Publications on Iran

@phdthesis{nokey,

title = {Au-Sn-W-Cu-Mineralization in the Astaneh-Sarband Area, West Central Iran: including a comparison of the ores with ancient bronze artifacts from Western Asia},

author = {Nima Nezafati

},

url = {https://publikationen.uni-tuebingen.de/xmlui/handle/10900/48972

},

year  = {2006},

date = {2006-00-00},

publisher = {Eberhard-Karls-Universität Tübingen},

abstract = {The present study deals with two primary aims; (1) geological, mineralogical, and geochemical investigations of the Deh Hosein, Astaneh, and Nezam Abad mineralizations in the Astaneh-Sarband area, west central Iran, with the aim to understand the characteristics of the occurrences and their conditions of formation, and (2) geochemical investigations on ancient bronze artifacts from Iran and Western Asia in order to compare their characteristics with the high-tin copper ore of Deh Hosein and examine their possible relationship. The Astaneh-Sarband area is located in the northern part of the NW-SE aligned Sanandaj-Sirjan metamorphic belt and consists mainly of Mesozoic schists, Middle Jurassic to Middle Tertiary intrusive rocks and related contact metamorphic aureoles, and pegmatites. Regional metamorphism in the area has reached a peak of greenschist facies, but further metamorphism has occurred locally, associated with granitoid emplacement. Magmatism has produced large felsic to intermediate intrusive bodies along a general northwest trend. The main trend of the faults, fractures and other structural features of the area is NW-SE. The Deh Hosein prospect is mainly hosted by Jurassic meta-sedimentary rocks, which have been intruded by the Astaneh complex. Mineralization continues into the southern part of the Astaneh intrusion. The meta-sedimentary rocks consist of alternating meta-sandstone, phyllite, schist, spotted slate and hornfels. The main faults and other structural features, with NW and NE trends, have controlled the mineralization, which occurs in the form of quartz, quartz-sulfide and quartz-gossan veins and veinlets, partly sheeted in structure. These veins are up to 1.5 m wide and several to tens of meters long. Mineralization also occurs as disseminations and impregnations, especially in the vein selvages. Adjacent to and within zones of intense quartz veining, the predominant alteration assemblage is quartz + sericite + tourmaline + monazite. Some 35 metalliferous minerals have been detected at Deh Hosein. Arsenopyrite is the dominant sulfide mineral, with lesser amounts of chalcopyrite > pyrite > pyrrhotite. Cassiterite and ferberite are the rather abundant oxide minerals. The sulfide content in the ore is generally less than two volume percent. Arsenopyrite associated with early alteration and veining typically contains 1-150µm large inclusions of native bismuth, bismite and bismuthinite. Gold occurs in “invisible” form in the arsenopyrite and bismuth-bearing minerals of Deh Hosein. Bulk gold contents determined by NAA in the ore ranged from 0.05 to 13.3 ppm, while the Cu, Sn, W, and Bi concentrations of veins range up to 10%, 6.7%, 2420ppm, and 1800ppm, respectively. At Astaneh, gold mineralization is confined to the NW-SE trending Astaneh intrusion that is composed mainly of biotite granite (98.9 ± 1.0 Ma; Masoudi 1997), which is locally accompanied by granodiorite, tourmaline granite and quartz diorite. The northeastern part of the Astaneh intrusion has been cut by the Shirmazd granodiorite. This stock is about 400 m in diameter and Eocene in age (Rb/Sr and single zircon evaporation methods, this study). The Shirmazd granodiorite has been cut by NE-trending microgranodiorite dykes. Gold mineralization occurs mainly as NE-trending quartz- and quartz-sulfide veins and veinlets, as well as in disseminations in the Shirmazd stock and the intersecting microgranodiorite dykes, and in some nearby, smaller, altered granitic stocks. Alteration minerals include sericite, chlorite, quartz, calcite and in some cases kaolinite. At Astaneh chalcopyrite and arsenopyrite are the major sulfide minerals, of which the latter contains 1-50 µm sized inclusions of native bismuth and bismite. Gold occurs in both visible and invisible forms at Astaneh. Visible gold has been reported in the form of very fine grained particles (<15 µm) either in goethite produced from the oxidation of chalcopyrite or in sericitized plagioclase (Hashemi 2002), while invisible gold occurs in arsenopyrite and bismuth-bearing minerals. Bulk gold contents determined by NAA ranged from 0.05 to 9.5 ppm, while the Cu, Sn, W, and Bi concentrations of veins range up to 1%, 0.05%, 100 ppm and 138ppm, respectively. The Nezam Abad mineralization is hosted by a Lower-Mid Eocene quartz diorite unit. This rock unit has been cut by several aplitic and quartz or quartz-tourmaline veins; the latter host the mineralization. The faults of the area are NW-, NE- and N-trending. Associated alteration minerals include quartz, chlorite, sericite, and tourmaline. At Nezam Abad, chalcopyrite, arsenopyrite and scheelite are the most abundant ore minerals. Gold occurs as “invisible” form predominantly in arsenopyrite with bismuth inclusions at Nezam Abad. Bulk gold contents determined by NAA ranged from 0.05 to 36.2 ppm while the Cu, Sn, W, and Bi concentrations of veins range up to %10, %0.87, %3.37 and 548ppm, respectively (Farhadian 1999). In all three occurrences, gold shows positive correlations with arsenic, bismuth, selenium, silver, tellurium and antimony. Microprobe investigations revealed that the arsenopyrites from Deh