جستجوی مقالات مرتبط با کلیدواژه "منگنز" در نشریات گروه "زمین شناسی"

The Mazraeh manganese deposit (southwest of Maku, north of West-Azarbaidjan Province, NW Iran) is developed in the form of scattered lenses at the contact of pillow basalts and pelagic limestones, belonging to the Khoy-Maku ophiolitic complex. Mineralogically, the ores mainly contain pyrolusite, psilomelane, manganite, and braunite which are accompanied by lesser amounts of hematite, goethite, quartz and calcite. The distribution pattern of REE normalized to chondrite along with some geochemical parameters related to lanthanides, such as La/Ce, (La/Nd)n and (Dy/Nd)n, show a hydrothermal origin for this deposit. This idea is supported by some geochemical diagrams (Co/Zn vs. Co+Ni+Cu, Zn-Ni-Co, and Mn-Fe-[(Co+Ni+Cu)]×10) and elemental ratios such as Mn/Fe, SiO2/Al2O3, U/Th, and Co/Zn. The high concentration of lanthanides in ores (on average of 767 ppm), compared to known hydrothermal manganese deposits, reveals the effects of diagenetic processes on this deposit. The occurrence of negative anomalies of Eu and Ce indicates the low-temperature hydrothermal fluids, responsible for the mineralization. The presence of detrital materials in the ores can be inferred by the concentration values of oxides like Al2O3 and TiO2.

Salardol manganese deposit is located 20km west of Aleshtar in the radiolarite subzone of Kermanshah ophiolite zone. The rock units include radiolarite, breciaition limestone and Cretaceous units. Manganese deposits are seen in the form of irregular lenses as interlayers with radiolarites. Manganese mineralization is visible in three generations. The first generation is syngenetic and is formed interlayer with radiolarity naps. The second and third generations are epigenetic, which can be seen in the form of streaks and mainly within the faults and seams and cracks of radiolarity. Mineralogically, XRD and SEM are important manganese paragenes including Ramsdellite, Romanechite, Rhodochrosite, Jacobsite, Bixbyite and the most important gangue minerals are quartz and calcite. Good agreement between Salardol manganese deposit and hydrothermal deposits has been confirmed by trace elements geochemical data, distinguishing diagrams and elemental ratios. The use of major and minor element ratios indicates the thermal conductivity of Salardol manganese reserves. Na/Mg ratio indicates the effect of fresh water on the formation of manganese reserves. The distribution pattern of normalized REE relative to chondrite indicates a positive Ce anomaly with an average of 20.1 and a negative Eu anomaly with an average of 0.47, which is clearly consistent with manganese hydrothermal deposits. According to the available evidence, the formation of Salardol manganese deposit due to the synthetic placement of primary manganese in the radiolaritic host rock and the epigenetic processes resulting from tectonic activities and under the influence of hydrothermal fluids has led to the formation of fossil-type reservoirs.

Temelieh area is located about 20 Km northwest of Selseleh (Lorestan Province). Geologically, the area is a small part of the Harsin radiolarite complex. Petrography consists of radiolarite, peridotite, gabbro, plate dikes, basalt and andesite, limestone, and marble. Manganese mineralization occurs as vein-veinlet and is mainly formed in faults, joints, and fractures that crosscut in radiolarites. Based on mineralogical studies, the manganese paragenesis is composed of pyrolusite, psilomelane, todorokite, cryptomelane, lepidocrocite, and manganese oxide-hydroxide (housmanite, hydrohousmanite, Manganite). The essential waste minerals are calcite and quartz. Based on geochemical data from major and trace elements, using different distinguishing charts and elemental ratios, there is a good relation between the manganese-rich region and the hydrothermal deposits. On the other hand, calculation of element designated ratios like Mn/Fe )mean 0.92), Ti/Al (mean 0.01), Co/Ni (mean 0.97), Co/Zn (mean 0.28), U/Th (mean 0.73), La/Ce (mean 0.32), LREE/HREE (mean 8.64) and ΣREE (mean 56.53) indicate Temelieh manganese ore is hydrothermal. Comparison of the REE normalized pattern of Temlieh manganese ore with other manganese deposits in the world indicates the hydrothermal origin of this deposit. REE distribution pattern indicates Ce positive anomaly with mean 24.5 and Eu negative anomaly with mean 0.54 that is compatible with hydrothermal manganese deposit. Accordingly, ore-forming fluids could be originated from meteoritic or magmatic water circulating through volcanic rocks, dissolve manganese and other metals and, while rising from suitable areas, deposits them in along the fault planes and fractures.

