جستجوی مقالات مرتبط با کلیدواژه "میان بار سیال" در نشریات گروه "زمین شناسی"

In the western boundary region of Central Iran with Sanandaj-Sirjan, considering the widespread carbonate units in the northeastern Isfahan area, the barite deposits have considerable potential. The Komsheche barite, hosted in the Middle Triassic Shotori dolomite Formation, is the most active mine in the region. Barite mineralization has occurred in two styles, banded-layered and veined-brecciated. Fluid inclusions in the bedded barite homogenize at temperatures from 78 to 122 ºC, with salinity between 10.9 to 17.0 wt.% eq. NaCl, while the homogenization temperature for two-phase inclusions of the second type barite is between 130 to 187 ºC and associated halite-bearing tri-phase inclusions range from 192 to 210 ºC, with an average salinity of 14.3 and 36.6 wt.% eq. NaCl, respectively. The δ34S values of the samples range from 18.40 to 26.34 per mil CDT, and their δ18O values range from 8.9 to 14.7 per mil SMOW. Based on conducted studies, ore-forming fluids were formed in an open and near-bottom seawater system during the early diagenetic stage. The heavy isotope values related to pore water are locked in a closed system during the final stages of diagenetic. Sedimentary type, associated minerals, REE composition, finding of fluid inclusion and isotope reveal that Komsheche barite has the most similarity to diagenetic/cold-seep types of marine barites.

The widespread Cenozoic magmatic assemblages in Iran host a variety of ore deposits including porphyry Cu-Mo-Au, skarn type ores, and epithermal base and precious metals deposits. Silicic zones of variable sizes are common in the Kerman belt in the southern section of the Urumieh-Dokhtar arc, and some might be representing the upper parts of porphyry copper systems known as lithocap. To investigate this potential relation, a silicic zone in Meideh, north Pariz, is studied. The silicic zone lies in an area with several known porphyry copper deposits (PCD) including Sarcheshmeh, Nochun, Seridun, Sarkooh, and Bagh-Khoshk. For comparison, silica ledges and veins in Seridun and a mineralized silica vein system to the east of the Sarcheshmeh mine are also studied.

The study is based on field studies and investigation of textures and structures, and sampling for mineralogy (microscopic and X-ray diffraction analysis), and fluid inclusions. The XRD analyses were accomplished in the Iranian Mines and Mining Industries Development and Renovation Organization (IMIDRO) and Kansaran Binaloud Co, Tehran. The fluid inclusion studies were performed in the Iranian Mineral Processing Research Center (IMPRC) using a Linkam THMS600 equipped with a Zeiss microscope.

