REE Enrichment Research Articles

The Subduction-Related Metavolcanic Rocks of Maroua, Northern Cameroon: New Insights into a Neoproterozoic Continental Arc Along the Northern Margin of the Central African Fold Belt

The metavolcanic rocks around Maroua in the Far North Region of Cameroon are located at the northern margin of the Central African Fold Belt (CAFB) and have not been studied to date. The petrographic and whole-rock geochemical data presented in this paper highlight their magma genesis and geodynamic evolution. The lavas are characterized by basaltic, andesitic, and dacitic compositions and belong to the calc-alkaline medium-K and low-K tholeiite series. The mafic samples are essentially magnesian, while the felsic samples are ferroan. On a chondrite-normalized REE diagram, mafic and felsic rocks display fractionated patterns, with light REE enrichment and heavy REE depletion (LaN/YbN = 1.41–5.38). The felsic samples display a negative Eu anomaly (Eu/Eu* = 0.59–0.87), while the mafic lavas are characterized by a positive Eu anomaly (Eu/Eu* = 1.03–1.35) or an absence thereof. On a primitive mantle-normalized trace element diagram, the majority of the samples exhibit negative Ti and Nb–Ta anomalies (0.08–0.9 and 0.54–0.74, respectively). These characteristic features exhibited by the metavolcanic rocks of Maroua are similar to those of subduction-zone melts. This subduction would have taken place after the convergence between the Congo craton (Adamawa-Yadé domain) and the Saharan craton (Western Cameroonian domain). Petrological modelling using major and trace elements suggests a derivation of the Maroua volcanics from primitive parental melts generated by the 5–10% partial melting of a source containing garnet peridotite, probably generated during the interaction between the subducted continental crust and the lithospheric mantle and evolved chemically through fractional crystallization and assimilation.

Timing and origin of the Lomagundi-Jatuli Event: Insights from U[sbnd]Pb geochronology, C-O-Fe isotopes and REE compositions from the Jingshan Group, North China Craton

The Lomagundi-Jatuli Event (LJE) represents perhaps the largest and longest positive carbon isotope excursion of Earth history. However, the synchroneity, scale, and linkage of the LJE to Earth's early history of atmospheric oxygenation remain controversial. Strata of the Paleoproterozoic Jingshan Group of the North China Craton that preserve the isotopic record of the LJE excursion in marble layers and abundant graphite deposits provide an opportunity to elucidate the significance of the LJE. Carbon isotopic values (δ13CV-PDB) of the LJE based on analysis of 20 samples of the Lugezhuang Formation, lower Jingshan Group, range from −0.8 to +9.6 ‰ and display positive co-variance with stable oxygen isotope values (δ18OV-PDB). The positive carbon isotope excursion is constrained to 2140.6 ± 8.5 Ma (MSWD = 0.82, n = 25) based on magmatic zircon UPb geochronology of biotite granulite. Variation of facies-dependent carbon isotope values, the presence of graphite deposits of the Douya Formation, upper Jingshan Group, and the absence of a Ce anomaly in PAAS normalized REE patterns of marble samples suggest that the positive carbon isotope excursion is not linked to a marked increase of organic carbon burial and associated significant atmosphere oxygenation. Elevated concentrations of iron and PAAS-normalized middle REE enrichment of analyzed Jingshan Group marble samples point to anoxic and ferruginous oceanic conditions during accumulation of Jingshan Group carbonate. A positive Eu anomaly (average = 1.58), low La (average = 0.23), (Nd/Yb)N (average = 1.27), and Y/Ho (average = 36.6) anomalies, and negative iron isotope values (average δ56Fe = −0.12 ‰) are consistent with accumulation of Paleoproterozoic Jingshan Group carbonate in a restricted marine setting that was affected by high temperature hydrothermal fluids. Enrichment of the studied samples in heavy carbon isotope suggests elevated bio-productivity in the restricted, redox stratified marine setting in which Jingshan Group carbonate accumulated. Thus, it is likely that the positive stable carbon isotope excursion associated with Jingshan Group strata as well as other contemporaneous isotope excursions are local signals that are linked to a global perturbation of the carbon cycle.

