Volume 12, numéro 2, june 1985

EN :

Plate tectonic models for the evolution of the Appalachians involve a Wilson Cycle of a late Precambrian-early Paleozoic ocean basin - the lapetus. On one side of the lapetus lay the continent of Laurentia, which included the ancient North American landmass. Continental rifting, which initiated the formation of the lapetus in late Hadrynian/early Cambrian times, left its mark on the continental margin of Laurentia in the form of structural damage and rift-related magmatic/volcanic products, and some of these are recognizable from the south-eastern parts of Canadian Shield and the adjacent platform. These include two well-defined aulacogens, zones of step faults parallel to the ancient continental margin and possible fracture zones transverse to the ancient margin. Carbonatite complexes yielding K-Ar ages of approximately 565 Maoccur in both aulacogens. Closely associated with one of them is a prominent dike swarm of probable Hadrynian age.

EN :

The Archean Hemlo gold deposit has many similarities with the sinters formed by two New Zealand hot springs, the Ohaki and Champagne pools. The New Zealand hot springs, therefore, warrant consideration as possible analogues of the mineralizing system which formed the Hemlo deposit.

The waters which issue from the Ohakiand Champagne pools are ultimately of meteoric origin. These waters have passed to depths of at least 1.5 km in a complex sequence of volcanic and sedimentary rocks, and have returned to the surface as neutral, weakly saline fluids near their boiling points. These fluids are undersaturated, by several orders of magnitude, with respect to the gold they contain, At the surface the fluids are cooled, oxidized and acidified, causing them to precipitate much of their dissolved load. The precipitated material forms aprons of siliceous sinter richin sulphur, gold, arsenic, antimony, mercury and thallium.