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Book Chapter

A Geochemical Model of Supergene Carbonate-Hosted Nonsulfide Zinc Deposits

By
Jörg Reichert
Jörg Reichert
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Published:
January 01, 2009

Abstract

The metallogenic model presented in this paper is based on observations from three Iranian nonsulfide zinc deposits: Mehdi-Abad, Iran-Kuh, and Kuh-e-Surmeh. The emplacement of nonsulfide ore can be generally subdivided into a “sulfide oxidation stage” followed by a “postsulfide oxidation stage.” The formation of carbonate-hosted nonsulfide zinc deposits is primarily controlled by three factors: climate, protore composition, and geology (lithology and structure) of the wall rocks. Typical minerals of the red zinc ore are iron oxyhydroxides, goethite, hematite, hemimorphite, smithsonite, and/or hydrozincite and cerrusite. Common minerals of the white zinc ore are smithsonite or hydrozincite and minor amounts of Fe oxyhydroxides. Metal separation is caused by a gradual change from an acidic oxidation zone to alkaline conditions in the adjacent carbonate wall rock. The formation of an acidic oxidation zone within carbonate host rocks is facilitated by the armoring of calcite by gypsum and hydrous ferric oxides (HFO) and by several pH-buffering reactions. The HFO within the oxide zone additionally adsorb various amounts of Pb and Zn, depending on the pH. The neutralization processes of the sulfuric acid with the carbonates of the host rock during the oxidation stage lead to the formation of CO2(g). Under these conditions most of the zinc precipitates as smithsonite. The partial graphic decreases during the postsulfide oxidation stage and reaches the level of atmospheric graphic, and hydrozincite becomes stable and replaces smithsonite. The postoxidation stage is also associated with the successive formation of local zinc (hydro-) silicates, depending on the availability of SiO2 within the solution.

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Contents

Special Publications of the Society of Economic Geologists

Supergene Environments, Processes, and Products

Spencer R. Titley
Spencer R. Titley
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Society of Economic Geologists
Volume
14
ISBN electronic:
9781629490380
Publication date:
January 01, 2009

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