جستجوی مقالات مرتبط با کلیدواژه « REEs » در نشریات گروه « زمین شناسی »

In this research, to contribute to the understanding of the geochemistry of trace elements in zircon, we determined the REEs, Y, Nb, Ta, Th, and U contents in zircon grains in three granitoids (Sarnowsar, Sarkhar and Bermani) by laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) in order to determining the magma sourcee and magmatism fertility. The zircon/rock partitioning coefficients of REE, Y, Nb, Ta, Th, and U contents indicate that the patterns of the trace elements of the studied granitoids are controlled by the liquid composition at the magmatic crystallization. Compared to Sarkhar and Bermani granitoids, the Sarnowsar granite has a higher temperature (736° to 915 °C), higher zircon/rock partitioning coefficient of REEs, Y and Th (up to 2770 for Zr) and it was formed in higher oxidant conditions (△FMQ values between -0.06 to 17.01). The results of this study show that oxidized and I-type magmas in subduction-related tectonic environments are more favorable for porphyry and skarn mineralization.

Zircon is the most commonly analyzed accessory mineral and is routinely employed in U–Th–Pb geochronology, (U–Th)/He and fission track thermochronology, radiogenic (Hf) and stable (O) isotopic studies, crystallization thermometry, and trace element geochemistry (Belousova et al., 2002). A critical presumption in zircon chemistry studies is that data obtained from zircon is a proxy for the parent igneous rock. This is evidently true for most types of analyses, however, relating trace element and rare earth element (REE) concentrations in zircon compared to bulk rock or melt concentrations has been verified for causing some difficulties. The incentive to establish more accurate estimates of parental bulk rock concentrations using in-situ zircon measurements is significant as it would link zircon to a large body of whole rock geochemical literature with numerous possible applications including studies of magma source, crustal thickness, mineral exploration, crustal evolution, metamorphism, and petrogenesis (Chapman et al., 2016 and references therein). In this research, we determined the contents of REEs, Y, Nb, Ta, Hf, U, and Th in the zircon grains of eight granitoid samples from the Sangan mining district, NE Iran, to calculate zircon/rock partitioning coefficients of REEs applicable to magma source studies and mineral exploration.

Zircon from Sarkhar and Bermani granitoids were analyzed at the State Key Laboratory of Geological Processes and Mineral Resources, China University of Geosciences, Wuhan, using laser ablation system, ICP-MS instrument (Agilent 7700a ICP-MS). Also, samples from Sarnowsar granitoids were analyzed at the Nanjing Hongchuang Geological Exploration Technology Service Co. Ltd., China. Zircons were analyzed for trace elements using a laser energy density of 3.6 J/cm2, a spot size of 30 μm, and a repetition rate of 5 Hz.
The estimations of melt composition and the measured trace element concentrations in zircon, values of DCezircon/rock was calculated. Estimates for DCe3+zircon/rock and DCe4+zircon/rock were implemented after Ballard et al. (2002) method. Partition coefficients of the trivalent REEs and the quadrivalent series Hf, Th, and U are used to constrain DCe3+zircon/rock and DCe4+zircon/rock, respectively. Blundy and Wood (1994) showed that the mineral melt partition coefficient for a cation i can be related to the lattice strain energy created by substituting a cation, whose ionic radius (ri) differs from the optimal value for that site (r0) (Equation 1).
lnDi=lnD0-4π ENA/RT (ri/3+r0/6) (ri- r0)2                                                                                     (1)
Plotting lnDi against the (ri/3 +r0/6)(ri−r0)2 yields a linear relation for an isovalent series of cations. With knowing the ionic radii of Ce3+ and Ce4+, partition coefficients of these species can be determined by interpolation. Since Ce will be a mixture of Ce3+ and Ce4+, the value of DCezircon/rock will lie between these two-partition coefficient end-members, and by combining Equations (1) and (2) oxygen fugacity fO2 of crystallization can be estimated.
ln[xmelt Ce4+/ xmelt Ce3+]= 1/4 ln fO2 + 13136 (±591)/T − 2.064 (±0.011) NBO/T −8.878(±0.112).xH2O −8.955 (±0.091)                                                                                                                                              (2)
Temperatures were calculated using the Ti content of zircon, by using the Equation (3) (Ferry and Watson, 2007):log(Tizircon) = (5.711 ± 0.072) – 4800 ± 86/T −logaSiO2 + logaTiO2                                                     (3)
where Tizircon is the concentration of Ti in zircon in ppm, T is temperature degrees in Kelvin, and ai (aSiO2 and aTiO2) is the ratio of component i concentration in the melt over the concentration of component i in the rock at saturation.

