Composition Of Monazite Research Articles

Late Triassic lithium pegmatites in Northwest China: A response to continental collision during Paleo‐Tethys Ocean closure

Spodumene‐bearing pegmatite dyke swarms have recently been discovered in the Chaqiabeishan area, at the northeastern margin of the Qinghai‐Tibet Plateau in northwest China. In order to elucidate the connection between the Chaqiabeishan lithium pegmatites and Triassic magmatism and mineralization within the West Kunlun – Songpan ‐Garzê rare‐metal belt, this study presents new columbite‐group mineral and monazite U–Pb dating results, mineral chemistry, monazite in situ Nd isotope analyses and gamma‐ray spectrometric measurements. Magmatism and mineralization at Chaqiabeishan mainly occurred ca. 216 Ma, and the mineralized pegmatites (Mn‐rich columbite‐group minerals, highly evolved monazite compositions and high effective uranium contents in the gamma‐ray survey) were generated from the high degree of the fractional crystallization in a volatile‐rich granitic magma. The source material of the Chaqiabeishan lithium pegmatites (εNd(t) values from −14.4 to −12.8) was more enriched than that of other pegmatite‐type lithium deposits (Jiajika and Bailongshan) in the West Kunlun – Songpan – Garzê rare‐metal belt and is ascribed to melting of ancient crustal materials in the basement. These late‐Triassic mineralizing events were closely related to the collision‐related tectonic setting at the northeastern margin of the Tibetan‐Qinghai Plateau, a product of Paleo‐Tethys Ocean closure.

Xenotime-(Y) from granitic pegmatites of the Monatsitovaya mine, Aduisky massif, Middle Urals (chemical composition and age)

The relevance of the work is due to the need to improve the chemical dating method as applied to high-uranium and high-thorium accessory minerals, which are difficult to study using isotopic research methods. The purpose of the work is to study the chemical composition of accessory xenotime from granite pegmatites of the Monatsitovaya mine (western part of the Aduisky massif) and determine its age. Research methodology. A quantitative analysis of the chemical composition of monazite was performed on a CAMECA SX 100 electron probe microanalyzer (IGG Ural Branch RAS, Ekaterinburg). Measurement conditions: accelerating voltage 15 kV, current 250 nA, electron beam diameter 2 μm. The pressure in the sample chamber is 2 × 10–4 Pa. The spectra were obtained on inclined wave spectrometers, the intensity measurements were carried out along the analytical lines: Y Lα, Si Kα, (TAP crystal analyzer), U Mβ, Pb Mα, Ca Kα, Th Mα, P Kα (PET), Yb Lα, Dy Lα, Er Lα, Gd Lα, Lu Lα, Sm Lβ (LiF). The overlap of peaks of spectral lines was taken into account, which is extremely important in the quantitative determination of lead content (the Y Lγ2,3 и Th Mζ1,2 lines are superimposed on the analytical Pb Mα line). The pulse accumulation time at the peaks of analytical lines was twice as long as for the background and was 60 s for Th, 40 s for U and Pb, and 10 s for other elements. When conducting research, linear experimental design was used to vary the time of measuring the intensities of the Mβ line of uranium, Mα lines of thorium and lead. The calculated detection limits are 345 ppm for U, 283 ppm for Th, 65 ppm for Pb, 205 ppm for Y. Results. It has been established that xenotime belongs to the yttrium variety and is characterized by an increased content of uranium (UO2 up to 8.8 wt. %) and thorium (ThO2 up to 4.5 wt. %). According to the results of chemical dating (based on 32 analyses), xenotime-(Y) shows a weighted average age of 276 ± 7 Ma (MSWD = 0.54). When constructing the dependence (ThO2 +UO2 eq) – PbO, the points fall on one isochron. Calculating the age using the isochron slope angle gave a dating of 276 ± 12 million years (MSWD = 0.94). Conclusions. The obtained age values for the xenotime are in good agreement with the dating of the pegmatoid granites of the Krutikhinsky massif, which is located on the western contact of the Aduisky granite massif and relatively close to the Monatsitovaya mine. It is quite possible that some pegmatites in the western part of the Aduisky massif were formed as a result of the formation of the Krutikhinsky massif.

