Determination of groundwater and geological factors using geoelectrical methods to design a suitable drainage system in Gol-e-Gohar iron ore mine, Iran

摘要

Various problems caused by the presence of underground water in Gol-e-^sGohar iron ore mine have made mining experts seek proper solutions. One of the best solutions is to make a suitable drainage system for leading the mine waters to an area outside of the mine limits. However, the groundwater situation and geological structures such as active faults present in the mining area should be, first, recognized and then considered carefully for designing an optimal drainage system. Since the presence of groundwater has almost stopped the mining operations in the main area (area No. 1) of Gol-e-Gohar mine, area No. 3 of this mine, which contains the largest iron ore deposit in southern Iran, has been considered for mining. Due to the expected negative influence of subsurface water on the mining activities in this area, a suitable drainage system should be installed before mining operations are commenced. Geoelectrical surveys using resistivity methods have been carried out in the area to determine subsurface geological features such as faults, depth to bedrock, and lithologic specifications of geological layers, and the groundwater situation (e.g. porosity or permeability, depth and thickness of waterbearing formation). Alluvial overburden and moderate topographic conditions in area No. 3 of Gol-e-Gohar mine have made it practically easy to apply the resistivity methods in the area. The above-mentioned groundwater and geological factors can be determined accurately as a result of correct interpretation of the measured resistivity data. A square grid of 500 m by 500 m was considered to cover the study area thoroughly for resistivity sounding surveys carried out using the Schlumberger electrode configuration with maximum electrode spacing of 1400 m. One-dimensional (1-D) interpretation of the sounding data showed the depth to water table to be 40-60 m with an average thickness of 20-30 m for the water-bearing formation in the area. The resistivity of the waterbearing formation was estimated to be 15-23 OMEGA -m, indicating high electrical conductivity (EC) of groundwater (due to high salinity and concentration of total dissolved solids (TDS) in groundwater) and clay content in the formation. These results were confirmed by 2-D section interpretation. Low correlation between the results of sounding in different places in the study area can be attributed to complex geology, especially various faulting systems in the area. To investigate lateral resistivity changes and faulting systems, it is recommended to carry out resistivity profiling in the area. Using other geoelectrical methods, such as induced polarisation (IP) and self-potential (SP) methods, the ambiguities arising from the interpretation of resistivity data can be removed or reduced.