The Hajiabad manganese deposit is located about 40 km northeast of Hajiabad, Hormozgan Province. This deposit is structurally located in the southeastern border of the Sanandaj-Sirjan zone. The manganese mineralization in the study area is hosted by calcite-dolomitic marbles and mica schists of Devonian age, as layers, veins and massive ores. Based on microscopic investigations, the ores are dominated by manganese occurring as cement of fragments of mica schist rocks and host silicified dolomites by the open space filling process. The major minerals of this deposit include todorokite, spessartine, almandine and calcite and the minor minerals in this deposit are pyrolusite, goethite and quartz. According to geochemical data, the concentration of manganese in the ore bodies are more than 41 wt%. Low levels of P2O5 and TiO2 is inconsistent with magmatic origin of the study deposit. On the one hand, the absence of skarn-related features and on the other hand, field observations, mineralogical and geochemical data, show that these manganese deposits were formed by the entry of manganese fluids with a volcanic origin in a sedimentary basin and then has reconcentrated and upgraded by regional metamorphism in mica schists and metamorphic limestone of the Khabr complex.

In this paper, an inversion algorithm based on graph theory is applied on three real gravity data sets, including data from a chromite deposit in Camaguey, Cuba, from a manganese ore in Nagpur, India, and from a mafic unknown body in Slovakia. The goal, here, is to use this new inversion algorithm to model the skeleton of these subsurface targets, and then, to compare the obtained models with previous published results. We model a homogeneous subsurface body by an ensemble of similar point masses. Here, model parameters are the Cartesian coordinates of the point masses and their total mass. The set of point masses is associated with the vertices of a complete weighted graph. Kruskal’s algorithm is used to solve the minimum spanning tree (MST) problem for the graph yielding a stabilizer, which is called “equidistance function”. The non-linear global objective function is minimized using a genetic algorithm strategy. The methodology provides suitable information about the extent of the bodies in east and depth directions. Moreover, the results of previous investigation for these real data sets are given in the paper. An open source MATLAB package along with a full description of the algorithm implementation is available at https://math.la.asu.edu/∼rosie/research/gravity.html.

It is generally understood that manganese deposits have a diverse origin, based on their mineralogy, chemical composition and tectonic setting. Marine Mn-bearing deposits are classified as hydrogenous, hydrothermal and also biogenetic-bacterial deposits (Bonatti et al., 1972; Hein et al., 1997; Bau et al., 2014; Polgári et al., 2012; Schmidt et al., 2014). Hydrogenous processes can form ferromanganese crusts, which result from slow precipitation of seawater at the seafloor often via microbial mediation (Toth, 1980; Dymond et al., 1984; Bau and Dulski, 1999; Usui and Someya, 1997; Hein et al., 2000; Jach and Dudek, 2005). Diagenetic manganese deposits occur as nodules and precipitate from hydrothermal solutions or pore water (Polgári et al., 1991; Oksuz, 2011; Polgári et al., 2012), whereas hydrothermal ore deposits are stratabound or occur as irregular bodies and epithermal veins, where they are formed in a marine environment near spreading centers, intraplate seamounts or in subduction-related island arc setting (Roy, 1992; Roy, 1997; Hein et al., 2008; Edwards et al., 2011).

