مجله پژوهش های دانش زمین
پیاپی 58 (تابستان 1403)

Precipitation is one of the most important climatic elements that can be effective in determining the role and distribution of other climatic variables. This variable is the most unstable climatic variable in the temporal and spatial scale. The American Meteorological Society defines the characteristics of the seasonal distribution of precipitation in a particular place as a precipitation regime. The aim of this study is to evaluate the monthly rainfall data of ERA5 database compared to the rainfall measured in the synoptic stations of the country. Then, the spatial distribution of the rainfall regime and its coefficient of variation and skewness are analyzed in order to identify Iran's rainfall behavior in annual, seasonal and monthly time scales.

In the present study, the reanalyzed gridded precipitation data (ERA5) with a resolution of 0.25 x 0.25 was used from the years 1979 to 2021. According to the findings of Hassler and Lauer (2011), ERA5 data has made a clear improvement compared to ERA-Interim data and has shown small biases compared to other reanalysis data. To evaluate the monthly data of this database compared to the monthly rainfall data in synoptic stations of the country, the correlation coefficient, Normalized Root Mean Square Error (NRMSE), the Wilmot agreement index and the standardized Bias index were used.

The correlation coefficient showed that using the estimated precipitation of this database in rainy months has high reliability. Indicators NRMSE and Wilmot's agreement show the high efficiency of this database. Standard BIAS showed that the most underestimation of this database was in the months of August to October and July, respectively.Rainfall begins in September and lasts until May in Iran. The monthly rainfall time series shows the irregular behavior of rainfall in each month. Most regions of the country receive their highest percentage of precipitation in winter and spring. The rainiest and least rainy seasons of Iran are winter and summer, respectively. Also, the 42-year time series analysis of Iran's rainfall clarified the fluctuations of rainfall in the country in different years.The coefficient of monthly changes in precipitation is indicative of the intensity of month-to-month changes in precipitation. This index can provide a relative pattern of rainfall variability. In fact, the map of the coefficient of monthly changes in precipitation is reminiscent of extreme fluctuations in monthly precipitation; So that the range of monthly rainfall changes is less than 20% from December to March in the northwest, north and west of the country and reaches more than 450% in July to September in the south and southeast.Most regions of the country receive their highest percentage of precipitation in winter and spring. The rainiest and least rainy seasons of Iran are winter and summer, respectively. The most important advantage of winter rainfall is that it is scattered in all regions of the country. But summer rain can be seen only in the northern parts and sometimes parts of the east and southeast of the country.In the autumn season, there is an increase of about 17.5 mm of precipitation in the studied period. But in other seasons, there is a decreasing trend, and the maximum of this negative trend is related to the winter season, which shows a decrease of 28 mm in rainfall. The above changes are statistically significant at the 99% confidence level. ،hese changes show the shift of Iran's seasonal rainfall regime from winter and spring to autumn over time.

A similar rainfall pattern was seen between the two types of data in Iran. Rainfall begins from September and lasts until May. Peak of the average rainfall is received in the coastal areas of the Caspian Sea and then in the areas of the Zagros mountain. The share of winter precipitation in the country is 44.5% of the total precipitation of the year, in other words, the main regime of precipitation is mainly winter. The results to some extent indicate the gradual change of the country's rainfall regime. Because the precipitation of spring (8.2 mm decrease in 42 years) and winter (28.26 mm decrease in 42 years) in Iran has been reduced but autumn rainfall in Iran has been added.

Rivers are very sensitive to changes in discharge and sediment load as well as tectonic forces. Many of the changes that occur over time in the morphology of the channel can be related to the mentioned changes. Morphometric analysis is the first step understanding the basin dynamic activity. Combined variables and indicators can be effective in identifying the complications and surface landform of river channels and show their temporal and spatial changes. In addition, in addition, geomorphological indices (Morphotectonic indices) are considered to be very useful methods in evaluating and recognizing tectonic activities and can provide quantitative results and quantitative description of morphometric features in The basin scale can be used to explain the structural controls, geological history and geomorphology and processes of its drainage network. In addition, the morphometric parameters of the basin play an important role in the hydrological processes governing the basin because it largely determines their hydrological response.