The silicic zone in Meideh is developed in andesitic lava flows and pyroclastic materials, and covers an area of ~ 1 km2. Silica occurs in white to grey colors and in massive, brecciated and locally vuggy textures; the grain sizes range between 0.01mm to 1mm. The silica is locally associated by minor sulfides (pyrite and locally chalcopyrite) carbonates, and clay minerals.The silicic zone grades outward into a silicic-argillic halo and into the host volcanic rocks with propylitic alteration. Chemical analysis of samples from the zone indicated enrichments in Cu, Mo, Ag, As, Bi and Au relative to the average composition of intermediate-mafic volcanic rocks in the Kerman belt. Small outcrops of a quartz-tourmaline rock occur in the southeast of the silicic zone.In Seridun, silica ledges and veins occur in the periphery and in the upper parts of a porphyry copper deposit developed in Miocene shallow intrusive bodies and older volcanic rocks. In east of Sarcheshmeh, several N-S striking silica veins locally containing pyrite, chalcopyrite, malachite, and Fe-oxides/hydroxides occur in Cenozoic volcanic and intrusive host rocks. In both areas, the silicic zones are products of pervasive silicic alteration, and occur in massive, breccia, and vuggy textures. Vuggy texture is well developed in Seridun. XRD analysis of representative samples from Meideh indicated the occurrence of kaolinite and illite, in addition to quartz. Minerals characteristic of advanced argillic alteration (i.e. alunite, pyrophyllite, diaspore and andalusite) are missing. The minerals, however, were identified in Seridun.Fluid inclusions in quartz from all three areas are dominated by two-phase liquid-vapor. Homogenization temperature (TH) varies between 140-263 oC (average: 202 oC) for Meideh, 195-320 oC (average: 247 oC) for Seridun, and 140-264 oC (average: 177 oC) for east of Sarcheshmeh. Salinities vary between 0.18-5.71 (average: 1.62), 1.22-4.18 (average: 2.27), and 0.7-3.39 (average: 1.57) wt.% NaCl eq., respectively. The quartz-tourmaline rock from Meideh is distinguished by the occurrence of liquid-vapor-halite±hematite and liquid-vapor-opaque inclusions, in addition to liquid-vapor inclusions. The TH and salinity for the liquid-vapor inclusions, homogenizing to liquid, varies, respectively, between 202-269 oC (average: 231 oC) and 3.71-7.16 (average: 5.43) wt.% NaCl eq. The TH and salinity for the halite bearing inclusions, homogenized by halite dissolution, varies between 240-480 oC (average: 345 oC) and 33.40-56.90 (average: 42.80) wt.% NaCl eq.

The textures, structure, and spatial relations with the host volcanic rocks suggest that the Meideh silicic zone developed as a result of pervasive silicic alteration, rather than open space filling. Textures indicative of open space filling, including crustification and symmetric banding, are absent in Meideh. The silicic ledges in Seridun, and the N-S striking silicic zones in east of Sarcheshmeh, are the products of pervasive silicic alteration of the host volcanic and intrusive rocks.The XRD analysis of representative samples from Meideh indicated the occurrence of kaolinite and illite, in addition to quartz. Minerals characteristic of advanced argillic alteration (i.e. alunite, pyrophyllite, diaspore and andalusite) are missing. The minerals, however, were identified in Seridun. Fluid inclusions in quartz from the three silicic zones are dominated by two-phase liquid-dominant L-V inclusions. No distinction in salinity can be made between the three zones; Seridun, however, is distinguished by higher homogenization temperature. The local quartz-tourmaline zones in Meideh developed from distinctly higher temperature and salinity fluids (240-480 oC and 33.9-64 wt.% NaCl eq., respectively). A comparison of fluid inclusion data with several epithermal base and precious metals systems in the Urumieh-Dokhtar arc and elsewhere in Iran suggest that no meaningful distinction can be made between barren (i.e. Meideh, at current exposure level) and productive epithermal systems.Our data indicate that the silicic zone in Meideh cannot be considered as a porphyry-related lithocap at current exposure. The quartz-tourmaline rock developed from fluids of higher salinity and temperature suggests a link with magmatic-hydrothermal systems and warrants further investigation.

The Gharehkand area is located in the southeast of Maragheh city and in Takab metallogenic district. According to the structural divisions of Iran, this area is situated south of the volcanic Mount Sahand in the Central Iran zone (Stocklin, 1968). This paper aims to investigate the characteristics of gold-bearing vein-veinlets and physicochemical conditions of ore-forming fluids in the Gharehkand area.

About 40 rock samples were collected from mineralized zones and host rocks. The thin and thin-polished sample sections were studied in the geology department of the Mohaghegh Ardebili University, Ardebil. Microthermometric data were obtained from fluid inclusions using the Linkam THMS600 stage at the Payame Noor University of Tabriz.