The First Discovery of Archean Dolerite Dikes in the Western Part of the Aldan Shield

Dolerite dikes were studied in the western part of the Aldan terrane, in the middle reaches of the Tokko River. These dolerite dikes form a swarm of submeridional trend about 1 km wide. The dolerites of the thickest dike preserve their primary textural and structural features and mineral composition: plagioclase + pigeonite + augite + titanomagnetite. Dolerite in the chilled margins and central parts of the dike are homogeneous in composition, corresponds to low-Mg tholeiites, has low contents of Ti and other HFSE, with weak enrichment in light REE and small negative Nb anomalies. Sm–Nd isotope data on magmatic minerals of dolerite from the central part of the dike yield a good linear regression in an isochron diagram that gives to an age of 2510 ± 64 Ma, which probably corresponds to the crystallization age of the basalt. Metadolerites in a thin dike retain plagioclase porphyritic structures, but the pyroxenes are completely replaced by amphibole and chlorite. The metadolerites are contrastingly different in low contents of MgO, Cr, and Ni and in higher contents of TiO2, Fe2O3, P2O5, Nb, and all REE. The differences in the composition of the dikes may be explained by the longterm (about 65%) crystallization differentiation of the initial melt and the emplacement of the residual melt from a shallow intermediate magma chamber via opening cracks. Such conditions probably may have existed in tectonically stable intraplate settings. The age of the dolerites of the dike swarm is comparable to that of the anorogenic granites of the Nelyuki complex (~2.4–2.5 Ga), which are widespread in the western part of Aldan granulite–gneiss terrane. Our data bridge some gaps in characteristics of intraplate anorogenic magmatism that occurred in the western Aldan Shield in the Late Archean and marked the final consolidation of a large block of Archean crust in the Chara–Olekma granite–greenstone area.

Petrogenesis of Eocene A-Type Granite Associated with the Yingpanshan–Damanbie Regolith-Hosted Ion-Adsorption Rare Earth Element Deposit in the Tengchong Block, Southwest China

The ion-adsorption-type rare earth element (iREE) deposits dominantly supply global resources of the heavy rare earth elements (HREEs), which have a critical role in a variety of advanced technological applications. The initial enrichment of REEs in the parent granites controls the formation of iREE deposits. Many Mesozoic and Cenozoic granites are associated with iREE mineralization in the Tengchong block, Southwest China. However, it is unclear how vital the mineralogical and geochemical characteristics of these granites are to the formation of iREE mineralization. We conducted geochronology, geochemistry, and Hf isotope analyses of the Yingpanshan–Damanbie granitoids associated with the iREE deposit in the Tengchong block with the aims to discuss their petrogenesis and illustrate the process of the initial REE enrichment in the granites. The results showed that the Yingpanshan–Damanbie pluton consists of syenogranite and monzogranite, containing REE-bearing accessory minerals such as monazite, xenotime, apatite, zircon, allanite, and titanite, with a high REE concentration (210–626 ppm, mean value is 402 ppm). The parent granites have Zr + Nb + Ce + Y (333–747 ppm) contents and a high FeOT/MgO ratio (5.89–11.4), and are enriched in Th (mean value of 43.6 ppm), U (mean value of 4.57 ppm), Zr (mean value of 305 ppm), Hf (mean value of 7.94 ppm), Rb (mean value of 198 ppm), K (mean value of 48,902 ppm), and have depletions of Sr (mean value of 188 ppm), Ba (mean value of 699 ppm), P (mean value of 586 ppm), Ti (mean value of 2757 ppm). The granites plot in the A-type area in FeOT/MgO vs. Zr + Nb + Ce + Y and Zr vs. 10,000 Ga/Al diagrams, suggesting that they are A2-type granites. These granites are believed to have formed through the partial melting of amphibolites at a post-collisional extension setting when the Tethys Ocean closed. REE-bearing minerals (e.g., apatite, titanite, allanite, and fluorite) and rock-forming minerals (e.g., potassium feldspar, plagioclase, biotite, muscovite) supply rare earth elements in weathering regolith for the Yingpanshan–Damanbie iREE deposit.

Silicate and iron phosphate melt immiscibility promotes REE enrichment

Silicate and iron phosphate melt immiscibility promotes REE enrichment

Extra-terrestrial mantle samples: Rare Earth Element variations and evidence for melt metasomatism in ureilite meteorites

Ureilites are meteorites derived from the mantle of a reduced differentiated asteroid, the “Ureilite Parent Body” (UPB), which was later disrupted by impact with another Solar System body. They have ultramafic compositions dominated mostly by olivine and pigeonite with rare orthopyroxene and augite; aluminous phases are generally absent. Ureilites vary from abundant peridotites to much rarer pyroxenites, and their core olivine compositions range from Fo74 to Fo97 across different samples. The UPB experienced sufficiently high temperatures to undergo silicate partial melting, as shown by depletion in the Light Rare Earth Elements (LREE) in bulk restitic ureilites. Plagioclase and merrillite were probably present in the UPB mantle but have been completely removed during silicate partial melting. Partial melts of the UPB mantle are represented by glassy melt inclusions, igneous clasts in ureilite breccias, cumulus augite in some ureilites, and rare trachyandesitic fragments. These melts are generally intermediate and sub-alkaline in composition, although a few are alkaline. They have more enriched and flatter bulk REE patterns than the restitic ureilites and often show positive Eu anomalies. Glasses (representing melts) in ureilites from this study range from 57 to 79 wt% SiO2. One sample (AhS 22) shows petrographic and geochemical evidence for interaction between magma and the solid UPB mantle by forming metasomatic augite.Silicate minerals in ureilites analysed by LA-ICP-MS are generally LREE-depleted, with negative Eu anomalies. Ureilitic olivines have the lowest REE contents and the smallest negative Eu anomalies. Low-Ca pyroxenes have similar patterns with slightly stronger Eu anomalies. Augites have the highest REE contents and the most negative Eu anomalies. Augites show REE disequilibrium with olivine and low-Ca pyroxene, suggesting that they were not part of the restitic assemblage but were added by silicate melts passing through the UPB mantle, i.e. they are metasomatic in origin. We also discuss the size of the original UPB, using silicate minerals as evidence for it being a typical asteroid rather than a planet-sized object.