Concentrations of trace elements in the zircon grains are given in the Supplementary Table and are summarized in Table 1, where the geometric mean (G), the variation coefficient CV (which corresponds to the ratio of standard deviation by the arithmetic mean), and the number of determinations (n) are listed. Heavy rare earth elements (HREEs) show a relative enrichment. (Lu)N in the Sarnowsar granitoids range from 1522.40 to 8869.00 (DA sample), 1477.00 to 6442.00 (TP sample) and 1655.37 to 53.00 7523 (CSK sample). These values for Sarkhar and Bermani granitoids are in the range of 835.43 to 4077.95 (BR-01 sample), 1233.46 to 4337.80 (SK-01 sample), 1984.37 to 5681.81 (SK-1-1 sample), 2281.71 to 4955.97 (SK-1-2 sample) and 2268.68 to 6422.57 (SK-2-2 sample). Furthermore, the LREEs show lower concentrations, resulting in an (La/Yb)N that is generally less than 0.1. A negative Eu anomaly and a positive Ce anomaly are observed in studied granitoids. Contents and patterns of REEs in the studied granite samples are similar to those reported by other authors with higher HREEs contents than LREEs (e.g., Hoskin and Schaltegger, 2003).
Zircon Ti concentrations used to constrain its crystallization temperatures, and T is calculated by the revised Ti-in-zircon thermometry of Ferry and Watson (2007) (Supplementary Table). Calculated Ti-in-zircon temperatures for Sarnowsar intrusions (736° to 915 °C) are higher than those of Sarkhar (646° to 819 °C) and Bermani granitoids (653° to 861 °C). The △FMQ values (calculated by equation of Trail et al., 2011; Trail et al., 2012) for Sarnowsar range from -0.06 to 17.01. For Sarkhar and Bermani intrusions, the △FMQ values are in the range -4.43 to 4 and -8.53 to 0.07, respectively. These data indicating different magmatic conditions for productive (Sarnowsar) and barren (Sarkhar and Bermani) granitoids.

Defining the magma source and fertility of acidic to intermediate magmatism within the Cenozoic volcano-plutonic magmatic belts of Iran has immense scientific and mineral exploration significance. By using the zircon/whole rock partition coefficient in the Sangan mining area (Sarnowsar, Sarkhar and Bermani granitoids), we discuss the magma source and fertility of magmatism. The magmatism of Sangan mining district area is alkaline and classified as I-type granitoids, which have a direct genetic association with iron skarn mineralization in the area. The current results show that Sarnowsar granitoid was formed at a higher temperature (736° to 915 °C), lower negative Eu anomaly (with geometric mean 0.35 to 0.4), higher values ​​of Ce4+/Ce3+ (25.56 to 718.62) ratios compared to Sarkhar and Bermani granitoids. Also, the Sarnowsar granitoid has lower Hf values ​​(700 to 1199 ppm) and higher Zr/Hf (65 to 87) values, which shows that it formed in an earlier magmatic stage compared to Sarkhar and Bermani granitoids. The results of this research can be used for identifying productive Cenozoic intrusions in Iran that are related to porphyry and skarn mineralization systems.

