Glacial geology and till geochemistry in ore exploration in the Tervola area, southern Finnish Lapland

Abstract

Glacial geology and till geochemistry were studied in an ore exploration project in the Palaeoproterozoic Peräpohja Schist Belt in the Tervola area of southern Finnish Lapland. The starting point for the exploration were numerous Au-Cu-rich erratics, the source rock of which was unknown. The mapping of the glacial landforms was based on aerial photo interpretation. The structure, texture, lithology and geochemistry of the till were studied using test pits. Three sieved fractions together with a heavy mineral fraction of the till were analyzed chemically. The glacial landforms of the area include cover and ground moraines, drumlins, flute ridges and Rogen moraines. The ridges of the Rogen moraine were found to be composed of three different till beds. The surficial parts of the Rogen ridges showed very short transport distance, whilst the lower till was of more distant derivation. Gold and Cu contents in the till are above their regional background level sin every analyzed fraction in the two case study areas of Petäjävaara and Vammavaara. High metal contents in till are associated with basic volcanic rocks and their contact zones with quartzite in bedrock. Metal anomalies in till are usually very sharp-contrasted and dilute quickly with increasing distance from the source rock. The most useful indicator elements in till geochemistry, in addition to Au, are Cu, Te and Co. The combination of careful studies of glacial geology and till geochemistry proved to be a powerful means in locating source rock of glacially transported ore boulders in this area. As a result of the exploration, Cu-Au mineralization was localized at Petäjävaara.

Keywords

• mineral exploration
• geochemical methods
• till
• stratigraphy
• geochemistry
• gold
• copper
• pathfinders
• heavy minerals
• glacial transport
• erratics
• Tervola
• Finland