جستجوی مقالات مرتبط با کلیدواژه "مغناطیس هوابرد" در نشریات گروه "زمین شناسی"

The Malayer-Esfahan metallogenic belt hosts large deposits of Zn-Pb with sedimentary host rocks. In addition to Zn-Pb mineralization, Cu, Cr, Au, Fe, Mn, W have been mineralized in this area with different host rocks. In the present study, using airborne magnetic data, promising mineral areas in Malayer-Esfahan metallogenic zone have been introduced. Using reduction to pole (RTP) filters, signal analytical and vertical derivative were processed and airborne magnetic data were interpreted. The map derived from the vertical derivative is considered as the final map to identify anomalies resulting from airborne magnetic data. Due to the sedimentary nature of the Malayer-Esfahan area and the fact that the minerals in the rocks of this area usually have low magnetic properties, the anomalies obtained from the airborne magnetic data showed a relative overlap with some the Zn-Pb deposits in the area; According to this case, the anomalies obtained in this study can be used to identify iron reserves other than Zn-Pb in this area. Anomalies resulting from the vertical derivative filter with iron deposits more than Zn-Pb deposits such as Shams-Abad and Akhtarchi Fe deposits, Astaneh and Muteh Au deposits, Rousht W deposit, Ghaleh-Arab Cu deposit, Ahangaran Zn-Pb deposits, Saleh-Payghambar, Ab-Bagh, Dardahaneh, Khan-Abad, Lakan and etc show overlap. In general, the results of this study showed that in the northwestern, central, and southeastern parts of the Malayer-Esfahan metallogenic zone, there are areas as new and hidden anomalies that can be used for sampling of promising mineral areas by sampling and spectroscopy.

Geophysical methods are suitable methods for prospecting and exploration of mineral deposits. Using two or more exploratory methods together and combining them with other information such as geological studies can increase the probability of discovering and reaching promising areas. According to the evidence of metallic and sulfide mineralization in the study area (the exploratory area of Pirmardan), the use of magnetic, induced polarization (IP) and electrical resistivity (Res) for prospecting and exploration of the mineralization in the area is of great importance. The position and the spatial relationship between mineralization and lineaments have long been considered by geologists. Airborne magnetic data and geological information are used to diagnose and distinguish the general trends of structures, lineaments, and large faults using tilt filter on magnetic data. By processing and interpretation of the airborne magnetic data of the region, the existing structures in the region have been investigated. Moreover, considering the available geological information in the region, the induced polarization and the electrical resistivity data have been acquired using the rectangle arrangement to detect the subsurface anomalies and also using the dipole-dipole arrangement along two survey lines to obtain the lateral and depth extension of the anomalies. Airborne magnetic data processing has been performed using Oasis Montaj software, and also, processing and modeling of induced polarization and electrical resistivity data have been carried out using RES2DINV and ZONDRES2D software packages. The final results obtained from the interpretation of airborne magnetic, induced polarization and electrical resistivity data confirm the relationship between lineaments and the probability of hidden copper reserves in the study area. These results have led to propose five spots for exploration drilling.

The magnetic data collected from airborne surveys need to be interpreted after processing. The most important information gathered from the interpretation stage, is the depth and horizontal position of anomalies. Various methods are developed for gathering these data. One of these methods is Euler deconvolution that is based on Euler’s homogenous equation. Euler's method is one of the fastest semi-automatic methods for determining the depth of buried magnetic and gravity anomalies. Its results are highly dependent on the structural index, Euler window size, and depth calculation error. This method identifies the depth and trend of changes in the depth of anomalies very well. The geological information of the study area is important for the application of this method. In this method, the potential field and its first-order derivatives are used in different directions to determine the position and depth of the potential field source. In this paper, by using this method, the depth, and boundaries of anomalies in the Lake Blatchford area of Canada are investigated. The obtained results indicate that most anomalies in this region have shallow to medium depth.

