The main sulphide ore belt of Finland between Lake Ladoga and the Bothnian Bay

Abstract

The formation of the Main Sulphide Ore Belt of Finland (containing 80‒90 % of its known sulphide ore resources) can be divided into four main stages: the (1) formation of the Outokumpu- (Cu, Co, Zn) and Vihanti-type (Zn, Pb, Cu) stratabound mineralizations close to the Archean continental shelf at the evolutionary stage of the Svecofenno- Karelidic orogeny; the (2) partial remobilization, redeposition and recrystallization of the Outokumpu- and Vihanti-type of ores during the revolutionary stage of the Svecofenno-Karelidic orogeny about 1800—1900 Ma ago; the (3) formation of the Kotalahti Ni, Cu Ore Zone together with the basic and ultrabasic intrusions in connection with deep movements about 1900 Ma ago; the (4) stepwise sinking (in both space and time) of the Main Sulphide Ore Belt to form steps or grabens, in which the ores were preserved from the erosion during the Proterozoic and Phanerozoic eons. These block movements took place after the Svecofenno-Karelidic orogeny, they are believed to have been caused by the isostatic forces resulting from the denudation of the ancient Svecofenno-Karelidic mountain ranges, situated mainly on the SW side of the Archaean continental shelf. Five points are presented to support the final hypothesis.