Significant Eu Anomalies Research Articles

The seasonal variations in the interactions between rare earth elements and organic matter in tropical rivers

The escalation of global demands for critical minerals to facilitate the green energy transition creates emerging needs to better understand their environmental behaviours. Several nations recognize rare earth elements (REEs) as priority critical minerals and emphasize the necessity to evaluate their environmental mobility and potential effects on natural ecosystems and human health. Here, we investigated the seasonal variations in dissolved concentrations of REEs and their leachable fractions from suspended particles in samples collected bi-weekly from the Sai Gon and Dong Nai Rivers in Southern Vietnam. The investigation period extended over sixteen months, including a transition from wet to dry seasons. We reported significant mobility of REEs in the river waters during the wet season due to watershed runoff, especially in Sai Gon River with the occurrence of acid-sulphate soils. Dissolved REE concentrations in the dry season were significantly lower because of the interactions with organic-rich particles (up to 13% of particulate organic carbon, POC) mainly derived from phytoplankton materials. The conditional distribution coefficients (logKD from 5 to 7 for Pr) were proportional to POC content. The scavenging capacity of particulate organic matter also led to affect the fractionation between light REEs and heavy REEs in solution, and the characteristic Middle REE-enrichment patterns for the leachable REEs fraction. We also reported significant Eu anomalies (Eu/Eu* up to 7) in the Dong Nai River during the dry season and associated this observation with the decomposition of organic matter that previously accumulated Eu. However, further studies are required to confirm this hypothesis because of small reservoir effects; elevated Eu anomalies were observed in water samples with low dissolved Eu concentrations.

Genesis and depositional environment of the Carboniferous Baishanquan iron deposit in Eastern Tianshan, Northwestern China

Submarine volcanic-hosted iron deposits are the most important iron deposit in Northwestern China. However, their origin remains controversial. Here, we present detailed studies of the petrology, geochronology, geochemistry and FeSi isotopes of iron ores from Baishanquan deposit in Eastern Tianshan, Northwestern China. Similar to Precambrian banded iron formations (BIFs), the Baishanquan deposit is hosted in a volcanic-sedimentary succession, the iron ores are characterized by banding with alternate iron-rich and silica-rich layers, and the mineral assemblage is dominant by magnetite, quartz and Fe-silicates. The iron ores show distinct light rare earth elements (REE) depletion [(La/Yb)PAAS = 0.24–0.47], no significant Eu anomalies (Eu/Eu⁎ = 0.88–1.16), relatively high Y/Ho ratios (30–34), and δ30Si values in quartz from the iron ores ranging from −0.80 to 1.67‰. These data indicate mixed seawater and low-temperature submarine hydrothermal source for both the iron and silica. The absence of negative Ce anomalies suggests that the depositional environment was characterized by low oxygen conditions similar to modern oxygen minimum zones. Positive δ56Fe values in most magnetite (−0.45 to +1.02‰) suggest partial Fe(II) oxidation of the iron ores. Interestingly, the iron ores also contain relatively high Al2O3, CaO, MgO, and Zr concentrations, indicating that the sedimentary basin was subject to periodic clastic input. Indeed, zircon LA-ICP-MS UPb dating of interlayered dacite indicates that the Baishanquan volcanic-sedimentary rocks and associated iron ores were deposited at 327.3 ± 2.8 Ma (N = 25, MSWD = 0.52). This is significant because the appearance of these iron deposit provides direct evidence that marine ferruginous conditions – at least locally - may have still been present at Carboniferous period.

The rare earth elements of sequentially leached phases in the loess-paleosol sequence at Weinan on the southeastern Chinese Loess Plateau

The rare earth elements (REEs) in loess sediments may preserve key information of paleoenvironmental changes in East Asia but remain poorly explored. Here we present the REE compositions of sequentially leached phases of loess sediments from a 16 m long loess-paleosol sequence collected from Weinan at the southern margin of the Chinese Loess Plateau (CLP). The REEs associated with carbonates, easily reducible oxides, reducible oxides, clay minerals, and the residual silicate minerals were sequentially leached with Na-acetate, hydroxylamine-HCl, Na-dithionite/Na-citrate, 12 mol L−1 HCl and concentrated HF-HNO3 solutions. The results show that the REE concentrations of different phases vary in the loess-paleosol layers and are most enriched in the easily reducible phase (except for the residual phase), which is likely explained by the association of REEs with Mn-oxides. Significant Eu anomalies can only be found in the carbonate and easily reducible phases, with the carbonate phase being characterized by appreciable positive Eu anomalies and the easily reducible phase being characterized by negative Eu anomalies, indicating the incorporation of Eu2+ into secondary carbonates that leaves the authigenic Mn-oxides with depleted Eu relative to other REEs. The carbonate phase shows significant negative Ce anomalies, which is likely due to the preferential removal of Ce4+ by Mn oxides before the formation of secondary carbonates. Nevertheless, appreciable positive Ce anomalies for the easily reducible phase can only be found at the bottom of the paleosol S1 while significant negative Ce anomalies were found within the paleosol S1, indicating the downward leaching of Ce4+ that shows stronger complexation with the organic matters than REE3+ in the soil solution. This may partly account for the negative Ce anomalies previously found in the paleosols. Overall, our results suggest a two-stage evolution of Eu and Ce anomalies of the carbonate phase, with the first stage controlled by the formation of both Mn-oxides and secondary carbonates and the second stage dominated by the precipitation of secondary carbonates. The comparison of carbonate Eu and Ce anomalies with other paleoclimatic proxies indicates that the combination of Eu and Ce anomalies of the carbonate fraction of loess may be applied as novel proxy records of climate change in East Asia.