The origin of alkali granites and Th-U ± REE enrichments in Kestanbol Magmatic complex (NW Anatolia) revisited: Evidences from bulk-rock geochemistry and isotopic data, zircon U[sbnd]Pb, biotite Ar/Ar and apatite (U[sbnd]Th)/He geochronology

This paper presents new field, petrographic, geochemical, SrNd isotopic and geochronological data from Kestanbol Magmatic Complex (KMC) in the western Anatolia. Zircon UPb ages from the KMC were in the range 21.91 Ma and 21.52 Ma, indicating Miocene emplacement. 40Ar/39Ar dating results of biotites from the same samples show a narrow range of ages between 20.0 and 22.7 and a weighted mean of 21.41 ± 0.40 Ma, and those of hornblende analysis yield ages between 21.52 and 31.19 Ma with a weighted mean of 22.70 ± 0.99 Ma, are interpreted as the cooling age of the KMC. The average (U-Th/He) ages from the KMC yielded an average of 21.5 Ma and 19.8 Ma. These new age data indicate rapid cooling following the emplacement of the KMC at ∼21 Ma. We suggest that the cooling was due to rapid uplift in the western Anatolia. The studied monzonitic, syenitic and alkaline subvolcanic rocks of the northern KMC are characterized by high K2O (4.34–10.7 wt%), low to moderate SiO2 (50.0–69.9 wt%), and P2O5 (0.03–1.07 wt%). They have moderate initial 87Sr/86Sr (0.707245–0.707875) and high initial 143Nd/144Nd (0.512441–0.512508) ratios, consistent with some crustal contamination. The studied rocks are enriched in Th (up to 204 ppm), U (up to 54.9 ppm), REE (up to 565.9 ppm) and, some LILE's including K (up to 8.85%), Rb (up to 447.1 ppm), Sr (up to 2053 ppm) and Ba (up to 2578 ppm). The geochemical and isotopic data suggest that the magmatic evolution of KMC is dominated by events including post-collisional tectonics, flux induced partial melting, fractional crystallization. The enrichments of incompatible elements are mostly caused by the fractional crystallization and K-metasomatism that affected the earlier magmatic phases during the cooling of the complex.

Lithium-Rich Deposits in the Liangshan Formation during the Permian in the Upper Yangtze Plate, China

With the increasing demand for lithium (Li) resources in industry, there has been new attention on clay-type lithium-rich deposits recently. In this study, a Li-rich clay deposit with a Li2O content up to 0.3% in the Liangshan Formation in the upper Yangtze, South China Block was demonstrated. We analysed the mineralogy and element geochemistry of the samples from the Liangshan Formation and its underlying and overlying layers. Kaolinite (average 53%, up to 93%) was the major mineral in the samples from the Liangshan Formation. The Li concentrations increased with increasing kaolinite compositions and Al2O3 concentrations. Furthermore, based on the geochemical indicators, it was suggested that the clay formation and Li enrichment were related to the weathering processes of the bottom impure limestone under the hot and wet climate, and the sedimentary processes in the anoxic, still, and flat land–sea interaction area in the Upper Yangtze. The Li was probably sourced from the bottom impure limestone during the weathering stage. The samples from the Liangshan Formation also showed REE enrichment from 117 to 729 μg/g.

Amphibole geochemistry in the Haobugao skarn Zn-Fe-Sn deposit in the southern Great Xing’an Range: Implications for the ore-forming process

