نشریه پژوهش های ژئوفیزیک کاربردی
پیاپی 1 (بهار و تابستان 1394)

Summary There are several important factors to be determined in heap leaching operations such as the depth of pregnant leach solution (PLS) within the heap, saturated and unsaturated zones, and the quality of the solution in different parts of the heap. In this paper, integrated geophysical surveys including electrical resistivity, induced polarization (IP) and ground penetrating radar (GPR) methods were used to investigate the internal structure of heap No. 3 at Sarcheshmeh copper mine. The main purpose was to determine acid saturated zones and investigate the preferential flow paths within the heap. To do this, acid sprinkling on pad No. 903 of heap No. 3 in Sarcheshmeh copper mine was stopped for ten days before doing geophysical surveys. Geophysical field data were collected along five parallel lines. Due to the small area of pad No. 903, spreading of the electrode array for resistivity and IP measurements was limited, thus, that maximum depth of 20 m was investigated. The depth of investigation in the GPR method was also reduced as a result of radar wave attenuation in high conductive subsurface material. PLS saturated zones of the heap, dry zones and solution paths were finally determined based on the results of field data interpretation and the results obtained from laboratory resistivity measurements carried out before making geophysical surveys.
Introduction Considering the advantages of the hydrometallurgical methods, copper production industry is growingly using these methods. In heap leaching process, low-grade copper ores are exposed to sulfuric acid percolating down through the heap and solving the copper. The PLS is then collected at the bottom of the heap to be processed for the extraction of the metals. Knowledge of the saturated and unsaturated zones within theses heaps is one of the most important problems to be understood. Geophysical surveys, considering their great advantages such as being non-destructive, efficient, rapid and cost effective, are a very good alternative compared to the expensive and local drilling operations. Electrical methods are especially useful in such application because there is an electrical contrast between saturated and nonsaturated zones. Therefore, in this research, electrical resistivity, IP and GPR methods have been used on a test part of heap No. 3 at Sarcheshmeh copper mine to investigate subsurface solution behavior.
Methodology and Approaches Application of the heap leaching technology to extract low-grade copper ores was decided by the National Iranian Copper Industries Company (NICICO) in the 1990s. There are now six heap leaching utilities constructed at Sarcheshmeh copper mine and the copper is being leached with dilute sulfuric acid. In order to provide favorable electrical measurements, acid sprinkling on pad No. 903 of heap No. 3 was stopped for ten days before acquiring the electrical data, comprising of resistivity, IP and GPR data, along five parallel profiles on the heap surface. 2D resistivity and frequency-domain IP surveys employing the Wenner-Schlumberger electrode array were carried out using ASTRA-100 transmitter and Mary-24 receiver. The electrode spacing of 5 m was selected for these surveys. Frequency values of 0.61 and 9.8 Hz were applied for the IP data acquisition and as a result, the percent frequency effect (PFE) was calculated. In order to have a good GPR penetration, the 50 MHz LOZA GPR system with the antenna length of 3 m was used in the GPR surveys.
Results and 1. The electrical resistivity values were obtained in the range of 2-13 Ω-m, in which the higher values were likely related to low moisture and dry zones. The acid saturated zones were determined as the areas having the lower electrical resistivity values in the range.
2. Low resistivity values extending to the deeper parts of the pad revealed the preferential flow paths of the leaching solutions
3. PFE values were in the range of 0.5-14 % in which the higher IP values were the result of mineral concentration and saturation in the area.
4. Due to the small area of pad No. 903, spreading of the electrodes used for resistivity and IP measurements was limited, and as a result, maximum depth of 20 m was obtained.
5. Maximum GPR depth of investigation of about 30 m was obtained as a result of radar wave attenuation in high conductive material within the heap.
6. Among the performed geophysical methods, the electrical resistivity method was determined as a superior one in comparison to the IP and GPR methods used for monitoring of the heap leaching in the subsurface.

