Bum Han Lee

X-ray Raman scattering study of MgSiO3 glass at high pressure: implication for triclustered MgSiO3 melt in Earth's mantle.

Silicate melts at the top of the transition zone and the core-mantle boundary have significant influences on the dynamics and properties of Earths interior. MgSiO3-rich silicate melts were among the primary components of the magma ocean and thus played essential roles in the chemical differentiation of the early Earth. Diverse macroscopic properties of silicate melts in Earths interior, such as density, viscosity, and crystal-melt partitioning, depend on their electronic and short-range local structures at high pressures and temperatures. Despite essential roles of silicate melts in many geophysical and geodynamic problems, little is known about their nature under the conditions of Earths interior, including the densification mechanisms and the atomistic origins of the macroscopic properties at high pressures. Here, we have probed local electronic structures of MgSiO3 glass (as a precursor to Mg-silicate melts), using high-pressure x-ray Raman spectroscopy up to 39 GPa, in which high-pressure oxygen K-edge features suggest the formation of tricluster oxygens (oxygen coordinated with three Si frameworks; [3]O) between 12 and 20 GPa. Our results indicate that the densification in MgSiO3 melt is thus likely to be accompanied with the formation of triculster, in addition to a reduction in nonbridging oxygens. The pressure-induced increase in the fraction of oxygen triclusters >20 GPa would result in enhanced density, viscosity, and crystal-melt partitioning, and reduced element diffusivity in the MgSiO3 melt toward deeper part of the Earths lower mantle.

Nature of chemical and topological disorder in borogermanate glasses: insights from B-11 and O-17 solid-state NMR and quantum chemical calculations.

Knowledge of the extent of chemical and topological disorder in topological disordered oxide glasses and melts is essential for understanding the atomistic origins of their macroscopic properties. Here, we report the high-resolution B-11 and O-17 triple quantum magic angle spinning (3QMAS) NMR spectra for binary borogermanate glasses. The NMR results, together with quantum chemical calculations of cluster energy difference, allow us to estimate the extent of chemical disorder and topology variation with composition. The B-11 NMR result shows that the boroxol ring fraction decreases nonlinearly with increasing mole fraction of Ge and is smaller than that in binary borosilicate glasses, suggesting that the Ge/Si content influences the topological changes. Whereas oxygen clusters are not well resolved in O-17 NMR spectra, the Ge-O-Ge fraction apparently increases with increasing GeO(2) content. The estimated degree of framework disorder (Q) in borogermanate glasses is approximately 0.4, according to quantum chemical calculations based on density functional theory. This is halfway between chemical order (Q = 1) and a random distribution (Q = 0). In contrast, Q is approximately -0.6 for borosilicate glasses, indicating a moderate tendency toward complete phase separation (Q = -1). This result confirms that the degree of framework disorder shows a strong dependence on the type of framework cations (Si or Ge). The predicted configurational enthalpy of borogermanate glasses, explicitly considering both chemical and topological disorder, shows a negative deviation as predicted from the positive Q value. The results demonstrate that the macroscopic properties of topologically disordered noncrystalline solids can be established from the detailed quantification of topological and chemical disorder.

Effect of lattice topology on the adsorption of benzyl alcohol on kaolinite surfaces: Quantum chemical calculations of geometry optimization, binding energy, and NMR chemical shielding

