higher than the toxicological standard values for contaminants indicating adverse effects to the neighbouring environment, whereas, soil-tailings mixture have higher As (263), Pb (56) and Al2O3 (17 wt%) reflecting the metavolcanics and granite composition of country rocks. At lower depths of tailings, escalated concentrations of Al2O3, K2O, Na2O, and Fe2O3, and little CaO, MgO, As, Pb, Zn, Cu, and Ni are indicate variable input from intermediate rocks, grey granites, felsite dykes and pink granites. Chemically altered granites showed replacement of hornblende into actinolite, calcite, pitted ilmenite and in-situ formation of Fe-oxides/hydroxides. Low hydraulic conductivity of the rocks increased the intensity of weathering. Gypsum and goethite are recorded due to repetitive sulfides decomposition. The element enrichment that exceeds the standard toxicological values in tailings, soil-tailings mixture, weathered rocks and stream sediments have severe effects on health. Integrating the chemistry, mineralogy and microtextural analyses in the study area is required for accurate geoenvironmental forecasting that facilitate mine rehabilitation with an effective management plan.

New evidence from heavy minerals and detrital zircons in Quaternary fluvial sediments for the evolution of the upper Yangtze River, South China

AbstractIn the Three Gorges and adjacent areas, there are three planation surfaces and five terraces along the Yangtze River that record the evolution history of the river system. Here, we used diagnostic heavy minerals, U-Pb geochronology, and trace elements of detrital zircons from one planation surface, two terraces, and a modern point bar to reconstruct the evolution history of the upper Yangtze River, specifically the Chuan River in the Sichuan Basin. The sediments in the lowest planation surface had different felsic source rocks derived from east of the Three Gorges, which indicated that before the disintegration of the lowest planation surface (0.75 Ma), there were two paleorivers: the westward-flowing paleo-Chuan River and eastward-flowing paleo-Yangtze River separated by the Huangling Dome. At 0.75–0.73 Ma, the dominant detrital zircons from the Sichuan Basin in the sediments of terrace T5 (the highest terrace) confirmed that the paleo-Yangtze River cut through the Three Gorges and captured the paleo-Chuan River, and the Daliang Mountains became the new drainage divide. Finally, the appearance of materials from the upper Jinsha River in terrace T2 indicated that the paleo-Yangtze River progressively captured the paleo-Jinsha River, and the modern upper Yangtze River formed before 0.05 Ma. These river capture events of the upper Yangtze River confirmed the Quaternary uplift of the SE Tibetan Plateau.

Elemental composition and mineralogy of NW Venezuelan Guasare coals: Provenance study and role of illite in methane sorption capacity

A series of coal seams (groups 4 to 11) of Paleocene age in the Marcelina Formation have been open pit exploited in two mines (Paso Diablo and Mina Norte) in the Guasare Coalfield (NW Venezuela). An investigation has been conducted on the elemental composition, mineralogy, and coalbed methane (CBM) in Guasare coals. For this study, 46 core coal samples of 16 seams (groups 2 to 7) were collected from 16 exploratory boreholes that were drilled in both mines. It was also considered unpublished proximate-ultimate and gross calorific data of other 66 coals of 31 seams intersected in most of these wells. The coals under study showed low ash yields (3.4 wt % on average) and were classified as high volatile bituminous A. Mean values of trace element and lanthanide (REE) contents in Marcelina coals generally indicate depletion compared to average values for world hard coals. The statistical evaluations indicate that elements (except Se) show inorganic affinity or intermediate association and mixed mode of occurrence. La/Sc, Th/Sc, La/Co, and Th/Cr ratios support a felsic or metamorphic felsic source for the mineral matter present in Marcelina coals. Most coal samples exhibited similar normalized REE patterns, showing light REE enriched, as well as negative Ce and Eu anomalies. The comparison of REE patterns to those of some nearby granitoids suggests that Marcelina coals received a supply of sediments from theses granitic source rocks. The mineralogical compositions of representative coal samples are notably similar, kaolinite and quartz were noted as the major mineral species in all coal seams. The measured gas volumes available for CBM production from Marcelina seams vary approximately between 5 and 11 cm3/g. Variation in the illite content has an appreciable positive effect on gas adsorption capacity of Guasare coals. Lastly, a numerical model of the gas generative potential of the coals in the Marcelina Formation was also developed.

