Higher Total Rare Earth Element Research Articles

Petrogenesis of the eudialyte-bearing syenite and indication for Nb-Zr-REE mineralization in Bashisuogong, Northwest China

The Bashisuogong alkaline igneous intrusion is located between the South Tianshan Orogenic Belt and the Kepingtage foreland thrust belt at the northern margin of the Tarim Craton and hosts economically significant Nb–Ta–Zr–rare earth element mineralization. Eudialyte has recently been discovered in the syenite unit of this intrusion, which is the primary host mineral for high-field-strength and rare earth elements. Based on detailed petrographic investigations, this study investigated the behavior of trace elements during magma evolution and the enrichment of ore-forming elements using whole-rock geochemical analyses of eudialyte-bearing syenite and compositional analyses of aegirine–augite and different types of eudialyte. We also undertook in situ titanite U-Pb dating. The Bashisuogong syenite comprises aegirine–augite and aegirine–augite–eudialyte syenite, the latter of which have higher total rare earth element contents. Both types of syenite exhibit slight enrichments in light rare earth elements, significant enrichments in high-field-strength elements (Nb, Ta, Zr, Hf, and Th), depletions in large-ion lithophile elements (Ba and Sr), and large negative Eu anomalies. There are two types (I and II) of eudialyte. Eudialyte I has higher Mn/Fe, Zr/Hf, and Nb/Ta ratios but lower Th/U ratios compared with eudialyte II but similar Y/Ho ratios. Eudialyte II crystallized earlier than eudialyte I, and aegirine–augite, titanite, and apatite crystallized earlier than eudialyte I. Both aegirine–augite and eudialyte have similar trace element characteristics to the host rocks, exhibiting enrichments in highly incompatible high-field-strength and rare earth elements, as well as marked negative Eu anomalies and depletions in Sr. These characteristics suggest that the Bashisuogong alkaline rocks formed by low-degree partial melting of geochemically enriched, metasomatized lithospheric mantle, which formed an alkaline basaltic parental melt that then underwent protracted magma evolution and fractionation in the shallow crust. The eudialyte syenite yield a titanite U-Pb age of 277.3 ± 1.2 Ma, which is consistent with the ages of different types of alkaline igneous rocks in the study area, indicating they were the products of the same magmatic event. Temporally and spatially, the Bashisuogong ore-bearing alkaline rocks were associated with the Tarim mantle plume, and the mantle plume provided the heat for their formation.

Formation of dolomites from the newly discovered ancient cold seep in the Middle Dongsha area of the South China Sea

Remotely operated vehicle (ROV) observations have recently revealed seep dolomite deposits covering the seafloor on Middle Dongsha of the South China Sea (SCS). Spurred by these findings, we studied the mineralogical and geochemical properties to examine the seep dolomite’s origin, precipitation mechanism, and formation environment. These carbonates mainly comprise dolomite (from 64 to 84 wt%), followed by small amounts of calcite (from 1 to 3 wt%), locally containing magnesite (∼4 wt%), and goethite (∼14 wt%). Extensively developed mineralized cells containing high Mg and Ca contents found in chimneys imply that microbially-mediated processes probably participated in the reactivation of dolomite precipitation. The moderate and concentrated δ13C values (from −36.64 to −39.16‰, V-PDB) indicated that the carbon in carbonates was mainly derived from thermogenic methane. The methane fluids most likely ascended beneath the volcaniclastic unit and inherited enriched positive Eu anomalies due to fluid–rock interactions during their seepage along tectonic faults to the seafloor. The δ18O values (4.2–4.8‰, V-PDB) of carbonate suggested that an 18O-depleted fluid was involved in carbonate precipitation. The high total Rare-Earth Element contents (ΣREE) of seep carbonates varied from 61 ppm to 92 ppm, reflecting the chemical composition of surrounding pore waters at the time of carbonate precipitation, exhibiting less mixing with seawater. It may also indicate higher alkalinity and pH of the pore water. Although the sea-like REE patterns (HREE-enriched, negative Ce anomalies) are not caused by seawater, they may be due to the complexation competition between humic acid (HA) and carbonate for REE at high pore-water alkalinity and high CO32− concentrations. This is consistent with the dolomite chimney pointing toward a formation environment in relatively deep sediments, in particular, close to the sulfate-methane interface in sediments, where the bicarbonate concentration reaches its maximum due to AOM. Moderate Mo and no U enrichments appeared in the carbonates, suggesting a relatively lower intensity of methane seepages with relatively reduced AOM rates. The wide range of (Mo/U)EF values and U–Mo covariation indicates the very dynamic AOM rate (slow to moderate) and redox conditions (mostly suboxic–anoxic, occasionally sulfidic conditions) during carbonate formation due to episodically changing seepage activity.

Water-soluble rare earth elements (REEs) recovered from uranium tailings

The global energy transition from fossil fuels to renewable sources poses substantial challenges to increase metal production, including industry-critical rare earth elements (REEs). Environmental and social concerns obfuscate the production of these ‘green’ metals and only ∼1% of REE demand is met from recycling. This work highlights the potential for the ‘economic rehabilitation’ of the Mary Kathleen Mine, a relinquished uranium (U) mine with very high (∼3 wt%) total REE concentrations within the tailings storage facility (TSF). Leaching of the tailings revealed that approximately 5% of the REEs are water-soluble, suggesting the possibility for in situ extraction. Using an in situ water leach, the projected total REE recovery is >10,000 t, which would exceed the total amount of U recovered (7,532 t) during the initial mining operation. The proposed in situ recovery would offer a truck-free mine, using solar energy and water recycling technologies to recover REEs from a waste source, reducing environmental contamination.

