Lanthanide Tetrad Effect Research Articles

Magmatic–hydrothermal evolutionary processes in highly evolved granitic systems: Insights from zircons of the Baishitouquan pluton, NW China

Abstract As a robust accessory mineral in igneous rocks, the mineralogical and geochemical characteristics of zircon can record the lithological differentiation and magmatic–hydrothermal evolution of highly evolved granitic systems. The F-Rb–rich, highly evolved Baishitouquan pluton of NW China exhibits gradual lithological changes from leucogranite, amazonite-bearing granite, and amazonite granite in the lower levels of the pluton to topaz-bearing amazonite granite, topaz albite granite, and pegmatite in the upper levels. In this study, three types of zircon grains were identified in five lithological zones based on textural and chemical characteristics. Type I zircon, which mostly occurs in leucogranite and amazonite-bearing granite, exhibits oscillatory zoning in cathodoluminescence images and experienced low degrees of radiation damage (0.21–0.68 × 1015 α-decay events/mg), which is indicative of its magmatic origin. Type II zircon, which mostly occurs in amazonite granite and amazonite pegmatite, exhibits textures that are indicative of hydrothermal alteration (e.g., spongy texture, porosity, and microcracks), and has elevated concentrations of some cations, such as Ca and Al. Type II zircon contains a higher concentration of non-formula elements, including rare earth elements (REEs), and Hf, Th, and U, than Type I and III zircons. Additionally, Type II zircon exhibits a significant M-type lanthanide tetrad effect and experienced varying levels of radiation damage (3.75–11.72 × 1015 α-decay events/mg). These characteristics suggest that Type II zircon has a hydrothermally altered origin. Type III zircon, which is restricted to the topaz-albite granite, has the smallest crystal size among all types of zircon grains, shows a euhedral to anhedral mottled appearance, and is characterized by patchy, cloudy, or irregular zoning, with numerous fluid inclusions. This type of zircon contains higher concentrations of Ti (110–1030 μg/g) than other types of zircon grains. Additionally, this type of zircon experienced limited radiation damage (2.18–3.69 × 1015 α-decay events/mg), and has a smooth surface and homogeneous internal textures. These characteristics suggest that Type III zircon is the product of fluid interaction with hydrothermally altered Type II zircon. Accordingly, this type of zircon crystallized directly from a Zr-saturated hydrothermal fluid during the later stages of magmatic–hydrothermal evolution. These contrasting textural and compositional features of the three types of zircon grains are indicative of three stages of magmatic–hydrothermal evolution of the Baishitouquan pluton: magmatic, magmatic–hydrothermal transition, and hydrothermal. These magmatic and hydrothermal processes were involved in the enrichment, transport, and precipitation of rare metals, such as Rb. Accordingly, this contribution demonstrates that the textures and chemistry of zircon grains can serve as petrogenetic indicators for assessing magmatic–hydrothermal evolution and rare-metal mineralization in highly evolved granitic systems. Furthermore, this study presents a model of the magmatic–hydrothermal evolution of F-rich, highly evolved granitic systems through the lens of zircon.

Petrogenesis and rare-metal mineralization of the Ririwai alkaline granitoids, north-central Nigeria: mineralogical and geochemical constraints

ABSTRACT The Ririwai anorogenic alkaline complex harbours extensive rare metal (Nb-Zr-Sn-Zn) mineralization. However, uncertainty still surrounds their origin and magmatic-hydrothermal processes responsible for their rare metal mineralization. The complex is composed of peralkaline arfvedsonite ± albite-bearing granites, mildly peralkaline fayalite-bearing granite porphyries, and weakly peraluminous biotite-bearing granites, all of which show diagnostic A1-type characteristics. Zircon U-Pb dating reveals emplacement ages between 181.4 ± 0.81 and 188.6 ± 7 Ma for the three rock units. Sm-Nd and Pb isotopes (εNd (t) = –0.6 to −5.4, 206Pb/204Pb = 17.68–17.93) constrained the Ririwai A-type granites to represent highly fractionated products of enriched mantle-derived magmas. Mass-balance modelling suggests that magma evolution was fuelled by extensive fractional crystallization of 50 ~ 60 vol.% K-feldspar, 30 ~ 35 vol% fayalite, 5 ~ 10 vol.% amphibole, and ~ 5 vol.% apatite under reduced and water-undersaturated (ΔFMQ = –1.55; logfo2 = –18.63; H2O = <2.0 wt.%) conditions and assimilation of ~ 50 vol.% crust. Whole rock and amphibole compositions revealed an increasing degree of fractionation from the fayalite-bearing granite porphyries through biotite-bearing granites to the arfvedsonite ± albite-bearing granites. This extended fractionation at the late stage of magma differentiation, facilitated by fluorine dissolution and concentration of excess HFSE and REE as alkali-fluorocomplexes in the fluorine-rich silicate melt, allowed the accumulation of economic rare metal pyrochlore and columbite mineralizations in the highly fractionated arfvedsonite± albite- and biotite-bearing granites, respectively. Nonetheless, the metasomatic reaction rim textures around the magmatic pyrochlore, coupled with the M-type lanthanide tetrad effect (TE1,3 >1.10) indicate the subsequent effect of hydrothermal processes. Tectonically, reactivated shear fractures and transcurrent faults following lithospheric stresses in a transtensional regime allowed magma uprising and emplacement of A-type granites in the Ririwai complex.

