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

Dorojin area in the Southwest of Ardestan city is part of the Urmia-Dokhtar magmatic zone. In the area of study, the intrusion of the Early Miocene granodiorite into the Middle-late Eocene sedimentary-volcanic complex caused the formation of hydrothermal propylitic alteration zones with green color. The vlcanics range in composition from basalt-andesite, trachyandesite, andesite, to rhyolite. These rocks under study are characterized by LREE and LILE enrichment compared to HFSE, calc-alkaline nature, and meta-aluminous composition related to the subduction zone. The most abundant mineral in the alteration zones is epidote formed by saussuritization of plagioclase. Average Pstacite [Fe3+/(Fe3++Al)×100] composition is 22% (PS22). Comb and radial textures are its remarkable textural features. Calcite is the second most abundant mineral in alteration zones. The nodules tourmaline is chemically dravite and alkaline. They have FeO/ (FeO+MgO)<0.6 and lower Al amount, high Mg, and low X site vacancy. Dravite composition and the Mg abundant reflect their alteration origin. Hence, they are regarded as hydrothermal tourmalines.  Titanite with CaO<25wt%, Al2O3<2wt% as well as Al2O3+TiO2 versus CaO, and Al/Fe on variation diagrams are indication of hydrothermal alteration. Ore mineral potential in the region points to the effect of hydrothermal fluids.

Cretaceous sedimentary sequence in the Yazdan area is consisting of four rock units as, from the old to the new, clastic-carbonate (Kc), carbonate (Kl), Shale and marl (Km) sequences, and Sandy limestone and sandstone (Kls). The Kls unit is host of ore mineralization in the study area and formed from four members. Ore mineralization in the Yazdan Deposit has occurred as a stratiform horizon in the sandstone units of the third member. Texture and structures studies, shown three ore facies with elemental zonation in the Yazdan Deposit. These ore facies includes, stringer zone, massive ore facies and the bedded ore facies. This ore facies formed from laminated and layered sulfide and sulfate minerals. Fluid inclusions studies represents 255-136 ° C of homogeneity temperature with an average temperature of 189 ° C. Also, the salinity of fluid inclusions was calculated to be between 14.6-6% NaCl (on average, 9.5% NaCl). Geological evidence, host rocks type, texture and structures, existence of ore facies with elemental zoning as well as fluid inclusion investigations indicate the Yazdan Deposit has most similarity with Sedex-type deposit.

Introduction: The Tappeh-Khargoosh area is located at the 15 km SW of Ardestan, in the middle section of the Urumieh-Dokhtar magmatic arc (Aghanabati, 2004). Exploration in the study area began in 2006 by Kani Pajohan-e- Spadana Company and continued in detail by the Ardestan Copper-Gold Company. Their exploration activities consist of preparing the geological map (1:5000 in scale), drilling trenches and boreholes. Also minor extraction has been done. In this paper, our focus is on mineralogy, alteration, geochemistry and fluid inclusion of the Tappeh-Khargoosh deposit for determining the genesis of mineralization. The results of this study can be used for more exploration in the study and adjacent areas. Methodology: Samples collected along a traverses perpendicular to the mineralized veins and their alteration haloes. The geometry, morphology, mineralogy and texture of mineralization were examined. After careful microscopic studies, 7 samples were analyzed by the XRF method in the laboratory of the Tarbiat Modarres University and Iranian Mineral Processing Research Center (IMPRC) in Karaj. Six thin-polished sections and 8 polished sections were examined. Also, 32 samples of mineralized and altered zones were analyzed by Inductively Coupled Plasma with optical emission spectrometer (ICP-OES) in IMPRC. Six samples were analyzed for gold by Atomic Absorption Spectroscopy (A.A.S) method in the Kimia Pajoh Alborz laboratory. Three double polished sections prepared from mineralized quartz vein and micro thermometric studies had been analyzed by a model HF-S90 microscope in the University of Isfahan. For detail understanding of mineral composition and determination of some fine and rare minerals, the electron microprobe analyzing (EMPA) technique (model SX100) is used in IMPRC. Discussion and results: The Tappeh-Khargoosh deposit consist of quartz vein and veinlets which occur as open space filling in Eocene andesite and dacite. The mineralized veins mainly occur in the fault zones. The subparallel fault systems of dextral strike sleep Qom-Zefreh crustal scale fault (Tajmir Riahi et al., 2012) has had the main role in localization of mineralizing fluids. The alteration mainly consist of silicificaion, propylitization with minor sericitization and argillization represented as vein-veinlets, dissemination and pervasively in host volcanics. These alteration assemblages are indicative of near neutral to little alkaline hydrothermal fluids (Simmons et al., 2005). The silicic alteration has occurred in a wide range of pH and temperature, while the argillic alteration has occurred in low temperature and a wide range of pH. So where the silicic and argillic alterations have occurred together, the temperature of the causing fluid must be lower in the range of clay mineral stability field (Robb, 2005). The fluid inclusion in the quartz shows the low temperature (137-194˚C) and low to medium salinity (4-12.5 %) which coincide with low to medium sulfidation epithermal deposit conditions. According to fluid inclusion data, bisulfides were the main ligand for metals transportation. The absence of halite/sylvite daughter minerals in fluid inclusions and low salinity of fluid inclusions show that the chloride complexes not act as effective ligands. Opposed to high sulfidation epithermal deposits in which the magmatic waters are common, in the low sulfidation type, the meteoric waters are dominant (Foster, 1991; Vahabi Moghadam, 1993). Dilution by cold and low salinity meteoric water has the main role in mineral deposition. Pyrite, chalcopyrite, bornite, chalcocite and native gold are the primary minerals and hematite, goethite, covellite, chalcocite, cuprite, malachite, chrysocolla, azurite and atacamite are the secondary minerals, which have occurred as veinlets, open space filling, colloform, amygdal filling and dissemination in quartz vein and host rocks. Fine grain gold had be seen in the colloidal secondary Fe-oxides, which indicate that the gold probably occurred primarily in sulfide minerals and was released in the supergene process. According to microprobe analysis, Ag was measured as impurity in chalcocite. These features coincide with high correlation coefficient between precious metals and copper. So, the Cu can be used as a pathfinder element for gold exploration in this and adjacent areas. The abundance of Cu-bearing secondary minerals in the surface, indicate that the Cu has not leached effectively as a result of the little amount of pyrite and aridity of the area. In this condition, Cu which was created by oxidation of primary Cu minerals was fixed in the surface as silicate, carbonate and oxide minerals (Chavez, 2000). Geology, geometry, texture and structure, geochemistry, alteration schema, fluid inclusion and mineralogical data of the Tappeh-Khargoosh make it similar to low sulfidation (L.S) epithermal deposits.

