Granite hosted archaean lode-gold mineralization: example from the chalice gold deposit, western Australia

摘要

The Chalice gold deposit is hosted by a sequence of mafic and ultramafic rocks, which have been metamorphosed to the mid-amphibolite facies. Pre-, syn- and post-mineralization granitic dykes cross-cut the mine lithostratigraphy. Gold mineralization is structurally controlled, with wall rock alteration expressed as a pervasive quartz-albite-diopside-titanite+-garnet replacement of mafic amphibolite, and as foliation parallel calcsilicate veins that consist of quartz-albite-dioside-titanite+-garnet. Gold occurs locally as inclusions in: (1) plagioclase and quartz within the mafic amphibolite, (2) diopside and albite within quartz-albite-diopside-titanite+- granet veins, (3) monomineralic hornblende vein selvages, and (4) quartz and plagioclase, and at quartz-plagioclase interstices of a syn-mineralization granite. Amphibole-gold and molybdenite-gold veins cross-cut the dominant foliation in the mafic amphibolite, and indicate a second gold mineralization event. The occurrence of gold in both granitic and mafic rocks suggests a potentially close link between gold mineralization and magmatism.