Geophysical research: article

Аnnotation: The results of studying the magnetotelluric method capability for reveling potential ore-bearing regions are presented. The investigations were carried out within the metallogenic zones of the Western Sayan and Tuva, for which data of dense magnetotelluric (MT) observations are available. Our study was greatly facilitated by the fact that earlier one of the authors had already considered in detail the problems associated with the analysis of experimental and model impedance matrices, the results of 1D and 2D inversions of maximal and minimal curves, the construction of starting geoelectric cross-sections, the analysis of the impedance matrix for 3D models. The setting of the structural and formational zones of the Western Sayan and Tuva and their ore mineralization are described. The methodology of 3D interpretation of magnetotelluric sounding curves is outlined. MT data interpretation involved the determination of striking of regional structures, of the phase tensor axes and of the impedance matrix dimension; the dispersion relations were verified for invariant maximal (minimal) experimental and model impedances; electrical noise from near-surface inhomogeneities was removed. The initial geoelectric model was constructed on the basis of 1D inversion of normalized curves of apparent electrical resistivity, and 3D mathematical modeling of MT fields provided the solution of the inverse problem, the calculation of electrical conductivity of vertical (faults) and horizontal crustal blocks, and the estimation of resolution of determining the parameters of the conducting blocks. The resulting 3D model was reconstructed using interactive fitting of 3D model curves to the experimental ones with an estimate of uncertainties. To reveal the potential ore-bearing areas, the electrical conductivity of blocks with known types of ore occurrence was first determined, and then these types of minerals were associated with the low-resistivity blocks in the given structural unit. As a result, 3D geoelectric models of the metallogenic zones of the Western Sayan and Tuva were constructed. It is shown that the areas of hydrothermal mineralization are concentrated near the deep faults characterized by a low electrical resistivity related to an increased content of fluid in the pores and matrix of rock formations. Using this indicator together with the data obtained in the adjacent areas of the Altai-Sayan region, potential ore-bearing zones were identified.