Eighteen Ore samples (~ 500 g each) were collected systematically from the Gezeldash Daghi manganese deposit. All these ore samples were taken representatively from the surface outcrops ore beds in different places for geochemical analyses. Ore samples were powdered under 200 meshes and analyzed at Iran mineral processing research center laboratories, Tehran. After being prepared by the Lithium Borate Fusion method, their major oxide and trace element contents were determined with ICP-OES. The results of the analyses are given in Tables 1 and 2.

The deposit is hosted in various lithology and horizons consisting of: 1) tuffite interlayered with limestone, 2) conglomerate and sandstone lithology into volcano-sedimentary basin located at 25 km northwest of Marand city (N38°35ʹ40ʺ, E45°42ʹ40ʺ). Major and trace element assessments show that hydrothermal solutions were effective in the formation of the Gezeldash Daghi manganese deposit. Also, field observations reveal that manganese mineralization occurred as laminated-layered and fracture-filling form in limestone and tuffite at horizon I and the space-filling form between conglomerate clasts and veinlet form in sandstone at horizon II with quaternary age. Therefore, it can be concluded that hydrothermal solutions were caused in the formation of the manganese deposit which may be described as related to volcano-hydrothermal occurrence.

The Borujerd-Kermanshah ophiolite is a part of the ophiolite complex belonging to the Zagros Mountains and is a part of the Alpes-Himalayan belt (Alavi, 1994). The Boroujerd-Kermanshah Ophiolite complex consists of serpentinized peridotite, layered metagabbro, isotropic gabbro, diabase dyke, plagiogranite, pillow lavas and sedimentary rocks (Miocene radiolarite and limestone). In the upper part, the radiolarite layers are covered by jasperoid rocks and pelagic limestone (Mohajjel et al., 2003; Saccani et al., 2013). The Noorabad Delfan manganese deposit is subjected to mineralogical and geochemical studies in order to elucidate its petrogenesis. The Noorabad Delfan manganese deposit is located along the ophiolite belt of the upper Jurassic-lower Cretaceous period. Manganese mineralization occurs as syngenetic to epigenetic with jasperoid and silicified veins in the carbonate and radiolarian chert units. Geochemical studies show that some elements such as Ce, Cu, Ni are enriched in the mineralized zone. Mobile and trace elements (Sr, As, Zn, Ba, Fe, Mn, Si) and the ratio of Mn/Fe, Al/Ti, show similar characteristics with submarine hydrothermal-hydrogenous manganese deposits. In geochemical studies, SEM, XRD and EPMA results show that pyrolusite is the majar mineral in the ore deposit, and nsutite and rhodochrosite are formed as the accessory phase.

During the field work, 53 samples were collected from the mineralization zone and host rocks. A total of 30 polished and thin sections were studied by Zeiss polarized microscope (Axioplan-2), in the Kharazmi University and the Iran Mineral Processing Research Center (IMPRC). Suitable sections were selected for more study by Zeiss 1450vp SEM at the Iranian Mineral Processing Research Center (IMPRC). The SEM-EDS analyses and secondary electron (SEM-SE) images at the IMPRC were acquired on beam currents between 0.05 and 5 nA, and electron acceleration potentials of 5 to 20 kV. The Electron microprobe analysis of selected points by SEM was carried out using a Cameca SX100 at IMPRC in the 20 kV and 20 nA current and 1 to 5 mm beam long. The Cameca PAP correction software was used for data reduction. Backscattered electron images were used in order to select more analytical points. A total of 15 samples were selected for whole rock chemical analysis. Samples were prepared with regular methods and finally they were analyzed for major and rare elements by the XRF and ICP-MS methods in Zarazma and Iran Minerals Processing Research Center Laboratory.

