PETROLOGY AND ALTERATION GEOCHEMISTRY OF THE EPITHERMAL BALYA PB-ZN-AG DEPOSIT, NW TURKEY - A RECONNAISSANCE STUDY

The 1.5 km-large hydrothermal system of Balya is characterized by thre e alteration styles which from the outer halo towards the center are: (i) propylitic alteration with the hydrothermal mineral assemblage of calcite-daphnite-albite-epidote-quartz-pyrite; (ii) argillic/phyllic a lteration with the hydrothermal mineral assemblage of sericite/muscovi te-kaolinite-rutile-quartz +/- pyrite; (iii) advanced argillic alterat ion with the hydrothermal mineral assemblage of alunite-jarosite-kaoli nite-quartz-sericite +/- pyrite. Hornblende andesite is the protolith of the hydrothermal alteration system. Enrichment in Si, Sb and Rb, an d depletion in Na, Ca, Mg, Fe, Mn, P, Ba, Sr, and Zn distinguishes the argillic/phyllic and advanced alteration types from propylitic altera tion and the unaltered hornblende andesite protolith. REE distribution patterns indicate an essentially immobile behaviour of REEs during th e alteration cycle. K-Ar age data for unaltered and hydrothermally alt ered rocks define a synchronous age of 25.3 +/- 1.2 Ma for both igneou s and hydrothermal activity.