Formation mechanism of skarn iron deposit: Evidence from Fe-rich enclave in porphyritic monzonite

Skarn deposits constitute a significant reservoir of high-grade iron (Fe) ores in China, yet the metallogenic processes remain debated. This study focuses on the iron-rich enclaves embedded within porphyritic monzonite, aiming to unravel the metallogenic mechanisms underlying skarn Fe deposits. The host porphyritic monzonite intrudes into porphyritic diorite. Within the iron-rich enclaves three types of magnetite (Mt) are discerned. Mt-I, ranging from 50 to 100 μm in size, predominantly occupies the core of the enclave, enshrouding diopside at its center. Mt-II, with a size range of 20–40 μm, is primarily distributed in the middle of the enclave. The smallest variant, Mt-III, measuring approximately 1 μm, typically manifests at the peripheries of Mt-I and Mt-II. Comparative analysis reveals that Mt-II exhibits higher total rare earth elements (REE), Sr, Ca, alongside lower TiO2 content in contrast to Mt-I. Notably, Mt-II displays a characteristic W-type tetrad effect of REE, indicative of crystallization in a fluid-saturated environment. In contrast, Mt-III, characterized by microcrystalline magnetite, is inferred to have formed under conditions of rapid cooling.Our interpretation posits a two-stage genesis for these enclaves. The initial stage involves the formation of iron-rich magma within a magma chamber situated at depths of 8–10 km, during which Mt-I crystallizes. Subsequently, the second stage unfolds as mantle-derived fluids infiltrate the magma chamber, leading to the formation of Mt-II. The fluid overpressure within the magma chamber triggers a swift ascent of iron-bearing melt-fluid, localized at depths ranging from 1.5 to 2.6 km, resulting in the crystallization of Mt-III. Our results provide valuable insights into the metallogenic processes governing skarn Fe deposits, and the complex geological evolution of these deposits.

Metallogenesis of Porphyry Copper Deposit Indicated by In Situ Zircon U-Pb-Hf-O and Apatite Sr Isotopes

The origin of the Dexing porphyry Cu deposit is hotly debated. Zircon and apatite are important accessory minerals that record key information of mineralization processes. SHRIMP zircon U-Pb analyses of granodiorite porphyries yield ages of 168.9 ± 1.2 Ma, 168.0 ± 1.0 Ma, and 172.8 ± 1.3 Ma, whereas zircons in the volcanic rocks of the Shuangqiaoshan Group have Neoproterozoic ages of 830 ± 7 Ma, 829 ± 8 Ma, and 899 ± 12 Ma. The porphyry displays zircon in situ δ18O of mantle values (5.5 ± 0.2‰), low apatite 87Sr/86Sr ratios (0.7058 ± 0.0005), and high εHf values (5.1 ± 1.5), which are consistent with mantle-derived magmatic rocks. Apatite from the porphyries has relatively high total rare earth elements (REEs) and negative Eu anomalies, with relatively high Cl and As contents. These features are distinctly different from apatite in the Shuangqiaoshan Group, which shows lower total REE, Cl, and As contents but higher F content and positive Eu anomalies. Zircon in porphyries yields a relative high oxygen fugacity of ∆FMQ + 1.5 based on zircon Ce4+/Ce3+. Apatite in porphyries also shows high oxygen fugacity based on its SO3 and Mn compositions, reaching ∆FMQ + 2, which is different from that of the lower continental crust in general, but similar to subduction-related magmas. In contrast, the oxygen fugacity of the Shuangqiaoshan Group is much lower, suggesting a different origin for its wall rock. Therefore, the Dexing porphyries were not derived from the lower crust but derived from partial melting of the subducting Paleo-Pacific plate.

Characteristics and origin of Lower Triassic Feixianguan Formation dolostones on the west side of Kaijiang–Liangping Trough, northeastern Sichuan Basin, China

High-quality reservoirs of the Feixianguan Formation of the northeast Sichuan Basin contain abundant natural gas and are dominated by dolostones. Their origin is controversial, which impedes the exploration of these high-quality carbonate reservoirs. Petrographic observation and geochemical analysis were performed on various carbonates to trace the source of dolomitizing fluids and clarify the formation mechanism of the Feixianguan dolostones. Three types of dolostones were distinguished, including fine dolomite, fine-medium dolomite, and medium dolomite according to the grain size of dolomites. Fine dolomite was characterized by crystal sizes of 5–60 μm and high total rare earth elements (ΣREEs) of 1.87–2.45 ppm. The thin layers of fine dolomite mainly occur at the top of the depositional cycles and have the highest δ18O values and the lowest SmSN/YbSN values of 0.65–0.87 of the three types, suggesting that they were formed by evaporation pumping dolomitization from the restricted evaporated seawater. Fine-medium dolomite was characterized by the inheritance of the original particle texture with crystal sizes of 60–120 μm. Medium dolomite was characterized by crystal sizes of 100–200 μm and the highest porosity among the three types of dolostones. The similar REE patterns to seawater and the same 87Sr/86Sr ratios as Feixianguan seawater for fine-medium and medium dolomites indicate that the dolomitizing fluids originated from coeval seawater with the Feixianguan limestone. Both the high concentrations of Na and low concentrations of Fe and Mn imply the shallow burial or near surface condition of dolomitization. According to higher δ13C and δ18O values than coeval limestones, and the descending tendency of δ18O values and Na concentrations from the top to bottom of the sedimentary cycles, fine-medium and medium dolomites were formed by reflux dolomitization of evaporated Feixianguan seawater restricted by beach bridges. However, slightly brighter cathodoluminescence of medium dolomite than fine-medium dolomite and the decreasing of δ18O values as the crystal size increasing imply that medium dolomites were slightly recrystallized from fine-medium dolomites. Moreover, a small number of coarse dolomites in pores are derived from exogenous non-seawater fluids in the burial environment.

