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Bromine contents of a 17-cm halite core from drilling hole of K203 in the Khorat Basin were analysed at 1 cm intervals (17 samples in total). The Br contents range from 99 to 184 ppm with a rapid variation. The K/Mg ratios of halite samples are tens of times higher than those of primary halite fluid inclusions. There is no positive correlation between Mg and Br contents, suggesting that fluid inclusions impose very little or negligible influence on Br contents of halites. The Br contents are not controlled by potash minerals either because the SEM examination shows no potash minerals and there is no relationship between K and Br contents. The Br contents of halite are thus primarily controlled by the Br concentrations of parent brines. The rapid variation of Br contents of halite within this section suggests a shallow saline pan wherein the giant Khorat evaporites were formed. This is contradictory to previous Br profiles of the Lower Salt Member which showed relatively stable and continuously increasing trends. The shallow saline pan model evidenced by high-resolution Br profile is consistent with sedimentary facies and salt mineral textures.

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Alteration in the subaqueous basaltic rock of the Lam Narai volcanic belts, Lop Buri province, central Thailand has resulted in the formation of bentonite deposits. The bentonite deposits have been geological, mineralogical and geochemical studied to determine their genesis. The characteristics of the bentonites were examined by using X-ray Diffractometer and Scanning Electron Microscope with Energy Dispersive Spectroscopy. The mineralization zone of bentonite shown X-ray diffraction patterns of montmorillonite as the major constituent with minor hematite and calcite. Morphology of the minerals and groundmass in the bentonite deposits display the "cornflake," "oak leaf," or "cellular" textures that are typical and representative of montmorillonite in smectite group and composed of Si, Al, O, Ca, Mg and Fe in their chemical compositions. Geochemistry of the bentonite and their parental volcanic associations were analyses by using X-ray Fluorescence Spectrometry for major and trace elements. The representative samples were selected for the analysis of the rare-earth elements by using Inductively Coupled Plasma-Mass Spectrometry. The AI-CCPI alteration box plot revealed that the bentonite is mainly altered by hydrothermal alteration associated with basaltic layer in the Lam Narai volcanic belt. The basaltic layers in this area are composed of pillow lavas, inter-pillow and basic glassy inter-pillow (hyaloclastite) that indicated the subaqueous environment. The smectite formed by hydrothermal alteration from altered basic glassy inter-pillow (hyaloclastite) in the basaltic layers. Hydrothermal fluids in this area are possibly derived from the major fault along Pa Sak River or the youngest intrusive rocks in the Lam Narai volcanic terrain.

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