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Bastnasite is widespread in alkali granite, carbonatite and REE ore deposits. The U-Th-Pb ages of bastnasite can constrain the mineralization age. Currently, the lack of suitable in situ analysis reference material is the major obstacle of bastnasite U-Th-Pb geochronology. In this study, the matrix effects of U-Pb and Th-Pb age determination in bastnasite using glass NIST 610 as the external calibration reference were evaluated with the 193-nm excimer LA-ICP-MS analysis in normal and additional gases laser ablation modes. The obtained U-Th-Pb ages of bastnasite were approximately 7–11% lower than their reference values in the normal analytical mode (without additional gas). Fortunately, the determined systematic age biases in U-Th-Pb dating were significantly reduced (less than 1–2%) with the addition of water vapor within the ablation chamber. This reduction may be attributed to the observed significant suppression of 206Pb/238U and 208Pb/232Th downhole fractionation in both NIST 610 glass and bastnasite by introducing a small quantity of water vapor in the ablation chamber. In addition, the obtained 206Pb/238U and 208Pb/232Th ages of bastnasite K-9, LZ1384, and MAD809 showed great consistency with their corresponding recommended values. The obtained results show that accurate and precise U-Th-Pb ages of bastnasite can be simultaneously obtained by using glass NIST 610 as the primary calibration standard in 193-nm LA-ICP-MS with the water vapor-assisted method. This simple and effective water vapor-assisted non-matrix-matched laser ablation method helps to promote the geological application of bastnasite U-Th-Pb geochronology.

Detailed electron probe microanalyses (EPMA) of accessory minerals from Wadi Rod Elsayalla granitoids (SE Desert, Egypt) furnished insights into U, Th, Zr, and REE mineralization. Thorite and uranothorite are the main radioactive minerals, in addition to zircon and monazite. Thorite occurs in syenogranite and quartz syenite rocks with marked enrichment in UO2 up to 6.89 wt% in the former rock type. High Y and Zr elements content in thorite indicates marked replacement of Th by Y and Zr. Uranothorite in syenogranite contains up to 51.68 wt% ThO2, 19.12 wt% SiO2, and 20.62 wt% UO2, in addition to minor amount of Y2O3 up to 1.94 wt%. Zoned zircon shows thorium-rich core, with marked fluctuation in UO2 content, owing to extensive hydrothermal alterations. Total REE content as REE2O3 reaches to about 6 wt% in zircon rims from the syenogranite. Zircon from quartz syenite shows U, Th, and REEs below the detection limit of the electron microprobe. Identified REE prospects in the study area contain (i) REE fluorocarbonates and fluoride (bastnasite, synchysite, and flocerite), (ii) REE phosphates (monazite-Ce, xenotime, and florencite), and (iii) REE silicates (allanite-Ce and zircon), with a clear predominance of LREE minerals, in which Ce is the main REE. The average REE contents of bastnasite-Ce, flocerite, synchysite-Ce, and synchysite-Y are 77.28, 74.01, 52.89, and 49.09 wt%, respectively. Xenotime from syenogranite and quartz syenite has average HREE contents (Gd2O3–Lu2O3) of 20.45 and 23.72 wt%, respectively.

The genesis of Earth’s largest rare earth element (REE) deposit, Bayan Obo (China), has been intensely debated, in particular whether the host dolomite marble is of sedimentary or igneous origin. The protracted (Mesoproterozoic to Paleozoic) and intricate (magmatic to metasomatic) geological processes complicate geochemical interpretations. In this study, we present a comprehensive petrographic and in situ, high-spatial resolution Sr-Pb isotopic and geochemical investigation of the host dolomite from the Bayan Obo marble. Based on petrographic evidence, the dolomite marble is divided into three facies including coarse-grained (CM), fine-grained (FM), and heterogeneous marble (HM). All carbonates are ferroan dolomite with high SrO and MnO contents (> 0.15 wt.%), consistent with an igneous origin. Trace element compositions of these dolomites are highly variable both among and within individual samples, with CM dolomite displaying the strongest LREE enrichment. In situ 206Pb/204Pb and 207Pb/204Pb ratios of the dolomite are generally consistent with mantle values. However, initial 208Pb/204Pb ratios define a large range from 35.45 to 39.75, which may result from the incorporation of radiogenic Pb released from decomposition of monazite and/or bastnasite during Early Paleozoic metasomatism. Moreover, in situ Sr isotope compositions of dolomite indicate a large range (87Sr/86Sr = 0.70292–0.71363). CM dolomite is characterized by a relatively consistent, unradiogenic Sr isotope composition (87Sr/86Sr = 0.70295–0.70314), which is typical for Mesoproterozoic mantle. The variation of 87Sr/86Sr ratios together with radiogenic 206Pb/204Pb signatures for dolomite within FM and HM possibly represents recrystallization during Early Paleozoic metasomatism with the contribution of radiogenic Sr and Pb from surrounding host rocks. Therefore, our in situ geochemical data support a Mesoproterozoic igneous origin for the ore-bearing dolomite marble in the Bayan Obo deposit, which subsequently underwent intensive metasomatism during the Early Paleozoic.

