Orogenic gold mineralization at the Chah Bagh deposit, Muteh gold district, Iran

The Chah Bagh gold deposit, in the Muteh gold district, is located in the central part of the Sanandaj-Sirjan zone (SSZ), Iran. Gold mineralization at Chah Bagh is hosted by a Paleozoic sequence of rocks that is dominated by deformed schist, metarhyolite, and amphibolite that exhibits a greenschist- to lower amphibolite-facies metamorphism. Three deformation events are recognized in the Chah Bagh area, D-1, D-2, and D-3. The major NW-trending (N280-N290) dextral strike-slip shear zone in the area was formed during D-2 ductile events. Gold mineralization at Chah Bagh occurred over a prolonged deformation history, but is closely related to alteration, retrograde greenschist-facies assemblages, and ductile and brittle deformation during D-2 and D-3. The geometry of the Au-bearing quartz veins indicates that they are temporally related to the S-2 foliation and therefore to the D-2 flattening and shearing. Some veins, however, are spatially and temporally related to D-3 brittle normal faults and are brecciated and boudinaged during the associated shear movement. The presence of deformed Au-bearing quartz veins, and their concordant and discordant relation with respect to the main mylonitic foliation and the shear zone, indicates continuous mineralization during the D-2 and D-3 episodes. The Au-hosting shear zones are characterized by extensive development of heterogeneous mylonitic rocks that enhanced the permeability within the shear zones. This gave rise to further extensive dilatancy within major dilational jogs and produced a suitable structural regime for vein-hosted Au mineralization. The epigenetic Au mineralization resulted from metamorphic hydrothermal fluids circulating through major shear zones and associated structures during the late stages of orogeny. Our investigation shows that granitic intrusions have no genetic link with gold mineralization and we propose an orogenic gold model for Chah Bagh deposit, similar to Qolqoleh and Kervian in the northwestern part of the SSZ. This model is consistent with a dextral transpressional deformation kinematic model along the SSZ and, refutes the previous intrusion-related model suggested for the Muteh gold deposits. Metamorphic devolatilization and fluid flow within a ca. 30-m.y.-long period in Late Cretaceous and Early Tertiary is suggested for the genesis of the gold occurrences in both ductile and post-transpressional brittle structures. (C) 2014 Elsevier Ltd. All rights reserved.