Rare Earth Element Profiles Research Articles

Rare earth elements in mud volcano sediments from the Gulf of Cadiz, South Iberian Peninsula

Eight gravity cores (GC) were retrieved from the deep mud volcanoes Sagres, Bonjardim, Soloviev and Porto in the Gulf of Cadiz. Cores with 137 to 317 cm long were sliced in intervals of 15 to 20 cm thickness, and 46 samples were analyzed for grain size distribution, loss on ignition, Al, Fe, Ca, Mg, Mn, Sr, Ba and the rare earth elements (REE) La, Ce, Pr, Nd, Sm, Eu, Gd, Dy, Ho, Er, Tm, Yb and Lu. REE profile normalized to Post-Archean Australian Average Shale (PAAS) was dominated by a mid-REE bulge with a pronounced Eu enhancement. Sediment reducing conditions resulting from the anaerobic oxidation of methane probably contributed to the positive-Eu anomaly (1.18–2.19, PAAS normalization). Most likely, reactions near the sulfate-methane transition zone such as the precipitation of barium sulfate found at layers around 50-cm depth explain the enhancement of Eu/Eu* ratios. The Ce anomalies (0.93–1.09) were almost absent.

A complex history of silicate differentiation of Mars from Nd and Hf isotopes in crustal breccia NWA 7034

Resolving the possible mantle and crustal sources for shergottite meteorites is crucial for understanding the formation and early differentiation of Mars. Orbiter and rover characterization of the martian surface reveal that the major element composition of most of its surface does not match the shergottites (McSween et al., 2009) leaving the relationship between them poorly understood. The identification of the meteorite NWA 7034 and its pairs as a Mars surface rock (Cartwright et al., 2014) provides access to a representative sample of Mars' crust (Agee et al., 2013; Humayun et al., 2013). Utilizing the short-lived 146Sm–142Nd, and long-lived 147Sm–143Nd and 176Lu–176Hf chronometers, which are sensitive to silicate differentiation, we analyzed three fragments of NWA 7034. The very negative mean isotopic compositions for this breccia, μ142NdJNdi-1=−45±5 (2SD), ε143NdCHUR=−16.7±0.4 (2SD) and ε176HfCHUR=−61±9 (2SD) point to an ancient origin for this martian crust. However, modeling of the data shows that the crust sampled by NWA 7034 possesses a Hf/Nd ratio and coupled ε143Nd–μ142Nd model age that are incompatible with this crustal reservoir being an end-member that generated the shergottite source mixing array. In addition, this crust is not juvenile, despite its rare earth element profile, but has had a multistage formation history. Therefore, early crustal extraction alone was not responsible for the creation of the reservoirs that produced the shergottites. Instead mantle reservoirs formed via other early differentiation processes such as in a Mars magma ocean must be responsible for the trace element and isotopic signatures present in shergottites.

Preliminary geochemical data of the mafic rocks from the Ovacik and Pülümür Ophiolite Zone (Eastern Anatolia, Turkey): implications for the geodynamic evolution of the Northern Neotethyan Ocean

The Izmir-Ankara-Erzincan-Sevan-Akera Suture Belt (IAESASB) stretches from the Aegean Sea to the Lesser Caucasus and includes the remnants of the Northern Neotethys. The Ovacik and Pulumur Ophiolite Zone (OPOZ) to the north of Tunceli is less-known members of this belt. In this study, preliminary geochemical data from the basaltic and gabbroic rocks from this zone are presented to provide the first insights into their geochemistry. The studied mafic samples exhibit geochemical characteristics of an intra-oceanic subduction system. Three types of samples were differentiated on the basis of their major, trace and rare earth element (REE) geochemistry. The first one is boninitic and displays highly depleted elemental pattern (relative to N-MORB) and concave REE profile. The second type is akin to back-arc basin basalts (BABB) and generally reflects normal-MORB (NMORB)-like high field strength element (HFSE) patterns coupled with negative Nb anomalies. The last type is relatively similar to the BABB-type, but it lacks the marked negative anomaly in Nb and can be ascribed to the mid-ocean ridge basalt (MORB). The overall geochemical features suggest that these mafic rocks were predominantly generated in a supra-subduction setting from a subduction-modified mantle source. It is further suggested that the Ovacik and Pulumur Ophiolite Zone was formed in an oceanic arc-basin system within the northward subducting Northern Neotethys.

Wine Traceability with Rare Earth Elements

The traceability of foodstuffs is now a relevant aspect of the food market. Scientific research has been devoted to addressing this issue by developing analytical protocols in order to find the link between soil and food items. In this view, chemical parameters that can act as soil markers are being sought. In this work, the role of rare earth elements (REEs) as geochemical markers in the traceability of red wine is discussed. The REE distribution in samples from each step of the wine making process of Primitivo wine (produced in Southern Italy) was determined using the highly sensitive inductively coupled plasma-mass spectrometry (ICP-MS) technique. Samples analyzed include grapes, must, and wine samples after every step in the vinification process. The resulting data were compared to the REE distribution in the soil, revealing that the soil fingerprint is maintained in the intermediate products up to and including grape must. Fractionation occurs thereafter as a consequence of further external interventions, which tends to modify the REE profile.