Manganese deposits with hydrothermal origin are usually related to silica gels. These deposits are associated with submarine volcanic eruptions and hydrothermal-hydrogenous activity and they are rich in metal elements. This kind of deposits, is basically emplaced with interlayer marine sediments (Roy, 1992). Titanium in the hydrothermal fluids is an immobile element and can be used as an indicator for measuring the amount of continental crest sediment. The relatively high TiO2 levels in the manganese deposits indicate the composition of the material during sedimentation (Sugisaki, 1984). Therefore, in the hydrothermal deposits, the TiO2 ratio is lower than other kinds of manganese ore mineralization types. Nicholson (Nicholson, 1992a) believes that hydrothermal manganese deposits are known by enrichment of As, Ba, Cu, Pb, Sb, Sr, Li, Cd, Mo, V, Zn, Co, Cu, Ni and sedimentary deposits are distinguished by K, Na, Ca, Mg, Sr (Nicholson, 1992b). According to this statement, the manganese mineralization of the Noorabad Delfan deposit may be classified as hydrothermal to hydrogenous ore deposits related to oceanic crust ophiolitics.

The Noorabad Delfan deposit with 5 km long is formed in radiolarite sequences in the west of Iran. Based on field observation, mineralogy and geochemistry and the major/trace and rare elements ratio, Noorabad Delfan mineralization is classified as a hydrothermal-hydrogenous deposit. In the study area, the manganese mineralization is formed with interlayer of radiolarite as syngenetic to epigenetic mineralized zones.The hydrothermal systems are generated by submarine volcanic activity and seawater. Due to the rotation of submarine volcanic activity related fluids, the hot oceanic water carries metalliferous phases. The metalliferous phase has been deposited during cooling, pressure reductions and Eh-pH changes. The hydrothermal to hydrogenous activity is the main factor in manganese mineralization in the Noorabad Delphan deposit. Mineralogical and geochemical evidences support a primary hydrothermal source for Mn-mineralization.

In the Kurdistan Province (west of Iran), manganese mineralization has occurred in several locations including Shahini (south west of Sanandaj), Sianaw (west of Mariwan), Tawakalan (west of Diwandareh) and Golchidar (east of Marivan), but Tawakalan mineralization has characteristics which cannot be interpreted by Petrological principles. This mineralization is located at the end of northwest of Sanandaj-Sirjan zone and is located in Paleozoic formations. In this mine, ore deposits is a paragenesis of high temperature silicates like spessartite and rhodonite sometimes accompanied by tephroite that usually crystalize at high temperature and occur in absence of water; while ore deposits of Tawakalan appear as lens-shaped segments, intercalated within the shale, sandstone, volcanic tufts and radiolarites untouched by temperature and where no intrusive bodies are seen in the region. The order of crystallization of these minerals in ore deposits is: 1- spessartite and rhodonite, 2- bementite, 3- Hydreous silicates of manganese, 4- rhodochrosite, 5- manganese oxides. hydreous silicates of manganese include orientite, caryopilite, zussmanite, and manganese oxides is pyrolusite and Rancieite. Gangue is composed of quartz (mostly in form of Jaspe), minor amount of magnetite and antigorite. The carbonate and manganese oxides are secondary products of metasomatism of manganese silicates. Field studies, laboratory experiments and comparison of manganese of the Tawakalan mine with other locations in the world, suggest a two phase formation process of high temperature paragenesis as follows: in the first phase, the sedimentary manganese oxides are formed in the volcano-sedimentary layers and in the second phase, after a period of orogenese, metamorphism and plutonism, high temperature fluids released from solidification of profound plutonic body dissolve manganese oxides of the first phase and cause recrystallization of manganese in shallow levels as high temperature silicates. Metasomatism of silicates and production of carbonate and Mn oxides occur at the end of the second phase when the fluids cool down.