The Granitoid plutons in the Sanandaj-Sirjan zone host numerous pegmatitic dikes. This study is focused on mineral chemistry of zircons in the pegmatite dikes in the Malayer, Boroujerd and Shazand district to evaluate zircon crystallization temperature, oxygen fugacity and Ce4+/Ce3+ ratio and also zircon/rock partition coefficients of REEs and U, Th, Ta, Nb and Y. Trace element discrimination digrams such as Th versus Y and Yb/Sm versus Y and Nb, indicated studied zircons were located in the syenite pegmatite field. Zircon/rock partition coefficients indicate that zircon granis are enriched in the HREE than LREE. Zircon chemistry show that zircon in the Shazand and Malayer pegmatite dikes have more Hf and less REE distribution than zircons in the Boroujerd pegmatite dikes. Consequently, it indicates the role of latter hydrothermal process in the formation of Boroujerd zircons. Crystallization temperature, oxygen fugacity and Ce4+/Ce3+ ratios decrease from Malayer to Shazand and finally Boroujerd pegmatite dikes. Reduced condition of magmatism, Th/U contents below 1 and Y/Ho content higher than 20 indicate that these pegmatities are barren.

Carbonatites are among the rare kind of rocks on this planet. These igneous rocks are included by share of more than 50% carbonate minerals; dolomite, calcite & ankerite. Specific look in petrography and mineralography studies is needed to investigate these rocks, especially for silicates and minor phases from macroscopic as well as to microscopic scales. On the last databases of carbonatites of the world, Iran is represented empty of carbonatites. While there are many unexplored carbonatitic outcrops exists in the Bafq Metallogenic Area, (hereafter BMA). BMA as a significant metallogenic province of Iran, has the largest cluster of riftogenic Kiruna-type Iron Oxide-Apatite (IOA) deposits in the world, its iron resources are estimated over 2 bt in 50 aeromagnetic anomalies. The geological story of BMA at the middle of Posht-e Badam Block (hereafter PBB) is magnificently beautiful. The BMA recorded the oldest major geological events in Central Iranian Microcontinent (hereafter CIM). From the early years of field surveys and published geological maps to recent works which are cited in thousands of papers and dissertations, subvolcanic mineralized carbonatite intrusions within metamorphic complexes and trondhjemites of before Middle Cambrian age in the area, mistaken for marble interlayers, limestone enclaves or just non-important sedimentary carbonate rocks. In spite of the brief hints that carbonatites are related to the huge (IOA) mineralization in the area which is available in the old papers, unfortunately these rocks still remained invisible, even in the new studies. In here, on the basis of provided field and petrography evidences as well as to depicted petro-chemical diagrams, the nature of carbonatites of the area is discussed from different geological aspects. In fact, carbonatites are the most important riftogenic units in lithological columns of PBB, specifically in BMA. These naked virgin multiple peaks should get under the detailed study in the aim for valuable exploration potential of REEs. Moreover, these rocks provide a magnificent case of geodynamic investigation about the Earth history which has occurred during the changing season of Proterozoic to Phanerozoic. CIM is located at the heart of the greatest orogen in the world; The Alp-Himalaya orogenic belt in between Gondwana & Eurasia Paleo-Supercontinents. During late Precambrian to Early Cambrian, the study area had suffered by complicated gigantic orogenic phases. The late units of the phenomena described here unconformably overlaied by the Middle Cambrian trilobite-bearing Mila Formation. Thereupon, the unique, and major geological incidents of BMA have occurred right before Biological Big Bang which is also known as the Cambrian Life Explosion, beneath the only great ice grip of the planet throughout its entire history.

The lenticular Shahneshin barite deposit (N: 35°39'36'' and E: 46°36'11'') is located 80 km  northeast of Marivan, Kurdistan Province; north Sanandaj-Sirjan Zone (Stöcklin, 1968). The deposit consists of stratiform ore and stringer zone. The stringer zone has occurred with alteration sericite- quartz in the footwall dacitic unit (Kv) and evident in a series of vein-veinlets under stratiform ore. The stratiform ore has been located concurrently on the dacite unit and below the Sanandaj Shale unit (Hasankhanloo, 2015).The study area mainly consists of Mesozoic succession dominated by the dacite tuff, andesitic-basaltic lava and pillow lava (Kv: the host rock), black slate and phyllite (Kss: Sanandaj Shale), dolomitic limestone with intercalation of sandstone (Kl), and black shale and slate (Ks: Sanandaj Shale). In this study, samples of the Shahneshin barite deposit have been analyzed for their 87Sr/86Sr and δ34S isotopes and trace elements (plus REE) geochemistry to assess the source of the deposit.

