Rare Earth Element Abundances Research Articles

Petrogenesis of lamprophyre in Sawur, northern Xinjiang, China: Implication for volcanic hosted gold deposits

The Sawur gold belt, northern Xinjiang, China, is the eastward extension of the Zarma-Sawur Au-Cu belt in Kazakhstan. Many gold deposits and other mineral occurrences are distributed in volcanic rocks of the Sawur area. Systematic studies are in need to learn how gold is associated with volcanic rocks. This study applied whole rock and mineral geochemical analysis on lamprophyres in Qia’erdunbasixi gold deposit. Clinopyroxene (Cpx) xenocryst in lamprophyre and Cpx megacryst core is Mg- and Cr-rich diopside, which is commonly eroded by salite with resorption boundary. These Cpx grains with low rare earth element (REE) abundance, light rare earth element (LREE) depletion ([La/Yb]N < 1) and without Eu anomaly are likely formed in the spinel-facies lithospheric mantle. Xenocryst in lamprophyre has undergone metasomatism, which is proved by the occurrence of amphibole and phlogopite along the rim of Cpx. In situ trace element analysis of amphibole and metasomatized clinopyroxene unravels the property of metasomatic melt with large LREE/HREE fractionation and strong depletion in Zr-Hf and Ti relative REE, with the occurrence of pargasite, phlogopite and apatite, which are typical characteristics of alkali carbonatite melt from upper mantle. Fe-rich salite with low Mg# (61 ∼ 64) and right-leaning REE pattern is different from any other clinopyroxene in Sawur lamprophyre, should be the subducted mélange, which is captured by upwelling melt together with xenocryst caught from spinel-facies mantle. Cpx phenocryst with low Mg#, Cr and high abundance of REE in lamprophyre has different compositions with xenocryst, should be formed in a shallow magma chamber. The lamprophyre is thought to be derived from deep mantle and therefore carry these various xenocrysts into surface. We suggest the mantle origin with alkali carbonatite metasomatism likely results in the gold fertility of Sawur volcanic rocks, which explains the common association with gold mineralization.

Residual levels and health risk assessment of rare earth elements in Chinese resident diet: A market-based investigation

The widespread use of rare earth elements (REEs) in agriculture and high-tech industry resulted in significant release of REEs into the environment. However, there is a scarcity of studies focusing on the presence of REEs in the food worldwide. The present study investigated the residual levels of REEs in 14 representative food categories collected from 33 major cities of China. The measured total REEs (ΣREE) levels in the foods of aquatic origin were 174.97 μg kg−1 wet weight (ww), which was 6.35 times higher than those of terrestrial origin. It is interesting to observe a trophic dilution effect for REEs in both terrestrial and aquatic food samples. REEs in food samples at low trophic levels exhibited relatively high REEs levels; while for high trophic level food, relatively low REEs levels were observed. The distribution patterns of REEs varied across the different food categories and regions, with Ce being the most abundant REEs in all food samples, followed by La, Nd and Sm. High levels of ΣREE in food samples were observed in Midland, while low levels were found in the Northeast. Cereals was the dominant contributor to the estimated daily intake of REEs. The health risk of REEs by daily food consumption in China was acceptable.

Patterns and Abundance of Rare Earth Elements in Sediments of a Bedrock River (Miño River, NW Iberian Peninsula)

Bedrock rivers, whose sedimentary geochemistry has been scarcely investigated, are suitable to test geochemical approaches in order to assess the existence and extent of human alterations in the natural abundance of rare earth elements. This work presents the study of REE contents in fine-grained sediments of the (bedrock) Miño River, in an urban reach of its middle course. Different statistical procedures were employed in order to decipher the abundances and patterns of distribution of REE in different environments, showing a higher REE accumulation in surface sediments trapped by potholes and other rock cavities. Background contents were estimated by iterative simple regression. After checking several possible reference elements, Y showed the highest potential for the series of REE from La to Lu. The regression result, namely background function, is very useful to minimize the effect of the natural variability in sediment contents. Background functions also allow for environmental assessment by the calculation of the so-called local enrichment factors. As a general conclusion, contamination, if it exists, is negligible in the area and low enrichments can be attributed to postdepositional processes related to organic matter and the geochemistry of Fe and Mn.