Summary The Strait of Hormuz is a narrow waterway, which restricts water exchange between the Persian Gulf with the Gulf of Oman. This strait is exposed to inflow of Indian Ocean surface water and outflow of saline bottom water formed in the Persian Gulf. This water exchange leads to magnetic anomaly, which affects the
measured geo-magnetic field. In this research work, first, the marine currents in the Strait of Hormuz have been simulated using MIKE21 numerical model. Then, using extracted currents and appropriate relations the induced magnetic field due to marine currents has been calculated. The results show the space and temporal variability of current induced magnetic field in the study region. According to the study results, the maximum amount of vertical component of magnetic field in the study region varies between 0 to137 nT, while this amount for horizontal component of magnetic field varies between 0 to 153 nT.
Introduction Todays the applications of marine geo-magnetic field have been increased in several fields such as marine navigation, subsurface detection, etc. These applications cause to focus on the natural factors, which have direct impacts on marine geo-magnetic field. Among these natural factors, ocean or marine currents play a specific role on electromagnetic induction, and thus, influence ocean induced magnetic field, because of high electrical conductivity of marine waters and the dynamic impact of ocean currents. In the Iranian water, the Strait of Hormuz plays an important role on the magnetic field due to marine currents because of its complex regime of currents and its specific location. Therefore, this region has been selected for this study.
Methodology and Approaches In this research, the bathymetry map of study region has been obtained from GEBCO Database. Then, grid generation and interpolation of these data have been carried out using the mesh generation subroutine of MIKE21-MIKE ZERO software package. This mesh has been produced for introducing of geometry and bathymetry problems and includes irregular triangle elements. The final mesh, which has been used in this model, includes 49819 elements and 27915 nodes. In the produced model of the region, there are two open water boundaries at west and east of the Strait of Hormuz and two dry boundaries at south and north of the Strait. The required information for these boundaries has been forced to the model in the form of a data file, in which the data varies with time and space along the boundaries. The boundaries information is in format of P and Q parameters, which introduce the eastward and northward components of flow. After implementation of the model, for calculating the components of current induced magnetic field we use the model output data of flow and related formulation between components of magnetic field and components of flow.
Results and Conclusions According to the study results, the maximum amount of vertical component of magnetic field in the study region varies between 0 to137 nT, while this amount for horizontal component of magnetic field varies between 0 to 153 nT. In general, we can conclude that two factors of surface currents velocity and subsurface volume flow rate are the major factors influencing the magnetic field oscillations in the study region.

Summary Geo-electromagnetic (EM) forward modeling is a scientific accepted tool for understanding complex behavior of EM wave in the earth, and can be used for the purpose of inverse modeling, and also, for evaluation of geological interpretations based on EM field measurements. There are different EM forward modeling programs, which are capable of computing responses of electric and magnetic components of the EM field, generated from different dipole sources with variable source-receiver configurations. In this paper, an available forward modeling algorithm, coded in Fortran 77 and called “EMDPLER”, is used for computing frequency domain response of the vertical magnetic component of the EM field, generated from a horizontal magnetic dipole source over different one-dimensional (1-D) layered Earth models. Thus, by conducting the forward modeling code on different 2- and 3-layer earth models with different resistivity and thickness values, real and imaginary parts of vertical component of the secondary magnetic field (Hz), its phase variations, and normalized amplitude of the ratio of secondary to primary component of the vertical magnetic field (Hz/Hz0) in case of considering/ignoring the displacement currents, are calculated and plotted as a function of frequency.