Direct measurement of metal concentrations in fluid inclusions, a tale of hydrothermal alteration and REE ore formation from Strange Lake, Canada

Granites and pegmatites in the Strange Lake pluton underwent extreme enrichment in high field strength elements (HFSE), including the rare earth elements (REE). Much of this enrichment took place in the most altered rocks, and is expressed as secondary minerals, showing that hydrothermal fluids played an important role in HFSE concentration. Vasyukova et al. (2016) reconstructed a P-T-X path for the evolution of these fluids and provided evidence that hydrothermal activity was initiated by exsolution of fluid during crystallisation of border zone pegmatites (at ~450–500 °C and 1.1 kbar). This early fluid comprised a high salinity (25 wt% NaCl) aqueous phase and a CH4 + H2 gas. During cooling, the gas was gradually oxidised, first to higher hydrocarbons (e.g., C2H6, C3H8), and then to CO2, and the salinity decreased to 4 wt% (~250–300 °C), before increasing to 19 wt%, due to fluid-rock interaction (~150 °C). Here, we present crush-leach fluid inclusion data on the concentrations of the REE and major ligands at different stages of the evolution of the fluid.The chondrite-normalised REE profile of the fluid evolved from light REE (La-Nd)-enriched at high temperature (~400 °C, Stages 1–2a) to middle REE (Sm-Er)-enriched at 360 to 250 °C (Stages 2b–3) and strongly heavy REE (Tm-Lu)-enriched at low temperature (150 °C, Stage 5). These changes in the REE distribution were accompanied by changes in the concentrations of major ligands, i.e., Cl− was the dominant ligand in Stages 1, 2, 4 and 5, whereas HCO3− was dominant in Stage 3.Alteration of arfvedsonite to aegirine and/or hematite contributed strongly to the mobilisation of the REE. This alteration released middle REE (MREE) and heavy REE (HREE), which either partitioned into the fluid or precipitated directly as bastnäsite-(Ce), ferri-allanite-(Ce) or gadolinite-(Y). Replacement of primary fluorbritholite-(Ce), which crystallised from an immiscible fluoride melt and altered to bastnäsite-(Ce), was also important in mobilising the REE (MREE).This paper presents the first report of the distribution of the REE in an evolving hydrothermal fluid. Using this distribution, in conjunction with information on the changing physicochemical conditions, the study identifies the sources of REE enrichment, reconstructs the path of REE concentration, and evaluates the REE mineralising capacity of the fluid. Finally, this information is integrated into a predictive model for REE mobilisation applicable not only to Strange Lake but any REE ore-forming system, in which hydrothermal processes were important.

Magmatic evolution and porphyry–epithermal mineralization in the Taftan volcanic complex, southeastern Iran

The Taftan volcanic complex is located above the Makran subduction zone in Sistan and Baluchestan province, southeastern Iran. The earliest volcanic activity at Taftan started in the late Miocene (∼8 Ma) with eruption of andesitic to dacitic lava onto a Cretaceous to Eocene volcanic and sedimentary paleosurface ∼20 km to the northwest of the current volcanic edifice. Later Plio-Pleistocene volcanism consisted of voluminous andesitic and dacitic lavas and pyroclastic flows (∼3.1 to 0.4 Ma). Taftan, and the neighbouring Bazman volcano, are the southeasternmost and youngest manifestations of arc-related volcanism in Iran, which began with the Eocene–Miocene Urumieh-Dokhtar Magmatic Arc (UDMA) in northwest and central Iran, and extends into western Pakistan (Chagai Arc).Major porphyry Cu±Mo±Au deposits are associated with Miocene to Pliocene intrusive rocks in the Kerman section of the Eocene–Neogene Urumieh-Dokhtar Magmatic Arc in southeastern Iran (e.g., Sar Cheshmeh, Meiduk), and at Reko Diq and Saindak in the Late Cretaceous–Quaternary Chagai Arc in western Pakistan. In a gap of ∼300 km between these two belts, several porphyry and epithermal prospects are exposed in the Miocene–Pliocene sections of the Taftan volcanic complex, including the Kharestan (6.10 ± 0.80 Ma) and Bidester porphyry-epithermal Cu-Au deposits (∼4.3 Ma), and the Siah Jangal epithermal Au deposit (late Miocene). In addition, several argillic to advanced argillic and fumarolic alteration zones occur in Plio-Pleistocene volcanic rocks around the current volcanic edifice. These deposits have received limited exploration.Electron microprobe analyses of amphibole (magnesio-hastingsite) phenocrysts and magnetite–ilmenite mineral pairs from the Taftan and Bazman volcanic rocks indicate a change of crystallization temperature and magmatic oxidation state from ∼1000 °C and ΔFMQ ≈ +1 in andesitic rocks, to ∼900 °C and ΔFMQ ≈ +2 in dacitic rocks. Magmatic water content was >4 wt%, as indicated by the ubiquitous presence of amphibole phenocrysts.Major and trace element compositions of the Taftan and Bazman volcanic rocks show calc-alkaline to high-K calc-alkaline affinity, with relative depletions of Nb, Ta, and Ti and enrichments of large-ion c elements (LILE), Th, and U on normalized diagrams. These trace element patterns, including listric-shaped normalized rare earth element profiles and relatively high Sr/Y and La/Yb ratios, are similar to those of fertile Miocene igneous rocks from the Kerman Belt and Chagai Arc, and suggest that the Taftan suite in particular should be prospective for porphyry Cu ore formation.Regionally, there is no clear geochemical difference between the Neogene Kerman Belt rocks, which are thought to post-date the onset of collision between the Afro-Arabian and Eurasian plates (late Oligocene to earliest Miocene), and the subduction-related Bazman–Taftan and Chagai Belt magmas. The porphyry deposits formed in these distinct settings are also virtually indistinguishable. This suggests that most of the processes affecting the geochemistry and metallogeny of the magmas in both settings take place in the lithosphere, albeit that the ultimate source of the magmas is in the supra-subduction zone asthenospheric mantle wedge. In collisional environments, subduction-related material previously crystallized in the deep lithosphere is simply being remobilized.