Reworked Neoproterozoic sub-arc lithosphere beneath the Eastern Desert (Egypt): Evidence from geochemistry and geochronology of metabasites and granitoid gneisses, Gabal Um Gunud area

ABSTRACT High-grade granitoid gneisses (740–710 Ma) and elongate bodies of amphibolite and hornblende schist with cm-scale layers of garnet pyroxenite form an overturned fold in the Gabal Um Gunud area, South Eastern Desert of Egypt. Whole-rock geochemical data combined with zircon U-Pb-Hf isotope data suggest that the metabasites represent relics of oceanic crust with an N-MORB affinity, which has been derived from partial melting (2.0–1.4 GPa; ~65- ~ 45 km depth) of a depleted mantle source beneath an intra-oceanic, spreading forearc basin. Such increment of melting degree resulted in small basaltic melt batches with transitional tholeiitic to boninitic affinities. Progressive slab subduction and partial melting of the tholeiitic amphibolite produced high-Al and low HREE melts for trondhjemite at av. T = 854°C and low-Al and high HREE melts for tonalite at higher temperatures (av. 949°C). The low Mg# of the trondhjemite-tonalite rocks may be attributed to limited contamination of subduction components, as evidenced by the weak lanthanide tetrad effects (TE1,3~1) and near-chondritic Zr/Hf, Nb/Ta, and Y/Ho ratios, while the garnet pyroxenite was the residuum produced in equilibrium with the trondhjemite-tonalite melts.

Mineralizations of Nb–Ta–Li and rare-earth elements in the Jiabusi rare-metal deposit, Inner Mongolia, China: Constraints from monazite, cassiterite, and bastnasite U–Pb geochronology and geochemistry

The Jiabusi Nb–Ta–Li deposit is a medium-sized rare-metal deposit discovered in central Inner Mongolia in recent years, and it is accompanied by Rb-Cs-REEs mineralization. Its magmatic and metallogenetic ages, magmatic source attributes, and mechanisms of magmatic evolution and related mineralization are not known. To identify these characteristics, with multi-stage granitic intrusions of the Jiabusi deposit as study objects, investigations relating to petrography, lithogeochemistry, monazite–cassiterite–hydrothermal bastnasite LA-ICP-MS U–Pb geochronology, and Nd isotopes were systematically conducted. The following results were obtained: The LA-ICP-MS monazite U–Pb ages of the metallogenetic Li-mica albite granite and granitic pegmatite are 148±7 and 141±2 Ma and 141±3, 137±2, 136±3, and 132±2 Ma, respectively; the cassiterite U–Pb ages of the Ta–Rb ore bodies are 148±2 and 146±1 Ma; and the bastnasite U–Pb age of the magmatic hydrothermal fluid is 116±1 Ma. These ages indicate that there were two episodes of granitic magmatism and related rare (rare-earth) metal mineralization in the Jiabusi area during the Yanshanian period (Jurassic–Cretaceous). Geochemical analysis results reveal that the barren biotite granite is characterized by high SiO2 (75.89 wt%) and high alkali (Na2O + K2O = 8.48 wt%) and a relatively high FeOT/(MgO + FeOT) value (0.92) and a relatively high Zr + Nb + Ce + Y content (393×10−6), whereas Al2O3 (12.35 wt%), CaO (0.51 wt%), and MgO (0.13 wt%) contents are all relatively low. These results indicate that the biotite granite is A-type granite, with characteristics similar to those of A1-type granite. The Li-mica albite granite is characterized by high F (0.95%-2.76%) and strongly peraluminous nature (A/CNK = 1.26–2.34). Meanwhile, it is strongly enriched in Cs, Li, Rb, Nb, and Ta but extremely depleted in Ba, Sr, P, Ti, Zr, and light REEs, with quite a strong negative Eu anomaly (δEu <0.01), an evident lanthanide tetrad effect (TE1,3 = 1.36–1.44), and Zr/Hf (3.0–4.0) and Nb/Ta (0.5–1.0) ratios deviating from those of a normal magmatic system. X-ray fluorescence and electron probe microanalysis surface scanning imaging analysis revealed the activity of F-REE-rich hydrothermal fluid and related REE mineralization in the uppermost part of altered granites. These features indicate that the metallogenetic ore bodies underwent higher degrees of magmatic fractionation and F-rich fluid–present melt–hydrothermal interaction. The Li-mica albite granite and multi-stage granitic pegmatite have consistent Nd isotope characteristics (εNd(t) = −3.4 to −3.9) and relatively concentrated two-stage model ages (TDM,2 = 1174–1247 Ma), suggesting that they are quite likely syngeneic multi-stage products with different degrees of fractional crystallization. Through comprehensive analysis of the results in this study and from previous research, the Yanshanian (Jurassic–Cretaceous) granite in the Jiabusi area is inferred to quite likely have originated from the partial melting of the ancient lower crust caused by lithospheric thinning and asthenospheric upwelling along the northern margin of the North China Craton, and it is revealed that a large amount of juvenile crustal materials had contributed to this process.