Mineral composition is sensitive to variations in the composition of the magma and can be used to characterize the physical conditions of crystallization such as temperature, pressure, oxygen fugacity and water content. The studies have demonstrated that geobarometery by amphibole provides a tool for determining the depth of crystallization and knowledge of the depth of crystallization of hornblende through to solidification of calc-alkaline plutons (Anderson and Smith, 1995). The composition of pyroxene can be used as crystallization pressure and temperature indicators of pyroxene too.
Anlytical The mineral compositions of the Nasrand intrusion were determined by electron microprobe, with special emphasis on the amphibole, feldspar, and pyroxene at the Naruto University, Japan, the EPMA (Jeol- JXA-8800R) was used at operating conditions of 15 kV, 20 nA acceleration voltage and 20s counting time.
The Nasrand intrusion (33°13'–33°15' N, 52°33'–52°34'E) with an outcrop area of about 40 km2 is situated in the Urumieh–Dokhtar magmatic belt, SE of Ardestan. It is composed of granite and granodiorite and various dikes of diorite and gabbro which are intruded in it. It is intruded into Eocene volcanic rocks, including andesite, rhyolite, and dacite. The petrographical studies indicate that the granitic and granodioritic rocks contain major minerals such as quartz, K-feldspar, plagioclase, and amphibole, which are in an approximate equilibrium state. The gabbroic-dioritic dikes usually show microgranular porphyric texture. They mainly consist of plagioclase, amphibole, and pyroxene. The plagioclase shows variable composition from albite to oligoclase in the granitoid rocks and from oligoclase to bytownite in dioritic and gabbroic dikes (Deer et al., 1991). The amphiboles are calcic and their composition varies from hornblende to actinolite, whereas the composition of the basic dikes is inclined to hastingsite (Leake et al., 1997). Actinolitic probably crystallized as a subsolidus phase. Pyroxene in the dikes is clinopyroxene with augite- diopside composition (Morimoto, 1988).
The total Al content of hornblende is a sensitive linear function of crystallization pressure and temperature (Schmidt 1992; Holland and Blundy, 1994). However, the computed pressure may reflect the level at which the hornblende crystallizes rather than the pressure at which the granite consolidates. Therefore, Al content in hornblende geobarometer is only applicable in the presence of quartz and plagioclase; alkali feldspars, biotite, hornblende, clearly limit compositional influences (Ague, 1997). Oxygen fugacity has a marked effect on the mineral system, so only hornblendes with Fe/(Fe)

