Mineral exploration using trace element composition of pyrite grains from till: A case study from the Petäjäselkä Au occurrence, northern Finland

Abstract

Geochemical anomalies and indicator mineral studies in glacial sediments are commonly used to define mineral exploration targets in glaciated areas. Trace element composition of sediment-hosted heavy minerals, such as pyrite and chalcopyrite, can be potentially used to fingerprint mineral deposits. This study presents results from trace element compositions of pyrite in the heavy mineral concentrates of till and mineralized bedrock samples from the orogenic gold ore occurrences in the Petäjäselkä area, Central Lapland belt, northern Finland.The trace element contents of pyrite grains were evaluated by using a robust compositional data analysis workflow, including symmetric pivot coordinates and robust principal component analysis (PCA). Four different pyrite textures (A-D) were identified from the gold ore occurrences. Compositional data analysis showed that the heavy mineral pyrite correlated with Pyrite D in the ore occurrence and confirmed the discrimination power of pyrite in the heavy mineral grains as a tool for source characterization of transported sedimentary material. The study also discusses the difficulties of finding suitable grains for the LA-ICP-MS, highlighting the importance of proper heavy mineral grain recovery procedures and the factors of oxidization and weathering processes influencing the geochemical compositions of the pyrite grains.