Exotic REE behaviors of zircon in the Koktokay No. 3 granitic pegmatite, Xinjiang, northwest China

Rare earth elements (REEs) can be incorporated into zircon at significant concentrations that are controlled by the temperature, pressure, and composition of their growth environment. However, the distribution of REEs between zircon and melt does not always conform to the currently available partitioning data. This study presents evidence of exotic REE behaviors in zircon from the marginal zone of the Koktokay No. 3 granitic pegmatite in Xinjiang, northwest China. The behavior of the Koktokay REEs represents by large negative Ce anomalies, flat heavy REE patterns, and lanthanide tetrad effects. Two generations of zircon (Zrn-I and Zrn-II) are identified, which were formed by dissolution and re-precipitation processes. Zrn-I represents relic zircon domains with dissolution textures that formed from pegmatite melt during the late stage of the magmatic–hydrothermal transition. Zrn-II occurs as overgrowths and infilling fractures around or within Zrn-I, which formed by hydrothermal re-precipitation. From Zrn-I to Zrn-II, the zircon exhibits increasingly negative Ce anomalies and greater enrichment in light REEs and other non-stochiometric elements (e.g., Ca, Al, Fe, and Mg). Given the lack of Ce depletion in the host granite, the negative Ce anomalies in zircon can be attributed to Ce being sequestered into hydrothermal minerals (i.e., cerianite and/or Fe–Mn oxyhydroxides) as tetravalent Ce. In addition, the flat heavy REE patterns of both Zrn-I and Zrn-II likely resulted from the crystallization of heavy REE-enriched minerals, such as zircon and garnet, and were further enhanced by hydrothermal alteration. The two generations of zircon display identical M-type lanthanide tetrad effects in REE patterns, with similar TE3 values. This ubiquitous M-type tetrad effect of the REEs in garnet, zircon, and the host granite can be attributed to the exsolution and subsequent interaction with magmatically derived fluids containing F–aquo-complexes. Therefore, we conclude that such anomalous REE incorporation into zircon from a hydrous pegmatitic melt is controlled by the evolution of the hydrous melt and dissolution–re-precipitation processes. Our results suggest that the reliability of zircon REE partitioning data should be revaluated, and that further experimental studies are needed to fully understand the behavior of REEs in hydrothermal systems.

Relationship Between Nb-Ta Enrichments and Highly-Fractionated Granitic Magma Evolution in South China: Geochronological, Zircon Hf Isotopic and Geochemical Evidence From Jianfengling Granite

The Jianfengling granite is an important ore-forming rock unit in the Xianghualing orefield in Nanling region (South China), and its magmatic evolution is vital to understand the regional niobium (Nb)-tantalum (Ta) mineralization. The Jianfengling granite comprises three gradual transitional lithofacies: porphyritic biotite monzogranite (mesophase facies), biotite monzogranite (transition facies) and topaz biotite monzogranite (central facies). All the three biotite monzogranite lithofacies are characterized by being rich in SiO2 and Al2O3, poor in TFe2O3, CaO, MgO, TiO2, MnO and P2O5, and are peraluminous high-K calc-alkaline. These rocks are remarkably enriched in Rb, Th, U, Nb and Ta, strongly depleted in Ba and Sr, and slightly depleted in Zr. The LREE/HREE decreases gradually from porphyritic biotite monzogranite, through biotite monzogranite to topaz biotite monzogranite, with increasing convex (“M-type”) lanthanide tetrad effect, which similar to the highly-fractionated granite. The high Th-U (Thavg. = 2051.56°ppm; Uavg. = 1,498.23°ppm, respectively) and low Th-U (Thavg. = 708.14°ppm; Uavg. = 441.57°ppm, respectively) zircon grains from porphyritic biotite monzogranite yielded weighted average 206Pb/238U ages of 161.3 ± 1.6 Ma (MSWD = 1.3, n = 13) and 158.7 ± 2.0 Ma (MSWD = 1.7, n = 13), respectively, consistent with the large-scale magmatic-mineralization event in the Nanling region (ca. 160–150 Ma). The εHf(t) values of the high Th-U (-6.48 to -2.51) and low Th-U (-6.58 to -1.12) zircon grains from the porphyritic biotite monzogranite indicate that the causative magma was formed from partial melting of the Mesoproterozoic Cathaysian basement rocks in a lithospheric extension setting. The Nb and Ta contents increase with fluorine from the porphyritic to topaz biotite monzogranite, indicating that the Nb-Ta enrichment may have caused by the gradual increase of fluxing content (fluorine) during the fractionation of the Jianfengling granitic magma.

