جستجوی مقالات مرتبط با کلیدواژه "عناصر کمیاب خاکی" در نشریات گروه "زمین شناسی"

Shotorsang iron skarn is located in 60 km northwest of Neyshabour (Khorasan Razavi, Iran) in Quchan-Sabzevar magmatic belt. Subvolcanic intrusion rocks have intruded into Cretaceous limestones and created skarnization. These rocks are divided into syenite porphyry and granodiorite porphyry based on their geochemical characteristics. They are I type oxidizing, metaluminous, and tectonic. Setting of the subvolcanic rocks are the subduction zone of the continental margin (VAG). Comparing the mineralization potential of the subvolcanic rocks of this area based on the use of the graph of SiO2 against K2O, MgO, Na2O+K2O, and Ni-V shows that they are fertile in terms of the formation of Fe and Cu skarn. Syenite porphyry is the origin of this mineralization, and magnesium in skarn is taken from hydrothermal fluid. The diagram of Eu/Eu*, Ce/Ce*, (Pr/Yb)n ratios also confirms the presence of meteoric water in the formation of the skarn zone. The primary fluid, which has a positive anomaly of Ce/Ce* and Eu/Eu* had acidic and oxidant conditions and high temperature, and formed pyroxene skarn. A part of magnetite mineralization is formed in this zone, and in this condition, the highest amount of REE entered the pyroxene skarn zone and diluted the fluid in terms of REE. This issue has led to a sharp decrease in the amount of REE in the mineralization zone. Negative Ce/Ce* and Eu/Eu* anomalies indicate alkaline conditions with less concentrated REE content, consistent with chlorite skarn. The highest amount of Fe mineralization is formed in this zone.

The Arabshah Fe mineralization is the only known magnetite-apatite mineralization at the Takab–Takht-e-Soleyman–Angouran subzone in southeast of Takab. The oldest rock units in the mineralization area include sedimentary succession of the Qom Formation that was intruded by the Pliocene Ayoub Ansar volcanic dome. Magnetite- apatite mineralization at the Arabshah occurs as vein-veinlets with E-W stright within the Ayoub Ansar dacitic dome. Brecciated zones containing narrow magnetite vein- veinlets occur at footwall and hanging wall of the main vein. Hydrothermal alterations include sodic-calcic, silicification and argillic. Magnetite is the only ore mineral in this mineralization which is accompanied with apatite, clinopyroxene, albite and quartz as gangue minerals. Mineralization textures in the Arabshah deposit include vein-veinlet, brecciated, disseminated, and replacement. REEs concentration within apatite crystals are more than 1%, and demonstrate LREE enrichment with high LREE/HREE ratio and distinctive negative Eu anomalies which is indicative for Kiruna- type iron ores. The result of fluid inclusion studies indicates the presence of two-phase and poly-phase inclusions include LV, VL, LVH, LVS and LVHS fluid inclusions with homogenization between 230-550 °C. The salinity of halite bearing poly-phase fluid vary between 35-60 wt.% NaCl equiv. Fluid inclusion data indicates that Arabshah magnetite-apatite mineralization originated from magmatic fluids. Evidences like mineral assemblages, hydrothermal alteration, ore structure and textures, geochemical characteristics and fluid inclusion data, indicate that the Arabshah magnetite-apatite mineralization can be classified as Kiruna-type iron ores.

The study area is located about 8 km south of Bandar Abbas in Hormozgan Province. This area is in the south of the Zagros folded zone and part of the Hormuz series. The late Precambrian-early Cambrian rocks comprise intercalations of rhyolite-rhyodacite lava and tuff, crystal tuff, tuffaceous shale, sandstone and evaporite layers. Iron mineralization along with apatite are found as dike, massive, vein-veinlets and disseminated forms in tuffaceous shale and crystalline tuff rock units. Based on iron oxides and apatite contents, mineralization can be divided into iron-oxides (mainly magnetite), iron oxides- apatite and apatite types. The main ore-forming minerals include magnetite, oligist, hematite, goethite and limonite, apatite, and gangue minerals are calcite, quartz and clay minerals. The Hormuz Island ores have a high concentration of rare earth elements (REE) and the total amount of REE in apatite-rich ores is up to 3%. The geochemical studies show that a strong positive correlation between P and REE. Comparison of the chondrite-normalized REE pattern of the Hormuz magnetite-apatite ores with those from the Bafq-Posht-e-Badam block and the Kiruna type iron ore deposits represent genetic similarity of mineralization. The homogenization temperature in the two-phased liquid and vapor (L+V) fluids in apatite minerals vary from 309 to 565°C (average 388°C), and salinity varies between 14.16 to 33.87 (20/80) wt.% NaCl. Finally, based on the field geology, mineralogy, geochemistry and fluid inclusion features, the Hormuz magnetite-apatite mineralization is classified in the Kiruna-type magnetite-apatite deposits group with magmatic-hydrothermal origin.