Manganese deposits are classified as hydrogenous, diagenetic and hydrothermal deposits based on their mineralogy, chemical composition, and tectonic setting (Hein et al., 1997). Hydrogenous manganese deposits have slowly precipitated from seawater (2-10 mm/Myr) (Ingram et al., 1990). These deposits contain iron and are poor in manganese oxide. The Mn:Fe ratio is ~1 and Ni and Cu are represented by high concentrations (>3000 ppm) (Hein et al., 1997; Usui and Someya, 1997). Diagenetic manganese deposits occur as nodules and have precipitated from hydrothermal solutions or pore water within altered sediments (Klinkhammer et al., 1982). These deposits are usually related to organic matter oxidation and formation of Mn carbonate minerals (Polgari et al., 2012). Hydrothermal manganese deposits have directly precipitated from low-temperature hydrothermal solutions (Hein et al., 1997; Ingram et al., 1990). These deposits are generally laminated and stratabound or occur as irregular bodies and epithermal veins (Hein et al., 1997). Diagenetic and hydrothermal deposits are characterized by high Mn:Fe contents and low trace metal concentrations (Hein et al., 1994; Hein et al., 1996). Although there are similarities between these two deposit types, they are mostly distinguished by their morphologic, tectonic and growth rates (Kuhn et al., 1998). The Joun Abad manganese deposit is located 16 km southeast of the Joun Abad village, 72 km north of the city of Khash in the eastern longitude of 61° 06´ 0.7ʺ and the northern latitude of 28° 51´ 2.3ʺ. This zoning is structural-sedimentary that is located in the middle part of the flysch zone of Eastern Iran. In this paper, major, trace and rare earth element compositions of ores have been used as an approach to determine the conditions of ore formation. Twenty representative ore samples (~450 g) were selected from the Joun Abad manganese deposit. Geochemical analyses were made of samples taken from different surface mineral outcrops at various locations. Crushed and grounded ores (under 200 mesh) were analyzed at the Kansaran Binaloud Laboratories, Tehran, Iran. Major oxide and trace element contents were determined by X-Ray Fluorescence (XRF) and Inductively Coupled Plasma-Optical Emission Spectrometry (ICP-OES), respectively, and the REEs were analyzed using the Inductively Coupled Plasma-Mass Spectrometry (ICP-MS) method. The Joun Abad manganese deposit is located 16 km southeast of the Joun Abad village, north of the city of Khash, and with respect to structural-sedimentary zoning in the middle part of the flysch zone of Eastern Iran. The host rocks of manganese layers are red shale, manganese mineralization is visible on the upper parts, as interlayers and/or contamination. The geometry of the ore mineral is in layered form and it is often conformable with units including red shales. The chemistry of the major elements, Mn:Fe and Si:Al ratios and the positive correlation coefficients between Al2O3, TiO2 and Fe2O3 indicate that they were affected by hydrothermal processes in a shallow environment together with entering mafic clastic materials in sedimentary basin where the ore formed. All trace element diagrams show low contents of elements such as Ni, Co and Cu in the manganese ores. The deposits of the study area in these diagrams plot in the field of hydrothermal deposits. Co:Ni, Co:Zn, LREE > HREE contents and total REE and negative Ce anomalies also indicate the role of ore-bearing hydrothermal fluid in the deposit. REE distribution patterns of the deposit are quite similar to those of hydrothermal deposits.

Halalan Manganese ore deposit is located in Torud-Chah Shirin volcano-sedimentary band and the northern part of Central Iran structural-sedimentary zone. The outcropped rocks in the area include metamorphic complex with lithology composition of slate, phyllite, schist, marble, limestone, dolomite and slightly metamorphed sandstone with Early Jurassic age. Manganese mineralization has occurred in the form of stratiform (Layered and lens-shaped) and parallel to stratification. The main minerals forming the ore deposit are mainly pyrolusite, psilomelane, heulandite, braunite and hematite. The massive, layered, lentiform and bandy structures and the disseminated, the empty space filling and replacement textures are the most important structure and texture of the ore deposit. The existent alterations in the region include chloritic, epidote, argillic, silication and carbonatization alterations. Based on the geochemical studies, The high ratios of Mn / Fe and low concentrations of trace metals, especially Co, Ni, Cu, and high amounts of Mn, SiO2 and Fe are as evidences of Mn enrichment and depletion from submarine hydrothermal fluids (exhalative) in this deposit. Therefore, all the evidences indicate that the Halalan manganese ore deposit has formed under two mechanisms: the enrichment in seawater by exhalative-hydrothermal fluids and this deposition in sedimentary conditions influenced by changes in Eh and pH in marine environment and it is a volcano-sedimentary ore deposit. Based on the studies, the Halalan manganese ore deposit is most similar to the manganese ore deposits of Cuba type, with the exception that the Halalan manganese ore deposit has been affected by a metamorphic phase in the green schist facies.

