MINERALOGY, FLUID INCLUSION THERMOMETRY AND PETROLOGY OF SANGAN MAGNETITE IRON OXIDE AND TANNURJEH MAGNETITE IRON OXIDE GOLD DEPOSITS, NORTH EAST OF IRAN

Sangan is a Magnetite skarn deposit >450 million Ton high grade Fe, Low P and Tannurjeh is Magnetite-Au deposits (1 M-Ton). They are part of Tertiary volcanic-plutonic belt of Khaf - Doruneh. This belt hosts several types of Iron oxides Au-Cu (IOCG) and Magnetite deposits. Sangan contact skarn contains andradite, F-Cl-K Rich-Hastingsite, magnetite and calcite. Two main types of distal skarn at Sangan are: 1- Ca-type: magnetite, hedenbergite, ripidolite, Fe-actinolite, calcite pyrite ± chalcopyrite ± pyrrhotite. 2- Mg-K type: Mg-rich magnetite (4.5% MgO), phlogopite, dolomite, clinochlore, tremolite, pyrite ± chalcopyrite ± pyrrhotite. Tannurjeh is mainly a contact skarn.

Acid to Intermediate calc-alkaline and alkaline volcanic & sub-volcanic rocks of Tertiary are abundant at Sangan & Tannurjeh. They formed at different episodes in Tertiary. Mineralization is associated within a specific intrusive rock formed in Oligo-Miocene time. Host rock at Sangan is the Cretaceous carbonate. Source rocks at Sangan are I-type, ultra-potassic (K2O 8-12%), quartz biotite-hornblende alkali syenite porphyry. Source rocks in Tannurjeh are I-type, high potassic (K2O 3.5%), hornblende quartz diorite–diorite porphyry. HFSE elements (Cu, Ni, Co, Cr, V) are higher in Sangan source rocks and LILE elements (Th, Zr, Ba, Rb) are higher in Tannurjeh source rocks. La and Ce content of Tannurjeh is higher.

Fluid inclusion micro thermometry and chlorite composition temperature calculation showed that contact skarn at Sangan formed > 450º C and the distal skarn ~ 200ºC. The fluid inclusions are saline rich-type.

The Au grades at Tannurjeh is between 500-1100 ppb and Cu = 14-408 ppm. At Sangan Au is max. 32 ppb and Cu = 50-920 ppm. At Sangan, S is high in distal skarn (1-3%).

The source rocks for IOCG deposits in Chile, Peru, and Sweden are high to medium K-content, alkaline to calc-alkaline diorite-monzonite-granodiorite. Tannurjeh source rocks are close in composition to these rocks.

Keywords: Sangan, Tannurjeh, Gold, Ultra-potassic