Iron oxide-apatite deposits (IOA) are considered to be Kirune-type iron ores which have been formed during Proterozoic to Tertiary eras in different parts of the world. They usually have a connection with calc-alkaline volcanic rocks (Hitzman, 2000). Apatite occurs as a major constituent of these deposits which is accompanied with magnetite and some actinolite. One of the most important features of these deposits (Frietsch and Perdahl, 1995) is higher concentration of REEs.There are some iron oxide-apatite deposits in the Tarom-Hashtjin magmatic-metallogenic belt, northwestern Iran. The Golestan Abad iron oxide-apatite deposit is one of the IOA deposits at the Tarom-Hashtjin belt which is located about 30 km east of Zanjan. The Golestan Abad deposit was studied during the exploration studies, but its geological characteristics, mineralogy, texture, geochemistry and genesis have not been studied yet.

This research study can be divided into two parts that include field and laboratory studies. Field studies include recognition of different lithological units and mineralization zones along with sampling for laboratory studies. During field studies, 60 samples were selected for petrographical, mineralogical and analytical studies. Moreover, 12 thin sections and 15 thin-polished sections were used for petrographical and mineralogical studies. For geochemical studies, 6 samples from intrusive host rocks and 7 samples from mineralized zones were analyzed by XRF and ICP-MS methods at the Zarazma laboratory, Tehran.

The Golestan Abad area is composed of Eocene volcano-sedimentary rocks of the Karaj Formation which have been intruded by quartz monzodiorite, pyroxene quartz monzodiorite and porphyritic quartz diorite intrusions. Based on petrographic studies, the pyroxene quartz monzodiorites have porphyritic and felsophyric textures and are composed of plagioclase, quartz, clinopyroxene, K-feldspar and hornblende phenocrysts set in a quartz-feldspatic groundmass. Quartz monzodiorites show porphyritic and felsophyric textures and composed of plagioclase, hornblende, quartz, K-feldspar and biotite. The quartz monzodiorite and pyroxene quartz monzodiorites have high-K calc-alkaline affinity and may be classified as metaluminous I-type granitoids. Primitive mantle-normalized (McDonough and Sun, 1995) trace elements diagrams for these granitoids indicate LILE enrichment along with negative HFSE and distinctive positive Pb anomalies. Chondrite-normalized (McDonough and Sun, 1995) REE patterns for these granitoids demonstrate LREE enrichment (high LREE/HREE ratio) and weak negative anomalies in Eu. These granitoids were formed in an active continental margin to post collisional tectonic setting.Mineralization at the Golestan Abad occurs as lenses and vein-veinlets of iron oxide-apatite mainly within the quartz monzodiorite- pyroxene quartz monzodiorite intrusions. Stockwork ores occur in the footwall of the main veins. Mineralized lenses and veins have up to 300m length and 20m width. Hydrothermal alterations around the mineralized veins include silicification, calcic (actinolitization), argillic and propylitic. From a mineralogical point of view, this deposit is composed of magnetite, apatite, actinolite, pyrite and chalcopyrite as primary minerals, while hematite, covellite, goethite and gypsum were formed during supergene alteration. Mineralization textures in the Golestan Abad deposit include vein-veinlet, banded, massive, brecciated, disseminated, stockwork, replacement, relict and open space filling. Based on mineralogical and textural studies, 3 stages of apatite formation were distinguished which include: 1- coarse-grained idiomorphic apatite crystals within the magnetite matrix, 2- fine-grained apatite crystals as matrix of brecciated magnetites, and 3- coarse-grained idiomorphic apatite crystals within the actinolite-apatite veins which have been cut in the previous stages. Apatite crystals of the 3 mentioned stages have high concentrations of REE that include 0.98, 0.92 and 0.95%, respectively. Condrite-normalized (McDonough and Sun, 1995) REE patterns for 3 apatite generations demonstrate LREE enrichment with high LREE/HREE ratio and distinctive negative Eu anomalies.