Monazite from lithium-bearing pegmatites of the Lipovskoye vein field, Middle Urals (composition and chemical dating)

The relevance of the research is due to the need to improve the method of chemical dating as applied to high-thorium accessory minerals, which are difficult to study by isotope research methods. Purpose of the research is to study the chemical composition of monazite from lithium-bearing granite pegmatites of the Lipovskoye vein field and to determine their age. Research methodology. The quantitative analysis of the chemical composition of monazite was performed on a CAMECA SX 100 electron probe microanalyzer (IGG UB RAS, Ekaterinburg). Measurement conditions: accelerating voltage 15 kV, current strength 250 nA, electron beam diameter 2 μm. The pressure in the sample chamber is 2 ⋅ 10–4 Pa. The spectra were obtained on tilted wave spectrometers, the intensity was measured using analytical lines: Th Ma, U Mb, Pb Ma, Y La, Si Ka, Ca Ka, P Ka, Ce La, La La, Pr Lb, Nd La, Sm Lb, Dy La, Gd Lb. Standard samples: ThO2 , UO2 , Pb2 P2 O7 , diopside, synthetic rare-earth phosphates. The intensity measurement time at the peak for Th is 180 s, U is 100 s, and Pb is 500 s (240 s on one and simultaneously 260 s on another spectrometer), for Y and Si 20 s each, for the other elements 10 s; on the background – two times less. The detection limits for Th, U, and Pb in monazite are 290, 350, and 64 ppm, respectively. The oxygen content was determined under the assumption of the stoichiometry of the composition. Results. It has been established that monazite belongs to the cerium variety and is characterized by high contents of thorium (ThO2 up to 23.6 wt. %) and uranium (UO2 up to 2.5 wt. %). At the same time, cheralite-type isomorphism is realized in phosphate. In a closed Th–U–Pb-system (β = 0.92–0.97), according to the results of chemical dating (according to 20 analyses), monazite-(Ce) shows a weighted average age of 243 ± 7 Ma. When plotting the dependence (ThO2 + UO2 eq) – PbO, the points fall on one isochrone. Calculation of the age from the slope of the isochron gave a dating of 242 ± 17 Ma, MSWD = 0.21, probability = 1.00. Conclusion. It has been established that accessory monazite from lithium-bearing granitic pegmatites of the Lipovskoye vein field (Middle Urals) is of Triassic age. Apparently, this dating shows the time of the secondary transformation of lithium-bearing granitic pegmatites, which are often tectonized, and in some places even boudinaged.

Geochronology of plagioclasite veins from the Lipovskoye pegmatite field (Middle Urals)

The relevance of the research is due to the need to improve the method of chemical dating as applied to high-thorium and high-uranium accessory minerals, which are difficult to date by isotopic research methods. The purpose of the research is to study the chemical composition of monazite and uraninite from plagioclasite veins of the Lipovskoye pegmatite field and to determine their age. Research Methodology: quantitative analysis of the chemical composition of monazite and uraninite was performed on an X-ray spectral electron probe microanalyzer CAMECA SX 100. Measurement conditions: accelerating voltage 15 kV, current strength 250 nА, electron beam diameter 2 µm. Sample chamber pressure 2 ∙ 10–4 Pa. The spectra were obtained on tilted wave spectrometers, the intensity was measured using analytical lines: Th Ma, U Mb, Pb Ma, Y La, Si Ka, Ca Ka, P Ka, Ce La, La La, Pr Lb, Nd La, Sm Lb, Dy La, Gd Lb. Age calculation was carried out according to well-known methods of foreign authors in addition to their own developments. Results. According to the chemical composition, monazite belongs to the cerium variety and is characterized by high contents of ThO2 up to 13,4 wt. %, UO2 up tо 0,8 wt. % and PbO up to 0,18 wt. %. According to chemical dating, monazite-(Ce) gives an age of 266 ± 17 Ma. In undeformed plagioclasites, uraninite contains impurities of ThO2 up to 11,6 wt. % and PbO up to 3,0 wt. %, its calculated age is 258 ± 3 Ma. In tectonized plagioclasites, uraninite is characterized by impurities of ThO2 from 26 up to 45 wt. % and PbO up to 2,4 wt. %. According to chemical dating data, two ages are calculated in these uraninites: 255 ± 10 Ma in the central part of the grains, and 244 ± 4 Ma in the marginal parts of the grains. Conclusions. Microprobe data on the composition of these minerals have been obtained, and the complex geochronology of these rocks has been established by chemical dating. These plagioclasite bodies were formed after the Middle Permian quartz-potassium feldspar (topaz-beryl) granitic pegmatites, widely developed within the Lipovskoye field, and later underwent superimposed changes twice in the Upper Permian and Triassic times.

Monazite geochronology and geochemistry constraints on the formation of the giant Zhengchong Li-Rb-Cs deposit in South China