Zanjanrud is the main river basin completely limited to the area of ​​Zanjan province. The river originates from the heights of Soltanieh in the east and flows to the northwest and finally in the west of Rajein village it joins Qizil-Uzen. Regard to the objectives of the research, first, using the DEM of the basin (ASTER-DEM: 30m), the extractable sub-basins was identified in the WMS software environment. In this step the number of 107 sub-basins could be separated, of which 52 sub-basins were selected based on the minimum area of approx. 20 Km2 for the evaluation and analysis of shape indices and tectonic. These sub-basins were named according to the outstanding settlement inside them. After determining the shape indices and estimating and comparing the state of neotectonic of the sub-basins, a field survey was conducted to closely examine and validate the findings.

At the first, the shape of the studied sub-basins was quantified using different indices. Then, the morphology of the sub-basins was evaluated using different shape indices and then the different indices were checked in terms of correlation in terms of the results related to tectonic activity. Finally, the neotectonic of the sub-basins has been estimated using the results of the shape indices and the data related to the faults. The results show that the Kazbar sub-basin is most elongated sub-basin, which together with 7 sub-basins with very high elongation rate are located in the western half of the Zanjanrud basin.The frequency of sub-basins with the shape index 2 to 3 is in the SE half of the basin. Out of the 8 sub-basins with shape index less than 2 in the eastern half of Zanjanrud basin, 1 sub-basin is located in the northern part and 7 sub-basins are located in the southern part of the basin, which can be seen in the SE half. The upstream sub-basin is not included in the classification due to the unusual shape that cannot be compared with other sub-basins.

The results of classification of the indices shows that the accumulation of sub-basins with high rate of elongation and as a result with high neotectonic activity is in the NW part of Zanjanrud basin and especially in the northern side of this part.Out of the 51 sub-basins, the concentration of 8 sub-basins with mean index of higher than 5 and a total of 16 sub-basins with an average shape index higher than 3.5, indicates the highest level of neotectonic mobility in this part of the basin. This finding is consistent withthe region's latest map of active faults, in which the frequency of faults (including the Sohrein fault, the Qaracherian fault and the Kenavand fault) is in the NW part of the basin.According to the study results of the shape of the sub-basins, the SW side of the Zanjanrud basin has an average level of neotectonic activity. This finding, along with the results related to the NW part, can strengthen the hypothesis that the western half of the basin is more active than its eastern half. The neotectonic mobility in SE side of the basin is moderate and is higher than NE part of the basin. As previous studies have shown, many faults are involved in the morphology of the region.

The newly emerging and rapidly evolving technology of Unmanned Aerial Systems (UASs), covering a wide range of devices and enabling photogrammetric applications from user-driven platform, presents new possibilities for research in geomorphology by obtaining spatially accurate geographic data. The low-level altitude of flight allows researchers to obtain imagery at high levels of detail, which is necessary for a detailed analysis of even fine fluvial forms of the dynamic river channels or landslides. After the early 2010s, the use of UAVs equipped with an RGB camera has become widely applied in geomorphology. It has expanded the capability of low-altitude aerial photo shootings and subsequent SfM photogrammetry. The basic principle of SfM photogrammetry is the same as the conventional photogrammetry, but SfM enables automatic alignment of many (hundreds to thousands) images thanks to automated detection of numerous tie-points, and then produces dense point cloud and rasterized DEMs, as well as orthorectified mosaic images. One of the advantages of SfM photogrammetry is its flexibility across camera platforms. conventional aerial images, and ground-based images are commonly used platforms to 3D models by SfM.

The Vaz watershed is located in the northern slope of the Alborz Mountain range and in the south of Chamestan city, which in terms of political divisions, this basin is located in Noor city of Mazandaran province. First, using the library method, international and domaestic scientific literature was studied in order to examine the background and different methods of using UAVs in river studies and to prepare a study framework. After imaging, it was processed in Metashape software (Metashape 1.5.5) and orthophoto image and digital elevation model (DEM) were extracted in centimeters in order to prepare cross-sections and check the morphometric and hydrological characteristics of the river.

