Magmatism, alteration and their relations to mineralizationIn Ahar- Jolfa belt (Arasbaran

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

      Ahar ? Jolfa is one of the most active magmatic belts in Tertiary which its activities started from Early Cretaceous and went up on to Quaternary, not continuously. Regarding to the magmatic rocks exposed in the Ahar ? Jolfa belt, four different magmatic phases can be identified:
   -Magmatic phase of Early Cretaceous to end of Middle Eocene being exposed as volcanic and shallow small intrusive rocks
   -Magmatic phase of Late Eocene ? Early Oligocene consists only of batholitic intrusive of gabbro to granite which accompanied by skarn and vein type copper mineralization. No obvious exposure of volcanic rocks is visible.
   -Magmatic phase of Miocene ? Pliocene which consists of both volcanic and intrusive rocks. It seems that mainly mineralization of this belt should be due to this magmatic phase.
   -Volcanic phase of Quaternary which generated whole basaltic exposures of Azarbayjan and Ahar areas.
   In alteration point of view, this area is one of exceptional one in Iran, so it appealed concerns of geologists; especially those specialized in economic geology. There are three different alterations in different ages seen in this belt:
   -A regional alteration occurred in this area as argillitic zone occurred in the lower part, the hematitic one in the middle as a thick zone and finally a silicic zone on top. This type of alteration is controlled by lithology, faulting and old caldera and generally lacking of minerals.
   -Local alteration: Those locally occurred in the small scale through the Ahar ? Jolfa and consist of propylitic, potassic, silicic, argillitic and phyllitic zones. This type of alteration generally bears mineral and associated with shallow level intrusive of Miocene ? Pliocene.
   -Silicic alteration: this type occurred widely and is seen as silicic veins in the area and usually carries gold, though it is not economic.