Abstract The multimillion-ounce Fenelon gold deposit is a postvolcanic pre-Timiskaming deposit located in the north-western part of the Neoarchean Abitibi greenstone belt, Canada. Two stages of epigenetic gold mineralization are recognized: an early stage (M1) characterized by quartz veins with native gold and molybdenite, and a later stage (M2) with sulfide-rich mineralization accompanied by native gold and Bi-Ag tellurides. Both occur within high-strain zones along lithological contacts and foliation planes. Multiple sulfur isotope analyses of M2 pyrrhotite, chalcopyrite, arsenopyrite, and pyrite yielded near-zero Δ33S values and positive δ34S values (+2.0‰ avg), contrasting with those for diagenetic pyrrhotite in the sedimentary host rocks (Δ33S = +0.45‰ avg, δ34S = +0.6‰ avg). Some sedimentary-rock-hosted mineralization exhibits elevated Δ33S values (up to +0.54‰) and lower δ34S values (down to +0.90‰), consistent with local dissolution and reprecipitation of sedimentary sulfide. The sulfur isotope signature is that of fluids exsolved from crystallizing intrusions or metamorphic devolatilization of igneous rocks. A progressive increase in δ34S values is observed throughout the paragenesis, including within concentrically zoned M2 pyrite, where δ34S values increase from cores (+1.7‰ avg) to rims (+3.6‰ avg), accompanying inclusions of native gold and pyrrhotite. This trend is consistent with a progressive decrease in fluid fO2, likely due to interaction of the fluid with graphite in the sedimentary host rocks. These results show that the Fenelon deposit is either an intrusion-related deposit or, less likely, an early orogenic deposit formed from metamorphic fluids derived from igneous rocks. The results also underline the importance of fluid reduction by carbonaceous sedimentary rocks in gold mineralization.
Slater et al. (2026) studied this question.