Hosein, Astaneh and Nezam Abad contain 32.3 to 34.3, 30.7 to 31.4, and 33.6 to 35.6 atomic percent of arsenic. Average compositions lead to the conclusion that the mineralization formed at temperatures of 460°C, 410° to 380°C and 565° to 510 °C, respectively. Oxygen isotope ratios for gold-bearing quartz veins in the area range from 13.6 to 19.2‰ for Deh Hosein, from 11.5 to 13.7‰ for Astaneh and from 11.6 to 15‰ (V-SMOW) for Nezam Abad. The oxygen isotope data suggest a metamorphic or a mixed magmatic-metamorphic source for the quartz veins. Measured sulfur isotope values for pyrite, chalcopyrite, galena and arsenopyrite in quartz veins of the Deh Hosein, Astaneh and Nezam Abad range from -5.6 to 0‰, -0.5 to 1.8‰ and 1.2 to 4‰ (CDT), respectively. The sulfur-isotope values of all these occurrences are compatible with a magmatic sulfur source. Pb isotope ratios from the sulfide and host rock samples of the prospects indicate a good agreement between the lead ratios of the ore of Deh Hosein and the hosting meta-sandstone, the ore of Astaneh and the Shirmazd Stock and the ore of Nezam Abad and the hosting quartz diorite. The Pb isotope signatures of the ore from the three occurrences show also rather close ratios. According to the plumbotectonics model of Zartman and Doe (1981) the lead in the ores has a lower crustal Pb component. The studied occurrences share several similarities in terms of their mineralogy, geochemistry, formation temperatures, isotope ratios, alteration and occurrence of gold. They also indicate many similar features with the “intrusion-related gold systems” that have been described from Alaska, the Yukon and other parts of the world (e.g., Lang et al. 1997, 2000; McCoy et al. 1997; Thompson et al. 1999). According to the present data, it appears that a fertile magmatic source (probably of lower crustal origin) has affected the already present metamorphic rocks of the area (by remobilizing some of their elements) and caused a rather intensive gold mineralization in the area during the Pyrenean Orogeny. The extensive ancient mining relics at Deh Hosein, the simultaneous occurrence of tin and copper in it, together with frequent archaeological and ancient textual references which refer to the Iranian plateau as supplier of the raw material for the ancient Mesopotamia and southwestern Iran (Susa and Luristan) encouraged me to examine the possible relationship between the ore of this ancient mine and the ancient bronze artifacts. For this purpose, several bronze artifacts of typical Luristan style which date most probably to the Iranian Iron Age (from about 1300-1250 to 650 BCE) were investigated. The results were compared to the analyses of the Deh Hosein ore and other bronze artifacts previously published. Examination of 29 bronze artifacts from Luristan by energy-dispersive X-ray fluorescence analysis revealed that the Luristan bronzes show variable concentrations of As, Pb, Zn and Fe in addition to high concentrations of tin (0.48-15.4%). The ore composition of Deh Hosein is matched by several bronze artifacts from Luristan analyzed in this study as well as in previous investigations (Fleming et al. 2005). Even more noteworthy is the observation that the lead isotope ratios of the ore samples from Deh Hosein are in very good agreement with 25 samples of metal artifacts from Luristan and other bronze artifacts dated to the third millennium BCE from the southern Persian Gulf (Weeks 1999), the Aegean (Begemann et al. 1992), as well as from third millennium BCE sites in Luristan and Mesopotamia (Begemann & Schmitt-Strecker in preparation). At Deh Hosein, which is located at the western rim of the Luristan area and is close to ancient civilization centers of Susa and Mesopotamia, the ancient workings appear as numerous big ellipsoidal open depressions in two rows along the mineralized horizons. The old workings are up to 70 by 50m in size and up to 15m deep and are aligned over some 500m. Several hammer stones of silicified phyllite and granite, pottery shards and grinding stones have been found in the open-cast mines and adjacent ancient settlements. The pottery shards can be dated to the early first millennium BCE. Pieces of charcoal found in one of the diggings yielded a radiocarbon date of 3380 ± 55, which on calibration (2 sigma) results in an age range of 1775-1522 BCE. Several indications attest that Deh Hosein has been a major supplier of tin for ancient civilizations of Iran and Mesopotamia and perhaps even further west beginning in the third millennium BCE. In summary: i) The lead isotope compatibility of ores from Deh Hosein with many bronze artifacts from Bronze and Iron Age sites distributed from the southern Persian Gulf to the Aegean is good. ii) This is combined with a good match for trace element patterns of ores and artifacts. iii) Copper and tin occur within one mineralization. iv) Ancient textual references mention tin and bronze supply from regions east of Mesopotamia. v) The dating of surface finds of pottery and charcoal finally supports these findings. At present Deh Hosein is the only known copper-tin occurrence close to Luristan and Mesopotamia. The northern part of the Sanandaj-Sirjan zone which is characterized by intrusion of several intrusive bodies in metamorphic terranes favors the occurrence of similar deposits as in the Astaneh-Sarband area. Thus, the prospects are good for further exploration in the region which may also reveal some other ancient mines.

},

keywords = {Archaeometallurgy, Bronze},

pubstate = {published},

tppubtype = {phdthesis}

}