Exploration and Sources of Bauxite Deposit in the Boloven Plateau, Southern Laos

The Boloven bauxite deposit occurs either in the weathered basalt (alkali basalt and tholeiite), or in the Cretaceous sandstone. It is generally agreed that the bauxite deposits/laterites overlying the alkali basalt and tholeiite were derived from weathering of underlying basalt, however, the origin of bauxite deposit overlying the sandstone remains controversial. Chondrite-normalized REE patterns show that the bauxite ores/laterites overlying the sandstone exhibit quite similar chondrite-normalized REE patterns to those overlying the alkali basalt. Diagram of Al-Ti-Zr shows that the bauxite ores/laterites overlying the sandstone, tholeiite and alkali basalt are close to each other and to the calc-alkaline suite, however, significantly different from the sandstone and shales. Binary diagram of log Nb/Y vs log Zr/Ti further indicates that the parent rocks of bauxite ores/laterites overlying the sandstone belong to the suit of ultra-alkali to alkali basalt. Multivariate statistical analysis of geochemical data exhibit that the geochemical characteristics of HREE, Y, LREE and Al 2 O 3 for bauxite ores/laterites overlying the sandstone are similar to those overlying the alkali basalt (15.7 Ma), obviously different from those overlying the tholeiite (1.2 to 0.5 Ma). Consequently, it can be inferred that the bauxite deposits/laterites overlying the sandstone were derived from the alkali basalt.