Active weathering processes: composition and geochemistry of secondary sulphates from the Johan Hell mine, Maramureș, Romania

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DOI:

https://doi.org/10.7306/gq.1820

Keywords:

secondary sulphates, voltaite, römerite, halotrichite group, toxic elements

Abstract

The Johan Hell mine, part of the Breiner polymetallic ore deposit in the Băiuď mining area (Maramureę, Romania), hosts an exceptional diversity of secondary sulphate minerals formed through intense weathering of primary ore mineralization. This study provides a comprehensive mineralogical and geochemical characterization of efflorescent and crust-forming sulphates that developed under extreme acidic conditions. A total of 20 secondary minerals were identified, with halotrichite-group representatives being the most abundant and widespread, followed by römerite, voltaite, melanterite, rozenite, starkeyite, hexahydrite and szomolnokite. These minerals show strong compositional variability, influenced by local geochemical gradients and microenvironmental factors. Geochemical analyses (ICP-MS/ES) reveal significant enrichment of several elements – including Mn, Zn, Cu, As, REEs and Hg – particularly within the halotrichite group, voltaite and römerite. Mineral parageneses reflect a three-stage evolution of weathering conditions, controlled primarily by changes in pH and humidity. The progression from ultra-acidic (pH <2) to moderately acidic (pH 2.5–3.5) conditions governed the crystallization of the various hydrated sulphates.

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Published

2025-12-09

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Recently accepted paper

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