Abstract We investigate the effect of the lattice topology (ideal hexagonal rings vs. ditrigonal rings) and cluster size of model clusters (three-ring vs. seven-ring clusters) on the nature of benzyl alcohol adsorption on kaolinite surfaces using quantum chemical calculations with an emphasis on the equilibrium configuration, binding energy, and NMR chemical shielding tensors. The optimized structure of benzyl alcohol adsorbed on the tetrahedral layer of kaolinite varies according to the type and size of model cluster. While the calculated binding energy varies with the level of theory and the basis sets used for the calculations, the binding energies between benzyl alcohol and seven-ring clusters are smaller than those between benzyl alcohol and three-ring clusters partly due to the edge hydrogen for the latter. The results also indicate a stronger binding energy between benzyl alcohol and octahedral surfaces than between benzyl alcohol and tetrahedral layers. Although the calculated binding energies for seven-member rings with varying lattice topologies are rather similar, the detailed optimized structures are distinct, demonstrating the effect of lattice topology on the nature of adsorption. The optimized structures and binding energies indicate that an intermediate degree of hydrogen bonding is dominant for the three-member silicate rings and that the interaction between the benzene ring and basal O atoms in the seven-member rings is characterized by a weak hydrogen bond and dispersion force. The calculated 17O isotropic chemical shieldings of some basal O atoms decrease up to ~4-5 ppm after the adsorption (with an estimated uncertainty of ~2 ppm). Since the high-resolution 17O 3QMAS NMR spectroscopy of layer silicates yielded a resolution of 1-2 ppm for the basal oxygen sites in the layer silicates in previous work, the NMR technique may be useful in exploring the nature of adsorption between organic molecules and silicate surfaces, whereas further computational studies on the effect of the basis sets, the surface coverage, and the types of diverse organic molecules with larger model clusters for surfaces remain to be explored.

Gold in Peru: Present Status and Future Challenge

Total reported gold resources in Peru is about 192 Moz. Gold production in Peru was 4.9 Moz in 2013, which was ranked first in Latin America and sixth in the world. Historic cumulative gold production in Peru is 118 Moz, and production from main gold belts including Miocene epithermal belt, Carboniferous-Permian orogenic gold belt and Upper Cretaceous intrusion-related gold belt corresponds to 84%. Most of production areas are located in Northern part of Peru, which corresponds to 63.5% of the total domestic production. Annual production onces in Yanacocha mine and Alto Chicama were 1 Moz and 0.606 Moz in 2013, which were ranked first and second in Peru, respectively. Gold production in Peru is expected to be 6.5 Moz in 2017. To accomplish the expected production, ongoing 14 projects should be developed to the production stage in three years.

A Study on the Characteristics of W-Mo Ore Deposit in Bayan-Onjuul, Mongolia Using Magnetic Data

KIGAM (Korea Institute of Geoscience and Mineral Resources) and MRAM (Mineral Resources Authority of Mongolia) performed joint survey on Bayan-Onjuul W-Mo mineralized area. Following the survey, we carried out magnetic survey. W-Mo occurrences are located with keeping a certain distance from the northern boundary of granite which has higher magnetic susceptibility values. Also, the 3D imaging results of magnetic inversion show that granite bodies are extended to the W-Mo occurrence areas from the deep main body with decreasing of susceptibility. The results of magnetic data analysis are well matched with the general characteristics of ore solution involved with W mineralization. The further study about the hidden ore deposits which have similar spatial relationship between granite and known WMo occurrences are necessary to improve the economic feasibility.

General Geochemical Characteristics of Dashinchilen Nb-Ta and Sant Cu Occurrences in Southeastern Part of Khangai Area, Mongolia

We performed reconnaissance survey on Dashinchilen Nb-Ta REE area and Sant Cu area which are located in southeastern part of Khangai rare metals mineralized belt. In Dashinchilen area, Nb and Ta have been found in pegmatitic granite that is largely distributed in the survey area and muscovite in pegmatite which is an intrusion in paleozoic sedimentary rocks which are mostly composed of sandstone. While grades of Nb and Ta are not high, an outcrop that has high Th and U contents (542 ppm of Th and 56.9 ppm of U) has been found. Average and maximum REE contents in the survey area is three times and seven times, respectively, larger than average REE contents in the crust of the Earth. In Sant area, copper oxides such as malachite has been found in quartzite in paleozoic sedimentary rocks. A sedimentary rock formation that has high grade of Mn (12.4-34.6 %) has been found in the survey area. This sedimentary rock formation is the same formation with that of Ugii Nuur Fe-Mn mineralization which is located about 200 km northwest of the survey area. Average and maximum REE contents in the survey area is two and half times and seven times, respectively, larger than average REE contents in the crust of the Earth. According to the factor analysis for the data of the geochemical analysis, Nb and Ta in Dashinchilen area are highly correlated with muscovite and Cu in Sant area is highly correlated with Mo, Sn, and Bi. Furthermore, the factor analysis results show that Fe in Sant area was deposited with rare earth elements.