Metallogeny of volcanogenic massive sulfide deposits of Iran

Abstract

There are a lot of volcanogenic massive sulfide (VMS) deposits and numerous mineral occurrences of this type of mineralization in Iran. VMS deposits can be subdivided into different types, and Iranian VMS deposits represent all of the recognized types: mafic-, pelitic-mafic-, bimodal-mafic-, bimodal-felsic- and felsic-siliciclastic-type, and these are hosted in different tectonic settings. The major tectonic/structural zones of Iran that host VMS deposits are: (1) the Sanandaj-Sirjan Zone (SSZ; North: NSSZ; South: SSSZ), (2) the Urumieh-Dokhtar magmatic assemblage (UDMA), (3) the Central Iran (Sabzevar Zone/SZ and Kashmar-Kerman Zone/KKZ), and (4) the Mesozoic ophiolites (MO). The VMS deposits were formed during discrete time periods: (1) Late Neoproterozoic-Early Cambrian (Taknar bimodal-felsic-type Cu-Zn-Au-Ag-Pb and Nohkouhi felsic-siliciclastic-type Cu deposits in the KKZ), (2) Late Triassic-Early Jurassic (e.g., Sargaz bimodal-mafic-type Cu-Zn deposit in the SSSZ), (3) Early Jurassic (Bavanat pelitic-mafic-type Cu-Zn-Ag deposit in the SSSZ), (4) Middle Jurassic (e.g., Chahgaz felsic-siliciclastic-type Zn-Pb-Cu deposit in the SSSZ), (5) Cretaceous (e.g., Barika bimodal-felsic-type in the NSSZ, Nudeh and Garmab-e-Paein pelitic-mafic-type Cu-Ag in the SZ, Sheikh-Ali and Zurabad mafic-type Cu deposits which occur in the Upper Cretaceous ophiolites), and (6) Eocene-Oligocene (e.g., Dorreh and Varandan bimodal-felsic-type deposits in the UDMA).Magmatic arcs (volcanic primitive arcs, arc/intra-arc rifts and back-arc basins) are the principal plate tectonic setting for the Iranian VMS deposits. All of the VMS deposits of the SSZ and UDMA formed within Mesozoic and Tertiary arcs, respectively, that developed during subduction of the Neo-Tethyan crust beneath the Iranian plate. Intra-oceanic or continental mature back-arc spreading settings are recognized in the Neo-Tethys domain in Iran (i.e., MO), and these host several Cu-rich VMS deposits. The host rock sequences for all deposits can be divided into three groups: (1) bimodal calc-alkaline; (2) bimodal tholeiitic; and (3) tholeiitic basaltic. The sulfur isotope compositions of the VMS deposits in the SSZ indicate that significant sources for sulfur in these deposits were inorganically reduced seawater sulfate and sulfur leached from the footwall volcanic rocks.The main time period of the formation of VMS mineralization in Iran was form Jurassic to Cretaceous. The SSZ (particularly the SSSZ) is the most attractive metallogenic province in Iran for VMS exploration because it hosts different VMS deposit types, including the precious metal enriched Barika bimodal-felsic-type deposit in the NSSZ, and the Bavanat pelitic-mafic-type (mafic-siliciclastic-type), Chahgaz and Chahanjir felsic-siliciclastic-type, and Sargaz, Ghalerigi and Siahmadan bimodal-mafic-type deposits in the SSSZ.