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Zonous Kaol ini te bea ring c lay de pos it is made by
hydrothermal alteration of volcanic rocks mainaly of andesite ami dacite.
Kao linit e , quartz and calci te are the main mineral co mposi tions. As
quart z in the volcanic roc ks is cryptocrys talline, it is too dificult to
seperat e it from kaol inite. The phys ical properties and chemica l
composition of Zonous ceramic grade kaolinite bearing clay are directly
related to its nature and geOlogical formation.
The percenl age of SiOz in Zonous clay is highe r but the amount of
Alz0 3 is lower th an Diamond kaolinte. For th is re ason the ceramic
products of zonous cl ays have lower resistance to thermal shocks and
modul e of rupture. High roughness, low plsticity and possible greater
deformation during firing (Production of Ceramics) are o ther reasons
for lim it ing the use of Zonous ceramic grade clays. The percentage of
calcium oxide (CaO) in Zo no us clay is higer in co mparison wi th
Diamond Kaolin hut pot asium oxide (KzO) whi ch plays as a nux in
ceramic products is lower in zonous. The high pereentage of CaO which
has a high melting point can raise the viscosity as a result lead to Crack
in ceramic products. Fin ally with these colour pro pe rties, the Zonous
ceramic grade kaolinite bearing clays , can be used as a fill er in pape r,
paint and rubber industries.

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The studied area is a part of Tarom Mountains and is located in 40 km north of Zanjan. The area is formed mainly by Tertiary volcano-sedimentary and plutonic rocks, which are mostly altered. Based upon geological setting, the hydrothermal alterations in the area are divided into two groups: (1) Regional alterations consisting of potassic, sericitic and propylitic types. (2) Structurally controlled alterations consisting of three argillic & alunitic types. The mineralogical studies show that, the major minerals characterizing the argillic – alunitic alterations are APS minerals (especially alunite and jarosite) + clay minerals (kaolinite, montmorillonite, illite, mixed–layer illite/smectite) + chlorite + sericite + quartz + gypsum + pyrite, that their quantity, grain size and crystallinity vary in the different alteration types. In order to determine the temperature of argillization, the illite crystallinity factor is used and the results of calculations showed that the formation temperature of illites is about 200 to 240 ^oC. The results of this study indicate that the argillic-alunitic alterations of studied area considerably resemble high-sulfidation type of the epithermal argillic alterations in the continental arc subduction zones.

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The submarine volcanic rocks of Totmaj volcano-sedimentary sequence, located at 25 Km southeast of Kashan city, have suffered extensive non-uniform propylitization. Based on field and petrographical studies, the volcanic rocks can be classified into three alteration zones: chlorite-epidote zone, epidote zone and hematite zone. The secondary hydrothermal minerals formed in the volcanic rocks include epidote-chlorite, calcite and hematite. These minerals have pseudomorphly replaced the primary phenocrysts (e.g. plagioclase, amphibole, and pyroxene) or have filled veins and vesicles. Stable carbon and oxygen isotope analysis of the hydrothermal calcite indicate that the δ¹⁸O and δ¹³C values range from -9.2 to -11.3 and -2.02 to -6.02 per mil respectively. Thus, seawater has been a source for hydrothermal fluid which by circulation into the hot submarine lavas, caused to leaching of some elements such as Fe and Mg from the altered rocks with the exception of epidote-chlorite zone. Also, the seawater circulation leads to an increase in Na ratio in the rocks. Geothermometrical studies on hydrothermal chlorite showed that these minerals have formed at a temperature between 240 to 300˚C. Furthermore, the ranges of temperature stability of coexisting secondary minerals in the volcanic rocks are compatible with those of the green schist facies.