The Beshgaz manganese-bearing veins are located in ~45 km northeast of Birdjand, South-Khorasan, and east of Iran. These veins with 0.1-1.5 m thickness and 4-7 m length are engulfed discordantly within Paleocene (Eocene-Oligocene) volcanic-pyroclastic rocks. The host of Mn-bearing veins are dacite to rhyo-dacite tuff, lapilli tuff with andesitic and andsi-basaltic fragments in shear zones. The Mn grade reaches up to 45% in the vein/veinlets. The major Mn ore minerals are pyrolusite, cryptomelane, and psilomelane. Ore minerals showing colloform and open-space filling textures. Amorphous silica is the principal gangue mineral in the Mn ores and the SiO2 content of these veins vary from 2.41 in Mn-bearing veins to 20.98 % in silicic zone. Based on mineralographic and geochemical data, the Mn ores were preliminarily precipitated as amorphous Mn-oxide and hydroxide gels, and gradually psilomelane and then pyrolusite were developed in expense of the primary amorphous minerals. The average ratio of Mn/Fe in Beshgaz manganese-bearing veins is 26.31 and positive correlation of manages with Ba, Sr, U, and Zn in Mn-bearing veins indicate that these veins have formed as epigenetic by hydrothermal fluids.

Estaj manganese deposit is located close to the Estaj village, 40 km southwest of Sabzevar, in Central Iran and Sabzevar subzone. Based on field evidences and microscopic studies, the rock units of the study area are pyroxene hornblende tracy Andesite, crystalin andesitic tuff, pyroxen hornblende andesite, pyroxen andesite- basalt, chert and limstone. These rock units belong to Late Cretaceous and can be one of the geological evidences for the origin of volcano – sedimentary mineralization. Chemical and mineralogical analysis by XRF, ICP, XRD methods and microscopic studies were performed over Estaj manganese ores. The result of XRD analysis confirmed pyrolusite as the main Mn oxide but psilomelane was distinguished only by microscope. The Chemical analyses of Mn ore indicated the high values of Si (17.01 – 75.54 ppm), Ba (300 – 1965 ppm), Sr (200 – 844 ppm) and MnO/Fe2O3 (1.62 – 58.61) and low amounts of Zn (34 – 79 ppm), Co (2 – 16 ppm), Ni (2 – 10 ppm), U (20 – 71 ppm) and Th (2 – 5 ppm). The result of geochemical analysis is indicative of deposition of manganease solution along with silica due to physio -chemical changes of sea water and also reflects the submarine hydrothermal origin for this mineralization. Ore bodies form layer and lense within the pyroclastic rocks (andesitic green crystalline tuff and red tuff) and can be seen as strat form with host rocks. Also ore bodies form amygdaloidal with pyroxene andesite-basalt. The ore bodies has massive, dendritic, layer and spherulitic textures and the mineralogy is mainly pyrolusite, braunite and psilomelane. Wall rock alteration in foot wall cansists mainly of chloritic, argillic and silicification. Estaj mineralization according to it's various characters such as volcano-sedimentary nature of the host sequence and the host rocks geometry, texture and structure and mineralogy, shows the most similarities to the volcano-sedimentary (exhalative –type) manganese deposits.