The lateral changes of the Vaz River were studied across 2 different sections of the river. The first level of analysis included building an elevation model based on imagery provided by UAVs and processed in Metashape software, with a pixel resolution size of 4.6 centimeters. Through measuring cross sections of the channel at different flows at the edges and bankfull discharge of the channel, data was acquired. This data included active depth and width of the channel, cross sectional areas, average depth, hydraulic radius and width to depth ratio. These data could be combined with hydraulic data to calculate flow velocity, discharge, stream power, shear stress and other parameters which enable the quantification of river processes. In the statistical comparison of 2 reach at channel edge discharge, some parameters such as cross-sectional area, hydraulic radius, flow velocity, maximum and average channel depth, width-to-depth ratio, channel width susceptible to flooding, channel depth ratio, discharge and Froude number, decrease at the downstream section comparing to the upstream section. However, shear stress and specific stream power of the river increase in the downstream. At the bankfull discharge of the channel, all parameters except specific stream power of the river decrease comparing to the 1st section. The specific stream power increases at the 2nd section. Afterwards the research investigated the change in cross sections across the 2 sections. At the upstream, sand mining, road construction across the channel and construction of a secondary channel had changed the composition and material of the right banks of the river. At the downstream, dam construction, had changed the flow and sedimentation regime of the river.

The data acquired from UAVs enables extraction of relevant morphometric and hydrological data regarding the channel and its transverse sections, due to geometric precision and high resolution. The high precision of this data provides an appropriate alternative for field works such as mapping and surveying with different cameras. Orthophoto images prepared using UAVs have enabled the more accurate identification of geomorphic features and landforms. According to data acquired from the 2 different sections of River Vaz, it was demonstrated that upstream and downstream sections are not similar and variation in morphometric characteristics causes difference in hydraulic characteristics such as flow velocity, shear stress and specific stream power. These varieties have led to different geomorphic forms at the studied sections.

The formation and occurrence of any climatic phenomenon require conditions that, when the sum of these atmospheric and environmental conditions occur simultaneously, make it possible for the phenomenon to form and occur. Depending on the type of phenomenon, some of these atmospheric or environmental factors are formed in the atmosphere alone, while others are formed in the physical environment under it. A phenomenon like a dust storm is a combined atmospheric-environmental phenomenon. The existence of dry and highly fragmented soils provides favorable conditions for the rise of dust. For this reason, dry deserts, bare plains with soft and granular soils are always prone to this phenomenon as sources of dust production. Therefore, physical substrates with this feature should always be studied and investigated as potential places for dust phenomenon to occur. What is related to atmospheric conditions, severe instabilities without moisture or with little moisture are the basis of dust storms. This weather pattern is more likely to appear in arid and semi-arid climates. It is not possible to control or change the structure of atmospheric phenomena with current human technology. Therefore, the best way to reduce the effects of destructive phenomena such as dust storms in a geographical area is to first identify the source and path of dust storms.

The selected study area for this research is the southwest of Iran, an area that has experienced an increasing trend in the frequency and intensity of dust storms in recent decades. The study area includes the three provinces of Kohgiluyeh, Boyer Ahmad, Chaharmahal and Bakhtiari.In the first step of the research, all synoptic stations with complete statistics for 33 years (1986-2019) in the study area were identified and extracted. .In the second step, using the data (number of reports of dust phenomenon (nhz), number of reports with dust phenomenon (ndu), number of reports with sand and dust storm phenomenon (nbdu), wind speed and horizontal visibility less than 1000 meters and codes (06.07, 08.09, 30.31, 32.33, 34.35, 98) days with dust were extracted from the data of Meteorological Organization. In the next step, using the website [https://www.ready.noaa.gov/HYSPLIT, ↗] (https://www.ready.noaa.gov/HYSPLIT,) the origin of dust storms in the southwest of Iran was plotted using the backward method from the GDAS data system with a resolution of 0.5 degrees. This data is available from 2007. Therefore, for all the dust reports with the above characteristics from each of the sample stations, the origin of the storm has been determined.

