The Genesis of the Epithermal Gold Mineralization at North Glojeh Veins, NW Iran.

Abstract

The Glojeh mineralization district is part of Tarom-Hashtjin metallogenic province. Igneous rocks in Glojeh district include intrusive rocks (granodiorite, granite and quartzmonzonite), and volcanic and sub-volcanic rocks (rhyodacite, rhyolite, andesitic basalt, andesitic, tachyandesite, trachydacite, basalt, tuff and rhyolitic tuff), which are typically of high-K igneous rocks transitional to shoshonites. Rhyodacite are host rocks of North Glojeh veins. Alteration is consisting of propylilitization, sericitization, argillization and silicification. Hydrothermal alteration zones have well-developed and zoned, that extends ? 30 meters into the host rocks. Mass balance calculations indicate that Al, Zr, Ti, Y, Nb, and HREE were immobile elements during alteration. Mineralization occur in four stages: 1) pyrite-magnetite-quartz assemblage; 2) As-Sb-Fe-Au-Cu assemblages; 3) Pb-Zn-Cu-Ag assemblages; and 4) hematite-goethite assemblages associated by precious metals. The veins longitudinal sections show clearly that base metals occur at the deepest levels, whereas precious metals occur at higher elevations with respect to base metals. Silver occur overlapping and slightly above the base metals zone, generally above the zone rich in base metals and beneath of gold zone. This observation contradicts the typical zoning pattern caused by boiling in epithermal veins. The North Glojeh deposit is a typical of epithermal deposit, with features of either high-sulfidation (stage 1 and 2) or intermediate-sulfidation (stage 3) types of epithermal deposits. Also stage 4 (oxidation zone) have features of low sulfidation type.