Geokolloqium, Prof. Juraj Majzlan

- GEOWISSENSCHAFTLICHES KOLLOQUIUM -

Antimony isotopes from ore deposits to the global ocean

Vortragender: Prof. Juraj Majzlan
Friedrich-Schiller-Universität Jena

Abstract

Antimony isotopes represent one of the less studied systems of non-traditional isotopes. Even if only a few studies are available so far, interesting patterns begin to emerge. The average isotopic composition of the upper continental crust of the Earth is about +0.07 ‰ (with respect to NIST SRM 3102). The mantle rocks show a narrow range around 0.00 ‰ but the oceans and marine sediments are isotopically much heavier. The difference could be explained with our results that show that during the weathering of antimony ores, light isotopes remain in the secondary minerals and the heavy isotopes are carried away. Yet, the question of fluxes of this element during weathering, as a result of degradation of common rocks versus oxidation of antimony sulfides, is not resolved.

Ore deposits show a large range of isotopic compositions, either those investigated by us or by Chinese authors. Within this range, however, the isotopic composition correlates well with the position of the minerals in the precipitation sequence or their concentration of trace elements. Such regular and monotonous change can be modeled readily by simple Rayleigh fractionation within a body of fluid. The consequence is that the fluid reservoir must have had substantial connectivity. It can be shown that such systematic evolution of the isotopic composition can be detected in camps of deposits in larger volumes of the crust, suggesting a fluid front moving through the crust and depositing antimony minerals at different crustal levels. From this perspective, antimony isotopes possess the potential to understanding of large-scale fluid flow patterns and perhaps also for mineral exploration.