Rare earth element uptake mechanisms in plankton in the Estuary and Gulf of St. Lawrence

The global shift toward green energy alternatives escalates demands for new resources, including rare earth elements (REEs), as per their implications in various green innovations. However, our understanding of their environmental cycle, especially the interactions with aquatic organisms, remains deficient, ultimately hindering environmental protection efforts. Here, we investigate the accumulation of REEs and 18 other elements in bulk and sorted plankton collected with different net mesh sizes (30, 63, 200, 333, 500 μm) in the Estuary and Gulf of St. Lawrence in the summer and winter of 2020. We observed significant correlations between the concentrations of REEs and elements of different charge numbers and ionic radii (Ba, Co, Cs, Fe, Mn, Pb, Rb and V), indicating non-selective uptake of REEs into plankton. All these elements have their highest concentrations in the fluvial corridor and upper estuary, with more significant enrichment in phytoplankton ([La] = 26.4 ± 4.8 mg kg−1) than zooplankton ([La] = 11.6 ± 8.3 mg kg−1). Their concentrations decrease to the minimum in the Gulf of St. Lawrence, especially in zooplankton ([La] = 4.8 × 10−2 ± 3.2 × 10−2 mg kg−1). We also assessed REE patterns to identify differential REE fractionation processes and anomalies. The freshwater plankton exhibits enrichment of middle REEs (MREEs) relative to the light and heavy REEs (LREEs and HREEs), potentially because of the higher binding affinity of MREEs on cellular surface transporters and metal loading effects. In estuarine and marine settings, the REE patterns in biological samples align with suspended particles, exhibiting a linear trend with LREE enrichment. This process is more noticeable in sorted macrozooplankton, which have significant Eu anomalies (Eu/Eu* up to 2), indicating differential incorporation of REEs into the chitin shells. This study highlights the significant enrichment of REEs into freshwater primary producers and the accumulation pathway similar to other inorganic elements.

Generation and redox state of two episodes of Early Cretaceous granitoid in the Xiaoqinling area, North China Craton: Implications for lithosphere thinning and metallogenic potential

The late Mesozoic granitoids in the Xiaoqinling area are of great significance for their associated gold deposits and for understanding the geodynamics of craton destruction. The Niangniangshan pluton in the Xiaoqinling area records three phases of magmatic activity, with biotite monzogranites formed in Phases1 and Phases2 and monzogranites in Phase3. Field investigations and LA–ICP–MS zircon UPb dating indicate that the Niangniangshan pluton was formed during two episodes of magmatism at ~134 Ma (Phase1 and Phases2) and ~ 123 Ma (Phase3). The ~134 Ma granitoids exhibit higher Sr/Y ratios (57–164) and higher contents of Sr (563–1114 ppm) and Ba (1455–1958) than the ~123 Ma granitoids (Sr = 88–124 ppm, Ba = 60–117 ppm, Sr/Y = 16–52). In addition, the ~134 Ma granitoids do not display significant Eu anomalies (0.75–1.06), while the ~123 Ma granitoids show negative Eu anomalies (0.73–0.84). However, all of the granitoids have low contents of MgO, Cr, Co and Ni, relatively high initial 87Sr/86Sr ratios (0.7072 to 0.7108), and low values of εNd(t) (−16.97 to −14.49) and εHf(t) (−29.62 to −14.41). These geochemical characteristics indicate that the ~134 Ma granitoids were generated by partial melting of the ancient metamorphic basement at high pressures, whereas the ~123 Ma granitoids were formed by partial melting of the ancient metamorphic basement at relatively low pressures. The differences in the formation of the two episodes of granitoid provide further evidence that there was a transformation from lithospheric thickening of the North China Craton in the Xiaoqinling area to a stage of lithospheric thinning, this probably taking place between ~134 and ~ 123 Ma. Zircon trace-element geochemistry indicates that the ~123 Ma granitoids had higher oxygen fugacities and zircon crystallisation temperatures than the ~134 Ma granitoids. We also found that ΔFMQ values show a positive correlation with temperature for the ~134 Ma granitoids, but a negative correlation for the ~123 Ma granitoids. This indicates that the ~134 Ma magma became more reduced with evolution whereas the ~123 Ma magma became more oxidised. These features, combined with the redox state of typical magmatic hydrothermal gold deposits globally, suggest that the ~123 Ma granitoids had a greater potential to form magmatic hydrothermal gold deposits than the ~134 Ma granitoids.

