ABSTRACT

A symmetrical metamorphic alteration zone around the Broken Hill orebodies derives from retrogressive metamorphism. This zone is at least 300m wide and is characterized by a great increase in Rb/Sr and the replacement of earlier high grade metamorphic minerals by sericite. The alteration observed probably results from fluid ascent along permeable sulphide-silicate competency boundaries at the waning stages of granulite facies metamorphism.