Recent exploration revealed a number of rare earth element (REE) deposits that are distributed along the Qinling Orogenic Belt, Central China. These deposits have an estimated total reserve of about 2 Mt. REE2O3, thus making this belt a world-class REE metallogenic province. Understanding the metallogenesis of the belt requires direct dating of REE minerals. In this study, LA-ICP-MS U-Th-Pb dating on bastnasite and monazite from the Huangshuian, Taipingzhen, and Miaoya deposits in different units of the belt was used to precisely determine the timing of the REE mineralization. The Huangshuian deposit in the north is a carbonatite-related Mo-(REE) deposit in which the REE minerals are closely associated with molybdenite. After correction for common Pb and excessed 206Pb decayed from 230Th, a weighted average 206Pb/238U age of 207 ± 4 Ma (n = 17; MSWD = 1.9) is obtained for bastnasite grains from this deposit. Such an age is slightly younger than that of the final collision (peak at 230–220 Ma) of the Qinling Orogenic Belt, thus indicating that the Mo-REE mineralization is likely related to a post-collisional extension setting. The Taipingzhen REE deposit in the middle contains sheet-like ore bodies composed of veins where bastnasite, the dominant REE mineral, is closely associated with quartz, fluorite, and barite. In situ bastnasite U-Th-Pb dating shows that the REE mineralization in this deposit has formed at 421 ± 7 Ma (n = 17; MSWD = 1.5), synchronous with extension-related magmatism in the region. The Miaoya deposit in the south is the largest one in the belt, and it is essentially a REE-mineralized syenite-carbonatite complex. In this deposit, the monazite grains are closely associated with major minerals of the syenites or carbonatites (e.g., K-feldspar or calcite), but commonly exhibit complex internal textures. Different domains of monazite yield two groups of U-Pb ages at 414 ± 11 Ma (n = 5; MSWD = 0.91) and 231 ± 2 Ma (n = 21; MSWD = 3.1), whereas the bastnasite has an age of 206 ± 4 Ma (n = 14; MSWD = 1.5). The early age of 414 Ma is obtained from homogenous monazite grains and in good agreement with zircon U-Pb ages of the Miaoya syenite-carbonatite complex, and thus is considered to represent the timing of the major REE mineralization in the deposit. The younger ages of 231–206 Ma are obtained from monazite grains with complex internal textures and bastnasite in late veinlets, thus recording secondary, consecutive REE remobilization events likely related to the compression process during formation of the Qinling Orogenic Belt. Our new U-Th-Pb ages, in combination with previously geochronological data, demonstrate that there are two episodes of REE mineralization at 440–410 Ma and 220–200 Ma in the Qinling Orogenic Belt.

The standard Gibbs free energy of formation (ΔGof, 298) of bastnasite, (Ce, La, Nd, Pr)FCO3, was estimated using four different methods. The obtained average values were − 1589.5 kJ/mol for CeFCO3, − 1599.5 kJ/mol for LaFCO3, − 1589.1 kJ/mol for NdFCO3, and − 1595.4 kJ/mol for PrFCO3. The value for cerium bastnasite, CeFCO3, was used to construct a potential vs. pH (Eh-pH) diagram to investigate the stability relations of cerium bastnasite. The diagram shows that CeFCO3 is stable in neutral to basic conditions (pH ~ 6.5–11).

