Light Enrichment Research Articles

Cathodoluminescence and geochemical characteristics of Apatite: Implications for mineral exploration in the Xiongcun District, Tibet, China

Apatite grains from the No. 2 porphyry Cu–Au deposit in the Xiongcun district of Tibet, China, have a range of physical and compositional features. This study investigates the potential use of apatite associated with hydrothermal alteration as a tool for mineral exploration. In situ textural, cathodoluminescence (CL), and chemical analyses were performed on thin sections containing apatite from various alteration zones in the deposit. No clear variation was seen in apatite from rocks of the potassic, sodic–calcic, chlorite–sericite, phyllic, and propylitic alteration zones using visible light and scanning electron microscopy; however, distinct variations were observed in optical cathodoluminescence (OP-CL) (dark yellow to green, orange to green, yellow–brown to green, yellow-orange to brown, and light yellow–brown to green luminescence for the respective zones). The alteration-related differences in luminescence were a result of the interaction between Fe and Mn; the Na and Cl contents; and depletion in total heavy rare earth elements (ΣHREE) and Y. The variations in the REE contents of apatite from different types of altered rock record reactions with Cl- and F-rich fluids. The partitioning behavior of Cl between apatite and hydrothermal fluids is influenced by pressure, temperature, pH, and fluid composition, whereas the partitioning of F between apatite and fluids is dependent on the fluid composition and not the temperature. At high temperatures, Eu3+ is reduced to Eu2+, which results in negative Eu anomalies in apatite from the potassic-altered rocks and propylitic-altered rocks. Apatite grains in the sodic–calcic-altered rocks and chlorite–sericite-altered rocks show a similar enrichment in light REEs (LREEs) that resulted from REE and Y incorporation as follows: Na+ + (Y + REE)3+ = 2Ca2+. Apatite grains in the phyllic-altered rocks are enriched in the middle REEs. This study confirms that the luminescence, chemical composition (including Fe, Mn, Na, Cl, ΣHREE, and Y contents), and REE patterns of apatite can be affected by hydrothermal alteration; therefore, these results may be used to constrain the evolution of ore-forming hydrothermal fluids and may offer an effective tool for mineral exploration.

Geochemistry of the Leatherwood coal in eastern Kentucky with an emphasis on enrichment and modes of occurrence of rare earth elements

The Middle Pennsylvanian (Bolsovian) Leatherwood coal in the central part of eastern Kentucky is a moderately thick, moderate-S seam that has been one of the major energy resources in the region. Much of the seam profile consists of clarain, dull clarain, and durain with some brighter lithologies at the base of the seam and in the upper portion of the coal at one site. A previous study emphasized petrographic trends. In this investigation, the geochemistry of the coal is examined. Some elements, such as Ge and Ga, are enriched at 2× and 5× the World hard coal averages in the coal lithotypes adjacent to rock (roof, floor, partings). Arsenic and other chalcophile elements (Zn, Co, Ni) tend to be concentrated at the top and bottom of the seam profiles and below partings, generally in the coals with the highest pyritic sulfur content. Manganese enrichments occur in bright clarain lithologies at one site. No coal lithology reaches a 5× the World hard coal average, but samples between the 2× and 5× World hard coal averages tend to be at the top and bottom of the coal seam. Most coal samples tend to have a light rare earth element (LREE) enrichment. The basal lithotype at all sites, though, has a heavy REE enrichment and, via inference from the Zr and TiO2 concentrations, a smaller influx of detrital minerals than the basal lithotypes in many Appalachian coals. While the nature of REE associations is complicated by the high volatile A bituminous coal rank, the relatively high concentrations of the heavy REE suggest an original, albeit possibly not exclusive, organic association for those elements.

The origin of the ultrahigh-pressure Tso Morari complex, NW Himalaya: implication for early Paleozoic rifting

AbstractThe origins and age distribution of the Himalayan high-pressure (HP) and ultrahigh-pressure (UHP) metamorphic rocks are critical for understanding the pre-Himalayan history. Although the protoliths to the UHP Tso Morari eclogites in Ladakh, NW Himalaya are believed to be the Permian Panjal volcanics, the geochronological evidence is absent. Here, we demonstrate that the protoliths of the UHP Tso Morari Complex formed in a continental rift setting at the Indian margin associated with the northern East Gondwana during the Early Paleozoic. Zircon U–Pb dates from eight gneisses and one garnet amphibolite indicate the Early Paleozoic bimodal magmatism of 493–476 Ma, which could be associated with the separation of South China from North India. Except for arc-related eclogites found in the Nidar ophiolite, the eclogites and amphibolites are rift-related, exhibiting enriched light rare earth elements and high concentrations of incompatible elements, along with evidence for crustal contamination. Our findings support the previously reported diversity in the sources and ages of the protoliths of the Himalayan HP–UHP metamorphic rocks along the orogen.