The giant Zhengchong Li-Rb-Cs deposit (ore resource: 270 k tonnes (t) Li2O @ 0.557 wt%, 110 kt Rb2O @ 0.225 wt%, and 6 kt Cs2O @ 0.013 wt%) in South China is associated with quartz-zinnwaldite-topaz rock, which is composed mainly of quartz, zinnwaldite and topaz with a porphyritic texture. However, the genetic link between these rocks and their Jiuyishan granite batholith host is unclear, and the magmatic-hydrothermal process involved in the rare-metal mineralization remains enigmatic. In this study, we analyzed the in-situ U-Pb age and mineral chemistry of monazite, a ubiquitous accessory phase at Zhengchong, to reconstruct the precise geochronological framework of this highly-fractionated felsic magmatic system, and the origin of the Li-Rb-Cs-rich quartz-zinnwaldite-topaz rock. Based on petrographic observations and back-scattered electron (BSE) imaging, monazite crystals in different rocks at Zhengchong have the following characteristics: (1) Mnz-I is mainly BSE-zoned monazite disseminated in granite porphyry, coexisting with zircon or included in zinnwaldite, (2) Mnz-II consists of relatively fine-grained BSE-zoned or homogeneous monazite distributed in feldspar phenocryst-bearing quartz-zinnwaldite-topaz rock, (3) Mnz-III is BSE-zoned monazite with embayed texture in the core, distributed in coarse-grained quartz-zinnwaldite-topaz rock, and (4) Mnz-IV is homogenous, BSE-gray monazite from fine-grained porphyritic quartz-zinnwaldite-topaz rock (as the main orebodies). All monazite crystals are characterized by high Th content, indicating magmatic origin. The LA-ICP-MS monazite U-Pb ages indicate granitic magmatism and mineralization cluster around 150 Ma, implying a close genetic link between the granite porphyry host and the quartz-zinnwaldite-topaz rock. We compared the chondrite-normalized REE distribution patterns and principal component analysis and partial least squares-discriminant analysis of the monazite analyzed, and suggested that the BSE-zoned Mnz-I, II and III are likely of the same type, significantly different from the homogenous Mnz-IV. The gray rims (under BSE) of Mnz-I, II and III are similar to Mnz-IV, and differ markedly from the bright core (under BSE) in their lower HREE and ThO2, but higher Eu and Eu/Eu* contents. When combined with the whole-rock composition data, the monazite compositional variation cannot be attributed to rapid changes in magma composition, depressurization, and increased water content, but rather to the increasing oxygen fugacity and the decreasing temperature and Si activity, accompanied by the elevated fractionation of granitic magma. Thus, the variation in monazite composition reflects the formation of Zhengchong Li-Rb-Cs deposit, which may be the result of high magmatic differentiation of fluorine-rich A-type magmas. Although multistage rare metal metallogenic events have been identified in the Nanling region, it is suggested that the Late Jurassic Zhengchong Li-Rb-Cs mineralization occurred within a short duration (<1 million years). Overall, the monazite chemical and geochronological signatures are good pathfinders for magmatic evolution and Li-Rb-Cs mineralization in the Jiuyishan complex, which could be used as a potential prospecting tool for highly-evolved granite-related rare metal deposits.

Postisland-arc fayalite-containing plagiogranites of mt. Kastel within mountain Crimea Kimmerides

The hypabissal intrusive of Mt. Kastel fayalite plagiogranites intruded in the center of the South Bank uplift within Crimean kimmerides. Plagiogranites crosscut and local metamorphose the complexly folded flysch mass of Tauride series T2-J1, the bodies of island-arc gabbroids of Early Bayos Pervomaysk-Aju-Dag complex and basalts bodies of Late Bayos Karadag complex. Judging by the pattern of partings and the contact conditions, the intrusive is relatively weakly tectonized. Kastel postisland-arc plagiogranites (72,02 wt% of SiO2; 4,57 wt% of Na2О; 1,26 wt% of K2O; Na2О/K2O = 3,6; 92,4% of ferruginosity; Th &gt;&gt; U) contain high ferriferous olivine — fayalite, eulite and annite, rich in accessory zircon, monazite and xenotime. During the crystallization differentiation of plagiogranites of Mt. Kastel there was an accumulation of Fe and Mn in olivine composition, Na and K in plagioclase composition, Mn in ilmenite composition, Hf in zircon composition and Th in monazite composition, a narrowing of zircon and xenotime solid solutions composition. Endemic fayalite plagiogranites could arise under the conditions of orogenic regime, which, apparently, should be distinguished in the history of Mountain Crimean mesozoids.

Příspěvek k poznání exotických hornin flyšového pásma Západních Karpat: chloritoidová břidlice z Nového dvora u Kvasic (Chřiby)

New occurrence of pebbles of chloritoid schists, found in Eocene-to-Oligocene conglomerates of the Zlín Formation, Rača Unit, Magura Flysch, Outer Western Carpathians, Czech Republic, is characterized in this contribution. The rock has very simple mineral composition, including chloritoid, quartz, white mica and trace amount of apatite, rutile, and monazite. Chloritoid contains only very small proportions of magnesiochloritoid (7 - 11 mol. %) and ottrelite (up to 0.4 mol. %) components. The composition of white mica corresponds to muscovite and illite. The significant differences in mineral assemblages of rocks as well as in chemical composition of chloritoid and white mica usually appeared during comparison with those of similar rock types occurring in potential source areas in the Czech Republic, Slovakia, and Austria. The best comparable chemical composition showed only chloritoid in chloritoid schist from Bělá in the Hrubý Jeseník Mts., Silesicum, Czech Republic.

