Abstract

Arabshah gold deposit formed through hydrothermal activity with an age of about 11 Ma (based on zircon U-Pb dating by LA-ICP-MS), in northwestern Iran. This hydrothermal activity is part of the Urumieh-Dokhtar magmatic arc, leading to mineralization in this area, similar to Zarshouran, Aghdarreh and Sarigunay gold deposits. Host rocks are a series of lower Paleozoic sedimentary sequences cut by calc-alkaline to alkaline (high potassium) dacitic domes. Gold mineralization in the deposit is mainly observed as vein-veinlets, open space filling, disseminated and brecciation. The mineralization in terms of hydrothermal alteration (decalcification, minor argillic, sulfidisation, dolomitisation and silicification) and mineralization development process is associated with brecciation and deposition of base metal sulfides, iron, arsenic and antimony similar to deposits associated with geothermal systems (low sulfidation epithermal) in volcanic arcs, but the host rock here is sedimentary. Sulfides in the ore include pyrite, arsenopyrite, orpiment and realgar, stibnite, galena, sphalerite and minor chalcopyrite. Gold mineralization occurred in the form of released grains of oxidised pyrite, the tiny (invisible) in the sulfide phases such as arsenian pyrite for solid solution. The Arabshah deposit shows characteristic alteration assemblages and ore minerals (As, Sb, Hg, base metals) of epithermal low sulfidation deposits. It has been formed in relation to the mid-upper Miocene, high-level magmatic–hydrothermal activity within an extensional regime at the last stages of the UDMA activity in northwestern Iran.