Study On The Application Of Borehole-to-ground Resistivity Method Detect Metal Ore

Electrical prospecting, as an important branch of geophysical methods, has played a key role in solving the problems in metal resources exploration, deep structure, hydrological and geological engineering, environmental protection and geological disasters. Traditional ground-to-ground pattern refers to surface supplying and surface receiving. The current density exponentially decay from depth, so, the resolution will rapidly decrease as the gradual increase in the depth of the target body. Compared to the ground-to-ground pattern, borehole-to-ground electrical method injects the high-current into the depths of the underground, then measures on the surface. The electrode can be quite close to the target body. We can obtain several sets of observational data with the different depths of the electrode. It will improve the imaging resolution of the target body as much as possible.In this thesis, we realized multi-channel resistivity acquisition by second development based on commercial potential of multi-channel acquisition module. The instrument provides support for borehole-ground resistivity synchronous acquisition.Through field practice, according to the actual situation and referencing from existing work standard of resistivity method, we establish a set of field work program suit for metal resources exploration by multi-channel borehole-to-ground resistivity method. We use averaging method and sorting method to separate and removal natural potential from manually potential in the original collecting data. In addition, we specify different processing windows and add noise of varying degree to verify the processing method. Then, the influence rule made by separated windows for separating and de-noising is summarized.For the three-dimensional borehole-to-ground resistivity forward modeling calculation, we solve the forward modeling problem with point source at different depths by finite difference method. The large sparse matrix equations in forward modeling problem are solved by super relaxation iteration method (SOR). By a large number of numerical modeling experiments, we have analyzed that how the positions of electrode affect the forward modeling results, which lays the foundation for inversion.For the three-dimensional borehole-to-ground resistivity inversion, we complete the inversion calculation by Gauss - Newton method. We use Quasi-Newton method to calculate and solve the Jacobi matrix in inversion calculation. It effectively improves the solution speed and ensures the inversion efficiency of large amount of data.Finally, the program was applied to the inversion calculation and comprehensive interpretation of measured borehole-to-ground resistivity method data of a multi-metal mining area in Inner Mongolia. The Comparison with the known geological information shows that the method can achieve good results.