Saprolitization’s Characteristics of Rare Earth Elements in Volcanic Regolith on Drill Core #65 in Western Sulawesi, Indonesia

Abstract

The enrichment of Rare Earth Elements (REEs) in regolith depends on greatly number of chemical weathering degree, the ability of the ion-adsorption on clay, precipitation of REEs, minimum uptake by plants, and minor REE leaching out by lessivage. The degree of chemical weathering depends on the decaying of four base weathering elements (Mg, Ca, Na, K) in minerals and is relatively less dependent on the slow leaching of silica. Therefore, a study of regolith profile from weathering’s Adang Volcanics (western Sulawesi, Indonesia) is performed to understand the relationship between degree of chemical weathering, nature migration of REE and the characteristics of saprolitization REEs. The result of drill core samples shows the increasing of degree of chemical weathering (Degree of Saprolitization; DOS) is equal to gradual increasing of alumina by saprolitization, and has also gradual increase in Fe-Ti-oxides by ferruginization; furthermore, there is also a gradual enrichment of REEs occurred in the saprolite zone on Adang Volcanics regolith. The enrichment of REEs in the saprolite zones (E and B horizons) is 2.73 times (TREY = 2,579 ppm, in avg) compared to the parent mafic trachytic rocks (944 ppm) reveal the high adsorption ability on lateritic-ferruginous clay. The thickness of high concentration REEs (2,435 ppm, in avg) is starting from A to E, and B-horizon which is about 5 m. The ratio of LREE and HREE is 87.42% and 12.58%, respectively in parent rock which indicates the genesis of rare-earth is more influenced by replacement of Ca2+, Na+ and K+ in minerals of diopside, apatite and leucite/pseudoleucite rather than the substitution by zircon (Zr4+).