Saeed Nazari; Alireza Arab Amiri; Abolghasem Kamkar Rouhani; Fereydoun Sharifi
Abstract
In this work, we simulate the frequency-domain helicopter-borne electromagnetic (HEM) data over the two-dimensional (2D) and three-dimensional (3D) earth models. In order to achieve this aim, the vector Helmholtz equation is used to avoid the convergence problems in Maxwell’s equations, and the ...
Read More
In this work, we simulate the frequency-domain helicopter-borne electromagnetic (HEM) data over the two-dimensional (2D) and three-dimensional (3D) earth models. In order to achieve this aim, the vector Helmholtz equation is used to avoid the convergence problems in Maxwell’s equations, and the corresponding fields are divided into primary and secondary components. We use the finite difference method on a staggered grid to discretize the equations, which can be performed in two ways including the conventional and improved finite difference methods. The former is very complex in terms of programming, which causes errors. Furthermore, it requires different programming loops over each point of the grid, which increases the program’s running time. The latter is the improved finite difference method (IFDM), in which pre-made derivative matrices can be used. These pre-made derivative matrices can be incorporated into the derivative equations and convert them directly from the derivative form to the matrix form. After having the matrix form system of linear equations, Ax = b is solved by the quasi-minimal residual (QMR). IFDM does not have the complexities of the conventional method, and requires much less execution time to form a stiffness or coefficient matrix. Moreover, its programing process is simple. Our code uses parallel computing, which gives us the ability to calculate the fields for all transmitter positions at the same time, and because we use sparse matrices thorough the code memory space, requires to store the files is less than 100 MB compared with normal matrices that require more than 15 GB space in the same grid size. We implement IFDM to simulate the earth’s responses. In order to validate, we compare our results with various models including the 3D and 2D models, and anisotropic conductivity. The results show a good fit in comparison with the FDM solution of Newman and the appropriate fit integral equations solution of Avdeev that is because of the different solution methods.
F. Jamali; A.R. Arab Amiri; A. Kamkar Rouhani; A. Bahrami
Abstract
In any geophysical exploration, the final goal is to achieve an accurate image of the relevant underground property. In order to achieve this, the geophysical operation using the electrical resistivity and induced polarization (IP) methods is conducted to explore the sub-surface sulfide mineralization. ...
Read More
In any geophysical exploration, the final goal is to achieve an accurate image of the relevant underground property. In order to achieve this, the geophysical operation using the electrical resistivity and induced polarization (IP) methods is conducted to explore the sub-surface sulfide mineralization. Considering the mineralization evidence in the Kaboudan area near the Bardeskan city, first, geophysical surveying of the polymetallic deposit is carried out using the electrical resistivity and IP methods by employing the rectangle array in order to detect the electrical anomalies in the area. Then for delineation of the identified anomalies and investigation of the mineralization in the area, the 2D resistivity and chargeability cross-sections are prepared and interpreted with the help of the geological information. This geophysical survey in the area has led to the identification of several potential areas for mineralization. Then in order to obtain a detailed picture of the sub-surface mineralization and an overview of the in-depth mineralization distribution, a 3D modeling of the acquired data is made, and the results of this modeling are shown in 3D forms. The mineralization zones are identified in the studied area from their high chargeability values as well as the low to medium electrical resistivity amounts. This can be attributed to the metal mineralization and the presence of sulfide minerals in the mineralization zones. Mineralization in many places of the studied area is determined with an approximate east-west trend as well as somewhat varying the intensities of the electrical resistivity and chargeability amounts. The geological and drilling information obtained from the area confirm the interpretations.
S. Najafi Ghoshebolagh; A. Kamkar Rouhani; A.R. Arab Amiri; H. Bizhani
Abstract
As many gold deposits are associated with sulfide zones, and the direct exploration of gold deposits using the geophysical methods is very difficult due to its low amount in the sub-surface, the direct exploration of sulfide zones by the geophysical electrical resistivity and induced polarization (IP) ...
