Mineralization and geochemistry of sediment-hosted stratabound copper (SSC) horizons in the Garedu Red Bed Formation of the Khormo-Gazak mining district, Tabas Block, Iran

The eastern part of Ravar town in the southeastern portion of the Tabas Block of Iran hosts several sediment-hosted stratabound copper (SSC)-type deposits. They have occurred within the Late Jurassic Garedu Red Bed Formation including red sandstone, conglomerate, siltstone, and reduced siliciclastic layers with evaporite interbeds. This research is attentive on five chief orebodies/occurrences comprising Khormo, Mianrood, Dehoj, Godar-Rigi and Gazak, collectively known as Khormo-Gazak mining district (KGMD). Copper mineralization in this district is primarily contained by the woody fragment's substance and paleo-permeability from intragranular open space and evaporite beds. The paleo-permeability has been improved by carbonate dissolution of diagenetic cements in the bleaching zones. The spatial distribution of woody fragment had a fundamental role in the Cu mineralizing system. Two different stages of mineralization were distinguished based on the mineralogical and textural relationships and morphology of the mineral's studies: (1) reddening, bleaching and formation of framboidal pyrites in the early diagenesis stage; and (2) replacement of woody fragments, framboidal pyrites and cements with copper sulfides in the late diagenesis stage. The red zone, bleaching zone and ore zone are indicative of the main ore-forming event and are volumetrically the most important zones. Chalcocite, bornite, chalcopyrite, digenite, yarrowite, djurleite, roxbyite, native copper, native silver, pyrite, atacamite, covellite, malachite and azurite, are the major ore minerals, in order of abundance, found in the studied deposits, accompanied by the minor amounts of chrysocolla, neotocite and hematite. The geochemistry data of ore-bearing ore horizons in the KGMD deposits indicates a distinct variation in Cu and Ni concentrations during the formation of different ore zones. On the basis of mineral chemistry inspections, chalcocite in the Khormo deposit were enriched in Ag, in contrast to Gazak chalcocite's. Isotopically very light sulfur indicates that the chalcocite was supplied from diagenetic framboidal pyrite and the derived from the destruction of woody fragments. Destruction of organic matter leads to the creation of reducing environmental conditions and reducing geochemical traps for the deposition of sulfides. The KGMD deposits are considered as a typical case of SSC-type mineralization, in which minerals deposited when oxidized brines flushed through the basin successions, the liberated copper was transported to units containing carbon-rich horizon and the metals were deposited.