Tourmalinites in supracrustal rocks in the Bjørnesund area, West Greenland

Abstract

In the mid-Archaean supracrustal rocks of Bjørnesund south of Fiskenæsset metre wide anthophyllite-rich zones are found hosted in mafic volcanics. These zones, which are locally associated with sulphides, are interpreted as alteration zones from hydrothermal solutions which circulated through the volcano-sedimentary pile; in places they contain thin tourmalinites. The tourmaline composition and geologic setting of the occurrences closely resemble stratabound tourmalinites of submarine hydrothermal origin which elsewhere are associated with metalliferous deposits. It is concluded that the presence of the Bjørnesund tourmalinites associated with anthophyllite zones indicates that hydrothermal processes were once active in the depositional environment where the Bjørnesund supracrustals were formed; in other regions such processes are known to have generated massive sulphide ore bodies.