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

The Saveh-Kashan-Qom copper belt, in the northern part of the Urumieh-Dokhtar Magmatic Arc (UDMA) consists of two of the oldest (gold and copper) zones in Iran (Samani, 1998; Rajabpour et al., 2017) where Upper Eocene-Oligocene Mard Abad-Bouin Zahra volcanic suite is situated. This volcanic suite hosts several copper deposits including Jarou, Gomosh Dasht, Ghezel Cheshme, Bidestan and Afshar Abad that are known as the "Kuh-e-Jarou Mining District". The Kuh-e-Jarou Mining District has a total potential ore reserve of 2 Mt Cu with an average grade of 3 wt.% (Zar-Azin Gostar Consultant Engineering Co., 2009). Upper Eocene volcanic and pyroclastic rocks of rhyodacite, trachyandesite, andesite, and trachytic tuff with high-K calc-alkaline to shoshonitic affinity consist of the main host rocks for Cu mineralization. These units are primarily intruded by post Eocene intrusive bodies.  The geochemistry and genesis of ore bodies have not been fully understood since most previous studies in this area have been focused on petrology of volcanic and intrusive rocks. Moreover, the main purpose of this study is to investigate mineralization style, geometry, and textural-structural features of orebodies, alterations, and fluid inclusions with implication for genesis of Jarou, Gomosh Dasht, Ghezel Cheshme, Bidestan and Afshar Abad copper deposits. In addition, this research provides more insight into understanding geology and mineralization conditions in the study area with an implication for future exploration.

Seventeen thin polished sections from the ores and the host rocks were prepared and they were studied by a transmitted/reflected polarizing microscope in the Iran Mineral Processing Research Center (Karaj, Iran). Five rock powdered samples were also analyzed using X-ray diffraction (XRD) spectrometry (X′ pert Philips) in order to identify the mineralogy of clay minerals in the mineralogy laboratory of Salamanca University (Spain). Fluid inclusion microthermometry was performed using a Linkam THMS600 heating-freezing stage (-190 to +600 °C) mounted on a ZEISS Axioplan2 microscope in the fluid inclusion laboratory of the Iranian Mineral Processing Research Center (Karaj, Iran). Salinities (wt.% NaCl eq.), density (g/cm3) and pressure (bars) were calculated using the FLINCOR v.1.4 (Brown, 1989) and FLUIDS (Bakker, 2012).

The orebody is controlled by a series of feather-like ruptures and faults and its dominant mineral compositions are chalcopyrite and chalcocite with minor amounts of pyrite, galena, bornite and sphalerite. The gangue minerals are quartz, barite, calcite and chlorite. Four types of hydrothermal alterations including chloritization, sulfidization, silicification and epidotization were recognized. Based on field and petrographic studies, three mineralization stages were distinguished including (1) the pre-ore mineralization stage characterized by fine-grained disseminated pyrites, (2) the main hydrothermal stage consisting of three substages: I) an early quartz-chalcopyrite ± bornite vein, II) middle bornite-chalcocite ± covellite breccia ore, III) late galena and sphalerite inclusions, and (3) late-stage barite and calcite veins.Based on petrographic studies, five types of aqueous fluid inclusions have been distinguished in the quartz-chalcopyrite ± bornite and barite veins including two-phase liquid-rich (LV), two-phase vapor-rich (VL), liquid monophase (L), vapor monophase (V) and minor halite-bearing liquid-rich fluid inclusions (LVS). The results show that parental fluids with a density of >1 g/cm3 and an approximate depth of 400 meters were formed and they were followed by fluid inclusions with a density of <1 g/cm3 and a depth of <300 meters due to fluid depressurization, faults. Moreover, introducing low temperature meteoric waters have caused fluid mixing and subsequently copper ore deposition (Henley et al., 2015; Cheng et al., 2019). Considering all geological mineralization styles, textures and structures of the orebody, types of alteration and fluid inclusions in copper deposits of the Kuh-e-Jarou Mining District, it can be suggested that these deposits have similarities with the Manto-type copper deposits in Chile or volcanic red beds in northern America.

Soil erosion and land subsidence in Iran have become known and important issues. Recently, the vital arteries of urban and interurban areas include the nation's power line face with secondary effects of soil erosion and land subsidence. In this research, the place of power line and different upstream marls (M1, M2, M3 units) from Eshtehard to Bouin-Zahra area were studied from a sedimentology erodibility and geoelectric point of view. In the laboratory, granulation, calcimetry, electrical conductivity, Aterberg limits, type and the amount of different elements and clay minerals were determined. The types of erosion include surface, furrow, stream, and trench erosion on the Upper Red Formation deposits and Quaternary sediments. The results show that the area is covered by highly erodible marl and contains abundant non-cohesive silt particles, alkali cations, and soluble anions. A silty layer about one-meter-thick is located on the surface substrate consisting of dense clay and on the clayey sand layer and due to high erosion, they cause large tunnels and gullies that go towards the electric towers. The clay mineral of this layer is montmorillonite with highly sensitive to soil erosion factors. Geoelectric studies show this layer as well as sandy layers deposited in 45m and more depths. The main reason for the general subsidence of this region can be considered as water extraction for the steel industry in the Eshtehard region, which has been used as a driving force to create cracks and erosive cracks in the soil.