Carbonate gangue in historically important post-Variscan polymetallic Pb-Zn-Cu-Ag vein systems in the Upper Harz Mountains has elevated rare earth element contents (ΣREE+Y, 1500 ± 340 ppm; n = 16) in bulk samples. This enrichment is due to the occurrence of abundant micrometer-sized synchysite inclusions in calcite, identified via Raman spectroscopy. Calcite bulk analyses have roof-shaped PAAS-normalized REE patterns with a Eu peak but without Ce or Y anomalies and with a steeply dipping HREE pattern. Microbeam analysis (electron microprobe and LA-ICPMS) identifies these patterns as dominated by synchysite-(Ce–Nd) with strong Eu enrichment in the weight percent range and LREE/HREE fractionation (La/Lu ~ 100, PAAS-normalized). The synchysite component in calcite gangue is detected in polymetallic veins all over the Harz Mountains, which seems to be a diagnostic feature of the region and suggests a large-scale Mesozoic fluid system. However, the Upper (western) Harz systems with no fluorite have more elevated REE content, compared with the Lower (eastern) Harz fluorite-rich systems with less REE content. Carbonate gangue in the Upper Harz systems has homogeneous 87Sr/86Sri around 0.714 and eNdi of ~ − 9, while carbonate gangue in the Lower Harz systems has 87Sr/86Sri around 0.716 and eNdi of − 2 to − 5. Fluorite in the Lower Harz Mountains has strong positive Y anomalies and variable Eu anomalies at generally low REE abundances and no REE-mineral inclusions. Both Sr and Nd isotope compositions in the fluorite are very variable and indicate an open system (87Sr/86Sri, 0.710–0.718; eNdi, − 3 to − 17). The synchysite MREE enrichment in calcite gangue in the Upper Harz Mountains compares favorably with carbonatite-related LREE-dominated bastnasite from China and elsewhere and allows an interesting perspective as a by-product of Pb–Zn mining.

More recent data of Greek bauxites from the Parnassos-Ghiona active mines prove that rare earth elements (REEs) occur mainly in the form of authigenic/diagenetic LREE3+ carbonate and phosphate minerals (bastnasite/parisite group and florencite). Bulk geochemistry of representative samples, from underground mines and open pits, showed an increased content in LREE (ΣLREE—from La to Gd—varying between 106 and 913 ppm; avg. ΣLREE = 321 ppm; n = 17), and lower HREE (ΣHREE—from Tb to Lu including Y—varying between 45 and 179 ppm; avg. ΣHREE = 95; n = 17). The overall REE concentration (ΣREE + Y+Sc) varies from 192 to 1109 ppm (avg. 463 ppm; n = 17). The most abundant REE is Ce (min: 67 ppm; max: 655 ppm; avg. 193 ppm; n = 17), exhibiting in general a positive geochemical anomaly (avg. Ce/Ce* -CeA-: 2.6), identical to the case of marine Fe–Mn-crust and terrestrial desert vanish, implying also that Ce4+ may exist either in REE-oxides and/or epigenetically sorbed in Fe-oxides. On the other hand, Nd content, which is more interesting for the industry, is lower (avg. 41 ppm; n = 17). The concentration of REEs is much higher in Fe-rich (red) bauxite, compared to Fe-depleted (white) bauxite (avg. ΣREE + Y+Sc = 569 ppm and 268 ppm, respectively). The new data presented herein show a rather lower REE potential of Parnassos-Ghiona bauxites, compared to previous literature, but similar values compared to karst-type bauxites of the globe. Although their REE concentration is higher compared to that of various geochemical reference materials (i.e., positive REE geochemical anomalies in comparison with chondrites, UCC, PAAS, NASC, and ES), it is vitally lower compared to REE resources being mined, such as REE–Fe–Nb–Th deposits. A trend similar to REE geochemical trend also stands for most of the trace elements that are present in Greek bauxites—mainly HFSE—except for LILE. Besides, Greek bauxite metallurgical residue’s (red mud) REE content seems to be remarkably increased by almost two times compared to that of the Parnassos-Ghiona bauxite parent material. Scandium is another critical element. In the studied bauxites, it varies from 29 to 73 ppm (avg. 47 ppm; n = 17); it is typical for the Mediterranean and EU bauxites and laterites, but much lower compared to the exploitable Australian laterites. The Fe-rich samples contain higher concentrations of Sc compared to Fe-depleted (avg. 54 and 33 ppm, respectively). This means that common red Greek bauxite is rather more exploitable, with regard to Sc (and the rest REE), but not the white one (which is of high quality in terms of Al). Bulk geochemistry indicates that Sc is correlated to Fe but not to Zr, while microscale observations demonstrated the presence of fine-grained scandian-zircons. This is in line with a very recent study proving that Sc is mainly present in Fe-oxide minerals (mainly hematite and goethite) and zircons. Bulk geochemical Fe–Pb and Fe–As positive correlations are also verified among the associated trace elements. Finally, the investigation of the REE vertical distribution in a characteristic deposit of the B3 horizon (i.e., Pera Lakkos mine case study), showed that the REE concentration is increased in the Fe-rich domain (lying above the footwall limestone), as well as in the coal layer interstratified between the Fe-depleted domain and the hanging wall limestone. However, it is revealed that the Ce/Ce* (CeA) is increased in the coal layer and is raised to the uppermost Fe-depleted domain, but not the lowermost Fe-rich bauxite domain. This might be attributed to the Ce3+ ↔ Ce4+ and the LREE re-mobilization during the supergene/epigenetic processes.