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The Astaneh granitoid massif is located about 40 km to Arak city, central Iran, is a part of Sanandaj-Sirjan structural Zone. These intrusive rocks which are mainly composed of grnodioritic rocks, widely affected under hydrothermal alteration. The alteration zones, on the basis of field studies and mineralogy as well as the study of the REE behavior, are investigated in this paper. Eight alteration zones including phyllic (sericitic) with quartz, sericite and pyrite; chloritic with quartz, sericite and chlorite; propylitic with chlorite, epidot, calcite and albite; argillic with clay minerals (chlorite and illite); silicic with abundant quartz; albitic with albite, chlorite and quartz; hematitisation with hematite, Fe-carbonates (ankerite and siderite) and tourmalinisation with tourmaline (dravite) are identified. The results demonstrate notable differences in the REE behavior in the different alteration zones. Accordingly, comparison with the fresh rocks, in the phyllic (sericitic) alteration, LREE are enriched, but HREE, except Yb which enriched, unchanged. Also in chloritic alteration zone, LREEs are depleted, but HREEs represent different behaviors. In the argillic and propylitic alteration zones, all REE are depleted, but compared with HREE, the LREE represent more depletion. In the silicic and hematitisation alteration zones, compared with HREE, the LREE are enriched. Finally, in the albitic and tourmalinisation alteration zones all REE are depleted. These features indicate that the behavior of REE in the hydrothermal alteration zones of the Astaneh granitoid rocks is mainly controlled by PH, availability of complexing ions in the fluid as well as the presence of secondary phases as host REE minerals.

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Astaneh granitoid intrusion is located in southwest of Arak city that is part of Sanandaj-Sirjan zone.  This intrusive mass alterated under influence of hydrothermal fluids and so propylitic alteration is one of the most important types of alterations in this granitoid. Epidote, sphene, prehnite and quartz are important minerals in this alterated rocks. The weight percent of pistacist in epidote is about 24 so this base epidote origin if saussuritization of plagioclase took place. On the bases of Al and Fe in structural formula of sphene, these minerals are secondary in origin and forms during the alteration processes. Prehnites have low enrichment of iron so formed in low temperature and oxygen fugacity. Normalization of altered rocks to parent rock is indicator of depletion of REE and this depletion increased from propylitic to phyllic alteration. The variations of major oxides relative to immobile oxides of Al₂O₃ are indicative of increasing of Na₂O in all zones except phyllic zone that it is reason of reduce plagioclase basicity. CaO increasing in propylitic zone and finally MgO is only depleted oxide in all alteration zones.

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In order to investigate the alteration products of rhyolitic tuffs under alkaline hydrothermal condition, samples of acidic pyroclastic rocks from Darabad area (N-E Tehran) were selected. Rock samples were examined under petrographic microscope, X-Ray powder diffraction, X-Ray Fluorescence and were eventually powdered and mixed with Na⁺ and K⁺ bearing solutions in hydrothermal autoclaves. The effect of changes in temperature, time and concentration of cations in solution, alteration of aforementioned tuffs have been studied. The solutions with 1.25- 7.5 mol/lit cation concentrations from KOH and NaCl salt have been prepared and used in hydrothermal experiments in 100 °C and 150 °C. The results revealed that in alteration of rhyolitic tuffs, in presence of KOH and NaCl solutions, with increasing temperature, concentration of Na⁺ and pH, the quality of quartz decreases and the quality of albite increases (sodic alteration). At 150 °C  and high concentration of Na⁺ and K⁺ (7.5 mol/lit), quartz dissolves completly, albite changes to orthoclase with cationic exchange of Na⁺ by K⁺ (potassic alteration) and forms hydroxy sodalite (zeolitic alteration). XRD studies proposed cubic system with unit cell dimensions of a₀= b₀= c₀= 8.8760 Å for hydroxy sodalite.

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Quartz-monzonitic porphyry stock at Kighal is located about 12 km north of Varzeghan, East Azarbaidjan Province, NW Iran. It has intruded older volcanic units during magmatic activities of Pyrenean orogenic phase and produced Cu-Mo mineralization and hydrothermal alteration zones in the region. The stock was intruded by numerous cross-cutting dikes mainly of dioritic to quartz-dioritic compositions. The hydro-fracturing brought about permeable zones within the stock and surrounding rocks facilitating the circulation of hydrothermal fluids that led to the development of potassic, phyllic, argillic, advanced argillic and propylitic alteration zones within the area. The general pattern of REE spider diagrams of different alteration zones show distinct negative trend from LREE toward HREE. In potassic and phyllic zones, REEs display depletion because of high activity of sulfate complexes, low pH and high ratio of water/rock during alteration, but in argillic zone, besides LREE depletion, HREEs display enrichment, which can be referred to their absorption by clay minerals and low activity of sulfate complexes within fluids responsible for argillic alteration. In propylitic zone, HREEs were immobile but LREEs display enrichment relative to nearly fresh sample. In leached zone, depletion of LREEs and MREEs is conspicuously higher than HREEs. Eu/Eu* ratio in nearly fresh and altered samples is <1 but Ce/Ce* ratio is >1. On this basis, relatively negative anomaly of Eu can be produced by fractional differentiation of ca-rich plagioclase from parental magma or their absence within the magma-source materials. The highest value of Eu/Eu* ratio belongs to the leached zone which is likely due to the dominance of oxidizing condition and immobility of this element. In argillic zone, this ratio is similar to nearly fresh sample and in potassic and phyllic zones is higher than fresh sample, probably because of concentration and precipitation of this element by hydrothermal oxides and sulfides.

