Background Au levels in ancient greenstone belts

Background gold levels have been estimated in Archean-Proterozoic metavolcanites. The Archean protovolcanites show the maximal spread in regional mean Au levels, with a tendency for the values to fall from the ultrabasic-basic varieties to the acid ones. The Proterozoic metavolcanites show a more compact distribution, no matter what the basicity or acidity. Regional low-grade metamorphism (greenstone regeneration) has not had a substantial effect on the distribution of gold in ancient greenstone-belt magmatites. Only metasomatism occurring at various times has assured gold migration and accumulation in the metasomatic columns, K_a of 0.2-0.9 and 2.3-320. the sources of such solutions were plutonic magmatic sites, namely, zones of andesite-magma generation in asthenoliths. -Journal summary