Geology and Genesis North of Semnan Pb - Zn Deposits

Category Economic geology & mineral exploration
Group GSI.IR
Location The 24 Symposium of Geosciences
Holding Date 15 August 2007

The area of north Semnan, part of Centeral Alborz, has 25 Lead and Zinc abondened mines and accurences. The most of these deposits have formed in upper Cretaceous succession. In this work 3 abondened mines Reza-Abad, Heydar-Abad and Darband and Bozmolla occurrence studied from this succession. Using thin microscopic sections which were staind by Alizarin Red-s and Potassium Ferro Sianor, polish section, XRD graphs, Wet chemical analysis, XRF and ICP-MS, 2 types of hypogene and supergene mineralization and also dolomitic alteration and little silicification have been recognized. Hydrothermal dolomites detected with more than 55% carbonat calcium. Above-mentioned 3 deposites and 1 accurences have been placed in one horizone stratigraphy, but hypogene, supergene and gangue minerals differ from each other. These differences relate to the direction of migration of meteoric and strata water and effect this fluid and hydrothermal fluid on included rock and presipitation mechanism from one deposite to the other deposite. These deposites are Mississippi valley type because mineralization simple hypogene, larg scale galen crystal, existance of limited minerals in hydrothermal dolomite bed rock and emplacement scattered of galen is accompanied by calcite veins   and in collaps and tectonic breccias cement