Copper-bearing skarn zone in east of Sungun-Chay river is
located about 100 km NE of Tabriz, and was developed along the contact of
the mineralized porphyry granitoid stock (Oligo-Miocene) with impure
carbonate rocks (Upper Cretaceous). Both endoskarn and exoskarn occurred
in this zone. Endoskarn is narrow (~0.5-2m) whereas exoskarn is relatively
broad (25-55m) and contains minerals such as calc-silicates (grandite,
diopside-hedenbergite, tremolite-actinolite, epidote), silicates (quartz,
chlorite, and clays), sulfides (pyrite, chalcopyrite, sphalerite, galena,
bornite), oxides (magnetite, hematite), and carbonates (calcite, ankerite).
Skarnification processes occurred in two distinct stages, including
progradation and retrogradation. Calculations of chemical index of alteration
(CIA) indicate that the exoskarn underwent metasomatic alteration within
the range of 8.41% to 57.29%. Analysis studies of mass changes of
elements, on the basis of Nb (as a monitor immobile element), indicate that
considerable amounts of elements such as Fe, Si, Mg, S, Cu, Pb, and Zn
were added to the skarn system by hydrothermal fluids from the side of
pluton, while substantial amounts of Ca was leached out of the system. The
overall obtained results show that elements such as Fe, Si, and Mg were
introduced into the skarn system by metasomatizing fluids during both
progradatian and retrogradatian stages whereas the ore-forming elements
such as Cu, Pb, Zn, and S were added to the system mainly during retrograde
stage. The inharmonious mass increase of Al and portion of mass changes of
Si are due to the local variations of pelitic impurities within the carbonate
rocks (as protolith).