نوع مقاله : مقاله تحقیقی (پژوهشی)
دانشکده مهندسی معدن، دانشگاه بیرجند، ایران
عنوان مقاله [English]
Geophysical data inversion has a prominent role in geo-structural investigations. In this study, the corrected geophysical data of Doroh mining area were modeled to obtain the underground body's shape and other parameters such as susceptibility. At first, magnetic data were filtered and then modeled by the magnetic compact inversion method (Last & Kubik) and properties including depth, susceptibility and the deposit shape were provided. This inversion can be described according to basic principles to minimize the cross-sectional area of the sources. The under-surface area was divided into horizontal prisms with an extreme length and fixed magnetic susceptibility. The simulation was performed using synthetic magnetic anomalies generated by compact bodies embedded in an inducing magnetic field. It was shown that this modeling was capable of solving underdetermined problems with good accuracy in the presence of moderate noise data. At first, a MATLAB code was employed to implement the algorithm. The output results from the synthetic model demonstrated the accuracy of the code. The code was then applied to real magnetic data. The results showed acceptable accuracy.
A statistical analysis was also carried out on the IP&Rs normalized data. Normalization was done because the statistical analysis was tender to data dispersion. Therefore, the outlier data was identitfied by a box plot of SPSS software and replaced using the Q method. Then the correlation coefficient was used to determine the dispersion extent. The statistical analysis showed a compact and rich body under the surveyed profiles. Then for providing more information on this area, apparent resistivity and induced polarization data were modeled by the RES2DINV software. RES2DINV is a computer program that automatically creates a two-dimensional resistivity model for the electrical data of the subsurface. In this software, the under-surface area is divided into horizontal prisms with an extreme length. In some situations, particularly where there are large resistivity variations near the ground surface, better results can be obtained by using narrower model cells. In almost all cases, this gives the optimum results. A forward modeling subroutine was used to calculate the apparent resistivity values, and a non-linear least-square optimization technique was used for the routine inversion. The program supports both finite-difference and finite-element forward modeling techniques.
The studied area is located in Flysch zone in the Southeast of Doroh City in Sarbishe in the South Khorasan Province. Lithology of this area includes shale, sandstone and thin layer limestone, here and there. In this area, magnetic surveys were done via 40 profiles with a north eastern-south western strike and 1200 survey points. Apparent resistivity and induced polarization surveys were done in five profiles with a dipole-dipole array and 700 survey points. The magnetic consideration results showed three compact bodies under the surveyed profiles which were named A, B and C. The depths of these bodies were 80 – 100 meters. The results of IP & Rs modeling showed that these anomalies were located near the surface and are dyke-shaped. The results of magnetic compact inversion methods and modeling are in agreement with IP & Rs inversion results. For an exact review of this body, a few point were eventually proposed for drilling.