Urmia University
Abstract: (335 Views)
The argillic alteration zone of the Shanin area (west of Takestan, Gazvin province, Tarom-Hashtjin metalogenic province) is the product of intrusion of granitic igneous bodies of Oligocene age into middle Eocene dacite-rhyodacite rocks. X-ray diffraction (XRD) analyses indicate that Quartz and kaolinite are the two main mineralogical phases of this alteration zone, which are accompanied by accessory mineal phases such as halloysite, smectite, alunite, pyrite, rutile, goethite, illite, plagioclase, and svanbergite. Calculations of mass balance changes of elements show that immobile elements such as Zr, Nb, Th, Ta, and Y have been depleted during the argillic alteration processes. This abnormal behavior is a reason for the low pH of the fluids responsible for alteration, the high ratio of water to rock, and the abundance of complexing ions in the solution. The decrease of the mass of U indicates the oxidizing nature of the fluids responsible for the alteration. Combining the results obtained from mass balance geochemistry and correlation coefficients between elements reveal that absorption by clay minerals and isomorphic substitution by rutile played an important role in the distribution and fixation of Ga, Hf, and V in the studied alteration zone. The significant enrichment of Mo, Sb, and As, the very low Rb/Sr ratio, the mineralogical composition of the alteration zone, and the occurrence of vein-veinlet type ore mineralization (pyrite, chalcopyrite, galena, and goethite) show that the Shanin area has suitable conditions for high-sulfidation epithermal mineralization. Further investigations reveal that the distribution and fractionation of rare earth elements (REE) during the formation and evolution of the argillic alteration zone of Shanin area was controlled by phyllosilicate minerals, alunite and svanbergite.
Keywords: Phyllosilicate minerals, argillic alteration, REE fractionation, mass balance, Shanin, Takestan.
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