REE Enrichment Research Articles

Evidence of crustal reworking in the Mesoarchean: Insights from geochemical, U-Pb zircon and Nd isotopic study of a 3.08–3.12 Ga ferro-potassic granite-gneiss from north-eastern margin of Singhbhum Craton, India

Evidences of Mesoarchean crustal reworking are not very common in geological records, being only found from Precambrian terrains like Kaapvaal and Pilbara Cratons where it is preserved as anorogenic/post-collisional granitic activity of 3–3.2 Ga age. The present study focuses on a granitoid unit of similar age, found near the eastern margin of the Precambrian Singhbhum Craton of eastern India. This ellipsoidal, N-S trending, well-foliated granite-gneiss body is found within the polydeformed, metasedimenatry rocks of Singhbhum Group, belonging to the North Singhbhum Mobile Belt. LA-ICP MS U-Pb analysis of zircon grains from one sample give crystallization ages ranging from 3079.4 ± 6.8 Ma to 3115 ± 10 Ma. These rocks hereby dubbed as “Bangriposi Granite Gneiss”, are composed of quartz, alkali feldspar, ferroan biotite (Fe/Fe + Mg: 0.7–0.9), titanite, illmenite, hastingsite, apatite, and numerous U-Th-REE- bearing accessory phases. They have high SiO2 (67–77 wt%) and Na2O + K2O (8.19–9.01 wt%), low CaO (0.35–1.5 wt%), MgO (0.05–0.36 wt%) and shows enrichment of Nb, Rb, Zr, Y, Th, and REEs, and depletion of Cr, Ni, U, with high FeOt/FeOt + MgO (~0.9), Ga/Al (2.04–3.51), (La/Yb)N (6.5–13), and low Eu/Eu* (0.11–0.47). Geochemically and mineralogically they are categorized as metaluminous to weakly peraluminous (A/CNK: 0.9–1.1) ferro-potassic alkali feldspar granites. These rocks show unequivocal affinities towards ‘A-type” granites and from geochemical evidences it is suggested that the parent magma was produced in response to crustal anatexis under low fO2 with P-T estimates of ~900 °C and 7–8 kbar. Geochemical modelling has revealed that the probable source was lower crustal amphibolites belonging to the Paleoarchean Older Metamorphic Group, which suffered low degrees (5–15%) of melting. Negative ƐNd values (−0.5 to −1.5) are also in favour of reworking of older crust and their Nd isotopic signature bears similarities with other coeval anatectic granites. Bangriposi Granite-Gneiss, along with Mayurbhanj Granite and Bonai Granite, represent a major phase of Mesoarchean anorogenic/post-collisional granitic activity in Singhbhum Craton, indicating the onset of its stabilization. Similar Mesoarchean crustally reworked felsic units are encountered in Pilbara and Kaapvaal cratons suggesting a possibility of correlation with the hypothesized “Vaalbara” supercontinent.

Unique sodic–calcic skarn hosted by ultramafic rocks and albitite at the Ulsan skarn deposit, Gyeongsang Basin, South Korea

The Ulsan Fe–W skarn deposit is located within the Cretaceous Gyeongsang Basin in the southeastern part of the Korean Peninsula. The skarn and mineralization formed along contacts between the Paleogene Gadaeri granite, limestone, partially serpentinized ultramafic rocks (dunite and harzburgite), and hornfelsed volcanic and siliciclastic rocks. These various country rock types produced a system with multiple types of skarn. Typically, skarn within limestone occurs as clinopyroxene–magnetite skarn, clinopyroxene–garnet skarn, and garnet skarn, but the unique host rocks (ultramafic rocks + albitite) at Ulsan also produced unusual skarn types such as a sodic–calcic skarn system. Na–Ca skarn formed by chemical interactions between albitized granites and adjacent ultramafic rocks. This Na–Ca skarn contains unusual Na-rich clinopyroxene (acmite), Na-rich amphiboles, Cr-rich clinopyroxene, Cr-rich amphiboles, Sr-bearing plagioclase, and Ba-bearing K-feldspar. Clinopyroxene and amphibole have Na2O concentrations up to 6.5 wt%, and these minerals contain up to 12.1 and 2.5 wt% Cr2O3, respectively. Na was derived from albitite, and the formation of Cr-bearing acmite (kosmochlor) and Na-amphibole (richterite) appears to have been related to the release of Cr into the fluid phase by the breakdown of chromite in ultramafic rocks during prograde skarn formation. K-feldspar K–Ar dating yields an age of 50.3 ± 1.7 Ma for the prograde garnet skarn. The related Gadaeri granite exhibits a high-K calc-alkaline signature and a weakly metaluminous to peraluminous I-type affinity with a total alkalinity (Na2O + K2O) of 8.5–8.8 wt%. The Gadaeri granite shows an enriched REE pattern compared with albitite, as well as negative Eu anomalies, which together with the K/Rb values (200–500) are suggestive of a highly evolved magma from a continental-margin setting.