Geochronology and geochemistry of Late Mesozoic diabase in the Litun ore district, North China Craton

Mesozoic mafic dykes in the Litun ore district provide an opportunity to study the nature of the Mesozoic lithospheric mantle beneath the Luxi area of the North China Craton. U–Pb dating of zircon from the Litun diabase using laser ablation inductively coupled plasma mass spectrometry yields an age of 124.6 ± 1.7 Ma, indicating an Early Cretaceous emplacement age. Samples from the Litun diabase display a medium‐ to fine‐grained texture, consisting of plagioclase (60–65 vol%), clinopyroxene (30–35 vol%), and minor biotite (~2 vol%). They are characterized by enrichment of large‐ion lithophile elements (LILEs, such as Rb, Ba, Th, and U) and light rare‐earth elements (LREEs) without significant Eu anomalies (0.83–1.07), depletion of high‐field‐strength elements (HFSEs, such as Nb, Ta, and Ti). The Litun diabase has relatively high initial 87Sr/86Sr ratios (0.7049–0.7060) and negative εNd(t) values (−11.7 to −9.7). The Litun diabase also shows high MgO (10.52–13.84 wt%), Cr (956–1,162 ppm), Co (26.5–65.6 ppm), and Ni (240–514 ppm) contents and low Rb/Sr ratios (0.01–0.03). These geochemical features suggest that the Litun diabase may have originated from an enriched lithospheric mantle source with amphibole as an essential phase, and that the Litun diabase was not significantly affected by fractional crystallization and crustal contamination. In combination with the Sr–Nd isotopic compositions of mafic rocks in the Luxi area (such as the Mengyin mafic dykes and Jinan gabbro), our results suggest that the lithospheric mantle beneath the Luxi area may have been rapidly enriched between ~144 and ~124 Ma, which was induced by sequential hybridization of sinked lower crust.

A new insight into the eastern extension of the Proto-Tethyan margin of Gondwana by Early Paleozoic volcanic rocks in South China

South China is located in a key area of East Gondwana. The volcanic rocks in the unambiguous tectonic setting of Hainan Island were systematically studied based on detailed field, petrological, geochemical, and UPb zircon geochronological data. The petrology and geochemistry reveal three types of volcanic rocks, i.e., andesites, N-MORB-type metabasalts, and E-MORB-type metabasalts. Their eruption ages are well defined between 446 and 430 Ma. The andesite is characterized by negative Nb, Ta, and Eu anomalies and positive Th and U anomalies. The E-MORB-type metabasalt is characterized by Rb, Ba and Sr depletions, slight Nb and Ta enrichments, and negative Eu anomalies. The N-MORB-type metabasalt has more depleted trace element compositions and is generally enriched in Rb, Ba, and Sr; depleted in Nb and Ta; and it does not exhibit significant Eu anomalies. The whole rock SrNd isotopic analyses show that the andesites, N-MORB-type metabasalts, and E-MORB-type metabasalts have εNd(t) values of −0.2 to −3.6, +3.7 to +6.8, and + 5.5 to +6.7, respectively. These results suggest that their formation is closely related to the subduction of Proto-Tethyan oceanic crust. These detailed descriptions of the Early Paleozoic volcanic rocks on Hainan Island indicate that South China was likely the eastern extension of the Proto-Tethyan margin and was located on the easternmost periphery of East Gondwana.

Redox series assessment, petrogenetic, and geodynamic appraisal of Neoarchean granites from the Bundelkhand Craton, Central India: Constraints from phase petrology and bulk rock geochemistry

Based on field relationships, microstructure, phase petrology, and whole‐rock elemental geochemistry, we have unravelled the redox conditions and petrogenetic evolution of Neoarchean granites (sensu lato) from the central part of the Bundelkhand Craton, Central India. The studied Neoarchean granites are sanukitoids (sensu lato), high‐K, low‐magnesian granites (HKLMG), and oxidized A‐type granites (OAG). Chemistry of biotite in conjunction with amphibole compositions from sanukitoids indicates their crystallization in calc‐alkaline felsic host magma formed in a subduction setting at elevated fugacity of oxygen (fO2), buffered at +2 fayalite‐magnetite‐quartz (FMQ), corresponding to magnetite series granite. Chemistry of biotite and amphiboles from HKLMG suggests that host melts of these phases buffered above +1 FMQ, that is, moderate fO2 condition corresponding to magnetite series granites. The nature of the HKLMG magma is peraluminous to alkaline which originated at a relatively high‐P condition. The biotites from OAG exhibit pronounced Al‐Fe substitution buffered above +0.5 FMQ to represent oxidized A‐type host granite magma, belonging to magnetite series granite. The sanukitoids bear high ferromagnesian minerals (FeOt + MgO + MnO + TiO2 (FMMT) >4.5; Mg# = 28–45), and enriched incompatible elements without significant Eu anomalies, probably originated from melt‐enriched mantle source in a subduction setting. The HKLMG are characterized by relatively low Mg#, TiO2, high K‐LILEs‐REEs with negative Eu anomalies, and high Th/Nb, Ce/Pb, and La/Nb ratios, which suggest mixed source signatures, derived from the enriched mantle and continental crust. A‐type granites (OAG) bear high NK/A (molar Na2O + K2O/Al2O3 ~ 1.17), FeOt/MgO, K2O/Na2O, Ga/Al, and Ce–Y, which indicate the emplacement of OAG magmas in syn‐ to post‐collisional tectonic environments. Thus, the Neoarchean granites from the Bundelkhand Craton represent a collage of subduction related sanukitoids to high‐K magnesian granites, and syn‐ to post‐collisional oxidized A‐type granites.