Garnet trace element geochemistry of Yangla Cu deposit in NW Yunnan, China: Implications for multistage ore-fluid activities in skarn system

Garnet is a common hydrothermal mineral in skarn-type deposits, and is useful for constraining the ore-fluid composition. Based on the mineralogy and geochemical features of different types of garnets from the Yangla Cu deposit, we discuss the factors and mechanism of rare earth elements (REE) incorporation into skarn-type garnet, together with the skarn-forming environment. Garnet from Yangla belongs to the grossular–andradite solid solution series, and can be divided into two types (i.e., zoned and unzoned). Early garnet (Grt I) aggregates (avg. And84.96 Gro9.62 Spe + Pyr + Alm5.42) in the proximal skarn is clearly oscillatory-zoned, whilst most of late garnet (Grt II) (avg. And96.26Gro0.58Spe + Pyr + Alm3.16) in the diopside skarn is unzoned. Grt I is slightly LREE-enriched and HREE-depleted with positive Eu anomalies, whereas Grt II is obviously LREE-enriched and HREE-depleted with positive Eu anomalies. Grt I has higher total REE, Y and HFSE contents than Grt II. We suggest that fluid composition and physicochemical conditions greatly controlled the REE incorporation into garnet. The Grt I oscillatory zoning was likely formed by self-organization under relatively low growth rate, leading to Al/Fe fluctuation in the fluid related to the change of external factors (such as fluid boiling). Based on the differences of microscopic texture and geochemical characteristics between Grt I and Grt II indicate that Grt I was likely formed under a mildly acidic and reducing environment and low W/R ratios, whereas Grt II may have formed in a more acidic and oxidizing environment with higher W/R ratios. The changes in redox, pH and W/R ratios cause the compositional variation from Grt I to II during the ascent of the early hydrothermal fluid. During the process of the crystal formation, the oxygen fugacity increased, and the mildly acidic to acidic ore-forming solution shifted from a low W/R ratios condition to a high W/R ratios condition, causing the precipitation of metal sulfide. The fissures of Grt II are infilled by pyrrhotite, chalcopyrite and pyrite, showing that the garnets form prior to the mineralization of copper and can provide space for the precipitation and enrichment of metals.

SHRIMP U–Pb ages, mineralogy, and geochemistry of carbonatite–alkaline complexes of the Sillai Patti and Koga areas, NW Pakistan: Implications for petrogenesis and REE mineralization

Carbonatites and related alkaline igneous rocks are important hosts of rare earth elements (REEs). Carbonatite–alkaline complexes in NW Pakistan represent rare examples of carbonatite emplaced in a collisional orogenic belt. However, the precise age, magmatic source, and petrogenesis of carbonatites emplaced in collisional settings and associated REE mineralization remain uncertain. The present study focuses on the origin and REE mineralization potential of alkaline–carbonatite complexes exposed in the Koga and Sillai Patti (SP) areas, NW Pakistan.The Koga carbonatites occur as minor plug-like intrusions in syenites. SHRIMP U–Pb dating of zircons from the Koga syenites, which are spatially associated with carbonatites, yield weighted mean ages of 283.6 ± 1.7(1σ), 281.9 ± 1.6(1σ), 282.6 ± 1.6(1σ), and 306.5 ± 3.7 Ma (1σ). The Koga syenites are characterized by high SiO2 (62.79–65.58 wt%) and Al2O3 (16.92–18.55 wt%) and low TiO2 (0.10–0.59 wt%) contents and are enriched in alkalis (Na2O > K2O). Sr and Nd isotopes from the Koga carbonatite complex are characterized by positive εNd(t) values (+3.10 to + 3.47) and low (87Sr/86Sr)i values (0.70233–0.70382), which are consistent with rift-related carbonatites.The SP carbonatites yield high total REE contents (1768–1920 ppm) and are enriched in light REEs (LREEs) relative to heavy REEs (HREEs; LREE/HREE = 20.0–20.7). The results of Sr–Nd isotope analyses show that the SP carbonatite has high Sr and low Nd isotopic ratios with negative εNd(t) values ranging from − 1.71 to − 2.21, variable 207Pb/206Pb ratios, and anomalous Pb–Sr and Pb–Nd patterns, suggesting Pb contamination during ascent of the primary carbonatite melts. Values of δ18OSMOW and δ13CPDB (‰) for the SP carbonates vary from + 14.45‰ to + 18.12‰ and from − 6.57‰ to − 9.70‰, respectively, which can be attributed to low-temperature alteration.On the basis of data for bulk-rock trace elements and Sr–Nd–Pb–C–O isotopes, it is concluded that the Koga carbonatite–alkaline complex was formed during the rifting and break-up of the northern margin of Gondwanaland. In contrast, carbonatite of the SP carbonatite–alkaline complex was probably generated by partial melting of sub-continental lithospheric mantle in a post-collisional tectonic setting. Although the SP carbonatite contains abundant REEs, it does not host significant REE mineralization owing to the lack of a mature sequence of evolutionary phases and to possible phosphate mineral saturation in the primary magmas, which caused REE depletion in the later carbonatitic magmas through fractional crystallization. Therefore, we conclude that carbonatites that are relatively rich in apatite but poor in fluorite and barite may not be prospective for REE mineralization.

