A metamorphogenic alteration zone around the stratiform Broken Hill ore deposits, Australia.

Abstract

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.

Garnet-biotite relationships in high grade metamorphic rocks at Broken Hill, Australia

“…Fifty garnet-biotite pairs from the pelitic, psammopelitic and quartzofeldspathic rocks enclosing the orebodies were analysed. Potassium and manganese metasomatism of psammites and quartzites adjacent to the sulphide rocks produced sericite-and spesartite-rich alteration assemblages from quartz-orthoclase±plagioclase-almandine-biotite± sillimanite ± ilmenite ± magnetite assemblages (Jones, 1968;Plimer, 1975) and it was thought that this may have had a significant effect on garnet-biotite relationships. Analyses for SiO 2 , TiO 2 , A1 2 O 3 , Cr 2 O 3 , total iron as FeO, MnO, CaO, K a O and Na^O were performed on a TPD electron probe microanalyser with energy dispersive detection and analysis system and an automated correction procedure (Reed & Ware, 1973).…”