Gold Mineralization in Ductile and Brittle form of ShearZonesMute Mining Area (SW Delijan.Isfahan)

Category Economic geology & mineral exploration
Group GSI.IR
Location 21th symposium on geosciences
Holding Date 21 May 2008

      Chah-Bagh Gold deposit is located in northwestern part of Sanandaj-Sirjan zone, 60km of Delijan. The complex of igneous and sedimentary rocks in the studied area which are metamorphosed to the greenschist facies is affected by ductile NW-SE trending shear zone which is deformed and shows mylonitic fabrics. Two style of gold mineralization are distinguished in the Chah-Bagh, the principal one occurs in a zone 1km long by 60m average thickness. The geometry of ore body is lenticular, trending N30-40E, and is situated in ductile type shear zone. This type of mineralization, which reported for the first time, is distinguished by the development of rhyolitic tuff intercalated with meta-rhyolite with red color. The second style of mineralization, the brittle sheared ones, like other deposits in Muteh mining area, is also observed here in Chah-Bagh. It is 150m long by 3-5m average thickness (in the main sulfide-bearing silicifided vein) along N40W trending fault. The host rocks of these two types of shear zones mainly consist of acid volcanic and volcano-sedimentary rocks (meta-rhyolite and felsic schist) which are metamorphosed and strongly deformed intruded by basic dikes and sills (meta-dolerites).Granitic and meta-rhyolitic bodies outcropped in ductile shear zone, are affected by strong deformation, the mylonitic foliation of which led to gneissic structure in meta-rhyolite. The above lithology in Chah-Bagh shear-zone, have undergone alteration. Intensity and types of alteration behave various in different lithologies. Silicified and sulfidic alteration in brittle part and silicified, sulfidic, seresitic and kaolinitic alterations in ductile part are among various alterations observed in the shear zones. Silicified and sulfide alteration observed in the inner parts of alteration zones and closely intimated with ore-bearing zones. Analysis of samples which collected from trenches and tunnels which are parallel or perpendicular to the foliation in lithologies, indicate that there is a close relationship between high gold grades and silicified highly-deformed mylonitic and ultera-mylonitic units and Sulfide-bearing silicified veins coinciding with the inner parts of alteration zones. Pyrite, the major sulfide mineral, is of two generation: euhedral and coarsely-crystallized and anhedral and finely crystallized. Pyrite occurs as laminated and oriented in host rocks and disseminated, veins and veinlets in silicified rocks as well. Gold mineralization, in ductile shear zone of Chah-Bagh, can be used as a model for reconnaissance and exploration of this type of gold in Mute mining district and other districts of similar geology.