Intrusion-related gold occurrences in the Astaneh-Sarband area, west central Iran

Abstract

The Astaneh-Sarband area is located in the Sanandaj-Sirjan metamorphic belt in west central Iran. The area hosts five intrusion-related tungsten and/or gold systems, including the Deh Hosein and Astaneh, gold occurrences and Nezam Abad tungsten-gold occurrence. The Astaneh-Sarband area contains Mesozoic schist, Late Cretaceous-Early Tertiary intrusive rocks and related contact metamorphic aureoles, and pegmatites. The Astaneh and Nezam Abad systems are hosted in granitic to grnaodioritic intrusive rocks of Early to Late Eocene age. At Deh Hosein, mineralization occurs, mainly in Jurassic-Triassic meta-sedimentary rocks which have undergone greenschist facies metamorphism and intrusion by the Astaneh granite-granodiorite complex. Gold occurs in quartz and quartz-sulfide veins and veinlets, and as disseminations. Major ore minerals are arsenopyrite, chalcopyrite, pyrrhotite, sphalerite, marcasite, bismite, native gold, and rare stannite. Adjacent to and within zones of intense quartz veining the predominant alteration assemblage is quartz + sericite + tourmaline + chlorite. The sulfide mineral content in the veins is generally less than 3 vol.%. The gold contents of samples from Deh Hosein, Astaneh and Nezam Abad range up to 9.5, 13.3, and 36.2 ppm respectively. Gold contents correlate moderately well with As, Bi, and Se. Arsenopyrite geothermometry, yields deposition temperatures of 580° to 380°C for these occurrences. Stable-isotope data include ´18O values of 11.5 to 19.2 (quartz), and δ34S values of −5.6 to 4 (galena, pyrite, arsenopyrite, chalcopyrite). The sulfur data are compatible with a magmatic fluid source. Lead isotope results are consistent with a lower crustal source for the ores at Deh Hosein.