Ultra-Refractory Peridotites of Phanerozoic Mantle Origin: the Papua New Guinea Ophiolite Mantle Tectonites

AbstractHarzburgites and dunites forming the base of the Late Cretaceous–Paleocene Papuan Ultramafic Belt (PUB) and Marum ophiolites of Papua New Guinea (PNG) are among the most refractory mantle peridotites on Earth. We present a new integrated dataset of major element, bulk plus mineral trace element and Re–Os isotopic analyses aimed at better understanding the genesis of these peridotites. The PUB harzburgites contain olivine (Fo92–93), low-Al enstatite (less than or equal to 0.5 wt. % Al2O3 and CaO), and Cr-rich spinel (Cr# = 0.90–0.95). The Marum harzburgites are less refractory with olivine (Fo91.9–92.7), enstatite (~0.5–1.0 wt. % Al2O3 and CaO), minor clinopyroxene (diopside), and spinel (Cr# = 0.71–0.77). These major element characteristics reflect equivalent or greater levels of melt depletion than that experienced by Archean cratonic peridotites.Whereas bulk-rock heavy rare earth element (HREE) abundances mirror the refractory character indicated by the mineral chemistry and major elements, large-ion lithophile elements indicate a more complex melting and metasomatic history. In situ olivine and orthopyroxene REE measurements show that harzburgites and dunites have experienced distinct melt-rock interaction processes, with dunite channels/lenses, specifically, showing higher abundances of HREE in olivine. Distinctive severe inter-element fraction of platinum group elements and Re result in complex patterns that we refer to as ‘M-shaped’. These fractionated highly siderophile element (HSE) patterns likely reflect the dissolution of HSE-rich phases in highly depleted peridotites by interaction with subduction-related melts/fluids, possibly high-temperature boninites.Osmium isotope compositions of the PNG peridotites are variable (187Os/188Os = 0.1204 to 0.1611), but fall within the range of peridotites derived from Phanerozoic oceanic mantle, providing no support for ancient melt depletion, despite their refractory character. This provides further evidence that highly depleted peridotites can be produced in the modern Earth, in subduction zone environments. The complex geochemistry indicates a multi-stage process for the formation of the PNG mantle peridotites in a modern geodynamic environment. The first stage involves partial melting at low-pressure (&amp;lt;2 GPa) and high-temperature (~1250°C–1350°C) to form low-K, low-Ti tholeiitic magmas that formed the overlying cumulate peridotite–gabbro and basalt (PUB only) sequences of the ophiolites. This is inferred to have occurred in a fore-arc setting at the initiation of subduction. Later stages involved fluxing of the residual harzburgites with hydrous fluids and melts to form replacive dunites and enstatite dykes and interaction of the residual peridotites in the overlying mantle wedge with high-temperature hydrous melts from the subducting slab to generate the extremely refractory harzburgites. This latter stage can be linked to the eruption of low-Ca boninites at Cape Vogel, and other arc-related volcanics, in a nascent oceanic island arc. Both ophiolites were emplaced shortly after when the embryonic oceanic island arc collided with the Australian continent.

The message of oldhamites from enstatite chondrites

We have determined rare-earth element (REE) abundances in oldhamites (CaS) from 13 unequilibrated and equilibrated enstatite chondrites (5 EH and 8 EL) and in a few enstatites by in situ, laser ablation ICP-MS. In EH chondrites, oldhamite REE patterns vary from the most primitive petrographic types (EH3) to the most metamorphosed types (EH5). In EH3, CI-normalized REE patterns are convex downward with strong positive Eu and Yb anomalies, whereas EH5 display flat patterns with enrichments reaching about 80 times CI abundances. The positive anomalies of Eu and Yb found in oldhamites of primitive EH chondrites indicate that they represent the condensation of a residual gas fraction, in a manner similar to fine-grained CAIs of carbonaceous chondrites. The early condensate may have been preserved in the matrix of unequilibrated EH. Equilibrated EH oldhamite patterns may result from metamorphic evolution and REE redistribution on the EH parent body. On the contrary, all the oldhamites from EL chondrites (EL3 to EL6) display a single kind of patterns, which is convex upward and is about 100 times enriched relative to CI, with a negative Eu anomaly. In addition, the EL pattern is similar to that of oldhamites from aubrites (enstatite achondrites). The latter observation suggests that oldhamites of all EL metamorphic types (including primitive ones) bear the signature of a magmatic event accompanied by FeS loss as vapor, prior to the assembly of the EL parent body. Given the difficulty of obtaining precise ages on enstatite chondrites, it is not possible to discuss the chronology of the events recorded by the oldhamite REE patterns.