An early Paleozoic accumulation-foundering cycle of ultramafic cumulates in the Harlik arc and its implications for continental crustal growth in the Altaids

Lower crustal ultramafic cumulates that are normally denser than the ambient mantle peridotites are prone to founder back into the convecting mantle, prompting the formation of continental Moho and andesitic crust at subduction zones. However, foundering events of ultramafic cumulates have not been widely reported in island arcs, including the Altaids, one of the largest accretionary orogens. The Altaids involved prominent continental crustal growth by the development of an archipelago in the Phanerozoic. But the scarcity of foundering events of ultramafic cumulates hinders a better understanding of the formation mechanism of andesitic crust in the Altaids. In this study, we report two dioritic plutons in the Harlik arc, southern Altaids, trying to identify the accumulation-foundering cycles of dense ultramafic cumulates. LA-ICP-MS dating revealed that the Miaoergou and Banfanggou plutons in the Harlik arc were intruded at ca. 445 ± 6 Ma and 423 ± 4 Ma, respectively. The homogeneous Miaoergou pluton is mainly composed of quartz diorites, they have a high- to medium-K calc-alkaline composition, and show enrichments in light rare earth elements (LREE) and large ion lithophile elements (LILE), but depletions in high field strength elements (HFSE, especially Nb and Ta) and heavy rare earth elements (HREE). They also have juvenile isotopic signatures (εNd(t) = +3.3 − +3.7, initial 87Sr/86Sr = 0.70399–0.70452), which together suggest that they were derived from fractional crystallization of the coeval hydrous basaltic magmas in an arc setting. The heterogenous Banfanggou pluton comprises a spectrum of lithologies from hornblende gabbro to diorite. The hornblende gabbros and diorites have a high- to medium-K calc-alkaline composition, and show enrichments in LREE and LILE, but depletions in HREE and HFSE. They all have juvenile isotopic compositions with εNd(t) ranging from +3.5 to +4.2, and (87Sr/86Sr)i from 0.70384 to 0.7047, respectively, indicating that their parental magmas were intruded in a subduction-related setting, and underwent fractional crystallization of clinopyroxene, plagioclase, amphibole and quartz. Both pulses of hydrous basaltic magmatism involved open-system conditions, with the development of mafic microgranular enclaves (MMEs) in the diorites and their mingling. In a synthesis of the published data, we found that the Harlik arc was continuously affected by subduction in the early Paleozoic, through extensive arc magmatism from ca. 452 to 440 Ma, the Harlik arc matured with the accumulation of thick ultramafic cumulates in its lower crust. The foundering of these ultramafic cumulates occurred later, which led to strong extension and related A-type granitic magmatism at ca. 436 Ma. This accumulation-foundering cycle of ultramafic cumulates facilitated the formation of andesitic composition and continental Moho in the Harlik arc, and contributed to the significant continental crustal growth in the Altaids.

Petrogenesis and geochemistry of WNW-ESE to NW-SE trending doleritic dykes of the Paleoproterozoic Liptako basement (West African Craton, West Niger)

Doleritic dykes with regional orientations WNW-ESE to NW-SE, cut the Paleoproterozoic Birimian formations of the Liptako basement (Ouest-Niger). Mineralogical compositions studied from these doleritic dykes consist of augite (Wo21-40-En24-45-Fs13-54), pigeonite (Wo8-12-En45-59-Fs31-41), plagioclase, alkali feldspars, titano-magnetite, ilmenite, edenite, apatite, biotite and chlorite. The geochemical affinity of the doleritic dykes in the two trends is similar to oceanic plateau basalts (OPB), with high iron content relative to Mg. Negative Nb, Ti and Ta anomalies and the Y/Nb ratio (1.59–3.15) indicate a continental tholeiitic character for while light rare earth element enrichment, low to moderate Ti contents and the Th/Yb (0.28–0.59) and Nb/Yb (3.25–7.46) ratios suggest sources similar to E-MORB. Their Th/Nb (0.06–0.10), Th/Yb (0.28–0.59), TiO2/Yb (0.54–0.82) ratios suggest that the magma was generated by partial melting (5–17%) of a residual spinel-garnet lherzolite, that could have been part of a mantle plume. Relatively low Mg# (36–51) reflect some degrees of fractional crystallization, with some of this differentiation recorded between the margins and interiors of dykes. This differentiation was accompanied by unusually low degrees of crustal contamination, as indicated by relatively low Th/Ta ratios (1.18–2.03). This petrological and geochemical information provides new constraints on the origin of these WNW to NE trending mafic dykes of the West African Craton.