Monazite as an Exploration Tool for Iron Oxide-Copper-Gold Mineralisation in the Gawler Craton, South Australia

The chemistry of hydrothermal monazite from the Carrapateena and Prominent Hill iron oxide-copper-gold (IOCG) deposits in the IOCG-rich Gawler Craton, South Australia, is used here to define geochemical criteria for IOCG exploration in the Gawler Craton as follows: Monazite associated with IOCG mineralisation: La + Ce &gt; 63 wt% (where La &gt; 22.5 wt% and Ce &gt; 37 wt%), Y and/or Th &lt; 1 wt% and Nd &lt; 12.5 wt%; Intermediate composition monazite (between background and ore-related compositions): 45 wt% &lt; La + Ce &lt; 63 wt%, Y and/or Th &lt; 1 wt%. Intermediate monazite compositions preserving Nd &gt; 12.5 wt% are considered indicative of Carrapateena-style mineralisation; Background compositions: La + Ce &lt; 45 wt% or Y or Th &gt; 1 wt%. Mineralisation-related monazite compositions are recognised within monazite hosted within cover sequence materials that directly overly IOCG mineralisation at Carrapateena. Similar observations have been made at Prominent Hill. Recognition of these signatures within cover sequence materials demonstrates that the geochemical signatures can survive processes of weathering, erosion, transport and redeposition into younger cover sequence materials that overlie older, mineralised basement rocks. The monazite geochemical signatures therefore have the potential to be dispersed within the cover sequence, effectively increasing the geochemical footprint of mineralisation.

The genesis of the Ashram REE deposit, Quebec: Insights from bulk-rock geochemistry, apatite-monazite-bastnäsite replacement reactions and mineral chemistry

Growing demand for the rare earth elements, particularly the heavy REE (HREE), has fuelled a boom in mineral exploration and scientific research on carbonatite-hosted deposits, especially those with unusual HREE enrichment. The Ashram REE deposit is such a HREE-enriched carbonatite-hosted REE deposit. Magmatic processes were important in the genesis of the deposit, but hydrothermal mobilization was the main process responsible for the concentration of the REE to potentially economic levels and the fractionation of the HREE.The REE minerals in the Ashram deposit were precipitated from hydrothermal fluids. They comprise monazite-(Ce) and bastnäsite-(Ce), with lesser monazite-(Nd) and trace xenotime-(Y) and aeschynite-(Nd). This mineralization occurs as disseminations in breccia matrices, in veins, and as vug fillings. Monazite-(Ce) was the earliest mineral to form, followed by xenotime-(Y) and bastnäsite-(Ce). The composition of monazite-(Ce) varies with location in the deposit and is preferentially enriched in the light REE (LREE) with increasing distance from a large, irregular breccia body, underlying the zone of HREE enrichment. This body is interpreted to have been the main conduit for the mineralizing fluids which, on exiting, deposited monazite as a result of the cooling and pH buffering that accompanied their interaction with the adjacent carbonatites. Bastnäsite-(Ce) replaced monazite-(Ce) through ligand exchange (F−, CO32− for PO43−), preserving the original REE distribution. Interaction of a compositionally evolving fluid with host rocks of variable bulk composition and buffering capacity resulted in a deposit-scale fractionation and zonation of the REE.

Chemical composition and age of monazite-(Ce) in granitoids of the crystalline basement from the South Yamal

The relevance of the work is due to the need to improve the method of chemical dating as applied to high-thorium accessory minerals, which are difficult to date by isotope research methods. Purpose of the work: study of the chemical composition of accessory monazite from granitoids of the crystalline basement of the South Yamal and determination of its age. Research methodology: quantitative analysis of the chemical composition of monazite was carried out using X-ray spectral electron probe microanalyzer CAMECA SX 100 (electron beam diameter from 1 μm, BSE, SE, Cat modes, determination of elements from beryllium to uranium). The spectra were obtained with the help of inclined wave spectrometers, the intensity was measured using analytical lines: Th Ma, U Mb, Pb Ma, Y La, Si Ka, Ca Ka, P Ka, Ce La, La La, Pr Lb, Nd La, Sm Lb, Dy La, Gd Lb. The age calculation was carried out according to the well-known methods of foreign authors in addition to some developments of the author. Results. The chemical composition of monazite makes it possible to classify it as a cerium variety, the content of radiogenic components varies greatly (in wt.%): ThO2 – 5.37–16.31, UO2 – 0.40–0.81, PbO – 0.08–0,19. There are significant concentrations of SiO2 (up to 3.5 wt.%), Y2 O3 (up to 1.8 wt.%) and CaO (up to 1.2 wt.%). It turns out that monazite implements hattonite (Th4+(U4+)+Si4+ → REE3++P5+) and cheralite (Th4+(U4+)+Ca2+(Sr2+,Ba2+,Pb2+) → 2REE3+) isomorphism types. The decent content of lead and high crystallinity of the substance makes it possible to use this mineral as a geochronometer mineral. Conclusions. New data on the chemical composition of monazite have been obtained, and the late Permian age of granitoids has been determined by microprobe dating. The values of the point U–Th–Pb ages of monazite together give a weighted average age of 256 ± 10 Ma (MSWD = 0.15) and an isochron of 254 ± 19 Ma (MSWD = 0.28), which almost ideally coincides with the results of isotopic U–Pb zircon dating from the same rock, 254 ± 3 Ma.