Rare-earth deposits associated with intrusive carbonatite complexes are the world’s most important source of these elements (REE). One of the largest deposits of this type is Maoniuping in the Mianning-Dechang metallogenic belt of eastern Tibet (Sichuan, China). In the currently mined central part of the deposit (Dagudao section), REE mineralization is hosted by a structurally and mineralogically complex Late Oligocene (26.4 ± 1.2 Ma, 40Ar/39Ar age of fluorphlogopite associated with bastnasite) hydrothermal vein system developed in a coeval syenite intrusion. Low-grade stockworks of multiple veinlets and breccias in the lower part of the orebody grade upwards into progressively thicker veins (up to 12 m in width) that are typically zoned and comprise ferromagnesian micas (biotite to fluorphlogopite), sodium clinopyroxenes (aegirine to aegirine-augite), sodium amphiboles (magnesio-arfvedsonite to fluororichterite), K-feldspar, fluorite, barite, calcite, and bastnasite. The latter four minerals are most common in the uppermost 80 m of the Dagudao section and represent the climax of hydrothermal activity. Systematic variations in the fluid inclusion data indicate a continuous hydrothermal evolution from about 230–400 °C (fluid inclusions in feldspar, clinopyroxene, and amphibole) to 140–240 °C (fluid inclusions in bastnasite, fluorite, calcite). Hydrothermal REE transport was probably controlled by F−, (SO4)2−, Cl−, and (CO3)2− as complexing ligands. We propose that at Dagudao, silicate magmas produced orthomagmatic fluids that explored and expanded a fissure system generated by strike-slip faulting. Initially, the fluids had appreciable capacity to transport REE and, consequently, no major mineralization developed. The earliest minerals to precipitate were alkali- and Fe-rich silicates containing low levels of F, which caused progressive enrichment of the fluid in Ca, Mg, F, Cl, REE, (SO4)2−, and (CO3)2−, leading to the crystallization of aegirine-augite, fluororichterite, fluorphlogopite, fluorite, barite, calcite, and bastnasite gradually. Barite, fluorite, calcite, and bastnasite are the most common minerals in typical ores, and bastnasite generally postdates these gangue minerals. Thus, it is very probable that fluid cooling and formation of large amount of fluorite, barite, and calcite triggered bastnasite precipitation in the waning stage of hydrothermal activity.

The results are presented of a textural and mineral chemical study of a previously undescribed type of hydrothermal alteration of chevkinite-(Ce) which occurs in a syenitic pegmatite from the Vishnevye Mountains, Urals Region, Russia. The progressive alteration of the chevkinite to a bastnasite-(Ce)-ilmenite-columbite-(Fe) assemblage through a series of texturally complex intermediate stages is described and electron microprobe analyses are given of all the major phases. Unusual Nb ± Th-rich phases formed late in the alteration sequence provide evidence of local Nb mobility. The main compositional fluxes are traced, especially of the REE, HFSE, Th and U. It appears that almost all elements, with the exception of La, released from the chevkinite-(Ce) were reincorporated into later phases, such that they did not leave the alteration crust in significant amounts. The hydrothermal fluids are inferred to have been F- and CO2-rich, with variable levels of Ca activity, and with fO2 mainly between the nickel-nickel oxide and magnetite-hematite buffers. This occurrence represents a new paragenesis for a columbite-group mineral.

By mineral liberation analyzer (MLA) automated quantitative system, the niobium–tantalum ore in this study was classified as refractory mineral of low-grade which was mainly composed of fergusonite, polycrase, ilmenorutile, and bastnasite. Most of niobium and rare earth metals were disseminated in these minerals (particle sizes of 95 % rare earth elements 90 %, and the leaching extent of niobium can reach 84 %.