The effect of caustic soda treatment to recover rare earth elements from secondary feedstocks with low concentrations

Caustic soda (NaOH) treatment has enhanced rare earth element (REE) extraction from monazite. This study examined the effectiveness of caustic soda for RE-phosphates with lower concentrations for extraction from coal overburden, an alternative feedstock derived from mining waste. Pourbaix (Eh-pH) diagrams were constructed for La, Ce, Nd, Eu, and Y-PO4-H2O systems to understand the thermodynamics of NaOH-facilitated acid leaching for low-concentration RE-phosphates and oxides and to elucidate the difference in recoveries among individual REEs. The Eh-pH diagrams indicated that low crystallinity is beneficial for extraction. Nd was thermodynamically most favorable for the extraction process among the five elements examined, and Y was the least promising. Experiments were conducted using three Pennsylvania coal overburden samples to validate the effect of caustic soda on rare earth leaching. The experimental results showed that for NaOH (6 M), a leaching time of 2 h at 125 °C was sufficient to obtain twice the recovery values compared to those without the NaOH treatment. After implementing the caustic soda treatment, a high total REE recovery (>60%), especially for Nd and Pr, could be achieved with diluted HCl and more environmentally friendlier citric acid. The results were similar for both coarse and fine particles. This novel approach is likely to improve the feasibility of REE extraction from coal-associated feedstock in a more environmentally benign manner.

Petrogenesis and tectonic setting of the early-middle triassic subduction-related granite in the eastern segment of East Kunlun: evidences from petrology, geochemistry, and zircon U-Pb-Hf isotopes

ABSTRACT The subduction process of the Paleo-Tethyan Ocean is still under controversy. We report zircon U-Pb ages and geochemistry (major and trace elements, and Hf isotopic compositions) for the Xiangjiananshan granitic plutons in the eastern segment of the East Kunlun Orogenic Belt, northern Tibetan Plateau, to constrain the subduction-related granitoids in its petrogenesis and to reconstruct the subduction prosess of the Buqingshan-A’nyemaqing Ocean. Zircon U-Pb dating yields coeval ages of 246.6 ± 4.1 Ma for granodiorite and 246.4 ± 3.9 Ma for biotite monzogranite of the Xiangjiananshan granitoid pluton. The granitoids include granodiorites, biotite monzogranites, and pseudo-porphyritic monzogranites. The granitoids have high contents of SiO2 (66.60–73.19 wt.%) and Al2O3 (13.28–16.38 wt.%), consistent with the high-K calc-alkaline series. The A/CNK ratios range from 0.98 to 1.02, indicating that the granodiorite is metaluminous and weakly peraluminous. The mafic microgranular enclaves (MMEs) in granodiorite and biotite monzogranite have a restricted SiO2 range (57.24–60.03 wt.%), and have higher Fe2O3 T, and MgO contents than the host granitoids, as well as higher total rare earth element (REE) concentrations. All samples are depleted in high field strength elements (HFSEs; e.g., Nb, Ta, Ti and P) and heavy rare earth elements (HREEs), and are enriched in large ion lithophile elements (LILEs; e.g., Rb, Nd and La) and light rare earth elements (LREEs). Zircons from the pseudoporphyritic monzogranite yield two-stage model ages of 1137.32 to 1588.12 Ma, together with εHf(t) values from −5.01 to +2.11. These results indicate that the parental magma of pseudoporphyritic monzogranite was generated by partial melting of Paleoproterozoic to Mesoproterozoic rocks of the lower crust with contamination of ancient crustal material. Field and petrological observations, together with elemental and Hf isotopic data, indicate that the Xiangjiananshan granitic plutons was formed by magma mixing of mafic and felsic magmas. The felsic magma was derived from partial melting of the lower crust, while the mafic magma was derived from partial melting of an enriched lithospheric mantle metasomatized by slab-derived fluid due to the subduction of the Buqingshan-A’nyemaqing Ocean. Therefore, we propose that the northward subduction of the Buqingshan-A’nyemaqing ocean north to the Bayan Hara block under East Kunlun initiated in the Middle Permian (ca. 270 Ma), yielding calcium metaluminous arc magmatic rocks with I-type granite characteristics at East Kunlun, including the XG pluton in this study. Subsequently, the Buqingshan-A’nyemaqing ocean closed and resulted in collision of the Bayan Hara and East Kunlun blocks from 240 to 230 Ma.

High-temperature fluids in granites during the Neoarchaean-Palaeoproterozoic transition: Insight from Closepet titanite chemistry and U-Pb dating (Dharwar craton, India)

The aim of this paper is to determine the composition and age of high-temperature (HT) hydrothermal fluids in Closepet granites (Dharwar craton, India). The magmatic origin of the Neoarchaean Closepet batholith has been recognized and dated many times, whereas a HT fluid system, strong evidence for which has been partly investigated, has never been dated. Titanite was chosen for a geochemical study on its pristine and altered domains to illustrate the fluid composition; the domains were dated to recognize the timing of fluid activity.Titanite presents distinct trace element enrichments in non-altered domains and strong depletions in trace elements in marginal, irregular, patchy zones. The high total rare earth element (REE) concentrations and the marked negative Eu anomalies suggest crystallization from a residual melt. The negative Eu anomalies diminish progressively in the REE patterns of altered parts and become positive. Trace element ratios (Nb/Ta, Y/Ho, and U/Th) indicate fluid-crystal interactions. Strong U/Th fractionation might be linked to the presence of CO2 and Cl−. Zr-in-titanite thermometry yields a crystallization/recrystallization temperature of ~700 °C for both magmatic and altered domains. The titanite factor Ti+4/(Al+3 + Fe+3) reveals an affinity with significant mantle input to the fluid system.Pristine and altered titanite domains have been successfully dated by laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS). Reversely discordant apparent ages suggest interaction with fluids, which modified the Pb composition of the magmatic titanite. The oldest semi-concordant analyses of titanite cores indicate an age of approximately 2500 Ma, which we interpret as the minimum age of magmatic titanite crystallization. Narrow dark rims of titanite with considerably lower Th/U ratios form a more coherent group of analyses defining an upper concordia intercept age of 2345 ± 0.016 Ma, interpreted as the best estimate for the time of complete titanite resetting associated with the metasomatic event. The HT fluid system appears to have remained active into the Palaeoproterozoic.Confirmation by dating that the tested fluids belonged to the Archaean hydrothermal system gives us information about this system at the time, but the information that it worked at least until the Palaeoproterozoic provides additional valuable information about the hydrothermal systems during the Neoarchaean-Palaeoproterozoic transition.