The Kuh-e Dom intrusion with calc-alkaline nature, in the northeast of Ardestan is located in the central part of the Urumieh-Dokhtar Magmatic Arc and includes the felsic and intermediate-mafic units. The felsic unit consists of monzogranite, granodiorite, quartz monzonite and quartz monzodiorite, whereas the intermediate-basic rocks comprise gabbro, diorite, quartz diorite, monzodiorite and monzonite. The acidic dykes intruded this intrusion and its surrounding rocks. The various mafic microgranular enclaves of dioritic, quartz dioritic, monzodioritic and quartz monzodioritic composition exposed in the acidic rocks. The zircon U-Pb dating by the LA-ICP-MS method indicates that the ages of the felsic rocks, intermediate-mafic rocks, acidic dikes and enclaves are 51.1±0.4 Ma, 53.9±0.4 Ma, 49.95±0.64 Ma and 50.3±0.8 Ma respectively. These ages are in good agreement with the lower-middle Eocene age of the intrusive body, which is simultaneous with subduction of the Neotethys oceanic crust underneath the Central Iran. This result is in agreement with the previous geochemical result.

The Nasrand intrusion، in the central part of Uromieh-Dokhtar magmatic belt is mainly composed of granite and granodiorite. The intrusive rocks are hosted by various dikes trending NW-SE. The granites and granodiorites are dominated by plagioclase، K-feldspar، quartz، biotite، amphibole، whereas the dikes are characterized b similar mineralogy in addition to pyroxene. The amphiboles are calcic with (Na+K) A≤0. 5 and magnesio -hornblende composition in the granitic rocks with (Na+K) A>0. 5 and AlIV3 are magnesio-biotites. The pyroxenes in the studied dikes are clinopyroxene with augite composition. The mineral chemistry of the biotites، amphiboles and pyroxenes indicate that this intrusion is calc-alkaline and have been crystallized in a subduction zone setting.

The alkali feldspars and plagioclases in the Kuh-e Dom intrusive rocks show compositionally and microtexturally zoning structure. The feldspar crystals in the various lithologies such as granite- granodiorite samples, diorite- gabbro samples and relatively high frequency microgranular mafic enclaves existing in the acidic intrusion were analyzed using electron microprobe. The results of the microprobe analysis in the acidic, basic- intermediate rocks and enclaves indicated the normal and reverse zoning in the samples. The chemical compositions of plagioclases ranges from albite (An 9.4) in the rim to labradorite (An: 50.6) in the core for acidic rocks, and from andesine (An: 30.5) in the rim to labradorite (An: 56.4) in the core for the basic- intermediate rocks, and from oligoclase (An: 19.8) to labradorite (An: 66.5) in the enclaves. The frequently of rare elements such as Ba, Sr, Fe and Mg in the feldspars show various and oscillatory patterns. The oscillatory pattern of the major and minor elements from core to rim in the feldspar crystals suggests an effective role of magma mixing phenomena in forming of the Kuh-e Dom intrusion.

Subsurface dams are technologies that are adaptable to nature and can be efficient for water resources management، especially for preventing unused underground water from exiting. These dams are structures that block the natural flow of underground water and cause water supplies to be underground. Further that investigated the engineering geological and geotechnical characteristics of reservoir alluvium have been important. In this study investigated characteristic of reservoir alluviums Mastbandy underground dam located in 15 kilometer to the south west of Ardestan. Therefore determined physic and mechanic characteristics alluviums reservoir coverer in form laboratory and field. The results of the experiments show that alluvium are of the kind which is dense granular and non-uniform with no plasticity. These sediments regarding permeability are categorized as being medium to high. Careful porosity gain of this tests in face creation underground dam surface، that is capacity reservoir equal about 200000 cubic meter. Load and unload as a result of charging and discharging of water، lead to settlement. For attention that reservoir particles are to form more often by sand and gravel and small quantity of silt. Settlement on the alluviums reservoir are from the type at once. For attention mechanical parameters gain، rate settlement for unit area in case that reservoir is decharge of the water equal to 16 milimeter.

The Nasrand pluton of Oligo-Miocene age، which is located approximately 40 km south-east of Ardestan، intruded into the Eocene volcanic rocks of the Urumieh-Dokhtar magmatic belt. This pluton consists mainly of granite and granodiorite. The Nasrand plutonic rocks are metaluminous، weakly peraluminous، with mineralogical and geochemical characteristics of I-type، calc-alkaline to K bearing calc-alkaline granite. The granitic rocks as well as their host volcanic rocks have been crosscut by a series of NE-SW trending diabasic dikes. The plutonic rocks are characterized by enrichment of LREE and LILE، depletion of HREE and HFSE، the negative anomalies of Ti، Nb interpreted to reflect the emplacement of the granitic rocks as well as the diabasic dikes in an active continental margin. The positive anomalies of Rb، K، Th، U and the negative anomalies of Nb،Ti، Eu، Ba، Sr associated with high Ba/Nb (46-139) and Ba/La (17-77) ratios suggest that fusion of continental crust has played an important role in the genesis of the Nasrand granitic rocks and diabasic dikes.