Fractional crystallization of garnet in alkali basalts at >1.8 GPa and implications for geochemical diversity of Large Igneous Provinces

A suite of lavas from northwest Mull, British Palaeocene Igneous Province, exhibit major and trace element characteristics that are best explained by very high pressure (>1.8 GPa) crystallization of an assemblage comprising aluminous clinopyroxene (Al-Cpx) plus garnet. The resulting series of consanguineous magmas are mildly Si-undersaturated. The trace element effects of this crystallizing assemblage are manifested in increasing light rare earth element (LREE) enrichment and heavy REE (HREE) depletion with decreasing whole-rock MgO, a predictable consequence of the bulk distribution coefficient (D) of this assemblage being > > 1 for HREE but <<1 for the LREE. Early crystallization of Al-Cpx and replacement of plagioclase feldspar by garnet in the crystallizing assemblage also results in increasing or near constant Al2O3 abundances in cotectic compositions with MgO < ∼7 wt%. Garnet as opposed to plagioclase crystallization is also reflected in the incompatibility of Sr and compatibility of Y resulting in very high Sr/Y lavas (up to 100) with high Sr (∼1200 ppm) and low Y contents (∼12 ppm). Lavas also have high Zr/Y (up to 30). Major element constraints suggest the crystallizing assemblage comprised ∼40% garnet and 60% Al-Cpx.Magmas that fractionated at ∼1.8 GPa rose to the surface without interacting with the continental crust. Immediately underlying basalts and picrites show evidence of crustal contamination and assimilated fusible portions of the crust, therefore effectively lining the plumbing system and allowing later magmas to rise to the surface without crustal contamination. A local change in tectonic regime from extension to passive appears to be linked to a change from low pressure to very high-pressure crystallization of magmas. Whilst evidence for garnet fractionation in continental flood basalts is very rare, this paper provides a characterization of its geochemical consenquences.

Distribution of rare earth elements (REEs) in supergene environment around a typical ion adsorption–type REE deposit

The exploitation of ion adsorption-type rare earth element (REE) deposits using in-situ leaching technology has become increasingly popular in recent years. However, the migration of REEs into the surrounding environment has raised significant concerns. This study aimed to systematically investigate the migration and species of REEs in two streams (northern and southern streams) surrounding a typical IAD in China. The results showed that in the northern stream, which was directly injected with the leaching solution, REEs were primarily present in the dissolved state as REE(SO4)2− and REE(SO4) +. Conversely, in the southern stream that did not receive indirect injection of leaching solution, REEs were present in both particulate and dissolved states (i.e., REE(CO3) + and REE(CO3)2−, REE(SO4)2− and REE(SO4) +). The southern stream had a higher enrichment of light REEs (LREEs) compared to the northern stream, with a L/H ratio of 1.8 and 1.6, respectively. This was attributed to the higher stability of dissolved complexes formed between heavy REEs (HREEs) and CO32−. As pH increased in the northern stream, REEs were removed from stream water and deposited in sediment, leading to secondary enrichment of REEs in the sediment. X-ray absorption fine structure (XAFS) analysis revealed that REEs mainly formed outer-sphere (OS) and inter-sphere (IS) complexes in the sediment of northern and southern streams, respectively. Furthermore, a high proportion of ion-exchangeable REEs in the sediment of the northern stream indicated potential for recycling of REE resources, similar to those found in IADs. These findings contribute to the understanding of the transportation and secondary enrichment of REEs in the environment and provide a scientific basis for the comprehensive utilization of REE resources.

Variations of Sr–Nd–Hf–O isotopes and redox conditions across a Neoproterozoic arc magmatic belt in the western margin of the Yangtze craton

We use zircon trace elements and HfO isotopes, plus whole-rock chemical and SrNd isotope compositions to investigate the controls on the chemistry of Neoproterozoic arc magmas. The samples are from the gabbrodiorite intrusion of the Gaojiacun mafic-ultramafic complex and from the Tongde diorite batholith of the Panxi Neoproterozoic magmatic belt in the western margin of the Yangtze craton, western China. Zircon UPb ages reveal that both intrusions are coeval, emplaced at ∼820 Ma. Major element compositions of whole rocks and major silicate minerals indicate that the Tongde batholith formed from more evolved magma than the parental magma for the Gaojiacun intrusion. The mantle-normalized trace element patterns of whole rocks from both intrusions are similar, showing light REE enrichments and pronounced negative NbTa anomalies. The SrNd isotopic compositions of the whole rocks are also similar, plotting within or very close to the mantle array, indicating no to minor contamination with the upper crust. Zircon HfO isotopes indicate that the Gaojiacun magma has much higher ƐHf (6.26 ± 0.52) and δ18O (7.0 ± 0.3 ‰) than the Tongde magma (ƐHf = 4.81 ± 0.39; δ18O = 5.7 ± 0.2 ‰). The δ18O values of the Gaojiacun zircons are also higher than the normal mantle (δ18O = 5.3 ± 0.6 ‰). Zircon trace element compositions show that, despite their close spatial association (<10 km), the coeval intrusions have contrasting redox states, with the estimated fO2 values of ΔFMQ+1.0 and ΔFMQ-0.7 for Tongde and Gaojiacun, respectively. The former is within the range of modern arc basalts, whereas the latter is lower than the average value of MORBs. The very low fO2 of the Gaojiacun magma could be due to the presence of subducted oceanic sediments enriched in organic matter (OM) in the source or due to contamination with OM-rich sedimentary rocks in the upper crust. Since such crustal rocks have not been reported for the region, we prefer the former explanation. The preferred model is also supported by Sr–Nd–Hf–O isotopes. The results from this study reveal that both reduced and oxidized magma could be produced simultaneously in a subduction zone.