The Choghart magnetite-apatite deposit situated in the Bafq district, Central Iran, has been scrutinized for rare earth elements (REEs) by precise geochemical investigation. The Central Iran is a susceptible area of rare earth elements. One of the Choghart’s prominent points is the existence of hydrothermal zones which made prediction of REEs occurrence within the deposit possible. Choghart is placed within felsic volcanic tuffs, rhyolitic rocks, and volcanic sedimentary sections belonging to the lower Cambrian. Abundance and distribution pattern of REEs in Choghart iron deposits reveal a part of deposit formation and its mineralogical modifications. Petrography and mineralogy of the ore body demonstrated two main types of alterations (sodic and calcic) associated with iron ore mineralization in Choghart deposit. The main ore includes a large quantity of massive magnetite in the lower part of Choghart deposit. The minor mineralization involves apatite, pyrite, alkaline amphibole, especially actinolite and tremolite, calcite, talc, quart, monazite, and bastnasite. Geochemical sampling from north–northeast (N-NE) side of the mine denotes the presence of these elements in hydrothermal zones. Statistical populations of the area were categorized by fractal geometry into four main differentiations: host rock type (albitofyre), iron, metasomatose, phosphate zones, and a subset of the phosphate zone which is named high iron high phosphate type. REEs like lanthanum, neodymium, yttrium, and niobium constitute the most quantity of Choghart. Deposit characteristics demonstrate its similarity to Kiruna type. The significant feature of iron oxide-apatite deposits of Kiruna ore type is the existence of monazite inclusions within apatite. These inclusions were also observed within apatite type I and II of Choghart mineralization. Moreover, REEs geochemistry in Choghart deposit was identified by investigation on geochemical data analyses. The analysis represents negative Eu anomaly and further enrichment of light REEs compared to the heavy ones. Chondrite normalized REEs patterns are defined by negative anomalies of Eu, which is the main characteristic of Kiruna ore type. The results showed that REEs concentration in phosphate zone, as a high absorption of REEs, is much higher than metsomatose, albitofyre, and iron zones. REEs distribution in N-NE side of the mine indicated that the contact of iron ore with tailings in N-NW side of the mine leads REEs to be enriched nearly 1% , as well as that of NE with high contents of REEs 1.5% ), which is very significant.

The Bastnas-type deposits, with mineral assemblages of Fe oxides, Ca-Mg silicates, rare earth element (REE) silicates, REE fluorocarbonates, and Cu-Fe-Mo-Bi sulfides, are associated with marble horizons in a strongly Na, K, and/or Mg altered, metavolcanic succession, over a distance of at least 80 km in a SW-NE trending zone in western Bergslagen. Two subtypes occur: (1) enriched (relative to the other type) in light REE (LREE) and Fe, exemplified by the Bastnas and Rodbergsgruvan deposits, and (2) enriched in heavy REE (HREE), Y, Mg, Ca, and F, represented by deposits in the Norberg district. Bastnasite hosts primary fluid H2O-CO2 inclusions with salinities of 6–29 eq. wt% CaCl2 and with total homogenization temperatures (Th tot) of ca. 300–400 °C. Subtype 2 has late-stage fluorite with fluid inclusions that show 1–16 eq. wt% NaCl and Th tot of ca. 90–150 °C. Molybdenite Re-Os ages obtained from three deposits are 1,904 ± 6, 1,863 ± 4, and 1,842 ± 4 Ma. Nd isotopic data from five different REE minerals yielded no defined isochron, but a range in eNd (1.88 Ga) of +0.2 to +1.6. The oxygen isotope values (δ18OSMOW) of dolomite and calcite from the associated REE-mineralized skarn and recrystallized carbonate assemblages lie in the range 6.1–8.6 ‰, overlapping with those of the host marbles. Carbon isotope values (δ13CPDB) show typical magmatic signatures of −6.7 to −4.4 ‰, while the host marbles group around ca. −2.4 ‰. The sulfur isotope (δ34SCDT) values of associated sulfides range between −10.8 and +0.2 ‰. The combined evidence suggests REE mineralization, beginning at 1.9 Ga, from mainly Svecofennian, juvenile magmatic (>400 °C) fluids carrying Si, F, Cl, S, CO2, and the REE in addition to other metals; mineralization occurred through reactions with dolomitic layers in the supracrustal units coevally with regional metasomatic alteration associated with fluid circulation through an extensive active volcano–plutonic complex.

