Ammonium content of Archean rocks of the Superior Province

Ammonium contents were determined for clastic sediments and associated volcanic rocks of the Kirkland Lake area, Abitibi greenstone- granite belt and metamorphic, migmatitic and granitic rocks of the Ear Falls-Dryden area, English River gneiss-granite belt. The NH(4) centents of Archean volcanic rocks (2700~2710m.y.) are very low (0~6 ppm) and immature argillites have also low contents of NH(4) (27~43ppm). On the other hand, a black shale from the Timiskaming Group (2100m.y.) are rich in graphite and pyrite and contain much NH4 (130ppm), providing a firm evidence of relatively abundant presence of an Archean biota compared with a sparcity of morphological record of Archean fossils. The NH(4) content of the rock mentioned above is about a third of those of the upper Proterozoic sediments and it remains to be established whether it reflects the abrupt break in the evolution of life near the Archean-Proterozoic boundary or not. A considerable amount of NH(4) is inherited by highly metamorphic pelitic gneisses and there may be a possibility for indirect prospection of early life by a study of NH(4) in highly metamorphic rocks of the early Archean. It was also found that the gneissic granitoid has much higher content of NH(4) than the post· kinematic massive granitoid