  The East Azarbaijan geothermal area is located in northwest of Iran, which hosts several hot springs. It is situated mostly around the Sabalan and Sahand mountains. The Sabalan and Sahand geothermal area is now under investigation for the geothermal electric power generation. It is characterized by high thermal gradient and high heat flow. In this study, our aim is to determine the fractal parameter and top and bottom depths of the magnetic sources. A modified spectral analysis technique named “de-fractal spectral depth method” is developed and used to
estimate the top and bottom depths of the magnetized layer. A mathematical relationship is used between the observed power spectrum (due to fractal magnetization) and an equivalent random magnetization power spectrum. The de-fractal approach removes the effect of fractal magnetization from the observed power spectrum, and estimates the parameters of the depth to top and depth to bottom of the magnetized layer using iterative forward modelling of the power spectrum. This approach is applied to the aeromagnetic data of the East Azarbaijan Province. The obtained results indicated variable magnetic bottom depths ranging from 9.8 km to about 16.8 km. In addition, the fractal parameter was found to vary from 1.6 to 3 within the study area. The interpretation of potential fields is generally carried out in the frequency domain due to (1) simplicity in the implementation of signal processing tools, and (2) easy and concise characterization of potential field signals caused by a large variety of source models. In the frequency domain, the geophysical source parameters such as density have been assumed as uncorrelated distribution. To the contrary, source distribution of the physical parameters is correlated following the scaling or fractal laws. Fractal source distributions have power spectra proportional to , where k is the wave number (i.e. length of the wave vector) and β denotes the respective fractal parameter. This has been discovered by the detailed analysis of the densities
and susceptibilities of several borehole data around the world including the German continental deep drilling program in southeastern Germany. The fractal parameter reflects the proportion of long and short wavelength variations of a signal. The higher the value of the fractal parameter, the stronger is the relative intensity of the long wavelength variations of the signal. The main objective of the current work is to develop an algorithm for estimation of the fractal parameter using a defractal spectral analysis of the aeromagnetic data from the study area in order to determine the bottom depths of magnetic sources. This approach for analysis of magnetic data assumes that the observed power spectrum is equivalent to the random magnetization model multiplied by the effect of fractal magnetization. It is believed that the de-fractal method can reduce the ambiguity related to the selection of fractal parameter to provide an estimate of bottom depths of magnetic sources more reasonable than the estimates using conventional methods. However, the ability of the de-fractal method has not been verified so much in practical exploration applications. Hence, in this work, an attempt has been made to use this approach to remove the effect of fractal magnetization from the power spectrum of real magnetic data to have a reasonable depth estimate of magnetic sources. In the last four decades, variations on several methods have been proposed and applied for estimation of the bottom depths (zb) of magnetic sources using azimuthally averaged Fourier spectra of magnetic anomalies. The mathematical formulae of these methods are based on assumptions of flat layers with particular distributions of magnetization, namely: 1) random (uncorrelated) magnetization models or 2) self-similar (fractal) magnetization model. The idea of using models with fractal magnetization distribution comes from the concept of self-similarity. The de-fractal method is based on the assumption that the observed power spectrum is adequately represented by a simplification of the fractal magnetization power spectrum where the magnetization in the x and y directions is fractal and is constant in the z direction. In this case, the observed power spectrum is equivalent to the result of power spectral density of the random magnetization model multiplied by k-α. Having removed the fractal effect, one can treat the resulting de-fractal power spectrum as though it was the power spectrum of a random magnetization model. The present approach can be considered as a correction to the power spectrum of the magnetic field for the fractal distribution of magnetization. In this work, we have determined the bottom depths to magnetic sources using de-fractal spectral analysis method. This method applies a transformation to the observed magnetic field based on an estimated fractal parameter such that the power spectrum resembles the power spectrum that would be generated by a random magnetization distribution. The advantages of this method are that the range of the feasible de-fractal parameters can be estimated, and the bottom depths of the magnetic sources or anomalies are obtained based on simultaneously estimating the depth values from the centroid method and visual inspection of the forward modeling of the spectral peak. The method has been applied to 50% overlapping 11 blocks having 100 * 100 square km dimensions of aeromagnetic data in Ardabil area. As a result, the fractal parameter has been determined between 1.6 and 3 The obtained results also indicate that the bottom depths of
sources of the magnetic anomalies vary from 9.8 km to about 16.8 km.

Summary To optimize the widespread use of fossil fuels in Iran, different resources of renewable energy can be considered as promising challenges. The everincreasing energy demands of the country can be satisfied by the very rich resources of renewable energy such as wind, solar, biomass, and geothermal energies. This paper presents the results of Curie point depth calculations from spectral analysis of aeromagnetic data for preliminary exploration of geothermal resources in central region of Kerman Province. The calculations were performed for an area of 22010 km2 located north of Jiroft city and east of Baft city. RTP correction and band pass filtering were first applied to the data. Then, the block dimension of 80×80 km with an overlap of 50% was selected for the spectral analysis. The spectral power was calculated for all the blocks and the Curie depth map was obtained for the study area. The results showed that the shallowest Curie depths are about 9 km observed in the southeastern part of the study area. Different information layers including geological and surface information layers were, then, onvestigated in the ArcMap software. Concentration of several hot springs and presence of faults, intrusive structures, and volcanic rocks prove a high probability of geothermal anomaly in the area of shallowest Curie depth.
Introduction Although there are evidences of rich geothermal potential regions in Iran, very few exploration studies have been carried out so far, especially in the eastern and central regions of the country. Geothermal heat flux is one of the main parameters to be investigated in geothermal exploration programs but few direct heat flux measurements are available in Iran. Given the proved relation between Curie depths and heat flux, we can use magnetic data to calculate the Curie depths in areas where few or no direct heat flow measurements are available. Hojat et al. (2016) used an iterative forward modeling approach to calculate the Curie depth of Kerman province from satellite magnetic data. The obtained Curie map revealed an area with very shallow Curie depth in the southeastern region of Kerman province. Their finding was confirmed by geological evidence for the probability of a geothermal potential zone. In this paper, aeromagnetic data are used to calculate the Curie depth map for an area of 22010 km2 located in the central region of Kerman Province, part of which overlaps with the probable geothermal zone revealed from the previous study.
Methodology and Approaches The aeromagnetic data have first been processed in the Oasis Montaj software. The IGRF model has been used to remove the main field from the observations. RTP and Bandpass filtering have then been applied to the data. The block dimension of 80×80 km with the overlap of 50% has been selected for the spectral analysis method. After calculating the Curie depth map of the study area, different information layers including hot springs, faults, intrusive bodies, and volcanic structures have been combined in the ArcMap software to validate the interpretation of the results.
Results and Conclusions 1. Curie depth values were obtained in the range of 9-9.9 km. 2. The shallowest Curie depths occurred in the southeastern part of the study area. 3. The main concentration of hot springs, intrusive bodies, and volcanic structures was in the area with the shallowest Curie depths. 4. It is suggested to perform detailed land surveys in the most probable area detected in this study.