The Age of Monazite from the Ichet’yu Occurrence, Middle Timan (CHIME and LA–ICP–MS Methods)

Abstract—A study of the morphology, composition, and age (by the CHIME and LA–ICP–MS methods) of monazite from the Ichet’yu occurrence, located in Middle Timan, revealed some principal differences in the typomorphic features and genesis of its two varieties. The common yellow monazite from this occurrence is monazite-(Ce), in which the content of La is higher than that of Nd. The time of its crystallization (recrystallization) is estimated by the CHIME method as 518 ± 40 Ma. Kularite (a grayish-brown globular variety of monazite, in which Nd is higher than La) was dated at 978 ± 31 Ma. The age of some kularite grains is 520 ± 27 Ma, which may be interpreted as the date of a hydrothermal event that resulted in the simultaneous recrystallization of both monazite and kularite. However, these two monazite varieties were formed in two completely different sources and were combined in the mineral parasteresis of the Ichet’yu occurrence. The CHIME age of monazite from the Ichet’yu occurrence that belongs to two intervals (500–600 and 960–1000 Ma) is consistent with the age determined in the same monazite grains using the LA–ICP–MS technique.

Study on the Extraction and Separation of Samarium from Chloride Medium Using D2EHPA and [P66614][D2EHP] and Their Application to Monazite Ore

The present work deals with the investigation of solvent extraction of Sm(III) from chloride medium using di-(2-ethylhexyl)phosphoric acid (D2EHPA) and trihexyl tetradecyl phosphonium bis(2-ethylhexyl)phosphate ([P66614][D2EHP]) as extractants. In the extraction stage, the effect of contact time, aqueous phase pH, extractant concentration, NaCl concentration, temperature effect, stripping and O:A ratio variation are investigated to compare the extraction abilities of D2EHPA and the ionic liquid made from that. The complex formation ability and extraction mechanism of samarium with two extractants are explained by FTIR spectra and slope analysis method. Solvent extraction of samarium is better noticeable with D2EHPA than that of [P66614][D2EHP]. It is evident that with rise in pH of the aqueous medium, the extraction percentage of samarium is increased for both the extractants. Optimum extraction (100%) of Sm3+ is obtained with 0.1 mol/L D2EHPA and 0.1 mol/L [P66614][D2EHP], respectively. HNO3 is the best stripping agent for back-extraction of samarium from the loaded extractants. Separation studies are carried out in the presence of transition metal ions (mostly present in magnets) to know the efficiency of D2EHPA and ionic liquid [P66614][D2EHP]. The extraction studies with mixture of other rare earth metal ions similar to monazite composition follow the order as Gd(III) > Sm(III) > Nd(III) > Ce(III) > La(III) for both the extractants. Using 0.03 mol/L D2EHPA, complete separation of Gd and Sm from the rare earth mixtures is found at two stages with O:A ratio of unity.

Nd isotope re-equilibration during high temperature metamorphism across an orogenic belt: Evidence from monazite and garnet

Monazite is a powerful U-Th-Pb geochronometer commonly used to determine the tempo of orogenic processes. As a light rare earth element (LREE)-enriched mineral, monazite also records key information for understanding the behavior of Sm-Nd isotope systematics during tectonothermal events. However, Sm-Nd isotope studies of monazite have received far less attention than its use as a U-Pb geochronometer. Here we investigate coupled U-Pb ages and Sm-Nd isotopic compositions of monazite from partially melted metasedimentary rocks in the Jiao-Liao-Ji orogenic belt (JLJB), North China craton, to provide insight into Sm-Nd isotope behavior during high-temperature metamorphism and crustal melting. We utilize several complementary dating systems in the same sample, including garnet Lu-Hf and Sm-Nd, zircon U-Pb, and monazite U-Pb geochronology, to gain precise time constraints on the P-T evolution of the JLJB. Garnet Lu-Hf isochron dates of 1.97–1.94 Ga are interpreted to represent prograde garnet growth, consistent with the prograde metamorphic zircon dates of 1.96–1.90 Ga; garnet Sm-Nd dates agree with retrograde metamorphic zircon dates, and all monazite U-Pb dates define a relatively narrow age range of 1.86–1.83 Ga, interpreted to represent retrograde cooling. The lack of older monazite grains matching zircon or garnet dates suggests the dissolution of pre-existing monazites into partial melt. Monazite in all samples, irrespective of occurring as garnet inclusions or in the matrix, yields homogenous Nd isotope compositions (εNd ~ −5) at ~1.85 Ga, which are consistent with the garnet and bulk-rock values. Thus, Nd isotope re-equilibration between bulk-rock and minerals occurs synchronously across the orogenic belt during high-T metamorphism (~750 °C) where melting was involved, with no evidence of a pre-metamorphic isotope signature. This suggests mobility in the Sm-Nd isotope system during high-grade metamorphism and melting, where the Nd isotope signature of monazite likely represents the most recent tectonothermal event.