Tonian Continental Arc Magmatism of the Porongos Complex, Dom Feliciano Belt, Southern Brazil

This study provides new information on the deformation, metamorphism, and tectonic setting of the metavolcanic rocks of the southern portion of the Porongos Complex, southern Brazil. The structural analysis enabled the identification of three deformational phases, formed under ductile to semi-ductile conditions. D1 progressed through deformation partitioning, comprising closed to isoclinal folds and an axial plane foliation. Then, simple shear prevailed, resulting in isoclinal folds, sigma-type porphyroclasts, foliation transposition, and mylonitic rocks. D2 comprises open to gentle folds and an axial plane cleavage. The formation of shear bands is ascribed to the semi-ductile D3. The mineral assemblage represented by phengite + chlorite + clinozoisite-epidote + actinolite + albite + quartz associated with the temperatures obtained through the chlorite geothermometer (316°C) indicates greenschist facies conditions. The protoliths of these metavolcanic rocks are geochemically discriminated as calc-alkaline, dacite-to-rhyodacite, with peraluminous compositions. The bulk trace element compositions show enrichment in large-ion lithophile elements and light rare-earth elements and depletion in heavy rare-earth elements. Also, negative Nb, P, Ti, and Ta anomalies are observed in the multielement diagram. All these geochemical features are typical of rocks formed in continental magmatic arcs. Geochemical comparison with other pre-collisional Tonian orthometamorphic rocks from the Dom Feliciano Belt demonstrates strong similarities, which corroborates the prior interpretation of a continental arc setting for the origin of these Tonian rocks.

Late Paleozoic Tectonic Evolution of the Northern Great Xing’an Range, Northeast China: Constraints from Carboniferous Magmatic Rocks in the Wunuer Area

Northeast China composes the main part of the Central Asian Orogenic Belt. Traditionally, Northeast China has been considered a collage of several microcontinental blocks. However, the tectonic evolution of these blocks remains uncertain. Igneous rocks can be used to infer the magmatic histories of the blocks and thus help reconstruct their evolution. In this study, we present new zircon U–Pb and whole-rock geochemical data for Carboniferous igneous rocks from the Wunuer area, northern Great Xing’an Range, Northeast China, to constrain the Carboniferous amalgamation of the united Xing’an–Erguna and Songnen–Zhangguangcai Range massifs. On the basis of zircon U–Pb dating results, we identify two main stages of magmatism, i.e., early Carboniferous (332–329 Ma) and late Carboniferous (312–310 Ma). The early Carboniferous igneous rocks include diorites and granodiorites, with the former being classified as calc-alkaline to tholeiitic and the latter as tholeiitic. Both rock types are enriched in Th and U and depleted in Nb and Ti. The rocks display slightly fractionated rare earth element (REE) patterns, with an enrichment in light REEs and a depletion in heavy (H)REEs. The geochemical characteristics of the early Carboniferous rocks indicate that they formed in a subduction-related continental-arc setting. The late Carboniferous igneous rocks include monzogranites and syenogranites, both of which are classified as high-K calc-alkaline rocks and show enrichment in Th, U, and Rb and depletion in Nb and Ti. The rocks display strongly fractionated REE patterns, with an enrichment in light REEs and a depletion in HREEs. The geochemical characteristics of the late Carboniferous rocks indicate that they formed in a syn-collisional tectonic setting. Combining the new geochronological and geochemical results and inferred tectonic settings with regional magmatic data, we propose a new three-stage model to interpret the late Paleozoic tectonic evolution of the united Xing’an–Erguna and Songnen–Zhangguangcai Range massifs of Northeast China: (1) early Carboniferous (360–340 Ma) subduction of the Paleo-Asian oceanic plate beneath the united Xing’an–Erguna Massif and formation of the Wunuer oceanic basin in the Yakeshi area; (2) early to late Carboniferous (340–310 Ma) sustained subduction of the Paleo-Asian oceanic plate beneath the united Xing’an–Erguna Massif and initiation of subduction of the Wunuer oceanic basin; and (3) late Carboniferous–early Permian (310–275 Ma) syn-collisional to post-collisional tectonic transition between the united Xing’an–Erguna Massif and the Songnen–Zhangguangcai Range Massif.

