HR: 11:05h
AN: U52B-03    [Abstracts]
TI: The Fate of
AU: * Becker, U
EM: ubecker@umich.edu
AF: University of Michigan, Dept. of Geological Sciences, 2534 CC Little, Ann Arbor, MI 48109, United States
AU: Reich, M
EM: mreich@ing.uchile.cl
AF: University of Michigan, Dept. of Geological Sciences, 2534 CC Little, Ann Arbor, MI 48109, United States
AU: Utsunomiya, S
EM: utu@umich.edu
AF: University of Michigan, Dept. of Geological Sciences, 2534 CC Little, Ann Arbor, MI 48109, United States
AU: Ewing, R C
EM: rodewing@umich.edu
AF: University of Michigan, Dept. of Geological Sciences, 2534 CC Little, Ann Arbor, MI 48109, United States
AU: Wang, L
EM: lmwang@umich.edu
AF: University of Michigan, Dept. of Nuclear Engineering and Radiological Sciences, 2958 Cooley 2355 Bonisteel Blvd., Ann Arbor, MI 48109, United States
AU: Wang, J
EM: jwwang@umich.edu
AF: University of Michigan, Dept. of Geological Sciences, 2534 CC Little, Ann Arbor, MI 48109, United States
AB: Natural nanoparticles are attracting a great deal of attention due to their unique role as agents of elemental transport and their increased reactivity in geologic systems. Although significant progress has been made in understanding their behavior in the Earth's critical zone (i.e. near-surface environments), there is a severe lack of information on their stability for a wider range of geologically relevant temperatures. Here, we describe the first direct observations of the dynamic behavior of natural nanoparticles at near atomic scale, revealing that their thermal stability is not only dependent on particle size, but also on the surrounding host mineral. Native Au nanoparticles (mean diameter ~4 nm) incorporated in an As-rich pyrite from "invisible" Au ores were observed during in-situ heating up to 650°C. While isolated Au nanoparticles melt, with their melting point being a function of size, we show that when incorporated in a sulfide host, Au nanoparticles react to increased temperature by dissolving into the pyrite matrix and forming larger particles in an Ostwald-type ripening process. The dissolution temperatures are much lower than melting temperatures of isolated nanoparticles and are as well strongly size-dependent. These findings provide new insights into the fate of nanoparticulate Au and other metals during geological processes and throughout their metallurgical recovery from refractory ores. The size distribution of the particles may be an indicator of the geologic history of the ore because, as we show, the mean particle diameter sets un upper limit to the maximum temperature of the host rock. Furthermore, results suggest that nanoparticulate minerals, usually documented in low-temperature (T<100°C) aqueous environments, can also occur and survive at higher temperatures when incorporated into refractory host phases.
UR: http:www.geo.lsa.umich.edu/compmin/
DE: 0350 Pressure, density, and temperature
DE: 1042 Mineral and crystal chemistry (3620)
SC: Union [U]
MN: 2007 Joint Assembly