Read More
As many gold deposits are associated with sulfide zones, and the direct exploration of gold deposits using the geophysical methods is very difficult due to its low amount in the sub-surface, the direct exploration of sulfide zones by the geophysical electrical resistivity and induced polarization (IP) methods may lead to the indirect exploration of gold deposits. The gold deposit in the Kervian area is located in the Kurdistan shear zone, and is directly related to the sulfide, silica, and carbonate alteration units. After acquiring the resistivity and IP data, 2D modeling of the data is made in order to indirectly identify the gold-bearing zones in the surveyed area. As some of the identified geophysical anomalies indicating the sulfide zones may not be associated with the economic amounts of gold, in order to obtain an exploration pattern for the gold deposit in the studied area, a combination of the geophysical data modeling and interpretation results with the geological information and other exploratory data is used to reduce the uncertainty in identifying the gold-bearing zones in the studied area. Thus, modeling and interpretation of the geophysical data lead to identify the sub-surface anomalies as the locations of possible gold mineralization in the area, and then the drilling points are suggested in the area. Considering the geological studies and chemical analysis of the samples taken from the drilled boreholes crossing some of the geophysical anomalies, we conclude that the geophysical anomalies occurring inside the phyllite and carbonate units in the area can contain an economic amount of gold, and thus are recommended as the top priority for further exploration.
F. Sharifi; A.R. Arab Amiri; A. Kamkar Rouhani
Abstract
The generalized effective-medium theory of induced polarization (GEMTIP) is a newly developed relaxation model that incorporates the petro-physical and structural characteristics of polarizable rocks in the grain/porous scale to model their complex resistivity/conductivity spectra. The inversion of the ...
Read More
The generalized effective-medium theory of induced polarization (GEMTIP) is a newly developed relaxation model that incorporates the petro-physical and structural characteristics of polarizable rocks in the grain/porous scale to model their complex resistivity/conductivity spectra. The inversion of the GEMTIP relaxation model parameter from spectral-induced polarization data is a challenging issue because of the highly non-linear dependency of the observed data on the model parameter and non-uniqueness of the problem. To solve these problems as well as scape the local minima of the highly complicated cost function, the genetic algorithm (GA) can be applied but it has proven to be time-intensive computationally. However, this drawback can be resolved by incorporating a faster algorithm, e.g. particle swarm optimization (PSO). The aim of this work is to investigate whether recovering the model parameter of the ellipsoidal GEMTIP model from SIP data using the combined GA and PSO algorithms is possible. To achieve this aim, we set the best calculated individuals using GA as the search space of PSO, and then the best location achieved by PSO in each iteration is assigned as the updated model parameters. The results of our research work reveal that the model parameters can effectively be recovered using the approach proposed in this paper but the time constant of a noisy data that arises from the adverse dependency of this parameter on the ellipticity of a polarizable grain. Moreover, the execution time of the ellipsoidal GEMTIP modeling of complex resistivity data can be significantly improved using the proposed algorithm.
S. Moghaddam; S. Dezhpasand; A. Kamkar Rohani; S. Parnow; M. Ebrahimi
Abstract
Protection of water resources from contamination and detection of the contaminants and their treatments are among the essential issues in the management of water resources. In this work, the time-lapse electrical resistivity tomography (ERT) surveys were conducted along 7 longitudinal lines in the downstream ...
Read More
Protection of water resources from contamination and detection of the contaminants and their treatments are among the essential issues in the management of water resources. In this work, the time-lapse electrical resistivity tomography (ERT) surveys were conducted along 7 longitudinal lines in the downstream of the Latian dam in Jajrood (Iran), in order to detect the contamination resulting from the direct injection of a saltwater solution in to the saturated zone in the area. To investigate the pollutant quantities affecting the resistivity of this zone, the temperature and electrical conductivity measurement were carried out using a self-recording device during 20 days (before and after the injection). The results obtained from the self-recording device measurements and ERT surveys indicated that in addition to the salt concentration changes in water, the resistivity changes in the saturated zone were dependent on other factors such as the lithology and absorption of contaminants by the subsurface layers. Furthermore, the expansion of contamination toward the geological trend, sedimentation, and groundwater flow direction of the area were shown.
M. Filbandi Kashkouli; A. Kamkar Rouhani; Ali Moradzadeh; H. Assi
Abstract
Magnetotelluric (MT) method is an electromagnetic technique that uses the earth natural field to map the electrical resistivity changes in subsurface structures. Because of the high penetration depth of the electromagnetic fields in this method (tens of meters to tens of kilometers), the MT data is used ...
Read More
Magnetotelluric (MT) method is an electromagnetic technique that uses the earth natural field to map the electrical resistivity changes in subsurface structures. Because of the high penetration depth of the electromagnetic fields in this method (tens of meters to tens of kilometers), the MT data is used to investigate the shallow to deep subsurface geoelectrical structures and their dimensions. In order to have a higher accuracy in modeling the MT data, dimensions of the subsurface structures should be determined. The objective of this research work is to determine the dimensions of subsurface structures in an oil field located in the southwest of Iran. Using parameters such as the normalized weighted index, ellipticity, and Wall's rotational invariant measure, this goal could be achieved. Using the ellipticity factor at the frequency range of 1-320 Hz, the earth can be represented as a 2D form. However, at lower frequencies, the earth should be represented as a 3D form. In most MT stations, the normalized weighted index has indicated that the earth is in a 2D form on the surface or shallow subsurface, although it is represented by a 3D shape at higher depths. In this regard, the Wall's rotational invariant measure shows more heterogeneity. This measure indicates that the earth is in the 2D and 3D forms on the surface or shallow subsurface, and is perfectly 3D at higher depths, although the earth dimensions cannot be determined in some certain frequency ranges. The earth in both the shallow and deep parts of the studied area has a high heterogeneity.