Provenance of sediments from the Niger Delta, Gulf of Guinea: Evidence from geochemistry

The Gulf of Guinea is surrounded by numerous waterways, where several rivers flow into the ocean, and the Niger River brings large amounts of land-derived debris into the Niger Delta every year. However, geochemical characteristics and sources of sediments in this region are still poorly constrained. Here, we collected two cores (GC09 and GC10) on the shelf and one core (GC05) on the shelf break of the Niger Delta, Gulf of Guinea to assess their provenance using total carbon (TC), total organic carbon (TOC), major elements, and trace elements. The results indicate that sediments on the Niger Delta are classified as iron-rich silty clay and silty clay based on their geochemical compositions. Surface sediments are enriched in quartz and feldspar, evidenced by relatively high levels of SiO 2 , Al 2 O 3 , NaO 2 , K 2 O and CaO. Trace element ratios and TOC demonstrate organic matters were mainly derived from terrestrial inputs and were deposited under aerobic conditions. Geochemical index data (TOC, REEs, δCe, δEu) reflect that the redox conditions of deposition are more inclined to aerobic environment; the sea level gradually decreased and induced more oxic depositional environment over time. According to the location of the three sampling sites, the proportion of felsic in the provenance of sediments increased towards the mainland while the proportion of mafic decreased. With the increasing of water depth, the proportion of felsic source decreases from ~67% at GC10 site (Water depth is 1418 m) to ~50% at GC05 site (Water depth is 3245 m). In contrast, the proportion of mafic source increase from ~25% at GC05 site to ~50% at GC09 site (Water depth is 1377 m). Using chemical index of alteration (CIA), it is manifested that the sediments show high maturity and have experienced strong chemical weathering. Statistical analyses indicate terrigenous inputs contribute more than half materials for the Niger Delta sediments. The relatively stable depositional environment in this region favors the formation and development of gas hydrates. This study could be used to infer the sediment sources and paleoenvironment changes during sedimentation and also provide reliable information for a better understanding of sedimentary processes in global gas hydrate-related deltas. • Provenance of marine sediments in Niger Delta, Gulf of Guinea by geochemistry methods. • The evolution of sedimentary environment in the Niger delta region. • Inorganic geochemical signatures of marine sediments from where gas hydrates can form.

A geochemical and mineral chemical assessment of sediment provenance and post-depositional alteration of auriferous conglomerates in the Singhbhum Craton

The Mesoarchean Dhosrapahar Group and the Phuljhari Formation in the Singhbhum Craton host so far subeconomic gold occurrences in metaconglomerate beds, similar to the world-famous conglomerate-hosted gold deposits of the Mesoarchean Witwatersrand Basin in South Africa. In the studied metaconglomerates from India, gold occurs as invisible inclusions in pyrite and as native gold grains associated with detrital chromite, quartz, zircon and metamorphic chlorite. Unlike most Archean paleoplacer deposits, the inferred detrital gold here appears unrelated to detrital pyrite, thereby highlighting the decoupling of the sources for the various placer components. To this end, we attempt to delineate the possible source rocks and assess the extent of post-depositional alteration to better understand the controls on gold accumulation in these conglomerates. Elevated Ni, Co and As, to a lesser extent V, Cu, and Se contents in Au-bearing inclusion-rich detrital pyrite are suggested to be derived from Paleoarchean banded cherts in the Gorumahisani Greenstone Belt. Relatively immobile trace element ratios, as recorded by the conglomerate matrix, reflect a predominantly felsic source with minor sediment input from mafic/ultramafic sources. Fractionated chondrite-normalized light rare earth and flat heavy rare earth element patterns, along with a distinct negative Eu-anomaly, obtained for the samples from the Phuljhari Formation point to a differentiated felsic source, most likely the c. 3.05 Ga K-rich Mayurbhanj Granite. In contrast, depleted heavy rare earth element patterns and a weak negative Eu-anomaly in the conglomerates from the Dhosrapahar Group indicate derivation from a felsic source that had experienced garnet fractionation, the obvious candidate being the underlying c. 3.37 Ga Rairangpur tonalite-trondhjemite-granodiorite (TTG) suite. Detrital rutile is rich in Cr and V, and Zr-in-rutile geothermometry yielded crystallization temperatures between ~800 and 1000 °C. The most likely source of this rutile are 3047±17 Ma gabbro-anorthosite bodies in the basement. Post-depositional modification of the conglomerates is dominantly manifested as greenschist-facies metamorphic overprint, and is reflected also by detrital chromite texture and chemistry, and the occurrence of secondary rutile, euhedral pyrite, and secondary gold with metamorphic chlorite. Our provenance interpretations do not indicate any likely point-source of detrital gold, suggestive of the entire Archean hinterland, irrespective of composition, as a potential source, as already indicated for the Mesoarchean auriferous conglomerates of the Witwatersrand Basin. This contention is further substantiated by the evidence presented here for moderate-to deep chemical weathering of the Archean hinterland of the Singhbhum Craton.

