The Breznik epithermal Au occurrence, Western Srednogorie - Bulgaria: an 'atypical' (?) low-sulphidation hydrothermal system

摘要

The Breznik Au occurrence formed in an Upper Cretaceous volcano-intrusive structure with extrusive andesite-basaltic volcanoclastics and a gabbrodiorite body at 300-350m depth. Zonally developed argillic alterations (quartz-kaolinite-alunite, quartz-sericite, propylite) are signs of the first hydrothermal event. Abundant quartz-sericite-carbonate Au-bearing mineralisation of LS type overprinted earlier altered rocks. Sub-economic Au ore occurs in linear zones in the southern part of the structure among propylitic alteration. Scarce HS (enargite-luzonite) mineralisation developed under and into quartz-kaolinite-alunite and quartz-sericite alterations. It is suggested that such a close spatial formation of LS and HS mineralisations caused the influence of interaction of a LS hydrothermal system with different rock-buffers resulting in precipitation of different in sulphidation state ore minerals: acidic -HS ; acidic to neutral -IS ; alkaline -LS.