GEOCHEMISTRY IN FINLAND

Finland is a world leader in the development and application of geochemical surveys in exploration and environmental science, in particular in the use of geochemical methods in glaciated terrains. Geochemical methods have been developed since the 1940s and nation­wide mapping projects were carried out between 1970 and 1990, resulting in a till geochemical Atlas and various databases. These data are well supported by nationwide bedrock and surficial geological map databases, high-resolution airborne geophysical databases, and mineralization databases. In many areas, very detailed datasets are available based on the exploration studies by the Geological Survey of Finland (GTK) and mining companies such as Outokumpu Ltd and Rautaruukki Ltd.

Geochemical research and development are carried out by GTK and the universities. Close communication and cooperation between those institutes provides a strong foundation for the work of private companies in Finland. This has resulted in a great deal of activity by foreign exploration and mining companies in Finland since 1994, when Finland joined the European Union. Presently more than 40 exploration and mining companies are working in Finland looking for gold, nickel, PGE, uranium and base metals. There is also active industrial mineral exploration and mining in the area. Besides mineral exploration, geochemistry is also important in terms of environmental monitoring and ensuring sustainability.

 
Geological environment

The Archaean and Palaeoproterozoic Fennoscandian Shield constitutes large parts of Finland, northwest Russia, and Norway and Sweden. The Archaean contains only a few nickel-copper sulphides and VMS-type deposits, but orogenic gold deposits are more abundant and form part of an important global mineralising event at 2.7 Ga. The Archaean Siilinjärvi carbonatite, intruded in an anorogenic setting at 2.6 Ga, hosts a major apatite mine in central Finland.

Late Archean to early Proterozoic layered mafic-ultramafic intrusive complexes host major chromitite, nickel-copper and platinum group metals (PGM) deposits, including the world-class Kemi Cr and Suhanko PGM deposits of southern Finnish Lapland. Paleoproterozoic rifting led to voluminous ultramafic to mafic volcanism and plutonism, resulting in nickel-copper deposits found in komatiites to ferropicrites (Pechenga type). Rifting of the Archaean craton at 1.96 Ga is related to Outokumpu-type copper-cobalt ores, interpreted to be variants of Cyprus-type VMS deposits occurring in mantle rocks, later reworked during metamorphism and deformation.

Amalgamation of several microcontinents and island arcs with the Archaean nuclei at 1.92-1.80 Ga involved multiple orogenic events. Economic ore deposits in the Fennoscandian Shield are largely restricted to this time span and include VMS, nickel-copper, iron oxide and gold deposits.

Well-established stratigraphies were established for Fennoscandian continental glaciation during the Quaternary. The identification of different glacial events has implications for mineral exploration and it should be considered in the planning of till sampling programs.

Pre-Quaternary weathered bedrock has been preserved beneath glacial deposits in many areas in Northern Finland. It is typically strongly fractured, with secondary enrichment of iron minerals like goethite. Trace elements such as Cu, Ni, Co, Zn and Mo have been enriched in the fine fraction of this goethitic weathering crust, and the concentrations of these elements can be many times higher than in the underlying fresh bedrock. The mixing of this weathered material in till causes problems in till geochemistry and can distort the geochemical pattern, so in some cases, large amounts of secondary enriched weathered material in till maybe not necessarily relate to ore deposits.

Current activities

Mining has gradually been increasing in Finland since 1995, with currently (in 2010) 6 metal mines, 40 industrial mineral mines and approximately 60 dimension-stone quarries currently in operation. The metal mines include the world-class Kemi chromite and Pyhäsalmi copper-zinc mines as well as gold mines at Kittilä and Pahtavaara, in central Lapland. Two mines are under construction and several projects are at near-mine stages of development.

Exploration is at a correspondingly high level. GTK’s role continues to be fundamental in the discovery of economically significant ore deposits and mineralization. The foundation of this success story is the continuous generation of databases in conjunction with the active development of new exploration methods. Examples of these new methods are prospectivity mapping based on the use of geostatistic and spatial analysis, the effective use of GIS in integrating geological and geochemical data, and the application of extensive knowledge of surficial geological processes in glaciated terrain with efficient till geochemistry and heavy mineral exploration.

The potential for discovery of a variety of commodities in the Fennoscandian Shield continuously attracts new international companies to Finland. Layered intrusions in southern Lapland with high potential for PGM mineralization, as well as for nickel, copper, chromium and gold ores, continue to provide some of the most important targets. The amount of mineral claims has accelerated in recent years, in marked contrast to the significant drop seen elsewhere in exploration expenditures from the peak year of 1997. Instead, exploration spending has been stable, at around €40 million per annum – the highest level in Europe.

There are many reasons for the increased interest in mineral projects in Finland

• It is internationally accepted that the shield geology in Finland, being of the same age and type as the shield areas of Canada and Australia, holds a similar potential as these countries.

• The political and economic stability, mining and environmental legislation and the clear pro-mining attitude, especially in Northern and Eastern Finland, are important factors in encouraging exploration.

• Finland has a well-established infrastructure, combined with a sparse population, the high performance of GTK and the exceptional quality and coverage of geodata.

At the same time, an increasing awareness of post-treatment of closed mines and related environmental issues are important targets for research, development and education. Geochemical surveys are essential during feasibility studies in order to determine natural background levels for potential mining districts as well to monitor natural and manmade changes in the environment. Geochemistry is also needed when planning the treatment for process water, sand and other wastes in mines. Furthermore, geochemistry is also needed in planning and monitoring of the urban environment including land use and remediation of polluted soils, waters and landfills.