Geochronology and geochemistry of the granites from the Jiabusi Ta-Nb-(Li-Rb-Cs) deposit at the northern margin of the North China Craton

The newly discovered Jiabusi Ta-Nb deposit occurs within the latest Jurassic-Early Cretaceous multiphase granites, which are composed of felsic, peraluminous intrusions including biotite, two-mica, Li-mica, and topaz-lepidolite granites (abbreviated as BG, TMG, LAG, and TLG, respectively). Ore mineralizations are mainly hosted in the LAG and TLG, with subordinate mineralization occurring in the pegmatitic dykes. In this contribution, we present a systematic work of geochronology, whole-rock geochemistry, and Sr-Nd-Hf isotope composition for determining the timing of mineralization, petrogenesis, geodynamic setting, and ore-forming processes. Zircon U-Pb dating constrains the emplacement ages of 148–151 Ma for the BG, TMG, and LAG and reveals at least three episodes of Ta-bearing granitic pegmatites formed at ∼150 Ma, 127 Ma, and ∼100 Ma, respectively. Disseminated cassiterite grains from the LAG, TLG, and KPD yielded U-Pb ages of 149, 149, and 104 Ma, respectively. These granites have similar and limited features of (87Sr/86Sr)i = 0.7099, εNd(t) = −2.8 to −5.1, and εHf(t) = −4.7 to +5.5 and relative old Nd and Hf model ages of 1166–1442 Ma and 840–1500 Ma, respectively, indicating that Jiabusi multiphase granites are likely derived from the same magma reservoir by the partial melting of Mesoproterozoic crust in the destroyed northern margin of the NCC and are characterized by having involved significantly juvenile crustal materials.From the BG, TMG to LAG and TLG, bulk-rock Li, Rb, Cs, Be, Sn, Nb, and Ta contents increase with decreased Zr/Hf, Nb/Ta, and K/Rb ratios. Such systematic variations denote that these multiphase granites are cogenetic and that the LAG and TLG have experienced a higher degree of magmatic fractionation than the BG and TMG. The decrease in bulk-rock (La/Yb) N ratios, ΣREE, and Sr-Ba concentrations from the BG to TMG and LAG suggest an evolution involving the fractional crystallization of monazite and feldspar. The remarkable M−type lanthanide tetrad effect (TE1,3 = 1.22–1.75) matches low Nb/Ta (<1.2) and Zr/Hf (<5.0) ratios, indicating both the magmatic fractionation and melt-hydrothermal interaction were closely associated with Ta-Nb super enrichment in the LAG and TLG stocks. The combined evidence of compositional gaps and geologic spatial relationship between the BG batholith and Ta-bearing plutons confirm that the western part of the Jiabusi LAG stock and its surrounding concealed muscovite granites (MSG) are the further prospecting targets for Ta-Nb and W deposits.

A tetrad effect in the glass transition of lanthanide‐doped sodium disilicate glasses

AbstractScanning calorimetric determination of the glass transition temperatures (Tg) of sodium disilicate doped individually with 25 wt.% of the oxides of La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu reveals the presence of the so‐called “lanthanide tetrad effect” in their glass transition temperatures. This is to the best of our knowledge the first observation of a tetrad effect in the macroscopic properties of a high‐temperature silicate phase.

Source and evolution of the ore-forming fluid of the Cuonadong Sn-W-Be polymetallic deposit (southern Tibet, China): Constraints from scheelite trace element and Sr isotope geochemistry

The Cuonadong Sn-W-Be polymetallic deposit is the first rare-metal deposit with an extraordinary metallogenic potential that has been discovered in the Tethyan Himalayan metallogenic belt. The deposit shows a wide range of different mineralization types, including greisen-, pegmatite-, skarn-, and hydrothermal vein-type mineralization. Of these mineralization types, the skarn-type has the largest inferred resources. In order to constrain the source and evolution of the ore-forming fluid, we conducted a detailed study of the skarn-hosted scheelite, including cathodoluminescence imaging, in-situ trace elemental analysis, and bulk Sr isotope analysis. In addition, bulk Sr isotope analysis of fluorite, phlogopite 40Ar-39Ar dating, and marble whole-rock geochemical analysis were also conducted. Phlogopite 40Ar-39Ar dating indicates that the skarn was formed at ca. 15 Ma, which is close to the formation age of the Cuonadong muscovite granite reported in previous studies. Cathodoluminescence images indicate that skarn-hosted scheelite can be subdivided into an older type 1 scheelite and a younger type 2 scheelite. Type 1 scheelite is characterized by a negative Eu anomaly, whereas type 2 scheelite shows a positive Eu anomaly. Considering the close temporal and spatial relationship between the Cuonadong Miocene leucogranite and the ore-bearing skarn, and their similar lanthanide tetrad effect as observed in the REE patterns, we propose that the negative Eu anomaly was inherited from the Cuonadong Miocene leucogranite, while the positive Eu anomaly resulted from the addition of Eu2+ to the ore-forming fluid during greisenization. Sr isotope data show that the fluorite (87Sr/86Sr)i value of 0.728885 is within the range of the Cuonadong Miocene leucogranite (87Sr/86Sr)i values, while scheelite (87Sr/86Sr)i values (0.709717–0.713480) are similar to those of the Cuonadong marble (0.709525–0.712146). Since scheelite is intergrown with fluorite, we propose that the hydrothermal fluid that exsolved from the Cuonadong Miocene leucogranite is responsible for formation of both fluorite and scheelite. Water-rock interaction between this magma-derived fluid and the marble is responsible for the loss of the scheelite magmatic Sr isotopic signature.