Similar REE patterns of apatite crystals and mineralized samples with host quartz monzodiorite-pyroxene quartz monzodiorite samples demonstrate a genetic link between iron oxide-apatite mineralization and granitoids. Furthermore, REE patterns of the Golestan Abad deposit are similar to other iron oxide-apatite deposits of the Tarom-Hashtjin metallogenic belt (Nabatian and Ghaderi, 2014; Mokhtari et al., 2017), and those of Central Iranian iron ores (Mokhtari et al., 2013). Finally, the REE patterns of the Golestan Abad deposit are similar with the REE patterns of the Kiruna-type iron ores (Frietsch and Perdahle, 1995). Totally, based on mineralogical assemblages, hydrothermal alteration, mineralization textures and geochemical characteristics, the Golestan Abad iron oxide- apatite deposit can be classified as the Kiruna-type iron ores.

Garnet–mica schist and hornfels rock units are exposed in the east and southeast of Boroujerd. These rocks consist primarily of quartz, K-feldspar, plagioclase, garnet (almandine–spessartine), chlorite, cordierite, andalusite, sillimanite, biotite, muscovite, and minor amounts of apatite, iron oxides (ilmenite and magnetite), and zircon. Whole-rock geochemical analyses reveal that the dominant protoliths are pelitic rocks. Major and trace element compositions suggest that the Boroujerd pelites were deposited along an active continental margin. Garnet porphryblasts in some hornfels samples are compositionally homogeneous with respect to major, trace and rare earth elements; this is attributed to the diffusional re-equilibration at high temperatures (>600 ºC). Garnet in schists and some hornfels samples show reverse compositional zoning with increasing Mn and decreasing Fe and Mg from core to rim. Higher concentrations of Mn in garnet rims are attributed to resorption during retrogression. The presence of chlorite around garnet porphryblasts in these schists also supports resorption during retrogression. In schists, concentrations of HREE and Y in garnet decrease from core to rim. These zoning patterns are interpreted to record garnet growth in a closed system (i.e., Rayleigh fractionation of compatible elements). Core–rim variations in the concentrations of trace elements and rare earth elements in garnet in the hornfels samples is negligible. The lack of prominent zoning of these elements in garnet from hornfels is interpreted as minimal fractionation due to rapid garnet growth.