The origin of fluid in calcite veins and its implications for hydrocarbon accumulation in the Shunnan-Gucheng area of the Tarim Basin, China

The high-angle, structural genetic calcite veins of the Ordovician in the Shunnan-Gucheng area in the Tarim Basin provide a convenient study of fluid properties, hydrocarbon migration, and accumulation events in the fault zone of this area. Based on detailed core investigation, studies on fluid inclusions in calcite veins and comparison of geochemical characteristics of limestone matrix and calcite veins were carried out. Multiple types of hydrocarbons inclusion (e.g., dry asphalt inclusion,three-phase hydrocarbon inclusion, oil and water inclusion,gas-rich inclusion) were found in calcite veins. Furthermore, the coexisted aqueous inclusions with the gas–liquid phase had a high homogenization temperature (130–160 °C). The distribution characteristics of 18O-depleted (δ18O: −13.1‰ to −8.7‰), 87Sr-enriched (87Sr/86Sr: 0.708 879 to 0.710 432), relatively high total Rare Earth Elements (REEs), and positive Europium Anomalies indicated that the structural origin of calcite veins was mainly derived from the dissolution of surrounding rocks and diagenetic-hydrocarbon fluids. Participation signs of meteoric water were not proved. The rich hydrocarbon inclusions in the calcite veins indicated that the north-east strike-slip fault zone in the Shunnan-Gucheng area is an essential channel for hydrocarbon migration and accumulation.

Formation and stabilization of the Dunhuang Block, NW China: Constraints from the Late Paleoproterozoic A-type granites of the Dunhuang Complex

The geochemical composition and temporal evolution of A-type granites may hold key information regarding critical geodynamic processes that occurred during the evolution of the continental crust. Moreover, these aspects may provide an indication of when orogenic processes ended and craton formation/stabilization began in Early Precambrian blocks. In this study, we report the results of zircon U–Pb ages, Hf isotope data and whole-rock geochemistry for the Proterozoic Huoyanshan potassic granites in the Dunhuang Block, northwest China. Zircon U–Pb dating reveals that the Huoyanshan granites were emplaced at ca. 1791–1786 Ma, representing a Late Paleoproterozoic magmatism event. The granites have high SiO2 (70.71–72.20 wt%), total alkali contents (K2O + Na2O = 8.81–8.96 wt%; K2O/Na2O = 1.57–1.66), TiO2/MgO ratios (2.19–2.57), low CaO (0.77–1.27 wt%), MgO contents (0.12–0.16 wt%), and Mg# values (7.72–8.67), with A/CNK ratios of 0.96–1.04, pointing to alkaline and metaluminous to weakly peraluminous affinities. These granites are characterized by high total rare-earth element concentrations (∑REE = 419–755 ppm) and variable (La/Yb)N values (8–24) with significantly negative Eu anomalies (Eu/Eu* = 0.31–0.42). The primitive mantle-normalized trace element patterns suggest that the Huoyanshan plutons are depleted in Ba, Nb, Ta, Sr, P, and Ti, but enriched in Rb, Th, and Pb. Additionally, the granites have a high zirconium saturation temperature of 855–897 °C, with an average of 878 °C. These geochemical characteristics indicate that Huoyanshan potassic granites are an aluminous A-type granite, and further classified as A2-type. Together with the zircon Hf isotope data (εHf(t) = −11.21 to −2.76), indicates that these granites were generated from a crustal source. The heterogeneous Hf isotope compositions in zircons are principally caused by the disequilibrium melting of Zr-bearing sources. In addition, two-stage Hf model ages of zircons from the granites are ca. 2.6–3.1 Ga and plot on the average crustal evolution trend of Archean tonalite–trondhjemite–granodiorite (TTG) gneiss (~2.5 to 3.0 Ga) in the Dunhuang Block. Thus, we propose that A-type granites in the study area were generated from the disequilibrium partial melting of Archean tonalitic to granodioritic rocks under high-temperature and low-pressure conditions according to their low Al2O3 + CaO + Na2O + K2O (molar) values and high 10000 × Ga/Al values (>2.9). Subsequently, the magma experienced prominent fractional crystallization of K-feldspar, plagioclase, orthopyroxene, and/or magnetite. Our results, withavailabledata, suggest that the Huoyanshan granites formed in a tectonic transform regime within a collisional to extensional setting, and serve as a precursor for the formation and stabilization of the Dunhuang Block during the Late Paleoproterozoic. Furthermore, it is probable that the post-collisional magmatism event at ca. 1.79 Ga in the Dunhuang Block was closely related to the assembly of the Columbia supercontinent.