Mesozoic reworking of the Paleozoic subducted continental crust beneath the south-central margin of the North China Block: Geochemical evidence from granites in the Xiaoqinling-Xiong’ershan region

Mesozoic granites are common in the south-central margin of the North China Block, beneath which the North Qinling microcontinent was subducted northwards in the early Paleozoic to subarc depths for ultrahigh-pressure (UHP) metamorphism. Although the continental deep subduction would have produced UHP eclogite facies metamorphic rocks in the North Qinling orogen, it is intriguing whether the Mesozoic granites record reworking of the crustal rocks from the subducted North Qinling microcontinent. This issue is addressed by an integrated study of zircon in-situ U-Pb ages and Hf-O isotopes as well as whole-rock geochemistry for four typical granitic plutons from the Xiaoqinling-Xiong’ershan region in the south-central margin of the North China Block. These plutons are metaluminous to weakly peraluminous, and belong to high-K calc-alkaline to shoshonitic series. They are enriched in LREE and LILE but depleted in HREE and HFSE. In terms of trace element and Sr-Nd-Hf isotope compositions, these granites can be categorized into two groups. Group I granites from the Huashan, Wenyu and Heyu plutons are high in Sr concentrations and Sr/Y and (La/Yb)N ratios without any significant Eu anomalies and thus similar to adakitic rocks, and have more enriched Sr-Nd-Hf isotope compositions. In contrast, Group II granites from the Funiushan pluton have low Sr concentrations and Sr/Y and (La/Yb)N ratios with negative Eu anomalies, and show less enriched Sr-Nd-Hf isotope compositions. Although zircon U-Pb dating for syn-magmatic zircons from the two groups of granite gives consistent emplacement ages of 120 to 137 Ma, relict zircons in them show different U-Pb ages. In detail, relict zircons from Group I granites exhibit Neoarchean to Paleoproterozoic U-Pb ages, with Hf-O isotope compositions similar to those of the ancient basement such as the Taihua Group and the Xionger Group in the south-central margin of the North China Block. In comparison, relict zircons from Group II granites display not only Paleoproterozoic U-Pb ages but also Neoproterozoic and early Paleozoic U-Pb ages. The Paleoproterozoic relict zircons exhibit Hf-O isotope compositions similar to those of the ancient basement in the south-central margin of the North China Block, whereas the younger ones have Hf-O isotope compositions consistent with those of the Neoproterozoic protoliths of metamorphic rocks and early Paleozoic granitoids in the North Qinling orogen. Therefore, Group I granites were derived from partial melting of the ancient basement in the south-central margin of the North China Block, whereas Group II granites were produced by partial melting of a mixing source that was composed of not only the ancient crust from the North China Block but also the juvenile crust from the North Qinling microcontinent. This provides the geochemical evidence for late Mesozoic reworking of the crustal rocks from the North Qinling microcontinent through its northward subduction in the early Paleozoic beneath the south-central margin of the North China Block.

Geological and geochemical characteristics and genesis of the Cishan gold deposit in Tongling ore cluster area, Anhui Province

The Cishan gold deposit is a newly discovered medium-scale independent skarn gold deposit located in the Tongling ore cluster area of the Middle-Lower Yangtze Metallogenic Belt, and the ore-related intrusion is the Cishan pyroxene diorite. In this study, we investigated the zircon U–Pb Geochronology, whole-rock geochemistry of the Cishan ore-related pyroxene diorite, and C–O–S isotope compositions of hydrothermal calcites and metal sulfides in the ores. The pyroxene diorite was emplaced at ca. 141.7 ± 0.36 Ma. They are metaluminous and record high-K calc alkaline and shoshonite series with the characteristics of high Al and alkali (K, Na), enriched in LREEs and LILEs (Rb, K, Ba, Sr), depleted in HREEs and HFSEs (Th, U), without significant Eu anomalies. We suggest that the magma of the Cishan pyroxene diorite was probably derived from partial melting of the enriched lithospheric mantle mixed with a small amount of crustal derived melts, and then underwent crystallization differentiation and weakly upper crustal contamination during the magmatic ascending. The δ13CV-PDB and δ18OV-SMOW values of the hydrothermal calcites range from −5.1‰ to −0.5‰ and 11.7‰ to 16.2‰ respectively, and the δ34SV-CDT values of sulfide ore minerals range from −0.7‰ to 6.0‰, showing that the ore-forming fluids and materials were derived from the magma. Combined with previous studies, we proposed that both the Cishan intrusion and skarn gold deposit were formed under the tectonic transition period from compressional to extensional setting, and the Middle–Lower Yangtze Metallogenic Belt was located in the inland side of the continental margin arc under the subduction of the paleo-Pacific plate.

ESTIMATION OF THE ABUNDANCE AND DISTRIBUTION OF RARE EARTH ELEMENTS IN SOIL AROUND KADUNA REFINING AND PETROCHEMICAL COMPANY USING NUCLEAR TECHNIQUE

Instrumental neutron activation analysis (INAA) technique was used to investigate the abundance and distribution of rare earth elements (REE) in soil around Kaduna Refinery. The aim of the study is to assess the rare elements potential of Nigeria for economic exploitation. Five REEs (La, Dy, Eu, Yb, and Lu) were detected in varying concentrations ranging from a minimum of 0.6 µg/g (Lu) to a maximum of 249.0 µg/g (La). The elements existed with trends consistent with the natural pattern of REEs in soil, showing significant Eu and Dy anomalies which characterize upper plains and flood plains. The levels of REEs in soil in the study area were generally slightly above background levels, with minimal (La, Dy, and Eu), moderate (Yb), and significant (Lu) enrichments and trending: Lu ˃Yb ˃ Eu ˃ Dy ˃ La. The abundance of the REEs investigated cannot establish a potential of Nigeria for economic exploitation of the mineral, hence, rare earth project in the study area is not viable at the moment.

