Congratulations to Peng Ni who successfully defended his dissertation on April 18, 2017.
Advisor: Youxue Zhang
Abstract: Magmatic sulfide deposits and porphyry-type Cu deposits are two major types of Cu deposits that supply the world’s Cu. In particular, porphyry-type Cu deposits provide ~57% of the worlds’ total discovered Cu. Recent studies suggest a potential role of diffusive transport of metals (e.g. Cu, Au, PGE, Mo) in the formation of magmatic sulfide deposits and porphyry-type deposits. Diffusivities of Cu in silicate melts, however, are poorly determined. In Chapter II and III of this thesis, Cu diffusion in anhydrous basaltic melt, and anhydrous/hydrous rhyolitic melts are studied by diffusion couple and chalcocite “dissolution” experiments. Our results suggest high diffusivities of Cu and a general equation for Cu diffusion in silicate melts is obtained. Our data are used to discuss the role of Cu diffusion in formation of Cu ore deposits and also Cu isotope fractionation in tektites.
Volatile abundances in lunar mantle have profound implications for the origin of Moon. The Moon was thought to be bone-dry till about a decade ago, after which trace amounts of H2O were detected in lunar volcanic glass beads, nominally anhydrous minerals and olivine-hosted melt inclusions. In particular, high H2O concentrations comparable to mid-ocean ridge basalts were reported in lunar melt inclusions. A more recently study estimated volatile abundances in lunar mantle to be similar to or slightly lower than the depleted mantle. Problems still occur, however, for lunar melt inclusion studies in at least two aspects. One is that whether the low H2O/Ce ratios measured in homogenized crystalline inclusions are affected by the homogenization process. The other is that current estimation of volatile abundances in lunar mantle relies heavily on 74220, which is argued to be a local anomaly by some authors. In order to reach a conclusive answer on volatile abundances in lunar mantle, the above two questions have to be answered. To improve our understanding about these questions, in Chapter IV of this thesis, a series of experiments are done to understand possible volatile loss from lunar melt inclusions during homogenization. In Chapter V of this thesis, previous lunar melt inclusion study is extended to a wider range of lunar samples to understand volatiles in lunar mantle on a broader scale.