Occurrences of Rare Earth Element (REE) Bearing Minerals in Migmatitic Gneiss and Granitoids of Chhotanagpur Granite Gneissic Complex, Bihar, India

Abstract This paper presents the geochemical characteristics, petrogenetic processes and source characteristics of Rare Earth Elements (REE) bearing migmatitic gneiss and granitoids near Tangeshwar village, Banka district, Bihar, in order to demarcate the potential zone of REE mineralization. These migmatitic gneiss and granitoids belongs to the Chhotanagpur granite gneissic complex (CGGC). The study of migmatitic gneiss and granitoids of CGGC suggest that they have high content of SiO2, low contents of Fe2O3 and MgO and SiO2 vs. Na2O and K2O shows positive correlation which suggest, they are dominated by sodic and alkali rich minerals and were derived from a felsic (granitic) source. Also LREE-LILE enrichment, HFSE depletion and calc-alkaline nature indicates that the magmatism is related to the subduction zone. Petrographic and EPMA studies of these migmatitic gneiss and granitoids confirms the presence of REE bearing mineral phases such as allanite, xenotime, monazite, and basnasite. They are generally present at the rim of biotite, as an inclusion in biotite and also along the grain boundaries and within the cracks of major silicate minerals. This suggest that the REE formation takes place at the deuteric stage of magma crystallisation followed by the formation of granite. Chemical analysis of bed rock samples for rare earth elements using ICPMS shows that the highest concentration is in migmatitic gneiss and granitoids, which varies from 47.85- 925.67 ppm and 47.85- 626.48 ppm respectively.

Sedimentary, climatic, and provenance controls of mineral and chemical composition of the Ediacaran and Cambrian mudstones from the East European Craton

Mineralogical and geochemical compositions of mudstones were used for untangling provenance and climatic signals preserved in the upper Ediacaran - lower Cambrian strata from the western part of the East European Craton (ECC). Quantitative mineralogy and geochemistry data were obtained for 735 argillaceous rock samples from 71 wells and outcrops and compared with the analyses of Proterozoic palaeosols from the same area. Additionally, sedimentological analyses of well-preserved cores were performed to reconstruct predominant Ediacaran and early Cambrian environments. Seven major facies associations were distinguished and interpreted as both continental and basinal in nature. Terrestrial environments include weathering crust, alluvial fans, and associated interlobe areas, fluvial channels, floodplains, and lakes. Transitional environments are represented by tidal lithofacies, whereas central bay and upper offshore facies associations are typical of distal deposits. The central basin area is interpreted as an estuary opening toward the east, while a separate basin developed in Podillya. Provenance heavily influenced the mineralogical and geochemical characteristics of the sediments and affected derived weathering indices. The change from mafic to felsic sources in the western ECC is evident towards the Cambrian. All geochemical and newly introduced mineralogical weathering indices show advanced kaolinite-type weathering, evidence of a hot and humid climate during this interval. Based on these indices, mudstones are weathered to a greater extent than palaeosols. This observation is interpreted as resulting from the redeposition of highly weathered topsoils, combined with additional weathering on-route to the basin. Mineral authigenesis (berthierine, pyrite, goethite, fluorapatite, and carbonates) was particularly intensive in the terrestrial interlobe areas. Berthierine is common in most environments, which reflects the reaction of kaolinite with iron oxides, mediated by microorganisms, in shallow dysoxic tropical waters, with high lateritic sediment input. Marine, more oxic conditions in the Cambrian are indicated by a pervasive appearance of glauconite.