The chemical composition and age of monazite and kularite from titanium ore of Pizhemskoye and Yarega deposits (Middle and Southern Timan)

A study on the typomorphic characteristics and age of the monazite the two giant titanium deposits of the Timan – Pizhemskoye and Yarega, which revealed differences in morphology in the species composition of the inclusions, the grain size, distribution of chemical types of a mineral associated with conditions of crystallization and different sources of the substance. The isochronous Th-Pb monazite age was calculated using the «CHIME» method. For Yarega monazite built three isochrone with age 1301, 1105 and 778 Ma; for Pizhemsky monazite-kularite one isochrone with age 782 Ma. Source of hith-Th monazite Yarega oil-titanium deposit could be ancient granite batholith and the origin Yarega less-Th monazite and Nd-Ce-monazite-kularite Pizhemskoye deposit with an age of ~ 780 Ma could be related to the hydrothermal conversion of the weathering crusts on lamprophyres close in age with lamprophyre (spessartite and kersantite) of Chetlassky Kamen.

Laser ablation split-stream analysis of the Sm-Nd and U-Pb isotope compositions of monazite, titanite, and apatite – Improvements, potential reference materials, and application to the Archean Saglek Block gneisses

Continued improvements in both ICPMS (inductively-coupled plasma mass spectrometry) and laser ablation technologies are fueling advancements in accessory mineral investigations and their related isotope systems of interest, and are now being applied to a wide range of geological applications. In this contribution we present an updated methodology for laser ablation split-stream (LASS) analysis of the light rare earth element (LREE) enriched minerals monazite, titanite, and apatite for simultaneous analysis of the U-Th-Pb age (or trace element content) and the Sm-Nd isotope system. The data were collected with the current generation of high-sensitivity ICPMS and laser systems (ThermoFinnigan NeptunePlus MC-ICPMS and Element XR SF-ICPMS- coupled to a RESOlution 193 nm ArF excimer laser system). The increased sensitivity of these ICPMS instruments allows for improved spatial resolution and the ability to target minerals which previously contained insufficient concentrations of elements of interest (e.g., Sm-Nd in apatite), making their analysis difficult, if not impossible, using less sensitive instruments. Furthermore, the higher sensitivity allows less aggressive ablation parameters that facilitate thin section sampling and reduces inter-element and isotopic fractionation.To assess and improve the accuracy, precision, and efficiency of the technique, three new potential LASS reference materials (RMs) are evaluated for dual U-Pb and Sm-Nd analysis (Tory Hill apatite, Tory Hill titanite, and Steenskralkamp monazite). The homogeneity of these materials was first assessed using reconnaissance laser ablation analyses, with final characterization of U-Pb age and Sm-Nd isotope composition using isotope-dilution thermal ionization mass spectrometry (ID-TIMS). The precision and accuracy of the LASS method is explored using secondary mineral reference materials of known age and Sm-Nd isotope composition. The utility of the technique is evaluated with a case study of monazite and apatite from the Eoarchean Uivak Gneiss complex of Labrador, Canada. Finally, we suggest that there is a wide variety of geological applications for this methodology, such as multi-mineral detrital provenance, crustal growth, and petrogenic studies.

Magmatic-hydrothermal evolution of rare metal pegmatites from the Mesoproterozoic Orange River pegmatite belt (Namaqualand, South Africa)

