Interpretation of magnetic data acquired on polymetal deposit of Oshvand and comparison results with resistivity and induced polarization by inverse modeling

Authors

1 M.Sc. Student, School of Mining, Petroleum and Geophysics Engineering, University of Shahrood, Iran

2 Assistant Professor, School of Mining, Petroleum and Geophysics Engineering, University of Shahrood, Iran

3 Expert in Geophysics, Exploration Directorate, Geophysical Survey of Iran, Tehran, Iran

Abstract

There are various approaches for depth estimation of anomalous potential field data. Spectral analysis of gravity and magnetic data has been used extensively for many years to derive the depth to certain geological structures, such as the magnetic basement or the Curie temperature isotherm. The interpretation of the gravity and magnetic data is preferred in frequency domain because of simple relation between various source models and fields. The estimation of the depth of anomalous sources is usually carried out by Spector and Grant method and its variants in frequency domain. This method, which assumes a uniform distribution of parameters for an ensemble of magnetized blocks, leads to a depth-dependent exponential rate of the decay. In the frequency domain, geophysical source parameters have been assumed as uncorrelated and randomly distributed. Assumption of the uncorrelated random sources is not true as revealed from many borehole data in the German continental deep drilling project (KTB) around the globe. Susceptibility data of pilot hole is analyzed and its power spectrum shows a generalized behavior. Therefore, the generalized spectral method for gravity and magnetic data, based on the realistic distribution of anomalous sources, is found useful for finding the depth values and statistical properties of the source distribution. The scaling spectral method has been applied in many parts of the world. An important aspect of this method is that the scaling properties of the source distributions are related to the scaling properties of the fields in a general way. This relationship can be used to derive information on local geology. A technique to estimate the depth to anomalous sources from the generalized power spectra of magnetic profiles is presented. The power spectrum corresponding to low wavenumber may be dominated by scaling properties alone rather than the depth values. If the logarithm of obtained power spectrum of potential field data that transformed in Fourier domain, is plotted versus wave number values, although some factors affect the plot, but the depth is a dominant factor. The depth various source is thus found from the slope of this plot. If there is more than one ensemble, the slope at smaller frequencies gives the depth to deeper sources, and subsequent slopes at higher frequencies give the depth of shallower source. The depth values calculated by this method are close to the realistic values. To test the reliability of any technique it is necessary for the technique to be tested on the synthetic data. In present research work, the efficiency of generalized power spectrum has been investigated using theoretical model of magnetic and the results have been compared with commonly power spectrum. At the end the generalized power spectrum method has performed well in the depth estimation of anomalous sources of magnetic data acquired on polymetal deposit of Oshvand located in Hamedan Province and the results compared with the commonly power spectrum, IP and RS methods. Based on the previous studies conducted in the area, our estimation of the depth of anomalous sources by means of generalized power spectrum approach has been evaluated and confirmed.
 

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References

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Journal of the Earth and Space Physics
Volume 41, Issue 2 - Serial Number 2
August 2015
Pages 193-204

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