Multistage magmatism recorded in a single gneiss dome: Insights from the Lhagoi Kangri leucogranites, Himalayan orogen

Determining the geochronological framework and geochemical nature of magmatism associated with orogenic processes is crucial to decipher the evolution of orogenic belts. The Himalayan orogen has recorded considerable information regarding deformation, metamorphism, and magmatism related to orogenic processes. Here, we identify four stages of granitic magmatism on the basis of monazite U–Th–Pb dating of rocks from the Lhagoi Kangri dome, north Himalayan antiform, southern Tibet: middle Eocene (42–40 Ma), late Eocene (ca. 36 Ma), Oligocene (ca. 26 Ma), and Miocene (16–13 Ma). The middle Eocene tourmaline-bearing leucogranite is characterized by (1) relatively high SiO2 (78.7 wt%), Al2O3 (12.6 wt%), and Na2O (6.3 wt%) contents; (2) enrichment in light rare earth elements (LREEs), depletion in heavy REEs, high abundances of REEs, and pronounced negative Eu anomalies; and (3) relatively low values of whole-rock SrNd isotope compositions (87Sr/86Sr(t) = 0.72101 and εNd(t) = −9.8). And the coeval garnet–bearing two–mica granite has a pronounced negative Eu anomaly (Eu/Eu* = 0.07) and a significate lanthanide tetrad effect (TE1,3 = 1.46). These geochemical data suggest that these leucogranites underwent fractional crystallization. They provide a robust evidence for that anatexis of the lower crust of Indian plate began at 42–40 Ma in the central Himalayan orogen. The Oligocene and Miocene two–mica granites share broadly similar geochemical characteristics, such as moderate REE contents and weak negative Eu anomalies, and are distinct from the garnet-bearing muscovite leucogranite. Whole-rock SrNd isotope compositions of the Oligocene and Miocene leucogranites differ from those of the middle Eocene leucogranites, with higher 87Sr/86Sr(t) ratios (0.73524–0.74188) and lower εNd(t) values (−14.7 to −13.7). These geochemical data indicate that the Oligocene and Miocene leucogranites are products of muscovite-dehydration melting of metasedimentary rocks. The garnet-bearing muscovite leucogranite shows the REE tetrad effect, which suggests that it is more evolved than the coeval two–mica granite. We therefore infer that the variations in age and isotopic characteristics of the studied leucogranites were caused by a change in melt source resulting from the compression–extension evolution of the Himalayan collisional orogenic system.

Evidence for extreme Sm[sbnd]Nd fractionation during chemical weathering

During subaerial chemical weathering, submarine weathering and other intracrustal processes, SmNd chemical fractionation remains uncertain, while a little is known about the conditions, scale and magnitude, specific processes and actual mechanism for possible SmNd fractionation. Here, an in situ terra rossa weathering profile developed on dolostone is chosen for the study. Based on sequential extraction experiments and measurements of the mineral and geochemical compositions including SrNd isotopic compositions, we suggest that subaerial chemical weathering not only leads to considerable SmNd mobilization, redistribution and secondary enrichment, but also gives rise to extreme SmNd fractionation, apparent 143Nd isotope homogenization, nearly complete resetting of the 147Sm143Nd isotope system, anomalous initial 143Nd/144Nd ratios, and meaningless 143Nd model age (TDM) for weathering products. We found that the lanthanide tetrad effect, rather than mineralogical control, is responsible for the observed substantial SmNd fractionation and for the other rare earth element fractionation. Under domination of the lanthanide tetrad effect, the mobility of Sm is preferential to that of Nd during their migration in the form of dissolved organic complexes. Our results also illustrate that resetting of the 147Sm143Nd isotope system in weathering products is controlled by the combined effect of the extraneous dissolved SmNd input and additional SmNd fractionation. Finally, we argue that similar scenarios may occur in submarine weathering, diagenesis and other geological processes.

Hydrothermal alteration in Eshtehard volcanoes, Iran: Constraints from trace elements redistribution and stable isotope geochemistry