Zircon U–Pb and molybdenite Re–Os dating and geological implications of the Shimadong porphyry molybdenum deposit in eastern Yanbian, northeastern China

The Shimadong porphyry Mo deposit is located in eastern Yanbian, in the eastern part of the north margin of the North China craton, northeastern China. Here, we present the whole-rock major and trace elements, zircon U–Pb and Hf isotope data, and molybdenite Re–Os data for the Shimadong deposit. The porphyry was emplaced at 163.7 ± 0.9 Ma and the mineralization at 163.1 ± 0.9 Ma, suggesting that the mineralization was associated with the emplacement of the Shimadong porphyritic monzogranite. The porphyritic monzogranite had high SiO2 (70.09–70.55 wt%) and K2O + Na2O (7.98–8.27 wt%) contents and low MgO (0.51–0.53 wt%), TFeO (2.4–2.47 wt%), CaO (2.19–2.26 wt%), and K2O/Na2O (0.8–0.82) contents. The porphyry was rich in large ion lithophile elements Rb, Ba, K, and Sr, depleted in high-field-strength elements Y, Nb, Ta, P, and Ti, without significant Eu anomaly (δEu = 0.86–1.00), and depleted in heavy rare earth elements with light rare earth elements/heavy rare earth elements = 18.25–20.72 and (La/Yb)N = 27.10–34.67. These features are similar to those of adakitic rocks derived from a thickened lower crust. Zircon εHf(t) values for the porphyritic monzogranite ranged from –19.2 to 6.3, and the two-stage Hf model ages (TDM2) were 2421–811 Ma. These data indicate that the primary magma of the Shimadong porphyritic monzogranite was mainly derived from partial melting of the thickened lower crust consisting of juvenile crust and pre-existing crust. Combined with the results of previous studies, our data suggest that the Shimadong porphyry Mo deposit was emplaced along an active continental margin related to the westward subduction of the paleo-Pacific Plate.

Petrogenesis of the Bakoudou TTGs and high-K biotite granites and associated gold mineralization, southern Gabon: An Archean example of a porphyry–epithermal transitional gold system

The Bakoudou gold deposit, southern Gabon, is hosted in the Archean basement granitoids of the Chaillu Massif. These granitoids of the Bakoudou deposit are subdivided into two main groups: TTGs and porphyritic biotite granites. The TTGs show geochemical characteristics similar to those of other TTGs worldwide, such as high Al2O3 (13.49–18.93 wt%) and Na2O (3.27–4.66 wt%) and low K2O (1.01–1.98 wt%), with low K/Na (0.15–0.32) ratios. Their Mg# (Mg/(Mg + Fe)*100) values vary from 34.81 to 50.76, with low to moderate Nb/Ta and Zr/Sm ratios (7.03–23.43 and 19.13–75.25, respectively). They are characterized by moderate (La/Yb)N (6.70–41.71) and Sr/Y (20.80–72.13) ratios similar to those of adakites, negative Nb, Ta and Ti anomalies and LREE-enriched and HREE-depleted patterns, without significant Eu anomalies (Eu/Eu* = 0.93–1.11, average = 1.00). These geochemical characteristics suggest that the TTG rocks were formed by partial melting of hydrous basaltic crust, such as garnet-rich amphibolite. The porphyritic biotite granites show high-K calc-alkaline affinity. They are characterized by high SiO2 (71.01–74.86 wt%) and K2O (3.29–4.92 wt%) but relatively low MgO (0.38–0.92 wt%), with Mg# values varying between 31.78 and 40.27. The rocks show low to moderate Sr/Y (13.75–26.66) ratios and LREE-enriched and HREE-depleted patterns, with negative Eu anomalies (Eu/Eu* = 0.36–0.58, average = 0.47). These geochemical features indicate that the porphyritic biotite granites originated from partial melting of TTG lithologies.The orebody of the Bakoudou gold deposit occurs as quartz veins hosted in the TTG shear zones. Quartz is the main gangue mineral, with minor sulfides such as pyrite and chalcopyrite. Gold is present in solid solution (Au+1) and as nanoparticles of native gold (Au0) in pyrite and mostly as free gold. Pyrite samples analysed by laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) show high Ni (3.24–3600 ppm) and Co (4.68–4140 ppm) and low As (<34.50 ppm) and Au concentrations (<2.90 ppm) compared to Cu, which has rather high concentration of <3570 ppm. Moreover, the Au–As relationships of pyrites show a porphyry–epithermal transitional signature. Therefore, the Bakoudou gold deposit can be considered an example of Archean porphyry–epithermal transitional gold system, formed from magmatic fluids originating from a hidden porphyry system at depth during cooling and emplacement of the potassic granites. The disseminated free gold grains in the quartz veins may have originated from boiling of the mineralizing fluid (phase separation) and/or from remobilization of invisible gold in pyrite by later tectonic events and surficial weathering.