In this research, Ce0.8Zr0.2-xMnxO2 nano particles (x = 0.0, 0.05, 0.10) were synthesized at 600AWT IMAGE calcination temperature by co-precipitation method. The starting materials were cerium and zirconium nitrates, manganese chloride and ammonia as a precipitating agent. The crystalline structure of the synthesized samples was studied by X-ray diffraction (XRD) technique. TEM images of the prepared Ce0.8Zr0.2O2­ and Ce0.8Zr0.1Mn0.1O2 showed that their average particle size are about 8.2 and 7.3 nm, respectively. Fourier transform infrared (FTIR) spectroscopy was used to investigate the present bonds in the synthesized samples.

Ghareh-bolagh area is located in 20 Km of east of Mahabad, south of West-Azarbaidjan province. Carbonate rocks of Bayandour formation and dolomites of Soltanieh formation in this area are the host of mineralizations for Barium, iron and manganese. Based upon mineralogical investigations, barite, magnetite, hematite, goethite, limonite, pyrolusite were major mineral assemblages of these mineralizations which that is accompanied by chalcopyrite, malachite, azurite, and calcite in low amounts. The most important geochemical characteristic these mineralizations are relative weak differentiation of LREE from HREE in barite and iron-manganese ores, Eu negative anomalies in iron-manganese ores (0.26-0.76) and Eu positive anomalies in barite (7.7-10.51). Incorporation of the obtained results from investigations of field, petrographic and geochemical (analytic data and correlation coefficients between elements) indicate that factors such as changes in physicochemical conditions of environment (pH, Eh, temperature), activity of complexing ligands, and presence of minor mineral phases (clay minerals, zircon, zenotime, and monazite) played important role in distribution of rare earth elements during mineralization and development of these ores.

Manganese ore deposits occurred in various types of syngenetic، diagenetic and epigenetic mineralization in association with radiolarian cherts in colored melange of Neyriz ophiolite in Abadeh Tashk area، eastern Fars Province. Microscopic study and XRD analyses show a simple mineralogy for manganese compounds in all types. Psylomelane and braunite are the primary manganese compounds in syngenetic type that are found as alternative bands with amorphous silica and quartz in a sedimentary environment. Braunite and bixbite occur in lens shape deposits، showing diagenetic type of mineralization that formed in fold hinges during diagenesis process. Pyrolusite، auororite and rancieite are major minerals of epigenetic type that formed during remobilization and reprecipitation of manganese compounds in radiolarian cherts from upper horizons as open space fillings by supergene processes. Manganese ores show low values of TiO2 (0. 012-0. 13 %)، Fe/Mn (0. 02-5. 45) and Al2O3 (0. 019-2. 13) and high values of Si/Al (21. 84-427. 46). The ores contain low contents of Co (31-131 ppm)، Cu (17-277 ppm) and Ni (12-193 ppm) and have negative anomalies of Ce and positive Eu، low total REE and enriched LREE compared to HREE، indicating that primary manganese compounds and host cherts formed close to mid oceanic ridges above seafloor hydrothermal fluid channels.