Tafoni weathering refers to large cave-like holes ranging from a few decimeters to several meters wide. They develop often in the medium and coarse-grained silicate rocks such as sandstones, conglomerates and granites in various areas, under arid and semi-arid climate condition

To identify the tafoni forms, we measured the morphological features (such as the dimensions and extent) of the tafoni in the sandstone layers in the north of Eshtehard and Mardabad sections. A total of ten medium to coarse-grained sandstone samples were selected from the lens-liked channel deposits. Framework mineral composition (modal analysis) was quantified using the point-counting method (300-500 point) of Gazzi and Dickinson, as described by Ingersoll et al. (1984).

Field survey To calculate the dimensions of the tafoni in the sandstone layers, the width (W), height (H) and depth (D) of the ninety eight tofoni were measured in different parts of two sections. The higher average values of W than the mean values of H and D and also the higher W/D values than H/D indicate that the tafoni forms in the sandstone layers are more elliptical and semicircular (W> H> D).

Based on the petrographical and modal analysis, the mean grain size in the sandstone samples are about 0.5 mm with weak to moderate sorting and rounded to subrounded grains. Sandstone samples from the Eshtehard section include high amount of the igneous, sedimentary and metamorphic rock fragments (average 53.8%), and the feldspar (orthoclase and plagioclase) (average 35.4%), and low amount of mono-and poly-crystallin quartz grains (average 10.8%) with point, straight to concavo-convex grain contacts. In turn, the Mardabad sandstone samples show higher proportion of the igneous and sedimentary rock fragments (average 83%) and lower proportion of the feldspar (average 12%) and quartz (average 2.5%). The average amount of calcium carbonate in the Eshtehard and Mardabad sandstone samples are 6.4% and 10.4%, respectively.

 of unstable grains such as feldspars (plagioclase and orthoclase) and carbonates (microcrystalline and fossil particles) and rock fragments due to the infiltration of acidic waters, promotes the development of porosity in the rock and reduces its resistance during chemical and physical weathering (Hamblin and Christiansen 2008). The Eshtehard sandstones include higher feldspar amount (Q11 F35 RF54) than that of the Mardabad sandstones (Q5 F12 RF83). According to microscopic studies, the Eshtehard sandstones have higher propotion of feldspar and in turn, higher chemical alteration. The development alteration in the feldspar grains can cause the weakness or loose texture and finally physical destruction of rock zones. Dissolution of calcite and dolomite cement Low proportion of calcite and dolomite cement due to dissolution have caused an increased amount of porosity of grains in the process of tofoni formation in the Eshtehard sandstones. The relatively high amounts of calcite cement and calcium carbonate rock fragments, low intergranular porosity and also point, straight to concavo-convex grain contacts created a relatively strong texture in the sandstones of the north of Mardabad section.

The presence of feldspar grains (in high amounts) and low amounts of calcite and dolomite cement, and consequently the increase of intergranular porosity (due to the alteration of feldspars and dissolution of calcite and dolomite cement) are important factors in the formation of tafoni in sandstone layers of the Eshtehard compared to the Mardabad sections. In general, the high thickness and extent of sandstone layers, chemical alteration of feldspars, and patch carbonate cement due to dissolution, control the formation and development of tafoni in the Eshtehard section.

Ground subsidence in eastern part of Eshtehard, built on the alluvial deposits, is linear and gradual. Preparing geological map and profiles; we studied the structural geology of the area. The sort and situation of aquifer, evolution of ground water levels and hydrochemistry were studied and the presence of ancient channel was detected by geoelectric method. The geotechnical studies suggest that the soils in the area (USCS Classification) belong to Lean clay (CL), Fat Clay (CH) and Silty Sand (SM). The maximum soil settlement is more than allowable settlements and soils recognized to be dispersive to semi-dispersive soils. The possible entrance of waste water from Eshtehard Industrial town into Eshtehard Qanat, from septic wells and transfer water system seems to provide necessary moisture for dispersive soils and have caused the subsidence in the area. Hydrogeology of alluvial aquifer was evaluated and indicates a negative debit. Although the hydrographs of pizometric wells are not compensated but it display any role in linear subsidence. Soils prone to dispersion by infiltration of water from septic wells and urban water system and the presence of ancient Qantas hidden in the depth of 15 meters caused linear ground subsidence. The results of this study show the development of ancient Eshtehard city and the selection of new site was not carried out on the geotechnical basis. Therefore it is recommended that before constructing any projects, geotechnical studies are necessary.