A biosorption-based approach for selective extraction of rare earth elements from coal byproducts

Coal byproducts represent an abundant and untapped potential source of critical rare earth elements (REEs). In this study, we tested the efficacy of a biosorption-based approach to recover REEs from leachate solutions derived from North Dakota lignite coal and Powder River Basin (PRB) coal fly ash. A pairwise comparison was performed using a range of cell densities of two distinct bacteria, including an Escherichia coli strain previously genetically engineered for cell surface display of lanthanide binding tags, and Arthrobacter nicotianae, a native bacterium that exhibits high REE adsorption capacity. At optimal cell densities, we observed a recovery efficiency of 80% for total REEs and > 90% for middle and heavy REEs from the lignite leachate. Higher cell densities were required to achieve a similar total REE recovery efficiency in the PRB leachate due to its higher non-REE content, which negatively impacted light REE recovery. Despite the chemical complexity of both feedstocks, separation factors ≥ 30 were observed for Nd relative to nearly all non-REE metals after a single adsorption/desorption cycle, highlighting the high adsorption selectivity for REEs. Quantification of impurities in the extracted metal solutions revealed that Ca and Mg content in the leachate solutions play a dominant role in both the REE recovery yield and purity. The Mg/Ca impurities can be further reduced by incorporation of a low pH wash step between the adsorption and desorption steps, yielding extracted concentrates with a REE purity (mass fraction REE of total metals) of 80% and 50% for lignite and PRB, respectively. Thermodynamic speciation analysis of the REE-enriched eluents from both feedstocks suggests that at a post-biosorption hydroxide precipitation step can be employed to yield high purity total REE precipitates. Collectively, these results highlight the utility of biosorption for selective REE recovery from coal byproducts and pave the way for a sustainable route to diversify the REE supply chain.

Titanite geochronology and geochemistry of the Cenozoic alkali-rich intrusions in the Ailaoshan-Red River Shear Zone, Yunnan Province

榍石作为副矿物在哀牢山-红河剪切带新生代富碱侵入岩中广泛存在。原位获取榍石矿物内部微量元素、U-Pb年龄和Sm-Nd同位素的空间变化对获取矿物和岩石的成因演化信息具有重要意义。本文使用四级杆/多接收电感耦合等离子体质谱（Quadrupole/Multi-Collector Inductively Coupled Plasma Mass Spectrometry，Q/MC-ICP-MS）与激光剥蚀系统（Laser Ablation，LA）联用，对哀牢山-红河剪切带5个富碱侵入岩体（桃花岩体、宁蒗-永胜岩体、哈播岩体、铜厂岩体和十里村岩体）中榍石开展了微区原位微量元素、U-Pb年代学和Sm-Nd同位素研究。微量元素分析结果表明，三江富碱侵入岩中榍石为岩浆成因，亏损Rb、Ba、Pb、Sr等大离子亲石元素，富集Th、U、Nb、Ta、Zr、Hf等高场强元素。榍石的稀土配分图均表现为明显右倾，不具有或具有弱的Eu负异常。与云南北衙、马厂箐矽卡岩矿床中的热液榍石相比，本文榍石在稀土元素组成上，具有较高的稀土元素总量、较高的Th/U、LREE/HREE和Ce/Ce^*比值，具有较低的Eu/Eu^*、Nb/Ta、Zr/Hf比值。微区原位LA-Q-ICP-MS U-Pb定年结果表明，研究区富碱岩体中榍石结晶年龄在32.5~37.9Ma之间，代表了岩体形成时代，与三江地区哀牢山-红河剪切带及其附近新生代富碱岩浆活动高峰期（~35Ma）一致，属于青藏高原晚碰撞期岩浆作用的产物。榍石微区原位LA-MC-ICP-MS Sm-Nd同位素分析结果显示，榍石颗粒的Nd同位素组成均一，表明榍石结晶过程中寄主岩浆的Nd同位素组成没有发生明显变化。各个富碱岩体之间的榍石Nd同位素组成变化范围在-6.8~-2.1之间，与全岩的同位素特征一致，表明榍石的原位微区Sm-Nd同位素可以作为富碱侵入岩研究中有效的示踪手段之一。;Titanite is a common accessory mineral in the alkali-rich intrusions in the Ailaoshan-Red River Shear Zone. In situ trace elements, U-Pb ages and Sm-Nd isotopes in titanites are of great significance for obtaining genesis and evolution information of minerals and rocks. In this study, trace element compositions, U-Pb dating and Sm-Nd isotopic compositions of titanites from five alkali-rich intrusions along the Ailaoshan-Red River Shear Zone in the Sanjiang Region have been successfully analyzed by Laser Ablation-Quadrupole/Multi-Collector Inductively Coupled Plasma Mass Spectrometry (LA-Q/MC-ICP-MS). Trace element chemistry of these titanites indicate that they are igneous titanites, depleted in large ionic lithophile elements such as Rb, Ba, Pb and Sr, and enriched in high field strength elements such as Th, U, Nb, Ta, Zr and Hf. Titanites in this study have relatively high total rare earth element (REE) concentrations, chondrite-normalized patterns show that they are LREE enriched with no or weak Eu negative anomaly. Titanites in this study show higher values for ∑REE, Th/U, LREE/HREE and Ce/Ce^*, and lower values for Eu/Eu^*, Nb/Ta and Zr/Hf than those of hydrothermal titanites from Beiya and Machangqing skarns. Results of in situ LA-Q-ICP-MS U-Pb dating show that the crystallization age of titanites from alkali-rich intrusions are ranging from 32.5Ma to 37.9Ma, consistent with the peak age of alkali-rich magmas along the Ailaoshan-Red River Shear Zone in the Sanjiang Region. In situ LA-MC-ICP-MS Sm-Nd isotopic analyses show that the Nd isotopic compositions of titanite grains are homogeneous, indicating that the Nd isotopic composition of host magma did not change during the crystallization of titanite. The ε_Nd(t) values of titanite in the alkaline intrusions in this study are ranging from -6.8 to -2.1, which are consistent with the Nd isotopic composition of the whole rock, indicating that in situ Sm-Nd isotopes of titanite can be used as a useful tracer in the study of alkali-rich intrusive rocks.

