Geochemistry and origin of the Şaphane alunite deposit, Western Anatolia, Turkey

Abstract

A replacement type alunite deposit occurs in the Şaphane area, western Anatolia. The orebody within the rhyolitic–rhyodacitic Civanadag Tuff Member is mainly composed of alunite, with quartz, kaolinite and small amounts of pyrite. The deposit is laterally zoned from inner advanced argillic alteration to an outer propylitic–argillic zone. Vertical zoning is expressed in a transition from a silicified zone downwards through silica–alunite (alunite–kaolinite–quartz–opal-CT), limonite and propylitic–argillic zones (K-feldspar–quartz–smectite–illite). A barren silicified zone at the north of Main pit forms a silica cap over the alunitization. Due to strong acid sulfate alteration, K-feldspar and volcanic glass in the host rock were altered and released K and Al, facilitating the formation of alunite. Silica was transported upwards and deposited at the surface as quartz and/or opal-CT. Similar K–Ar ages (12 to 13 Ma) obtained for both the deposit and volcanic host rocks indicate that volcanism and alunite mineralization are cogenetic. Isotope analyses reveal that sulfur in the deposits has a magmatic origin. Acid sulfate alteration resulted in strong leaching of major elements, but most of the trace elements were generally retained in the original rock.