Rare earth element contents in high pCO2 groundwaters of Sakhalin Island (the Far East of Russia)

The geochemistry of rare earth elements in cold, high pCO2 mineral waters was studied through the sampling of springs and boreholes of Sakhalin Island (the Russian Far East). The main common features of studied waters are the Na-Cl-HCO3 hydrochemical type, high TDS (6–20 g/L), alkaline pH (6.2–7.4), and reducing environment (-195 to +62 mV). The North American Shale Composite-normalized patterns of groundwaters exhibited a heavy REEs enrichment with high positive Eu anomalies. Both, positive and negative Ce anomalies were detected in CO2-rich mineral waters. The distinct positive Eu/Eu* in waters indicates water-rock interaction processes and positive Ce/Ce* corresponds to reducing conditions. The various processes responsible for negative Ce anomaly in reducing environment are described.

The unique Abramovka REE-rich mineralization is a potential source of REE for the Pavlovsk coals deposit (Primorsky Krai, Russia)

The unique REE mineralization of the Abramovka ore occurrence, associated near-surface waters, and REE-rich coals of the Pavlovka basin were studied. The authors, on the base of new isotope-geochemical data and K-Ar dating, suggest that the Abramovka REE minerals (hydrocarbonates, hydrophosphates and hydroxides) formed as a result of interaction of the Palaeozoic metasedimentary and Mesozoic volcanic rocks with near-surface waters. In the Pavlovka metalliferous coals, REE are concentrated predominantly in a humic matter that sorbed REE from water solutions during the peat accumulation stage. A similar distribution of REE in the Abramovka ores, associated near-surface waters, and metalliferous coals of the Pavlovka basin suggest that the Abramovka-type mineralization might be a major source of REE enrichment in the Pavlovka coals.

REE patterns and trustworthiness of stable carbon isotopes of Salitre Formation, Irecê Basin (Neoproterozoic), São Francisco Craton

Neoproterozoic limestones have been subject to variations in their original isotopic ratios, which has led to studies to verify the reliability of isotopic data obtained in these rocks. A Brazilian example of Neoproterozoic carbonate succession is found in Irecê Basin (BA) (Salitre Formation, São Francisco Supergroup). The present research aims to evaluate the reliability of the δ13C, mainly through REE patterns of samples gathered in Upper Nova America Unit. This unit represents an intermediate section included in a thick carbonate cover that represents the Salitre Formation. X-Ray fluorescence and inductive plasma mass spectrometry (ICP-MS) techniques were used to obtain elemental geochemistry. X-ray diffraction, including the fraction < 4 μm, and microscope with coupled fluorescence were used to verify the presence of carbonate, organic matter, siliciclastic phases and their proportions. Samples are mainly calcitic and have REE patterns with enrichment of light REEs, strong positive La anomalies, slightly positive Ce anomalies, variety of Gd anomalies, absence of strong Y anomaly and Y/Ho ratio of 31.5 ± 1.5. These anomalies indicate a mixture of oceanic and fresh waters during precipitation. Ce positive anomalies indicate anoxic states of early digenetic conditions of the environment. δ13C values have little contrast around 0‰. As a result, calcareous from Nova América Unit precipitated under shallow depths on carbonate platform. High concentration of Zr and SiO2 suggests high rates of weathering on marginal belts of São Francisco craton through high energy input of detrital material by freshwater. On the other hand, low concentration of Al2O3 indicates deposition of clay minerals occurred in a mild area of the plataform. The Mn/Sr and Fe/Sr ratios did not indicate the presence of significant diagenetic or metamorphic alterations. From the petrographic point of view, the samples do not present preserved organic matter, but they are recrystallized instead, sometimes dolomitized and dissolution features are present. The results indicate that Nova América limestones were precipitated on shallow carbonate restricted platform close to the coastline prone to fresh water and detrital input, therefore, δ13C does not correspond to the isotopic composition of the global ocean.

Geochronology and geochemistry of the Yazidaban ophiolitic mélange in Qimantagh: constraints on the Early Paleozoic back-arc basin of the East Kunlun Orogen, northern Tibetan Plateau

The East Kunlun Orogenic Belt of the northern Tibetan Plateau can be divided by the Qimantagh–Xiangride, Aqikekulehu–Kunzhong and Muztagh–Buqingshan sutures into, from north to south, the Northern Qimantagh, Central Kunlun and Southern Kunlun belts. The Yazidaban ophiolitic mélange, located in the westernmost region of the Qimantagh–Xiangride suture between the Northern Qimantagh and Central Kunlun belts, consists predominantly of serpentinite, basalt, diabase and andesite. The serpentinites are characterized by low total rare earth element (ΣREE) concentrations and depletion of mid-REEs, showing an ophiolitic ultramafic affinity. The basalts have low ΣREE concentrations, a slight enrichment in light REEs, depletion of large ion lithophile elements and insignificant fractionation of high field strength elements, which are attributed to an incompatible element-enriched mid-ocean ridge basalt. Both diabases and andesites are characterized by high ΣREE, strong enrichment in light REEs, depletion of Nb, Ta, P and Ti, and significant fractionation of high field strength elements. These geochemical characteristics indicate that the diabase and andesite were mostly generated in a subduction-related setting. Igneous zircons from the diabase yielded a 206 Pb/ 238 U age of 421.5 ± 2.2 Ma (MSWD = 0.44), representing the formation time of the subduction-related rocks. Together with the regional geology, these constraints on the ultramafic rock, basalt, andesite and diabase suggest that the Yazidaban ophiolitic mélange represents the remnants of oceanic crust from a back-arc basin and the associated subduction-related magmatic rocks. Supplementary material: Details of U–Th–Pb laser ablation inductively coupled plasma mass spectrometry data of zircons from the diabase, and major and trace element compositions for the samples from the Qimantagh mélange, East Kunlun Orogen are available at https://doi.org/10.6084/m9.figshare.c.4283219