Cretaceous Nb-enriched basalts in the western Gan-Hang belt, South China: A response to slab window opening during the Paleo-Pacific ridge subduction

The role of recycled slab-mantle interaction in the formation of mantle-derived rocks during the Paleo-Pacific subduction remains to be tested. In this study Nb-enriched basalts (NEBs) are identified in Shanggao, western part of the Gan-Hang belt, South China. These volcanic rocks have 40Ar/39Ar ages of ∼90 Ma. They are tholeiitic to calc-alkaline in composition and have low SiO2 (50.1–53.4 wt%), high MgO (5.86–7.10 wt%), and Nb (10.7–14.3 ppm) contents. These NEBs have high Nb/La (0.91–0.99) and Nb/U (14.8–21.0) ratios and chondrite-normalized patterns with slightly enriched light rare earth elements (LREEs) ((La/Yb)N = 5.32–6.52). Their primitive mantle-normalized patterns are similar to E-MORB-like characteristics. These features indicate that these NEBs were derived from a mixed source between the asthenospheric mantle and slab-derived adakitic components in the garnet stability field. Their Sr-Nd-Pb-Hf isotopic compositions also reflect the contribution of the subducted oceanic crust including minor sediments in the source. These NEBs are spatially associated with adakitic rocks, A-type granites, and related mineral deposits in the Gan-Hang belt, clearly supporting a tectonic model in which the Cretaceous ridge subduction and slab window opening occurred during the enhanced slab rollback of the Paleo-Pacific plate. The melting of residual eclogites caused by episodic upwelling of the asthenospheric mantle can account for the formation of the NEBs in a back­arc extensional setting.

Petrogenesis of Middle Triassic andesitic rocks in the Weixi area, Southwest China: Implications for the tectonic evolution of the Paleo-Tethys

The Paleo-Tethyan tectonic evolution of the central Sanjiang orogenic belt remains unclear, particularly regarding the types and tectonic setting of volcanic rocks in the Cuiyibi Formation in the Weixi area, southwest China. These volcanic rocks were previously thought to be bimodal, but our detailed geological mapping revealed that the Cuiyibi Formation volcanic rocks include basalt, andesite, and rhyolite. In this paper, we present new geological, geochronological, and geochemical data for the andesitic rocks in the Cuiyibi Formation. Zircon UPb ages of the andesitic rocks indicate they formed at 245–242 Ma. The andesitic rocks are part of the high-K calc-alkaline/shoshonite series, and they exhibit light rare earth and large-ion lithophile element (e.g., K, Rb, Th, and U) enrichment and heavy rare earth and high-field-strength element (e.g., Nb, Ta, and Ti) depletion. High Mg# values and Nb contents, low Sm/Yb and Lu/Yb ratios, and negative zircon εHf(t) and whole-rock εNd(t) values suggest these rocks were derived from an enriched mantle source. The Cuiyibi Formation volcanic rocks are geochemically similar to those formed in a continental arc. These rocks formed along a vast continental arc in the North Qiangtang–Lanping–Simao Block related to the subduction of the Paleo-Tethyan oceanic slab.

Whole Rock, Mineral Chemistry during Skarn Mineralization-Case Study from Tongshan Cu-Mo Skarn Profile

Studying the activation, migration and precipitation processes of ore-forming elements is essential for understanding the genesis and mechanisms of skarn deposits. A typical skarn profile formed by the intrusion of Yanshanian granodiorite into the Carboniferous carbonate strata was studied. The profile is highly consistent with the classic skarn profile, ranging from the intrusion, weak alteration belt, skarn belt (inner and outer skarn belt) and mineralization belt (mainly characterized by Cu mineralization) to the surrounding marble without being affected by late-stage low-temperature or supergene weathering alteration. Whole-rock data show that the major and trace elements exhibit relatively small changes in the granodiorite and inner skarn, but huge variation in the boundary between the inner and outer skarn; Na, Al, Ti and Sr show significant decreases, while Fe, Mg, Zn, V and Ni show significant increases. The elemental content in the outer skarn is 10–100 times or more higher than that in the marble, but the elements such as Ca, Sr and Cs diluted from the marble. During the migration process from the inner skarn to the outer skarn, some elements (such as K, Rb and Ba) were depleted in the inner, but not enriched in the outer, indicating that they may migrate to farther locations. Grossularite developed in the inner skarn, with light rare earth element (LREE) depletion and heavy REE enrichment, as well as positive and negative anomalies of Eu (δEu = 0.42–3.95). Andradite developed in the outer skarn, with zonation development, light REE enrichment, and heavy REE depletion and a positive Eu anomaly (δEu = 0.36–46.83). Some negative Eu anomalies appear at the edges of garnets in the outer skarn, indicating fluctuations in fO2 during the late skarn process. A positive correlation between Fe3+ and REE3+ in the garnets from the inner skarn, as well as between Al3+ and REE3+ from the outer skarn indicated that there are different YAG substitution mechanisms of REE between the inner and outer skarn. Low garnet REE contents and highly variable Y/Ho ratios in outer skarn suggest that the significant fluctuations in REEs may be primarily controlled by water-rock interactions. Considering the whole-rock major and trace element contents, as well as the trace element features of garnet, we found that whole-rock Na, Al, Ti and Sr elements, garnet Ti, Zr and Nb elements exhibit significant differences between the inner and outer skarn. These characteristics can be used to distinguish the boundary between the rock body and carbonate during the skarnification process.