Statistical analysis of dust storm reports from selected stations showed that 3027 cases of dust storm have been reported during the 33-year statistical period from a total of selected stations. In terms of monthly distribution, the months of January, February and December respectively have reported the highest number of dust storms. In terms of seasonal distribution, the highest number of pollen reports were from winter (1153 cases, 38.1%) and spring (711 cases, 23.5%) respectively. The highest number of dust storms was reported from the two dry years of 2008 (225 cases) and 2009 (243 cases). In terms of stations, the highest number of dust storms was reported from Ahvaz and Abadan stations. Based on the routing performed in this study, the input dust storms came from six areas:Iraq (from four parts), eastern Mediterranean countries, Saudi Arabia, central and northeast Africa, distant sources in eastern Europe, and local sources within the study area.The origin of 93.25% of the input dust storms to the study area was from sources in central Iraq, and about 20% of the dust storms originated from eastern Mediterranean countries, while 16% of the dust storms were from local sources in Khuzestan province. The origin of dust storms in high-altitude stations in the eastern part of the study area, such as Shahr-e Kord, Yasuj, and Kuhrang, was from distant sources in Syria and Jordan or northeastern Africa.

Given that, 84% of the dust storms entering the region originate from outside the border. Considering that the two sources of the west and the center of Iraq are the source of 35% of the storms entering the region. Diplomatic efforts for the cooperation of the country of Iraq to stabilize the soil in these resources are very necessary.

Geophysical modeling is divided into one-dimensional (1D), two-dimensional (2D) and three-dimensional (3D) types in terms of dimensions. In some cases, especially in areas with inherent complications, performing 1D or even 2D modeling is not enough to achieve exploration goals, whereas 3D modeling is needed. One of the advantages of 3D modeling compared to the other two types is the more realistic responses and higher accuracy of the results. However, 3D modeling requires 3D data collection, while in many cases, geophysical surveys are done in 2D along a series of profiles, therefore, the related modeling will also be 2D. In such cases, in order to achieve a more realistic 3D model, it should be resort to a series of logical mathematical-computational tricks while based on physical principles. Magnetometric and geoelectrical methods, including resistivity and induced polarization, are the most suitable geophysical methods for discovery of copper deposits. In the present research, the processing, comparison and analysis of geophysical data of magnetometry, resistivity and induced polarization have been carried out along the profiles surveyed in the Yazd, Aliabad copper deposit and their relationship with mineralization has been determined. Then, 3D modeling of 2D geophysical data containing resistivity and induced polarization surveyed at the deposit has been done through geostatistical processes and employing RockWorks16 software. Aliabad copper deposit is located in the Taft city in Yazd province in the middle part of Urmia-Dokhtar zone between eastern longitude of 768000 to 771000 and northern latitude of 3503000 to 3507000. According to the report of copper deposits in Iran, the lithological diversity in this region is very high and the ancient rocks of the region are the Shirkoh mountain range with granite and granodiorite rocks. The oldest rock outcrops in the Ali-Abad area are conglomerate and sandstone (Sangestan Formation) from the late Jurassic and early Cretaceous. Copper mineralization in Ali-Abad deposit mainly occurred into granitoid intrusive stock and with less extent in conglomerates and metamorphosed sandstones around it.

In Aliabad copper deposit, 1666 magnetic data-points with 20-meter interspacing as well as resistivity and induced polarization have been surveyed through rectangular configuration along four profiles called DD-1 (with dipole-dipole array), PD-2, PD-3 and PD-4 by pole-dipole array with the length of 1320, 1240, 600 and 640 meter, respectively. In this study, first, 2-D smooth inverse modeling of resistivity and chargeability data for four profiles was carried out by the least squares error method using Res2dinv software. Afterward, the operations of processing, comparison and analysis of magnetic, resistivity and chargeability data from the geophysical profiles was performed and their relationship with mineralization was determined. To achieve the goal, magnetic surveyed corresponding to four inverted resistivity and induced polarization sections from geoelectrical profiles, were drawn and analyzed.

