Carbothermal metasomatism of alaskitic granite, St. Lawrence, Newfoundland, Canada

Quartz K-feldspar porphyry forming the chilled margin of the alkaline-peralkaline St. Lawrence granite has been intensely metasomatized where fluids were ponded against gently-dipping impermeable shales which form a roof to the pluton. The original quartz and K-feldspar have been completely replaced by albite and calcite, with a net loss of K and net gain of Na, Al, Ca, CO2 and Si. This was accompanied by a significant gain of Zn and Pb, with variable gain of Sr, Y, Cu and total REE, and loss of Ba and Rb. There is no significant enrichment of heavy REE, unlike what would be predicted from the high CO2 activity which characterized the metasomatic fluids. Some uranium and tin enrichment has also been noted at the granite-shale contact in this locality. (Auth.)