Stable isotope geochemistry of Chargar epithermal deposit: Constraints on epithermal systems in the Tarom metallogenic belt, NW Iran

Abstract

Abstract The Chargar deposit in the southern part of Tarom metallogenic belt of the Alborz structural zone, NW Iran, shows a volcaniclastic-hosted, low-sulfidation epithermal gold mineralization. The host rocks are part of the Eocene volcanic and volcaniclastic sequence of the Karaj Formation. The main host rock is an andesitic lapilli-lithic tuff. The main ore minerals include chalcopyrite and gold and the gangue minerals are quartz, barite, and calcite. The calculated δ 34 S H2S values based on sulfide minerals for the Chargar shows a homogeneous signature ranging from −7.6 to −5.6‰, in the Khalifelou deposit range between −5.2 and −1.9‰ and in the Aliabad-Khanchay deposit from −8.1 to −5.5‰. Negative sulfur isotope values and the occurrence of framboidal pyrite in the volcaniclastic host rocks suggest a volcano-sedimentary origin for the sulfur. The Chargar calculated δ 34 S H2S values based on barite supplied δ 34 S values between +16.5 and +22.5‰. These are heavier than possible magmatic distribution and require heavier non-magmatic reduced sulfur sources. The sulfur isotope data imply essentially a volcano-sedimentary and sulfate origin for sulfur. The calculated δ 34 S H2S values from the Chodarchay deposit ranging from −1.6 to +5‰ and in the Goloujeh between −9.6 to +7.2 compatible with a magmatic sulfur source. The Calculated δ 18 O values for Chargar hydrothermal ore-forming fluids range from +1 to +1.3‰. The δ 18 O values for Khalifelou and Aliabad-Khanchay hydrothermal ore-forming fluids vary from +0.6 to +3.6‰ and from +0.8 to +3.6‰, respectively. The oxygen data suggest that hydrothermal fluids resulted from meteoric fluids. The δ 18 O values of Goloujeh hydrothermal ore-forming fluids are between 0.7 and 7.7‰ and emphasize on magmatic fluid - meteoric water. Oxygen and S isotopic signatures of barite combined with mineralogical features show characteristics of a magmatic-hydrothermal system. Chargar demonstrates similarity with Khalifelou and Aliabad-Khanchay epithermal deposits in the southern part of Tarom belt. These deposits are different from Chodarchay porphyry-epithermal and Goloujeh epithermal deposit in the northern part of the belt in terms of isotopic data, sulfur and fluid sources.