The results of the research show that in general, there is a good accordance between magnetic and geoelectrical data whereas the anomalies in the area are often related to metallic mineralization. Afterward, the primary statistical analysis was performed for the inverted data in the common range of four geophysical profiles and rectangular array. Based on these studies, the distribution of induced polarization and resistivity data are normal and log-normal, respectively which was transformed into a normal distribution with a two-parametric logarithmic transformation. Then, to achieve the spatial structure governing on resistivity and chargeability data of the region, strike variograms were drawn in two horizontal directions of north-south and east-west as well as vertical (depth) direction. The results revealed that all theoretical variogram models according to experimental variograms are spherical type and the region has geometric anisotropy. In the next step, based on the results of variography operation, 3-D models of resistivity and chargeability data were produced using Rockworks software through interpolation algorithm of advanced inverse distance weighted. At the end, on the basis of 3-D performed modeling the position of the most promising and appropriate mineralization area was determined as well as proposing a vertical borehole with the length of 80 m in this location.

On the basis of the findings, drilling a borehole in the proposed location, carefully drawing of the borehole strip-log, comparing the results of drilling cores assay, lithology and alteration with the results of 3D geophysical modeling in this place are necessary. Drilling of the proposed borehole will lead to more recognition of the deposit, possibility of evaluating the effectiveness of the carried out geophysical operation and 3D modeling in the Aliabad copper deposit.

The purpose of physical modeling in structural geology is to reconstruct the formation, development and evolution of structures on a laboratory scale with materials similar to crustal rocks. The physical-mechanical properties of the materials used in these modeling are of particular importance; So that the characteristics of these materials should be similar to the physical and mechanical characteristics of crustal rocks, and there should be a proportionality between the model and nature in terms of rheology, viscosity, and frictional resistance. Sand, mud-clay, gypsum and silicon are among the materials used in physical modeling. Gypsum powder, plaster, or hemi-hydrate in dry and wet form (killed gypsum) has also been used in modeling. In this study, the effect of humidity on viscous behavior of wet plaster in physical modelling of strike- slip fault system has been investigated. In these modellings wet plaster with 320%, 285% and 175% of humidity as a viscous material has been used. In determination of physical and mechanical (Atterberg limits) properties of wet plaster, the liquid limit of 178% and plastic limit of 96% was obtained. This study also provides data on behavior of wet plaster with changes in its humidity.

Atterberg measurements were first used to measure the water content of wet (or dead) plaster. Based on this criterion, three limits are defined for the amount of wetness in the material, which includes the shrinkage limit, the plastic limit, and the liquid limit. In this study, due to the non-use of wet plaster in the humidity range of the shrinkage limit in physical modeling, the shrinkage limit test was not performed. In the plastic limit test, the minimum moisture required to turn the soil into mud is measured. In this regard, some balls of mud prepared from wet plaster are placed on a glass and by rotating the hand on the plaster, a rod with a diameter of 3mm is prepared. If cracks on the mud is developed, its humidity is at the level of mud. To determine the liquid limit of wet plaster, the penetrator cone device was used. Then the physical modeling of strike-slip faulting has been done using wet plaster with different wetness percentages. Three tests of physical modeling of strike-slip fault system in the basement and investigation of the effect of these movements on the sedimentary cover have been carried out using wet plaster with different humidity levels of 320%, 285% and 175%.

The results of Physical modelling on strike- slip fault system shows that by decrease in humidity of wet plaster from 320% to 175%, the Riedel shear fractures distance is increased from 0.3cm to 1.9 cm and their lengths have increased from 2.5cm to 4.5cm. These results obtained from the distribution and frequency of shear fractures in the form of a decrease in the number of fractures, an increase in the distance and length of fractures, and the uneven development of fractures qualitatively indicate a decrease in the elastic limit of wet plaster because of the decrease on its humidity. Reduction on the humidity of the wet plaster resulted in development fault related folding in the modeling. The variations on the numbers, distance, type and lengths of shear fractures in wet plaster with different percent of humidity demonstrates that wet plaster acts as viscous behavior when its humidity is between plastic limit (96%) and liquid limit (178%). These experiments also confirm the results of previous studies on the brittle behavior of plaster at lower wettnes levels.

The results obtained from this study in the investigation of Riddle shear fractures and folds related to the fault in the physical modeling of the strike-slip fault system showed that the water content in wet plaster to the extent of the plastic limit causes its plasticity behavior. The increase of water content more than this amount due to the relative decrease of adhesion and viscosity is associated with the decrease in the plasticity behavior of wet plaster. These changes are associated with the increase in the number of Riddle shear fractures and the decrease in the development of folds related to the thrust fault has been accompanied in the experiments. This conclusion is in agreement with the former studies that documented the brittle behavior of plaster with lower humidity than the humidity of the plastic limit.

