Combination of Magnetic and Resistivity methods for determination of the mineralization extension in Moeil Iron ore, Meshkin-Shahr

Moeil Goethite iron mineralization zone related to Moeil hot streams system is located in 1 Km south of the Moeil village, at 17 km southeast of Meshkin Shahr town in Ardebil province. This zone is at the western slopes of Sabalan caldera in the northwest part of Iran. The studied area is located in Central Iran zone according to Geological Structures’ classification by Stoklin (1988) and in Alborz-Azerbayjan zone according to Nabavi (1355). General lithology of this area consists of Cenozoic and Quaternary volcanic rocks and pyroclastic material related to the Sabalan volcanism. The reason for the high thermal gradient of the region is because of hot intrusive bodies in depth. In this area, geothermal liquids move upward via fractures and fault systems when the atmospheric water is penetrated and contacted with deep intrusive bodies then hot water springs (e.g., Geinarja and Moeil) have been generated consequently. Chlorinated hot water leaches iron of Ferro-magnesium minerals, through moving beside the mafic and intermediate rocks, and deposits iron hydroxides (Goethite and Limonite) on the surface. Moeil iron ore in the south of Meshkin Shahr is considered as a prominent iron ore related to the hot water springs in Iran. In this ore, the average amount of iron oxide (Fe2O3) is 70 percent. In this paper, extension of Iron ore body, and mineralization situation was studied in depth and horizon by implementation of two geophysical approaches, including magnetic method as an indirect way for exploration of Hematite and as a method for checking possibility of magnetite mineralization in depth (about 750 data points) and electrical resistivity method as a direct measurement (seven data profiles all with lengths between 150 to 350 meters) by utilizing three different arrays at the same time (Gradient, Schlumberger and Wenner arrays) and exploration boreholes (16 boreholes with depth of 15 meters). As a result of the magnetic survey, firstly, the possibility of magnetite mineralization has been rejected. Secondly, high positive magnetic anomalies are related to granitic rocks, intermediate positive anomalies are related to Iron ore body, and low anomalies are related to springs that the minerals become precipitated. Besides, the existence of two conjugate faults with NW-SE and NE-SW directions is clear in magnetic anomaly map. In electrical resistivity pseudo sections, the presence of a nearly vertical fault is obvious. In addition, the existence of an aquifer with a very low resistivity at the bottom is detectable. Iron mineralization as a nearly horizontal layer is located between this aquifer in deep and high resistivity volcanic sediments at the top. Finally, as an outcome of this study, it can be mentioned that results of both magnetic and electrical resistivity activities, geology evidences and exploration drilling results confirm each other. In general, the below results have been achieved through Magnetic and resistivity approaches: - Magnetite mineralization is not expected in this ore due to the relatively low intensity of recorded magnetic signals.
- From the magnetism viewpoint, iron layers do not have a sharp difference with base rocks (tuff).
- In some points, non-ferrous volcanic rocks (granitic) show high magnetism in comparison with mineralized zones. High intensity (more than 48550 nT) is related to these granitic bodies.
- The intensity between 48550 nT and 48800 nT is related to the iron mineralized zone.
- Results from geoelectric studies show that the specific resistivity between 150 and 700 ohm-meter is related to the iron layers, and the figures between 700 and 800 ohm-meter is associated with pyroclastic materials and volcanic rocks.