Introduction Considering EM primary source, EM methods are divided into two groups: 1. EM methods with natural sources that incorporate natural electric and magnetic fields of the earth, and 2. EM methods that incorporate man-made sources. The man-made EM sources, which transmit either transient currents or continuous sinusoidal waves, have variable physical, electronic and geometric specifications. In EM-geophysics, continuous sinusoidal wave transmitters are known as frequency domain EM (FDEM) sources. Based on geometry and shape, FDEM sources are categorized into four common types: 1. vertical magnetic dipole (VMD), 2. horizontal magnetic dipole (HMD), 3. vertical electric dipole (VED) and 4. horizontal electric dipole (HED). A horizontal transmitting loop or a small vertical transmitting loop of wire that carries alternating current, if distance to observation point is five times greater than length of the loop radius, can be treated as HMD or VMD source, respectively. A source, consisting of a short wire and carrying an alternating current, can be treated as an electric dipole, if the distance to the observation point is at least five times greater than the cable length. For a FDEM source that generates EM field only in transverse magnetic (TM) mode, e.g. a vertical electric dipole, the tangential magnetic field at the earth surface is double the primary field, while the tangential electric field is zero and the earth appears to be a perfect conductor; hence, in practical geophysics only dipole sources that generate primary EM field in transverse electric (TE) and/or TE and TM modes simultaneously, are used as transmitter. In recent years, electronic and software developments in designing EM instruments have resulted in gathering more reliable field datasets, but despite to many successful progresses in the area of forward modeling and inversion of the EM geophysics, it is still a challenging and interesting area of work for the geophysicists. At present, there are different EM forward modeling programs, e.g. EMDPLER which is capable of computing response of electric and magnetic components of the EM field, generated from the most common dipole sources with variable source-receiver configurations.
Methodology and Approaches In this paper, by considering a Cartesian system (x,y,z) with vertically downward directed z-axis and an x-directed HMD carrying an alternating current (I) and the dipole moment m, frequency response of magnetic components of EM field from an isotropic non-magnetic layered earth in observation point is thoroughly formulated in SI units. Moreover,an FDEM forward modeling algorithm, coded in Fortran 77 and called “EMDPLER”, is used for computing frequency domain response of the Hz components of the EM field from different 1-D layered earth models. Computations of this program are performed by assuming variable transmitter-receiver configurations and considering displacement currents in the frequency range (50 KHzResults and Conclusions In this paper, by referring to scientific references, frequency response of the magnetic components of EM field, generated from an HMD source, from an isotropic non-magnetic layered earth in observation point is concisely formulated. Moreover, by conducting the EMDPLER forward modeling code on different 2- and 3-layer earth models with different resistivity and thickness values, real and imaginary parts of vertical component of the secondary magnetic field (Hz), its phase variations, and normalized amplitude of the ratio of secondary to primary component of the vertical magnetic field (Hz/Hz0) in case of considering/ignoring the displacement currents, are calculated and plotted as a function of frequency. This paper can provide geophysicists with the idea of computing other magnetic components of the secondary EM field in the case of layered earth models, and also, 1-D inversion of these components. Moreover, the results of the present paper would guide geoscientists for better geological interpretation of the models based on the EM field measurements.

Summary Nowadays attempts to detect and achieve buried structures and underground resources have developed widely and geophysics is a means of identifying these structures. One of the main goals of geophysical data interpretations, is to incorporate additional information to the process of inversion in order to define the characteristics of geological structures as precisely as possible. In this paper, a three-dimensional (3-D) constrained inversion of gravity data acquired from Qom salt dome using Grav3D program is presented, and then, the results are compared with the results of 3-D constrained inversion of the data using constraints including smoothness, positivity, reference model and bounded model. For testing the algorithm, a step by step constraint inversion including smoothness, positivity, reference model and bounded model has been performed on an artificial model, and then, the algorithm has been used for modeling the gravity data acquired from Qom salt dome.
Introduction The recent ability to produce 3-D models of the sub-surface, coupled with an increasing need to explore concealed resources, results from geophysical inversions that provide more and more significant information to the explorers. Since our country is rich in mineral resources, the use of optimized modern and efficient methods to prevent additional costs in exploring these resources is very important. Thus, in the first step of this exploration procedure, we should try to collect as much information as possible about the underground structures. In this direction, 3-D modeling of geophysical data can lead to successfully interpreting the data. The outcome of modeling is to have a better understanding of target such as the shape and depth of source. Finding these specifications of the source directly influences the subsequent decisions for management of major costs.
