R. Umam, S. Suharno, and R. Junaidi, “Geochemical Evidence from Major and Trace Elements in Geothermal Waters of Empat Lawang, Southern Sumatra: Clues to Mineralization and Hydrothermal Sources”, Leuser J. Environ. Stud., vol. 3, no. 2, pp. 87–98, Oct. 2025.