Fluid inclusion and stable isotope constraints on the genesis of epithermal base-metal veins in the Armaqan Khaneh mining district, Tarom-Hashtjin metallogenic belt, NW Iran

Abstract

Rashtabad, Aqkand and Jalilabad are neighbouring epithermal base-metal deposits in the Armaqan Khaneh mining district of the Tarom-Hashtjin metallogenic belt, northwestern Iran. Mineralised veins in these deposits consist of pyrite, chalcopyrite, galena, sphalerite with lesser bornite and minor amounts of specular hematite. The gangue mineralogy includes quartz, chlorite, and calcite in ore veins and sericite/illite, and sericite–epidote–chlorite–calcite in vein haloes. At Rashtabad and Jalilabad, primary LV fluid inclusion assemblages homogenise into liquid at 150–285 °C and 120–342 °C, respectively. The corresponding salinities, respectively, vary between 7.4–12.9 and 7.8–13.5 wt% NaCl equiv. At Aqkand, LV inclusions show a T h(total) of 229–353 °C and salinities of 7.4–9.8 wt% NaCl equiv. Calculated δ18Owater values of quartz samples at Rashtabad, Aqkand, and Jalilabad are +1.0‰ to +9.6‰ Vienna-Standard Mean Ocean Water, signifying that the ore-forming fluid progressed from magmatic to meteoric water. Sulfur isotopic values of sulfides range from −6.0 to −2.2‰ Vienna Cañon Diablo Troilite (averaging −3.7‰), indicate sulfur was derived from a rather homogeneous magmatic source that was oxidised by meteoric water through fluid mixing. Our data suggest that Rashtabad, Aqkand and Jalilabad are an intermediate-sulfidation type of epithermal mineralisation formed from a well-mixed source that experienced extensive fluid mixing and boiling. KEY POINTS The Rashtabad, Aqkand and Jalilabad deposits of the Armaqan Khaneh mining district are intermediate-sulfidation style of epithermal mineralisation. Fluid boiling and mixing facilitated hydrothermal alteration and mineralisation. Oxygen isotope values suggest that the ore–fluid system evolved from magmatic to meteoric. Sulfur derived from a magmatic source was oxidised by meteoric water through fluid mixing.