Isotope and Geochemistry Characterization of Hot Springs and Cold Springs of Sembalun – Rinjani Area, East Lombok, West Nusa Tenggara – Indonesia

Abstract

The presence of several hot springs in Sembalun – Rinjani, East Lombok, West Nusa Tenggara is an indicator of geothermal potential in the area. This study aims to determine the characteristics of hot springs and cold springs and also the geothermal potential in Sembalun – Rinjani area using isotopes and geochemistry methods. The result of d18O and d2H stable isotopes analysis shows that most of the hot springs are meteoric water. Except for Kalak hot spring, other hot springs are a mixing product of meteoric water and andesitic water, with meteoric water composition between 64 to 87%. While 14C radioisotope suggests that the age of hot springs in the Sembalun area is about 10,000–12,000 years BP, the surrounding cold springs are mostly Modern except Jorong cold spring. The results of gas analysis (He, Ar, and Ne) also suggest the same origin of geothermal fluid, i.e., meteoric water origin. Based on chemical composition, Kalak hot spring is plotted as sulfate type water, while Sebau hot spring is plotted near mature water composition but not representing reservoir fluid due to its relatively low temperature and high Mg content. Na/K geothermometer calculation from Sembalun area shows that subsurface temperature is varied between 111-161 °C, while from Rinjani hot springs indicates higher subsurface temperature, i.e., 250-260 °C. It is estimated that reservoir fluid has high TDS with chloride content up to 4000 mg/L.

Comparison Of Isotope And Hydrochemical Characteristics Of Springs In Sembalun – Rinjani Area, East Lombok, West Nusa Tenggara, Indonesia Before And After The Earthquake Events In 2018

“…Sebau warm spring is located at the southern side of Sembalun, at 1345 masl. Compared with previous study in 2012 (Satrio et al, 2020), the current study in 2019 shows that the water is still blackish with temperature decreasing 0.6 °C from 35.4 °C to 34.8 °C and TDS is also decreasing from 1334 mg/L to 1064 mg/L, while the pH is relatively the same, i.e. 7.20.…”

Kearifan Lokal Dalam Konservasi Sumber Mata Air Pada Situs Arkeologi di Kabupaten Dompu

“…Kearifan leka dana ini perlu disosialisasikan kepada masyarakat terutama dalam upaya konservasi mata air, dalam upaya menjaga area hijau secara kolektif pada kawasan tertentu sebagai area resapan yang didapatkan areanya melalui studi isotop ini. CO2 yang didalamnya terkandung isotop 14 C ( 14 CO2) ditampung dalam tabung stainless steel kemudian diserap oleh 30 ml larutan Carbosororb-E/Permafluor-E dalam kolom absorbsi sehingga terbentuk larutan Carbamat (Satrio et al, 2020). Sebanyak 21 ml larutan Carbamat tersebut diambil dan dituangkan ke dalam vial gelas kapasitas 21 ml untuk selanjutnya dilakukan pencacahan menggunakan Liquid Scintillation Analyzer (LSA).…”