RARE EARTH ELEMENT SOIL GEOCHEMISTRY CONTROLLED BY ACTIVE GEOTHERMAL SYSTEM

• Main Author: Paskalia Nipu, Lidia
• Format: Theses
• Language: Indonesia
• Online Access: https://digilib.itb.ac.id/gdl/view/44041
• Institution: Institut Teknologi Bandung

Hydrothermal fluid in active geothermal system may carry a concentration of rare earth elements (REE) as it percolates to the surface. During the convection through permeable zones, the fluid alters the surrounding rocks and may as well be enriched along the way. Therefore, a number of altered soil outcrops, including in craters, hot springs, and along the lineament in Wayang Windu geothermal ield, were sampled and analysed with X-Ray Fluorescence (XRF), X-Ray Diffraction (XRD), and Inductively Coupled Plasma-Mass Spectrometry (ICP-MS). These manifestations and general NE lineaments are suggested as the surface control of REE. Major elements (in oxides) SiO2, Al2O3, Fe2O3 dan K2O are dominant in the research area. The majority of alteration mineral identified is advanced argillic consisting of silicates, kaolinite, and halloysite. The highest REE concentration is 207 ppm of cerium, while the lowest is 0,02 ppb of thulium. A quite random correlation between REE and other controls (lineament, manifestations, alterations, and lithology) suggests that REE distribution factor includes more complex variable such as magma origin, rock origin, and the mobility of the elements. Chondrite normalised spider diagram shows that light REE (LREE) is more enriched than heavy REE (HREE). Lanthanum (La), cerium (Ce), and europium (Eu) are 100x enriched relative to its chondrite value; normalised Eu positive anomaly, Ce positive anomaly, and Ce negative anomaly values range from 1.75-45.29, 1.02-22.69, and 0.58-0.99 respectively. Positive anomaly of Eu shows similar pattern to some REE in geothermal field researches. Advanced argillic minerals indicate the temperature forming >2000 and provide the evidence of this positive Eu anomaly.