1) The mineralization in the Gharehkand area took place principally as vein-veinlets within the host sedimentary rocks during two main stages. Mineralization occurred in quartz vein-veinlets during the first stage. The quartz crystals within the quartz vein-veinlets display brecciated, boxwork, drusy, and comb textures. During the second stage barite mineralization occurred as vein-veinlets. The mineralization of sulfides (galena, sphalerite, pyrite, and chalcopyrite) and gold occurred within the quartz vein-veinlets of the first stage.2) The values of homogenization temperature (Th) and salinity of fluid inclusions vary from 80°C to 220ºC and 6 to 13 wt.% NaCl eq., respectively.3) The study of fluid inclusions demonstrated that boiling and simple cooling were the most important mechanisms in the ore deposition at Gharehkand, and the sulfide complexing ligands played an effective role in transporting metals within the ore-forming hydrothermal fluids.4) The quartz crystals textures (brecciated, boxwork, and comb) in quartz vein-veinlets and microthermometric data (low salinity and Th) of the ore-forming fluids indicate that mineralization at Gharehkand is of epithermal type with low-sulfidation style.

The mineralization in the Gharehkand area took place principally as vein-veinlets within the host sedimentary rocks. Two main stages of mineralization were distinguished at the Gharehkand area. Stage-1 mineralization is represented by the quartz vein-veinlets. The quartz crystals within the quartz vein-veinlets display brecciated, boxwork, drusy, and comb textures. The formation of quartz crystals in quartz veinlets and micro-veinlets were temporally divided into three sub-stages: early, middle, and late. Stage-2 mineralization is represented by barite vein-veinlets. The hypogene alteration is mainly observed as the development of silicic halos around quartz vein-veinlets within the host sedimentary rocks. The mineralization of sulfides (galena, sphalerite, pyrite, and chalcopyrite) and gold have occurred within the late sub-stage quartz veinlets and micro-veinlets. Oxidized processes have caused formation of goethite, hematite, jarosite, malachite, and azurite. Copper sulfides (covellite, chalcocite, and digenite) are formed in the supergene zone. Based upon phase content, the studied fluid inclusions in late sub-stage quartz crystals may be classified into three types: liquid-rich two-phase (L+V), mono-phase vapor (V), and vapor-rich two-phase (V+L). The values of homogenization temperature (Th) and salinity of the analyzed liquid-rich two-phase fluid inclusions vary from 80°C to 220ºC and 6 to 13 wt.% NaCl eq., respectively (Fig. 11A, C). Given the Th and salinity values of the fluid inclusions, ore-forming hydrothermal fluids during development of the quartz vein-veinlets at Gharehkand experienced hydrostatic pressures within the range of 20-25 bars. This is almost equivalent to depths of 200-250 meters below the underground water table level. It is consistent with the estimated depths of most epithermal deposits (Bodnar et al., 2014). The Gharehkand microthermometric data points on the bivariate plot of Th versus salinity (Wilkinson, 2001) show that the densities of fluid inclusions vary from 0.9 to 1 g/cm3. The occurrence of boiling and simple cooling are the most effective mechanisms in deposition of ore and gangue minerals at Gharehkand.  The Gharehkand microthermometric data points on the bivariate plot of Th versus salinity (Pirajno, 2009) indicate that the bisulfide complexing ligand most likely played the important role in transporting ore metals (particularly gold).