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The Yaralujeh vein index is located about 40 km NW of Ahar, East Azarbaijan. The host rock of mineralized vein is an altered subvolcanic body, intermediate in composition. The mineralization of sphalerite-galen-chlcopyrite recognized as intersected veinlets. Based on field observations, textural and mineralogical evidences, the mineralization occurred in 4 stages. The subvolcanic rocks are affected by pervasive sericitc and carbonate alterations and overprinted by supergene assemblages. The plot of the Ishikawa alteration index (AI) Vs. chlorite - carbonate - pyrite index (CCPI), Known as alteration box plot, shows the main alteration species. The assemblage of quartz, sericite, illite, albite, kaolinite, leucoxene, pyrite and late carbonate minerals, indicate the fluids with a near-neutral pH and temperature of approximately 200 to 300 °C. The mineralogical, alteration, and geochemical characteristics of study area in comparison with other hydrothermal deposits indicate that the Yaralujeh vein index is similar to the intermediate-sulfidation epithermal deposits and intermediate  temperature polymetalic veins related porphyry copper deposits

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Jalal-Abad iron deposit is located about 38 km northwest of Zarand town in Kerman Province. It contains 200 Mt iron ore with average chemical composition of
Fe = 45%, S =1.18% and P = 0.08%. Iron mineralization occurs in an Early Cambrian volcano–sedimentary sequence of Rizu series which is composed of sandy siltstone, siltstone, volcanoclastic rocks and dolomite. Small intrusive bodies of gabbro and dioritic dykes are exposed in the area. Iron mineralization at Jalal-Abad is concealed with scarce outcrop. The main ore mineral is magnetite, which is located deeply, and  has been oxidized to hematite in shallow dopth and along fractures. Pyrite and chalcopyrite are the main sulfide minerals and bismuthinite, arsenopyrite and covellite are present in minor amounts. Cu mineralization occurred in sulphide and oxide stages as dissemination, veins, veinlet and open space filling. Malachite, azourite and atacamite are common minerals at oxide stage. Native gold was detected as inclusions smaller than 50 µm in pyrite, chalcopyrite and magnetite hosts. Alteration in Jalal-Abad is widespread and sodic-calcic, chloritic, sericitic and silicic alteration halos formed around orebody. Sodic-calcic alteration (actinolite,tremolite, magnesiohornblend and magnetite assemblage) is common in the deep levels. The main gangue mineral is quartz in association with talc, chlorite, ferroactinolite and calcite. Fluid inclusion investigation in quartz shows that inclusions are formed at three phase (L+V+S) with halite as a solid phase. Homogenization temperature varies from 260 to 440 ºC and salinity varies from 30 up to 52 NaClwt% equivalents. The high salinity and homogenization temperature of fluid inclusions is similar to fluids with magmatic origin. Mineralogy, alteration, geochemistry and fluid inclusion studies indicate Jalal-Abad deposit is similar to IOCG deposits.

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The Hizeh-Jan kaolin deposit (NW Varzaghan, East-Azarbaidjan Province) is a typical clayey deposit with andesitic host of Eocene age in northwestern Iran. Based on XRD analyses, the minerals of this deposit include kaolinite, pyrophyllite, quartz, smectite, muscovite-illite, hematite, goethite, anatase, alunite, diaspore, feldspar, hornblende, and calcite. Increasing SiO₂/Al₂O₃ ratio from the center toward outward in the studied profile indicate the presence of hydrothermal zoning in the deposit. Evidence such as the presence of silicic caps in the upper part of the deposit, local brecciation, mineralization of pyrophyllite, diaspore, and alunite, enrichment of LREEs relative to HREEs, pattern of mass changes of elements Al, Fe, Ti, Sr, and Nb, and positive correlations in trend of changes between (La/Lu)_N, P, Sr, and S with LOI suggest that the development of the Hizeh-Jan kaolin deposit is affiliated to function of  hypogene processes on andesitic rocks. Geochemical analysis indicates that occurrence of negative Eu anomay (0.39-0.78) in kaolinized samples is in relation to destruction of feldspar and hornblende minerals of the andesitic rocks by hydrothermal fluids and occurrence of negative Ce anomaly (0.62-0.81) is due to the destruction of zircon by acidic-oxidizing fluids.

