Relationship between physical and mechanical properties of jointed rocks in Central Iran (Bafgh Block)

Abstract

Central Iran is one of the active mining zones of Iran and has great mining potential. Large iron mines such as Choghart, Chadormalu, Sechahoon, Chahgaz, Lake Siah, Mishdavan, etc. are located in this zone. Other metals also exist in this zone Like lead and zinc in Koushk, Chahmir and Taj-Kooh mines. Also, non-metallic deposits such as Fahraj limestone mines and building stone mines such as Bishedar marble, Taft travertine, Shirkooh granite, etc. are being extracted in this zone. Considering mineral resources and current explorations, the mines continue to develop and one of the important topics in the exploration and exploitation phase is the study of geomechanical conditions in the zone under study. The relationship between the physical and mechanical properties of rocks makes it possible to predict the strength of intact rock which can be used in preliminary designing of the mine at less cost and less time and just with some simple tests on exploratory boreholes and surface samples. It can also be used in mines under extraction to gain more comprehensive knowledge of the mechanical properties of mine rocks. In this study, mechanical properties such as uniaxial compressive strength, point load, indirect tensile strength (Brazilian) as well as physical properties of rock such as density, porosity, compressive wave velocity (P-wave) and electrical resistivity were measured on selected samples taken from Choghart, Sechahoon, Lakeh Siah, Koushk, Bishehdar marble, Taft travertine, Ravar sandstone and the cores of 5 geotechnical boreholes from the Anomaly VI of Central Iran Iron Ore and 4 geotechnical boreholes of Chahgaz iron ore mine. The purpose of these measurements is investigating the relationship between mechanical and physical properties of the samples, especially electrical resistivity. In the first step, 300 surface and depth samples were collected from the mines mentioned above. After preparing the cores, effective porosity and density were recorded according to the standards (weighing the saturated and dry sample method). Also, the electrical resistivity was calculated by measuring the voltage and electrical current in the samples. The results demonstrated that there is a high correlation between P-wave velocity and electrical resistivity in all the samples. Furthermore, both parameters of P-wave velocity and electrical resistivity are dependent on porosity, and electrical resistivity like P-wave velocity, has a good relationship with mechanical properties of sedimentary rocks and volcano-sediments. Hence, the special electrical resistivity can be used as a non-destructive test to estimate the mechanical properties of rocks. Additionally, the presence of metal ores in the samples in low percentages does not cause errors in estimating physical and mechanical parameters as long as density is less than 2.8 gr/cm3. For samples with high metal content, induced polarization measurements can reduce uncertainty of the electrical resistivity.