Martian hydrothermal fluids recorded in the Sm-Nd isotopic systematics of apatite in regolith breccia meteorites

The observations of Martian orbiters and rovers have suggested that there were fluids on the surface of early Mars. However, the geochemical properties of those fluids are unclear. The Martian regolith breccia meteorites (MRB), the source materials of which are thought to have formed at 4.4 Ga, may have recorded interactions with fluids on Mars. Here, we have analyzed the in situ Sm-Nd isotopic compositions and trace element contents of apatite in MRB and have obtained a Sm-Nd isochron age of 1490±480 Ma. This young age indicates that the MRB apatites were altered by fluids and have exchanged trace elements with fluids. The very negative initial ε143Nd, combined with the previously reported positive δD and δ37Cl in the MRB apatites, indicate that Martian fluids originated from a geochemically enriched reservoir in the crust. The large ranges of rare earth element abundance (ΣREE) and of the chondrite normalized ratio of La and Yb [(La/Yb)N] indicate the chemical complexity of the fluids that interacted with the apatites in the MRB. The apatite REE compositions were used to further determine the pH values of Martian fluids equilibrated with the MRB apatites, which varied from ∼3 to ∼8. The apatite X-site Cl contents indicate that the Cl contents in Martian fluids in equilibrium with the MRB apatites at 400°C and 1 bar could be up to 1857 ppm, within the range of terrestrial hydrothermal fluids. Combined with previously reported geochemical data from Martian meteorites, our study suggests that fluids may have been present throughout the early geological history of Mars.

Prelude to Late Triassic Ni–Cu sulphide mineralization in the eastern Central Asian Orogenic Belt: Geochronological and geochemical constraints from Middle Triassic mafic‐ultramafic magmatism in central and eastern Jilin Province, NE China

The Hongqiling‐Piaohechuan region in the east Central Asian Orogenic Belt (CAOB) is an economically important Ni–Cu sulphide mineralization region in China. It is widely accepted that these Ni–Cu sulphide deposits mainly formed during the Late Triassic period. The early Middle Triassic mafic‐ultramafic plutons are therefore key in understanding the mineralization process. Here, we report the laser ablation inductively coupled plasma mass spectrometer (LA‐ICP‐MS) U–Pb dating of zircon and geochemical data for two Middle Triassic mafic‐ultramafic plutons and one felsic pluton in central and eastern Jilin Province, NE China. The mafic‐ultramafic plutons are composed of gabbronorite and olivine websterite. Zircon dating results indicate that these mafic‐ultramafic plutons crystallized at 243 ± 1 to 245 ± 1 Ma in the Middle Triassic. The coeval felsic pluton is mainly quartz diorite. Zircon dating results indicate that the felsic pluton crystallized at 239.7 ± 0.63 Ma in the later period of Middle Triassic. The mafic‐ultramafic plutons are low in SiO2 (43.49–49.66 wt%), depleted in K2O (0.28–2.74 wt%) and Na2O (0.70–1.18 wt%). They have low rare earth element (REE) abundances without Eu anomalies, exhibit depletion in high‐field‐strength elements (HFSEs), and hold various εHf(t) values (−15.3 to +2.9). These findings suggest that the primary magma of mafic‐ultramafic plutons was derived from the partial melting of the depleted lithospheric mantle, metasomatized by subducted‐slab‐derived fluids/melts. Remarkably, these mafic‐ultramafic plutons have extremely high Cu–Ni contents (23.6–669.4 and 419–1,956 ppm, respectively). The coeval quartz diorites have 59.55–64.86 wt% of SiO2, 3.02–4.21 wt% of K2O and 3.97–4.49 wt% of Na2O. They are enriched in light REEs (LREEs) and large‐ion lithophile elements (LILEs); depleted in heavy REEs (HREEs) and HFSEs, and they have εHf(t) values in the range −6.4 to +2.9. Additionally, the felsic rocks exhibit adakitic‐features with high Sr/Y (28.5–58.7) and (La/Yb)N (4.9–12.2) ratios, implying the thickening crustal sources of the North China Craton (NCC) and CAOB, respectively. The above findings, combined with the regional geological data, suggest that the Middle Triassic mafic‐ultramafic plutons are the prelude to the large‐scale Late Triassic mineralization. This was induced by the thickening event of the later period of Middle Triassic felsic rocks, accompanying the final closure of the Palaeo‐Asian Ocean (PAO) in the eastern CAOB.

