Factors controlling the geochemical variations of lateritic bauxites formed upon different parent rocks in Peninsular Malaysia

Abstract

Three lateritic bauxites representing felsic (Rompin area), intermediate (Johor area), and mafic (Kuantan area) parent rocks from Malaysia were subjected to detailed mineralogical and geochemical investigations to examine the factors controlling their geochemical variations. The bauxitic mineral gibbsite occurs as in all areas. Non-bauxitic minerals are represented by kaolinite, quartz, and goethite in bauxites from granites and intermediate tuffs and by goethite only in bauxite from basalts. Bauxites from basalts and intermediate tuffs have higher TiO2, Fe2O3, Ba, V, Cu, Pb, and Zn but lower SiO2, Th, Rb, and rare earth elements (REE) when compared with bauxite from granites. Bauxite from basalts has higher concentrations of Cr, Nb, Cu, and Zn and lower Ba, As, and REE when compared with bauxite from intermediate tuffs. Chondrite-normalized REE patterns of bauxite from granites showed heavy rare earth elements (HREE) enrichments over light rare earth elements (LREE), pronounced negative EuN/EuN* anomalies and strong positive CeN/CeN* anomalies. In contrast, bauxites from intermediate tuffs and basalts exhibited LREE enrichment relative to HREE, slight to strong negative CeN/CeN* anomalies, and absence or slight negative EuN/EuN* anomalies. Compositional variations among the studied bauxites are controlled not only by the parent rock compositions but also by the degree of lateritization and mineralogy of its products. The effect of each of these factors can be traced by a number of compositional parameters in these bauxites. The influence of parent rock compositions is indicated by absence of kaolinite and quartz, high TiO2 and Fe2O3 and low SiO2 in bauxites from basalts and intermediate tuffs as well as negative EuN/EuN* anomalies in bauxite from granites and absence of EuN/EuN* anomalies in bauxites from basalts and intermediate tuffs. The impact of lateritization degree was evident by abundance of quartz and kaolinite in bauxite from granites as well as relative LREE enrichments over HREE in bauxites from basalts and intermediate tuffs. The effect of lateritic products mineralogy was observed in the variations of REE patterns between bauxite from granites that are characterized by HREE enrichment and Ce anomaly due to occurrence of REE as residual zircon and bauxites from intermediate tuffs and basalts that are characterized by low HREE and high LREE due to occurrence of REE as authigenic florencite and/or cerianite. The distinct geochemical composition of Fe concretions such as lower TiO2 and most of the trace elements, enrichment of HREE relative to LREE and negative EuN/EuN* anomaly compared to the host bauxite at Johor area also indicates the effect of mineralogy of lateritic products on their geochemistry.