Modeling mineral potential based on the precise collection and processing of geological, geophysical, and satellite data enables us to predict the potential presence of mineral substances in a specific area. This process involves constructing complex mathematical models that, utilizing machine learning algorithms and thorough data analysis, assist authorities and decision-makers in the mining sector. It helps identify mineral-rich zones for optimal extraction and manage land resources in the best possible way. Given the diverse geological units present in the Saqez sheet, this sheet is considered one of the most promising areas for the formation of metallic deposits. The host rock for most Pb-Zn deposits in Iran is sedimentary, known as Sedimentary-Hosted Pb-Zn deposits. According to conducted surveys, it has been determined that the Pb-Zn mineralization occurring in the Saqez sheet is also of this type. Typically, calcite, dolomite, shale, sandstone, and igneous rocks serve as hosts for these deposits.

In this research, the exploratory layers of lithology, dolomite alteration, and geochemical of Pb-Zn were used to prepare a map of the prediction of Pb-Zn mineralization in the turpentine sheet. Utilizing the singularity technique on sediments stream, using various exploratory layers performing laboratory spectroscopy, and applying the spectral behavior curves obtained on Sentinel-2A images in this innovative and creative research. It shows its existence compared to another similar research. After fuzzification of exploration layers in GIS software, the prediction map of Pb-Zn mineralization was obtained by Fuzzy-Gamma function and gamma value of 0.85. The results of XRF and ICP-MS analysis on the discovered Pb-Zn samples showed a grade between 3 and 7%, which indicates the correct selection of the studied area and the exploratory layers and their correct integration. Further, by conducting laboratory spectroscopy in a dark room with a halogen lamp and obtaining the spectral behavior curve of the sphalerite mineral related to the samples of the study area, the SAM matching algorithm was applied to the Sentinel-2A satellite images.

According to the Pb-Zn mineralization prediction map of the Saqez sheet, this map is classified into four categories of low, moderate, high, and extreme mineralization potential. It is evident from this map that the northern, central, and southeastern regions have the highest potential for Pb-Zn mineralization. Upon examining the topography and road identification of the Saqez sheet, six areas were selected for exploratory drilling of Pb-Zn. Samples were collected for analysis and validation of identified points. XRF and ICP-MS analysis results indicated that the total Pb-Zn content ranged from 2 to 7% and 70,000 to 20,000 ppm. Finally, high-grade Pb-Zn samples were selected for petrographic examination. Petrographic studies revealed that minerals such as sphalerite, galena, and pyrite were predominant in the collected samples, with their texture filling the pore spaces. Specifically, sphalerite replaced galena, and galena replaced pyrite.The results obtained from laboratory spectral analysis and the application of spectral behavior curves for sphalerite minerals on Sentinel-2A satellite images were utilized to assess the accuracy of the work and identify promising new mineralized areas. By comparing the corrected spectra from the laboratory experiments with the USGS spectral library, it was determined that the obtained spectral behavior is similar to the USGS spectral library. Therefore, the predictive map of Pb-Zn mineralization resulting from the application of spectral behavior curves for sphalerite on Sentinel-2A satellite images indicates the correct selection of imagery, appropriate spectral analysis, and all processing steps.

Due to the fact that the host rocks of most Pb-Zn deposits in Iran are of sedimentary origin, the first step in modeling the mineral potential of these deposits is to accurately recognize the ore deposit type. Based on the evidence and samples observed in the study area, the ore deposit type in the study area can be considered as the Irish type. Therefore, based on this, modeling and prediction of Pb-Zn mineralization on the one hundred thousand scale map of Saqez were carried out according to the Irish type Pb-Zn mineralization.After evaluating the Pb-Zn mineral potential map, seven final areas were selected for exploration. Based on the exploration conducted in six areas (S1, S2, P, Q-Pb-Zn, Polygon12, and Polygon13), samples containing Pb-Zn mineralization were discovered, while Polygon5 was identified as lacking Pb-Zn mineralization, indicating the reliability of the exploration layers and integration method. XRF and Aqua Regia analysis results showed that the discovered Pb-Zn samples had grades ranging from two to seven percent, indicating economic-grade content for these metals.

