نشریه علوم زمین خوارزمی
سال هفتم شماره 2 (پاییز و زمستان 1400)

Fe-As sulfide minerals are the most important hosts of gold in various deposits, which sedimentary rock-hosted disseminated gold deposits is known by high content of gold in arsenian pyrite composition. In this study, the textural-geochemical charecteristics of arsenian pyrite is specifically aimed at understanding how gold is distributed in the form of nanoparticles (Au0) or participation in the mineral crystal lattice (Au+) in three ore deposits: Zarshuran (average grade: 2.63 g/t), Agdarreh (average grade: 3.7 g/t), and Arabshah (average grade: 1.2 g/t), at Takab-Angouran metallogenic zone, have been studied. According to the results, a negative chemical relationship between arsenic and sulfur (R2 = −0.61) was observed in the arsenian pyrite composition, which indicates the presence of As3+ with the empirical formula of Fe(AsxS1−x)2. Due to the paragenetic association of gold with pyrite and sphalerite ores, the absence of oxide minerals, near-neutral to acidic nature of pH (presence of argillic±sericitic alteration), and the high activity of sulfur, shown that the gold solubility and its transfer were conducted by Au(HS)2– bisulfide complex. Evidence suggests that pervasive fluid-rock interaction is caused decreased S2– activity - has resulted instability of bisulfide complex and gold deposition in the pyrite veins.

The natural emission of radon gas is an emerging phenomenon that modern lifestyles have turned into a potential danger to humans. It is a gas that has no physical properties that can be seen or understood by humans. Therefore, it is much more dangerous than other gaseous pollutants. This natural gas inside a building is determined by both the terrain on which it is built and the composition of its constructed materials. Today, the world's developed countries have prepared Radon atlases in their critical locations and big cities. As the second most important city in the country, the Mashhad, which is also considered one of the most touristic cities in Iran, is doubly important. In this study, first, the structural geology condition of the Mashhad in terms of Radon emission has been investigated, and then Radon has been measured. Using Arc GIS software, natural Radon emission zoning maps at urban and geological scales have been prepared. Also, a residential unit in one of the critical areas of natural Radon emission has been selected. A corrective method has been adopted to reduce Radon. The methods applied to the structure were able to significantly reduce radon gas by 27 to 50 percent. Given that natural radon emissions from subsurface rocks and fractures are present in all parts of the world. So identifying critical areas (with high radon emissions) can provide special control measures at the local and site scale buildings that reduce the risks of this natural gas.

Alam- kuh granitoid intrusion is located in the western part of kelardasht, Central magmatic Alborz structural zone. Alam- kuh granitoid intrusion consist of alkaligranite, syenite, and syenodiorite to monzonite rocks. In the northern part of Alam -kuh intrusion, there are mafic enclaves that represent the magma mixing and mingling process. it consists of plagioclase, quartz, alkali feldspar and biotite minerals. Types of pertite and myrmekite textures associated with granular, microgranular and microgranular porphyry textures observed in these rocks. According to mineral chemistry and whole rock chemistry studies, intrusion rocks are I-type which are typically of shoshonites and are aluminous, metaluminous. Alam- kuh samples are shown enriched in light rare earth elements (LREEs), and La, Rb, Th, Tb elements and depleted in Ba and Zr elements. Based on the major element oxides, tectonically, located in the volcanic arc granitoids (VAG) .Primary magma of district igneous rocks were produced by the melting of the underlying crustal protolith (amphibolite) and (meta-graywacke ), and the basaltic magma derived from the mantle which replaced in the lower crust could be thermal origin for partial melting of crustal source and mixed with crustal felsic magma. According to studis, In the stretching environment of Alborz Magma Bow, Lithosphere mantle and stenospheric mantle, Both were involved in the birth of a mantle with different stocks. Mixing two magmas with mantle and crustal origins and subtraction and crystallization, The most important processes were the development of magma and the diversity of rocks in the region.

In this study, the sediments of Kazhdumi Formation were evaluated as a possible source rock in Ahwaz, Aghajari, Parsi, Kilorkrim and Masjed Soleiman oil fields in Zagros basin located in southwestern Iran. For this purpose, the Arrhenius kinetic model was used to evaluate the maturity of the source rock as well as to investigate oil generation. According to the information obtained, the dominant kerogen in the Kazhdumi Formation is type II. Also, based on the values obtained from the Rock-Eval pyrolysis, this Formation has fully entered the oil window and has a high . Therefore, the kerogen of this Formation was classified in very good source rock, which has a very good hydrocarbon potential. Similar results were obtained in this study based on the Arneus kinetic model. Accordingly, the Transformation rateof hydrocarbons in different oil fields were the range of 66 to 100%. These changes are mainly due to different burial history in the oilfields studied.