The study area is covered by quartz diorites, monzogranites, and pegmatites. Geochemically, the monzogranites and pegmatites have peraluminous to slightly metaluminous calc-alkaline to alkaline affinity, emplaced in volcanic arc setting and crystallized under moderate water-vapor pressure (3–5 kb) and temperature of 800–850 °C for monzogranites and 700–750 °C for pegmatites. The monzogranites reveal small to moderate negative Eu anomaly (Eu/Eu* = 0.62 to 1.0) and averages Eu/Sm = 0.168 and light rare earth elements (LREEs)/heavy rare earth elements (HREEs) = 48.78. The pegmatites reveal moderate to large negative Eu anomaly (Eu/Eu* = 2.39 to 2.96) patterns and have averages Eu/Sm = 0.075 and LREEs/HREEs = 32.22. The monzogranites are altered along two fracture zones exhibiting propylitic, silicification and record high radioactive measurements. These alterations cause enrichment in SiO2, Fe2O3 t, Ni, Y, V, Co, Th, and REEs except Er and depletion in Al2O3, TiO2, CaO, MgO, Na2O, K2O, P2O5, Cu, Zn, Cr, Zr, Rb, Ba, Pb, Sr, Nb, Ga, Hf, Cs, Li, Sn, Be, Sc, U, and Ta. The normalized chondrite pattern denotes moderate REEs fractionation and shows a narrow range fractionation of HREEs in both fresh, altered monzogranites and pegmatites. The studied fresh and altered monzogranites do not show tetrad effect, while the pegmatites show tetrad effect. The average eU content in fresh monzogranites is 5.55 parts per million (ppm), and the average U content is 5.03 ppm, whereas the average eTh content is 18.93 ppm, and the average Th content is 20.90 ppm. The average eU content in pegmatites is 14.76 ppm, and the average U content is 4.75 ppm, whereas the average eTh content is 57.02 ppm, and the average Th content is 15.30 ppm. The eU and eTh in the alteration zones reach up to 16.50 and 296.20 ppm, respectively. These high radioactivities are attributed to the presence of thorite, bastnasite, fluorite, and columbite.

Roasted with sodium carbonate, bastnasite (Ln(Ce)CO3F) was converted to calcine containing rare earth oxides (REO), among them cerium, which existed mainly as CeO2. The calcine was first leached with diluted hydrochloric acid, which resulted in a sludge with the enriched cerium (IV) dioxide. The sludge was further leached with a concentrated hydrochloric acid, adding hydrogen peroxide as a reducing agent; in this manner, the enriched cerium tri-chloride (CeCl3) was prepared. The optimal technological parameters are suggested as follows: first, the hydrochloric acid concentration, the leaching temperature, the ratio of solid to liquid, and the leaching time are 1 mol/L, 60°C, 1:20, and 90 minutes, respectively; second, the hydrochloric acid concentration, the dosage of hydrogen peroxide in every 5 g of the sludge, the ratio of solid to liquid, the leaching temperature, and the leaching time are 6 mol/L, 6 mL, 1:20, 50°C, and 90 minutes, respectively. As a result, the cerium-enriched rare earth (RE) solution, containing over 95 pct cerium oxide, is obtained, which is in turn available for use in preparing a kind of polishing powder containing high cerium. The total recovery of cerium was 91 pct (85.3 pct, in the second step).

Metamorphosed carbonatites and related skarn deposits, located in Fuerteventura Basal Complex, contain unusual Sr-rich minerals. Maximum SrO concentration in the following minerals are: calcite, 7.23 wt%; apatite, 5.22 wt%; epidote, 11.64 wt%; clinozoisite, 1.25 wt%; allanite, 5.63 wt%; britholite, 4.11 wt% and a Sr–Na aluminosilicate (probably stronalsite), 16.44 wt% SrO. Calcite and apatite are chemically similar to those found in carbonatites and are therefore considered to be of igneous origin. Textural evidence indicates that the first skarn stage garnet+diopside+Sr–Na aluminosilicate formed as the result of chemical interaction between carbonatites and adjacent silicate rocks. The formation of Sr-bearing epidote/clinozoisite, allanite and britholite appears to be related to the release of Sr into the fluid phase from the breakdown of high temperature assemblages during the retrograde skarn stage. During the final evolution stages, further alteration of britholite by bastnasite and tornebohmite took place. The occurrence of REE minerals shows that the fluids responsible for this metasomatism must also have transported significant quantities of REE.

A fully cored drillhole was drilled to 1596 m by the Czech Geological Survey in 1961–1963 in the central part of the Cinovec (Zinnwald) granite cupola. Two types of granite were intersected: zinnwaldite granite (ZG), observed down to a depth of 730 m, and protolithionite granite (PG), occurring to the end of the hole. The core was used to study the distribution and chemistry of: zircon, thorite, xenotime, monazite, bastnasite, synchysite, REE oxyfluorides and hydroxyfluorides. Zircon occurs throughout the drillcore; it is strongly hydrated and fluorinated with about 18.5 wt.% H2O content in the apical part of the cupola. Its F-content reaches 2.41 wt.%. Within the PG, the F concentration in zircon is low. Zircon is poor in Th and U and its HfO2 contents vary from 1.01 to 5.24 wt.%. Thorite is common in the PG, becoming rare in the ZG. It is strongly hydrated (up to 14 wt.% H2O) and fluorinated (up to 2.04 wt.% F). Extensive solid solution between ThSiO4 and YPO4 was observed. Xenotime is strongly hydrated (up to 16 wt.% H2O), but its F content is low (

