Brought to you by Teemu Karlsson, Tuomas Leskelä, and Janne Hokka from GTK
In recent years, the growing demand for Critical Raw Materials (CRMs) has led to increased interest in extracting valuable resources from industry side streams, such as mine tailings. A new FutuRaM project study by the Geological Survey of Finland (GTK) focuses on the Otanmäki tailings storage facility (TSF) in Finland, which contains ilmenite, a crucial mineral for various industries. The research aims to evaluate the resource potential of the Otanmäki TSF and compare different sampling methodologies to ensure accurate and representative data collection.
Otanmäki mine
The Otanmäki mine, located in Central Finland, operated from 1953 to 1985, producing significant amounts of ilmenite, magnetite, and vanadium. The produced 9.8 Mt of tailings were deposited in a 145-hectare facility. With the European Union’s emphasis on recycling and sustainable resource management, the Otanmäki TSF presents an opportunity to recover ilmenite from these tailings. The Otanmäki TSF ilmenite recovery project is owned by the Otanmäki Mine Oy.
Different sampling methodologies
The study aimed to test the sensitivity of resource estimation with regard to spatial sampling density at the Otanmäki TSF using various geostatistical models, and to evaluate three different sampling methodologies to identify the most effective approach for collecting representative samples.
- Tube sampler with a valve, using a plastic tube with a flapper valve to collect samples. It is regarded as effective in varying conditions but can be time-consuming.
- Flow-through blade, featuring a blade with openings that allow material to flow through as it penetrates the ground.
- The auger drill, using a helical screw to penetrate the material, with samples being scraped off the drill. This method is quick but can result in contamination from material falling into the drill hole.
The study found that both the tube sampler and the auger drill provided similar results under low moisture conditions. However, the tube sampler was more accurate in varying conditions, despite its smaller sample volume. The flow-through blade was the least effective method, mainly due to sample loss during retrieval.
Geostatistical modelling
Geostatistical modelling of the Otanmäki TSF demonstrated high confidence in resource estimation, with minimal changes in grade and tonnage when sampling density was increased or model scale was adjusted. This indicates that the existing sampling grid of 100 x 100 meters is sufficient for accurate resource estimation.
Consequently, the modelling results suggest that the Otanmäki TSF could be classified under the United Nations Framework Classification for Resources (UNFC) system in high-confidence categories. However, an updated resource model for the entire TSF with the new data is required.
FutuRaM study
The study highlights the importance of tailored sampling strategies and robust geostatistical modelling for accurate resource estimation in mine tailings. The findings provide valuable insights for the effective investigation and classification of tailings storage facilities, contributing to the sustainable management of secondary resources. By demonstrating the potential of the Otanmäki TSF as a viable source of ilmenite, this research supports the broader goal of enhancing the availability of CRMs through the re-mining of extractive waste sites.
The study has been published in the Journal of Geochemical Exploration: Leskelä, T., Hokka, J. & Karlsson, T. 2025. Geostatistical modelling of mine tailings and comparative analysis of sampling methodologies: a case study of the Otanmäki ilmenite tailings storage facility project. Submitted to Geochemical Exploration on November 7th, 2024.