A Spatial Analysis of the Association Between Abandoned Hard-Rock Mining Locations, Granite Bedrock Stratigraphy, and Contaminated Streams

Abstract

This investigation examines spatial correlations between hard-rock mining, granitic bedrock stratigraphy, and stream contamination across three HUC8 sub-watersheds in central Montana. Using GIS methodologies and datasets from MBMG, DEQ, and USGS, I analyzed the geospatial relationships between abandoned mining sites and contaminated waterways, focusing on lead contamination. The analysis incorporated hydrologic mapping, elevation analysis, and strategic overlays of geological formations with mining sites. Results revealed that of 1,258 abandoned mines, 60.7% are situated within granitic formations. The study identified streams with lead concentrations exceeding the EPA’s 15 μg/L threshold, with 512 mining sites located within 0.6 miles of contaminated streams—a significant distance for potential contamination through runoff and acid-mine drainage. Five predominant metal contaminants were identified: lead, copper, aluminum, iron, and arsenic. While spatial analysis alone cannot establish causation, findings demonstrate an intriguing association between mining in granitic terrains and lead contamination in nearby fluvial systems. This research contributes to understanding mining impacts on watersheds and provides insights for remediation strategies. Future research could explore specific mechanisms between mining activities and pathways of contamination.