We use the mineralogy, trace element compositions and elemental mass balance of volcanic materials collected from propylitic, potassic and phyllic alteration facies in the Eshtehard area of Iran to document the nature and effects of hydrothermal alteration. Incompatible element abundances in hydrothermally–altered samples show transformations that include: (i) depletion of alkalis and alkaline earth elements (i.e., Ba, Sr), (ii) variable behavior of first series transition elements (depletion in Cr, Co and Ni; enrichment in Zn and Cu), and (iii) depletion of HREE, Hf and Th relative to U and LREE. In detail, potassic (associated with a major addition of Cu) and phyllic zones are characterized by enrichment of SiO2 and MgO whereas propylitization depleted SiO2 and MnO, enriched MgO and Fe2O3, and increased LOI. Whole rock geochemistry along hydrothermal facies revealed consistent negative Ce and Eu anomalies, indicating that reducing conditions persisted during hydrothermal processes. Substantial changes in isovalent elements ratios (i.e., K/Ba, K/Rb, Y/Ho, Sr/Eu, Zr/Hf and Eu/Eu*) along the facies illustrate non–charge and radius control behavior are construed as lanthanide tetrad–effect phenomena. The co–occurrence of zigzag patterns (i.e., M and W–shapes) is evidence for partial or incomplete tetrad effect reaction between REE3+ and F-and Cl-rich fluids in hydrothermal systems. Low T4 tetrad–effect values overall suggest rock–fluid interaction involving rather low temperature hydrothermal solutions. Mass (ΔM) and volume (ΔV) were slightly depleted in the propylitic (−3.80% and −5.66%) potassic (−3.48% and −5.66%), and phyllic (−2.52% and −2.91%) zones with isocon slopes of 1.06, 1.06 and 1.03, respectively. We envisage a secondary phenomenon in open system conditions which accompanied fluid–rock interaction as the plausible cause of slight REE tetrad effect observed in the hydrothermally altered samples. Fluid inclusions studies yield homogenization temperatures of 275–596 °C and salinity ranging from 34 to 39 wt% NaCl equivalent suggesting boiling during mineralization in the Eshtehard area. The calculated δ18O and δD of the fluids range between 5.3 and 7.1 and −75 to −62 per mil, respectively. On this basis, we suggest that the ore-forming fluids had a magmatic source and underwent boiling and/or exchange with hydrous minerals.

Banded iron formation from Antarctica: The 2.5 Ga old Mt. Ruker BIF and the antiquity of lanthanide tetrad effect and super-chondritic Y/Ho ratio in seawater

Here we report the first detailed geochemical data for Banded Iron-Formation (BIF) from Antarctica. Micro drill cores were taken from adjacent magnetite/haematite and metachert bands from the 2.5 Ga old Mt. Ruker BIF, Prince Charles Mountains, East Antarctica. Low concentrations of Al, Zr, Hf, and Sc reveal the purity of the samples. The chemical composition matches closely that of other early Precambrian BIF, except for an enrichment of Ni, and high Ba/Sr ratios in the metachert. Shale-normalized Rare Earths and Yttrium (REYSN) patterns show all the features of modern seawater such as depletion of light vs heavy REYSN, positive anomalies of LaSN, GdSN, and YSN (i.e. super-chondritic Y/Ho ratios) and the W-type lanthanide tetrad effect (LTE), but positive EuSN and no CeSN anomalies (and no positive Eu anomalies in chondrite-normalized REY patterns). This distribution is fully compatible with that of other pure Early Precambrian BIFs, suggesting high-temperature hydrothermal input of REY into seawater and a redox level of the atmosphere-hydrosphere system too reducing for Ce oxidation. The uniform, super-chondritic Y/Ho ratios in adjacent iron-oxide and metachert BIF bands most strongly suggest that the conspicuous banding does not result from post-depositional separation of an initially homogenous Fe-silicate precipitate, but argues for a primary origin of the banding. The super-chondritic Y/Ho ratios fit well within the range reported for other BIF worldwide, corroborating that positive Y anomalies, although possibly of smaller size than today, have always been a characteristic feature of seawater. The Mt. Ruker BIF further complements the set of Early Precambrian marine chemical sediments in which the W-type LTE has been observed, and demonstrates the antiquity of the LTE in seawater. These subtle features reveal that the distribution of the redox-insensitive REY in seawater did not change significantly over the almost 4 billion years geological record of seawater. The super-chondritic Y/Ho ratios and W-type LTE in this and other oxide-facies BIF are in marked contrast to the REY distribution in Modern and Cenozoic oxidic hydrogenetic ferromanganese crusts, pointing towards fundamentally different removal mechanisms of REY from Modern vs Early Precambrian seawater.

Petrogenesis of the peralkaline Dutsen Wai and Ropp complexes in the Nigerian younger granites: implications for crucial metal enrichments

ABSTRACT The Dutsen Wai and Ropp complexes are parts of the over 50 within-plate alkaline ring complexes in north-central Nigeria. These complexes consist mainly of A-type granites that were emplaced between 175 Ma (in Dutsen Wai) and 149 Ma (in Ropp). They are characterized by moderately negative zircon ԑHf(t) values (–9.8 to – 5.86) with Paleoproterozoic (1597–1884 Ma) crustal model ages (TDMc), suggesting the mantle-derived parental magmas have been substantially modified by assimilation of crustal materials. The granites exhibit elevated HFSEs (e.g., Nb and Zr) and LILE (e.g., Rb and REE) concentrations, with higher values in the peralkaline than in the aluminous granites, but are depleted in compatible elements (e.g., CaO, MgO, Ba and Sr). This is typical of highly differentiated granites associated with rare metal mineralization. The peralkaline plutons show REE patterns with strong negative Eu anomalies, significant M-type lanthanide tetrad effect (TE1,3 = 1.16–1.32), and non-CHarge and Radius Controlled (CHARAC) behaviour of some HFSEs. The positive correlation of Na2O vs. Nb (r2 = 0.92) and Nb vs. TE1,3 (r2 = 0.7), increasing degree of albitization and shift in eutectics of granite minimum towards Ab-Qtz sideline indicate that Na-rich fluid plays an important role in the complexation between F and other incompatible elements in open system processes. Fluorine also favoured the retention of these crucial metals in the peralkaline melt until late magmatic-stage during which the breakdown of the F-HFSEs and F-REE complexes was accompanied by crystallization of pyrochlore and REE-bearing accessory minerals. We proposed that the emplacement of these A-type granites was probably linked to the prevailing transtension regime before the fragmentation of Gondwana during the Mesozoic period which reactivated some deep-seated Pan-African transcurrent faults. This, in turn, caused pressure release and channelled fluid, which triggered partial melting of the lower part of the lithospheric mantle.

