Alteration and related mineralization in the Qalluviartuuq greenstone belt, northeastern Superior Province, Quebec.

Abstract

The <2 km wide and about 70 km long Qalluviartuuq greenstone belt consists of mafic and felsic metavolcanic schists, metasediments, and a lens of gabbroic anorthosite <1 km wide and ~3-5 km long. Peak metamorphic grade for the section of the belt studied is low pressure epidote amphibolite facies with retrograde metamorphism in the upper greenschist facies. The mafic metavolcanics classify as basalts to alkaline basalts and contain hornblende - epidote - plagioclase (An33 - An40) ± biotite ± sphene ± magnetite. Quartzofeldspathic metasediments consist of quartz - biotite - plagioclase ±garnet± magnetite ± pyrite± chalcopyrite. The gabbroic anorthosite consists of plagioclase (An60 - An70) ± hornblende± clinopyroxene ± orthopyroxene ± biotite. Plutonic rocks flanking the belt are primarily biotite ± muscovite foliated metagranodiorite which trend NNW and dip steeply to near vertical. Zones of extensive alteration within the mafic metavolcanics and the anorthositic lens contain plagioclase - anthophyllite - cordierite ± biotite ± sericite ± chlorite ±quartz. Within the mafic metavolcanics these altered zones are characterized by enrichments in Fe20 3T and MgO with depletions in K20, Cao, Na20, and Si02. Altered zones of the anorthositic lens are characterized by enrichments in Fe20 3T, MgO, and Na20. These zones are associated with areas of localized ductile deformation characterized by layering of mafic minerals, mylonitization, and kink folding. They are likely brittle-initiated zones of ductile deformation which have undergone recrystallization-accommodated dislocation creep. Sulfide mineralization is associated with ductilely deformed and altered sections of the anorthositic lens and consists of pyrite - chalcopyrite - pyrrhotite ± sphalerite ±magnetite. Mineralization within mafic metavolcanics is characteristic of a Cu-Zn type volcanogenic massive sulfide (VMS) deposit and contains pyrite-pyrrhotite - chalcopyrite ± sphalerite ± magnetite± galena. Mineralized zones have elevated Cu, Zn, and Ag values with localized enrichments in Au and Co.