Petrochemistry of the metasomatized Neoarchean Lower Transvaal Supergroup carbonate from the Kanye Basin (south Botswana)

The Taupone Dolomite Group (Lower Transvaal Supergroup) is a carbonate platform sequence that rimmed the north western Kaapvaal Craton during the Neoarchean-Paleoproterozoic (ca. 2.6–2.5 Ga). The dolostones of the Taupone Dolomite Group in Botswana are known as the Ramonnedi Formation. These carbonates have been intruded by the granitoids and dolerites of the Moshaneng Igneous Complex (ca. 2.1 Ga) and the Moshaneng Dolerites (ca. 1.9 Ga), which have induced alteration of the Ramonnedi Formation dolostones, thus resulting in calc-silicate metasomatism. Metasomatism of the dolostone host rock induced mobilization of Mg with formation of Mg-bearing silicates and calcite, which has replaced dolomite as dominant carbonate phase. The mineral assemblage of the metasomatised dolostones of the Ramonnedi Formation consists of calcite, chrysotile, talc, fibrous and equant crystals of amphibole, phlogopite, diopside and small amounts of epidote and forsterite. The electron probe-micro-analyzer (EPMA) data generally indicate the presence of Fe-poor amphiboles (tremolite) and minor amounts of Mn-rich fibrous tremolite. The overall Cl-chondrite-normalized REE patterns vary consistently across the studied samples with some samples showing light REE (LREE) and medium REE (MREE) enrichment. The samples show variable Ce and Eu anomalies and near chondritic Y/Ho ratio. The distribution of Eu anomaly suggests that the emplacement of the granitoids of the Moshaneng Igneous Complex has induced prograde metasomatism and fluids characterized by K enrichment and Eu depletion. On the other hand, the emplacement of plagioclase-rich Moshaneng Dolerites has induced formation of fluids characterized by high positive Eu-anomaly due to the breakdown of plagioclase in the dolerites.The presence of diopside, tremolite and phlogopite in the altered samples can be attributed to prograde contact metamorphism and/or prograde metasomatism reflecting an increasing hydrous condition away from the intrusion. The alteration minerals show a coarse-grained texture suggesting that these minerals most likely derive from prograde metasomatism, whereas evidences for contact metamorphism have not been observed.

Petrology of saprolite developed on gneisses in the Matomb region, south Cameroon

The petrological study of saprolite developed on gneisses in the Matomb region (South Cameroon) was carried out by petrographic, mineralogical and geochemical analyses. The gneisses have a granoblastic heterogranular texture and are made up of quartz, biotite, feldspars, kyanite, garnet, rutile and enstatite. Chemically, they show high contents in SiO2 (64.93%), Ba (723 ppm), Sr (347 ppm), V (135 ppm), Zr (126 ppm) and moderate contents in Al2O3 (15.24%). The REE content is low (99.12%) with a slight positive Eu anomaly and no Ce anomaly. From bottom to top, the soil is composed of a coarse saprolite and fine saprolite. The coarse saprolite is mainly sandy, showing gray, pink, red phases as well as white loamy sand and yellow sandy loam phases. The main minerals are quartz, kaolinite, gibbsite, goethite, hematite, biotite, muscovite, kyanite and rutile. In addition, the coarse saprolite also contains chlorite, smectite, vermiculite and chlorite-vermiculite. The fine saprolite is composed of white, pink and red brown phases. They have a similar mineral assemblage, with the exception of the concomitant disappearance of biotite and 2/1 clay minerals which certainly represent the first fugacity steps of biotite weathering. The SiO2 content decreases from the coarse saprolite to the fine saprolite compared to the parent rock, but the white sample of the fine saprolite shows high SiO2 (70.31%) content. The Al2O3 content increases up the profile while the Fe2O3 content is variable. The white samples show low Fe2O3 values (4.07–0.19%). The red material is particularly rich in Fe2O3 (15.32%). Ba, Zr, Zn and V show high contents in the profile. Cr (967.00 ppm) shows the highest value in the profile and U (1982 ppm) content is very high in one of the pink materials of the fine saprolite. SiO2 has negative correlation with Al2O3, Fe2O3, TiO2, Zr, Ni and V. The correlations of Fe2O3 with Cr and V are positive. The correlations between Zr and Th, Nb, Hf are positive. The REE contents increase up the profile and fluctuate in the saprolite phases. The white samples are very poor in REE. The Matomb soil samples show positive Ce anomalies and negative Eu anomalies probably due to the depletion of Eu, the relative enrichment of other REE or to the absence of carrier minerals. Contrary to what has always been observed in the South Cameroon plateau, the white samples of the fine saprolite show positive Eu anomalies. This could be indicative of the probable presence of other carrier minerals apart from feldspars which always occur in this milieu or the leaching of some elements. The (La/Yb)N < 1 ratio in some weathered phases indicates a high mobility of LREE in these materials. Mass balance shows that the transition from the rock to the weathered materials is accompanied by a strong depletion of several elements particularly HREE and a moderate LREE enrichment. Thus, the relative mobility of elements determines the colour differenciation of phases in the saprolite.

