Gold mobility in Archean metasedimentary belts: Implications for orogenic gold deposits

The southern Superior Province (Canada) comprises large metasedimentary belts, such as the Pontiac and Quetico subprovinces, adjacent to Au-endowed greenstone belts. The Pontiac sedimentary rocks have been proposed as a source of Au for the highly endowed southern Abitibi greenstone belt. However, a comparison with sedimentary rocks adjacent to poorly endowed greenstone belts is lacking. Here we examine a suite of metasedimentary and minor volcanic rocks collected from three transects in the Pontiac and Quetico metasedimentary belts adjacent to greenstone belts with variable Au endowments. We combine in situ Au data of sulfides in metasedimentary rocks with whole-rock ultra-low-detection Au data. Gold concentrations decrease across metamorphic isograds in the well- and moderately endowed transects, while limited Au mobility is observed in the poorly endowed transect. The release of Au from metasedimentary rocks is linked to the pyrite-pyrrhotite transition. This reaction is incomplete in the poorly endowed transect, explaining the limited Au mobility observed. Our data reveal a spatial correlation between Au mobility in metasedimentary belts and Au endowment in the adjacent greenstone belts.