Original paper

Geochemistry and hydrothermal evolution of the Mazraeh Shadi–Hizehjan precious and base metal deposit, northeastern Tabriz, Iran

Radmard, Kaikosrov; Zamanian, Hassan; Hosseinzadeh, Mohamad Reza; Khalaji, Ahmad Ahmadi

Abstract

The Mazraeh Shadi deposit is located about 130 km northeast of Tabriz (NW Iran) in the Arasbaran metallogenic belt. Mineralization in this area mainly includes Au-Ag bearing quartz veins controlled by fault distribution within andesite and tra- chyandesite. Rock samples from quartz veins shows maximun values of Au (17100 ppb), Pb (21100 ppm), Ag (9.43 ppm), Cu (611 ppm) and Zn (333 ppm). Field work, microscopic study and XRD analysis resulted in recognition of five, zonally distributed hydrothermal alteration assemblages that consist of propylitization, phyllic, argillic and advanced argillic alterations associated with silicification and ore deposition. The depth of mineralization at Mazraeh Shadi deposit ranges from 230 m to 380 m below the paleosurface. Fluid inclusions in ore bearing quartz veins generally vary in size from 5 to 90 μm. Three types of fluid inclusions are typically observed at Mazraeh Shadi; (1) liquid-rich 2-phase, (2) vapour-rich 2-phase and (3) vapour mono-phase. The homog- enization temperatures of the inclusions ranges from 160 to 324 °C with an average homogenization temperature of 228 °C. The salinity of the fluid inclusions ranges from 0.17 to 5.1 wt.% NaCl equivalent. The last ice-melting temperature is between ‐2.2 and –3.2 °C. Mineralization of Au is due to pyrite precipitation, boiling of hydrothermal fluids and decreasing pH. Plots of salinity versus homogenization temperatures of fluid inclusions indicate that two fluids were incorporated in the formation of Mazraeh Shadi deposit. Three-dimensional discriminative graphs confirm that the precipitation of Pb and Zn occurred during entrapping the high temperature-low salinity fluid while deposition of Au happened during entrapping of the low temperature-high salinity fluids. Based on energy dispersive analysis with a scanning electron microscope average assay of Ag in pyrite is 2.37 wt.%, in quartz is 1.71 wt.% and in galena is 2.05 wt.% whereas the highest Au concentration is measured in spherical pyrite enclosed in quartz. Based on mineralogy and cross-cutting relationships and SEM-EDS analysis it is possible to distinguish three main groups of quartz and pyrite by different properties.

Keywords

epithermalfluid inclusionboilingarasbaranmazraeh shadi