Geological structures and their role in control of mineralization in Bahramtaj Lead and Zinc deposit, Yazd province, Central Iran

Iran has large areas of carbonate rocks that host potential reserves of lead and zinc deposits due to suitable geodynamic conditions and carbonate platforms. So far, more than 300 zinc-lead deposits have been reported with sedimentary hosts in Iran. Bahramtaj lead and zinc deposit is located in Central Iran zone, which is hosted by Precambrian-Cambrian formations (Rizo, Dezo and Aqda). In this paper, an attempt has been made to present the structural formation model of Bahramtaj lead and zinc mineralization by combining the results obtained from the study of geological structures, the relationship between structures and specific mineralization.

In this study, various geological structures such as faults, joints and folds at the local scale as well as in the Bahramtaj prospect area have been studied. After identifying the main and important structures influencing the region, the structural and tectonic status of Bahramtaj area, the relationship between geological structures and mineralization are also studied. Due to the availability of Google Earth images with an approximate accuracy of 30 meters, as well as the use of digital topographic images with an accuracy of 30 meters and ETM + images, and using remote sensing software, the tectonic position of the region has been discussed.

Faults
Existence of different generations of faults and fractures each related to a generation across fault zones has caused confusion and complexity of rock units in Bahramtaj mining area. Investigation of fault zones and geological structures related to fault movements (formation of fracture zones, fault gouge and fault breccia) in the faults of the area indicate their formation in fragile and shallow environments. The main stress trends of the region based on diagrams related to faults and fractures of the region, indicate their compliance with the stress distribution due to the performance of the main faults in the region, which are N044 and N337 in the direction of maximum stress in the region.
Folds
In Bahramtaj mining area, different changes in the type of deformation have occurred at different times. In the oldest rocks of the area, which are most exposed in the northern parts, Cambrian carbonate units show at least two generations of folds and various types of open and closed folds, inverted and asymmetrical in different scales. In most cases, the old corrugated edges are limited and broken by longitudinal faults, and due to the undertaken different stresses in different directions, a lot of rotation has occurred in the direction of their axis and geometry. Considering the structural condition of the region and the distribution of stress based on the existing structural evidence in the range and geometry of the folds of the younger generations, it is possible to imagine older clockwise rotation trends for this generation of the folds of the range. Regarding the formation, the folds of the area have been affected by the performance of the main fault in the region. Therefore, the predominant direction of the folds, show the azimuth N120.

Based on field evidence and studies, it was found that mineralization coincided with the activity of the strike-slip fault with a northwest-southeast direction. The development and expansion of mineralization in different regions in the two systems are different. Expansion of zinc and lead mineralization in the direction of northwest-southeast faults express the positive effect of east-west fault activity on the number of openings. Creation of convenient places in tensile fractures related to the northwest-southeast fracture system, has caused lead and zinc mineralization to be more widespread in the tensile zones associated with this system.