Forty samples were collected from the Shahneshin barite deposit and country rocks. Polished blocks (6 samples) and thin sections (34 samples) were prepared for SEM images and petrographic examination at the University of Kurdistan. Trace elements (plus REE) were determined by ICP-MS in the Geological Survey center of Iran (Karaj). The detection limits for elements are between 0.08-0.6 ppm. Three whole-rock samples for Sr and S isotopes were analyzed at the Department of Earth and Space Sciences of the University of Science and Technology of China.Sulfur isotope analyses were measured by the use of a Delta V Plus Gas Isotope Ratio Mass Spectrometer. The analysis accuracy was determined to be ±0.2‰ (2σ) by using Canyon Diablo Troilite (CDT) as a standard (34S/32S=0.0450045). The strontium isotopic composition was completed on a Thermal Ionization Mass Spectrometry instrument by Phoenix. The measured strontium isotope normalized to 86Sr/88Sr=0.1194 and its NBS-987 standard was 0.7102477±0.000014 (2σ).

Strontium isotopes, sulfur isotopes, trace-element (plus REE) composition, fluid inclusion, and petrography of barites help to identify sources of mineral-forming components and environments of precipitation (Baioumy, 2015). The Shahneshin barite deposit includes sulfate barium without valuable Pb and Zn elements. Barite crystals are mainly coarse (>20µ m) with euhedral, tabular, and bladed morphologies. Fluid inclusion microthermometry indicates that the barite formed from low salinity (2.0-8.5 wt.% NaCl eq.) fluids at low temperatures, between 115 to 215oC (Hasankhanloo, 2015).Chondrite-normalized REE patterns for the barite samples reflect enrichment of the LREE/HREE ratios, as is shown by the high (Nd/Er)CN> 11 ratios. They also show Eu/Eu*CN (0.5-7.0), Ce/Ce*SN (0.1-1.16), La/Lu*CN >1, and ratios of the Ce/La (mostly>1), and Eu/Sm (0.1-2.83). The geochemistry of the barite samples represents variation in the abundance of trace elements and REECN patterns. The 87Sr/86Sr and S-isotopic values of Shahneshin barite samples are 0.70649-0.70651 and δ34S=19.05-21.53‰, respectively.

Barite has very little Rb in its structure, and the isotopic composition of the original Sr is preserved in it (Martin et al., 1995). The 87Sr/86Sr values of the barite samples are consistent with 87Sr/86Sr=0.70649-0.70651, which itself is higher than those for host volcanic rocks (0.704-0.705) but lower than that of the Cretaceous seawater (0.7075), the time of barites formation. We may conclude that strontium in the barites is a mixture of predominantly juvenile hydrothermal fluid of low Sr isotope and seawater that contains more radiogenic strontium. δ34S (=19.05-21.53‰) of the samples indicate that much of the sulfur in barite was derived from seawater (δ34S=20-22‰).Fluid inclusion salinities (Hasankhanloo, 2015), crystal sizes and morphology, abundance of sulfate mineral, lack of valuable Pb and Zn, distribution patterns of trace elements (plus REE) of barite reveal that mixture of magmatic fluid and seawater, with different ratios, were the source of the barite-forming fluid. That is supported by the δ34S values, the location of samples on the Th-U diagram (seawater sources), variations in trace element (plus REEs), and Au anomaly (magmatic sources) in the samples. REEs, La enrichment, variations in abundance of trace elements, as well as δ34S and 87Sr/86Sr isotope values of the samples are consistent with the Kuroko massive sulfide-type (Marumo, 1989) and submarine hydrothermal volcanic model. In this model, barium has leached from the bedrocks by circulation of reduced hydrothermal fluid and transported along the syn-sedimentary normal faults to the sea-floor. Then, fluid is mixed with SO42- of seawater and it causes the barite to precipitate. These barites have been formed in an open system, on or immediately below the sea-floor.The Shahneshin barite deposit was, most probably, formed within caldera structures on top of the volcanic complexes in the late-stage of submarine volcanic activity with andesite-dacite in composition. It has occurred at continental margin tectonic setting between subduction zone and passive continental margin due to oblique collision along the Sanandaj-Sirjan Zone in the Late Cretaceous.