Natural and anthropogenic contributions to the elemental compositions and subsequent ecological consequences of a transboundary river's sediments (Punarbhaba, Bangladesh)

An anthropogenically less affected transboundary river (Punarbhaba, Bangladesh) was studied to detect associated risks from the combined origin(s) of geochemically and toxicologically significant elements in benthic sediments. A total of 30 river bed sediments were analyzed by instrumental neutron activation analysis targeting the 15 chemical elements viz., Na, Al, K, Ti, Cr, Mn, Co, Zn, As, Rb, Sb, Cs, Ba, Th, and U. Among the estimated elements, the mean abundances (μg/g) of Rb (136), Sb (0.66), Cs (6.66), Th (14.6), and U (3.92) were 1.4–1.7 times higher than the crustal origin. These elements are primarily responsible for the contaminated state of the Punarbhaba River. The studied area is ‘moderately polluted’ (Igeo: 2.01 to 0.02) and possesses ‘minor enrichment’ (EF: 1.98 to 0.48) in terms of the measured elements. The output of statistical analyses projected that the studied elements are geochemically fractionated in an oxidizing environment (U/Th = 0.44) and mostly originated from felsic sources, thus confirming the mineral is comprised of aluminosilicates and alkali feldspar. However, SQGs-based and ecological risk indices invoked minor (Cr: 6.67%) to no potential ecotoxicological threats for Cr, Mn, Co, Zn, As, and Sb. Nonetheless, altered distribution patterns caused by geogenic activities increased Cr and Zn in the environment which may cause toxicity (Cr: 22–53%, Zn: 35–70%), and pose potential ecological risks, specifically in upstream locations (P-2, P-3, P-5). Further, this study broadened the perspective of sediment deposition from fractionation, fluvial transportation, and weathering events beyond the industrial disintegration of elements, which will aid researchers and policymakers to comprehend combined risks from suspended sediments.

Geochemistry of Permian carbonaceous shales from Raniganj sub-basin, Damodar Valley, India: Implications for provenance, weathering, tectonics and source of organic matter

Raniganj sub-basin, the easternmost depository of Damodar Valley encompasses the entire succession of Gondwana Supergroup, the lower and upper Gondwana sequences. The present investigation of Permian carbonaceous shales belonging to Barakar, Barren Measure and Raniganj formations of lower Gondwana sequence from this basin is an integrated study of inorganic and organic geochemical characteristics viz. major/trace elements, stable isotopic composition and kerogen type to ascertain source rock attributes such as provenance, tectonic setting, prevailing weathering/climatic conditions as well as source and type of organic matters. Trace element indices, such as La/Sc, Th/Co, Th/Sc, (Gd/Yb)CN, Eu/Eu*, Cr/V, Y/Ni, reveal that the shales are originated from felsic/granitic source rock. Prominent Eu-anomaly, enrichment of chondrite normalised light rare earth element (LREE) values and a flat heavy rare earth elements (HREE) pattern reflect post-Archean felsic source for the shales. The major element composition, especially relative enrichment of Al over readily soluble elements, Ca, Na and K yielding high CIA (74.9–84.6%) and CIW (87.1–97.5%) as well as low ICV (0.64–1.32) values, establishes significantly weathered and matured nature of the shales. The distribution of redox-sensitive elements (U/Th, V/Cr, Ni/Co, Ce/Ce*) as well as low ICV, depleted K2O/Al2O3 ratios and high CIA values point towards an oxic environment and warm-humid climatic condition during deposition of these shales. The conventional method for determining tectonic setting using major and trace element composition fails to clearly delineate the tectonic setting for the current shales. The samples show wide scattering across active and passive continental margin in the K2O/Na2O–SiO2 diagram, whereas the samples are concentrated near the active in the continental margin in the Th–Sc–Zr/10 diagram contradicting the geological framework of Raniganj sub-basin. Discriminant functions-based approach which categorises the tectonic setting into continental/oceanic arc, continental rift and continental collision settings has been proved to be suitable in the present case and reveals continental-rift setting for the shales from Raniganj sub-basin. The carbon isotopic signature (δ13Corg) of the shales reveals a range (−24.5 − −22.9‰) intermediate between that of marine and terrestrial (C3 plants) organic matters indicating possible mixed type of organic matters. The fluvio-marginal marine depositional condition obtained from K2O/Al2O3 and MgO/Al2O3 ratios further implies the possibility of mixed nature of organic matter. The geochemical parameters of the organic matter (Rock-Eval pyrolysis parameters S1, S2, TOC, HI, OI etc.) indicate that the studied shales contain thermally matured mixed Type III/II gas-prone kerogen and are derived predominantly from terrestrial sources with significant marine input.