Iron-oxides constrain BIF evolution in terranes with protracted geological histories: The Iron Count prospect, Middleback Ranges, South Australia

When studied at appropriate scales of observation and using complementary methods, the intrinsic textural and geochemical complexity of iron-oxides can provide unparalleled insights into the evolution of iron ore resources from banded iron formation deposition to ore formation. Iron Count is one of >20 deposits and prospects within the Archean Middleback Ranges iron ore belt, South Australia, in which iron-oxides from BIFs and ores display variable textural and trace element signatures. Integrated petrography, iron-oxide laser-ablation mapping and geochemistry, and in-situ dating of BIF-derived ores was undertaken to assess whether features observed in samples from this representative prospect might be attributed to localized and superimposed overprint processes.The prospect consists of a West and East ridge, each characterized by a sequence of overprints expressed as interconversions between iron-(hydr)oxides and accompanying variation in trace element concentrations. Pseudomorphic replacement of early magnetite by hematite (martite), followed by replacement by iron-hydroxides is recognized in samples from the East Ridge. Further overprints are expressed as veining, brecciation and crystallization of (micro)platy hematite rich in granitophile elements (Sn, Mo, W, U). Martitization of early magnetite in the West Ridge is accompanied by enrichment in Zn, Co and Ni in martite. Subsequent recrystallization of martite/iron-hydroxides by granoblastic hematite is marked by enrichment in Ti, Ta, Nb, REE and granitophile elements, and co-crystallization of REE-minerals. This is followed by crystallization of (micro)platy hematite, similarly rich in these elements. Enrichment in Ti and granitophile elements in granoblastic hematite is interpreted to infer crystallization from highly saline fluids generated by interaction between evaporite-bearing sedimentary rocks and granite-derived fluids. Post-Archean Australian Shale-normalized REY fractionation trends of iron-oxides from the East Ridge are consistent with precipitation of iron-rich minerals from a mixture of anoxic seawater and hydrothermal vent fluids. Analogous trends from the West Ridge lack a seawater signature. Contrasts in REY fractionation trends between the two ridges is interpreted as a combination of the loss of primary seawater signature due to severe overprinting in the West Ridge, and to lateral variation in the marine depositional environment. Results validate the hypothesis that variation in iron-oxide trace element signatures seen throughout the Middleback Ranges iron ore belt results from overprinting due to superimposed tectono-magmatic events that have locally affected each deposit. Despite undergoing different sequences of ore-forming stages, as well as possibly distinct depositional environments, the two ridges share a common overprint, dated here at ~1790 Ma using in-situ UPb geochronology of co-existing hematite, monazite and xenotime. This age is considered to represent the timing of interaction between granite-derived fluids with ore-hosting rock. Such interpretation is supported by the geochemical signatures of the dated iron-oxides showing enrichment in granitophile elements and coincident ages for the Wertigo Granite and Myola Volcanics, which occur proximal to the prospect and were emplaced/erupted during intracontinental rifting. The approach undertaken here, combining petrography, iron-oxide geochemistry and in-situ dating of BIF-derived ores is generically applicable to other iron resources within the Middleback Ranges or analogous terranes elsewhere.

Mineralogy, geochemistry, petrography, and depositional environment of Gebel El-Qurn, Early Eocene, West Luxor, South Egypt

BackgroundLuxor represented the modern Egyptian city that occupies the site of ancient Thebes. Thebes Mountain on the West Bank of the Nile, opposite the town of Luxor, is among the most famous historical sites of the world. Carbonate rocks exposed at Gebel El-Qurn, west Luxor, south Egypt has been investigated for mineralogical, petrographical, and geochemical studies to illustrate its depositional environments.ResultsWe revealed that the carbonate rocks in the Gebel El-Qurn, west Luxor, are mainly of Lower Eocene age. The carbonate rocks that belong to the Thebes Formation were deposited under shallow, warm, oxidizing, open marine environment. Petrographically, they are differentiated into five microfacies: (1) nummulitic bioclastic wackestone/mudstone, (2) nummulitic biosparite grainstone, (3) nummulitic rudstone microfacies, (4) pelecypod biomicrite wacke/packstone, and (5) biomicrite dolomitic lime-mudstone. Diagenetically, carbonate rocks were subjected to cementation, compaction, neomorphism, dissolution, and dolomitization processes. Mineralogically, XRD revealed that the studied carbonate samples consist mainly of calcite as well as dolomite, quartz, halite, pyrite, and clay minerals. EDX data indicated that the dolomite of the Gebel El-Qurn is non-stoichiometric in composition, and the size of crystals is up to 80 μm.Geochemically, the carbonate rocks of the Gebel El-Qurn are impoverished in Sr and Na content. This may be attributed to the diagenetic processes, which took place under less saline environment than seawater. Dolomite crystals were formed by re-crystallization under mixed marine-meteoric environment. The positive correlation between Sr and Fe2O3 indicates that the studied carbonates were deposited under control of bacterial activity. The studied carbonate rocks are characterized by light REE (LREE) enrichment with respect to heavy REE (HREE). The total radioactivity measurements are ranging from 4 to 5.9 ppm for U and from 5.5 to 6.6 ppm for Th. The radioactivity measurements are less than the background level of carbonates, and they are in the permissible limits for carbonates used in cement industries and as building stones.ConclusionsThe petrographical and geochemical observations, as well as mineralogical investigation, indicate that the carbonate rocks in the Gebel El-Qurn were deposited in a shallow, warm open marine environment.