Rare earth elements profile in a cultivated and non-cultivated soil determined by laser ablation-inductively coupled plasma mass spectrometry

Rare earth elements (REEs) have several applications but the effects on environment are not well known. Therefore, the aim of this work is to establish a method for direct solid sample analysis by laser ablation-inductively coupled plasma mass spectrometry (LA-ICP-MS) to evaluate the concentration and distribution of REEs in cultivated and non-cultivated soil. Samples were collected in two areas to 40 cm of depth. The LA-ICP-MS method is easy to be implemented and the sample treatment is very fast comprising only its drying, grounding and pressing as a pellet. The accuracy of the method was evaluated by using a certified reference material (BCR 667 – Estuarine Sediment, Institute for Reference Materials and Measurements (IRMM)) where good agreement with the certified values was obtained. Analyte recovery at two levels of concentration (2.5 and 15.0 μg g−1) was also performed and recoveries in the range of 85%–120% were achieved, values that are acceptable for LA-ICP-MS analysis. In general, the concentration of the REEs is higher in the cultivated soil and increased from the surface to deeper layers, which can be a consequence of fertilizer application.

Constraints on the uptake of REE by scheelite in the Baoshan tungsten skarn deposit, South China

Scheelite is the main ore mineral in skarn-type tungsten deposits, and a common accessory mineral in a variety of rock-types. The Baoshan deposit in South China is one of the most important polymetallic scheelite skarn deposits in China, hosting 40,000t of WO3 with economic concentrations of Zn, Cu, and Ag. It is hosted by a calcic skarn that is zoned outwards mineralogically from garnet-clinopyroxene, through clinopyroxene-garnet, to wollastonite, and overprinted by retrograde minerals. Scheelite occurs in both the prograde and retrograde skarns, and is complexly zoned. On the basis of its textures, the scheelite was classified into three types. Scheelite I and II belong to the early and late prograde stages, respectively, and Scheelite III precipitated during the retrograde stage. The molybdenum (Mo) content of these scheelite types ranges from 54ppm to 24wt%, and the total rare earth element content ranges from 12 to 321ppm. Rare earth element (REE) concentrations and chondrite-normalized REE profiles vary with the distribution of major elements. The profiles indicate variable degrees of REE enrichment, which correlates negatively with the Mo content. Molybdenum-rich scheelite displays a negative Eu anomaly, and Mo-poor scheelite a positive Eu anomaly. Crystal structure provided the first-order control on the minor and trace element composition of the scheelite. Incorporation of REE3+ into scheelite was controlled partly by a coupled substitution involving Mo. The lattice strain model was used to estimate scheelite-fluid partition coefficients for the REE from the contents of these elements in the scheelite and to predict the relative distributions of the REE in the ore-forming fluids. It is proposed that conditions were initially oxidizing, leading to strong incorporation of Mo in Scheelite I, that they became more reducing with the crystallization of Scheelite II containing lesser Mo, and that during retrograde skarn formation there was a return to oxidizing conditions due to an influx of meteoric waters, which altered Scheelite II giving rise to the formation of Scheelite III. The study shows that the composition of scheelite recorded the history of the Baoshan hydrothermal system, and that the behaviour of the REE could be used to quantitatively reconstruct the changing physicochemical conditions during ore formation.