Geochemical characteristics of surface aeolian sand in the Badain Jaran Desert, northwestern China: Implications for weathering, sedimentary processes and provenance

Knowledge of the provenance of the aeolian sand in deserts is crucial for revealing their development and the corresponding driving mechanisms. As the second-largest desert in China, the Badain Jaran Desert (BJD) has developed the tallest megadunes on Earth. However, the material source of these dunes, especially the provenance of different particle size fractions, is debated. Here, we address these issues using new geochemical data, consisting of the major, trace, and rare earth elemental signatures of different particle-size fractions of dune sands in the BJD and sediments from potential source areas. The source area sediments are from the rivers originating in the Qilian Mts., the Gobi regions between the Heihe River and the BJD, the piedmont of the Gobi-Altay Mts., and the alluvial fan of the Beida Mts. The results show that the dune sands of the BJD are mainly derived from felsic source rocks subjected to weak chemical weathering in the source area. The fine fraction (<63 μm) of the aeolian sand in the BJD has experienced some degree of sedimentary sorting and recycling, despite its mineralogical immaturity. Furthermore, comparison of the immobile trace elements and rare earth element (REE) ratios of the samples from the BJD with those from the potential source regions, together with the results of multidimensional scaling and principal component analysis, shows that the coarse fraction (63–250 μm) of the dune sand in the BJD originated mainly from fluvial and Gobi deposits eroded from the Qilian Mts.; whereas the fine fraction has a mixture of provenances, including the Qilian Mts. and the Gobi-Altay Mts., although the latter contribution is of limited significance.

Formation of polymetallic ores in the metasedimentary rocks of Rangpo area, Sikkim Lesser Himalaya, India: Mineralogical and geochemical attributes

Present work investigates the ore mineralogy, geochemistry of host metasedimentary rocks, and the mineral chemistry of the main sulphide minerals, namely, sphalerite, chalcopyrite, galena, and pyrite from the Rangpo sulphide mineralization, Sikkim. Based on the textural relationships of the oxide and sulphide minerals such as mutual boundary, exsolution blebs, and replacement features, three stages including two stages of primary ore mineral formation, and an alteration stage of secondary mineral development is established. Oxide and sulphide minerals predominantly magnetite, chalcopyrite, sphalerite, galena, pyrrhotite, and cobaltite occur as stage‐I ore minerals, and the sulphide minerals namely galena, pyrrhotite chalcopyrite, arsenopyrite, sphalerite, and pyrite are identified as stage‐II minerals. The alteration minerals malachite and azurite represent stage‐III. The geochemistry of host metasedimentary rocks is characterized by SiO2 in the range of 53.28 to 85.62 wt%, Mg# values between 25.48 and 49.60, MgO and K2O having a strong negative correlation with SiO2, high values of Zr/Sc (32.5) versus Th/Sc (3.44), and enrichment of trace elements like Cr (30–87 ppm), V (27–81 ppm), Ni (13–49 ppm), and Sc (3–12 ppm). The Th/Sc versus Zr/Sc, K2O/Na2O versus SiO2, and Th/Co versus La/Sc plots attribute that the host metasedimentary rocks are recycled sediments largely of passive continental margin with a felsic source. However, the Mg# versus SiO2 and K2O/Na2O versus SiO2 point to the incorporation of mantle material from the orogenic margin, possibly arc‐related and mafic in nature. The features such as the mineral assemblage, the simultaneous crystallization shown by mutual boundaries and exsolution blebs, and the mineral chemical data of ore minerals favour a high‐temperature hydrothermal environment of ore deposition. This inference is substantiated by general high Fe concentration in sphalerite and other ore minerals, 800 to 2,400 ppm Cd in sphalerite, Ag and Sb in galena from 1,000 to 2,500 ppm and 400 to 800 ppm respectively, and noticeable Ag in chalcopyrite. The inferred depositional and tectonic environment of host metasedimentary rocks, the petrographic features of ores, and their mineral chemical data altogether invoke that the Rangpo ore mineralization in metasedimentary rocks was formed at high temperature in an environment where mafic mantle material from the active arc was amalgamated with the passive margin sediments derived from the felsic source rocks.