Detrital zircon record of Mesozoic volcanic arcs in the Lower Cretaceous Mural Limestone, northwestern Mexico

The northwestern part of Mexico, southern Arizona, and southern California witnessed extensive arc magmatism during Late Triassic to Early Cretaceous. Here, we present results from petrography, whole‐rock geochemistry (major and trace including rare‐earth elements), and detrital zircon geochronological studies that were carried out on sandstones and shales of the Mural Limestone exposed in the Rancho Bufalo area. Based on the petrography, sandstones are classified as sublitharenite, litharenite, feldspathic litharenite, and lithic arkose. The sandstones contain higher proportion of monocrystalline quartz than polycrystalline quartz. Sandstones and shales from the various members of the Mural Limestone show large variations in major and trace elements concentrations. The average concentrations of ΣREE (total ΣREE) are lower in sandstones than in shales. The chondrite‐normalized REE patterns of the sandstones and shales are moderately fractionated with light REE (LREE) enrichment relative to heavy REE (HREE) and with flat to slightly depleted HREE patterns. The chemical index of alteration values and A–CN–K relationships of sandstones indicate low to moderate intensity of weathering in the source region; however, shale samples suggesting the source rocks were subjected to moderate intensity of chemical weathering. The chondrite‐normalized REE patterns, Al2O3/TiO2ratio, elemental ratios like Cr/V, Y/Ni, and Eu‐anomaly (Eu/Eu*), and bivariate plots suggest that the sandstones and shales were derived mainly from felsic source rocks. Detrital zircon U–Pb geochronology of sandstones from Fronteras, Rancho Bufalo, and Cerro La Ceja members of the Mural Limestone show five main groups of detrital zircon age populations: (a) Proterozoic, (b) Palaeozoic, (c) Triassic, (d) Jurassic, and (e) Early Cretaceous. Our study suggests that continental volcanic arcs in northwestern Mexico, southern Arizona, and southern California served as the provenance for the Late Triassic‐Jurassic detritus, whereas the Early Cretaceous zircon grains were derived mainly from the active Alisitos volcanic arc along the northwestern coast of Mexico.

Ghosts of Apatite Past: Using Hyperspectral Cathodoluminescence and Micro-Geochemical Data To Reveal Multi-Generational Apatite in the Gifford Creek Carbonatite Complex, Australia

Apatite can host significant levels of trace elements, including REE, within its crystal lattice, making it particularly useful for deciphering geological events and processes. This study employs hyperspectral cathodoluminescence (CL) and in situ microchemical techniques to identify and characterize various generations of apatite occurring in the phoscorites, carbonatites, and fenites of the Gifford Creek Carbonatite Complex (GCCC), Western Australia. Hyperspectral CL revealed that apatite crystals in all samples have complex internal zoning, including multiple distinct generations, with zones of relatively bright CL generally having more complex spectra compared to darker CL zones. Most of the CL spectra have prominent sharp peaks at similar to 1.4 eV and similar to 2.l eV as well as a broad peak between 2.3 eV and 3.5 eV. We relate these different peaks to individual REE activators and groups of activators, in particular Nd3+, Eu3+, Sm3+, and Ce3+. Trace element analyses of apatite confirm the relative enrichment of REE in the CL brighter zones. Most apatite generations exhibit concave-down to sinusoidal REY patterns lacking Eu anomalies, but often feature distinct negative Y anomalies. The depletion in LREE is interpreted to be due to LREE sequestration into monazite, which is relatively abundant in most of the samples. Most apatite samples contain very low Si contents, but appreciable Na, so REE incorporation into apatite was primarily via a coupled substitution of REE + Na replacing 2Ca, which is consistent with the highly alkaline, low SiO(2 )environment under which the apatite formed. Based on the combined trace-element signatures and CL textures, we interpret the multiple generations of apatite to reflect magmatic growth from alkaline magmas followed by recrystallization during subsequent metamorphic/hydrothermal events. The notable exception is the apatite core domains from a fenite sample that contain relatively high Si and Mn contents, low Sr, and relatively HREE-enriched REY patterns with distinct negative Eu anomalies. This apatite is interpreted to be relict from the granitic precursor to fenitization. The apatite samples also show systematic compositional variations across the GCCC, with apatite from phoscorite samples from the southeast part of the complex containing higher Sr, lower Gd/Ce, and lower lambda(3 )values (normalized REE pattern inflections) compared to apatite from the northwest part of the complex. Recognition of these spatial variations in apatite compositions from the intra-grain micro-scale through to the district scale demonstrates the utility of combining advanced petrographic methods, such as hyperspectral CL, with micro-chemical analysis to reveal complex geological records preserved in apatite. As apatite is a common accessory mineral, these techniques may be more broadly applicable to igneous source tracing, understanding metamorphic and/or metasomatic processes, provenance studies from detrital mineral records, and studies of the evolution of ore systems.