¶Mong Hsu rubies of the “trapiche” type are sporadically seen in the gem market. However, they have never been described in the field. The study of the nature of solid inclusions, the variation of trace-element contents, as well as the cathodoluminescence behaviour of six “trapiche” rubies permit the conclusion that these rubies crystallised in the same geological environment (marble-type deposit) as the normal rubies from Mong Hsu: (1) Cr and V are the main chromophorous elements in both ruby types; they act, together with Ti, as activators or quenchers for cathodoluminescence; (2) calcite, dolomite, rutile, mica, diaspore, apatite, chlorite, and feldspar are solid inclusions found in both ruby types; (3) the presence of bastnasite in trapiche ruby and fluorite in non-trapiche ruby indicates the circulation of F-bearing fluids during ruby deposition; (4) the distribution of trace-element contents in the crystal is similar for both ruby types. In the Cr2O3 vs. Fe2O3 and Cr2O3 vs. Fe2O3/TiO2 diagrams, the population fields of Mong Hsu “trapiche” and non-“trapiche” rubies overlap. They are distinct from those of rubies and sapphires hosted in basalts from South-east Asia.

Textural relationships occurring in a range of settings from the Bayan Obo Fe-REE-Nb deposit, Inner Mongolia, China, indicate reaction between monazite [(REE)PO4], bastnasite [(REE)(CO3)F] and apatite. Within dolomite marble-hosted ores monazite grains occur surrounded by zones of intergrown bastnasite and apatite. In fluoritised dolomite marble-hosted amphibole-calcite veins, co-existing apatite and bastnasite are separated by zones of monazite plus calcite, whilst in aegirine-apatite veins hosted by banded aegirine-fluorite-magnetite-bastnasite rocks, they are separated by zones of monazite and fluorite. Modal proportions for minerals in the reaction zones have been used to derive reaction stoichiometries, and suggest the following reactions: Consideration of these reactions, along with published experimental data and other reported mineral assemblages, suggests that the factors controlling the relative stabilities of monazite and bastnasite are the pH, and the activities of HF °, CO3 2−, Ca2+ and PO4 3−. Textures indicating reaction between REE phosphates and fluorocarbonates have been reported from a number of other settings and are consistent with the controls on reaction inferred from this study. The range of assemblages seen at Bayan Obo is a result of the variation between relatively unbuffered fluid compositions, and those buffered by the fluoritisation of the carbonate host rock. Mass-balance calculations suggest some mobilisation of the REE into the fluid phase during reaction, although this did not significantly alter the REE distribution in monazite and bastnasite. The mineral compositions also reveal variation in the REE distribution with different paragenetic settings indicating variation in the composition of the metasomatic fluids. These changes may be related to changes in the fluid source region, or to variations in the fluid chemistry, particularly X CO2, leading to different REE solubilities at different periods in the development of the deposit.

Within the Nkombwa Hill carbonatite complex, bastnasite-(Ce), (Ce,La)CO3F, has been identified as an abundant mineral in xenoliths hosted by late-stage ferrocarbonatite sills and dykes. Bastnasite-(Ce) occurs as fibrous yellow crystals, about 1 µm in size, replacing monazite and in association with baryte, in a matrix of dolomite. In common with bastnasite-(Ce) from other locations, the bastnasite-(Ce) of Nkombwa Hill contains up to 70% RE2O3, almost entirely as light rare-earth oxides. However, Nkombwa Hill bastnasite-(Ce) is relatively deficient in La and enriched in Pr and Nd.

A simple operational method for separating cerium from other lanthanides in natural mixtures of cerium dioxide with lanthanide(III) hydroxides, obtained from Vietnamese parisite and Mongolian bastnasite, has been developed. The method is based on drying crude Ln(OH)3×H2O material in air at about 200°C within 6h, followed by leaching Ln(III) with concentrated nitric acid added carefully with stirring to the dried material/water 1∶1.5 slurry. Under optimum conditions cerium (and Th, if present) virtually does not pass into solution while the yield of leaching and the sum of REE oxides (REO) concentration in the after-leach solution reach the maximum values of 97% (mass) and 0.18 kg·dm−3, respectively. Besides an expected decrease of the leaching yield, roasting the starting material at 600°C results in over 7% Ce content in the Ln leached.

