Trialling novel surface geochemical techniques for bedrock mapping in the peatland and glacially covered terrains

Abstract

In glaciated and peatland covered terrains bedrock and boulder mapping are often challenging. The lack of boulders and exposed bedrock in these environments emphasizes the need for new mapping and mineral exploration techniques. Geochemical methods in mineral prospecting consider materials which are not traditionally used in exploration but are abundant and available in the Nordic areas of overburden. Some of them, like bottom of till sampling, are already used in exploration programmes. However, sampling medias closer to the surface, like plants, peat, and top till, have also been studied for exploration interests, as sampling these would come closer to the effort, sustainability, and expense of bedrock and boulder mapping. In areas void of rocks they would offer an additional option for mapping and exploration.

The aim of this thesis was to trial surficial geochemical methods in and around the Hirviaapa peat production area, a former aapa mire with thick peat and till layers covering bedrock. Copper mineralisation potential of the bedrock was studied through these methods and their results. Branches and leaves of downy birch and Marsh Labrador tea, top peat and top till (40-100 cm), and lower peat and till (1-8 m) were sampled in three survey lines and analysed in a laboratory for element contents. The results were processed, analysed, and visualised using MS Excel and QGIS.

The analysis of the laboratory results of the samples revealed that downy birch and Marsh Labrador tea vary in copper content less than the other sample materials. The largest value ranges were observed in till geochemistry. Some anomalous copper values were detected in upper and lower tills as well as in the top peat. Minimum mineralisation indication limits of Cu were reached in the plant samples but nothing clearly anomalous was detected. The sample materials did correspond to each other in their respective value ranges in some areas, but this was not a general trend. The underlying bedrock and lithological contacts appeared to affect the copper contents of sampled materials, some more than in others.

The methodology employed in this thesis provided confidence in its efficacy; the results matched previous research and the general copper values of their counterparts in the area and in Finland, and the element contents of the sample materials followed the lithological boundaries of the bedrock. However, the sample media investigated in the thesis require more research to become a creditable part of prospecting and mapping programmes, especially the plants. The survey area, Hirviaapa, yielded mixed results. To confirm or rule out a copper mineralisation in the bedrock more research must take place.