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The north western part of volcano-sedimentary complex of Davazdah-Emam mountain in north of Central Iran is located about 135 km SE Tehran. The Eocene to Oligocene volcanic rocks and dikes of intermediate to mainly basic of complex under the influence of hydrothermal fluids, probably associated with the involvement of meteoric water, experienced different degrees of alteration. The alteration occurred in two steps forming mafic phyllosilicates (celadonite, mixed layers of celadonite-nontronite, smectite), calcite and sodic zeolites (analcime, tetranatrolite, natrolite and chabazite-Ca) at the first step and in the second step, hydrothermal associated possibly with the involvement of the meteoric water facilitated the disposition of calcic-sodic zeolites such as stilbite-Ca, mesolite and thomsonite. Variatians in temperatures, pH, CO₂ and H₂O values, Si/Al ratio and host rocks types are the parameters that causes the diversities of mineralization through out the two steps. Maximum and minimum temperatures of zeolite formation for the first stage can be estimated around 145^°C for analcime and 90^°C for chabazite-Ca and for second stage, around 75^°C for stilbite-Ca and 65^°C for thomsonite.

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The Esfordi deposit is located at northeastern Bafq and is one of the well-known magnetite-apatite deposits in the area which consists of ore minerals hosted REE. Among the various ore minerals, apatite is one of the unique minerals because of its significant properties such as providing a budget of elements (especially in the case of REE), stability over widespread temperature and pressure domains and exclusively ionic interchanges as a respond to re-equilibrium with new environment. All of which can fit the apatite as a main source feeding the new mineral nucleation like monazite during a hydrothermal alteration. Based on petrography and geochemistry studies, mineralization of four generation apatite accompanied with dropping of REE amount in each stages and increasing of residual Ca and P in the next generations. In contrast, culminating amount of REE beside Na, F and limited Cl reached in nucleolus monazite and led to the formation of two generation of monazites. On the BSE images of apatite, the depleted areas are associated with micro-channels and micro-pores containing monazite. Consequently dissolution of nucleolus monazites provides a well chance to form the second generation of monazite as bigger grain than the first ones. 

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The Eocene suite of volcanic rocks in Parandak area is located about 30 km NE of Saveh and is the host of different species of zeolites filling vesicles, amygdales and fractures. The elements forming for the formation of zeolites derived from the alteration of volcanic glass matrix and primary magmatic minerals. Based on their frequency, these zeolites are: natrolite, mesolite, tetranatrolite, scolecite, thomsonite, chabazite, analcime, stilbite, and epi-stilbite. In addition, other secondary related minerals are: chlorite/smectite, calcite (I), calcite (II), quartz and chalcedony. Development of zeolites in the basalts of the study area starts with lower Si/Al, Na-bearing and gradually grade into higher Si/Al Ca-bearing. It seems that the formation of zeolites might have occurred in two hydrothermal fluid stages. first stage, natrolite, mesolite, tetranatrolite and second stage, scolecite, thomsonite, chabazite, stilbite and epi-stilbite. It is estimated that the temperature of zeolite crystallization was less than 150 ⁰C.

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The Kamar-Gov study district is located south of Hashtjin city in the Ardabil Province (NW Iran). The geological units in this district include lavas (with composition of basaltic trachy-andesite to rhyolite), sub-volcanic rocks (as dyke and stock with composition of porphyritic trachy-andesite and trachyte) and crystal, vitric (lithic) tuffs (intermediate and felsic composition). Extensive zones of silicic, sericitic-argillic, advanced-argillic, and chloritic alteration have formed in these rocks. Pyrite is the prevalent metal mineral in the study area and approximately extended in all rock units. Besides pyrite, chalcopyrite, chalcocite, galena, sphalerite, hematite, and magnetite are also present. Covellite, digenite, and goethite are supergene minerals. Ore minerals have formed in crystal, vitric tuff and rhyolite as veinlet, dissemination, strata-bound dissemination, and inside silicic veins/veinlets. Three types of primary fluid inclusions are present within quartz minerals of silicic veins/veinlets and accompanied by disseminated ore minerals, including liquid-rich two phases, vapor-rich two-phases, and salt-saturated three-phase fluid inclusions (liquid, vapor, and halite + sylvite). Micro-thermometric analysis of these fluid inclusions shows the salinity of 1.05-14 wt% NaCl equivalents with the highest frequency of homogenization temperatures between 200 and 300 °C. The ore formation type is similar to intermediate sulfidation epithermal deposits, based on features like the vein-veinlet shape of ore mineralization, colloform and crustiform textures, base metal mineralization, the mineral assemblage of kaolinite – muscovite – pyrite ± sphalerite, intermediate salinity and temperature of the fluid, and probable effect of the boiling process.
 

