The Bavanat Cu-Zn-Ag orebody: First recognition of a Besshi-type VMS deposit in Iran

摘要

The Bavanat strata-bound Cu-Zn-Ag sulfide deposit forms two ore horizons within the Permo-Triassic Surian volcano-sedimentary complex, in the Sanandaj-Sirjan belt of southern Iran. Mineralization occurs as stratiform sheet-like and tabular ore-bodies mainly hosted by meta-mafic volcanics and meta-clastic sedimentary rocks, which are associated with chloritic and argillic alterations. Ore minerals are mainly pyrite, with subordinate amounts of chalcopyrite, pyrrhotite, sphalerite, and rare occurrences of cubanite and galena. The ore is massive to semi-massive, banded, laminated, disseminated and occurs locally as open space fillings. Geological, petrological, mineralogical and geochemical studies suggest that the mineralization, which is hosted in Surian meta-volcano-sedimentary sequences, resulted from Permo-Triassic submarine volcanic-exhalation in the early stages of the continental rift development in the Bavanat area. Later, the Surian complex and its associated ore deposits were deformed and metamorphosed under amphibolite fades and subsequent, retrograde greenschist facies conditions during the Late Cimmerian Orogeny. Thus, it is indicated that the Bavanat deposit as well as similar deposits and mineralizations are metamorphosed VMS-type deposits. The Bavanat VMS deposit reveals close similarities to the Besshi-type deposits such as Cu-Zn metal proportions, sheet-like geometry of the orebodies, meta-mafic volcanic and meta-sediment host rocks, galena-poor sulfide assemblage and high contents of Co and high Co/Ni ratios in the ores. The Bavanat VMS deposit is the first Besshi-type deposit recognized in Iran.