Integrated major and trace element study of clinopyroxene in basic, intermediate and acidic volcanic rocks from the middle Okinawa Trough: Insights into petrogenesis and the influence of subduction component

Magmatism is very common in the Okinawa Trough. However, the influence of magmatic processes, including fractional crystallization and magma mixing, on the petrogenesis of volcanic rocks is poorly understood. The in situ major and trace element compositions of clinopyroxene in co-genetic basalts, andesites, trachyandesites and rhyolites from the Iheya Ridge in the middle Okinawa Trough are examined to determine their petrogenesis and the influence of slab subduction. Regarding the types of mineral zoning, in basalt and andesite, clinopyroxene phenocrysts are unzoned. In trachyandesite, the clinopyroxene phenocrysts can be classified into three groups: normal zoned, oscillatory zoned and unzoned. Similarly, unzoned and reverse zoned clinopyroxene phenocrysts are the two main structures in rhyolites. According to the major element contents and distinct distribution patterns of rare earth elements (REEs), we identify various clinopyroxene domains in their host volcanic rocks. Type 1 clinopyroxene domains in basalts and trachyandesites are dark, have high Mg# values and are strongly depleted in light REEs (LREEs) with no significant Eu anomalies. The Type 2 clinopyroxene domains in basalts and trachyandesites and all clinopyroxene phenocrysts in andesites are bright, have low Mg# values and are strongly depleted in LREEs and have significant negative Eu anomalies. Clinopyroxene domains in rhyolites have significant negative Eu anomalies and can be divided into two types: Type 1 clinopyroxene domains are characterized by strong depletion in LREEs, Sr, P and high field strength elements (HFSEs), while Type 2 clinopyroxene domains are slightly depleted in LREEs and have small negative P anomalies. The continuously changing major element composition and parallel distribution of trace element spider diagrams suggest that all these clinopyroxene phenocrysts in the studied volcanic rocks were derived from co-genetic magmas and the compositional transition of clinopyroxene from basalts to rhyolites attributed to different extents of fractional crystallization of various minerals (e.g., clinopyroxene, orthopyroxene, plagioclase and apatite). The oscillatory zoned and reversed zoned clinopyroxene phenocrysts show that magma mixing and recharge events with co-genetic magmas are common in the middle Okinawa Trough magma system. The origin of clinopyroxene phenocrysts involves contributions from subducted sedimentary components of 2.5% sediment melts and 1.5% sediment fluids and is deduced based on the equilibrium melts of clinopyroxene phenocrysts in basalts. The geochemical study of clinopyroxene provides evidence for the contributions of magmatic processes and slab subduction to the petrogenesis of Okinawa Trough volcanic rocks.

Indosinian magmatism and rare metal mineralization in East Tianshan orogenic belt: An example study of Jingerquan Li-Be-Nb-Ta pegmatite deposit

The East Tianshan orogenic belt, a part of the Central Asian Orogenic Belt like Altai orogenic belt, has shown great potential for rare metal mineralization. Jingerquan Li-Be-Nb-Ta deposit is the largest pegmatite deposit in this region. Muscovite granite, quartz monzonite and gabbro have developed in the Jingerquan Li-Be-Nb-Ta pegmatite deposit in the eastern part of East Tianshan orogenic belt. Based on the content of elemental Li and the presence of Li-bearing minerals, we recognize two sets of intrusive assemblages, namely, class I, including muscovite granite and quartz monzonite, which are rich in Li with presence of spodumene and/or lepidolite, and class II mainly gabbro, which are poor in Li and absent of Li-bearing minerals. Class I rocks are rich in Si, Al, Na, K, calc-alkaline to high-K calc-alkaline series, and poor in Ca, P, Fe, and Mg, with A/CNK ≥ 1.1, which are similar to S-type peraluminous granites. Class I rocks are characterized by Rb, Ta, Nb, and Hf enrichments and significant Ti, Ba, and Sr depletions. The chondrite-normalized rare earth element (REE) patterns exhibit significant Eu anomalies (δEu = 0.01–0.20), “tetrad effect,” and increased fractionation of rare earth elements with relatively low ΣREE. Class II rocks are calc-alkaline rocks that are rich in Ca, Al, and P and poor in Si, K, with A/CNK < 1; they are characterized by Ba and Sr enrichments and Th, Nb, and Ta depletions. The chondrite-normalized REE patterns exhibit no significant Eu anomalies (δEu = 0.97–1.40) and a smooth curve that slopes to the right. The monazite SIMS U-Th-Pb ages of class I (246–252.9 Ma) and the zircon LA-ICP-MS U-Pb ages of class II (247–250.7 Ma) indicate that both types of intrusions were formed in intraplate environment in Indosinian period. The εHf(t) values (12.0–15.2) and the depleted mantle model ages TDM (279–411 Ma) of class II rocks indicate that the magmas were mainly derived from partial melting of the depleted mantle. In the intraplate extensional setting, the mantle magmas represented by class II basaltic magmas intraplated into the crust and induced partial melting of the middle and upper crust to produce class I S-type granitic magmas. After that, the granitic magmas underwent continuous differential evolution and volatile enrichment, and finally form Li-Be-Nb-Ta mineralized granitic pegmatite. The geological setting, diagenetic and metallogenic chronology, and mineral assemblages of the East Tianshan orogenic belt and the Altai orogenic belt can be compared, and rare metal mineralization of both belts were controlled by the Indosinian tectonic-magmatic event.