Boznein vein-type has penetrated in the porphyric rhyolite-hosted and along a single northeast-trending reverse fault. Microscopic studies and electron microprobe data, show the presence of a variety of Mn minerals such as spessartine, rhodochrosite, bixbyite, hausmannite, braunite, pyrolusite, psilomelane, cryptomelane, manganite and mangano-calcite in the Mn deposit as well as braunite, pyrolusite, psilomelane, calcite, mangano-calcite and rhodochrosite in volcanoclastic sub-unit of Fe-Mn-carbonate-bearing tuff (E6vct). The mineralogical characteristics of workshop No. 1 along with its higher topography indicate that it has experienced more intense supergene activity. Field evidence, mineralogical studies and electron microprobe analyses on carbonate volcanoclastic unit (E6py & E6t) confirm genetic relationships between Mn deposit and sedimentary-volcanic sequences. It is thus concluded that hydrothermal fluids leached manganese and carbonates from the volcanoclastic rocks and then upon reaching favorable conditions, deposited these minerals along major and main faults in the region.

Zafarghand granitoid pluton with approximately 80 Km2 in the extent with early to middle Miocene age cropped out in 35 Km of SE Ardestan. The pluton composed mainly of gabbro to tonalite and intruded in the Eocene volcanic and volcanosedimentary rocks of Uroumieh-Dokhtar structural zone. For the first time، variations of anisotropy of magnetic susceptibility in Zafarghand granitoid pluton have been investigated by using anisotropy of magnetic susceptibility (AMS) method. Based on obtained data، the measured mean magnetic susceptibility values (Km in µSI) of the different rock groups of Zafarghand pluton are as follows: gabbros (32536)، diorites (23768)، granodiorites (18436)، granites (8068) and tonalites (68). Therefore، the Km values decrease from grabbros and diorites to granodiorites، granites and tonalites. Gabbros and tonalites have the highest and the lowest Km values، respectively. The measured Km values indicate that، the studied granitoid belongs to ferromagnetic type (according to magnetite series and I-type granitoids).

Bagham pluton is located in 23 km of the southeastern of Ardestan and it is near the main road of Esfahan-Ardestan. The study area is a part of central Iranian zone and Urumieh-Dokhtar magmatic belt. Minerlogically, the rocks include plagioclase, pyroxene, amphibole and opaque. The rocks have SiO2 = 44.75-47.08 and occur in gabbroic field. The chondrite normalized REE pattern show low enrichment in the LREEs relative to HREEs. The negative Nb and Ti anomalies in primitive mantle and MORB-normalized multi-element diagrams of the rocks are characteristic of island arc magmas. Also, enrichment in LILE and depletion of HFSE may indicate a subduction-related tectonic setting. Moreover, on based of the values of specific ratios (e.g. low Ti/V, Ti/Sc and high CaO/TiO2 and Al2O3/TiO2) can define a depleted or refractory magma source and on other hand, demonstrate the similarity of the mentioned rocks to tholeiitic rock with low boninitic affinity.

The Kuh-e Dom intrusion is a small section of Upper Eocene Urumieh- Dokhtar magmatic belt in the Central Iran tectonic zone. This intrusion is composed of two separate phases which include an acidic and intermediate- mafic units. The acidic rocks consist of monzogranite, granodiorite, quartz monzonite and quartz monzodiorite whereas the intermediate-mafic rocks comprise gabbro, diorite, quartz diorite, monzodiorite and monzonite. Mafic microgranular enclaves of dioritic, quartz dioritic, monzodioritic and quartz monzodioritic composition are common in the acidic rocks. Based on geochemical data, magma mixing along with fractional crystallization has important role in evolution of the plutonic rocks. Also, Kuh-e Dom intrusive rocks have low TiO2, P2O5 and Nb/Zr ratio which are characteristics of active continental margin. The isotopic signature of plutonic rocks is not exactly like those of mantle- or crustal-derived magma, but these rocks have some features commonly found both in the crustal and mantlic sources so that the enclaves tend to illustrate mantlic composition and the acidic rocks tend to show crustal composition, but the intermediate- mafic rocks are in the range from acidic rocks to enclaves. This result along with field and petrographical studies indicate that magma mixing/magma or mingling processes may play an important role in evolution of the intrusion. The upper mantle magma forming the microgranular enclaves, after emplacement in the crust may lead to partial melting of lower crust and because of magma mixing between crustal and mantlic melts, the mafic to intermediate rocks may form.