The Saghand mining district is a part of Bafq- Saghand metallogenic zone in the Central Iranian geostructural zone which is located in northeast of city of Yazd. This area is known to be more susceptible to mineralization of U and Th radioactive elements, but in fact is that its main importance is for relatively large iron deposits. However, in this region similar to some of the ore deposits within the Bafq area, rare earth elements have a high anomaly. Alkali-metasomatism occurs in a large variety of environments and geological periods. It can be spatially associated with ore deposits, as for some IOCG deposits or exists in barren systems such as metasomatism within the ocean crust (Johnson and Harlow, 1999). Although average U and REEs contents of the ore bodies associated with alkalimetasomatism are not high, they represent a promising exploration target because the resources of such deposits are relatively large (Cuney et al., 2012). The alkali-metasomatism could take place in all kinds of rocks. In addition to wide distribution in granite and granodiorite, it could be also identified in all kinds of metamorphic rocks, pegmatites, subvolcanic and volcanic rocks, and they all have mineralization (Zhao, 2005). After field studies, host rocks and metasomatites were sampled from outcrops, trenches, and core drillings. Since the rare earth elements and radioactive elements are present within the same mineralogy (Samani, 1985), surface spectrometry measurements were used in the selection of appropriate samples. For microscopic studies, 210 samples were prepared and studied. Ore minerals were investigated in polished and polished thin sections using optical microscope and Scanning Electron Microscopy (SEM) analysis was done in the Iranian Mineral Processing Research Center. An LEO-1400 SEM with energy dispersive X-ray spectrometry and back-scatter electron (BSE) imaging capabilities was used (accelerating voltage, 17-19 kV, and beam current of 20 nA). The 16 samples were analyzed by the ICP-MS method at Zarazma Mineral Studies Company, Iran, for major and trace elements at the various radiations and lithological ranges. The detection limit and precision for determination of REE, U and Th concentration were 0.2 to 1 ppm and 1 to 0.1 ppm, respectively. Discussion and results: Based on field evidence and microscopic studies, four main stage of metasomatism with continuous evolution have been distinguished in the Saghand area, including: 1) Na-metasomatism, 2) Ca-Mg metasomatism, 3) K-metasomatism, and 4) Epidote±chlorite±calcite±quartz vein and veinlets. All metasomatic zones are generally enriched in U and REE and compared with the host rocks but economic grades are less widespread and limited to Ca-Mg metasomatite zones near pinkish to red color albitites. The major Ti-REE-U(Th) minerals are davidite and brannerite, which have mainly crystallized during the Ca-Mg metasomatic stage. Ti or Tibearing minerals as paragenesis with davidite and brannerite are also deposited in amphibole-albite metasomatic zones. All these minerals are usually fractured and along fractures and its margin is replaced by titanite, leucoxene and rutile. In this study, geochemical analysis results of igneous rocks in the Saghand ore deposit, confirm the active continental margin arc setting and the nature of calc-alkaline magmatism in the region. The good adaptation of the REEs patterns in granites with the quartzdiorite-diorite rocks, can be a strong reason for their common tectonomagmatic origin. This Geodynamic environment had been the appropriate background in terms of protolith, heat engine for metasomatism cycle and supply hydrothermal solution and controlling structural pathways. The proximity of mineralized metasomatic rocks with the granitic rocks and intrusion of the granite apophysises into the metasomatic rocks, mobility of REE elements in the metasomatic environments, adaptation of geochemical properties of REE, U and Th elements in the mineralized metasomatitic rocks with the granitic rocks and finally, there was no evidence of intrusion of unusual magmas such as the carbonatite or alkaline magmas at the current level of ore deposit outcrops. Thesesuggest a close relationship between mineralization and metasomatic events with the granite intrusion. Fluids differentiated from the Douzakh-Darreh granite have entered the fault and crushed zones in a tectonically active regime of marginal continental arc. Due to reaction of the high temperature fluid with the protolith rocks, the ratios of Na+/K+ and Na+/H+ in fluid in equilibrated to feldspars of protolith rock elevated (Cuney et al., 2012). A basically alkaline medium to low temperature hydrothermal fluid is a suitable environment for the activation and transfer of U and REE in the form of hydroxyl complex (Romberger, 1984). Conversely, Th remained essentially immobile during the metasomatic processes (Cuney et al., 2012) and therefore, cannot be in abundance carried by this fluid. Hematite pigmentation of albite and transfer of U shows that oxygen fugacity in the early hydrothermal fluid has been quite high. These geochemical conditions simply allow U, and REEs enter from wall rocks to fluids and form hydroxyl complex of these elements, which are sustainable and are portable. Titanium bearing minerals within the quartzdiorite-diorite rocks and Douzakh Dareh granite easily decompose under hydrothermal activity and form titanium hydroxides, which is a very strong absorbent for U. After mineralization of albite and hematite, oxidation degree of fluid quickly drops and as a result, conditions for instability of complexes containing Ti, REE and U are provided. Acknowledgements: This paper is based on a part of the first author's Ph.D thesis at Shahid Beheshti University. This research was also supported by Skam Company and Iranian Mines & Mining Industries Development & Renovation Organization.

