Geology and gold–molybdenum porphyry mineralisation of the Archean Taschereau–Launay plutons, Abitibi, Quebec

Porphyry gold deposits constitute a new challenge for mineral exploration in Archean greenstone belts, yet the relationships between intrusive rocks and mineralisation remain poorly understood. The Messegay gold occurrence is situated in the Taschereau–Launay plutonic complex of the Northern Volcanic Zone of the Abitibi greenstone belt. The Taschereau intrusion (2718±2 Ma) represents a complex network of sills composed of tonalite with minor amounts of diorite, monzonite and gabbro. The Launay granite, which intrudes the Taschereau pluton, is late-orogenic and its emplacement was controlled by an early reverse ductile N–S shear zone. Intrusive rocks have been subjected to four episodes of alteration: epidote–chlorite–carbonate, magnetite–hematite–microcline, albite–pyrite, and sericite–quartz. Shear zone hosted and metasomatic Au–Mo mineralisation is mainly associated with albite–pyrite assemblages, but also occurs within zones of intense magnetite–hematite–microcline and sericite–quartz alteration. The Messegay gold occurrence is interpreted as a new type of disseminated gold–molybdenum porphyry deposit associated with a zone of magmatic differentiation in a magnetite-series pluton.