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Mineral exploration
Published in Odwyn Jones, Mehrooz Aspandiar, Allison Dugdale, Neal Leggo, Ian Glacken, Bryan Smith, The Business of Mining, 2019
Odwyn Jones, Mehrooz Aspandiar, Allison Dugdale, Neal Leggo, Ian Glacken, Bryan Smith
Groundwater is generally sampled from exploration drillholes, water bores, windmills and wells (Gray et al., 2011). Ideally, the drillholes and wells need to be cased and screened. However, for exploration, such equipped bores are rare and most groundwater surveys are done with open drillholes and wells. Water is acquired by bailing from a bore or drillhole or from a windmill. The sample then needs to be immediately filtered through a 0.45 µm filter and stored in clean HDPE plastic bottles in a cool place. The pH, temperature, conductivity (EC) and oxidation/reduction potential (ORP) are measured immediately on exposure to air. Electrodes used to measure the water parameters need to be calibrated regularly. Gold concentrations in groundwater are extremely low (in the ng/L range) and, therefore, gold needs to be concentrated before analytical measurement. This is achieved by placing activated carbon sachets in 1 L of extracted groundwater as the carbon adsorbs and concentrates the gold from the water. Subsequently, the gold concentration in the carbon is measured. Unlike solid samples, the water samples need to be analysed for anions using ion chromatography (IC) and cations using ICP-OES or ICP-MS. Isotopes are increasingly being measured in groundwaters and the main methods to measure radiogenic isotopes (strontium and lead) is thermal ionisation mass spectrometry (TIMS), but increasingly multi-collector ICP-MS instruments are also used. Stable isotopes in groundwater are measured via the Isotope Ratio Mass Spectroscopy (IRMS).
Characterisation of methane sources in Lutjewad, The Netherlands, using quasi-continuous isotopic composition measurements
Published in Tellus B: Chemical and Physical Meteorology, 2020
Malika Menoud, Carina van der Veen, Bert Scheeren, Huilin Chen, Barbara Szénási, Randulph P. Morales, Isabelle Pison, Philippe Bousquet, Dominik Brunner, Thomas Röckmann
The isotope measurement system is based on a continuous flow isotope ratio mass spectrometry (CF-IRMS) system. One IRMS instrument (Thermo Delta Plus XP, Thermo Fisher Scientific Inc., Germany) was used to measure alternatively 13C-CO2 and 2H-H2. Before injection into the mass spectrometer, CH4 needs to be isolated from the other air components and converted to CO2 or H2. To extract the CH4, ambient air is first pumped through magnesium perchlorate, a drying agent. Then, the dry air is sent through two successive cryogenic traps, cooled to −120 °C and filled with HayeSep D in the center and glass beads on each end. The cooling is achieved by a Polycold compact cooler compressor (Brooks Automation Inc., USA), filled with coolant PT-30. The cold end is attached to a copper block on which the traps are mounted. The traps are kept under vacuum to avoid condensation of water and to allow a fast and precise temperature control of each of them. The methane is released by heating the traps to −45 °C, and then it is converted to CO2 and H2 in combustion and pyrolysis furnaces, at temperatures of 1150 and 1350 °C, respectively. CO2 is further purified on a gas chromatography (GC) column, at a temperature between 0 and 10 °C. The whole extraction process is illustrated in Fig. S1, and described in more detail in Röckmann et al. (2016). A picture of the extraction system installed at Lutjewad is shown in Fig. S2.