The pegmatites of Darreh Vali region is located in the north-east of Boroujerd which is a part of Sanandaj-Sirjan zone. In the Darreh Vali area, granodiorite bodies are cut by small pegmatitic dykes with NW–SE trend. The mineralogy of studied pegmatites consists of quartz, alkali-feldspar (orthoclase and microcline), plagioclase, muscovite, garnet (almandine-spessartin), andalusite, tourmaline, and apatite. Chondrite-normalized patterns of the Darreh Vali pegmatite are characterized by low enrichments of LREE relative to HREE (LaN/YbN=1.76-4.04), with a relatively flat HREE distribution, and a strong negative Eu anomaly (Eu/Eu* =0.20-0.54). Major element chemistry of garnets in these pegmatites indicates a compositional zoning with decreasing MnO and increasing FeO from core towards the rim. In the case of the Darreh Vali pegmatites, all garnet crystals contain low CaO (0.15 to 0.29 wt.%) and high MnO (10.27 to 13.18 wt.%), which are similar to magmatic garnets from pegmatitic melts. On the MnO+CaO versus FeO+MgO (in wt. %) diagram, the composition of garnets shows that they probably crystallised in contact zones of pegmatite vein and from less evolved melts. LA-ICP-MS analyses show that analysed garnets have a high HREE, low LREE contents, and strong negative Eu anomaly (Eu/Eu*=0-0.41) in the core along with positive Eu anomaly (Eu/Eu*=0-3.22) at the rim. Y, HREE, Ti, Zr, Nb, Ta, Hf, U and Mn decrease from core to rim. These core-to-rim elemental variations are attributed to increasing fluid-phase and H2O activity in magma, along with increasing magma fractionation. REE patterns and Eu anomalies in zoned garnets suggest that they probably formed in reducing to oxidizing conditions.

Neyzar iron deposit is located about 50 km southwest Mashhad, northeast Iran. It was developed as layered and discontinuous lenses in a fault zone within quartz-arenite and sub-litharenite sandstones of Lalun Formation (Lower Cambrian).  Mineralographical studies show that hematite is the principal iron ore mineral accompanied by goethite and lesser amounts of pyrite. Microscopic examinations confirm the presence of skeletal, relic replacement, marginal replacement, and pseudomorphic textures within the ores. Based on petrographical data, two series of alteration minerals, hypogene (sericite, pyrite, pyrophyllite, barite, chalcedony, and calcite) and supergene (goethite, jarosite, gypsum, limonite, and hematite) were developed in this deposit. Based on the results obtained from field works, mineralographical and geochemical studies, it appears that the evolution of the studied ores is genetically related to the host rocks.  Both hydrothermal processes and fault systems (existing in the host rocks) played important roles in leaching of elements and depositing of the ores. Results of chemical analyses show that the REE values vary in the iron ores from 6.97 to 18.26 ppm. Eu and Ce anomalies in the ores are within the ranges of 0.01-1.36 and 0.28-1.89, respectively. Geochemical considerations reveal that distribution of rare earth elements within Neyzar iron ores was controlled by pH, abundance of complex-forming ions (CO32-, F־, Cl־, PO43-, and SO42-), scavenging processes, and fixation in neomorph mineral phases.

Kalkafi area is located about 76 km northeast of Anarak (Isfahan Province), in Central Iran structural zone. Based on field observations, petrographical and XRD examinations, three major alteration zones were identified in the studied area including potassic, phyllic-argillic, and silicic zones. Potassic alteration is characterized by orthoclase + biotite + quartz ± sericite assemblage. Phyllic alteration is composed of sericite + quartz + pyrite associated with clay minerals ± calcite, and argillic alteration is characterized by kaolinite + dikite + sericite + quartz + hematite + limonite + goethite. Two major ore mineralization were identified in the studied area: (1) Cu-Mo mineralization and (2) Au-Pb-Zn polymetallic mineralization. Cu-Mo mineralization is mainly related to porphyry quartz monzonites and granites. Chondrite normalized REE patterns of unaltered intrusive bodies (quartz monzonites) indicate a‎ strong LREE and a weak HREE differentiations. Lower content of total REEs in‎ the altered samples of the studied area indicates their mobility in hydrothermal environment. Microthermometric analysis of fluid inclusions of the studied samples indicates that salinity of mineralizing fluid ranges from 1.74 to 21.11 NaCl equivalent wt%. Collected homogenization temperatures confirm the existence of at least two generations of fluid inclusions or mineralizing fluids in this area.