Depositional conditions of the Upper Cretaceous shales from the Anambra Basin, SE Nigeria: Constraints from mineralogy and geochemistry

Thirty-four core shale samples from the Upper Cretaceous Mamu Formation, southeastern Nigeria, were studied using XRD and geochemical analyses to constrain their provenance, tectonic setting, palaeoweathering and palaeoredox conditions during deposition. X-ray diffraction analysis revealed the presence of clay minerals (kaolinite, illite and illite-smectite mixed layer) and non-clay minerals (quartz and feldspar). The dominance of kaolinite and the high kaolinite/illite (K/I) contents indicate warm and humid climatic conditions during sediment accumulation. The total organic carbon (TOC) content of the shales ranges between 0.31 and 55.34%. The high Chemical Index of Weathering (CIW; mean∼98.8%), Chemical Index of Alteration (CIA; mean∼92%) and Plagioclase Index of Alteration (PIA; mean∼98.7%) for the shales, including a high content of kaolinite, indicate intense chemical weathering in the source area. The positive correlations between V, Cr, Ni, Co, Ga, Cd, Be, Sc, TiO2, MgO with Al2O3 and Ba with K2O suggest that these elements in the shales are mainly held in clay minerals. The elevated contents of Zr and the high Zr/Cr and Zr/Sc ratios imply that the shales were derived from predominantly felsic source rocks. However, TiO2/Zr and Y/Ni ratios suggest a derivation from an admixture of complex felsic and mafic basement rocks. The low average enrichment factor values of Mo (MoEF), V (VEF) and U (UEF), along with low concentrations of redox-sensitive trace element ratios (Mo/U, Ni/Co, V/Cr and Cu/Zn) and high TOC contents infer oxic conditions during deposition. Furthermore, Fe2O3–S-TOC relationships, along with DOPT, V/(V + Ni) and Fe2O3/Al2O3 ratios, suggest dominantly oxic to slightly dysoxic/anoxic conditions during the accumulation of the Mamu Formation shales. Binary plots of K2O/Na2O ratio versus SiO2 indicate a passive margin tectonic setting for the shales.

Textural and geochemical characteristics of the Yikpata river channel sands, Nigeria

The Yikpata river is one of the major rivers that empty into the River Niger, Nigeria. River Niger cuts across the Bida Basin thereby contributing to the alluvium deposits found within the Bida Basin. The properties and compositions Yikpata river channel sediments input in the River Niger where alluvium deposits are found is yet to be documented. Furthermore, the geology of where the studied river is located is sparse. Therefore, the textural, petrological, and geochemical analyses were used to examine the Yikpata river channel sediments for their compositions and characteristics in other to infer their provenance, tectonic settings and chemical weathering intensity as well as give information about sediments that are been transported as recent alluvium along River Niger in the Bida Basin. This study likewise lays some foundations for the comprehensive assessment of watershed environmental quality. This study revealed that the Yikpata river channel sediments are moderately well to poorly sorted sediments and were classified as sub-arkose based on log Na2O/K2O vs SiO2/Al2O3. Low CIA, PIA, ICV, Rb/Sr values, and ternary plot of A-CN-K demonstrate that the river sands were derived from low to moderately weathered source rocks and the major-element-based discrimination diagrams revealed that sediments were from a rift tectonic setting (passive margin). Additionally, the river sediments are derived from weathered sedimentary rocks that are of the felsic source, based on the major element discriminates functions, TiO2 vs Zr, Al2O3/TiO2, La/Sc, La/Co, Th/Sc, Cr/Th and LREE/HREE. The pollution status of the river from the sediments revealed that the river is currently not polluted and the sediment is not toxic.

Major and Rare Earth Element Characteristics of Late Paleozoic Coal in the Southeastern Qinshui Basin: Implications for Depositional Environments and Provenance.