Rare earth elements in brown algae of the genus Cystoseira (Phaeophyceae) (Black Sea)

Rare earth metals are widely used in various technologies, and their environmental impact needs to be assessed. Brown algae are recognized bioindicators of xenobiotic pollution in coastal marine areas, so we studied the rare earth element contents in short-lived branchlets of the two most abundant species of Cystoseira (C. barbata and C. crinita) on Black Sea coasts. The abundance of rare earth elements including scandium (Sc), yttrium (Y), lanthanum (La) and 14 lanthanides in the algae, seawater and sediments were determined using inductively coupled plasma mass spectrometry. The average contents of the prevalent elements in the algae decreased in the following order: Sc ≥ La > Europium (Eu) > Y > Neodymium (Nd) > Cerium (Ce). The factors affecting rare earth element content were age > locality > species of the alga. Most of the rare earth metals reached their maximum levels in branchlets > 5 month old, presumably associated with biosorption processes, whereas others (Eu, Terbium (Tb), Lutetium (Lu)) were most concentrated in 2–5 month old branchlets. In contrast to existing reports on the possible use of brown seaweeds for monitoring rare earth elements in coastal waters, the suitability of Cystoseira spp. branchlets, which have a 7 month life cycle, for short-term rare earth contamination monitoring was not confirmed in this study. Highlights Cystoseira spp. branchlets accumulate many rare earth elements with age. The dominant elements in Cystoseira spp. are Sc ≥ La> Eu > Y > Nd > Ce. The most significant factors affecting rare earth element content are age > locality > species.

Enhanced hydrological cycle during Oceanic Anoxic Event 2 at southern high latitudes: New insights from IODP Site U1516

The Oceanic Anoxic Event 2 (OAE 2) represents one of the most profound global environmental disturbances of the Mesozoic Era, which was associated with a positive carbon isotope excursion due to widespread organic carbon burial. However, the character, evolutionary history, and exact driving mechanisms of OAE 2 are still much debated, exacerbated by the lack of records from climate-sensitive southern high latitudes. Here we present a multi-proxy record of a stratigraphically continuous succession spanning the late Cenomanian to early Turonian at the International Ocean Discovery Program Site U1516 in the Mentelle Basin off southwest Australia, which was located at southern high latitudes (~ 60–62°S) during the Late Cretaceous. Sedimentary records at Site U1516 allow the first detailed insights into source-to-sink processes in the Mentelle Basin and associated paleoenvironmental reconstruction in the southern Indian Ocean during OAE 2. Rare earth element abundances and clay-bound neodymium isotopes of the siliciclastic sediment fractions indicate that southwest Australia was the main detrital source of sediment at Site U1516 during OAE 2, with volcanogenic sediments representing only a minor component. A major provenance shift is observed across OAE 2, indicating an increased sediment contribution from distant sources (i.e., Yilgarn Craton and Albany-Fraser Orogen) relative to proximal sources (i.e., Perth Basin and Leeuwin Block) in southwest Australia, interpreted as reflecting a major reorganization of the drainage system due to enhanced fluvial runoff. Based on these findings, we infer that the OAE 2 interval showing the most prominent δ13C excursion was associated with an intensification of the hydrological cycle in the high-latitude southern hemisphere, with potential impacts on regional ocean chemistry and marine productivity. In particular, we suggest that enhanced terrigenous input and riverine nutrient export likely played a key role in controlling siliceous productivity at nearby ocean margins. As a consequence, the intense burial of organic matter (i.e., black shale) at Site U1516, which occurred episodically throughout OAE 2, possibly resulted from the combination of enhanced riverine-driven marine productivity and increased burial efficiency associated with the development of anoxic/euxinic bottom water conditions.

Tectonic transition from Ediacaran continental arc to early Cambrian rift in the NE Ardakan region, central Iran: Constraints from geochronology and geochemistry of magmatic rocks

• Zircon U-Pb dating shows that the Ardakan granitic plutons crystallized at ∼550 Ma and a doleritic sill at ∼528 Ma. • Granite was produced by interaction of mantle-derived melt with continental crust . • Dolerite was generated by partial melting of asthenospheric mantle. • The Ardakan magmatic rocks were formed in a long-lived continental arc and neighboring back-arc. Ediacaran-early Cambrian magmatic rocks from the Ardakan region of central Iran include deformed granites from deformed granitic plutons and dolerites from doleritic sills. The granites contain zircon grains with U-Pb ages of 552–550 Ma, and dolerites have a zircon U-Pb age of 528 Ma. These granites are high K calc-alkaline in nature and have variable concentrations of SiO 2 (69.1–76.3 wt%), Na 2 O (2.06–4.82 wt%), K 2 O (3.08–4.79 wt%) and MgO (0.57–2.02 wt%). They represent I-type granite and are metaluminous to weakly peraluminous, with negative primitive mantle-normalized Nb, Ti and Eu anomalies. 87 Sr/ 86 Sr(i) and εNd(t) in the granites vary from 0.7075 to 0.7120 and from −3.0 to +7.3, respectively. Dolerites are alkaline, with low contents of SiO 2 (45.7–48.6 wt%), Cr and Ni (13.6–313 and 15.7–146 ppm, respectively) and overall high contents of TiO 2 (2.0–4.6 wt%). TiO 2 contents define high-Ti and low-Ti dolerite types, which show similar high field strength and rare earth element abundances. The high-Ti dolerites may be evolved equivalents of the low-Ti type. The 87 Sr/ 86 Sr(i) and εNd(t) values of both types are highly variable (0.7029 to 0.7077 and −6.1 to +7.7, respectively). The data indicate melting of an asthenospheric mantle source, with additional fractionation, and mixing with crustal melts to produce the evolved dolerites. Geochemical data from granites in NE Ardakan are consistent with late Ediacaran arc magmatism ∼550 Ma. The ∼528 Ma OIB-like dolerites may indicate continental extension at this time.