The Haobugao Zn-Fe-Sn deposit is a typical skarn deposit in the southern Great Xing’an Range of NE China. Despite many advances in understanding its genesis, the detailed ore-forming processes of Zn, Fe and Sn are still unclear. Amphibole, a rock-forming mineral, has been well studied as an indicator of diverse magmatic and metamorphic processes; however, the geochemistry of hydrothermal amphibole has previously received less attention. The Haobugao deposit contains two generations of hydrothermal amphibole (Amp-I and Amp-Ⅱ), which provides a good opportunity to use amphibole geochemistry to trace the mineralization process. Early Amp-I coexists with cassiterite, magnetite and quartz, whereas late Amp-II coexists with quartz and sulfides and can be further divided into two subgroups: Amp-Ⅱa (in skarn) and Amp-Ⅱb (in the country rocks of siltstone). The oxygen isotopic compositions of the fluid (δ18Ofluid 2.9‰) responsible for the Amp-I formation indicate that the amphiboles formed from mixed magmatic fluid with meteoric water. Amp-I is LREE-depleted and HREE-enriched with obvious negative Eu anomalies. Amp-Ⅱ is generally slightly LREE-depleted with negative or positive Eu anomalies and positive Ce anomalies. The incorporation of trace and rare elements is mainly controlled by the fluid composition. Detailed petrological observations and amphibole geochemistry, combined with previous research results, confirm that Sn, Fe, Pb and Zn mineralization occurred during a single mineralization event. From the oxide to the quartz sulfide stage, the ore-forming fluid evolved from high-temperature and oxidized conditions with enrichment of Sn, Li, Be and REEs to low-temperature and reduced or oxidized conditions with enrichment of Cu, Co and Zn. The concentrations of Cu, Co and Zn in different amphiboles vary with the mineral crystallization sequence. This study shows that amphibole geochemistry can be useful for tracing fluid evolution and mineralization processes in hydrothermal systems.

Using zircon and apatite chemistry to fingerprint porphyry Cu – Mo ± Au mineralization in the Delamerian Orogen, South Australia

To evaluate the fertility of porphyry mineralization in the Delamerian Orogen (South Australia), zircon and apatite from four prospects, including Anabama Hill, Netley Hill, Bendigo, and Colebatch, have been analyzed by LA-ICP-MS and electron microprobe. The zircon is characterized by heavy REEs enrichment relative to light REEs, high (Ce/Nd)N (1.3–45), and weak to moderate negative Eu/Eu* (0.2–0.78). The apatite has right-sloped REE patterns with variably negative to positive Eu anomalies. Low Mg (< 670 ppm) and Sr/Y ratios (< 5) in apatite likely illustrate fractional crystallization trends for the granitic melts in shallow crust. The Yb/Gb and Eu/Eu* in zircon reveal that intrusions at Anabama Hill, Netley Hill, and Bendigo underwent fractional crystallization controlled by amphibole (< 50–60%), garnet (< 15%), apatite (< 0.6%), and/or titanite (< 0.3%). These stocks have average fO2 values reported relative to fayalite-magnetite-quartz buffer (ΔFMQ), from 0.7 ± 0.9 to 2.1 ± 0.4, ascribed to prolonged magmatic evolution or sulfur degassing during post-subduction processes. Our data imply that both Anabama and Bendigo complexes experienced prevalent (garnet-) amphibole crystallization from hydrous melts that have moderately high oxidation (ΔFMQ + 1 to + 3) and elevated sulfur-chlorine components (Anabama, 37 ± 9 to 134 ± 83 ppm S and 0.30 ± 0.24 to 0.64 ± 0.89 wt% Cl; Bendigo, 281 ± 178 to 909 ± 474 ppm S and 0.45 ± 0.47 to 3.01 ± 1.54 wt% Cl). These are crucial ingredients to form porphyry Cu–Mo ± Au ores with economic significance, which provides encouragement for mineral exploration in this orogen.

Age and composition of perovskite in ultramafic lamprophyres from the Zima alkaline-ultramafic carbonatite complex, the southern margin of the Siberian craton: Petrogenetic implications

This paper presents data on the age and trace element composition of perovskites from dykes of ultramafic lamprophyres (aillikites) of the Zima alkaline-ultramafic carbonatite complex (Bolshaya Tagna and Bushkanay) located within the Urik-Iya graben, Eastern Sayan region, southern margin of the Siberian craton. The studied samples exhibit similar textural and structural features but differ slightly in the mineral composition of the groundmass. They have a porphyritic structure, a massive texture, and consist of olivine macrocrystals embedded in a fully crystallized groundmass composed of perovskite, apatite, spinel, phlogopite, garnet, carbonates, clinopyroxene and other minerals. The macrocrystals quantity varies between 40 and 50 vol%. With the exception of a single sample from the Bushkanay dyke, olivine is entirely replaced by serpentine and/or talc.Perovskites from aillikites of the Bolshaya Tagna intrusion exhibit crystals with normal zoning showing a decrease in Na, REE, and Nb contents with center-to-rim increasing Ca content. In contrast, minerals from the aillikites of the Bushkanay dyke demonstrate reverse zoning, with an increase in Na, REE, and Sr and decrease in Ca contents from the center to the rim. We suggest that during crystallization of perovskites, the magma parental to the aillikites of the Bolshaya Tagna intrusion and the Bushkanay dyke had nearly similar trace element composition, but after crystallization of the cores of perovskite crystals each melt portion evolved independently. The samples from the Bushkanay dyke show an increase in fO2 and the residual magma enrichment in REE, Na, and Sr as evidenced by their elevated contents at the rims of perovskite grains. In the Bolshaya Tagna aillikites after crystallization of perovskite cores, the melt was depleted in REE, Na, and Nb.Based on U-Pb dating of perovskites, the age of aillikites from the Bolshaya Tagna intrusion is 583–654 Ma. Perovskite from aillikites of the Bushkanay dyke is relatively young, with an age of 575 ± 39 Ma. The obtained ages are consistent with the age of formation of Neoproterozoic alkaline-ultramafic carbonatite complexes of the Siberian craton and other occurrences of aillikites in a response to extension of the Rodinia lithosphere.

