Translating mineral systems criteria into a prospectivity model; Kolari region, Finland

The Mineral Prospectivity Mapping (MPM) methodology can be used to delineate favorable mineral exploration areas and minimize time and costs. The mineral deposits in Finland are an ideal testing ground for these methods due to limited outcrops, thick overburden because of soil cover and dense vegetation and snow cover during long winters. Here, we apply MPM to predict favorable areas for Iron Oxide-Copper-Gold (IOCG) deposits in the Kolari region, northwestern Finland. We use a GIS-based knowledge-driven approach (fuzzy logic overlay), which is integrating evidential layers derived from geological (scale-free geology map), geochemical (till and bedrock samples), and geophysical data (magnetic, radiometric, electromagnetic measurements and gravity worms). The regional-scale analysis aimed to evaluate various mineral system components specified for IOCG deposits, including the anomalies of elements in till and rock geochemistry (i.e., Au, Cu, Co, Fe, and Th), pathways, energy sources/drivers, traps, and the relevant geological factors influencing the ore-forming processes. Utilizing the Centered Log-Ratio transformation (CLR) proves beneficial in enhancing the identification of weak anomaly areas and improving the prospectivity assessments by directing attention to relevant geological features. The produced prospectivity map shows a positive association between known IOCG deposits and high-favorability areas, and it also indicates new promising targets. Receiver Operating Characteristic (ROC) analysis and average Area Under the Curve (AUC) values consistently yielded scores > 0.7 which could be considered favorable outcomes (promising targets).