Alkaline magmas in zones of continental convergence: The Tezhsar volcano-intrusive ring complex, Armenia

Alkaline igneous rocks are relatively rare in settings of tectonic convergence and little is known about their petrogenesis in these settings. This study aims to contribute to a better understanding of the formation of alkaline igneous rocks by an investigation of the Tezhsar volcano-intrusive alkaline ring complex (TAC) in the Armenian Lesser Caucasus, which is located between the converging Eurasian and Arabian plates. We present new petrological, geochemical and SrNd isotope data for the TAC to constrain magma genesis and magma source characteristics. Moreover, we provide a new 40Ar/39Ar age of 41.0 ± 0.5 Ma on amphibole from a nepheline syenite that is integrated into the regional context of ongoing regional convergence and widespread magmatism.The TAC is spatially concentric and measures ~10 km in diameter representing the relatively shallow plumbing system of a major stratovolcano juxtaposed by ring faulting with its extrusive products. The plutonic units comprise syenites and nepheline syenites, whereas the extrusive units are dominated by trachytic-phonolitic rocks. The characteristic feature of the TAC is the development of pseudomorphs after leucite in all types of the volcanic, subvolcanic and intrusive alkaline rocks.Whole-rock major element data show a metaluminous (Alkalinity Index = 0–0.1), alkalic and silica-undersaturated (Feldspathoid Silica-Saturation Index <0) character of the TAC. The general trace element enrichment and strong fractionation of REEs (LaN/YbN up to 70) indicate a relatively enriched magma source and small degrees of partial melting. All TAC rocks show a negative NbTa anomalies typical of subduction zone settings. The initial 87Sr/86Sr ratios (0.704–0.705) and positive εNd values (+3 to +5) indicate an isotopically depleted upper mantle and lack of significant crustal influence, which in turn suggests the TAC magma has formed via differentiation from lithospheric mantle melts.Regionally, the age of ~41 Ma places the TAC amid a Lesser Caucasian Eocene period of dominantly calc-alkaline magmatism. The TAC's arc-like geochemical signatures are interpreted to result from prior subduction of the Tethyan slab beneath the Eurasian continental margin. The alkaline character, distinct from regional trends, is attributed to Neotethyan slab rollback causing extension and inducing small degrees of decompression melting of metasomatised lithospheric mantle.

The ca. 2785–2805 Ma High Temperature Ilivertalik Intrusive Complex of Southern West Greenland

Ferroan granitoid intrusions are rare in the Archaean rock record, but have played a large role in the evolution of the Proterozoic crust, particular in relation to anorthosite-mangerite-charnockite-granite suites. Here we discuss the petrogenesis of the ca. 2785–2805 Ma ferroan Ilivertalik Intrusive Complex, which has many geochemical similarities to Proterozoic iron rich granitoids. We present major and trace element whole rock chemistry and combined in-situ zircon U-Pb, Hf and O isotope data. The intrusive complex divides into: (i) minor tabular units of mainly diorite-tonalite compositions, which are typically situated along contacts to the host basement and (ii) interior larger, bodies of mainly granite-granodiorite composition. Geochemically these two unites display continuous to semi-continuous trends in Haker-diagrams. Whole rock REE enrichment display increases from Yb to La, from 10–25 to 80–100 times chondrite, respectively. The diorite-tonalite samples are generally more enriched in REE compared to the granite-granodiorite samples. The complex has hafnium isotope compositions from around +1.5 to −2.5 epsilon units and δ18O compositions in the range of 6.3 to 6.6‰. The complex is interpreted to be derived from partial melting in a crustal source region during anomalously high crustal temperatures.

Petrology, geochemistry and U-Pb zircon and baddeleyite ages of the alkaline rocks from the central-southern Guyana Shield, northern Amazonian Craton

The Apiaú Alkaline Complex (AAC) represents a rift-related intracontinental magmatism and occurs as intrusions within the Precambrian basement of the central-southern portion of the Guyana Shield, Amazonian Craton. The complex extends for over 200 km and comprises monzonites, syenites, nepheline syenites, nepheline-bearing syenites, trachytes and phonolites. It differs from other alkaline rocks of the craton both in age and tectonic setting. Here we report new petrologic, geochemical, and zircon and baddeleyite U-Pb geochronological information on the nepheline-bearing syenites and phonolites to discuss the petrogenetic and tectonic evolution of the AAC. Our new bulk rock major and trace elements analyses show that the complex is predominantly miaskitic, with potassic and sodic affinity, strong enrichment in light REE and negative Eu, Ba, Sr, P, and Ti anomalies. The phonolites and syenites geochemistry suggests similar fractionation processes from closely related parental melts for their genesis. Zircon and baddeleyite U-Pb crystallization ages of 111 ± 1 Ma and 116 ± 3, respectively, indicate a relationship between the alkaline magmatism and the opening of the Equatorial Atlantic Ocean. The spatial disposition of the alkaline rocks following major faults of the Amazonian Craton denotes a structurally controlled emplacement history by reactivation of ancient weakness zones. Crystallization ages are coincident with the Tacutu basin filling, evidencing a relative tectonic stability period and suggesting that the progressive subsidence contributed to the reactivation of the main structures in the region. The presence of inherited zircon from the orthoderived granitic basement (U-Pb ages of 1931 ± 4 Ma and 1958 ± 7 Ma) in a nepheline-bearing syenite, addition to petrography features and geochemical behaviour indicate that the alkaline magma was contaminated with Precambrian crustal rocks.

