ABSTRACT

Oxygen from a range of minerals has been liberated by fluorination under the radiation from a Nd/YAG laser, and the isotope ratio of oxygen measured with a conventional ratio mass-spectrometer. During the fluorination, generation of fluorine gas often takes place through the dissociation of chlorine trifluoride (CIF₃) and interferes with the measurement of the isotope ratio later on. Using mercury on gold to remove the F₂ also led to a loss of oxygen. A simple trap made of stainless steel wool has proved to be very effective at removing of fluorine without any measurable loss of O₂. The minerals analysed include quartz, feldspar, hornblende, mica, garnet, pyroxene, olivine, and spinet. The accuracy and precision of the method was evaluated. There is good agreement with data obtained by conventional fluorination for the analyses of hornblende, garnet and spinel. In the case of quartz, feldspar and pyroxene, the laser method gave isotope ratios (¹⁸O/¹⁶O) lighter than the ratios obtained by the conventional method by less than 1‰, but its application to olivine and mica gave lighter isotope ratios by as much as 1∼2‰. The precision of this method is better than 0.3‰ for all the minerals investigated.