The Sarvak Formation was deposited on shallow-marine carbonate platforms under the controls of tectonic and eustatic changes during the Upper Cretaceous in the Zagros area. It forms on of the most important reservoir intervals in SW Iran. Complex depositional setting and diagenesis history have resulted in a heterogeneous carbonate reservoir. This study, integrates the results of petrographic (facies and diagenesis) studies with petrophysical and reservoir data (core porosity-permeability and wireline logs) to evaluate the controls of depositional and diagenetic processes on the distribution of reservoir quality in the Sarvak Formation. Ten hydraulic flow units are determined using the FZI concept. Twelve reservoir and non-reservoir (baffle and barrier) units are identified using the Lorenz approach. Finally, dominant depositional facies and diagenetic alterations are evaluated in each HFU and reservoir zone. Results of this study showed that meteorically-dissolved rudist-dominated facies and high-energy facies of shoal complexes formed the best reservoir units in the Sarvak Formation. In sequence stratigraphic point of view, these zones are located in the RSTs of third-order sequences, beneath the disconformity (paleoexposure) surfaces. In contrast, the compacted and cemented mud-dominated facies concentrated in the TSTs and around the maximum flooding surfaces (MFS) formed the non-reservoir units of the Sarvak Formation.

Dohneh area is located in the northeast of Zanjan and in the Western Alborz-Azarbayjan zone along the Tarom subzone. The outcropped rock units in the Dohneh area include Eocene volcanic and volcano-sedimentary rocks (equivalent to the Karaj Formation) which consist of tuff units including lithic crystal tuff and crystal lithic tuff as well as basaltic lava flows (amygdaloidal basalt and porphyritic basalt). Rock forming minerals in the Dohneh basalts include plagioclase, pyroxene and olivine. The secondary minerals in the basalts are chlorite, zeolite, carbonate (calcite), epidote, serpentine and iron oxides. The opaque minerals and apatite are present as minor minerals. The data resulted from electron microprobe suggest that the pyroxene composition in the Dohneh basalts are as Ca-Mg-Fe bearing pyroxene (low Na) and mostly show diopside, augite and minor clinoenstatite compositions. The feldspar composition is labradorite and sanidine. Based on microprobe analyses on chlorites, their composition is Mg rich which are grouped as diabantite and pininite. Moreover, the clinochlore is also detected in this area by XRD analysis. The results obtained from the electron microprobe analysis on zeolites show that zeolites of Dohneh area are low-content to medium-content silica. Na bearing zeolite namely natrolite is also recognized by XRD analysis. The chemical composition of pyroxene from the Dohneh area suggests that these minerals crystallized in pressure lower than 5 Kbar from alkaline to sub-alkaline magmas in the back-arc and subduction related setting.

Permeability is one of the important parameters in reservoir petrophysical studies, and evaluation of this parameter can be used as a key tool in the oil fields development. This study aim is permeability estimation and modeling of the Upper Surmeh Formation in one of the oil fields in the Persian Gulf. The Surmeh Formation with Jurassic age is considered as one of the most important oil and gas reservoirs in the Persian Gulf basin. In this study, we have used petrophysical well logs and 3D post-stack seismic data in the permeability evaluation process. The structural reservoir model has been prepared using the interpretation of seismic sections and well logs in the reservoir section. This model includes the interpretation of fault surfaces, geocell network and reservoir horizons. The geocell network used in this study used columns and geocells with dimensions of 50 * 50 meters in the X and Y directions. The thickness of the geocellular layers of each reservoir zone is designed to fit that zone in the reservoir section. The values permeability estimation was performed using the artificial neural network with a back-propagation algorithm. The results obtained from the artificial neural network were generalized in the studied reservoir well logs. The correlation coefficients value obtained from permeability estimation values with drilling core data is equal to 88%. Comparison of geostatistics results with permeability value shows that the proposed methods can provide acceptable results for reservoir permeability modeling.

This research is performed to investigate earthquake hazard using Geographical Information System (GIS) and Fuzzy Logic method. First, the necessary factors like active faults; historical, pre-instrumental and instrumental earthquakes; focal mechanism of instrumental earthquakes; geomorphology (elevation and dip), toughness of sediments and active tectonic and also their sub-criteria, which impress earthquake hazard are investigated and changed as information layer in GIS. For the first time, preference of sub- criteria like magnitude and depth of the earthquakes have been regarded. Fuzzy Logic (weighting layers and preferencing them using ArcGIS and Expert Choice software) is applied in earthquake hazard investigation. Finally, in earthquake hazard map of Kerman province, achieved information layers in Arc GIS were merged and various areas (earthquake hazard point of view) were classified to high risk (Kuhbanan, Lakarkuh, Golbaf, Bam, Bardsir and Rigan), moderate risk (Shar-e Babak, Sirjan and Rafsanjan) and low risk (west of the province, Lut and Jazmurian) areas.

The stress field and its spatial and temporal changes are important in various branches of geosciences such as geotechnics, engineering geology and hydrocarbon reservoir geomechanical stuidies. It is also important in describing the geodynamics of the area. In this study, a new method of determining the slip direction from 3D seismic interpretation data in one of the hydrocarbon fields in southern Iran on different horizons with different geological age is used for paleostress studies by nonlinear stress tensor inversion. Also the present state of stress field is calculated from the focal mechanism of earthquakes data by the same method. The present state of stress and its comparison with the global stress map indicates that there is a good agreement between the obtained stresses directions and the regional stress orientations. This study showed a clockwise gradual rotation in the direction of maximum horizontal stress over time, so that the maximum horizontal orientation of the NW-SE orientation of SHmax in Cretaceous has become NE-SW in the present day.