Infrared thermographic investigation of the oxidation behaviour of sulfide minerals from antimony-bearing rocks exemplified by the Podkozara deposit, Bosnia-Herzegovina

Abstract

To date, prediction of the drainage chemistry of geologic materials at mine sites commonly relies upon well-established mineralogical and geochemical test work. Antimony (Sb) deposits require water quality risk assessments that consider the contaminant's solubility and mobility behaviour. To investigate the oxidation reaction of sulfides, a newly designed infrared (IR) thermographic test protocol was used to visualise oxidising sulfide minerals and to classify the rock types from the Podkozara Sb project, Bosnia-Herzegovina according to their oxidation reactivity. Furthermore, the sample materials were geochemically and mineralogically analysed using pXRF, powder XRD, ICP-AES, ICP-MS and NAGpH techniques. Four rock types have been recognised in the deposit: (i) stibnite mineralised quartz veins (SMQV); (ii) stibnite mineralised carbonate rocks (SMCR); (iii) pyritic phyllites; and (iv) mylonitic marbles. As indicated by the defined rock types, stibnite and pyrite are the only two sulfide minerals detected in the sample materials, causing reactions of varying intensities during IR testing. The intensity and duration of the oxidation reaction depends on various factors, including the sulfide mineral itself, the ore content and galvanic reactions between the sulfide minerals. Based on IR testing, it could be demonstrated that SMQV and SMCR are highly reactive and have a high risk for sulfide oxidation and associated Sb release into waters in any pH environment. Pyritic phyllites and tailings show less oxidation reaction intensities and no oxidation reactions could be recorded for marbles. Tailings pose a low risk and pyritic phyllites as well as marbles do not show a risk at all for Sb deportment. For pyritic phyllites, however, a release of Fe must be considered. In addition, underground mine and local surface waters were analysed for their pH, Eh as well as dissolved metal, metalloid and sulfate contents. The mine waters possess especially strongly elevated Sb values (5–244 μg/L) at neutral to alkaline pH values (7.0–8.1). Thus, in the Podkozara deposit, there is a general excess of neutralising carbonate minerals that result in adequate buffering of generated sulfuric acid, limiting mobility of base metal cations in solution but this supports the mobilisation of Sb into mine waters. In this study, complementary conventional mineralogical and geochemical testing as well as novel IR visualisation of possible sulfide oxidation have revealed useful information on the likelihood of different rock types causing metalliferous drainage issues. In particular, IR thermographic testing provides valuable insights on the presence of oxidising Sb- and Fe-sulfides in ores and wastes. This information can be used to prepare suitable mitigation strategies for Sb-rich neutral mine drainage waters and serves as a sample pre-selection for long-term environmental studies and tests. Furthermore, this analysis shows that different management and separate disposal plans will be needed for different lithological wastes.