Geochemistry and mineralogy of the Upper Ordovician Wufeng formation, Southwestern China: Implications for Paleoclimate construction

Wufeng Formation shale is an important source rock of unconventional hydrocarbons in the Lower Paleozoic shales of Sichuan Basin. However, the study on its provenance and paleoclimate is still relatively limited. In this study, mineralogical and geochemical data of the shales from the Upper Ordovician Wufeng Formation in southwestern China has been used to interpret the provenance and conditions of weathering and paleoclimate. The Wufeng shales have intermediate to high SiO2 (57.72–82.38 wt. %, av. = 68.84 wt. %) and Al2O3 (5.26–16.17 wt. %, av. = 10.62 wt. %), are rich in transition metal elements (i.e. V, Ni, Cu, Co and Cr) and Y as well as moderate depletion in Na2O and Sr, relative to the concentrations of the upper continental crust (UCC). In the chondrite-normalized (CN) rare earth elements (REE) distributions, these rocks display light REE (LREE) enrichment (La/YbCN = 6.69–12.63, av. = 9.28), flat heavy REE (HREE) (Gd/YbCN = 1.35–2.41, av. = 1.70), and clearly negative Eu anomalies (Euan = 0.50–0.66, av. = 0.58), showing similar characteristics with the CN post-Archean Australian Average Shales (PAAS). Wufeng Formation shales are immature composition without evident recycling sediments, and they are originated from an intermediate-felsic igneous source composed of tonalite–trondhjemite–granodiorite (TTG), granitic and andesitic igneous rocks. The chemical weathering conditions of studied shales decreased from moderate to low in the provenance region, suggesting a gradual cooling trend of the climate at Late Ordovician Thus, this article will be helpful to discern the provenance and variations of chemical weathering conditions and paleoclimate of Wufeng Formation shales.

Early diagenetic mobilization of rare earth elements and implications for the Ce anomaly as a redox proxy

The Rare Earth Elements (REE) archived in carbonate rocks retain a wealth of information on paleo-seawater chemistry and local-regional redox conditions. However, interpretations are often ambiguous due to the potential for REE remobilization in marine environments. In this regard, many carbonate rocks that retain primary seawater isotopic signatures exhibit non-seawater-like REE patterns, implying either unusual REE behaviour in seawater or diagenetic overprinting of otherwise well-preserved rock samples. Here, we apply sequential leaching to constrain the possible effects of different REE-bearing phases on measured carbonate REE patterns in order to address this quandary. Our results show that the exchangeable phase contains negligible REE, but could be an important host phase for other elements such as Sr, Ba and K. The acidified hydroxylamine hydrochloride leach is shown here not only to dissolve Fe–Mn oxides but also phosphate minerals, which induces middle REE enrichment in corresponding leachates of dolostone samples in our study. The demonstrable Fe–Mn oxide phase in limestone samples is characterized by middle and/or light REE enrichment and positive Eu anomalies, which are attributed to hydrothermal processes and continuing exchange with marine fluids after initial precipitation. The non-seawater-like REE patterns observed in the carbonate phase of otherwise well-preserved limestones resemble those of the co-existing Fe–Mn oxide fraction, and are interpreted to reflect the dissolution of REE carrier phases during early diagenesis. This view is supported by fluid-rock interaction modelling, which shows how REE can be mobilized at relatively low fluid/rock ratios in shallow porewaters. Non-seawater-like REE patterns may therefore be caused by the incorporation of REE from shallow porewaters before final lithification due to an elevated flux of particulate REE carrier phases, e.g. Fe–Mn oxides and organic matter, to the seafloor. In spite of the sensitivity of carbonate REE patterns to early diagenetic exchange, the co-occurrence of non-seawater-like patterns with primary strontium and carbon isotope values suggests that REE should not be viewed as a general indicator for the preservation of other geochemical proxies. Importantly, Ce anomalies of the carbonate phase will also be affected by porewaters, masking primary seawater values. Our results favour a reevaluation of redox interpretations by taking into account REE patterns as a whole.

