Metallogeny and temporal–spatial distribution of sediment-hosted stratabound copper (SSC-type) deposits in Iran; implications for future exploration

Abstract

Iran is hosting to numerous sediment-hosted stratabound copper (SSC-type) deposits/occurrences. The major structural zones of Iran that host SSC-type deposits are: (1) the Zagros zone, (2) the Tabas Block, (3) the Central Iranian geological and structural gradual zone (CIGS), (4) the Sabzevar zone, and (5) the Kopeh Dagh zone. The SSC-type deposits formed during discrete time periods and in Iran mostly comprise: (1) the Early Cambrian- Ordovician (with the Dehmadan and Khongah deposits in the Zagros zone), (2) the Permian (with the Ghareh Tapeh deposit in the CIGS), (3) the Upper Jurassic (that include Cu mineralizations in the Garedu Red Bed Formation of the Ravar-Tabas-Eshghabad area (RTEA)), (4) the Upper Jurassic to Lower Cretaceous (with SSC mineralization in the Shurijeh Formation of the Kopeh Dagh zone), (5) the Oligocene to Miocene (including the Bande-Gheychi deposit, the SSC deposits of the Boustanabad-Tabriz-Tasuj area, Avaj-Dozkand-Moshampa area and the Torbat-e-Heidarieh SSC-type deposits), and finally (6) the Pliocene (with the Ghareh Aghaj deposit in the CIGS). Extensional basins that have passed through phases of continental rifting and post-collisional extension are the principal plate tectonic setting for the Iranian SSC-type deposits. All of the SSC-type deposits in the Jurassic and Oligocene-Miocene clastic sedimentary rock sequences formed within continental rifts and postcollisional extension settings, respectively, that developed during subduction of the Neo-Tethyan crust beneath the Iranian plate. Intra continental back-arc spreading settings are recognized in the Paleo-Tethys domain in Iran, and these host Cu-bearing dolomitic host rocks (Dehmadan and Khongah area) in the Zagros zone. The stratigraphic sequences of Iranian SSC-type deposits commonly formed from clastic continental red beds, evaporites and limestone, which are similar to other sediment-hosted stratabound copper districts around the world. The copper mineralization is generally closely related to plant fossils (e.g. wood fragments) and the main ore minerals include chalcocite, chalcopyrite, bornite, pyrite, galena, sphalerite, covellite and chrysocolla, the latter two generally have supergene origin. Copper sulfides occur mainly as replacement of diagenetic pyrite, which in turn, replaced organic matter (e.g. wood fragments). Copper mineralization is mainly controlled by the organic matter content and paleo-permeability from intragranular pore space, evaporate layers and brittle fractures. The paleo-permeability has locally been enhanced by calcite dissolution of diagenetic cements. The main period formation of SSC-type mineralization in Iran is from the Jurassic to Miocene. The Tabas Block and CIGS zone are the most promising metallogenic provinces in Iran for SSC-type exploration, because these domains have the greatest abundance and the largest of these copper deposits. These include the Markasheh deposit in the Tabas Block and substantial copper mineralization in the Miocene Red Bed sequence of the Boustanabad- Tabriz-Tasuj and Avaj-Dozkand-Moshampa regions in the CIGS.