Geological, geochemical, and fluid inclusion evidences for the origin of the Ravanj Pb Ba Ag deposit, north of Delijan city, Markazi Province, Iran

Abstract

The Lower Cretaceous sequences of the Ravanj anticline in Iran host the Ravanj Pb Ba Ag mineralization. Economicorebodies are restricted to the thrust zone within the brecciated massive limestone and immediately above the Jurassic shale and/orshale limestone intercalations of the Lower Cretaceous. Paragenetic sequence and distinct zoning of mineral assemblages indicate thatore-forming fluid migrated through thrust zones along the NE-trending faults. The REE pattern of mineralized host rock is characterizedby HREE-enrichment ((La/Lu) PAAS= 0.24). The Ce/Ce* ratio of mineralized host samples shows negative Ce anomalies, which is mostlikely inherited from seawater. The positive Eu/Eu* anomaly suggests highO 2during ore deposition. Negative δ 34 S values of theRavanj sulfide minerals ( 27 to 11 ) suggest bacteriogenic sulfate reduction, whereas positive δ 34 S values of barite (+20 ) fallin the range of Tertiary marine sulfates. Multiple isotopic sulfur sources of sulfides and sulfate minerals support mixing of a reducednegative isotopic sulfur-bearing fluid and a positive isotopic sulfate-bearing fluid. The average of homogenization temperatures of fluidinclusions from the early and late-stage mineralization calcites are 165 and 160 °C, respectively. The salinity of fluid inclusions variesbetween 0.66 and 18 wt% NaCl equivalent with an outlier at 22.2. Wide variation in the salinity of fluid inclusions can be explainedby fluid mixing between a higher salinity group with 14 18 wt% NaCl equivalent and a lower salinity group with 0.66 8 wt% NaClequivalent. In the Ravanj, fine grained sulfide minerals are consistent with a sulfur supersaturated fluid. High concentrations of Pb canbe present in oxidized, chlorine-bearing fluids if the concentration of total H 2 S is very low. Therefore, mixing of two geochemicallydifferent fluids could precipitate both galena and barite. These data show that the Ravanj Pb Ba Ag deposit is comparable with Pb-richMississippi Valley-type deposits such as the Viburnum Trend district in the USA.