Petrogenesis of basaltic shergottite Northwest Africa 8657: Implications for fO2 correlations and element redistribution during shock melting in shergottites

AbstractNorthwest Africa (NWA) 8657 is an incompatible trace element‐enriched, low‐Al basaltic shergottite, similar in texture and chemistry to Shergotty, Zagami, and NWA 5298. It is composed of zoned pyroxene, maskelynite, merrillite, and Ti‐oxide minerals with minor apatite, silica, and pyrrhotite. Pyroxene grains are characterized by patchy zoning, with pigeonite or augite cores zoned to Fe‐rich pigeonite mantles. The cores have rounded morphologies and irregular margins. Combined with the low Ti/Al of the cores, the morphology and chemistry of the pyroxene grains are consistent with initial crystallization at depth (30–70 km) followed by partial resorption en route to the surface. Enriched rare earth element (REE) equilibrium melt compositions and calculated oxygen fugacities (fO2) conditions for pigeonite cores indicate that the original parent melts were enriched shergottite magmas that staged in chambers at depth within the Martian crust. NWA 8657 does not represent a liquid but rather entrained a proportion of pyroxene crystals from magma chambers where fractional crystallization was occurring at depth. Variation between fO2 and bulk‐rock (La/Yb)N of the enriched and intermediate shergottites suggests that oxidation conditions and degree of incompatible element enrichment in the source may not be correlated, as thought previously. Shock melt pockets are characterized by an absence of phosphates and oxide minerals. It is likely that these phases were melted during shock. REEs were redistributed during this process into maskelynite and to a lesser extent the shock melt; however, the overall normalized REE profile of the shock melt is like that of the bulk‐rock, but at lower absolute concentrations. Overall, shock melting has had a significant effect on the mineralogy of NWA 8657, especially the distribution of phosphates, which may be significant for geochronological applications of this meteorite and other Martian meteorites with extensive shock melt.

Phase equilibria and geochemical constraints on the petrogenesis of high-Ti picrite from the Paleogene East Greenland flood basalt province

Phase equilibrium experiments have been performed on an extremely high-Ti (5.4wt.% TiO2) picrite from the base of the Paleogene (~55Ma) East Greenland Flood Basalt Province. This sample has a high CaO/Al2O3 ratio (1.14), a steep rare-earth elements (REE) profile, is enriched in incompatible trace elements, and is in chemical equilibrium with highly primitive olivine. This all suggests that the picrite is a near-primary melt that did not suffer major chemical evolution during ascent from the mantle source and through the crust. Near-liquidus phase relations were determined over the pressure range of 1atm, 1 to 1.5GPa and at temperatures from 1094 to 1400°C. They provide an important constraint on the petrogenesis of these lavas. The high-Ti picritic melt is multi-saturated with olivine (Ol)+orthopyroxene (Opx) at 1GPa but has only Ol or Opx on the liquidus at lower and higher pressures, respectively. This indicates the primitive melt was last equilibrated with its mantle source at relatively shallow pressure (~1GPa). Melting probably started at 2-3 GPa and the picritic melt was produced by 15-30% melting of the mantle source. Such a degree of partial melting requires a mantle with a high potential temperature (1480-1530˚C). The relatively low CaO content and high FeO/MnO ratios of the most primitive East Greenland picrites, the high Ni content of olivine phenocrysts and the presence of low-Ca pyroxene (i.e., pigeonite) at high pressure in our experiments all suggest that the mantle source contained a major component of garnet pyroxenite. Residual garnet in the source could adequately explain the low Al2O3 content (7.92 wt.%) and steep REE patterns of the picrite sample. However, simple melting of a lherzolitic source, even with a major pyroxenite component, cannot explain the formation of magmas with the very high Ti contents observed in some East Greenland basalts. We therefore propose that magmas highly-enriched in Ti were produced by melting of a metasomatized mantle source containing Ti-enriched amphibole and/or phlogopite.

An impact of moss sample cleaning on uncertainty of analytical measurement and pattern profiles of rare earth elements

The main source of rare earth elements (REE) in mosses is atmospheric deposition of particles. Sample treatment operations including shaking, rinsing or washing, which are made in a standard way on moss samples prior to chemical analysis, may lead to removing particles adsorbed onto their tissues. This in turn causes differences in REE concentrations in treated and untreated samples. For the present study, 27 combined moss samples were collected within three wooded areas and prepared for REE determinations by ICP-MS using both manual cleaning by shaking and triple rinsing with deionized water. Higher concentrations of REE were found in manually cleaned samples. The comparison of REE signatures and shale-normalized REE concentration patterns showed that the treatment procedure did not lead to fractionation of REE. All the samples were enriched in medium rare earth elements, and the δMREE factor remained practically unchanged after rinsing. Positive anomalies of Nd, Sm, Eu, Gd, Er and Yb were observed in both, manually cleaned and rinsed samples. For all the elements examined, analytical uncertainty was below 3.0% whereas sample preparation uncertainty computed with ANOVA, RANOVA, modified RANOVA and range statistics methods varied from 3.5 to 29.7%. In most cases the lowest srprep values were obtained with the modified RANOVA method.

