Composition and geochemistry of recently formed secondary mineral parageneses from the Breiner mine, Maramureș, Romania

The Maramureș region in Romania is renowned for its extensive mining history and rich polymetallic mineralization. This study focuses on the Breiner mine near Băiuț (~35 km east of Baia Mare), where historical Au-Ag-Pb-Cu-Zn exploitation took place. The weathering of ore minerals has led to the formation of rich assemblages of secondary minerals (SM). The dominant SM identified are melanterite, halotrichite group minerals, jarosite, goslarite, and schwertmannite. Their crystallization is significantly influenced by low pH, humidity, groundwater supply, temperature, microorganism activity, and saturation with the particular cations and SO₄²⁻. The availability of a variety of ions contributes to the formation of a diverse range of supergene phases, including Mg, Zn, and Al sulfates. Melanterite exhibits high enrichment in Zn (>1 wt%) and, in certain instances, Cu (>2800 ppm). Halotrichite group minerals demonstrate a notable capacity for retention of >1 wt% Zn, 1700–3500 ppm As, and 1900–3500 ppm Mn. Arsenic, Pb, and Hg are mainly captured by jarosite (As >1 wt%; Pb >3300 ppm; Hg >1 ppm) and schwertmannite (As >1 wt%; Pb >500 ppm; Hg >9 ppm). Goslarite and rozenite exhibit enrichment in Ni (~1000 ppm) and Co (~700 ppm). Properties of mine waters within this site are characterized as low pH (pH 2.1–3.7) and extreme-metal concentration. Waters with the highest contamination levels are rich in As (>1500 mg/l), Zn (>9500 mg/l), Mn (>1000 mg/l), Cu (>350 mg/l), Cd (>40 mg/l), and Ni (>40 mg/l). Such high levels of dissolved contaminants are correlated with the presence of melanterite. The obtained values for toxic metals and semi-metals emphasize that these weathering zones pose a significant threat to the local environment.