Petrogenesis and Tectonic Setting of the Baluogenguole Mafic Dykes, Zongwulong Belt: Implications for Evolution of the Northern East Paleo-Tethys Ocean

The late Paleozoic tectonic setting of the Zongwulong Belt (ZWLB), a significant unit located in the northern Qaidam margin, Qinghai province, remains uncertain. Diabase dykes in the western part of the Zongwulong Belt offer insights into this issue. Field investigations reveal that the dips of the dykes are almost vertical, and they have sharp boundaries with the host rocks. These dykes consist of plagioclase, clinopyroxene, and opaque minerals exhibiting a characteristic porphyritic texture and massive structure. Zircon U-Pb dating of the dykes yields a weighted 206Pb/238U age of 289 ± 1 Ma. The dykes exhibit relatively high concentrations of TFeO, K2O + Na2O, and TiO2, while the SiO2 and MgO concentrations are relatively low. They display relative light-over-heavy REE enrichment, and lack negative Nb-Ta and Eu anomalies. The dykes underwent negligible crustal contamination, and experienced extensive fractional crystallization of olivine, clinopyroxene, and Fe-Ti oxides. Originating from the spinel–garnet transition zone at depths of approximately 75 km, the dykes result from garnet facies low-degree melting (5%–10%) in a continental rift setting. Combining these findings with regional geological data, we propose that the ZWLB likely experienced a continental rift in the west and exhibited a narrow oceanic environment in the east in the late Paleozoic period, potentially representing the most distant north branch of the East Paleo-Tethys Ocean.

Influence of Organic Matter Thermal Maturity on Rare Earth Element Distribution: A Study of Middle Devonian Black Shales from the Appalachian Basin, USA

This study focuses on understanding the association of rare earth elements (REE; lanthanides + yttrium + scandium) with organic matter from the Middle Devonian black shales of the Appalachian Basin. Developing a better understanding of the role of organic matter (OM) and thermal maturity in REE partitioning may help improve current geochemical models of REE enrichment in a wide range of black shales. We studied relationships between whole rock REE content and total organic carbon (TOC) and compared the correlations with a suite of global oil shales that contain TOC as high as 60 wt.%. The sequential leaching of the Appalachian shale samples was conducted to evaluate the REE content associated with carbonates, Fe–Mn oxyhydroxides, sulfides, and organics. Finally, the residue from the leaching experiment was analyzed to assess the mineralogical changes and REE extraction efficiency. Our results show that heavier REE (HREE) have a positive correlation with TOC in our Appalachian core samples. However, data from the global oil shales display an opposite trend. We propose that although TOC controls REE enrichment, thermal maturation likely plays a critical role in HREE partitioning into refractory organic phases, such as pyrobitumen. The REE inventory from a core in the Appalachian Basin shows that (1) the total REE ranges between 180 and 270 ppm and the OM-rich samples tend to contain more REE than the calcareous shales; (2) there is a relatively higher abundance of middle REE (MREE) to HREE than lighter REE (LREE); (3) there is a disproportionate increase in Y and Tb with TOC likely due to the rocks being over-mature; and (4) the REE extraction demonstrates that although the OM has higher HREE concentration, the organic leachates contain more LREE, suggesting it is more challenging to extract HREE from OM than using traditional leaching techniques.

Geochemical characteristics, hazards impact assessment and radiogenic heat production of the alkaline rocks.