Metavolcanic host rocks, mineralization, and gossans of the Shaib al Tair and Rabathan volcanogenic massive sulphide deposits of the Wadi Bidah Mineral District, Saudi Arabia

ABSTRACTThe Wadi Bidah Mineral District of Saudi Arabia contains more than 16 small outcropping stratabound volcanogenic Cu–Zn–(Pb) ± Au-bearing massive sulphide deposits and associated zones of hydrothermal alteration. Here, we use major and trace element analyses of massive sulphides, gossans, and hydrothermally altered and least altered metamorphosed host rock (schist) from two of the deposits (Shaib al Tair and Rabathan) to interpret the geochemical and petrological evolution of the host rocks and gossanization of the mineralization. Tectonic interpretations utilize high-field-strength elements, including the rare earth elements (REE), because they are relatively immobile during hydrothermal alteration, low-grade metamorphism, and supergene weathering and therefore are useful in constraining the source, composition, and physicochemical parameters of the primary igneous rocks, the mineralizing hydrothermal fluid and subsequent supergene weathering processes. Positive Eu anomalies in some of the massive sulphide samples are consistent with a high temperature (>250°C) hydrothermal origin, consistent with the Cu contents (up to 2 wt.%) of the massive sulphides. The REE profiles of the gossans are topologically similar to nearby hydrothermally altered felsic schists (light REE (LREE)-enriched to concave-up REE profiles, with or without positive Eu anomalies) suggesting that the REE experienced little fractionation during metamorphism or supergene weathering. Hydrothermally altered rocks (now schists) close to the massive sulphide deposits have high base metals and Ba contents and have concave-up REE patterns, in contrast to the least altered host rocks, consistent with greater mobility of the middle REE compared to the light and heavy REE during hydrothermal alteration. The gossans are interpreted to represent relict massive sulphides that have undergone supergene weathering; ‘chert’ beds within these massive sulphide deposits may be leached wall-rock gossans that experienced silicification and Pb–Ba–Fe enrichment from acidic groundwaters generated during gossan formation.

Age and origin of the Cannon Point syenite, Essex County, New York: southernmost expression of Monteregian Hills magmatism?

Two syenite sills intrude the local Paleozoic strata of eastern New York State and are exposed along the western shore of Lake Champlain. The sills are fine-grained, alkali feldspar syenites and quartz syenites, with phenocrysts of sanidine and albite. The two sills are compositionally distinct, with crossing rare earth element profiles and different incompatible element ratios, which eliminates the possibility of a simple petrogenetic relationship. Zircon extracted from the upper sill yields a U–Pb age of 131.1 ± 1.7 Ma, making the sills the youngest known igneous rocks in New York State. This age is similar to that of the earliest intrusions in the Monteregian Hills of Quebec, >100 km to the north. Sr and Nd radiogenic isotope ratios are also similar to those observed in some of the syenitic rocks of the eastern Monteregian Hills. The Cannon Point syenites have compositions typical of A-type, within-plate granitoids. They exhibit unusually high Ta and Nb concentrations, resulting in distinct trace element signatures that are similar to those of the silicic rocks of the Valles Caldera, a large, rift-related magmatic system. We suggest that the Cannon Point syenites were melts derived primarily by anatexis of old, primitive, lower crustal material in response to Mesozoic rifting and to the intrusion of mantle-derived magmas. The sills indicate that the effects of continental rifting were spatially and temporally extensive, resulting in the reactivation of basement faults in the Lake Champlain Valley hundreds of kilometers west of the active rift boundary, and crustal melting >50 Ma after the initiation of rifting.

KREEP basalt petrogenesis: Insights from 15434,181

AbstractReturned lunar KREEP basalts originated through impact processes or endogenous melting of the lunar interior. Various methods have been used to distinguish between these two origins, with varying degrees of success. Apollo 15 KREEP basalts are generally considered to be endogenous melts of the lunar interior. For example, sample 15434,181 is reported to have formed by a two‐stage cooling process, with large orthopyroxene (Opx) phenocrysts forming first and eventually cocrystalizing with smaller plagioclase crystals. However, major and trace element analyses of Opx and plagioclase coupled with calculated equilibrium liquids are inconsistent with the large orthopyroxenes being a phenocryst phase. Equilibrium liquid rare earth element (REE) profiles are enriched relative to the whole rock (WR) composition, inconsistent with Opx being an early crystallizing phase, and these are distinct from the plagioclase REE equilibrium liquids. Fractional crystallization modeling using the Opx equilibrium liquids as a parental composition cannot reproduce the WR values even with crystallization of late‐stage phosphates and zircon. This work concludes that instead of being a phenocryst phase, the large Opx crystals are actually xenocrysts that were subsequently affected by pyroxene overgrowths that formed intergrowths with cocrystallizing plagioclase.