Potassic/ultrapotassic intrusions at the southwestern margin of the Yangtze Craton, southwestern China: Petrogenesis and implications for the metal and fluid source of non-arc porphyry Cu–(Mo–Au) deposits

Magmatic rocks can reveal partial melting processes in the lower crust and mantle. Therefore, the petrogenesis of both ore-barren and ore-bearing magmatic rocks can provide key insights into the deep geological processes that control porphyry Cu–(MoAu) deposits (PCDs). Here, we investigate the petrogenesis of potassic/ultrapotassic igneous rocks in the southwestern Yangtze Craton (SWYC) to constrain their magmatic sources and assess their role in the formation of PCDs. These igneous rocks can be divided into three suites, ore-barren granite porphyry, lamprophyre, and ore-bearing quartz monzonite. UPb dating of zircons indicates that these potassic/ultrapotassic intrusions crystalized simultaneously between 35.4 and 33.6 Ma. The lamprophyres have low SiO2 contents and high MgO and K2O contents, exhibiting an ultrapotassic affinity. They are depleted in high field strength elements (HFSEs; Nb, Ta, Zr, Hf, and Ti) and enriched in large ion lithophile elements (LILEs; Rb, K, Sr, and Ba). The enriched Sr, Nd, and Hf isotopic compositions of the ore-barren lamprophyres suggest that they were derived from low-degree partial melting of lithospheric mantle that had been metasomatized by subduction-related fluids during the Proterozoic. The ore-barren granite porphyries have high SiO2 and K2O contents, with high-K calc-alkaline to shoshonitic characteristics. These rocks have low MgO, Cr, Ni, and Co contents. All samples exhibit high Sr/Y ratios, and highly fractionated rare earth elements (REEs) patterns with weak Eu anomalies. Combined with their low total REE contents (75–81 ppm) and εHf(t) values, which are similar to Neoproterozoic granulite xenoliths, we conclude that the ore-barren porphyries are adakites derived from thickened Neoproterozoic lower crust. The ore-bearing intrusions show variable SiO2 and high Na2O + K2O contents, plotting in the monzonite to quartz monzonite fields in a SiO2 vs Na2O + K2O diagram. These samples have much higher total REE contents (346–671 ppm) than the ore-barren intrusions. The homogeneous SrNd isotopic compositions and linear trends on Harker diagrams suggest that the magma that formed the ore-bearing rocks underwent fractional crystallization of mainly amphibole and accessory minerals. Water contents are estimated to have been 9–12 wt% at 0.8 GPa on the basis of the retention of plagioclase and low zircon saturation temperatures, which suggests that the primitive magmas of the ore-bearing intrusions were derived from water-fluxed melting rather than dehydration melting. The additional water, required to promote water-fluxed melting, was probably derived from underplated poassic/ultrapotassic mafic magmas. The high total REE contents, Sr/Y and (La/Yb)N ratios indicate that the primitive magmas of ore-bearing intrusions were probably derived from partial melting of potassic/ultrapotassic lower crust, formed by the underplating of mantle-derived potassic/ultrapotassic magma. These results, combined with previous research, show that mantle-derived potassic/ultrapotassic magmas can provide metals and fluids required for the formation of PCDs.

Influence of volcanic and hydrothermal activity on organic matter enrichment in the Upper Triassic Yanchang Formation, southern Ordos Basin, Central China

Abstract Based on the field investigation of oil shales in the southern Ordos Basin, detailed observations, and systematic sample analyses of core samples from a well that penetrated an oil shale, the influence of volcanic and hydrothermal activity on the Chang 8–Chang 7 members of the Yanchang Formation on organic matter (OM) enrichment was geochemically and petrologically analyzed. According to maceral analyses and rock pyrolysis, the kerogen types of the samples in the study area are widely distributed. Those of the oil shale with the highest OM abundance are mostly type II-I, and are immature or in a stage of low-maturity. Six layers of tuff and tuffaceous mudstone were identified by core observation and element characteristics; they are characterized by higher total rare earth element (∑REE) and δCe values and Th contents, and lower (La/Yb)N and δEu values. Mineral assemblages of anhydrite–pyrite–marcasite and relevant diagrams of the elemental geochemistry confirmed the existence of hydrothermal deposits. The high Yn/Hon and U/Th ratios and total sulfur (TS) contents indicate that the Chang 7 Member experienced four episodes of intense hydrothermal activity. Early in the Chang 73 Member, volcanic ash and hydrothermal fluids brought in a large amount of nutrients, which not only increased primary productivity, but also increased the salinity of the water column, enhanced anoxia in the sedimentary environment of the lake bottom, promoted the preservation of OM, and finally formed the oil shale layer with the richest OM. However, the strong volcanic eruption in the late Chang 73 Member led to changes in the regional climate, causing it to dry and become colder and resulting in a decrease of primary productivity. Earthquakes triggered by volcanism resulted in turbidite deposits, which destroyed the preservation and diluted the enrichment of OM. This study reveals in detail the influence of volcanic and hydrothermal activity on OM enrichment during the evolution of the basin, and thereby deepens our theoretical understanding of OM enrichment.

Ecological Risk Assessment of Neodymium and Yttrium on Rare Earth Element Mine Sites in Ganzhou, China.

