Geochemical Approach to Reveal The Genetic Occurrence of Gibbsite, Relative to The Parent Rock Type in Lateritic Bauxites

Situating in a tropical climate, will be favourable for Indonesia and Malaysia to have an intensive weathering and a concentration of lateritic bauxite. The study area takes place in Kuantan, Pahang State, Malaysia and Landak area, West Kalimantan, Indonesia. The study area has different type of parent rock, topography and drainage condition, which will also cause the different characteristics of alumina minerals in bauxite. One of the common form of alumina minerals is known as Gibbsite [Al(OH) 3 ]. The objective of this research is to investigate the genesis of gibbsite from two different parent rocks. Samples were taken and collected from pitting, analyzed for Al 2 O 3 , Fe 2 O 3 , SiO 2 and TiO 2 using XRF and XRD examination. The parent rock of bauxite in Kuantan is basalt, meanwhile, in Landak, ranges from granodiorite to andesite. Petrography and XRD analyses of Kuantan bauxite shows predominant gibbsite, with minor amount of geothite, hematite, kaolinite, illite, quartz and feldspar, while in Landak, mineralogically consists of variant amount of gibbsite, goethite, hematite, kaolinite, illite and quartz. In Kuantan, the amount of Al 2 O 3 varies from 23.6% - 51.01%, nearly similar than that in Landak that varies from 31.35% - 55.03%. Gibbsite in Kuantan is assumed as a transformation of Ca-rich plagioclase and Ferromagnesian- silicate minerals, on the other hand, gibbsite in Landak was produced from direct weathering of primary Al- silicate minerals (Na- plagioclase and K-feldspar). From study, it can be inferred that gibbsite formed from a layer of silicates and will concentrated in finer clay as a weathering product. Moreover, the different types of parent rock will produce different types and amount of alumina minerals. The study will be beneficial to predict the existence of potential alumina minerals in lateritic bauxite.