New constraints on the tectono-magmatic evolution of the central Gangdese belt from Late Cretaceous magmatic suite in southern Tibet

In the Gangdese magmatic belt of southern Tibet, widespread Late Mesozoic magmatism has been reported, although their petrogenesis and tectonic evolution remain ambiguous. Here we present new zircon U-Pb and geochemical data on a gabbro-diorite suite near the Namling County in the central Gangdese belt, that provide insights into the geodynamic processes in this region. Zircon U-Pb data from LA-ICP-MS and SHRIMP II analyses indicate that the granite crystallized at ca. 87 Ma, and the gabbro-diorite suite was emplaced at ca. 91–95 Ma, both suggesting an early Late Cretaceous magmatism in the central Gangdese belt. The gabbro-diorite suite displays wide ranges of SiO2 (57.21–44.25 wt%) and MgO contents (9.04–3.18 wt%), with high Al2O3 (21.47–16.14 wt%) and Na2O/K2O (1.10–5.84) values. Compared to these, the granite rocks show limited variations of SiO2 (76.97–76.40 wt%), high Na2O + K2O (8.84–8.04 wt%), K2O/Na2O (2.33–1.30) and Sr/Y (48.99–80.36), with low Mg# (30.77–20.39) values and significant Eu anomalies (Eu/Eu* = 1.20–0.24). The gabbro-diorite rocks are characterized by typical arc-type features including enrichment of light rare earth elements (LREE) (LaN/YbN = 11.52–5.06 > 1) and large ion lithophile elements (LILE) (e.g. Cs, K and Rb), but are depleted in high strength field elements (HSFE) (e.g. Nb, Ta, Ti and P). The granitic rocks are also enriched in LREE (LaN/YbN = 55.42–26.55 > 1) and LILE (e.g. Cs, Rb, K and Pb), but depleted in HSFE (e.g. Nb, Ta, Ti and P). The gabbro-diorite rocks show distinctly positive εNd(t) (+3.5 to +4.2) and εHf(t) values (+8.5 to +15.6) values with a restricted range, with relatively homogeneous and low (87Sr/86Sr)I ratios (0.704213–0.703820). The granitic rocks also show positive εNd(t) values (+4.1 to +4.4) and consistent (87Sr/86Sr)I ratios (0.703977–0.703180). Our data suggest that the gabbro-diorite rocks were mostly sourced from partial melting of the depleted mantle that was metasomatized by fluids released from the subducted Neo-Tethys oceanic slab. The granite was probably produced by partial melting of the juvenile crust with no participation of mantle material. We correlate the magmatism with tectonics associated with the roll-back of the Neo-Tethys oceanic slab during the early Late Cretaceous.

Geochemistry of volcanic rocks from Oldoinyo Lengai, Tanzania: Implications for mantle source lithology

Oldoinyo Lengai is the only active carbonatite volcano within the East African Rift Valley in northern Tanzania. The volcano is dominated by peralkaline silicate rocks with natrocarbonatites. This study presents new mineralogical and geochemical data, including Sr–Nd–Pb–Hf–Mg isotopic compositions, for volcanic rocks at Oldoinyo Lengai and lavas from the nearby Gregory Rift Valley. The samples analyzed in this study include olivine melilitite, melanephelinite, wollastonite nephelinite, and phonolite. The olivine melilitites and melanephelinites have highly fractionated rare-earth-element (REE) patterns with (La/Yb)N values of 26.4–64.9, suggesting that they formed from magmas generated by low-degree (up to ∼7%) of partial melting within the garnet stability field. The wollastonite nephelinites have much higher (La/Sm)N values but lower (Sm/Yb)N values relative to typical oceanic island basalts (OIB), with flat heavy REE patterns [(La/Yb)N = ∼22]. The phonolites have elevated REE abundances but with patterns intermediate between the other two sample groups [(La/Yb)N = ∼41]. All samples have primitive-mantle-normalized incompatible element patterns that are characterized by negative K and Rb anomalies but no significant Eu anomalies. They also have elevated Yb contents relative to the compositions of modeled garnet peridotite-derived melts, suggesting that they were derived from a sublithospheric source containing enriched HIMU-like recycled oceanic crustal material. However, the wollastonite nephelinites have significantly positive Ba, U, Sr, and Pb anomalies similar to those found within the Oldoinyo Lengai natrocarbonatites. The wollastonite nephelinites might have been sourced from a region of sub-continental lithospheric mantle (SCLM) that was previously metasomatized by interaction with carbonatite melts. The phonolites in the study area have also weakly positive Pb and Sr anomalies indicative of some interaction with the SCLM. All samples have δ26Mg values (−0.39‰ ± 0.07‰) lighter than the composition of normal mantle material (−0.25‰ ± 0.04‰). In addition, a negative correlation between δ26Mg values and MgO concentrations suggests derivation from a source region containing recycled carbonate. The samples from the study area define a mixing array between HIMU- and EM1-type OIB in Sr–Nd and Pb–Pb isotopic correlation diagrams, and have pronounced Nd–Hf isotopic decoupling, plotting below the mantle regression line in Nd–Hf isotopic space. The negative deviation from the Nd–Hf isotopic mantle array and the presence of an EM1-type mantle component in the Sr–Nd isotopic compositions of the Oldoinyo Lengai volcanic rocks can be generated by recycling of E-MORB-type oceanic crustal material with an age of 1.5–1.0 Ga.