The Nasirabad manganese deposit is located 5 km south of Nasirabad، 8 km SW of Neyriz in the Fars province. Structurally، the area is placed in the southeastern part of Zagros thrust belt. In this area، the manganese mineralization occurred as ore layers and nodules، interlayered with Pichakun radiolarite chert deposits. In this study، mineralogy and geochemistry of uranium، thorium and lead isotopes were used to investigate the primary and secondary processes. In this way، in addition to petrographic and XRD studies، ICP-MS analysis was carried out in order to measure the U، Th and Pb isotopes. The strong fractionation of Fe and Mn phases and also the absence of Fe-bearing minerals in the XRD results، presence of syngenetic todorokite and quartz crystals، high U/Th ratios in some samples and Th versus U diagrams، all indicate entrance of Mn-bearing hydrothermal fluids into the sedimentary basin of the Nasirabad manganese deposit. The pyrolusites in radiolarites tests as replacement textures، host rock space filling and fracture filling pyrolusites، indicates the influence of secondary exogenic processes on primary hydrothermal mineralization. Non-homogenous 206Pb/Pb204، 207Pb/Pb204 and 208Pb/Pb204 values show non-steady hydrothermal processes in the sedimentary basin and indicate mixing of hydrothermal lead isotopes with another secondary source. Strong positive correlation between absolute values of radiogenic lead isotopes and insoluble High Field Strength Elements (HFSE) such as 207Pb vs Nb (r=0. 81)، 207Pb vs TiO2 (r=0. 93)، 207Pb vs Th (r=0. 79) and strong correlation between these elements and some mafic components like 208Pb vs Fe2O3 (r=0. 94) and Th vs MgO (r=0. 86) represent entrance of radiogenic lead with mafic detrital materials into the sedimentary basin. Similar linear trend among 206Pb/Pb204 vs 208Pb/Pb204 and 207Pb/Pb204 ratios in nodules and manganese layers show the same geochemical condition in Mn-nodules and layers formation and indicate that isotopic ratios were unaffected by secondary processes including leaching and redeposition of manganese.

Robat Karim manganese deposit is located in 7 km northwest of Robat Karim (southwest of Teharan), within northeastern margin of Orumiyeh-dokhtar volcanic belt. Based on regional geology, the studied area is situated in the northern Saveh Eocene volcanic assemblage, composed of rhyolite, trachyte, andesite and basalt. Manganese mineralization is occurred as veins, in faults, joints and fractures that crosscut the volcanic rocks. According to mineralogical studies, the manganese ore of the studied area is composed of pyrolusite, psilomelane, ramsdelite and hollandite, as well as calcite and quartz. Intergrowths of manganese oxides and quartz (or calcite) associated with various open space filling textures support the epithermal origin of the ore forming fluids in this area. Geochemistry of major and trace elements in Robat Karim manganese ores, similarity of their chondrite normalized REE pattern with volcanic host rocks and other hydrothermal manganese deposits of the world, as well as negative Ce anomaly indicate a probable epithermal origin of the deposit. Ore forming fluids could be originated from meteoric and/or magmatic waters circulating through Eocene volcanic rocks, dissolve manganese and other metals and deposit them in fault planes and major fractures. High pressure of the ore forming fluid has caused the formation of brecciated trachyte.

The purpose of this study is to determine the genesis of the manganese occurrences around the Hashtroud city, with special regard to Idahlu- Jokandy region. In this region Mn mineralization is sparse and rather extensive. Mineralization has originated from hot springs and precipitated on the earth surface. The mineralization is mainly massive and vein form. Due to the presence of hot springs and their traces in the study area, it can be concluded that Fe and Mn components were in the hot springs as solution and precipitated on the earth surface or penetrated into existing fractures and faults of the region by the hot springs and consequently caused the mineralization. The main Mn minerals are pyrolusite and psylomelane accompanied by gypsum, travertine, barite and jasper.

The Narigan ferro-manganese deposit is located in 30 km NE of Bafq, and 20 km of Chogart mine. The deposit is situated in Central Iran. Dolomitic limestone and rhyolitic tuffs are the main host rocks.Petrological and ore microscopic data indicate that ore and associated host rocks formed in shallow water, on a platform. Furthermore, geochemical studies show that hydrothermal genesis was responsible for the formation of the ore deposit.Field and petrographical studies show that two stages of hydrothermal activities were involved:1- Exhalation of hydrothermal fluids from seafloor, then primitive ore forming process in the form of precipitation of Fe and Mn oxide and hydroxide gels followed by final crystallization.2- Migration of secondary hydrothermal fluids from reducing to oxidizing area, and transportation and precipitation of Fe and Mn in the latter area; therefore, an increase of ore grade in the oxidizing area.Finally, it could be concluded that at the time of ore formation, rifting had probably occurred in the area, and large volumes of felsic magmas formed. In this way and due to hydrothermal activities, Fe and Mn leached from these rocks and precipitated on the sea floor.