Geochemical composition of dykes along the Cameroon Line (CL): Petrogenesis and similarities with the Central Atlantic Magmatic Province

We report whole-rock geochemistry and Sr–Nd–Pb isotopic compositions of mafic dykes intruded in the Precambrian granito-gneissic basement complex, exposed at Nyos, Batibo, Dschang and Foumban on the Cameroon Line. The dykes are alkaline (Batibo), transitional (Foumban), and subalkaline (Nyos, Batibo and Dschang) with SiO2 of 45–54 wt% and MgO of 2–9 wt%, similar to dykes reported in other areas of the Cameroon Line (CL) and the Central Atlantic Magmatic Province (CAMP). The abundances of rare earth elements (REE) and the Primitive Mantle normalised patterns for the Nyos, Batibo and Dschang dykes are similar to those of MORB, indicating that the dykes formed at shallower depths by a higher degree of partial melting relative to the Foumban dykes and the alkaline lavas of the CL. The transitional basaltic dykes with steeper REE patterns have their sources at deeper levels in the lithospheric mantle, possibly the garnet-spinel transition zone and were generated by a lower degree partial melting of the lithospheric and plume components. The Nyos and Batibo subalkaline dykes show similar isotopic compositions with a spectrum extending from depleted (DMM-like) to enriched (EM1-like) mantle, indicating the similarity in their source components. The Dschang dykes show distinct isotopic characteristics with relatively unradiogenic Nd-Pb isotope compositions compared to the Batibo and Nyos dykes. The Foumban transitional dykes with characteristic wide ranges in Sr-Nd-Pb isotopic compositions reveal varying contributions from enriched mantle components (EM1 and EM2) in addition to its plume signature similar to those of CL lavas. The Nyos and Batibo dykes alongside other dykes on the CL have low TiO2 abundances (<2 wt%), negative PM-normalised Nb-anomalies, and moderately to strongly enriched REE patterns, and isotopic composition that overlaps with those of CAMP, suggesting a similar lithospheric origin.

Petrogenesis of Pre-Tertiary A-Type Granitoid in Jambi Area and its Implications of Rare Earth Element Potential on Main Range Sumatra Belt

Granitoid rocks are one of the main sources of rare earth elements (REE). This makes granitoid characterization become important in the early stages of REE exploration. Almost all granitoids in Indonesia have been mapped. However, more detailed granitoid studies in Indonesia are still focused on Bangka and Belitung granites (tin belt granite). In contrast to Bangka and Belitung granites, studies related to petrogenesis and granite characteristics on the mainland of Sumatra Island (Sumatra Main Range) are rarely done, such as granitoid in Jambi area. The aim of this study is to determine the characteristics of the Pre-Tertiary granitoids located in the Tigapuluh and Duabelas Mountains, Jambi. The Tanjungjabung Barat granitoid represent the Tigapuluh Mountains area while the Sarolangun granitoid represent the Duabelas Mountains area. These two granitoids interpreted to be Triassic to Jurassic in age. Granitoid characteristics include petrological and geochemical characters. This study also focuses on the petrogenesis of Pre-Tertiary granitoid and its implications for the abundance of REEs. Megascopic observation, petrographic, and geochemical analysis are done in this study. Geochemical analysis was done at the Center of Geological Survey Laboratory, Bandung using the ICP-MS Thermo Icap-Q and XRF ADVANT XP Thermo ARL9900 instruments. Based on megascopic and petrographic observations, both of the granitoids are classified as granite. Geochemically, these two granitoids show the character of A-type granite which is formed in the post-collision environment, and derived from the crustal melting with ferrous alkalic to alkali-calcic peraluminous affinities. This crustal melting happened due to the collision of the Sibumasu Block with Indochina resulting in crustal thickening and crustal melting. The magma then contaminated effectively in the rift environment due to the subduction roll-back of Meso-Tethys in the Late Triassic. Subduction in the West Sumatra also play roles in the genesis and it is shown by the geochemical character of the Sarolangun granitoid. Effective contamination derives the characteristics of A-type granite so that the REE content in both granites are abundant. The abundance of REE is indicated by the presence of the allanite, monazite, apatite, zircon, and titanite. The REE concentration of the Sarolangun granitoid reaches 330 ppm, while the Tanjungjabung Barat granitoid reaches 261 ppm. The REE concentrations of A-type granitoid in Jambi then compared with A-type granitoids from the world and showed relatively the same REE concentrations. The REE concentrations of these granitoids are also higher than the other type granitoids in Indonesia. However, the REE concentrations of Jambi granitoids are similar to the fractionated S-type granite in Bangka. With a recent study showing the presence of A-type granitoid in Sarudik (North Sumatra) and Bukit Batu (South Sumatra), the A-type granitoid in this study indicates the existence of A-type granitoid belt in the Sumatra Main Range. This belt will have a high abundance of REE concentrations and potentially become the source for REE deposits. The author hopes that this study could improve the understanding of tectonic in Sumatra and suggestion for REE exploration in the area.