Mineralogy, isotope geochemistry and ore genesis of the miocene Cuonadong leucogranite-related Be-W-Sn skarn deposit in Southern Tibet

The Himalayan orogenic belt is characterized by widespread leucogranites, which are mostly peraluminous with less than 5% mafic minerals. Previous studies mainly focused on the petrological characteristic, genetic mechanism, magmatic evolution and tectonic significance of these leucogranites. However, recently, a skarn-type Be–W–Sn polymetallic deposit, which is spatially related to the Cuonadong leucogranites of the Himalayan leucogranites belt, was discovered. The orebodies occur in the inner and outer contact zones between the Cuonadong leucogranites and their surrounding marble. This study focuses on the the characteristics of the skarn mineral assemblages. The deposit shows a typical skarn mineral zonation, from inside to outside, including dark pyroxene-garnet skarn zone, red garnet zone, dark green amphibole-specularite zone, light-green vesuvianite-epidote ribbon, and vesuvianite-chlorite zone. Zircon U-Pb dating shows that the ore-related leucogranite was emplaced at ca. 18 Ma. Geochemically, the leucogranite has high SiO2, Al2O3, Na2O, K2O and low CaO contents belonging to peraluminous granite. The Cuonadong leucogranite is characterized by right-dipping chondrite-normalized REE patterns with distinct negative Eu anomalies. Importantly, all samples show Lanthanide tetrad effect on chondrite-normalized REE patterns, indicating significant melt-fluid interaction has occurred due to strong fractional crystallization. Additionally, the Cuonadong leucogranite is enriched in large ion lithophile elements (such as Rb) and relatively depleted in high field strength elements (such as Nb, Zr, Hf), suggesting a crustal source region. High F and B contents in the magma could have significantly increased the solubility of water in the magma, while the magmatic-hydrothermal solution enriched in F and B should have remarkably enhanced the metal-carrying capacity and increased the permeability of surrounding rocks, which in turn effectively facilitated water–rock reaction.

Formation mechanisms of lanthanide tetrad effect in limestones: an example from Arbanos district, NW Iran

The Arbanos Limestone is a part of the Ruteh Formation of Upper Permian age located in NW Iran. No detailed geochemical characterizations of these limestones have been carried out to date. In this research, formation mechanisms of tetrad effect phenomenon in the lanthanide distribution patterns in these limestones are surveyed by applying different geochemical techniques. The mineralogical and geochemical characteristics of the limestones were examined using X-ray diffractometry (XRD) and chemical (ICP–AES and –MS) methods. Mineralogical studies indicate that calcite is the principal constituent accompanied by some minor accessory minerals such as quartz, kaolinite, plagioclase hematite, and smectite in the limestones. Geochemical parameters such as Ca/Mg, Sr, V/Cr, V/(V + Ni), U/Th, Ni/Co, and Mn* reveal that the limestones of the Ruteh Formation were probably deposited in a shallow, oxic, and low salinity environment. The distribution pattern of REE normalized to PAAS (Post Archean Australian Shale) display positive Ce and Eu anomalies in the limestones. The concentration of major and trace elements such as Si, Al, V, Cr, Ni, Rb, Th, U, Y, Zr, and Hf as well as Er/Nd ratio reveal contamination of the limestones by terrigenous materials. Furthermore, strong positive correlations between REE with elements such as Si and Al suggest detrital origin for REE, which is supported by non-seawater like PAAS-normalized REE distribution curves. Some geochemical rations such as Th/Co, Cr/Th, La/Co, Th/Cr, Eu/Eu*, and (La/Lu)N displayed that the terrigenous materials in the limestones were derived from shales of the Ruteh Formation. The zigzag forms in normalized REE patterns and non-CHARAC behavior of Y/Ho and Zr/Hf ratios are another geochemical characteristic of the limestones. According to calculated values for T1, T3 and T4 tetrad effect values reveal the occurrence of tetrad effect phenomenon in REE distribution pattern. Strong positive correlations between T1 and elements such as Hf, U, and V as well as negative correlation with Ca reveal that amount of detrital input and redox potential were likely be responsible for occurrence of lanthanide tetrad effect in the limestone. Meanwhile, strong positive correlations between T3-P, T4-Al, and T4-Nb suggest the important role of diagenetic fluids and contaminations in occurrence of lanthanide tetrad effect in limestones of the Arbanos district.

