Geological and geophysical studies for exploration of lead and zinc in Chumalu area, northwest of Zanjan

The host rock in Chumalu area includes the Eocene volcanic rocks and the Oligocene monzonite intrusive mass that have undergone propylitic-carbonate, silica, and silica-argillic hydrothermal alterations. The hydrothermal activities resulting from the injection of intrusive mass have produced two types of mineralization in the region: the first mineralization type is a silica-shear zone having N70E trend, and the second type is in the form of a bunch of veins with an approximate trend of northwest to southeast, located in the north of the first mineralization type. The mineralization is of the form of vein, veinlet, massive, scattered and replaced, and follows the trend of the faults. The ore contains lead, zinc and fluorine, along with copper, gold and silver, which are formed of chalcopyrite, pyrite, galena, sphalerite, cerussite, calcite and fluorite minerals. Based on the results of the geological studies conducted in this study, the mineralization characteristics of Chumalu area are of the type of lead and zinc hydrothermal deposits. Induced polarization (IP) and resistivity data acquisition were first designed and carried out using rectangular array to determine the anomalous zones, and then, using dipole- dipole array to determine the lateral and depth limits of these anomalies. Then, modeling of IP and resistivity data was done using smooth inversion method. For better representation of the results, all two-dimensional (2D) sections were combined and as a result, a three-dimensional (3D) model was presented. Consequently, an anomaly with an approximate east-west orientation in the south of the area has been extended on the silica-shear zone, and some anomalies with an approximate north-south orientation in the north of the area, in relation to the fractures of the basaltic deposits, which can be linked with metallic mineralization in the area. Anomalous areas with high chargeability and medium to low resistivity values have been determined. High chargeability values for some anomalies in the north of the area are probably due to the presence of scattered pyrites in depth. Finally, 6 points were proposed for drilling.

Application of IP and resistivity geophysical methods and their integration with geological studies is of great importance in the exploration of sulfide metal deposits. The Chumalu area is located 70 km northwest of Zanjan in the Tarom-Hashtjin metallogenic zone, which has possible potential for metal reserves and mineral resources. The purpose of this research is to collect and process raw IP and resistivity data using the smooth inverse modeling, interpretation of the results based on geological studies and finally determining the anomalous limits, depth and thickness of probable mineral masses in the area and at the end, suitable locations for drilling are suggested.

This research is based on field and laboratory studies. In order to conduct geological studies, alteration, mineralization and determination of the genesis of the mineralization, 8 thin sections and 9 polished sections of surface and subsurface samples from the mineralization ore and host rock were prepared and studied. Moreover, field operations of IP and resistivity data acquisition were first made in the form of 4 networks using rectangular array in order to determine the anomalous limits with a current line of 800 meters long, electrode spacing of 20 meters, and the distance between the lines 50 meters. Then, 6 lines using dipole-dipole array were surveyed in order to explore the lateral and depth limits of these anomalies with electrode spacing of 20 meters. Then, modeling of IP and resistivity data was made by 2D smooth inversion method using RES2DINV and ZondRes2D software packages. Furthermore, all 2D sections were combined using RockWorks software and a 3D model was presented. Ultimately, possible mineralization limits were identified and suitable sites for drilling were proposed.

Based on the geological studies, lead and zinc mineralization in olivine basalt volcanic host rock and part of the monzonitic intrusive mass in Chumalu area occurs during hydrothermal processes and in the form of veins along fault structures. Chumalu mineralization is of hydrothermal lead and zinc type. Based on geophysical and geological studies, anomalies have been introduced that have high chargeability and medium to low resistivity, as probable mineralization. Finally, 6 locations were proposed for drilling.