Annika Parviainen

Spectral induced polarization (SIP) response of mine tailings

Mine tailings impoundments are a source of leachates known as acid mine drainage (AMD) which can pose a contamination risk for surrounding surface and groundwater. Methodologies which can help management of this environmental issue are needed. We carried out a laboratory study of the spectral induced polarization (SIP) response of tailings from the Haveri Au-Cu mine, SW Finland. The primary objectives were, (1) to determine possible correlations between SIP parameters and textural properties associated with oxidative-weathering mechanisms, mineralogical composition and metallic content, and (2) to evaluate the effects of the pore water chemistry on SIP parameters associated with redox-inactive and redox-active electrolytes varying in molar concentration, conductivity and pH. The Haveri tailings exhibit well defined relaxation spectra between 100 and 10,000Hz. The relaxation magnitudes are governed by the in-situ oxidative-weathering conditions on sulphide mineral surfaces contained in the tailings, and decrease with the oxidation degree. The oxidation-driven textural variation in the tailings results in changes to the frequency peak of the phase angle, the imaginary conductivity and chargeability, when plotted versus the pore water conductivity. In contrast, the real and the formation electrical conductivity components show a single linear dependence on the pore water conductivity. The increase of the pore water conductivity (dominated by the increase of ions concentration in solution) along with a transition to acidic conditions shifts the polarization peak towards higher frequencies. These findings show the unique sensitivity of the SIP method to potentially discriminate AMD discharges from reactive oxidation zones in tailings, suggesting a significant advantage for monitoring threatened aquifers.

Evaluation of a total reflection X-ray fluorescence spectrometer in the determination of arsenic and trace metals in environmental samples

ABSTRACT Suitability of the PicoTAX total reflection X-ray fluorescence (TXRF) spectrometer was studied for determination of As and trace metals in the Haveri Au-Cu sulphide mine tailings leached with aqua regia and in water affected by acid mine drainage. Results for 12 water and 16 tailings samples were compared with accredited methods, inductively coupled plasma-atomic emission spectrometry (ICP-AES) and inductively coupled plasma-mass spectrometry (ICP-MS). Certified reference samples analysed were QC Metal LL from Eurofins A/S, and groundwater CRM 609 and lake sediment BCR-280R from the Institute for Reference Materials and Measurements (IRMM) of the European Commission. Approximate method detection limits (MDL) for water samples, based on reference sample analyses, are in the range of 20 μg l−1 for As, Cr, Pb and Zn and 5–10 μg l−1 for Co, Cu, Ni, V and Mn. MDLs for aqua regia leach, calculated using reagent blank values, were ≤20 (mg kg−1) for As, Co, Cr, Cu, Mn, Ni, V, and Zn. Random error of determination varied from 12 to 20 %. Inter-element interferences include: As and Pb on each other, and Fe on Cr and Co. Using the Mo anode of the X-ray tube excludes the determination of Cd, Mo, Nb, Tc and Zr. TXRF can be recommended merely as a preliminary technique for selecting samples.

Low-temperature, platinum-group elements-bearing Ni arsenide assemblage from the Atrevida mine (Catalonian Coastal Ranges, NE Spain).

The Atrevida vein is located at the south-western edge of the Catalonian Coastal Ranges, Spain. This vein extends for more than 3 km and is hosted by Silurian and Carboniferous metasediments, late Hercynian granites and continental conglomerates of Lower Triassic age. The Silurian metasediments contain massive sulphide layers with disseminations of platinum-group element (PGE)-bearing, Fe-Ni arsenides. Vein fi lling largely consists of banded and brecciated baryte rimmed by a complex polymetallic assemblage of Co-Ni-As-Bi-Ag(-U) ores. The Ni arsenide and sulpharsenide assemblage occurs only where the vein cuts the sulphide-bearing Silurian metasediments, and consists of nickeline, maucherite, rammelsbergite, gersdorffi te and Ni-skutterudite. These Ni arsenides and sulpharsenides display rosettes, spherules, colloform and botryoidal textures, as well as subhedral crystals. The chemical compositions of these arsenide-sulpharsenide minerals exhibit limited cation substitution but substantial anion substitution of As by S and Sb, exceeding the expected theoretical values at low temperatures. This suggests that most of them formed under disequilibrium conditions. Ni arsenides and sulpharsenides also contain trace PGE. Palladium (up to 157 ppm) is the most abundant PGE, and occurs in solid-solution in all the phases studied, but shows the highest values in rammelsbergite and Niskutterudite. Pt only occurs in massive nickeline (54–1338 ppm Pt) and in zoned gersdorffi te (29–360 ppm Pt) formed at the end of the depositional sequence of arsenides. The Ni arsenide and sulpharsenide ores at the Atrevida mine formed by reduction of PGE-bearing, oxidizing fl uids at temperatures close to, or slightly above 100 °C. These oxidizing fl uids most probably collected their PGE budget from the nearby mineralized black shales. During the crystallization of the veined, Ni arsenide and sulpharsenide ores, Pd partly concentrated in the early nickeline and maucherite, but mainly fractionated to the late solutions from which rammelsbergite and Ni-skutterudite precipitated. Pt concentrated only in the latest nickeline and gersdorffi te.