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 The studied area is located in the northwest of Iran, East Azarbaijan province, and at a distance of about 30 km from the north of Sarab city. This area is part of the structural zone of Alborz. Based on petrographic and field studies, the lithology of the area includes an intrusive mass of quartz monzonite porphyry, the mass of granodiorite porphyry, dykes branching from the mass of granodiorite porphyry, and basalts. The main mineralogy includes plagioclase, quartz, potassium feldspar, clinopyroxene, biotite, and amphibole, alteration minerals in the studied rocks include sericite, chlorite, kaolinite, and iron oxides and often have porphyric, glomeroporphyric and Poikilitic texture. The most important variations include phyllic, argillic, and propylitic zones. Sulfide minerals observed in the area are mostly pyrite, chalcopyrite, sphalerite, and molybdenite, which have been converted into iron oxides and hydroxides (hematite) at some points. The mineralized texture is mainly scattered grains and veins. Examining the changes of rare earth elements and rare elements of porphyry masses shows positive anomalies of elements Li, Pb, Th, and U and negative anomalies of elements P, Zr, Ti, and Nb. A specific enrichment of LREE/HREE elements can be seen. The ratio of Eu/Eu* in altered samples is lower than that of healthy samples, and the ratio of Ce/Ce* is almost the same for healthy samples and most of the altered samples. In addition, the subtraction factors of (La/Yb)N, (La/Sm)N, and (Gd/Yb)N in altered samples are higher than in healthy samples. Light rare earth elements show an increasing trend and heavy rare earth elements have increased and decreased during the region's transformation process. The enrichment of U and Th elements is probably due to the prevailing acidic conditions and surface absorption by clay minerals and also due to the presence of zircon in the mineral network. Elements with high field strength show enrichment in most of the altered samples compared to the source rock, and only the Hf element shows depletion.

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The Tazekand mineralization zones, as a part of Tarom-Hashtjin metallogenic belt, is located about 45 km northeast of Zanjan city, NW Iran. Based on field study, petrography, and geochemical investigations, the lithologic composition of the intrusive rocks in the area varies from monzonite, diorite, granodiorite to gabbro, and volcanic units ranging from trachy-andesite, andesite to basaltic andesite. Delineation of diagrams of the Ishikawa alteration index (AI), chlorite-carbonate-pyrite index (CCPI) (known as alteration box plot), and the chemical alteration index (CIA) illustrated the main types and intensity of alterations in this area. Consideration of depletion and enrichment of elements by noting the enrichment factor in the alteration and mineralization zones indicates the role of high-temperature and low-pH of the altering fluids which acted as an important factor in decomposition of minerals such as plagioclase, alkali feldspar, and ferromagnesian and absence of K₂O, Na₂O and CaO components. The general pattern of REE distribution normalized by both chondrite and primitive mantle in altered and relatively fresh granitoid and volcanic units (as host rocks), shows a conspicuous negative slope and enrichment in LREE and large ion lithospheric elements (LILE) and depletion in HREE and high field strength elements (HFSE) during the alteration processes. Ce, Eu and Pr anomalies (Eu/Eu*, Ce/Ce*, Pr/Pr*) were investigated in ores along with fresh and altered host rocks. What can be inferred from these studies are that the changes in the behavior of rare earth elements as well as their normalized distribution pattern for each type of alteration has its own peculiar physicochemical conditions influenced by the action of multiple injections of hydrothermal fluids during both hypogene and supergene processes. The supergene processes compared to hypogene processes played very important and prominent role in development and evolution of the alteration zones in the Tazekand mineralization area