Ore control factors of Zinc and Lead mineralization in the Tangedozdan area (NE Fereydounshahr-Isfahan Province)

The Tangedozdan area is located in the west of Isfahan province and 25 km northeast of Fereydounshahr. Structurally, this area is located in the Sanandaj- Sirjan zone. The rock units include greenish volcanic rocks, lime-sandstone, limestone to dolomitic-limestone, conglomerate, sandy-limestones and present-age alluviums. The existing rock sequence along with zinc and lead mineralization has been affected by tectonic phenomena, in the form of thrusting and the formation of open folds, joints and fractures. The main geological structures include thrust plates that have pushed scales of Jurassic and Cretaceous rock units from the northeast to the southwest on top of each other. The folding structures are very small and dense size and are mainly related to faults that have affected the rock units, especially thin-bedded limestone. Tectonic studies show the influence of two lateral faults with the NW-SE trend and a concentrated fault zone inside the dolomitic rocks in the mineralization process. Zinc and lead mineralization shows more expansion in the tension zones. Mineralogy, geochemistry and, EPMA studies indicate the presence of calamine and a small amount of zincian dolomite. The limestone to dolomitic-limestone rocks hosts zinc and lead mineralization and consists of lenses, non-sulfide minerals veins and, veinlets such as smithsonite, hemimorphite, cerussite and, barite, sulfide minerals such as sphalerite and galena. The dolomitization phenomenon due to the effects of acidic hydrothermal fluids has caused alteration of the carbonate wall rock. The structural factor is the main reason for the formation of this dolomite type and the replacement of magnesium with zinc.

High tectonic energy causes shear structures by deforming the crust (Ramsay and Huber, 1987; Lawrence, 2010; Peacock, 1992; Montest and Hirth, 2003). Different temporal and spatial distribution of mineral resources is the result of crustal orogenic actions during tectonomagmatic terms related to specific crust zones. (Aghanabati, 2006; Nabatian et al., 2015). Carbonate rocks under appropriate geodynamic conditions with specific platforms are potential hosts of lead and zinc resources (Rajabi et al., 2012a; Rajabi et al., 2012b; Amiri, 2017; Karimpour et al., 2019). Accordingly, in this we attempt to investigate the relationship between the structure and mineralization and provide a model for structural formation. The Tangedozdan zinc and lead mine 25km northeast of Fereydounshahr is located in the extreme western corner of Isfahan Province and adjacent to the Lorestan Province. For the geological location, this area is considered part of the Sanandaj-Sirjan zone. The limestone unit in the east of Tangedozdan hosts zinc carbonate mineralization. In this region, the mineralization is located between two faults inside the dolomite limestone concentrated directly on the trachyandesite volcanic rocks.

To accurately identify the minerals, thin-polished sections were prepared from the surface, boreholes, and trenches and studied by transmitted and reflected polarization microscope (Nikon E200). Also, many samples were studied by XRD and EPMA. 

The Tangedozdan zinc-lead mine includes rock units in the convergent and active margin of the neotethys Ocean in the Mesozoic. These rocks were formed in an eugeocynclinal medium during the Jurassic and early Cretaceous periods (Aghanabati, 2006). Tectonic phenomena, in the form of thrusting and the formation of open folds, joints, and fractures, are considered mineralogy controllers. Two important and major faults related to mineralization have been identified in Tangedozdan. The first fault at a distance of about 650m to the east of Tangedozdan and along the general direction of N158 caused contact between sandy limestone deposits and calcareous sandstone, and the fault has played an important role in mineralization. The second fault, at a distance of about 450 m to the east of Tangedozdan, with the general direction of N150, along with the past fault, has played an important role in mineralization, and together with the sub-faults, they are considered to be structural controllers of mineralization.
Mineralogical studies as well as the use of EDS spectra and XRD have shown presence of non-sulfide minerals such as smithsonite, cerussite, hemimorphite, barite, and sulfide minerals such as sphalerite and galena, which are paragenesis of each other. The transparent minerals are calcite and dolomite and barite and Quartz to a lesser extent, which are placed in the space between the opaque minerals. Quartz is mainly observed heterogeneously and only in some empty spaces. The formation of empty spaces between the crystals and the fractures is the result of the dolomitization phenomenon and it has made possible the concentration of ore-bearing fluids and the deposition of valuable zinc and lead ores. Hence, mineralization can be expected in parts of the deposit where developing dolomitization and creating empty spaces is possible. Calamine is very similar to carbonate minerals such as dolomite and calcite and has a variety of colors (Wilkinson, 2014; Lecumberri-Sanchez et al., 2014). Therefore, in Tangedozdan, the two-component reagent Zinc Zap was used, which qualitatively shows the presence of zinc-bearing minerals and leads to red and orange colors to identify calamine or non-sulfide minerals that cover zinc and primary sulfide minerals. Accordingly, calamine was identified in field studies in Tangedozdan.
The most important existing alteration includes dolomite, silicic, and carbonate, which can be seen with non-sulfide zinc mineralization such as calamine, and zincian dolomite, which is considered an important sign of mineralization in the region. The dolomitization phenomenon due to the effect of acidic hydrothermal fluids has altered the carbonate wall rock. The structural factor is the main reason for the formation of this type of dolomite and the replacement of magnesium with zinc (Boni et al., 2011; Mondillo et al., 2017).

Given field evidence, it can be said that zinc and lead have mineralized simultaneously with the faults with the current mechanism of normal dip-slip along with strike-slip component with the general direction of N150 to N158. Then, with penetration of fluids containing zinc and lead, mineralization has taken place along the existing faults and their sub-faults as mineralization structural controllers. According to the studies, the dolomitized process has led to the formation of empty spaces between the crystals as well as fractures and finally the concentration of ore fluids and deposition of valuable zinc and lead ores. The phenomenon of dolomitization has also changed the carbonate wall rock.