Textural and chemical variations of micas as indicators for tungsten mineralization: Evidence from highly evolved granites in the Dahutang tungsten deposit, South China

Abstract The Dahutang tungsten deposit, located in the Yangtze Block, South China, is one of the largest tungsten deposits in the world. Tungsten mineralization is closely related to Mesozoic granitic plutons. A drill core through a pluton in the Dalingshang ore block in the Central segment of the Dahutang tungsten deposit shows that the pluton is characterized by multi-stage intrusive phases including biotite granite, muscovite granite, and Li-mica granite. The granites are strongly peraluminous and rich in P and F. Decreasing bulk-rock (La/Yb)N ratios and total rare earth element (ΣREE) concentrations from the biotite granite to muscovite granite and Li-mica granite suggest an evolution involving the fractional crystallization of plagioclase. Bulk-rock Li, Rb, Cs, P, Sn, Nb, and Ta contents increase with decreasing Zr/Hf and Nb/Ta ratios, denoting that the muscovite granite and Li-mica granite have experienced a higher degree of magmatic fractionation than the biotite granite. In addition, the muscovite and Li-mica granites show M-type lanthanide tetrad effect, which indicates hydrothermal alteration during the post-magmatic stage. The micas are classified as lithian biotite and muscovite in the biotite granite, muscovite in the muscovite granite, and Li-muscovite and lepidolite in the Li-mica granite. The Li, F, Rb, and Cs contents of micas increase, while FeOT, MgO, and TiO2 contents decrease with increasing degree of magmatic fractionation. Micas in the muscovite granite and Li-mica granite exhibit compositional zonation in which Si, Rb, F, Fe, and Li increase, and Al decreases gradually from core to mantle, consistent with magmatic differentiation. However, the outermost rim contains much lower contents of Si, Rb, F, Fe, and Li, and higher Al than the mantle domains due to metasomatism in the presence of fluids. The variability in W contents of the micas matches the variability in Li, F, Rb, and Cs contents, indicating that both the magmatic and hydrothermal evolutions were closely associated with W mineralization in the Dahutang deposit. The chemical zoning of muscovite and Li-micas not only traces the processes of W enrichment by magmatic differentiation and volatiles but also traces the leaching of W by the fluids. Therefore, micas are indicators not only for the magmatic–hydrothermal evolution of granite, but also for tungsten mineralization.

Grouping separation of mixed rare earths from their coexisting aqueous solutions by liquid-column elution

Abstract A new approach was proposed for grouping separation of 14 lanthanide rare-earth ions from their co-existing mixed aqueous solutions, by performing liquid-column elution using the aqueous solution containing 14 lanthanide rare-earth ions as the stationary phase and the dispersed organic oil droplets containing P507 extractant as the mobile phase. It was revealed that 14 lanthanide rare-earth ions could be separated into four groups, according to the lanthanide tetrad effect, respectively eluting out from the liquid column at different time in a certain order. Various effects including the saponification degree of P507, the concentration of P507 in organic phase, the length and inner diameter of the extraction column on the performance of grouping separation of rare-earth ions were discussed. The changes of the mass transfer coefficients were also investigated. The separation efficiency of the four groups of rare-earth elements (REEs) was evaluated based on the elution resolution, Rs, of the elution peaks of La(III), Gd(III), Ho(III) and Lu(III), the four representative elements respectively from each of the four groups of REEs. Experimental results demonstrated that the separation of REEs by liquid-column elution mainly depended on the competitive adsorption of different rare-earth groups onto the surface of ascending P507 oil droplets. The affinity of different rare-earth groups with P507 extractant and a limited adsorption capacity of P507 molecules at the surface of the oil droplets ascending in liquid column play the important role. The present work highlights a promising technique for grouping separation of multiple lanthanide elements co-existing complex systems.

The Lanthanide Tetrad Effect in Argillic Alteration: An Example from the Jizvan District, Northern Iran

AbstractIntrusion of quartz‐monzodioritic igneous bodies of Oligocene age into Eocene lithic crystal tuffs and trachy‐basalts resulted in the occurrence of a widespread argillic alteration zone in the Jizvan district (northern Iran). Mineralogically, the argillic alteration zone includes minerals such as kaolinite, quartz, smectite, pyrophyllite, muscovite‐illite, alunite, rutile, calcite, feldspar, chlorite, hematite and goethite. Therefore, the non‐CHARAC behaviour for trace elements in the argillic samples is reflected in the non‐chondritic Y/Ho and Zr/Hf ratios and the irregular REE patterns, which appear related to the tetrad effect phenomenon. The chondrite‐normalized REE distribution patterns indicate both concave (W‐shaped) and convex (M‐shaped) tetrad effects in the argillic samples. Based on the field evidence and the results from geochemical studies, it can be concluded that the samples from the argillic alteration zone having high fourth tetrad effect values (&gt;0.30) were developed in the fault and breccia zones. The results indicate that factors such as preferential scavenging by Mn‐oxides, crystallization of clay minerals, fluid‐rock interaction, overprint of hypogene mineral assemblage by supergene ones, and the structural control, have all played an important role in the occurrence of tetrad effects in samples of the argillic zone in the Jizvan district.

Lanthanide tetrad effect in limestone: a tool to environment analysis of the Ruteh Formation, NW Iran.

Lanthanide tetrad effect in limestone: a tool to environment analysis of the Ruteh Formation, NW Iran.