Geochemical evolution of the Rabaul volcanic complex, Papua New Guinea - Insights from HFSE, Sr-Nd-Hf, and Fe isotopes

The Rabaul volcanic complex, Papua New Guinea, is among the few calderas worldwide with ongoing volcanic activity. Its volcanic lithologies vary from mafic lavas from outer caldera cones to differentiated lavas within. In this study, representative lavas have been analysed for their major and trace element concentrations and radiogenic Sr-Nd-Hf isotope compositions to study the geochemical evolution of the magmatic system. Stable Fe isotopes and concentrations of high field strength elements (HFSE) complement the analyses as novel tools to assess the effect of high-temperature fractional crystallisation during ongoing differentiation. Major element systematics reveal a typical fractional crystallisation sequence of olivine, pyroxene, and plagioclase as the critical process controlling the magmatic evolution. A distinct increase of Zr/Hf from the basaltic (older) outer caldera lavas (~39) to the dacitic (younger) inner caldera lavas (~41–44) can be explained by fractionation of clinopyroxene and amphibole. Ratios of Nb/Ta tend to decrease with an increasing degree of differentiation, consistent with fractional crystallisation of amphibole but not clinopyroxene. Additional fractionation of Ti-magnetite and rather oxidising conditions are further supported by the Fe isotope compositions in the inner caldera lavas (δ57Fe from +0.03 to +0.22‰, ±0.04‰, 2 SD). The high Nb/Ta in more primitive outer caldera samples are coupled with increasing rare earth elements (REE) abundances, and slab melt-like subduction components can explain high Sr/Y and GdN/YbN in the magma sources. Complementary enrichments in fluid-mobile trace elements indicate that slab dehydration controlled the sub-arc enrichment of the inner caldera volcanism. Coupled Hf-Nd isotope compositions reveal the presence of the Indian-Australian mantle domain beneath Rabaul and a temporal trend towards sediment melt components overprinting inner caldera lavas. In conclusion, geochemical features show a temporal evolution controlled by (i) variable influence of partial slab melts vs slab fluids and (ii) a change in fractional crystallisation patterns from solely olivine and pyroxene-controlled to increasingly titano-magnetite and amphibole-controlled fractionation.

REE-Bearing Minerals in Tin Waste Dumps of Singkep Island: Geochemical Identification and Recovery

DOI:10.17014/ijog.9.1.15-26Instead of environmental hazard, tailing might contain resources which could be reworked with the development of mining and separation technologies. Tailing dumps and waste ponds which associated with the long period of tin mining are easily found in Singkep Island. The waste should be processed to recover and purify precious metals within, and to reduce environmental degradation. REE-bearing minerals identification in tin tailing based on trace and rare earth element abundances is the aim of this study. Concise mineral beneficiation is illustrated for any further re-work strategy. The tailings collected from four locations in Singkep were analyzed for their trace and rare earth element compositions using ICP-MS at The Centre for Geological Survey. REE content in concentrates was upgraded at the range of 9 to 94 folds of the corresponding wastes. Monazite-(Ce), xenotime, and zircon are the REE-bearing minerals of the studied samples according to the elemental composition. Gravity, flotation, magnetic, and electrostatic methods would be applicable to separate the REE-bearing minerals from the tailing.