This study primarily investigates the natural radioactivity level in alkaline rocks collected from the Wadi El-Dib ring complex (WDRC) in North Eastern Desert of Egypt, and assesses potential health risks associated with their use as decorative building materials. The work was accomplished using a high-purity germanium detector as well as ICP-MS and ICP-AES techniques. The WDRC composed essentially of trachyte, quartz syenite, granite and syenite. Geochemically, these rocks contain high SiO2 and alkalis with metaluminous to slightly peraluminous features. All rocks contain high concentrations of rare earth elements (∑REEs = 109-1075ppm), with clear enrichment in light REEs compared to heavy REEs [(La/Yb)N = 8.3-25.3. Radiometrically, the concentrations of the natural radioisotopes (238U, 232Th, and 40K) in the studied rock types surpassed the worldwide average values assigned for building materials by UNSCEAR. This elevation of the radioisotope concentration values is due to the presence of supplement minerals such as monazite, zircon, allanite, and rutile. Granites exhibit the highest mean concentrations of 238U (av. 164.24 ± 14.76Bq/kg) and 232Th (av. 214.37 ± 23.33Bq/kg), while trachytes demonstrate the highest 40K (av. 1352.56 ± 65.56Bq/kg) concentrations. In contrast, syenites exhibite the lowest mean concentrations for 238U (av. 54.51 ± 6.81Bq/kg) and 232Th (av. 56.76 ± 6.25Bq/kg), while quartz syenites display the lowest mean concentration of 40K (av. 1144.78 ± 96.19Bq/kg). The radiogenic heat production (RHP) associated with U, Th, and K range between 1.41 to 9.33μW/m3, exceeding the typical crustal mean value of 0.8 to 1.2μW/m3. The radiological parameters and indices evaluating risks of the outdoor and indoor radiation doses due to the investigated rocks were assessed. The results indicated that these rocks meet globally accepted values and safety standards (approved by UNSCEAR, ICRP, and EC) for surface building materials, as well as they underscore the importance of adhering to safety protocols to safeguard workers from radiation exposure within the WDRC area. Ultimately, the data herein provide a valuable database for assessing the compatibility of geochemical data and natural radioactivity level in WDRC rocks. Additionally, it reveals that from the radiological perspective, the investigated rocks are considered safe for use as decorative construction materials.

Genesis of the Hujiazhuang apatite-rich carbonatite complex in North China and its implication for the REE fertility of the carbonatite system

Apatite is a common REE-compatible mineral in carbonatites, so its formation can affect the REE ore-forming potential of carbonatite systems. In nature, there are numerous apatite-rich carbonatite complexes, but the petrogenesis of these complexes has long been debated. To resolve this controversy, this study conducts elemental and isotopic analyses on the Mesozoic (∼120 Ma) Hujiazhuang carbonatite complex in North China. The Hujiazhuang complex contains magnetite-calcite-apatite carbonatites and calcite carbonatites. Calcite grains from these two rock phases exhibit identical initial 87Sr/86Sr ratios (0.71027–0.71038), indicating a common parental magma derived from a metasomatized lithosphere mantle. Then, from magnetite-calcite-apatite carbonatites to calcite carbonatites, the Mg, Fe, and Mn contents of calcite continuously increase while the Sr and REE contents decrease, consistent with elemental variations of calcite during fractional crystallization of carbonatitic magma. Therefore, these two lithologies are proposed to be formed through fractional crystallization of a common magma. Notably, the Hujiazhuang carbonatite complex was derived from a metasomatized lithosphere mantle and experienced intensive fractionation, which potentially facilitate the formation of REE deposits. However, this complex cannot meet REE's economic standard. The early-stage magnetite-calcite-apatite carbonatites have high REE contents (3,675–11,075 ppm), and a positive correlation can be observed between REE and P contents in this lithology. It indicates that early, extensive crystallization of apatite led to REE dispersion, largely hindering REE enrichment in later stages. In general, this study provides important insights into the genesis of the apatite-rich carbonatite complex and advances our understanding of the REE dispersion or enrichment behaviors in carbonatite system.

The Petrography and geochemistry of iron-bearing units from Mingo’o area (Ntem complex, southern Cameroon)

The banded iron formation (BIF) of the Mingo’o region is located on the northern edge of the Congo Craton. They constitute a significant component of the southern Cameroonian Archean to Paleoproterozoic. Petrographic description indicates that the most characteristic facies of the Mingo'o BIFs are quartz-magnetite BIFs (QMB), which are mostly composed of magnetite and quartz. Geochemistry analyses show that the major elements of this BIF are very simple, with SiO2 and Fe2O3 representing 95.25 wt. % of the bulk rock on average. The low concentrations of Al2O3, TiO2, and HFSE reveal that these chemical sediments are detritus-free. According to Paerson's major element correlation matrix, there is a slight contribution of detrital material to chemical sediment, as confirmed by the strong positive correlation (r = 0.72) of Al and Ti, also by the binary diagrams Al vs. Σ(Y + Nb + Zr) with a weak positive correlation (r2 = 0.31) and Al vs. ΣREE with a zero correlation (r2 = 0.08), indicating that the detrital input was insignificant. The transition metals Zn, Cr, Sr, and V are among the trace elements with low enrichments. This suggests the direction of the volcanogenic hydrothermal input in chemical precipitates. The mean ∑REE concentration of the studied BIF is 26.74 ppm, with a range of 8.82 to 36.74 ppm. Pure chemical sediments are comparable to that. The shale-normalized patterns display minor positive europium anomalies, a sharp decrease in heavy REE, and enrichment in light REE. These geochemical characteristics suggest that the hydrothermal activity in the deep ocean, coupled with seawater, was the source of the Fe and Si. Low-temperature hydrothermal solutions play a key role in the studied BIF, as shown by the absence of a notable positive Eu anomaly. Ce anomalies are seen in the chrondrite-normalized REE patterns, which are characterized by LREE-enriched (mean LaCN/YbCN = 5.28) and HREE depletion (mean TbCN/YbCN = 1.04) patterns. This may indicate that the BIF within the Mingo’o region was formed in place of the basin towards redoxcline, alternating at different times and under various influences from the influx of seawater that has been oxidized.

