M Nejadhadad; B Taghipour; A.R Zarasvandi; A.R Karimzadeh Somarin; S Salamab Elahi
Abstract
Located 20 km north of the Delijan city, the Pb-Ba-Ag ore deposit was mineralized in the lower Cretaceous carbonate host rocks in the Ravanj anticline. Geographically, the Ravanj anticline is part of the Urumieh-Dokhtar magmatic arc in the Zagros orogenic belt. Deposition of the ore took place in the ...
Read More
Located 20 km north of the Delijan city, the Pb-Ba-Ag ore deposit was mineralized in the lower Cretaceous carbonate host rocks in the Ravanj anticline. Geographically, the Ravanj anticline is part of the Urumieh-Dokhtar magmatic arc in the Zagros orogenic belt. Deposition of the ore took place in the lower part of massive limestones where they have been structurally thrusted over the shale and shale-limestone strata. Breccia filling, host rock replacement and disseminated ore are the main textural features of mineralization. Mineralization consists of fine-grained galena, barite, variable amounts of pyrite, and minor amounts of sphalerite, tetrahedrite, and chalcopyrite. Despite extensive pyritization, marcasite was not found in the ore, indicating that the ores were mineralized from a fluid having a pH > 5. Fluid inclusion microthermometric studies were done in the calcites of pre-main-stage mineralization (C2), in main-stage barite and in post-mineralization calcite (C3). Average homogenization temperatures of fluid inclusions are approximately equal: 165 ˚C in the pre- main stage calcite, 160 ˚C in post-mineralization calcite and 175 ˚C in barite, but their salinities change from lower than 1 to higher than 18wt% NaCl equivalent. Silica precipitation in the Ravanj deposit is very limited, in agreement with minor changes in temperature of fluid during mineralization. The wide range in salinity of the fluid inclusions plus contemporaneous deposition of barite and fine-grained galena are evidences for mixing of two geochemically different fluids. One of them was probably a low-salinity (5.6 wt% NaCl), CO2-beaing and sulfur-rich fluid. At a temperature of 160 ˚C, the neutral pH is about 5.8. Therefore the sulfides were deposited from fluids having a pH of 5-6. The effect of low-salinity, CO2-beaing fluid is to buffer the system. The second fluid, which was probably oxidized, saline (15.7 wt% NaCl) and metal-rich, shows salinity and homogenization temperatures characteristic of MVT ore forming fluids.
B Taghipour; M Nejadhadad; M.A Makizadeh; M Noghreian; P Rahimi
Abstract
Dunite and serpentinized harzburgite from northwest of the Neyriz ophiolites are host rocks of some podiform chromite deposits in Cheshmeh-Bid area. These chromite deposits occurred as aligned massive lenses in various sizes. The most important ore textures are massive, nodular, layered and disseminated ...
Read More
Dunite and serpentinized harzburgite from northwest of the Neyriz ophiolites are host rocks of some podiform chromite deposits in Cheshmeh-Bid area. These chromite deposits occurred as aligned massive lenses in various sizes. The most important ore textures are massive, nodular, layered and disseminated grains. These textures are goodevidences of crystals settling crystals during the process of magma cooling in the chamber. The mineralogical studies revealed that the pyroxene melting tookplace in the peridotite host rock and olivine is recrystallized in dunite envelope. Mineral chemistry of chromite indicates high Cr number(72-77), high Mg number(69-62) and low TiO2 content(0.04-0.14 %) in chromite samples. These amounts are comparable with those chromitites, which areformed from the high partial melting rate of mantle. The medium amount of PGE determined about 212ppb, which is much lessthan the Tang-e-Hana chromite (1556ppb) deposits. The trace element content of chromitite samples and dunite envelope like Ga, V, Zn, Co, Ni and Mn are between 17-24, 466-842, 852-1048, 22-84, 115-171, and 852-1220 ppm respectively. The U shape of REY pattern indicates the interaction of high volatile and REE bearing melt(boninitic source of parent magma) with host rock. Therefore,the Cheshmeh-Bid chromitite resulted likely from the intrusion of boninitic magma ofprimary mantle with high partial melting in the peridotite host rock. The geotectonic setting is above supra-subduction zone of island arc.