Improved borate fusion technique for determination of rare earth elements in electronic waste components

ABSTRACT The information regarding the abundance of rare earth elements (REEs) in electronic waste components (EWC) helps the recycling industry. However, after the end of use, improper disposal may be detrimental to the environment by releasing toxic substances. An optimised alkaline borate fusion method for REEs determination in electronic waste (e-waste) was developed. It is divided into three phases. Firstly, the sample preparation stages were investigated. Secondly, the optimisation of experimental particulars comprises the choice of oxidiser, flux composition, non-wetting agents, fusion time, and sample to flux ratio. The third phase consists of spectroscopic determination by inductively coupled plasma optical emission spectroscopy (ICP-OES) and X-ray fluorescence (XRF) spectroscopy. The highest REEs recovery (mg/g of e-waste) were found more in fine fractions of less than 0.09 mm compared to gross fractions. The optimum and safe fusion conditions for e-waste were achieved after slow thermal decomposition up to 550°C, pulverisation to 90% of –53 µm, flux composition (90%LiBO2 + 10% Li2B4O7), 3:1 oxidant ratio of Na2CO3: NaNO3, LiBr as the non-wetting agent. Also, a sample to flux ratio of 1:15 and a total fusion time of 10 min was optimised. The newly improved alkaline fusion results compared better to those obtained from classical mineral acid dissolution with at most 5% RSD on REEs studied. The alkaline borate fusion results in smartphones e-waste were at least 15% and 25% higher than in four acid digest and microwave-assisted digest techniques, respectively. The results indicated enrichment of REEs in smartphones followed by non-smartphones and computer waste.

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.

Relationships among the Geordie Lake Cu-Pd deposit, alkaline basalt, and syenites in the Coldwell Complex, Midcontinent Rift, Canada

ABSTRACT The Geordie Lake Cu-Pd deposit is associated with troctolite at the base of the Geordie Lake intrusion, located near the center of the Coldwell Complex (1106.5 + 1.2 Ma). It is the only platinum group element deposit in the Midcontinent Rift associated with alkaline rocks. This study focuses on the long-standing questions regarding genetic relationships among the Geordie Lake gabbros, the Wolfcamp basalt, and the various syenites that make up the east-central portion of the Coldwell Complex. Primitive mantle-normalized trace-element patterns for the Geordie Lake intrusion are nearly flat from Th to Ce and show negative Sr, Eu, and Zr anomalies. Characteristic ratios for the Geordie Lake gabbro and troctolite include Th/Nb (0.12), La/Nb (1.1), La/Lu (150), La/Sm (6.9), Zr/Sm (18), and Gd/Yb (2.8). Trace-element patterns that are useful for determining petrogenesis for gabbros are similar to the Wolfcamp basalt and augite syenite with some key exceptions, notably the middle rare earth element and Zr abundances. Affects due to metasomatism or crustal contamination in Wolfcamp basalt and Geordie Lake gabbros and syenites are negligible. Results of Rayleigh fractionation modeling show (1) the Geordie Lake intrusion and Wolfcamp basalt are very similar but not directly related by crystallization, (2) the gabbros and basalt are not related to the syenites, (3) the lower augite syenite can be related to the upper augite syenite and amphibole quartz syenite by fractionation of a hypothetical crystal cumulate composed of orthoclase (78%), clinopyroxene (15%), olivine (1%), and titanomagnetite (6%). We conclude that the Geordie Lake intrusion, Wolfcamp basalt, and saturated syenites in the Coldwell were derived by separate partial melting events in a common mantle source. The origin of the sulfide mineralization is enigmatic because it exhibits characteristics of both magmatic and hydrothermal processes. The sulfide assemblage changes from disseminated bornite and chalcopyrite in the basal zone to pyrrhotite plus chalcopyrite in the upper zones. Sulfides occur as coarse blebs interstitial to fresh or partly altered silicates, or as very fine grains intergrown with clusters of biotite and actinolite. Primitive mantle-normalized platinum group element patterns exhibit a W-shape for Pd-Pt-Rh-Ir-Ni, indicating a relative depletion of Pt and Ir. The Cu/Pd ratios in the mineralized zones are within the range of mantle values (1000–10,000), Pd/Pt is 14–19, Pd/Rh is 91 + 37, and Pd/Ir &amp;gt;16,000. The Pd/Pt, Pd/Rh, and Pd/Ir are considerably higher than in the Wolfcamp basalt (&amp;lt;1, 17, and 75, respectively). If the sulfides are magmatic in origin, then either the Geordie Lake magma was, unlike the Wolfcamp basalt magma, depleted in Pt, Rh, and Ir, or these elements were selectively removed from the sulfide assemblage. Alternatively, Pd was enriched by late-stage hydrothermal processes. Additional work is recommended to constrain petrogenesis of the sulfides by detailed base-metal and TABS (Te, As, Bi, Sb, and Sn) element analysis.