Fluid inclusions are small, usually microscopic, volumes of pore fluid, which are crystallographically trapped in rocks during diagenesis or fracture healing processes. Nowadays, various techniques are used for resource exploration. Application of a fluid inclusion is one of these methods that has been developed for mineral, geothermal, and petroleum reservoir exploration. The study of fluid inclusions represents our most reliable source of information on the temperature, pressure, and fluid composition data of the ore fluid, and it is one of the most important tools for research into the economic geology and genesis of ore deposits (Moon, 1991). To achieve these goals, transparent and polished slabs of rock material are prepared and optically studied with a petrographic microscope. Samples are viewed under transmitted plane-polarized white light as well as under reflected ultraviolet or blue-violet illumination. During the fluid inclusion petrography, the volume fractions of phases are routinely estimated at room temperature to deduce whether assemblages of cogenetic inclusions were originally trapped from a one-phase or a multi-phase pore fluid. In the present research study, the microthermometric properties of the fluid inclusion data through pressure, temperature, and salinity diagrams were computed by geometrical modeling of fluid inclusion (Bakker and Larryn, 2006). The proposed method provides a quick and low cost technique to preliminarily investigate the microthermometric parameters of the fluid inclusion.
To evaluate the proposed geometrical model, the Mehdiabad Pb-Zn deposit is selected as the case study. The Mehdiabad Pb-Zn deposit is located at the Yazd-Anarak metallogenic belt, 110 km southeast of Yazd, in the Central Iran structural zone. The host rocks of the deposit consist of lower Cretaceous silty limestone and dolomite. The main occurrences are the Calamine mine (CM), the Black-Hill ore (BHO), the East Ridge (ER) and the Central Valley Orebody (CVOB). The ore body consists of a primary sulfide ore and a supergene non-sulfide ore, the latter one having been mined at CM (Ghasemi, 2007; Rajabi et al., 2012). The shape and geometry of fluid inclusion are one of the most important parameters, which were applied to estimate 3D degree of filling and find the useful information about temperature, pressure, salinity and depth of trapping without using time-consuming and costly heating-cooling operation. Inclusions in normal thick-sections are rotated stepwise and their projected areas and area-fractions are plotted against rotation angle. The outputs are systematically related to inclusion orientation, inclusion shape, and filling degree. The dependency on orientation is minimized when area fractions are measured at the position where the inclusions project their largest total areas. The shape factor is employed to present a new objective classification of inclusion projections, based on the extracted parameters from digital image processing (Bakker and Larryn, 2006).
In this research, Mehdiabad Pb-Zn deposit has been chosen to evaluate the proposed method. Based on the fluid inclusion petrography, four fluid inclusion types are observed: 1) L+V; 2) L+L; 3) L; and 4) V; L+V phase is the most popular. After preparing 2D image of sections, 2D and 3D degree of fills were calculated by measuring the areas of total, bubble, and spot of fluid inclusion and computing the third dimension (Z) of fluid inclusion. Four geometrical models of volume fractions are defined, including cylinder, tetragonal prism, truncated cone, hexagon, and ellipsoid (Bakker and Larryn, 2006; Hossein Morshedy et al., 2008). In this case study, 3D proper models of the fluid inclusions are selected, depending on its geometry (hexagonal or ellipsoid). Then 2D degrees of filling (area fraction) is converted to 3D degrees of filling (volume fraction). The geometrical modeling results are well matched with computational outputs. In this research, the ratios of area to volume fractions in geometrical and computational modelling were calculated 0.75 and 0.77, respectively. In the Mehdiabad Pb-Zn deposit, the main geometrical shapes of fluid inclusions were followed up the hexagonal prism with hexagonal pyramids and ellipsoid models. 3D geometrical modeling of fluid inclusion showed vapor fraction, 25% and density, 0.7 g/cm3, which the microthermometric and other parameters were obtained homogenization temperature nearly 100-200 °C (average of 150 °C), pressure between 400-500 ATM, formation temperature about 250-350 °C, salinity within a range of 10 to 15 wt.% NaCl equiv. and depth of mineralization 150-200 m. This finally achieved results have a high similarity with the typical carbonate-hosted Pb-Zn deposit.