The Qara Sabalan manganese deposit belongs to the Qara Dagh-Sabalan metallogenic zone and is located in the eastern part of this zone (north of Meshginshahr). Geology of the area include volcanic (pyroclastic) rocks and the small outcrop of sub volcanic bodies (quartz-monzodiorite) with Eocene to Oligocene age. Mn deposit is hosted within the trachyandesite and tuff. Mn mineralization occurs as veins-veinlets, disseminated cement filler of brecciated zones. Faults and fractures with the trend of NE-SW have played a major roles for the formation of manganese mineralization. The main manganese mineralization consists of pyrolusite, manganite, psilomelane, hematite and goethite. variety of textures, such as open-space fillings colloidal, nodular, replacement and brecciation, are observed which are evidences for epigenetic manganese deposition. Rare earth elements patterns show a specific negative anomaly of Ce (0.04-0.13, mean 0.08) and a relatively positive Eu anomaly (0.28-0.38, mean 0.32). The significant geochemical characteristics of ore, such as Mn/Fe (mean 41.22), Co/Ni (mean 5.24), Co/Zn (mean 0.28), U/Th (mean 0.68), La/Ce (mean 1.77), Lan/Ndn (mean 2.82), Dyn/Ybn (mean 3.16), LREE/HREE (mean 9.51), ΣREE (mean 63.70), reveal a hydrothermal source for Qara Sabalan Mn mineralization.

The Shotorkhosb kaolin deposit is located about 7 km southeast of Torbat-e-Heydariyeh, Khorasan Razavi Province, northeast Iran. This deposit is a part of the Khaf-Kashmar-Bardaskan metallogenic zone. Field observations and laboratory studies indicate that this deposit is a product of alteration of Eocene andesitic rocks.  In this study, different analytical techniques, such as XRD, SEM-EDS, FE-SEM, DTA and TGA, were used to evaluate the characterization of the studied kaolin samples. Based on mineralogical examinations, kaolinite, illite, halloysite, montmorillonite, quartz, alunite, jarosite, natrojarosite, albite, muscovite, hematite, pyrite, gypsum, rutile, galena and barite are the most mineral phases in this deposit. Halloysite is a type 7 angstrom in this deposit and can be seen in the form of tubes and plate. Alunites have pseducubic and rhombuhedral forms. The distribution pattern of rare earth elements (REEs) and investigation of lanthanide ratios imply the effective role of pH and temperature changes in the development of this deposit. The correlation coefficients between elements reveal the effective role of clays, hematite, rutile and phosphorus-bearing minerals in the concentration of lanthanides. The decrease of Ce anomaly in the kaolin samples relative to the andesitic precursor rock  implies a decrease in oxygen fugacity during the development of kaolinitization processes in the Shotorkhosb deposit.

Thekaolinizedzonesof the Goorgoor area (north of Takab, West-Azarbaidjan province) are alteration products of andesitic rocks of Miocene age in northwest of Iran. Based on the mineralogical studies, kaolinite, quartz, jarosite, montmorillonite, albite, muscovite-illite, anatase, chlorite, orthoclase, calcite, goethite and hematite are mineral phases in these zones. The silicic veins existing within these zones include metallic minerals such as pyrite, chalcopyrite, galena, sphalerite, bornonite, and stibnite. The mass change calculations of rare earth elements (REEs), with assumption of Sc as a monitor immobile element, reveal that development of kaolinization processes were accompanied by enrichment-depletion of La-Nd and depletion of Sm-Lu. Geochemical analyses show that the degree of differentiation of Al from Fe and destruction of zircon by hydrothermal fluids are the most important controlling factors for variation of Eu (0.84-1.06) and Ce (0.83-0.93) anomalies in these zones, respectively. Positive and strong correlations of (La/Lu)N and (LREEs/HREEs)N values with components such as P, S, LOI, and Sr establish the effective role of hypogene solutions in progression of kaolinization processes. The combination of the obtained results from mineralogical and geochemical investigations suggest that changes in chemistry of altering solutions (e.g., pH and Eh) and diversity in type of fixing minerals are two key factors affecting differentiation and distribution of REEs in the kaolinizedzones at Goorgoor.

