Gold nanoparticles in acidic igneous rocks of Ramand area, south of Qazvin, northwest of central Iran

Ramand area is located 80 km south of Qazvin province, northwest of central Iran. The area is part of the magmatic belt of Orumiyeh- Doktar of the structural zones of Iran. The host rocks of the area consist of rhyodacite, rhyolites, rhyodacite tuff, crystalline tuffs and rhyodacite flow lavas. The pyroclastic and volcanic units are interrupted by major faults such as Korcheshmeh fault, Hassanabad fault and sub-faults that have a northwest-southeast extension. The main minerals of these rocks include K-feldspar, quartz, albite, biotite and rock fragments (in tuffs) with micro-granular - microporphyrite textures. The extensive alterations in the study area are argillic and silicifications. Pyrite, hematite and goethite are the main ore minerals of these rocks. The texture of these minerals is disseminated (primary) and of supergene replacement type to chloroform (secondary). Pyrites vary in size from coarsed to very fine in subhedral to unhedral forms scattered along fracture surfaces. The results obtained by capillary electrophoresis analysis shows that the pyrite minerals of these rocks contain of nanoparticles gold.