Archean Skarn and Porphyry Cu-Au-(Ag-Mo) Mineralization Associated with the Sanukitoid East Sullivan Stock in the Abitibi Greenstone Belt, Val-d’Or District, Quebec, Canada

Abstract The Val-d’Or gold district (Abitibi greenstone belt) hosts atypical Cu-Au occurrences associated with the Archean East Sullivan stock, located north of the Cadillac-Larder Lake fault zone. This study integrates geologic, geochemical, isotopic, and Re-Os geochronological data to characterize this intrusion-related system and its association with orogenic gold mineralization. The East Sullivan stock is a highly oxidized, water-rich, fertile, porphyritic, monzonitic-syenitic sanukitoid intrusion that crystallized at ca. 2684 Ma (U-Pb zircon). At least two mineralization styles are associated with the East Sullivan stock: (1) porphyry-style Cu-Mo-Au mineralization hosted within the East Sullivan stock, partly associated with a vuggy endoskarn facies; molybdenite from this style yields an Re-Os age of ca. 2695 ± 12 Ma, constraining the timing of porphyry mineralization; and (2) extensive Cu-Au-Ag exoskarn mineralization hosted in adjacent volcanic rocks of the Héva Formation. The exoskarn developed through a garnet-dominated prograde stage, followed by a calc-silicate–dominated retrograde stage that is associated with the main Cu-Au-Ag mineralization. We suggest that the East Sullivan stock is an Archean porphyry skarn system linked to sanukitoid magmatism that formed ~40 m.y. before the main orogenic gold events (~2643 Ma) in the district. These temporally distinct magmatic-hydrothermal and orogenic systems highlight the protracted, multistage metallogenic evolution of this major Archean gold camp.