Abstract

The Addington and Ore Chimney mines are Proterozoic gold-bearing quartz-carbonate vein deposits that occur in lower amphibolite facies metamorphic rocks, on and near a major regional unconformity.The Ore Chimney deposit has a typical opaque mineral association of galena-sphalerite-pyrite-chalcopyrite-pyrrhotite-Ag-rich tetrahedrite-ilmenite. The vein system is hosted by a 4-m-thick biotite schist enclosed by metabasaltic lava flows. The metavolcanic rocks are unconformably overlain successively by a 10-m-thick metapelitic garnet-biotite schist (the Ore Chimney Formation) and a coarse siliciclastic succession (the Flinton Group). The Ore Chimney deposit occurs 30 m below the unconformity.The Addington deposit has a typical opaque mineral assemblage of arsenopyrite-pyrite-chalcopyrite-pyrrhotite-ilmenite. This deposit is hosted by the Ore Chimney Formation and is located 8 km along strike from the Ore Chimney mine.Arsenopyrite geothermometry and sphalerite geobarometry yield temperature and pressure estimates ranging from 420 degrees to 530 degrees C and 0.35 to 0.59 GPa, respectively, consistent with estimated peak metamorphic conditions. Geochemical, textural, and structural evidence suggest that vein formation and mineralization occurred during the main episode of metamorphism and deformation and that gold was deposited by metamorphic fluids. The mineralizing process was associated with weak carbonatization of the wall rock. Gold and base metals may have been remobilized from preexisting concentrations resulting from hydrothermal and/or weathering processes.

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