Methodology and Approaches The inversion method, used in this paper, is based on the inversion algorithm developed by Li and Oldenburg. As a result of inversion of gravity data, the geometry of source or anomaly and also density contrast between the anomaly and the background are determined. In the inversion algorithm used in this research, the earth is modeled using a large number of rectangular cells of constant density, and the final density distribution is obtained by minimizing a model objective function subject to fitting the observed data. The model objective function has the flexibility to incorporate prior information, and thus, the constructed model not only fits the data but also agrees with additional geophysical and geological constraints. A depth weighting is applied in the objective function to counteract the natural decay of the kernels so that the inversion yields depth information. Incorporating additional information to the process of inversion is the strength of this algorithm which can be done with different constraints such as smoothness, positivity, reference model and bounded model. Constrained modeling leads inversion towards the production of logical models and as a result, the validity and reliability of the final model will increase.
Results and Conclusions For optimized use of the algorithm, at first, it has been tested on synthetic models in which the synthetic gravity data have been contaminated with noise. Then, according to the accommodation of the results with the right model, the algorithm has been used for inversion of real gravity data, acquired from Qom salt dome, and then, the final results have been visualized. The inversion results indicate that Qom salt dome has lengthened to the depth of at least 4500 meters beneath the earth surface.

Summary An approximation of the reflection coefficient in seismic imaging condition is described by dividing the upgoing wavefield to the downgoing wavefield in the image point. Calculation of the reflection coefficient would be unstable wherever downgoing wave field equals or is close to zero. The imaging conditions will be distorted in the presence of the lateral velocity change. In this study, we have used the strategy of smoothed imaging condition in the Gaussian beam (GB) imaging method. The new operator has been changed in order to handle lateral velocity change. Different imaging points, distributed on a non-circular imaging operator, have been analyzed by coherency analysis. The point that gives the highest coherency would be selected as the final imaging point. The new strategy has been applied on synthetic and real land seismic data. Results of the synthetic data have been promising in the final image. The real data have been processed by three different velocity models. These velocity models have been obtained by different velocity functions to model velocity changes in different levels. The final image has proved that smoothing imaging condition can handle the lateral velocity change in the propagation media.
Introduction Different methods and strategies have been introduced to handle the problem of imaging condition. In one study, the focal surface imaging method has been introduced for imaging in complex media. The imaging condition is evaluated in common offset domain rather than the zero offset domain. By this strategy, the imaging condition would be evaluated in a surface of points instead of a single one. Thus, the errors in these conditions will be distributed in different points and the final imaging point is selected by coherency analysis. In other study, thick rays have been used to reduce errors in imaging condition. The concept of thick rays has also been used to introduce the GB migration method. To better resolve the problem, imaging condition smoothing in wavefield propagation has been used to handle the lateral velocity change. In this study, the smoothing strategy is used in the GB imaging method.
Methodology and Approaches The GB imaging operator is an isochrone that is produced by a set of beams which will be propagated forward for shot wavefield and backward for receiver wavefield. The imaging is located on the isochrones, exactly in the cross point of the shot wavefield and receiver wavefield central beams. By smoothing the imaging condition, the imaging operator is not an exact semicircle, but could have any shape. This iscochrone is created by beams propagated in the media with lateral velocity change. Then, different points are selected as the image point on this operator. By a simple coherency analysis, the point that gives the highest coherency would be selected as the final image point.