Nowadays rare earth elements (REEs) are widely applied in high-technology and clean energy products, but their environmental risks are still largely unknown. To estimate the ecological risk of REEs, soil samples were collected from REE mine tailings with and without phytoremediation. The results showed that the tailings had rather low organic matter and high total REE concentrations, up to 808.5mg/kg. The 10% effective concentration (EC10) of neodymium (Nd) and yttrium (Y) were calculated based on the toxicity tests of seed germination and root growth. For both wheat and mung bean, the EC10 of Nd and Y in soils were in the range of 1053.1-1300.1mg/kg. The average hazard quotient of mine tailing soil without phytoremediation was higher than that with phytoremediation. All the hazard quotient of Nd and Y were less than 1, indicating that Nd or Y alone was unlikely to cause adverse ecological effects. Given to the coexistence of REEs on mine sites, the ecological risk of REE mixture could be potentially high towards local soil environments, even for soils with phytoremdiation.

New insights into Neoarchean–Paleoproterozoic crustal evolution in the North China Craton: Evidence from zircon U–Pb geochronology, Lu–Hf isotopes and geochemistry of TTGs and greenstones from the Luxi Terrane

Tonalite–trondhjemite–granodiorite (TTG) suites constitute dominant components of Precambrian continental crust and provide important insights into the crustal evolution history of the early Earth. Here we investigate a suite of TTGs and associated greenstones from the Luxi Terrane in the south–eastern part of the North China Craton (NCC). We present data from petrology, geochemistry, zircon U–Pb geochronology and Lu–Hf isotopes to characterize these rocks and understand their genesis. Mineral assemblage in the greenstones and TTGs suggests that the rocks have undergone amphibolite–facies metamorphism with regression under greenschist–facies. Zircon U–Pb data from the magmatic grains yield upper intercept ages of 2753 ± 37 and 2582 ± 40 Ma for greenstone, 2552 ± 13 Ma for TTG gneiss and 2476 ± 18 Ma for tonalite, and weighted mean 207Pb/206Pb age of 2507 ± 22 Ma for granodiorite. Lu–Hf isotope systematics show εHf(t) values ranging from −2.13 to 7.29 and crustal model ages (TCDM) in the range of 2603–3125 Ma for the TTGs, whereas the εHf(t) values are up to 8.53 with TCDM ages of 2644–3006 Ma for the greenstone. The results suggest that the protolith for the greenstone was derived from a Meso- to Neoarchean mantle contaminated by the crust source, whereas the TTGs were mostly sourced from juvenile crustal sources with reworking of older basement. The geochemical features of greenstone are similar to island arc basalt, with low Na2O, K2O and TiO2, low total rare earth elements (REEs) values, relative enrichment in light REEs and depletion in heavy REEs absence of obvious Ce anomaly, and negative Nb, Ta and Ti anomalies. The TTGs show similar features, except for the high K2O content and moderate total REEs values. We propose that the greenstone likely represent a part of the early and initial crustal growth at ca. 2750–2600 Ma, and the TTGs were generated subsequently at ca. 2550–2450 Ma. Our results are consistent with the previous models on the crustal growth models in the NCC and provide further insights into the Neoarchean to Paleoproterozoic tectonic history of the craton.

Petrology, geochemistry, and zircon U–Pb–Hf isotopes of Late Triassic enclaves and host granitoids at the southeastern margin of the Songnen–Zhangguangcai Range Massif, Northeast China: Evidence for magma mixing during subduction of the Mudanjiang oceanic plate

We report zircon U–Pb ages and geochemistry (major and trace elements, mineral compositions, and Hf isotopic compositions) for the Hailin pluton in the southeastern Songnen–Zhangguangcai Range Massif, northeastern China, to constrain the role of magma mixing in its petrogenesis and to reconstruct the tectonic evolution of the Mudanjiang Ocean. Zircon U–Pb dating yields ages of 215 ± 1 Ma, 217 ± 1 Ma, and 219 ± 1 Ma for the host granitoids of the Hailin pluton, and 221 ± 1 Ma for mafic microgranular enclaves (MMEs) within the granitoids, indicating they were emplaced coevally. The host granitoids are characterized by 63.18–70.44 wt% SiO2 and 0.69–1.94 wt% MgO, and are depleted in high field strength elements (HFSEs; e.g., Nb, Ta, and Ti) and heavy rare earth elements (HREEs), and enriched in large ion lithophile elements (LILEs; e.g., Rb, Sr, and Ba) and light rare earth elements (LREEs). The zircons in the host granitoids yield two-stage model ages of 1058 Ma to 1770 Ma, together with εHf(t) values of −6.6 to +3.1. These results indicate that the host granitoid magmas were generated by partial melting of Mesoproterozoic lower crust contaminated by ancient crustal material. The MMEs have a restricted SiO2 range (47.61–57.4 wt%), high contents of Ni, Co, and Cr, and high Mg# values (42–54). They have higher Fe2O3T, MgO, Cr and Co contents than the host granitoids, as well as higher total rare earth element (REE) concentrations. Their REE patterns are sub-parallel to those of the host granitoids, characterized by enrichments in LILEs and LREEs, and depletions in HFSEs and HREEs. Zircons from two samples of the MMEs yield single-stage Hf model ages of 666–1077 Ma and εHf(t) values of −5.4 to +5.2. The geochemical characteristics of the MMEs are similar to those of the host granitoids, indicating crust-mantle interaction during their formation. The mafic magmas were derived from melting of depleted lithospheric mantle that had been metasomatized by slab-derived fluids. MMEs are common in the host granitoids and are characterized by irregular spheroidal shapes, with sharp, rounded, or irregular transitional contacts, acicular apatites, and plagioclase reverse zoning, suggesting the importance of magma mixing during petrogenesis. Our geochemical and isotopic data suggest that the Late Triassic Hailin pluton formed by the mixing of felsic and mafic magmas in an active continental margin setting, closely related to the westward subduction of the Mudanjiang oceanic plate beneath the Songnen–Zhangguangcai Range Massif.