Enrichment and Fractionation of Rare Earth Elements in an Estuarine Marsh Soil Receiving Acid Discharges from Legacy Sulfide Mine Wastes

This paper provides new insights into the geochemical cycling of rare earth elements (REEs) in acid sulfate soils developed on salt marsh sediments of the Huelva estuary (Spain) as a result of sulfide mineral oxidation in abandoned ore stockpiles. The study was aimed at determining the REE abundance, fractionation pattern and mineralogical control of the dispersal and retention of REEs in the soil system. Forty-one samples were collected at 13 core sampling sites along two transects extending across the degraded marshland, and they were subjected to XRD, ESEM-EDS and ICP-MS analyses. Measurements revealed that the soil receiving acid discharges has relatively high concentrations of ΣREEs (174.77 ± 19.77 mg kg−1) compared to local baseline concentrations. Shale-normalized REE patterns are generally flat, but a slight middle REE (MREE) enrichment is consistently apparent in all soil samples, involving relatively low LaN/GdN ratios (0.83 ± 0.08) and GdN/LuN ratios up to 1.42. The convex-upward REE pattern supports the possibility that iron oxy-hydroxide minerals play an important role in MREE retention through adsorption and co-precipitation mechanisms. Efflorescent sulfate salts left on the topsoil by the evaporation of acid waters show a strong depletion of light REEs (LaN/GdN = 0.16 ± 0.10) and act as a temporary reservoir of labile MREEs and heavy REEs during dry periods.

Non-KREEP origin for Chang\u2019e-5 basalts in the Procellarum KREEP Terrane

Mare volcanics on the Moon are the key record of thermo-chemical evolution throughout most of lunar history1–3. Young mare basalts—mainly distributed in a region rich in potassium, rare-earth elements and phosphorus (KREEP) in Oceanus Procellarum, called the Procellarum KREEP Terrane (PKT)4—were thought to be formed from KREEP-rich sources at depth5–7. However, this hypothesis has not been tested with young basalts from the PKT. Here we present a petrological and geochemical study of the basalt clasts from the PKT returned by the Chang’e-5 mission8. These two-billion-year-old basalts are the youngest lunar samples reported so far9. Bulk rock compositions have moderate titanium and high iron contents with KREEP-like rare-earth-element and high thorium concentrations. However, strontium–neodymium isotopes indicate that these basalts were derived from a non-KREEP mantle source. To produce the high abundances of rare-earth elements and thorium, low-degree partial melting and extensive fractional crystallization are required. Our results indicate that the KREEP association may not be a prerequisite for young mare volcanism. Absolving the need to invoke heat-producing elements in their source implies a more sustained cooling history of the lunar interior to generate the Moon’s youngest melts.

Cerium exposure in Lake Taihu water aggravates microcystin pollution via enhancing endocytosis of Microcystis aeruginosa

Aggravating the pollution of microcystins (MCs) in freshwater environments is detrimental to aquatic living organisms and humans, and thus threatens the stability of ecosystems. Some environmental factors have been verified to promote the production of MCs in Microcystis aeruginosa, thereby aggravating the pollution of MCs. However, the effects of cerium (Ce), the most abundant rare earth element in global water environments, on the production of MCs in M. aeruginosa are unknown. Here, Lake Taihu water was selected as a representative of freshwater environments. By using interdisciplinary methods, it was found that: (1) the exposure level of Ce [Ce(III) and Ce(IV)] in Lake Taihu water is in the range of 0.271–0.282 μg/L; (2) Ce exposure in Lake Taihu water promoted the contents of three main MCs (MC-LR, MC-LW and MC-YR) in M. aeruginosa and water; (3) a cellular mechanism of Ce promoting the production of MCs in M. aeruginosa in Lake Taihu water was suggested: Ce enhanced endocytosis in cells of M. aeruginosa to promote the essential element uptake by M. aeruginosa for MC synthesis. Thus, Ce exposure in Lake Taihu water aggravates the pollution of MCs via enhancing endocytosis in cells of M. aeruginosa. The results provide reference for assessing the environmental risk of Ce in water environments, investigating the mechanism of the pollution of MCs induced by environmental factors, and developing strategies aimed at preventing and controlling the pollution of MCs.