Inverse modeling of resistivity and induced polarization data for Copper mineralization exploration in Chahshen area, east of Miami, Semnan

Document Type : Research Article

Authors

• Hossein Riahipour ¹
• Alireza Arab-Amiri ²
• Fereydoun Sharifi ³

¹ M.Sc. Student, Department of Exploration, Faculty of Mining, Petroleum and Geophysics, Shahrood University of Technology, Shahrood, Iran

² Associate Professor, Department of Exploration, Faculty of Mining, Petroleum and Geophysics, Shahrood University of Technology, Shahrood, Iran

³ Ph.D., Department of Exploration, Faculty of Mining, Petroleum and Geophysics, Shahrood University of Technology, Shahrood, Iran

10.22067/econg.2023.81784.1073

Abstract

In recent decades, various methods have been developed for mineral exploration. Geophysical methods are one example, which have seen significant development in recent years and have become a common approach in the field of mining exploration, particularly in Iran. The objective of this study is to investigate the exploration area of Chahshen in terms of the potential for copper mineralization using geophysical methods and to identify promising areas for drilling. During field visits, it was observed that the main mineralization on the surface is of the oxide type, specifically malachite and azurite. Therefore, to explore the potential expansion of sulphide mineralization at greater depths, induced polarization and resistivity methods were employed. For this purpose, a rectangular array with a data collection distance of 20 meters and a line distance of 40 meters was used to determine the general trends in the region. Subsequently, six profiles were designed and measured using dipole-dipole and pole-dipole arrangements at 20-meter intervals. Through modeling of the studied sections, two-dimensional models depicting chargeability and resistivity were generated. The two-dimensional models indicated that the eastern regions exhibited more anomalies. However, due to the relatively weak nature of these anomalies, the possibility of developing a sulphide zone at shallow depths was detected. To validate the obtained results, drilling points were proposed. Profile 1 suggested a drilling point at station -10 with a depth of 45 meters, while profile 2 proposed a drilling point at station -10 with the same depth.
 
Introduction
Iran possesses significant mineralization potential, although only a limited number of cases have been discovered and exploited thus far. Given the rising demand and the scarcity of exploratory information available, it becomes imperative to expand and enhance exploratory studies. This article focuses on a specific area located in the eastern part of Semnan province, covering approximately 30 square kilometers, known as Chahshen. The objective of this research is to assess the potential for copper mineralization in the region through the application of geophysical methods.
 
Methodology and Approaches
To conduct exploratory studies in the Chahshen area, geophysical methods, specifically Induced Polarization and Resistivity methods, were employed. The equipment utilized included a TX III transmitter model manufactured by GDD company, a GRx8-32 receiver model, a processing device, and a 5000-watt power generator provided by Honda company.
Initially, a rectangular array was utilized to gain a general overview of the area. The data collection points were spaced at 20-meter intervals, while the lines for data collection were set at 40-meter distances. The electric current line covered a distance of 600 meters. In the first stage of data collection, a total of 350 data points were gathered. These data points were then interpolated and mapped using Surfer software.
Following the determination of rock chargeability and resistivity variations in the region, as well as field observations, four profiles were designed. These profiles extended north-south and were 500 meters in length. The pole-dipole array was employed to collect data points along the profiles, with a data collection interval of 20 meters. In the second stage of data collection, an additional 150 data points were gathered. These data were used in Res2DINV software to model chargeability and resistivity sections in a reverse manner.
Based on the obtained results from profiles 1, 5, and 2, along with the presence of mineral outcrops, two control profiles measuring 440 and 500 meters in length were designed. Data collection using a dipole-dipole array was conducted along these control profiles, and chargeability and resistivity sections were generated using the same approach.
Finally, for a comprehensive comparison of the obtained sections, all the gathered information was visualized in a 3D block using Voxler software.
 
Results
Through interpolation of the data obtained from the rectangular array, it was observed that the eastern part of the study area exhibited the highest recorded chargeability, reaching approximately 18 mV/V. In terms of resistivity, the maximum value measured within the rectangular arrangement was approximately 180 Ohm meters.
Moreover, upon processing the data collected from the profiles, it was determined that profile 1 displayed the highest chargeability, reaching around 23 mV/V, while profile 2 exhibited the lowest chargeability, measuring approximately 4 mV/V. As for resistivity, profiles 1, 6, 5, 3, 2, and 4 recorded the highest values in consecutive order.
 
Discussion
In disseminated-type mineralization, regions and zones with high chargeability and high resistivity can indicate mineralization in those areas. In the study area, these mentioned zones have also been examined in the studied sections. Considering the conditions of the region, if mineralization exists, it is likely to be of the disseminated type. Therefore, geophysical methods were employed to identify the resistant and chargeable zones in the study area. The analysis of induced polarization and resistivity measurements in a rectangular arrangement revealed that the eastern part of the region has a higher potential for mineralization compared to other studied areas. Additionally, the results obtained from inverse modeling of the acquired profiles confirmed the higher potential in the eastern part, as the eastern profiles recorded higher chargeability and resistivity values. Although the measured resistivity values in this area have been very low, significant variations are observed in these zones. Considering the variations in resistivity zones, it appears that the fault zones predominantly exhibit a northeast-southwest trend, while the amphibolite zones show an east-west trend. Additionally, it seems that the sections with higher resistivity also have higher chargeability values. Based on geological investigations, it has been determined that there is a volcanic unit (andesite) in the mentioned area. Considering the low chargeability values, it should be considered that mineralization may exist within the body of the andesite rock, resulting in weak chargeability readings. However, on the other hand, the anomalies recorded in the chargeability sections, based on the range of variations in chargeability presented by Telford et al. (1990) for copper deposits, are weak. Therefore, the likelihood of the development of a sulfide zone at depth is low or weak if it exists. So, two drilling points were suggested for the validation of the results obtained from the geophysical operations.

Keywords

• Resistivity
• Induced Polarization
• Inverse Modeling
• Copper
• Miami

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