Complex magma sources of late Mesozoic granites along the southern margin of the North China Craton: constraints from geochemistry and geochronology of the massive Heyu and Lantian plutons

ABSTRACT Mesozoic granitoid rocks in the eastern Qinling terrane along the southern margin of the North China Craton are significant for understanding geodynamics processes related to lithospheric delamination in the Late Mesozoic. In addition, these rocks have close genetic association with the largest Mo-(Au-Ag) polymetallic mineralization belt in China. In the present study, zircon U-Pb ages and elemental and Sr-Nd-Pb isotopic geochemistry are reported for two representative granite plutons (Heyu and Lantian) exposed in the eastern Qinling terrane. Granitoid rocks from both plutons are metaluminous to weakly peraluminous and are classified as I-type granite with formation ages of 145 ~ 135 Ma and 150 Ma, respectively. These rocks are characterized by adakite-like affinity without significant Eu anomalies. Both plutons have relatively high initial 87Sr/86Sr ratios ranging between 0.7063 and 0.7109 and variable εNd(t) values of – 29.2 to – 6.5. Their Pb isotopic compositions are comparable to those of old high-grade metamorphic basement rocks from the North China Craton but are different from those of country rocks from the Xiong’er and Taihua groups. These features indicate genesis via reworking of the lower crust beneath North China and partial involvement of juvenile crustal material to different extents. Occurrences of ca. 1000-Ma-old inherited zircon in the Lantian granites imply the contribution of the Qinling Group in North Qinling to the magma source(s). This magmatism occurred intensively in a transitional setting from compression to extension and was likely induced by lithosphere thinning and asthenosphere upwelling beneath eastern China during the Cretaceous.

Porphyry Cu fertility of the Loch Lilly-Kars Belt, Western New South Wales, Australia

This study investigates the prospectivity for porphyry Cu mineralisation of the early Paleozoic Loch Lilly-Kars Belt, which follows the southern margin of the Paleoproterozoic Broken Hill (Willyama) Inlier in western New South Wales, Australia. The belt is thought to have resulted from the 515–510 Ma collision of a volcanic passive margin and an intra-oceanic island arc above a west-dipping subduction zone, with subsequent post-collisional magmatism. To identify fertility signals of selected magmatic intrusive rocks, we combined whole-rock analyses with in-situ zircon trace-element and isotopic measurements. Data reveal that both Cambrian (ca 496 Ma) and Devonian (ca 393 Ma) intrusive suites are present in the Loch Lilly-Kars Belt. Cambrian dioritic rocks are largely non-fertile for porphyry Cu mineralisation, whereas Devonian monzodiorites and monzonitic porphyries carry strong fertility signals that include high whole-rock Sr/Y (>35) and V/Sc (>10) values, associated with the occurrence of equant, stubby zircons showing relatively constant Eu/Eu* values without any significant Eu anomalies. Although only few samples were analysed and more intensive exploration is required, the results of this study indicate significant potential for porphyry Cu mineralisation in this poorly known belt.

The Early Eocene Ekmekçi granodiorite porphyry in the Karacabey region(Sakarya Zone, NW Turkey)

The Ekmekçi granodiorite porphyry is a unit in the E-W trending, postcollisional Eocene magmatic rocks of northern Anatolia. It occurs as a relatively small stock, but represents a link between plutonic and volcanic rocks. This Early Eocene granodiorite porphyry intruded into the Upper Triassic rocks of the Karakaya complex in the Sakarya Zone. In this study we present geochemical and zircon U-Pb LA-ICP-MS age data to contribute to understanding the Early Tertiary postcollisional tectonic setting of NW Anatolia. The granodiorite porphyry includes plagioclase, quartz, hornblende, K-feldspar, biotite, and minor zircon, apatite, sphene, and opaque minerals. The stock displays medium-K calc-alkaline I-type and metaluminous affinity. Similar to other Eocene magmatic rocks, it displays characteristic features of subduction-related magmatism, such as enrichment in large-ion lithophile elements relative to highfield strength elements and enrichment of light rare earth elements relative to heavy rare earth elements with a lack of significant Eu anomalies. They are characterized by homogeneous initial Sr and Nd isotopic compositions of 0.7044-0.7049 and 0.51255-0.51260, respectively. Zircon U-Pb data indicate that the Ekmekçi granodiorite porphyry was emplaced at 5.1 ± 1 Ma (2s Ypresian). Geochemically, the Ekmekçi granodiorite porphyry is similar to mafic volcanic rocks rather than the plutonic rocks of the same age. It was emplaced to the north of the İzmir-Ankara-Erzincan Suture (northern plutonic belt of NW Anatolia) and can be correlated with southern plutons such as Orhaneli, Topuk, Tepeldağ, Gürgenyayla, and Sivrihisar in the Anatolide-Tauride block in terms of age.