H. Shahi; R. Ghavami Riabi; A. Kamkar Ruhani; H. Asadi Haroni
Abstract
In this research work, the frequency domain (FD) of surface geochemical data was analyzed to decompose the complex geochemical patterns related to different depths of the mineral deposit. In order to predict the variation in mineralization in the depth and identify the deep geochemical anomalies and ...
Read More
In this research work, the frequency domain (FD) of surface geochemical data was analyzed to decompose the complex geochemical patterns related to different depths of the mineral deposit. In order to predict the variation in mineralization in the depth and identify the deep geochemical anomalies and blind mineralization using the surface geochemical data for the Dalli Cu-Au porphyry deposit, a newly developed approach was proposed based on the coupling Fourier transform and principal component analysis. The surface geochemical data was transferred to FD using Fourier transformation and high and low pass filters were performed on FD. Then the principal component analysis method was employed on these frequency bands separately. This new combined approach demonstrated desirably the relationship between the high and low frequencies in the surface geochemical distribution map and the deposit depth. This new combined approach is a valuable data-processing tool and pattern-recognition technique to identify the promising anomalies, and to determine the mineralization trends in the depth without drilling. The information obtained from the exploration drillings such as boreholes confirms the results obtained from this method. The new exploratory information obtained from FD of the surface geochemical distribution map was not achieved in the spatial domain. This approach is quite inexpensive compared to the traditional exploration methods.
Hossein Shahi; Abulghasem Kamkar Rouhani
Abstract
The method of weights of evidence is one of the most important data driven methods for mineral potential mapping in GIS. In this method, considering the characteristics of known mineralized locations, we can prospect new mineralized areas. In this research work, the method of weights of evidence has ...
Read More
The method of weights of evidence is one of the most important data driven methods for mineral potential mapping in GIS. In this method, considering the characteristics of known mineralized locations, we can prospect new mineralized areas. In this research work, the method of weights of evidence has been used for hydrothermal gold potential mapping in Torbat-e-Heydarieh area, east of Iran. As a relatively large number of gold mineral occurrences (i.e., exactly 27 known gold mineralized locations) have been recognized in the study area, the use of the weights of evidence method for prospecting new gold mineralized zones in the area may be quite efficient. In this study, a combination of the results of the airborne geophysical, geological, argillic, propillitic and iron oxide alteration, geochemical and structural data based on the method of weights of evidence, has been made to determine probable gold mineralization zones in the form of a posteriori map of the survey area. Consequently, four major zones in this area have been identified as high gold mineralization potential zones, in which many vein and veinlet mineralization forms can be found.
Alireza Arab-Amiri; Fereydoun Sharifi; Abolghasem Kamkar-Rouhani
Abstract
The need for clean groundwater resources to have sustainable development in a country is undoubted. Due to the importance and high quality of karstic waters in supplying water in Iran especially in Shahrood city, it is attempted in this research work to recognize and explore karstic waters in southwest ...
Read More
The need for clean groundwater resources to have sustainable development in a country is undoubted. Due to the importance and high quality of karstic waters in supplying water in Iran especially in Shahrood city, it is attempted in this research work to recognize and explore karstic waters in southwest of Tepal area, Shahrood. For this purpose, integration of the results obtained from the methods of vertical electrical sounding (VES) and resistivity profiling has been used in this research work. The VES surveys have been performed in 10 sounding points using the Schlumberger array with electrode separations of a maximum 500 meters. The resistivity profiling surveys using dipole-dipole electrode array with 75m electrode spacing and dipole steps 1 to 8 have been carried out along four lines having a length of more than four kilometers in the study area. Then, one-dimensional (1-D) modeling and interpretation of the sounding results using master curves and IX1D software, and two-dimensional (2-D) modeling and interpretation of the profiling results using Res2DINV have been made. As a result of the interpretation and integration of the results, karstic water zones in the study area have been recognized, and based on that, suitable locations for drilling to access and extract karstic groundwater have been introduced.