The 450 km long Orange River pegmatite belt intruded the Namaqua Sector of the Mesoproterozoic Namaqua-Natal Province, Southern Africa, at ca. 1 Ga. The western part of the belt is characterized by the occurrence of LCT pegmatites locally mineralized in Li, Ta, Nb, Be and Bi. Most of these mineralized pegmatites display zonation with a quartz-feldspar-muscovite-garnet-beryl-bearing aplite border and wall zone, a quartz-feldspar-spodumene-lepidolite-bearing intermediate zone, and a quartz-K-feldspar core. The pegmatites and their granodioritic country rocks commonly show evidence of albitization and greisenization (i.e. secondary muscovitization). In this study, detailed petrographic observations and the compositions of mica, feldspar, spodumene and Nb-Ta oxide minerals are reported. This information is combined with bulk country rock compositions and new U-Pb zircon and monazite ages plus Sm-Nd isotope compositions of monazite to constrain the origin and magmatic-hydrothermal evolution of weakly and strongly mineralized LCT pegmatites.The Li-Ta-Be Kokerboomrand I pegmatite emplaced at ca. 985 Ma during the main stage of pegmatite emplacement in the Orange River belt and regional strike-slip deformation. It has εNd(t)monazite = −14 ± 3 and potentially formed by partial melting of Paleoproterozoic rocks from the Richtersveld magmatic arc. Alternatively, Mesoproterozoic sediments of the Bushmanland Subprovince may also provide a suitable magma source for the Kokerboomrand I pegmatite.The rare metal contents of muscovite and columbite group minerals (CGM) increase from the weakly mineralized to strongly mineralized pegmatites, suggesting early-stage fractional crystallization or variable partial melting conditions. Mica Nb/Ta values of <14 and K/Rb ratios of <40 can be used as geochemical tools for Li-Ta-(Nb)-Be exploration in the region, and possibly in other pegmatite belts worldwide.Rare metal-bearing minerals crystallized throughout the magmatic-hydrothermal evolution of mineralized pegmatites. During the magmatic-dominated stage I, constitutional zone refining likely induced a decrease of spodumene Fe contents and increase of CGM Ta contents toward the pegmatite core. Stage II marks the pervasive circulation of an immiscible hydrosaline melt. This stage is characterized by the replacement of the primary mineral assemblage by lamellar albite (cleavelandite), (fluor)calciomicrolite and Cs-Ta-rich Li-muscovite and zinnwaldite. Stage III represents the progressive transition from a magmatic-hydrothermal system dominated by a Li-Cs-Ta-rich hydrosaline melt toward a system mainly involving (Li)-Cs-(Ta)-Bi-rich aqueous fluids. This stage is characterized by the crystallization of lepidolite and zero-valence-dominant pyrochlore as well as strong localized greisenization and Bi mineralization.Magmatic-hydrothermal alteration of the immediate country rock of the mineralized pegmatites is marked by the crystallization of albite, Li-Ta-Cs-rich mica, various Nb-Ta oxide minerals, and led to a strong decrease of the whole-rock Nb/Ta ratio plus significant rare metal enrichment.Our findings from the Orange River belt demonstrate that an important role can be ascribed to melt-melt and melt-fluid immiscibility and metasomatism in the formation of pegmatite-related rare metal deposits. Greisens and albitites associated with pegmatites and their immediate country rocks can be considered as favorable targets for Li-Ta mineral exploration. Strong and pervasive metasomatism across the mineralized pegmatites and their country rocks suggests involvement of a parental medium that was highly enriched in water.

Monazite behaviour during metamorphic evolution of a diamond-bearing gneiss: a case study from the Seve Nappe Complex, Scandinavian Caledonides

Abstract Monazite is a common mineral in metapelitic rocks including those which underwent ultra-high pressure (UHP) metamorphism. During metamorphic evolution monazite adapts its composition to the changing mineral assemblage, especially in its heavy rare earth element contents. We studied this process in diamond-bearing gneiss containing monazite, from Saxnäs in the Seve Nappe Complex of the Scandinavian Caledonides. Although the rock has been re-equilibrated under granulite facies and partial melting conditions, it still preserves minerals from the UHP stage: garnet, kyanite, rutile, and especially diamond. Microdiamonds occur in situ as inclusions in garnet, kyanite and zircon, either as single-crystals or polyphase inclusions with Fe-Mg carbonates, rutile and CO2. Both monazite and diamond occur in the rims of garnet showing the highest pyrope content and a secondary peak of yttrium. Such a position indicates thermally activated diffusion under high temperature at the end of prograde metamorphism. Monazite compositions show negative Eu anomalies, which we interpret to be inherited from the source rock, not reflecting the coexistence with plagioclase and/or K-feldspar which are unstable at UHP conditions. Our results suggest that the effect of whole-rock composition may be more important than that of coexisting phases. The UHP monazite was most likely formed from allanite during subduction and prograde metamorphism. The monazites included in garnet and kyanite are mostly unaltered, whereas those in the matrix show breakdown coronas consisting of apatite, REE-epidote/allanite and REE carbonate, likely formed due to pressure decrease and cooling. U-Th-Pb chemical age dating of monazites yields an isochron centroid age of 472 ±3 Ma. We interpret this age as monazite growth under UHP conditions related to subduction of the Baltica continental margin in Early Ordovician time.