Lithostratigraphic and structural reconstruction of the Zn-Pb-Cu-Ag-Au Lemarchant volcanogenic massive sulphide (VMS) deposit, Tally Pond group, central Newfoundland, Canada

The Lemarchant volcanogenic massive sulphide (VMS) deposit (1.24Mt grading at 0.58% Cu, 5.38% Zn, 1.19% Pb, 1.01g/t Au, and 59.17g/t Ag) is a bimodal-felsic VMS deposit hosted within the Late Cambrian (∼513–509Ma) Tally Pond group of the Exploit Subzone in central Newfoundland, Canada. The deposit is hosted by andesitic volcaniclastic and volcanic rocks with subordinate dacite flows. The mineralisation is hosted by the dacites and is overlain by pillowed and massive basalts.Four structural breaks offset the local stratigraphic sequences including: 1) the LJ syn-volcanic shear zone; 2) the KJ syn-volcanic shear zone; 3) the Lemarchant thrust; and 4) the Bam normal fault. Deformation of the Lemarchant likely occurred during the Penobscot orogeny (486–478Ma). Early deformation is marked with the local deformation of the LJ and KJ syn-volcanic shear zones during NW-SE compression which coincided with the development of the Lemarchant thrust. A late (<465Ma) east trending normal fault, the Bam fault, affected the central portion of the Lemarchant area and down-faulted the southern portion of the study area relative to the northern portion.Immobile element systematics of all the sequences from the Lemarchant deposit are tholeiitic with transitional Zr/Y ratios (1.9–6.6), Lan/Smn ratios <1 (normalised to upper crust), and have primitive mantle extended rare earth elements profiles with slight light rare earth element (LREE)-enriched patterns with flat heavy REE (HREE), and weak to strong negative Nb, Zr, and Ti anomalies. Together, these geochemical features, coupled with an FIIIa signature, and existing mineralogical and Nd-Pb isotope data, are consistent with the rocks at the Lemarchant deposit having formed within a shallow (<1500m) arc or migrating cross-arc seamount chain located within a young peri-continental rifted arc along the margin of Ganderia, within the Iapetus Ocean. The estimated shallow water emplacement of the deposit likely allowed boiling near or at the rock-sea water interface, ultimately resulting in precious metal enrichment of the Lemarchant deposit. It is suggested that cross-arcs within rifted arc environments may represent favourable exploration targets for precious metal-enriched VMS deposits.

Mo-mineralized porphyries are relatively hydrous and differentiated: insights from the Permian-Triassic granitic complex in the Baituyingzi Mo–Cu district, eastern Inner Mongolia, NE China

Mo–Cu mineralization in the Baituyingzi district of eastern Inner Mongolia occurs within a granitic complex. This paper presents and discusses zircon U–Pb ages and whole-rock geochemical and Sr–Nd–Pb isotopic data from the granitic complex as potential indicators for porphyry Mo fertility. The U–Pb ages indicate that five units of the granitic complex were emplaced between 265.2 ± 0.7 and 246.5 ± 1.0 Ma. Constrained by crosscutting dikes, Mo–Cu mineralization was probably related to the Baituyingzi monzogranite porphyry dated at 248.2 ± 0.64 Ma. The intrusions belong to high-K calc-alkaline to shoshonitic series that are characterized by highly fractionated rare earth element (REE) patterns and strong enrichments of large ion lithophile elements, relative to high-field strength elements. Apart from the ∼246-Ma dike that shows negative eNd (t) values (−14.9 to −13.1), the intrusions have eNd(t) values ranging from −3.9 to 1.0, relatively young depleted mantle model ages (811 to 1183 Ma), 206Pb/204Pb of 18.137–18.335, and 207Pb/204Pb of 15.591–15.625, which are consistent with a juvenile lower crustal origin. Among the intrusions, the ∼248-Ma porphyry and the ∼246-Ma dike show adakite-like characteristics (e.g., Sr/Y = 44.9–185) and listric-shaped REE patterns that indicate amphibole fractionation and a hydrous magma source. However, the porphyry exhibits a higher differentiation index (81.4–91.5) and a steeper REE profile (e.g., LaN/YbN = 25.6–87.0) than those of the ∼246-Ma dike, which suggests that it is highly differentiated. We propose that the complex was generated by the partial melting of juvenile mafic lower crust (containing minor old crustal relicts) that was triggered by collision between the North China Craton and Siberian Craton. As indicated by the Th/Nb, Th/Yb, Ba/Th, and Ba/La ratios of the intrusions, the crust may have been derived from the melting of the fertile mantle wedge that was metasomatized by various amounts of slab-derived fluids or melts due to earlier subduction and was heterogeneous in terms of water, Cu, Mo, and S contents and possible oxidation state. The fertility of the porphyry was likely associated with the addition of earlier subduction-related slab melts to the magma source (leading to a hydrous and possible high oxidation state) and the long-time (∼20 Ma) collision tectonic setting in which it formed (resulting in a highly differentiated state).

