Leachate chemistry and precipitates mineralogy of rudolfsgruvan mine waste rock dump in central Sweden

The chemical and mineralogical properties of leachates and precipitates formed in a sulfide ore mine waste rock dump were studied by atomic adsorption spectrometry, optical petrography, X-ray diffractometry, scanning electron microscopy with energy dispersive spectroscopy. The dump is divided into a leached horizon and an accumulation horizon. The intensity of sulfide oxidation decreases with depth. Leachates are characterized by acid and enriching Fe, SO₄ and other metals. Secondary minerals consist mainly of goethite, with some jarosite, schwertmannite ferrihydrite elemental sulphur and Cu and Zn compounds including copper iron oxides, Cu and Zn oxides (hydroxides) and Zn-sulfates. Dissolved Al, Cu, Zn, Si and S are partialy retained by goethite, precipitating in a microbanded texture. The banded formation indicates temporal variability in pore water chemistry influenced by episodic/seasonal hydraulic flushing. The dump is rather old and could provide an important information, or “natural analogue” to the future evolution of the rock dumps that are being generated at currently operating mines.