Further Characterization of the RW-1 Monazite: A New Working Reference Material for Oxygen and Neodymium Isotopic Microanalysis

The oxygen (O) and neodymium (Nd) isotopic composition of monazite provides an ideal tracer of metamorphism and hydrothermal activity. Calibration of the matrix effect and monitoring of the external precision of monazite O–Nd isotopes with microbeam techniques, such as secondary ion mass spectrometry (SIMS) and laser ablation-multicollector-inductively coupled plasma-mass spectrometry (LA-MC-ICPMS), require well-characterized natural monazite standards for precise microbeam measurements. However, the limited number of standards available is impeding the application of monazite O–Nd isotopes. Here, we report on the RW-1 monazite as a potential new working reference material for microbeam analysis of O–Nd isotopes. Microbeam measurements by electron probe microanalysis (EPMA), SIMS, and LA-MC-ICPMS at 10–24 µm scales have confirmed that it is homogeneous in both elemental and O–Nd isotopic compositions. SIMS measurements yield δ18O values consistent, within errors, with those obtained by laser fluorination techniques. Precise analyses of Nd isotope by thermal ionization mass spectrometry (TIMS) are consistent with mean results of LA-MC-ICPMS analyses. We recommend δ18O = 6.30‰ ± 0.16‰ (2SD) and 143Nd/144Nd = 0.512282 ± 0.000011 (2SD) as being the reference values for the RW-1 monazite.

Th-U-Pb-dating of monazite from the metamorphic rocks of the itkul formation of the Sysert Metamorphic Complex (Middle Urals)

«Вестник Санкт-Петербургского университета. Науки о Земле» — научно-теоретический рецензируемый журнал, обобщающий результаты исследований в области геологии, гидрогеологии и геохимии, петрологии и экологии, ландшафтного планирования и геоморфологии, экономической и социальной географии.

Neoproterozoic evolution and Cambrian reworking of ultrahigh temperature granulites in the Eastern Ghats Province, India

AbstractThe time‐scales and P–T conditions recorded by granulite facies metamorphic rocks permit inferences about the geodynamic regime in which they formed. Two compositionally heterogeneous cordierite–spinel‐bearing granulites from Vizianagaram, Eastern Ghats Province (EGP), India, were investigated to provide P–T–time constraints using petrography, phase equilibrium modelling, U–Pb geochronology, the rare earth element composition of zircon and monazite, and Ti‐in‐zircon thermometry. These ultrahigh temperature (UHT) granulites preserve discrete compositional layering in which different inferred peak assemblages are developed, including layers bearing garnet–sillimanite–spinel, and others bearing orthopyroxene–sillimanite–spinel. These mineral associations cannot be reproduced by phase equilibrium modelling of whole‐rock compositions, indicating that the samples became domainal on a scale less than that of a thin section, even at UHT conditions. Calculation of the P–T stability fields for six compositional domains within which the main rock‐forming minerals are considered to have attained equilibrium suggests peak metamorphic conditions of ~6.8–8.3 kbar at ~1,000°C. In most of these domains, the subsequent evolution resulted in the growth of cordierite and final crystallization of melt at an elevated (residual) H2O‐undersaturated solidus, consistent with &lt;1 kbar of decompression. Concordant U–Pb ages obtained by SHRIMP from zircon (spread 1,050–800 Ma) and monazite (spread 950–800 Ma) demonstrate that crystallization of these minerals occurred during an interval of c. 250 Ma. By combining LA‐ICP‐MS U–Pb zircon ages with Ti‐in‐zircon temperatures from the same analysis sites, we show that the crust may have remained above 900°C for a minimum of c. 120 Ma between c. 1,000 and c. 880 Ma. Overall, the results suggest that, in the interval 1,050 to 800 Ma, the evolution of the Vizianagaram granulites culminated with UHT conditions from c. 1,000 Ma to c. 880 Ma, associated with minor decompression, before further zircon crystallization at c. 880–800 Ma during cooling to the solidus. However, these rocks are adjacent to the Paderu–Anantagiri–Salur crustal block to the NW that experienced counterclockwise P–T–t paths, and records similar UHT peak metamorphic conditions (7–8 kbar, ~950°C) followed by near‐isobaric cooling, and has a similar chronology during the Neoproterozoic. The limited decompression inferred at Vizianagaram may be explained by partial exhumation due to thrusting of this crustal block over the adjacent Paderu–Anantagiri–Salur crustal block. The residual granulites in both blocks have high concentrations of heat‐producing elements and likely remained hot at mid‐crustal depths throughout a period of relative tectonic quiescence in the interval 800–550 Ma. During the Cambrian Period, the EGP was located in the hinterland of the Denman–Pinjarra–Prydz orogen. A later concordant population of zircon dated at 511 ± 6 Ma records crystallization at temperatures of ~810°C. This age may record a low‐degree of melting due to limited influx of fluid into hot, weak crust in response to convergence of the Crohn craton with a composite orogenic hinterland comprising the Rayner terrane, EGP, and cratonic India.