The East Sullivan Stock and its Gold-Copper Potential, Val d’Or, Quebec, Canada
The East Sullivan Stock (ESS) is a small, composite felsic alkaline pluton of presumed late Archean age in the Val d’Or mining district. Three main facies have been distinguished: monzonite
sensu stricto, porphyritic monzonite, and green trachytic porphyry. This monzonitic group of
rocks is of relatively homogeneous composition with high abundances of Na2O, K2O, Ba, Sr, Rb, Zr,
Mo and LREE. The alkaline ESS is distinguished from other igneous units in the Val d’Or mining
district, such as the Bourlamaque Batholith, by relatively high concentrations of Ba, Sr, Rb, Mo, Cu and Au. The ESS hosts many base (Cu, Mo) and precious (Au) metal occurrences, including: (1)
porphyry style Cu-Au-Mo disseminated sulfide deposits, (2) Cu-Au deposits in volcanic rocks near
the ESS contact, and (3) pyritic gold mineralization in east-west trending shear zones. The ESS is well defined by concentrical zoning on the aeromagnetic vertical gradient color map, and displays four linear trends, which are assumed to be structural lineaments, at 035°-055°, 320°-300°, eastwest, and north-south. The main mineral occurrences related to the stock display a preferred spatial association with the east-west linear magnetic trends.
The ESS is preferentially located along a major structure and was emplaced late in the evolution
of the Abitibi subprovince like other felsic alkaline plutons. This stock is similar to late-tectonic mineralized felsic alkaline intrusions of the Kirkland Lake and Larder Lake mining districts in Ontario, and to the Allard stock in the U.S.A. which is associated with gold and base metal mineralization. Similarities also exist with younger alkaline plutons associated with Cu-Mo-Au porphyry deposits in the Canadian Cordillera, which formed in tensional tectonic environments. The felsic alkaline magma may have formed by partial melting of deeply buried supracrustal rocks, concomitant with the development of deep fractures such as the Cadillac Fault. In such an environment, hydrothermal solutions carrying remobilized metals from deep supracrustal rocks may have deposited gold and base metals in structural traps. Plutons similar to the ESS should be good targets for mineral exploration.
East Sullivan Stock, Gold-Copper, exploration, Hydrothermal solution