Carbonate–silicate melt immiscibility, REE mineralising fluids, and the evolution of the Lofdal Intrusive Suite, Namibia

The Lofdal Intrusive Suite, Namibia, consists of calcio-carbonatite and silica-undersaturated alkaline intrusive rocks ranging in composition from phono-tephrite to phonolite (and nepheline syenite). The most primitive of these rocks is the phono-tephrite, which, on the basis of its Y/Ho and Nb/Ta ratios, is interpreted to have formed by partial melting of the mantle. Roughly linear trends in major and trace element contents from phono-tephrite to phonolite and nepheline syenite indicate that the latter two rock types evolved from the phono-tephrite by fractional crystallisation. The nepheline syenite, however, has a lower rare earth element (REE) content than the phonolite. The carbonatite has a primitive mantle-normalised REE profile roughly parallel to that of the silica-undersaturated alkaline igneous rocks, although the absolute REE concentrations are higher. Like the phono-tephrite, it also has a mantle Y/Ho ratio. However, the Nb/Ta and Zr/Hf ratios are significantly higher. Moreover, the carbonatite displays strong negative Ta, Zr and Hf anomalies on spidergrams, whereas the silicate rocks display positive anomalies for these elements. Significantly, this behaviour is predicted by the corresponding carbonatite-silicate melt partition coefficients, as is the behaviour of the REE. Based on these observations, we interpret the carbonatite to represent an immiscible liquid that exsolved from the phono-tephrite or possibly the phonolite melt. The result was a calcio-carbonatite that is enriched in the heavy REE (HREE) relative to most other carbonatites. Fluids released from the corresponding magma are interpreted to have been the source of the REE mineralisation that is currently the target of exploration.

Rare earth and trace element signatures for assessing an impact of rock mining and processing on the environment: Wiśniówka case study, south-central Poland.

A detailed hydrogeochemical study was performed in the Wiśniówka mining area (south-central Poland). This covered three acid pit bodies, historic tailings acid ponds, acid pools, and additionally two neighboring rivers. All these acid mine drainage (AMD) waters are characterized by the pH in the range of 1.7 (pools) to 3.5 (tailings ponds). The most interesting is the Podwiśniówka acid pit lake that shows a very low pH (2.2–2.5) and very high concentrations of SO4 2− (2720–5460 mg/L), Fe (545–1140 mg/L), Al (86.2 mg/L), As (9603–24,883 μg/L), Co (1317–3458 μg/L), Cr (753–2047 μg/L), Cu (6307–18,879 μg/L), Ni (1168–3127 μg/L), and rare earth element (REE) (589–1341 μg/L). In addition, seeps that drain the Podwiśniówka mine tailings and partly aggregate piles form strong acid pools in the mining area. Along with these pools, in which As and REE contents reach 369,726 and 6288 μg/L, respectively, these waters are among the most distinctive As- and REE-rich AMD surface waters across the world. It is noteworthy that the Podwiśniówka acid pit lake and Wiśniówka Duża acid pit sump exhibit different element signatures and REE concentration patterns normalized to North American Composite Shale (NASC): the Podwiśniówka acid pit lake always shows a characteristic roof-shaped medium REE (MREE) profile with distinct enrichments in Gd, Eu, and Tb whereas the other one displays a step-shaped heavy REE (HREE) profile with positive Tb and Gd anomalies. The REE undergo fractionation during weathering and the subsequent leaching of dissolved and suspended fractions from rocks to acid water bodies where these and other elements are further fractionated by geochemical processes. This study shows that the individual REE have greater affinities for Mn, HREE for Fe and SO4 2−, and only La and Ce for Al. This specific water geochemistry has enabled us to (i) pinpoint the location of AMD “hot spots” originated from quartzite mining and processing operations conducted by current and previous mining companies, (ii) predict the directions and effects of future strip mining for quartzites in the Wiśniówka Duża and Podwiśniówka open pits, and (iii) evaluate the potential impact of mining and processing effluents on the quality of rivers.

