Geophysics
Ghazal Janghorban; Seyed Mohammad Abtahi Forooshani; Keytash Moshtaghian; Hooshang Asadi Harooni; Hamzeh Sadeghi Sorkhani; Mohammad Hajheidari
Abstract
Kuh-e Lakht epithermal gold index is located on Urumieh-Dokhtar Volcanic Belt in Isfahan province. Geological studies indicate the presence of an epithermal gold mineralization system in the area. The geophysical exploration in the area includes magnetometry, resistivity, and induced polarization ...
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Kuh-e Lakht epithermal gold index is located on Urumieh-Dokhtar Volcanic Belt in Isfahan province. Geological studies indicate the presence of an epithermal gold mineralization system in the area. The geophysical exploration in the area includes magnetometry, resistivity, and induced polarization surveys. Then, we implemented Li and Oldenburg algorithm for 3D inversion of the magnetic data. The depth of the largest estimated magnetic susceptibility obtained from data inversion coincides with the average depth of the magnetic sources obtained from Euler deconvolution. Furthermore, we compared the estimated 2D resistivity and electrical changeability models and the estimated magnetic susceptibility. The comparison denotes the correlation of the estimated magnetic susceptibility variations with the reduction of resistivity, high electrical chargeability, and alteration zones. Combining the estimated magnetic susceptibility model with the geochemical analysis of the exploratory boreholes in the area indicates that the mineralization often occurred at the maximum variation of the magnetic susceptibility. Nonetheless, the results indicate the possibility of mineralization along the zones with large magnetic susceptibility variations.
Hydrology
Somayeh Esmaeili; Rahim Barzegar; Naeimeh Kazemian
Abstract
Qareh-Ziaeddin plain is located in the West Azarbaijan province, Northwest of Iran. The aim of this study is to investigate the effective factors and processes on the groundwater chemical quality of Qareh-Ziaeddin plain. For this purpose, 20 water samples were collected from groundwater resources in ...
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Qareh-Ziaeddin plain is located in the West Azarbaijan province, Northwest of Iran. The aim of this study is to investigate the effective factors and processes on the groundwater chemical quality of Qareh-Ziaeddin plain. For this purpose, 20 water samples were collected from groundwater resources in November 2016 and the concentration of the major ions, nitrate and silica was measured. Also, the pH and electrical conductivity of the samples were measured in the field. In this study, different bivariate and hydrochemical diagrams, chloro-alkaline index, saturation index and inverse modeling were used to achieve the mentioned goal. The results of the bivariate diagrams show that the saltwater intrusion from irrigation return flows, cation exchange, weathering and dissolution of rock minerals specially carbonates, silicates, gypsum and halite, and evaporation process, in a small amount, are the effective factors on the chemical quality of the groundwater in the study area. The calculated Chloro-alkaline indices indicate that these indices are negative in all samples, which reveal the normal ion exchange. The water samples are super-saturated with regards to the carbonate and quartz minerals, whereas are under-saturated with respect to the sulfate and halite minerals. The results of inverse geochemical modeling confirm weathering and dissolution of the carbonate, sulfate and halite minerals and ion exchange in different parts of the aquifer.
A.R. Arab-Amiri; A. Moradzadeh; D. Rajabi; B. Siemon; N. Fathianpour
Abstract
It is about 30 years that Helicopter electromagnetic (HEM) surveys are being used for rapid mineral and ground water exploration, environmental investigations and also geological mapping in extensive areas. Despite this, one of the most important problems in using obtained data from the surveys is accurate ...
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It is about 30 years that Helicopter electromagnetic (HEM) surveys are being used for rapid mineral and ground water exploration, environmental investigations and also geological mapping in extensive areas. Despite this, one of the most important problems in using obtained data from the surveys is accurate interpretation of the data. Otherwise, there will be no beneficial results while spending high costs. Thus the interpretation of the data is as old as the surveys. Several experts have tried to improve the interpretation of HEM data and they have achieved great successes. Almost the results of all these surveys are presented as resistivity (or conductivity)-depth sections. To reach this target, the first step is to solve the electromagnetic induction integral equation. As solving this integral is not possible using analytical methods, several numerical methods such as Laplace transformation, Hankel transformation and Jacobi-Matrix methods have been suggested for the solution of the integral, and different approaches have been presented with each method by various authorities. One of the most important solution methods is fast Hankel transformation. In this paper, it is attempted to use this method for finally obtaining resistivity-depth sections. For solving the induction equation by this method, we need the kernel function of the integral and weighting coefficients that replace the Bessel function in the integral. For this, first we use the Guptasarma-Singh method. Then results of this method are corrected and evaluated. Then, these results will be analyzed and tested with two synthetic models in addition to presenting the results of inverse modeling. Finally, by adding new parameter named α0 to induction equation, we will clearly see an improvement in the results of inverse modeling. Meanwhile, the problem of singularity that occurs at high frequencies is almost removed.
A.R. Arab-Amiri; A. Moradzadeh; D. Rajabi; N. Fathianpour; B. Siemon
Abstract
Today Helicopter-borne electromagnetic (HEM) data survey play important role for high resolution and fast 3D mapping of resistivity structures within the vast area. The standard method of interpretation of these data is to inverse them frequently. As surveying system is not fixed during the survey, hence ...
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Today Helicopter-borne electromagnetic (HEM) data survey play important role for high resolution and fast 3D mapping of resistivity structures within the vast area. The standard method of interpretation of these data is to inverse them frequently. As surveying system is not fixed during the survey, hence noise is accompanying the measured data. To process the measured noisy data they are fed into the several filters to get better data to be used for modeling. During the filtering stage some of signals are also lost. Therefore, it is required to choose modeling techniques that has minimum error and provide accurate subsurface model. In this paper, first the response of the three synthetic layered earth models were calculated by using three different Hankel transform forward modeling methods. Then with adding different percents of random noise to the synthetic data, they were modeled inversely by different methods. The obtained results indicate that the so-called improved Guptasarma-Singh inverse modeling method could provide better responses for all three synthetic models.
A. Nejati Kalateh; M. Mirzaei; N. Gouya; E. Shahin
Abstract
In this paper we used orthogonal basis functions and expansion coefficients for inverse modeling of magnetic data. The basis functions chosen are normalized eigenvectors of second derivation of the objective function (Hessian matrix) calculate for an initial model. Limited number of basis vectors obtained ...
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In this paper we used orthogonal basis functions and expansion coefficients for inverse modeling of magnetic data. The basis functions chosen are normalized eigenvectors of second derivation of the objective function (Hessian matrix) calculate for an initial model. Limited number of basis vectors obtained in this way defines a new subspace in model parameters space. A new objective function is defined in term of these new parameters and minimized in subspace of original space. As in geophysical inverse problems we need to inverse matrixes that are functions data and geometry of data and model parameters. The matrix inversion in new subspace of the original space will be better conditions due to less dimensionality in the inversion. Since the most significant eigenvectors corresponding the largest eigen values in Singular Value Decomposition ( SVD) of matrixes. Others eigenvectors have less influence in fitting data or lead inversion procedures to local minima. With apply subspace method inversion will be fast and stable against the noise. The efficiency of the method is tested with synthetic and real magnetic data (acquired from Moghan area, north-west of Iran). The results proved fast convergence and stability of inversion against the noise.