Silicate melt immiscibility as the cause of large-scale rare-metal mineralization in a peralkaline granite system: The case of the Baerzhe deposit in NE China

The Early Cretaceous peralkaline Baerzhe pluton hosts a potentially large REE-Nb-Zr-Be deposit in inner Mongolia, northeastern China. The mechanism responsible for the extreme enrichment of rare metals and rare earth elements in the pluton is still ambiguous. This study presents new evidence for silicate melt immiscibility as the key mechanism at Baerzhe using amphibole-group minerals from spherulite granite, which contains spherulites with abundant REE- and HFSE-bearing minerals. The spherulite from the transsolvus granite is composed of two distinct zones, i.e., a dark-colored core consisting of arfvedsonite aggregates and a light-colored rim consisting mostly of quartz and feldspar, rare amphibole, and abundant HFSE- and REE-bearing minerals. Four types of amphibole (AmpI, Amp-IIa, Amp-IIb and Amp-III) from the transsolvus granite and one type (Amp-IV) from the subsolvus granite are recognized, and all of them are magmatic fluoro-arfvedsonite. The earliest phase consists of euhedral inclusions of Amp-I within quartz or feldspar. They show an enrichment in HREEs relative to LREEs and a depletion in medium REEs, consistent with the REE pattern controlled by the mineral lattice. This implies that Amp-I likely formed in an initial homogeneous mel relatively depleted in REEs; thus, the mineral structure played a dominant role in REE partitioning. Compared with other types of amphiboles, Amp-IIa and Amp-IIb from the spherulite phase display the highest REE contents, with flat LREEs and MREEs and a slight upward HREE pattern. Combined with the significant accumulation of REE- and HFSE-bearing minerals in the rim zone, differences in REE patterns among different amphibole types imply that the spherulite crystallized in a volatile-rich silicate melt and was probably the product of silicate melt immiscibility. Interstitial Amp-III with lower REE contents from the matrix phase crystallized in the separate volatile-poor silicate melt. The Amp-IV from the subsolvus granite has the lowest CaO content, with strong depletion in LREEs relative to HREEs, suggesting a more evolved melt composition. It is concluded that silicate melt immiscibility may serve as an important key mechanism that occurred in the early stage of magmatic evolution, resulting in the enrichment of REEs and HFSEs, which played a critical role in the formation of large to giant ore deposits such as the Baerzhe deposit.

Petrogenesis of the alkaline complex in the Weishan REE deposit, Luxi Block, eastern North China Craton: Implications for REE mineralization

The Weishan REE deposit is one of the largest LREE deposits in China, which is hosted by the Weishan alkaline complex (WSAC) and late Archean gneisses. Two types of mineralization including vein-type and disseminated-type occur in this deposit, of which the former is characterized by large quartz-sulfate-calcite-REE mineral veins cutting all kinds of wallrocks, while the latter is featured by REE minerals disseminated in the alkaline rocks. The vein-type mineralization commonly occurs at shallow depths and has been numerously studied. The disseminated-type mineralization typically occurs at deeper depths, which was newly discovered by drilling exploration and has been poorly studied. In this contribution, zircon U-Pb dating and Hf isotopic analysis as well as whole-rock geochemistry and Sr-Nd isotopic analyses were conducted on the deeply drilled alkaline rocks, combined with molybdenite Re–Os dating on the disseminated ore, with the aim to unravel the petrogenesis of the alkaline rocks and their contributions to the REE mineralization. Zircon U–Pb dating suggests an intrusive age of 119.9 ± 0.9 Ma for the WSAC, which is quite consistent the Re–Os age of 120.0 ± 1.8 Ma for the disseminated ore, corroborating their close genetic correlation. The studied alkaline rocks show enrichment of LILEs, depletion of HFSEs and strong fractionation between LREEs and HREEs, indicating a crustal involvement in the magmas or a metasomatized mantle source. They are characterized by higher Hf (εHf(t) = -6.7 to −12.2) and Nd (εNd(t) = -8.8 to −9.7) isotopic compositions compared with those of the contemporaneous subcontinental lithospheric mantle (SCLM). Based on the above features, it is inferred that the parental magmas of the WSAC were mainly derived from an enriched SCLM with some involvement of asthenospheric mantle-derived materials. The mantle source was likely metasomatized by the subducted Paleo-Pacific oceanic plate, leading to the enrichment of REE and carbonate. Rollback of the oceanic slab during the early Cretaceous resulted in an extensional setting in the study region, which was favorable for partial melting of the metasomatized mantle and thus generated the REE-rich alkaline magmas.