Petrogenesis of the Palaeoproterozoic (1.87 Ga) Damyang amphibolites in the north‐western margin of the Yeongnam Massif and tectonic implications of the Korean Peninsula

The Yeongnam Massif is located in the southern part of the Korean Peninsula and holds key elements in understanding the Palaeoproterozoic tectonic evolution of north‐east Asia during the amalgamation of the Columbia supercontinent. In this study, we have conducted geochronological and geochemical studies on the mafic intrusive along the northern margin of the Yeongnam Massif. Sensitive high‐resolution ion microprobe (SHRIMP) U–Pb zircon dating on two amphibolite and one gabbro samples in the Damyang area show that the amphibolites crystallized at ~1.87 Ga and the gabbro crystallized at ~87.6 Ma. The 1.87 Ga Damyang amphibolites are simultaneous with the Muju and Okbang amphibolites along the northern margin of the Yeongnam Massif. They also show similar geochemical characteristics, including tholeiitic basalt composition, enriched Light Rare Earth Elements (LREE) and large ion lithosphile elements (LILEs), depleted high field strength elements (HFSEs), and slightly enriched but various Hf isotopes, indicating that they originated from an enriched but heterogeneous mantle source with fluid addition. Thus, the 1.87 Ga amphibolites along the northern margin of the Yeongnam Massif were probably emplaced in an arc‐related setting. Combined with the 2.02–1.96 Ga magmatism, it is proposed that the subduction might have lasted during the 2.02–1.85 Ga interval and mantle‐derived magma rose up due to the roll‐back process between 1.88–1.85 Ga.

Distribution of rare earth and other critical elements in lignites from the Eocene Jackson Group, Texas

Coal is increasingly evaluated as a source of rare earth elements (REEs) in the United States to address the overreliance on imported REEs. The objective of this study was to assess the distribution of REEs in lignites from selected mining areas in the Texas Gulf Coastal Plain region. Thirty-one archived lignite and rock samples previously collected by the U.S. Geological Survey were analyzed for their rare earth element and critical mineral content. These include samples from one core (5400 and 5500 lignite horizons) and two opencast lignite mines (Gibbons Creek 3500 and 4500 horizons, and San Miguel horizons A to D) in the Eocene Jackson Group of the Texas Gulf of Mexico Coastal Plain. Some lithologies in the Gibbons Creek 3500 and 4500 lignite-bearing sections have high total rare earth, yttrium (Y), and scandium (Sc) (REYSc) values, up to 7800 ppm (ash basis) REYSc. The lignite lithologies show an enrichment in rare earths, [samarium (Sm) through gadolinium (Gd)]. The basal Gibbons Creek 3500 lignite bench shows a heavy rare earth element enrichment pattern resembling that often seen in peats through high volatile A bituminous coals. The 5500 lignite sequence, overlying the latter lignite sections, shows a light rare earth enrichment. The San Miguel lignite benches have heavy rare earth enrichments with a negative europium (Eu) anomaly.

Heterogeneous Subcontinental Lithospheric Mantle below the South Margin of the Siberian Craton: Evidence from Composition of Paleoproterozoic Mafic Associations

Abstract —Paleoproterozoic mafic associations of the Irkut block from the Sharyzhalgai uplift are gabbro-dolerite dikes and small gabbronorite and monzodiorite massifs, which formed at 1.87–1.84 Ga and were coeval with granitoids and basite intrusions of the South Siberian magmatic belt (SSB). All the Paleoproterozoic mafic associations of the Irkut block are characterized by the presence of biotite and alkali feldspar, enrichment in K2O, LILE, Th, and light REE, highly fractionated multielement spectra with sharp Nb and Ti depletion, and extremely low εNd(T) from –5.1 to –10.1. In these compositional features, they are similar to mafic complexes in the central and eastern parts of the SSB (the Baikal uplift and the western Aldan shield). Their geochemical and isotopic characteristics did not result from crustal contamination but point to derivation from the subcontinental lithospheric mantle (SCLM) enriched by reaction with felsic subduction-related and OIB-like mafic melts formed at a low degree of melting. The geochemically contrasting Paleoproterozoic gabbronorites in the Onot block of the Sharyzhalgai uplift are marked by depletion in K2O, Ba, LILE, Th, and light REE, weak depletion in Nb, and higher εNd(T) from –0.3 to –1.4. The gabbronorites indicate not only an increase in the contribution of a depleted source to their genesis but also the heterogeneity of the subcontinental lithospheric mantle below the south margin of the Siberian Craton. The formation of enriched SCLM domains throughout the South Siberian belt was mainly the result of Archean subduction-related metasomatic processes. The wide distribution of Paleoproterozoic mafic complexes with subduction geochemical signatures and negative εNd(T) on most early Precambrian cratons is due to global change in the composition and an increase in the heterogeneity of the subcontinental lithospheric mantle toward the end of the Archean.