The lens-shaped Miaoya carbonatite complex, located west of the Wudang massif, Hubei Province, consists of several types of carbonatites associated with syenites. According to their composition, the carbonatites can be classified into four types, i. e., sovite, alvikite, carbon-bearing alvikite and ankeritic carbonatite. Their average composition is in agreement with the abundance values for carbonatites compiled by Gold (1966). There are three stages recognizable: the earliest sovite and alvikite followed by carbon-bearing alvikite, with ankeritic carbonatite being the latest. Some rules dominating the distribution of major and rare elements are observed with respect to the evolution of these carbonatites, for example, Nb is essentially enriched in sovite. Except for niobite and ilmenorutile, there are also pyrochlore, nioboeschynite and fersmite. RE are concentrated mainly in ankeritic carbonatite, within which bastnasite, parisite and monazite are found. In general, Ca, Nb, and Sr decrease, while Fe, Mg, Mn, and RE increase from earlier to later stages. It is suggested that the carbonatites are genetically connected with syenitic magma.

The commercial production of rare earth metals by fused salt electrolytic methods is described. These methods are used to make mischmetal, cerium, lanthanum, and didymium (Nd + Pr). The feed materials consist essentially of anhydrous chlorides of the metal to be produced, augmented by additions of nonrare earth salts to yield an electrolyte with satisfactory properties for reduction. The rare earths are derived either from monazite or from bastnasite ores. The anhydrous chlorides are manufactured from the hydrated chlorides by methods which minimize oxidation or hydrolysis. Alternatively, anhydrous chlorides may be used which result from the direct chlorination of rare earth ores by the Gold-schmidt process. These are particularly suitable for electrolysis due to their very low oxychloride content. Fluorides and oxides of the rare earths are produced by wet chemical methods to provide the relatively small quantities of these compounds now used for commercial fused salt electrolysis. Reduction cells in use today are constructed mainly from a) ceramics, b) graphite, or c) iron. The advantages and disadvantages of these types of cells are described together with the typical products which result from their use. Primary attention is given to production of mischmetal (mixed rare earth metal), which is the rare earth metal produced on the largest scale today. Brief reference is made also to production of cerium, lanthanum, and didymium (Nd + Pr) metal. Finally, a resume of the current uses of these metals is presented with reference to recent trends in the industrial applications of the rare earth metals.

A process for direct chlorination of rare earth ores without the necessary preparation of carbides or other intermediate compounds is described. Complete chlorination of all non-volatile components of the ores is obtained in a special, electrically heated furnace at temperatures between 1000 and 1200°C. The construction of the furnace permits quick replacement of some important components while the furnace is still hot. This reduces the unavoidable corrosion problem. The flowsheet of the process is presented. The process permits a high productive capacity with a small space, low investment, and low labor input. It is possible to process the most varied ores, such as Bastnasite, Monazite, Allanite, Cerite, Xenotime, Euxenite, Fergusonite, Gadolinite, etc., in the same installation. Reference is made to the treatment of off-gases. Fused anhydrous rare earth chlorides, without contaminants, are obtained as the final product, which is very suitable for the production of rare earth metals. This process can also be used to convert pure rare earth oxides to anhydrous chlorides.

A liquid-liquid extraction step has been incorporated into an automatic method for determination of europium in the presence of other lanthanides, yttrium and scandium. Europium(III) is selectively reduced on a Jones reductor and the europium(II) reacted with molybdophosphoric acid to produce a molybdenum blue which is extracted into isoamyl alcohol for spectrophotometric determination. Incorporation of the extraction step increases the sensitivity of the method by a factor of 5 enabling from 2 to 50 μg of europium per ml of aqueous sample solution to be determined but reduces the sampling rate from 20 to 10 samples per hour. The method has been applied to the determination of europium in lanthanide oxides and in the minerals bastnasite and monazite following a lanthanide group separation.

The isolation of macro amounts of pure element 126, whose observation has recently been reported, has important consequences for the discovery of elements from atomic number ∼ 106 to 126 and their chemical, atomic and nuclear properties. It is suggested that the organic extractant commercially used to purify Ce from the rare earth mineral, bastnasite, should be used to concentrate element 126. This extractant which is recycled in the treatment of large amounts of the appropriate ore, is usually effective in the concentration of244Pu which should be chemically similar to element 126.

A simple low-cost process with minimum use of reagents produces a satisfactory product at satisfactory yield.

LITTLE is known of the isotopic composition of lead in carbonatites, a rock type commonly considered to be derived from the mantle. Here I shall present data for galena from the Mountain Pass carbonatite, California1. All the samples are from the Sulphide Queen ore body which is composed essentially of calcite and barite together with minor bastnasite and galena.