To understand the geochemical characteristics of late Paleozoic coal in the Changzhi and Jincheng mining areas in the southeastern Qinshui Basin, major and rare earth element analyses were conducted through inductively coupled plasma–mass spectrometry (ICP–MS), X-ray fluorescence spectrometry (XRF), and proximate analysis. The results show that the study coals are bituminous A rank and anthracite C rank (Ro,ran: 1.6–3.24%) with low-ash, low-moisture, low-volatile, and low- to medium-sulfur characteristics. The main forms of sulfur in the study coals are organic sulfur, followed by pyritic sulfur, only some coals with high sulfur contents in the Taiyuan Formation (SGJ, WTP, FHS) are mainly pyritic sulfur, and the contents of sulfate sulfur are extremely low. The major elements of the late Paleozoic coal in the southeastern Qinshui Basin are mainly SiO2 (4.77%) and Al2O3 (3.64%), followed by Fe2O3 (1.22%), CaO (1.53%), FeO (0.48%), MgO (0.25%), Na2O (0.21%), P2O5 (0.18%), TiO2 (0.15%), and minor K2O (0.04%) (on a whole-coal basis). Through correlation analysis and cluster analysis, the occurrence states of major elements in the Shanxi and Taiyuan Formations are different. The average rare earth elements and yttrium (REY) value in the study area is 88.68 μg/g (on a whole-coal basis). The mean light REY (LREY)-to-heavy REY (HREY) ratio is 26.33. The mean values of δEu, δCe, Y, and Gd are 0.60, 0.99, 1.07, and 1.02, respectively. The Shanxi Formation is dominated by the L-type REY enrichment, while the Taiyuan Formation is dominated by the M–H-type REY enrichment. The fractionation degree of REY in the Taiyuan Formation is lower than that in the Shanxi Formation. Rare earth elements in Shanxi coal mainly occur in clay minerals, and some rare earth elements are adsorbed and enriched by vitrinite. Rare earth elements in Taiyuan coal mainly occur in clay minerals and pyrite, and some rare earth elements occur in inertinite. A warm, humid, low-salinity, oxidizing, and acidic environment was favorable for REY enrichment. The coal-forming environment was weakly oxidizing and reducing, and the paleosalinity of the water was relatively high during late Paleozoic coal deposition in the southeastern Qinshui Basin. The paleotemperature of the Shanxi Formation is higher than that of the Taiyuan Formation. The provenance is mainly from an upper crustal felsic source region, the source rocks are mainly post-Archean sedimentary and calcareous mudstones mixed with some granite and alkaline basalt from the Yinshan Upland, and the tectonic setting of the source area mainly includes island arcs and active continental margins.

Rare Earth and Trace Elements Composition of a Residual Clay from Sosan Akoko, Southwestern Nigeria: Implications for Weathering and Provenance

The aim of this study is to determine the source area weathering and provenance of a residual clay samples overlying Precambrian basement complex in Southwestern, Nigeria. Fifteen representative clay samples were collected from three pits dug in three locations across the study area. The mineralogy and chemical composition of samples was analyzed using X-ray diffractometer (XRD) and inductively coupled plasma-mass spectrometer (ICPMS) techniques respectively. The results of mineralogical analyses indicates that kaolinite (1.4%) and nontronite (2.77%) are the major clay minerals present while the non-clay minerals include quartz, orthoclase, labradorite and albite. Chemical indices of alteration (CIA) and weathering (CIW) values of 76.02% and 89.9% respectively, low alkali and alkaline earth elements content derived from the samples implies a comparatively intense source area. Furthermore, plots of TiO2/Al2O3 indicate provenance of predominantly acidic rocks and high concentrations of Rubidium (Rb) and Strotium (Sr) in the samples with values ranging from 113.4-138.2 ppm and 218.3-229.2 ppm respectively suggests ongoing chemical weathering of the clay body. The findings from this research through mineralogical composition, rare earth elemental normalized patterns, and ternary diagrams plotted implies that these samples are derived from felsic sources.