Geochronology, petrogenesis, and magmatic oxidation state of the Mangling intrusive complex, Northern Qinling Belt, Central China: Implications for magma fertility and tectonic setting

The Mangling intrusive complex has different dioritic to granitic phases and is spatially and temporally related to molybdenum deposits in the Qinling Orogen. Zircon U-Pb dating of the Mangling intrusive complex indicates that dioritic rocks (biotite diorite and biotite diorite enclave; ca. 150−147 Ma) formed earlier than granitic rocks (medium- to fine-grained and fine-grained monzogranite and K-feldspar granite; ca. 145−141 Ma). The Mangling dioritic rocks exhibit large ion lithosphere element (e.g., Rb) and light rare earth element enrichment and high field strength element (e.g., Nb, Ta, and Ti) depletion. They have low to moderate SiO2 (51.33−58.16 wt%), high MgO (3.10−4.75 wt%) and Mg# (48−60), and negative zircon εHf(t) values (−11.6 to −6.8), suggesting origination from the continental lithospheric mantle that may have been metasomatized by previous sediment-derived melts and slab-derived fluids constrained by high Nb/Y, Th/Yb, and Rb/Y ratios. The Mangling granitic rocks are I-type granites and have high SiO2 (67.90−81.88 wt%) and low MgO (0.16−0.74 wt%). They have low and negative zircon εHf(t) values (−18.7 to −1.9) and old zircon Hf two-stage model ages (2334−1287 Ma), as well as similar mineral fractionation (e.g., hornblende, biotite, sphene, and apatite) with the Mangling dioritic rocks, indicating that they were derived from the remelting of old crustal rocks (e.g., Xiong’er and Kuanping groups) by the evolved underplated mafic magma. Compared with the Taoguanping mineralized monzogranite in the Northern Qinling Belt, zircon geochemistry (e.g., Ce4+/Ce3+, Eu/Eu*, and ΔFMQ [relative fayalite-magnetite-quartz buffer]) indicates that magma of the Mangling intrusive complex (except the biotite diorite) has high oxygen fugacity and small fractionated granitic intrusions, which are coeval with the biotite diorite enclave or younger than the Mangling granitic rocks, may have potential for generating porphyry molybdenum mineralization. The combination of this study and previous studies corroborates that the Qinling Orogen underwent an intracontinental orogenic evolution in a post-collisional compression to extension transitional setting during the Late Jurassic to Early Cretaceous, affected by far-field Paleo-Pacific slab subduction.

Recycling of continental crust materials: Geochemical constraints from post-collisional alkaline intrusive rocks in the Dabie orogen

Post-collisional alkaline intrusive rocks from the Dabie orogen were studied for their whole-rock major-trace elements and Sr-Nd-Hf-Pb isotopes, as well as zircon U-Pb ages and Hf-O isotopes. The results provide geochemical constraints on the nature of their mantle sources and thus insight into crust-mantle interaction in the continental collision zone. The alkaline intrusive rocks are composed of syenite and nepheline syenite. Syn-magmatic zircon U-Pb dating by LA-ICP-MS for them yielded Early Cretaceous ages of 131.3 ± 1.4 Ma to 122.6 ± 0.6 Ma, coeval with the post-collisional magmatism in the Dabie orogen. One relict zircon with U-Pb age of 211 Ma is consistent with the timing of metamorphism for the ultrahigh-pressure (UHP) metamorphic rocks in this orogen. They have arc-like trace element distribution patterns, such as enrichment in LILE (large ion lithophile element) and LREE (light rare earth element) but depletion in HFSE (high field strength element), and enriched whole-rock Sr-Nd-Hf isotope compositions with high (87Sr/86Sr)i ratios of 0.7077–0.7131 but negative εNd(t) values of −16.0 to −9.4 and εHf(t) values of −17.5 to −12.7. Their syn-magmatic zircons have three groups of Hf-O isotope compositions comparable to those of UHP metamorphic rocks in Central-South Dabie and North Dabie, which represent the upper and middle continental crust of the subducted South China Block, respectively. In this regard, slab–mantle interaction is evident during the Triassic continental collision. We suggest that the melts derived from the subducted South China Block reacted with the lithospheric mantle wedge of the North China Block, resulting in phlogopite-bearing metasomatites, whose partial melting would generate the post-collisional alkaline intrusive rocks during the Early Cretaceous.