Results and Conclusions The smoothing strategy has been applied on synthetic and real land seismic data set. The synthetic data have been created by ray tracing technique on a velocity model having constant velocities on layers. However, complex structure of the model will produce the desired lateral velocity change in the media for wavefield propagation. The results of applying the strategy on free noise data and data contaminated with noise have been promising. To better understand the effect of the lateral velocity change in the media, the real land data set has been imaged by three different velocity models. These velocity models present three different degrees of velocity change, small, mild and high. Imaging with velocity model having small velocity change has been unable to accurately focus the reflectors. The velocity model with high lateral velocity change has also been unable to image minor truncations in the reflectors. It is may be due to the simple coherency analysis used. The final image obtained by the velocity model with mild lateral velocity change, however, has been promising as it contains better image of the faults, reflector truncations and more preserving of the continuity in the reflectors.

Summary In the 1970s, with the appearance of digital systems and the collection of large amounts of gravity and magnetic field data, a new era was started in developing interpretation techniques of potential field geophysical data. New automated inverse techniques were widely adopted for interpretation of gravity and magnetic profile data based on two-dimensional (2-D) models such as the thin sheet, thick dike, geological contact, polygonal bodies and dike. The tilt angle (TA) and its horizontal derivative are termed alternatively in the literature as local phase and local wavenumber, respectively, as these methods are closely associated with analytical signal definition of a potential field anomaly. In this paper, we use derivative ratio method to estimate the depth and location of magnetic dyke anomalies. This method has been applied on synthetic magnetic data as well on real magnetic data from a mining region in Sirjan area.
Introduction Tilt angle, a relatively newly defined attribute of potential field data, is becoming increasingly popular among geoscientists for interpreting potential field, especially, the magnetic data. The power of the tilt angle in delineating body edges and, especially, the linear structures from a high resolution magnetic anomaly image in the tilt angle domain has been demonstrated by Thurston and Smith (1997), Salem et al. (2007, 2005). They have explained that high resolution attained in a tilt angle image is mainly due to a high dynamic gain attributed by the natural property of the arctangent function, the value of which ranges between −90° and 90°. A buried fault is a common geological structure of interest in many geophysical applications. Geophysical signature of the fault is often subtle in total magnetic intensity images, where TA, which is a derivative field, should be an important tool for interpretation. Both normal and reverse magnetic anomaly of a fault can be modeled using a dike model. One of the most important specifications of such models is the variation of the vertical and horizontal derivatives directly on top of the body. Estimation of the depth and horizontal location of the anomaly play an important role in magnetic data interpretation. There are varieties of methods which can be used for definition of anomalies. Many of these methods are model-dependent, namely the estimation equation is dependents on individual geometrical models.
Methodology and Approaches Dykes are thin sheet-like intrusions of igneous rock that can have lateral extents of up to several 100 km. They are often strongly magnetic, and as a result, are clearly visible in images of aeromagnetic data. Depending on the situation, detailed modeling may be necessary to determine their locations and dips, and this can be time-consuming. A semiautomatic method for the interpretation of magnetic dyke anomalies, based on ratios of the gradients of the anomaly, is presented in this paper. The method is applicable to dykes with dips of multiples of 45 degrees.
Results and 1. The ratio between vertical and horizontal gradients of the magnetic anomaly related to dykes can be used to estimate depth and location of the subsurface bodies.
2. The problem of noise enhancement in the computation of the gradients can be solved via two approaches: a. acquiring the vertical and horizontal gradients in the field by magnetic gradiometer or b. calculating the vertical derivatives (amplifying noise more) by means of Hilbert transform. The Hilbert transform is more stable than fast Fourier transform (FFT) and the results are more consistent.
3. The method is applicable to thin dykes with dips of multiples of 45 degrees. Obviously, if any of the assumptions inherent in the method are invalid (i.e. the anomalies are not from thin dykes, the dip angle is not a multiple of 45 degrees or the magnetization vector is not vertical) then the results will be incorrect.
4. The sensitivity of the method to the dip of the dykes and to the departure of the geomagnetic field from the vertical has been investigated.
5. The method has been tested on synthetic magnetic data and on real magnetic data from Sirjan mining region.