Northern Hired mining area with an area of about 25 square kilometers is located in South Khorasan province and 140 kilometers south of Birjand city. In this area, intermediate to acidic intrusive masses with the composition of granodiorite to granite have infiltrated and affected the Tertiary volcanic-sedimentary sequence. In the studied area, mineralization is associated with siliceous, sericite, tourmaline, chlorite and carbonate alterations. The structure and texture of these deposits include planar veins and veins and rarely stockwork, scattered, sheared and massed.

The studied area is located in the southern part of South Khorasan province. This area is located 145 km south of Birjand city and north of Hired village. The way to access this mineral area is the paved road from Birjand to Khosf and then Hird or from Nehbandan to Hired. After reviewing the library studies, a field visit was made to the target area. According to the area, samples were taken from all existing lithological units, mineral mass and alteration around the mine. 57 samples were taken for ICP-MS and ICP-OES analysis. The characteristics of all collected samples and studied stations are carefully recorded. Then, the analysis results were analyzed in the relevant software.

In this range, intermediate to acidic intrusive masses with the composition of granodiorite to granite have infiltrated and affected the Tertiary volcanic-sedimentary sequence. According to the field observations, the most important changes that have been identified on the surface of the earth are: 1) quartz-tourmaline-sericite, 2) carbonate and 3) propylitic. In the samples, plagioclase crystals can be seen both in the background and as phenocrysts, which sometimes have zoning. A number of plagioclases have been dissolved and recrystallized. The mafic minerals in the rock are amphibole and pyroxene.Amphiboles and plagioclase have generally changed to chlorite and sericite, which indicates the effect of atmospheric waters on the rocks of the region. Mineralization in the studied area can be seen in the form of veins with different thicknesses along fractures and faultzones, and most of the mineralization has occurred in the basalts and basaltic andesite of the area. Amphibole and plagioclase have generally changed to chlorite and sericite, which indicates the effect of atmospheric waters on the rocks of the region. Pyroxenes are also seen in the composition of the background. In the analyzed samples, 29 samples have values higher than one percent of copper, of which 18 samples have values higher than five percent of copper. The maximum amount of molybdenum in the obtained samples was equal to 1.1%. 30 samples have values higher than 0.12% of lead and 12 samples have values higher than 1% of lead and the maximum amount of lead measured in the samples of this area was higher than 3%. 28 samples have values higher than 0.2% of sulfur and 3 samples have values higher than 1% of sulfur and the maximum amount of sulfur measured in samples of this area was higher than 3%. By drawing correlation diagrams. Cu element also has a good correlation with Mo element. (Al, Ti, Cr, Ni) Al with Ti and Also, Cr has a strong correlation with Ni. The gold element is also strongly correlated with iron and arsenic.

Geochemical investigations of associated elements show that the source magma of the mineralization in the northern Hired area is the result of subduction and hence it is type I. These investigations show that the existing gold is placed within the pyrite structure and according to the paragenesis of copper and molybdenum and also the presence of copper in the form of chalcopyrite minerals, it can indicate that the mineralization of copper and molybdenum is near The thermal source is formed, while gold mineralization is of epithermal type. Based on the conducted studies and field observations, the North Hired gold-copper deposit is mainly in the form of veins, and due to the high anomaly of elements such as lead, zinc and molybdenum, the term multi-metallic can be used for the North Hired deposit. In this range, intermediate to acidic intrusive masses with the composition of granodiorite to granite have infiltrated and affected the Tertiary volcanic-sedimentary sequence. The outcrop of these intrusive masses can be seen in the south of the range. Generally, the host rock of the mineralization in the range is basic to moderate, but in some places rhyodacite outcrops have also been observed.

