Scientific Quarterly Journal of Geosciences

Scientific Quarterly Journal of Geosciences

Gold Mineralization in Ductile Shear Zone of Kervian (Southwest of Saqez- Kordestan Province)

Document Type : Original Research Paper

Authors
Seyed Mehran Heidari
Ebrahim Rastad
Mohammad Mohajjel
Seyed Mohammad Javad Shamsa
Geological Department, Tarbiat Modaress University, Tehran, Iran
Abstract
      Gold bearing metamorphosed and deformed rocks (of green schist facies) are exposed in NE-SW trending shear zone, about 25 km southwest of Sagez in Kordestan province.
The protolith ore, supposed to be mafic and mostly acidic volcanic and sedimentary rocks (phyllite, re-crystallized limestone, metaferrodolomite), was intruded by several granitic plutons. Shallow to moderately dipping mylonite foliation towards NW and stretching lineation plunging to the N20ºE on the foliations imply that mylonites and ultra-mylonites were produced during oblique reverse left lateral tectonic regime. Hydrothermal alteration is both spatially and temporally associated with development of ductile shear zone.
The major types of alteration include sericitization, chloritization, silicification, sulfidation and carbonatization. Among them, sercitization and chloritization are pervasive; whereas, silisification, sulfidation and carbonatization are usually limited to the inner zone of altered shear zone and in close relation with the intensity of deformation. Two planar fabrics (S and C) of different morphology are recognized in the shear zone of Kervian gold field. These fabrics appear contemporary with deformation in Kervian's ductile shear zone.
The main mineralization zone, with lensoidal geometry, is about 2500 m long and 60 m wide, on average. The ores, predominantly auriferous hydrothermaly altered mylonites, have been over printed by intense hydrothermal alteration. Gold, existing along the shear fabrics either in the native form or in composition with sulfide such as pyrite and arseno- pyrite, was deposited due to ductile shearing and strong alteration.
Final emplacement of gold is an integral part of hydrothermal alteration system, i.e., the major auriferous minerals were deposited in association with hydrothermal alteration. Formation and occurrence of gold field are controlled by ductile shear zone, intensity of deformation and associated hydrothermal alteration. Based on present evidences and comparison with other gold types in the World, the characteristics of Kervian gold deposit are similar to ductile shear zone type gold mineralization. 
Keywords
Kervian Gold deposit
Ductile Shear zone
Mylonite
Deformation
Alteration
Sagez

Subjects

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Scientific Quarterly Journal of Geosciences
Volume 15, Issue 58
Winter 2006, Vol. 15, No.58
Winter 2006
Pages 18-37