Comparison of characteristics and geochemical behaviors of REEs in two weathered granitic profiles generated from metamictized bedrocks in Western Peninsular Malaysia

Abstract

Rare earth elements (REEs), an important group of non-energy minerals, are vital to industrialized societies worldwide. Southeast Asian granitic belts are potential sources of ion-adsorption REE clays comprising large weathered granitic crusts that often have high-grade ion-adsorbed REEs. Characterization studies were conducted on representative samples from two sites, namely Lumut (LU) and Telok Murok (TM), located within the Malaysian Western granite belt. In both profiles, parent rocks were documented as medium-grained mica (phlogopite)-rich, S-type, peraluminous, ilmenite-series granite with metamict texture. Quartz, K-feldspar, and mica were major minerals, while REE-bearing accessory minerals were apatite, allanite, monazite, xenotime, and zircon. Al2O3 and LOI contents increased with depth in both weathered profiles, whereas P2O5 tended to be constant. Long-tube halloysite and kaolinite are abundant clays in the upper portions of the profiles, whereas the lower parts were rich in short-tube halloysite with smectite. Moreover, the depletion of REE + Y (REY) content in horizon A (B1) was clear, whereas REY was abundant in horizon B and/or C. The maximum content of REY could reach up to approximately 850 and 2350 ppm in horizon B2 and/or C in the LU and TM sites, respectively. Total REE content of the weathered crust was relatively elevated compared with that of the parent rocks (3–7 times) in the lower portions of both sites due to “high adsorption capacity” of abundant clay minerals in the deep profiles. Enrichment in LREE and HREE was indicated in the LU and TM sites, respectively. Trial leaching experiments with high-grade samples from both sites were conducted using ammonium sulfate. High recovery in the results proved REE adsorption by the clays in the lower parts of the profiles.