The Panah-Kuh skarn is situated in 50km NW of Taft City in Yazd province. Inrtusion of granodioritic stock into the calcareous-dolomitic rocks of Permian Jamal Formation led to formation of calcic and magnesian skarns. The REE patterns of skarns and its forming garnets show Eu/Eu* and Ce/Ce*ratios increase with increasing of ∑REE, implying that skarn forming fluids were dominantly of magmatic origin, whereas (Pr/Yb)cn ratio decrease almost with increasing of ∑REE that implying the magmatic fluids granitoid-derived had not much REE during the Panah-Kuh skarn formation. Based on the fluid inclusion data from garnet, fluid temperature and salinity in the prograde stage vary between 308-380oC and 12.6-23.8 wt.% NaCl equivalent, respectively. Inclusion fluids in the calcite had lower temperature (T<280°C) and fluid salinity decline to 3.5 wt.% NaCl equivalent. Mixing and dilution of early magmatic fluids with external fluids (e.g., meteoric waters) caused a decrease in fluid temperature and salinity in latest stage of the skarn formation. Therefore, both REEs and fluid inclusions data suggest the dominant role of magmatic water in the formation of Panah-Kuh skarn.

The Khut and Panah-Kuh skarn deposit is located at about 50 km northwest of Taft in Yazd province. The analyses of major and REE''s by microprobe and LA-ICP-MS show that there are two major types of garnet at Khut and Panah Kuh skarns. The garnets in the Khut skarn range from (Ad74. 30Gr24. 81- d32. 06Gr66. 61) to almost pure andradite (Adr>96) in composition whereas all Panh-Kuh skarn garnets are almost pure andradite and isotropic. The REE become commonly enriched in garnets during metasomatic process. On the Fe/Ti versus Al/ (Al + Fe + Mn) diagrams، these rocks suggests that over 50% of hydrothermal fluid phase has been effective in the formation of garnets. Comparison of chondrite- normalized REE patterns garnets exhibit that all garnets have light REE (LREE) enrichment and heavy REE (HREE) depletion، with different Eu anomalies. Fe-enriched garnets are characterized with positive Eu anomaly whereas grandite show negative Eu anomaly. Differences in the magnitude of the anomaly reflect local heterogeneities of the system such as protolith as well as metasomatic fluid. The same abundance pattern of REE in the skarn and garnet suggests that garnet is the most important REE host mineral. Therefore، the study of REE geochemical behavior is benefiial in understanding the evolution of metasomatic fluids.

The Dalir phosphate horizon is located ~57 km southwest of Chalous، Mazandaran province. The horizon developed as stratiform within upper shale of Soltanieh Formation (late Neoproterozoic - early Cambrian). According to mineralogical data، the major minerals of the phosphate horizon are calcite، fluorapatite، dolomite، quartz، pyrite، muscovite، and illite. Microscopic evidence such as existence of the fabric similar to grumeuse fabric indicates a vital role for diagenetic processes and dynamic pressures in the evolution of the horizon. The distribution pattern of Rare Earth Elements (REEs) normalized to PAAS reveals weak fractionation of Light REEs from Heavy REEs and negative Ce anomaly during phosphatization. Incorporation of the obtained results from mineralogical and geochemical studies suggests that the behavior and distribution of REEs were affected by the function of factors such as diagenesis، preferential sorption، presence and decomposition of organic matter، oxidation-reduction potential، and function of pore-waters. Further geochemical considerations show that fluorapatite، xenotime، muscovite، Mn-oxides and illite are the potential hosts for REEs.