The thermal and chemical evolution of hydrothermal vent fluids in shale hosted massive sulphide (SHMS) systems from the MacMillan Pass district (Yukon, Canada)

At Macmillan Pass (YT, Canada), the hydrothermal vent complexes beneath two shale-hosted massive sulphide (SHMS) deposits (Tom, Jason) are well preserved within Late Devonian strata. These deposits provide a unique opportunity to constrain key geochemical parameters (temperature, salinity, pH, fO2, ΣS) that are critical for metal transport and deposition in SHMS systems, and to evaluate the interaction between hydrothermal fluids and the mudstone host rock. This has been achieved using a combination of detailed petrography, isotopic techniques (δ34S, δ13C and δ18O values), carbonate rare earth element analysis (LA-ICP-MS), fluid inclusion analysis (microthermometry, gas analysis via incremental crush fast scan mass spectrometry), and thermodynamic modelling.Two main paragenetic stages are preserved in both vent complexes: Stage 1 comprises pervasive ankerite alteration of the organic-rich mudstone host rock and crosscutting stockwork ankerite veining (±pyrobitumen, pyrite and quartz) and; Stage 2 consists of main stage massive sulphide (galena-pyrrhotite-pyrite±chalcopyrite-sphalerite) and siderite (±quartz and barytocalcite) mineralisation. Co-variation of δ18O and δ13C values in ankerite can be described by temperature dependent fractionation and fluid rock interaction. Together with fluid inclusion microthermometry, this provides evidence of a steep thermal gradient (from 300 to ∼100°C) over approximately 15m stratigraphic depth, temporally and spatially constrained within the paragenesis of both vent complexes and developed under shallow lithostatic (<1km; 250 bars) to hydrostatic (<400m; 40 bars) conditions. There is evidence of mixing between diagenetic and hydrothermal fluids recorded in chondrite-normalised rare earth element (REE) profiles of ankerite and siderite. Middle REE enrichments and superchondritic Y/Ho ratios (>28), characteristic of diagenetic fluids, are coupled with positive europium anomalies and variable light REE depletion, which are more consistent with chloride complexation in hot (>250°C) hydrothermal fluids. In this shallow sub-seafloor setting, thermal alteration of organic carbon in the immature, chemically reactive mudstones also had an important role in the evolution of fluid chemistry. Reduced sulphur generation via thermochemical reduction of Late Devonian seawater sulphate produced positive δ34S values in sulphide minerals (+7.5‰ to +19.5‰), coupled with a suite of volatile components (CO2, CH4, C1–C4 hydrocarbons, N2) trapped in Stage 2 quartz.Many of these geochemical features developed during the final stages of fluid ascent, in a system where the fluid cooled close to the site of mineralisation. Using this information, we have modelled the metal transporting capacity of the deep hydrothermal fluid, which even at modest salinities (6wt.% NaCl) was high (≫100ppm Pb, Zn), owing to the combined effects of high temperature and low pH (⩽4.5). Therefore in SHMS systems, enhanced geothermal gradients and rapid fluid ascent (with minimal fluid cooling) are considered to be the most important factors for transporting high concentrations of base metals to the site of mineralisation.

Dissolution-reprecipitation metasomatism and growth of zircon within phosphatic garnet in metapelites from western Massachusetts

Highly restitic garnet-kyanite-phlogopite metapelitic schists from the Goshen Dome of western Massachusetts contain: a population of prograde monocrystalline, megacrystic garnet, some with significant P in substitution for Si; precipitates of hydroxylapatite and rutile; and 5 /mm 3 . The unusual P content and the abundant internal precipitate suite are similar to features reported in garnet from ultrahigh-pressure (UHP) and mantle settings, suggesting a potential (U)HP origin for the garnet megacrysts. Zircon included in megacrysts is surrounded by radial fractures, indicating in situ volumetric expansion or new growth. Cores display rare earth element (REE) profiles and cathodoluminescence (CL) zoning consistent with magmatic growth, and yield only Paleozoic dates (447–404 Ma). The embayed core-rim boundary is marked by a several micrometers wide band of CL-dark zircon enriched in Y, P, U, and Th that is interpreted as the accumulation of redistributed xenotime component from the original zircon rim during metamorphism. Outside of this band, the rim has elevated Hf, Th/U ≪ 1, and steep heavy REE profiles. The metamorphic rims yield concordant dates from 400 to 381 Ma. Matrix zircon grains have magmatic cores (1726–415 Ma) with similar core–rim boundaries enriched in Y, P, U, and Th. Metamorphic rims on matrix zircon yield slightly younger dates (393–365 Ma) and are compositionally heterogeneous. The difference between the youngest core and oldest rim indicates a short interval (ca. 4 Ma) between deposition of detrital zircon and the onset of metamorphism in the earliest Acadian. The oldest zircon rim dates are found within phosphatic garnet megacrysts of possible very high-pressure origin. The compositional uniformity of these rims indicates equilibrium with a single source; the anomalous composition suggests a combination of dissolution-reprecipitation and new growth of zircon that is derived from garnet. The range in both composition and dates indicates that matrix zircon rims formed in response to local changes in mineralogy and fluid/melt composition and/or availability. New growth of zircon on these grains cannot be confirmed, suggesting that dissolution-reprecipitation reactions during continued metamorphism may be the dominant mechanism that formed these rims. The data collectively suggest that dissolution-reprecipitation may be a common mechanism for producing metamorphic rims on zircon that does not require additional Zr and Hf, which are limited within most metamorphic settings.