Gem-Quality Zircon Megacrysts from Placer Deposits in the Central Highlands, Vietnam—Potential Source and Links to Cenozoic Alkali Basalts

Gem-quality zircon megacrysts occur in placer deposits in the Central Highlands, Vietnam, and have euhedral to anhedral crystal shapes with dimensions of ~3 cm in length. These zircons have primary inclusions of calcite, olivine, and corundum. Secondary quartz, baddeleyite, hematite, and CO2 fluid inclusions were found in close proximity to cracks and tubular channels. LA-ICP-MS U-Pb ages of analyzed zircon samples yielded two age populations of ca. 1.0 Ma and ca. 6.5 Ma, that were consistent with the ages of alkali basalt eruptions in the Central Highlands at Buon Ma Thuot (5.80⁻1.67 Ma), Pleiku (4.30⁻0.80 Ma), and Xuan Loc (0.83⁻0.44 Ma). The zircon geochemical signatures and primary inclusions suggested a genesis from carbonatite-dominant melts as a result of partial melting of a metasomatized lithospheric mantle source, but not from the host alkali basalt. Chondrite-normalized rare earth element patterns showed a pronounced positive Ce, but negligible Eu anomalies. Detailed hyperspectral Dy3+ photoluminescence images of zircon megacrysts revealed resorption and re-growth processes

Removal of lead and other toxic metals in heavily contaminated soil using biodegradable chelators: GLDA, citric acid and ascorbic acid

In this study, we investigated the level of contamination of agricultural soil near an old recycling lead smelter in Vietnam and proposed an effective treatment for the remediation of the soil. The analysis of soil samples using an ICP-MS method revealed that the soil in the area was heavily contaminated by heavy metals, especially lead (Pb) with concentrations in surface soil of >3000 μg g. High concentrations of metals, including Pb, copper (Cu) and zinc (Zn), were found in whole soil profile. The FE-EPMA and Laser-Raman spectrometer results suggested that iron minerals and carbon materials in the soil are the important hosts of the toxic metals. Subsequently, a series of washing experiment were performed on the soil using biodegradable chelators, including N, N-dicarboxymethyl glutamic acid tetrasodium salt (GLDA), ascorbic acid and citric acid. The results showed that the mixture of GLDA-ascorbic (100 mM: 100 mM) can be considered as a potential candidate for Pb and Zn removal, which removes approximately 90% of Pb and 70% of Zn. Meanwhile, a mixture of GLDA-citric would be preferred for Cu removal based on its greater extraction efficiency compared to other mixtures

In-situ U–Pb isotope and REE analyses for zircons from ultrahigh temperature metamorphic rocks in the Kannak Complex, Kontum Massif, Vietnam.

Zircons from two pelitic granulites （corundum–spinel-bearing garnet–cordierite–sillimanite and garnet–spinel–cordierite granulites） of the western Kannak Complex, Kontum Massif, Vietnam were analyzed for in-situ U–Pb isotope age dating and rare earth elements（ REE） chemistry along with textural context by laser ablation inductively coupled plasma mass spectrometry. As the result, the correlation between zircon occurrence, its internal textural, U–Pb age and REE characteristics confirmed the ultrahigh temperature event during Permian–Triassic （230-260 Ma） and linked the age with the metamorphic process. The timing of peak metamorphism related with continental collision was constrained between ca. 250 – 260 Ma by the evidences of zircon inclusions in garnet from garnet–spinel–cordierite granulite and nearby cordierite–spinel symplectite from corundum–spinel-bearing garnet–cordierite–sillimanite granulite. The REE patterns of these zircons display the enrichment in the heavy REE （HREE） with gentle and steep positive slope, respectively. The youngest age group of ca. 230 Ma is yielded from the zircon contacting or included in secondary minerals such as chlorite or muscovite with the distinguishably depleted HREE, which corresponds to the timing of later intense hydration event during exhumation