Provenance and paleogeographic implications for the Cenozoic sedimentary cover of the Ghomaride Complex (Internal Rif Belt), Morocco

The Cenozoic sedimentary cover from the Ghomaride Complex (Internal Rif Belt) has been studied in the Tetuan area (N Morocco) where a suite of sedimentary successions from shallow-marine to deep-marine environments crops out. For that purpose stratigraphic relations and petrological and geochemical signatures have been analyzed. Sandstone suites of the overall succession are heterogeneous and testify a multi-source area, in response of accretionary processes of the Ghomaride-Maláguide units and the exhumation of the lower units of the Internal Rif Zone (e.g. Sebtide-Alpujárride Complex). Pre-orogenic and Syn-orogenic (according to the eoalpine phase) deposits have been identified consisting in two depositional sequences: lower Paleocene and Cuisian-Bartonian, and upper Oligocene-upper Aquitanian and lower Burdigalian, respectively. Pre-orogenic deposits are mainly intra-arenite and hybrid arenites made of a minor amount of siliciclastic detritus but with abundance of intrabasinal carbonate grains. The syn-orogenic sandstone suites are quartzolithic, having abundance of low-grade metamorphic and sedimentary lithic fragments. Sedimentary lithic fragments are derived from the Mesozoic successions of the Ghomaride-Maláguide Complex while metamorphic detritus is related to an unknow Internal Rif Zone basement that was exhumed starting from the late Oligocene and mainly early Miocene. Modal analyses of sandstone suites for the extrabasinal grains mainly indicate lower rank metamorphic and sedimentary source terranes of a recycled orogen. Major and trace elements coupled to the mineralogical composition of the mudrock samples indicate a provenance from felsic source area(s) with a minor but not negligible contribution from mafic rocks mainly in the syn-orogenic suites. Geochemical analyses (Al–Ti–Zr ternary plot) indicate minor reworking and recycling processes before the final deposition through prolonged processes of sedimentary transportation. The trends evident in both CIA and CIA’ diagrams indicate source areas characterized by moderate weathering in non-steady-state conditions with a weak change of weathering condition from the pre-orogenic to the syn-orogenic cycle. Deposition during the Paleocene and Eocene, took place in the southern continental margin of the Ghomaride-Malaguide domain as a carbonate ramp. Contrarily, sedimentation in the late Oligocene-late Aquitanian took place in wedge-top basins within the Ghomaride-Malaguide domain. These changes occurred during the Burdigalian, when back arc basins were developed in the Internal Betic-Rif Zone. The Cenozoic reconstructed record was contemporaneous of the structuring of the Circum-Mediterranean chains and the Ghomaride-Maláguide Complex played a key role in the geodynamic evolution of the Rif Cordillera, representing a key tectonic element of the western Mesomediterranean domains.

Geochemistry and depositional environment of the Mesoproterozoic Xiamaling shales, northern North China

The Mesoproterozoic Xiamaling shales from Xiahuayuan area, southeastern Xuanlong sag, Northern China, were examined the elemental analysis by applying the inductively coupled plasma-mass spectrometry (ICP–MS). The Xiamaling shales have good to excellent oil hydrocarbon generation potential with type II kerogenas demonstrated by high content of alginate macerals, TOC, HI, S1 + S2 and extractable organic matter (EOM). The Xiamaling shales were deposited under a marine environment according to boron (B) (56–111 ppm) and other trace elements concentration, which is consistent with the geological settings. These shales can be classified into three types: (1) Type I is a coastal facies, which is influenced by fresh riverine water and has low B content of 56–61 ppm; (2) Type II is a marginal marine with B content of 73–79 ppm; and (3) type III has high B content of 111 ppm, typical of a brackish, and open marine environment.The Xiamaling shales have high B (>50 ppm), low Na, Ca, Ce, Mn, and rare earth elements (REEs). According to the elemental composition and ratios, the Xiamaling sediments were derived from the felsic source, which has suffered from moderate to strong chemical weathering based on the CIA, ICV, and PIA values. The Xiamaling marine shales were mostly deposited under dysoxic-anoxic conditions. The paleoclimate during the deposition of the Xiamaling shales was warm and humid based on the cross plots of Sr/Ca vs Mn/Ca values and Sr/Cu vs Rb/Sr ratios. Their total REE (ΣREE) contents increase from coastal towards the open marine zone. The Xiamaling shales display a negative Ce anomaly, representative of marine shale, and show a negative Eu anomaly, which is representative of lacustrine oil shale and the Post-Archean Australian Shale (PAAS) and is different from typical marine shale of younger age, indicating the influx of terrestrial sediment.