Nezafati, N., Herzig, P.M., Pernicka, E., Momenzadeh, M.: Intrusion-related gold occurrences in the Astaneh-Sarband area, west central Iran. In: J. Mao, and F. P. Bierlein, eds.: Mineral deposit research: meeting the global challenge, Springer. 1: 445-448 (2005)
Astaneh Gold Prospect; an intrusion-related gold system in west central Iran N. Nezafati*, G. Markl Institute of Mineralogy, University of Tübingen, Tübingen D-72074, Germany E. Pernicka Institute of Prehistoric Archaeology, University of Tübingen, D-72070, Germany and M. Momenzadeh Zarneh Research Institute, No. 34, 4th street, Jenah Highway, Tehran, 14816-35451 Iran *E-Mail,
[email protected] The Astaneh gold prospect is located west-southwest of the town of Astaneh in west-central Iran (Fig.1). The area is situated in the northern part of the Sanandaj-Sirjan tectonic unit (Fig.1) and consists mainly of low-metamorphic Jurassic and Triassic schists, Late Cretaceous-Early Tertiary intrusives and related contact metamorphic rocks and pegmatites. There are 4 other tungsten and/or gold prospects in the Astaneh-(Sarband) area. The main trend of the faults, fractures and other structural features of the area is NW-SE, which corresponds to the main trend of the Sanandaj-Sirjan zone and the Zagros chain. The NW-SE trending Astaneh intrusive body that hosts the gold mineralization is mainly composed of biotite granite (98.9 ± 1.0 Ma; Masoudi 1997), which is locally accompanied by granodiorite, tourmaline granite, and quartz diorite. These rock units are locally altered and/or intersected by microgranodiorite dykes, and quartz or aplitic veins. The northeastern part of the Astaneh intrusion has been cut by the 400 m large Shirmazd granodiorite (35.05 ± 0.92 Ma Rb/Sr age, and 44 + 13 Ma single zircon evaporation age, own unpublished data). The Shirmazd granodiorite is cut by NE-trending microgranodioritic dykes. Gold mineralization occurs mainly in the Shirmazd stock and the intersecting microgranodioritic dykes, and in some nearby, smaller, altered microgranodioritic stocks. The dykes contain mostly disseminated chalcopyrite and pyrite, and are in some cases accompanied by arsenopyrite veins. Gold mineralization occurs in NE-trending quartz- and quartz-sulfide veins and veinlets, as well as in disseminations. Alteration minerals include sericite, chlorite, quartz, calcite and in some cases kaolinite (Hashemi 2002). Chalcopyrite and arsenopyrite are the major sulfide minerals, of which the latter contains 1-50 µm sized inclusions of native bismuth and bismuth oxides. Chalcopyrite sporadically contains exsolved sphalerite “stars”, which suggests formation temperatures above about 400°C (Hutchison and Scott 1981). Gold at Astaneh can be easily explored by heavy mineral panning of the sediments from the surrounding valleys of the Shirmazd mount. The grain size reaches 1000 microns, whereas the average size is 50-200 microns. Visible gold has been reported in the form of very fine grained particles (