Fluorite ore deposits are classified into three main groups: (1) magmatic deposits, (2) structures related deposits, and (3) sedimentary deposits (Dill, 2010). More than 30 fluorite occurrences with approximately 1.35 million tons of reserves have been recognized in Iran (Miller, 2014). Bagher Abad and Darreh Badam fluorite ore deposits, located in the southeast of Delijan (Markazi province) occur between the central Iran structural zone from the north and the Sanandaj- Sirjan structural zone from the south. The geology of the area is dominated by folded and faulted structures of Jurassic carbonates and shales (Thiele et al., 1968). The main host rocks for fluorite mineralization in the studied area are the Lower-Upper Jurassic carbonates and shales of Shemshak and Badamu Formations. In this study, 70 samples from the various rock types including fluorite veins, host rocks and related alterations were collected. 25 thin- and polished thin-sections were prepared and studied to explain the mineralogy and paragenetic sequence of the ore body. Eight double-polished sections were also prepared for microthermometric analysis. The micro-thermometric analyses were conducted on primary fluid inclusions using Linkam THM600 heatingfreezing stage connected to a TMS94 temperature controller and a liquid nitrogen pump (LNP) cooling system. The main host rocks for fluorite mineralization in the studied area are composed of the lower Jurassic slate and phyllite (Shemshak Formation) and the Middle to Upper Jurassic dolomitic limestone and calcareous sandstone (Badamu Formation). The main alterations associated with fluorite mineralization are sericitization, silicification and argillization. According to the fluid inclusions data, fluorite mineralization in Bagher Abad and Darreh Badam deposits were precipitated because of pressure reduction of ore bearing fluids and mixing of a primary moderate-salinity brine with less saline meteoric water. Estimation of trapping pressuretemperature of the mineralizing fluid in Bagher Abad fluorite deposit using the intersecting CO2 and H2O isochors for aqueous, aqueous-carbonic and carbonic fluid inclusions indicated that fluorite mineralization occurred at 180-260°C and 1-2 kbar pressure. According to the present study, circulation and upward flow of hydrothermal fluids (containing H2O and CO2) that originated from underlying altered bedrock provided appropriate conditions for increasing the solubility of metals and formation of halide (Cl¯ and F¯) metal complexes. Reaction with wallrock and gradual decrease in temperature due to mixing and dilution of the above-mentioned fluids with lowsalinity meteoric water resulted in fluorite mineralization in favorable structures such as veins. Bagher Abad and Darreh Badam fluorite ore deposits are examples of epigenetic mineralizations which are not related to igneous activities in Iran. The mineralization is formed in nearly vertical veins, which are relevant to local fractures hosted in the Lower-Upper Jurassic carbonates and shales with east-west trend. The main ore textures are open-space fillings, breccias, veins and cavities associated with sericitic, silicic and argillic alterations. Micro-thermometric measurements were carried out on primary fluid inclusions in fluorite, calcite and barite minerals from both Bagher Abad and Darreh Badam deposits. Three types of fluid inclusions were distinguished: (1) two phase aqueous fluid inclusions (LV), (2) liquid (L) or vapor (V) mono phase inclusions, and (3) aqueous-carbonic (L1+L2+V) fluid inclusions. The first ice melting temperatures (Te) of two phase aqueous inclusions (LV) in fluorite, calcite and barite from Bagher Abad and Darreh Badam deposits vary between -32 to -15°C and -35 to - 24°C, respectively, which represents a H2O+NaCl±KCl multiphase fluid (Van den Kerkhof and Hein, 2001). The last ice melting temperatures (Tmice) vary between -10.5 to -2.3°C and -12.0 to -5.6°C which are equal to salinities of 5.6-14.7 and 8.3-15.2 wt% NaCl equivalent for Bagher Abad and Darreh Badam deposits, respectively. The final homogenization temperatures (Thtotal) vary between 127 to 188 °C and 176 to 270°C for Bagher Abad and Darreh Badam deposits, respectively. The CO2 melting temperatures (TmCO2) of aqueous-carbonic inclusions in fluorite, calcite and barite show a range of -58.3 to -56.6°C which suggests CH4 and/or N2 impurities (Burruss, 1981). The clathrate melting temperatures (Tmclath) ranging from -6.0 to +1.0°C represent salinities between 5.5 to 18.2 wt% NaCl equivalent for both Bagher Abad and Darreh Badam fluorite deposits.

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.