Characterization of anhydrous to hydrous paragenetic sequence from pyroxene-bearing and pyroxene-absent variants of the late Carboniferous Baobei pluton in west Junggar of China

The Baobei pluton in west Junggar, composed of an earlier pyroxene-bearing granitoid and a variety of later pyroxene-absent hornblende–biotite-bearing granitoids (quartz diorite, granodiorite, monzogranite), intrudes early Carboniferous volcano–sedimentary rocks. Zircons separated from the granodiorite provide a U–Pb age of 306.5 ± 2.6 Ma, which represents the age of magma emplacement. The pyroxene-bearing granitoid is porphyritic with phenocrysts of orthopyroxene and plagioclase. Two types of orthopyroxene (Mg-rich Opx-1, Fe-rich Opx-2) occur in the pyroxene-bearing granitoid. Both the Opx-1 and Opx-2 show depletions of light REE and enrichments of heavy REE with negative Eu anomalies. The evolved melt in equilibrium with the Opx-2 contains higher light REE concentrations compared with the parental melt in equilibrium with the Opx-1 based on geochemical modeling. The pyroxene-bearing and pyroxene-absent variants of the pluton record the progression from the anhydrous orthopyroxene–clinopyroxene assemblage to the hydrous hornblende–biotite assemblage. These rocks are high-K calc-alkaline, metaluminous to weakly peraluminous and ferroan, and have similar trace element compositions characterized by light REE enriched and constant heavy REE patterns with enrichments of Pb and depletions of Nb and Ta. The melt corresponding to different granitoids was formed by dehydration melting of basaltic rocks at 4.8–9.7 kbar and 1060–1146 °C within a post-collisional geological setting in west Junggar.

El Seboah peralkaline A-type magmatism, South Western Desert, Egypt: evidences for the HFSE and REE enrichment

El Seboah peralkaline A-type magmatism is one of the numerous alkaline plutonic and volcanic (trachyte, rhyolite, and basalt)/subvolcanic rocks, which are occurring in the South West of Egypt along the Guinean-Nubian lineament. El Seboah magmatic rocks include fresh peralkaline granite and rhyolite dikes (pantellerite). The fresh peralkaline granite intruded the Late Cretaceous Nubia sandstones, and furthermore, the pantelleritic dikes cut it. The fresh peralkaline granite and the pantelleritic dikes show common features of the A-type granites. They contain alkalic mafic minerals such as aegirine and riebeckite in the peralkaline granite or aegirine in the pantelleritic dikes; they also have high alkalis and HFSE (e.g., Zr, Nb, REE, Th, and U) with high ratios of FeOt (total iron)/MgO and Ga/Al, and strong depletions in Ba, Sr, Eu, Ti, and P. Both of the fresh peralkaline granite and the pantelleritic dikes have peralkaline, ferroan, and fertile character, and belong to subgroup A1-type magmas. Additionally, these rocks were formed as separated batches, emplaced within the African plate along the volcanic zone of the Guinean-Nubian lineament, and the source for both rock types is suggested as the ocean island basaltic magmas. Moreover, the pantelleritic magma displays more enrichment in the HFSE than the alkaline granitic magma, suggesting highly fractionated and alkalinity association. The peralkaline granite was subjected to different degrees of hydrothermal alterations along the fault zones. The hydrothermally altered peralkaline granite shows a strong enrichment in the HFSE that occur in minerals such as zircon, bastnaesite-(Ce), monazite-(Ce), percleveite-(Ce), pyrochlore, fergusonite-(Ce), columbite-(Mn), thorite, uranothorite, and amorphous secondary uranium. In addition, it shows a strong increase in the FeOt and CaO and a depletion in Al2O3, MgO, Na2O, and TiO2 with a slight increase in K2O and a slight decrease in SiO2 compared to the fresh peralkaline granite. Consequently, I suggest that the hydrothermally altered peralkaline A-type granite within the El Seboah area as a potential source for the rare metal deposits, but further detailed studies are needed.