The Oligocene-Miocene dolomitized Asmari Formation has expanded all over the Arabian plate with numerous supergiant and giant hydrocarbons in SW Iran, Iraq, Saudi Arabia, and the United Arab Emirates. Concertedly, the Asmari Formation and age-equivalents in adjacent areas of Middle East include more than 90% of recoverable oil reservoirs (Ghazban, 2007). The best reservoir units of this succession occurs within dolomitic parts exhibiting better reservoir quality than do the intercalated limestones and silisiclastics. Dolomite sequences play an important role in the production of oil and gas in the world's major hydrocarbon basins (Fallah-Bagtash et al, 2020; Noorian et al, 2020; Omidpour et al, 2021; 2022; Fallah-Bagtash et al, 2022). Similarly, in the Asmari reservoir with poor primary reservoir properties, fracturing and dolomitization enhanced porosity and permeability and thus hydrocarbon production (Aqrawi et al, 2006). Shadegan Oil Field is one of the important oilfields of Iran, due to its carbonate- siliciclastic nature, different parts of this formation have been exposed to the process of dolomitization. This has led to the development of porosity and permeability in its different parts. Therefore, in this research, using various data such as detailed petrographic studies along with geochemical studies of dolomites, the dolomites types of the Asmari Formation in the Shadegan Oil Field, dolomitization models, diagenetic history, diagenetic alteration and evolution of dolomitized fluids have been discussed. The results of this study can finally be used to evaluate the effect of dolomitization on the reservoir potential of Asmari Formation in this field.

The present study is based on a petrographic analysis of 1123 thin sections from cores of five wells drilled in the Asmari Formation. All thin sections were stained with potassium ferricyanide and Alizarin Red-S to distinguish carbonate minerals (Dickson, 1965). Dolomites are classified based on dolomite-rock texture classification presented by Sibley and Gregg (1987), Mazzullo (1992) and Chen et al. (2004). Facies analysis and interpretation of the depositional environment was performed using by Burchette and Wright (1992) and Flügel (2010) schemes. Ten uncovered thin sections were also analyzed by cathodoluminescence microscopy. These analyses took place at the Central Laboratories of Ferdowsi University of Mashhad, Iran. Ten gold-coated samples were analyzed with backscattered electron imaging using a Scanning Electron Microscope (SEM) in order to evaluate dolomite types, crystal sizes, micro-textures and pore spaces. Finally, thirty-two dolomitic samples were analyzed for their trace and major element contents using atomic absorption spectrophotometry (AAS) at the Ferdowsi University of Mashhad, Iran. 

The Asmari Formation, in Shadegan Oil Field, with Oligocene-Miocene age, consists of carbonate unit and siliciclastic intervals, which is mainly composed of medium to thick layered limestone and dolomite with interlayers of shale and sandstone. Detailed description of the core samples along with petrographic studies of the Asmari succession led to the identification of 26 carbonate-evaporite microfacies. In general, mineralogical, geochemical, and especially the interaction of facies with the distribution of dolomite indicates dolomitization by five different mechanisms/models in the carbonate platform of the Asmari Formation. These models include: Sabkha model, Seepage-reflux model, Meteoric-mixing zone model, Burial model and Bacterial mediation model. Dolomitization, as the most important diagenetic process in the depositional sequence of the Asmari Formation, has formed in several diagenetic environments, including syndepositional diagenetic realm (near surface), shallow burial, and intermediate to deep burial.

Four texturally and geochemically different types of dolomite include D1 (<10 μm, fabric-retentive), D2 (16-62 μm, fabric-retentive), D3 (62-250 μm, fabric destructive), and D4 (150-250 μm, fabric destructive). The lateral and vertical heterogeneity in dolomite percent indicates that the Asmari reservoir was subject to the multiple dolomitizations that could be categorized by five models in the near-surface to deep burial environments. Thin-layered sabkha dolomites (D1) are formed at or just below the sediment-water interface in mud-supported facies soon after deposition or during shallow burial. The matrix dolomites (D2 and D3) are the most abundant type of dolomites with the most contribution to reservoir porosity. They were formed during intermediate burial stages of the Asmari succession, indicated by their close association with the formation of an early generation of stylolites and fairly high iron concentration. These dolomites formed from warmer and more saline basinal fluids and/or from the dissolution of high-magnesium calcite or earlier dolomites, or recrystallization of D1. The D4 and other dolomites associated with the shaley facies, formed in a deeper burial setting by hydrothermal processes, utilizing hot and slightly-saline fluids that were affected by brine enrichment.