Date of Award
Doctor of Philosophy
Geological and Atmospheric Sciences
Paul G. Spry
Variability in the "light" (e.g., H, C, O, N, S) stable isotope composition of minerals has long been used to elucidate geochemical processes. The development of multi-collector inductively coupled plasma mass spectrometry (MC-ICP-MS) techniques has led to the study of isotope variability in increasingly heavy elements due to the increase in precision and ionization potential compared to older isotope analytical techniques. Despite the increasing use of stable isotopes as geochemical tracers, those of the element tellurium have been relatively understudied. The three studies presented here provide the first analyses of tellurium isotope variability in tellurides and native tellurium, as well as tellurates and tellurites.
The first study presents a methodology for the extraction and purification of Te from such minerals, as well as for their analysis using MC-ICP-MS. Importantly, this study established that processing and analytical techniques do not induce isotopic fractionation. Furthermore, with a δ130/125Te range of 1.6 /, the preliminary isotope data from the methods development process suggested appreciable fractionation of Te, even at elevated temperatures.
The second study presents data for 82 Te-rich minerals of various oxidation states and compares those empirical data to experimental data from thermodynamic calculations. The samples were unlocated beyond the general area of their collection. The overall range of fractionation for Te is 2.85 / and seems to be dominated by mass-dependent processes. Redox reactions do not seem to induce large fractionations, which contradicts thermodynamic predictions, and suggests that disequilibrium processes may have occurred during changes in valence state.
The final study of this dissertation is related to well-located tellurides and native tellurium from the epithermal Emperor gold telluride deposit, Fiji. Here, we report a range of Te isotope values of 1.13 /. The preliminary dataset presented shows that samples hosted within the volcanic caldera have a more narrow range than those hosted in adjacent rock, suggesting that wall rock interaction during magmatic-hydrothermal fluid flow may be responsible for some amount of fractionation. Like other epithermal deposits, Te isotope values at Emperor are relatively tightly clustered, in contrast to those from the orogenic Kalgoorlie gold telluride deposit.
To complement this work on tellurium isotopes, I was also involved with two studies on the geology, mineralogy, and geochemistry of the Stanos, shear-zone related Au-Bi-Te ore system, in Greece. The first paper to come of this research, entitled `Bismuthinite derivatives, lillianite homologues, and bismuth sulfotellurides as indicators of gold mineralization in the Stanos shear-zone related deposit, Chalkidiki, Greece', by Voudouris et al. (2013) is in press in Canadian Mineralogist (v. 51, p. 119-142). The second, `Geochemical and geochronological constraints on the formation of shear-zone hosted Cu-Au-Bi-Te mineralization in the Stanos district, Chalkidiki, northern Greece' by Bristol et al. is to be submitted to Ore Geology reviews.
Fornadel, Andrew, "Stable tellurium isotope variability in ore-forming systems: A theoretical and experimental approach" (2014). Graduate Theses and Dissertations. 14075.