Hydrothermal alteration and evolution of Zr-Th-U-REE mineralization in the microgranite of Wadi Ras Abda, North Eastern Desert, Egypt

Ras Abda plutonic suite, North Eastern Desert of Egypt, consists predominantly of Neoproterozoic calc-alkaline older granites. Minor exposures of pink microgranite are occurring along Wadi Ras Abda within the older granites. Previous studies on this area demonstrated that the microgranite is altered in some parts and contains anomalous concentrations of rare metal elements (Zr, Th, and U). These altered and mineralized zones are re-assessed using field observations, chemical analysis, and by the application of various transmitted light and electron microscopic techniques. The rare metals exist as mineral segregation grew freely into open cavities of the microgranite and concordant with the NNE strike-slip fault movement. The mineralized zones contain an assemblage of secondary magnetite, zircon, uranothorite, columbite-(Mn), fergusonite-(Y), and allanite-(Ce). The extreme abundance of zircon in the mineralized zone, along with other evidence, indicates a hydrothermal origin of this zircon together with associated rare metals. The geochemical investigation and mass balance calculations revealed extreme enrichment of Zr, Th, U, Y, Nb, Ta, and REE. Post-magmatic hydrothermal alterations resulted in such pronounced chemical and mineralogical heterogeneity. The hydrothermal fluids are thought to be oxidizing, alkaline and of medium temperature (> 250 °C). The average contents of the elements Zr (1606 ppm), Th (1639 ppm), U (306 ppm), Nb (955 ppm), and REE (1710 ppm) in the mineralized microgranite reach sub-economic levels and could be a potential source of these elements.

Geochemical and Petrological Studies on the Early Carboniferous Sidingheishan Mafic–Ultramafic Iintrusion in the Southern Margin of the Central Asian Orogenic Belt, NW China

The Sidingheishan mafic–ultramafic intrusion is located in the eastern part of the Northern Tianshan Mountain, along the southern margin of the Central Asian Orogenic Belt in northern Xinjiang autonomous region of China. The Sidingheishan intrusion is mainly composed of wehrlite, olivine websterite, olivine gabbro, gabbro and hornblende gabbro. At least two pulses of magma were involved in the formation of the intrusion. The first pulse of magma produced an olivine‐free unit and the second pulse produced an olivine–bearing unit. The magmas intruded the Devonian granites and granodiorites. An age of 351.4±5.8 Ma (Early Carboniferous) for the Sidingheishan intrusion has been determined by U‐Pb SHRIMP analysis of zircon grains separated from the olivine gabbro unit. A U‐Pb age of 359.2±6.4 Ma from the gabbro unit has been obtained by LA‐ICP‐MS. Olivine of the Sidingheishan intrusion reaches 82.52 mole% Fo and 1414 ppm Ni. On the basis of olivine‐liquid equilibria, it has been calculated that the MgO and FeO included in the parental magma of a wehrlite sample were approximately 10.43wt% and 13.14wt%, respectively. The Sidingheishan intrusive rocks are characterized by moderate enrichments in Th and Sm, slight enrichments in light REE, and depletions in Nb, Ta, Zr and Hf. The εNd (t) values in the rock units vary from +6.70 to +9.64, and initial 87Sr/86Sr ratios range between 0.7035 and 0.7042. Initial 206Pb/204Pb, 207Pb/204Pb and 208Pb/204Pb values fall in the ranges of 17.23–17.91, 15.45–15.54 and 37.54–38.09 respectively. These characteristics are collectively similar to the Heishan intrusion and the Early Carboniferous subduction related volcanic rocks in the Santanghu Basin, North Tianshan and Beishan area. The low (La/Gd)PM values between 0.26 and 1.77 indicate that the magma of the Sidingheishan intrusion was most likely derived from a depleted spinel–peridotite mantle. (Th/Nb)PM ratios from 0.59 to 20.25 indicate contamination of the parental magma in the upper crust. Crystallization modeling methods suggest that the parental magma of the Sidingheishan intrusion was generated by flush melting of the asthenosphere and subsequently there was about 10vol% contamination from a granitic melt. This was followed by about 5vol% assimilation of upper crustal rocks. Thus, the high‐Mg basaltic parental magma of Sidingheishan intrusion is interpreted to have formed from partial melting of the asthenosphere during the break‐off of a subducted slab.

Element distribution in fruiting bodies of Lactarius pubescens with focus on rare earth elements

During growth and senescence, fungal fruiting bodies accumulate essential and non–essential elements to different extent in their compartments. This study bases on a dataset of 32 basidiocarps of the ectomycorrhizal Lactarius pubescens sampled in a former U mining area. Statistical analyses were combined with rare earth element (REE, La–Lu) patterns to study the element distribution within sporocarp compartments and between three different age classes. For this purpose, fruiting bodies were separated into stipe, pileus trama, pileipelles and lamellae, dried and digested with HNO3.While macronutrient (e.g. K, Mg, P, S) contents resemble those of a non–mining affected site, several elements (e.g. Co, Mn) were site–specifically taken up relative to elevated soil contents. With statistics, two main element distribution groups for L. pubescens were revealed: mainly essential (Cu, Mg, Mn, P, S, Zn, Cd, Co, Ni) and mainly non–essential elements (Al, Ca, Fe, Sr, U, REE). The highest REE contents were found in pileipelles and lamellae, corresponding to relatively small cell sizes. Stipes and pileus trama had low REE contents due to their function as transport systems. During growth, light REE (La–Nd) were strongly enriched in lamellae and pileipelles. Middle REE (Sm–Dy) enrichment was found both in soil and fungal biomass.Contents of nutrients decrease with age, while non–essential elements are enriched especially in pileipelles and lamellae. A weak positive Ce anomaly appeared in the bioavailable soil fraction and in the pileipelles of younger individuals. Substrate dependent uptake thus gets reduced with sporocarp senescence, possibly due to redistribution.