Discussion of the W-Sn-REE Metallogenic Background in the Nanling Region of South China: Evidence from Satellite Gravity and Magnetic Data

The Nanling region is located at the intersection of the Yangtze Block and Cathaysia Block and is characterized by complex geological and tectonic processes, as well as distinct W-Sn-REE mineralization. Despite extensive research on the mineralization of W-Sn and REE deposits in the Nanling region, the factors impacting the distribution pattern of eastern tungsten and western tin deposits, as well as the mechanism of REE enrichment in the parent rocks, remain uncertain. Deep structural and tectonic variability plays a crucial role in the formation of mineral deposits in the upper crust. Information on deep structural and tectonic variability is contained in the Moho depth, Curie depth, effective elastic thickness, lithospheric density, and thermal structure derived from the processing and inversion of satellite gravity and magnetic data. In this paper, we comprehensively analyse satellite gravity and magnetic data from the Nanling region, integrating the processing and inversion results with the tectonic evolution of this region and relevant geological information. It is hypothesized that the Chenzhou–Linwu fault serves as a channel for mineral and thermal transfer in the Sn ore aggregation zone, facilitating the material transport from the deep mantle to the surface and ultimately leading to the formation of Sn-enriched granite. The collection area of tungsten ore is more weakly associated with the Chenzhou–Linwu fault, and through deep heat transfer, tungsten components are primarily concentrated in the Earth’s crust to produce W-enriched granite. The primary source of REE enrichment in the parent rocks associated with REE mineralization is predominantly derived from the felsic crust, and the rapid intrusion of deep magma resulting from the subduction and retraction of the Palaeo-Pacific Plate is a contributing factor to the contrasting enrichment of light and heavy rare-earth elements. Mineral crystalline differentiation is relatively high, leading to the formation of ore-forming parent rocks with high heavy rare-earth element contents.

Subduction-related mafic-silicic magmatism in the Nubian Shield: Tectono-magmatic implications of ensialic island arc association at Central Eastern Desert, Egypt.

For the Wadi El Mayet, the metagabbro-granodiorite-tonalite intrusive complex (MIC) occupies the eastern sector of famous wadi Mubarak–Dabr complex which considered as the largest intrusion in the Egyptian Eastern Desert. The basement associations in the area include volcano-sedimentary rocks, metavolcanics, and ultramafics. The whole successions were intruded by MIC, and granites. The (MIC) comprises multifarious gabbroic varieties namely: olivine, pyroxene, hornblende, uralitized gabbros and rare amphibolites, while silicic portion includes tonalite and granodiorite. Microprobe analytical chemistry of gabbros and granites refers that: the amphiboles are calcic magnesio hornblende formed at low pressure conditions. Chlorites have corundophillite composition. Plagioclase range between labradorite, andesine and oligoclase. Biotite is mainly siderophylite. Muscovite minerals are mainly cheladonite. Geothermo-barometers calculations reveal crystallization temperatures of 550 °C and 860 °C for granites and metagabbros respectively. The (MIC) cover a wide silica range (44.5–74.5 wt %). It has transitional tholeiitic to calc-alkaline magmas. The gabbroic rocks show distinct fecundity with LILE (e.g. Rb, Ba, U and Th), but show observed shortage in most HFSE (e.g. Zr, Nb, Ta). The REE patterns show enrichment in light REE and posse variably positive Eu. It is suggested that, the gabbroic units were likely generated by fractional crystallization of mafic magmas produced through partial melting of metasomatized mantle within island-arc environments. Tonalite - granodiorite (TG) suite show calc-alkaline magmas of I-type settings. They also exhibit enrichment in Ba, Zr, Hf, Rb, U and Th, while P, Nb, Ta and Sr are depleted. Such reductions are harmonious with fractionation of K-feldspar phases. The (TG) show enrichment of (LREE) compare to (HREE) this proposes either the existence of persistent garnet or LREE fertile magma sources. The (TG) is believed to be formed through dehydration melting processes at lower crust settings. Based on the field, geochemistry and structure elements, the investigated mafic and silicic suites are not linked to a single magma origin. The (MIC) can be comparable with intrusions formed in ensialic island-arcs settings. At subduction zone integration between mantle (basaltic suites) and silicic magmas from lower crust forming the early stages of (MIC) crystallization. The whole association was suffered by insignificant fractionation processes and addition of crustal materials during the final stages of (MIC) emplacement.