The proposed metallogenetic model is based on observations from the Iranian non-sulphide zinc deposits Mehdi-Abad and Iran-Kuh. The emplacement of non-sulphide ore can be generally subdivided into an "oxidation stage", which is followed by a "post-oxidation stage". The non-sulphide zinc ore spectrum has two end members: red zinc ore, rich in Zn (>20%), Fe (>7%), Pb - (As) and white zinc ore with typically high zinc grades (up to 40%) but low concentrations of iron (42- ions during the oxidation stage leads to the precipitation of (under these conditions) highly insoluble anglesite. Most of the zinc (up to 80% at pH 6 or 97% at pH 5) leaves the oxidation zone and precipitates as smithsonite in adjacent parts of the carbonate host rock due to a high PCO2 environment. During the "post-oxidation stage" the PCO2 decreases and reaches the level of atmospheric PCO2. Under these conditions, hydrozincite becomes stable and starts to replace smithsonite. The "post-oxidation stage" is also associated with the successive formation of local zinc (hydro-) silicates, depending on the availability of SiO2 within the solution. Generally, arid climates provide the best conditions for the preservation of non-sulphide deposits. The limited availability of meteoric water and deep to very deep water tables protect the non-sulphide ore from subsequent dissolution. |