17:15 〜 18:45
[SVC25-P02] Hydrothermally altered mineral and sulfur isotope characteristic of acid crater in Dieng Volcanic Complex (DVC), Central Java, Indonesia
キーワード：DVC, advance argillic alteration, sulphur isotope, sulphur-bearing mineral
Dieng Volcanic Complex (DVC) is an active geothermal field consist of Holocene stratocones, parasitic vents, and an explosion crater within the caldera remnant of ancient volcanoes. Three active hydrothermal sectors divided by low permeability and low-temperature barriers between sectors are present: Sileri, Sikidang-Merdada, and Pakuwaja. The dome-shaped Sikidang-Merdada sector preserves the highest geothermal potential with a reservoir temperature of 280° – 320°C, and acid-circulated fluid. However, generating geothermal energy in the Sikidang-Merdada sector is greatly challenging due to the circulation of its acidic hydrothermal fluid. Therefore, it is essential to investigate the characteristics, distribution, and source of acid fluid in Sikidang-Merdada. We study the physico-chemical properties of acid hydrothermal fluid in Sikidang-Merdada through the characterization of hydrothermal alteration from its hydrovolcanic ash.
In order to identify distribution and variation of alteration mineral, 9-layer of highly altered hydrothermal deposit (BTG-A_1, BTG-A_2, BTG-A_3, BTG-A_4.1, BTG-A_4.2, BTG-A_5, BTG-A_6, BTG-A_7.1, BTG-A_7.2, respectively from top to bottom) surround Sibanteng crater were collected based on its discoloration. The alteration minerals of 9-layer samples were examined through XRD. A few selected samples were then analyzed to observe the presence and behavior of its alteration minerals through SEM-EDS. In understanding magmatic-hydrothermal interaction and identifying the acid sources, sulfur isotope analysis of sulfur-bearing minerals is conducted. The XRD and SEM-EDS analysis shows aluminosilicate (kaolinite + pyrophyllite) and silicate minerals as the majority of alteration minerals produced with TiO2 as mineral accessories. Alunite appears mostly as a vug filling, and other sulfur-bearing minerals are also present such as native sulfur, and pyrite. The sulfur mineral appears in layers BTG-A2, 4.2, and 5 located near solfatara manifestation. These mineral assemblages reflect an advanced argillic alteration in an acid environment with medium temperature and pH ± <2.5. This study may provide some clues about the origin of acid fluid in Sikidang-Merdada, as a fundamental guide to expand geothermal energy production from subvolcanic hydrothermal systems.
In order to identify distribution and variation of alteration mineral, 9-layer of highly altered hydrothermal deposit (BTG-A_1, BTG-A_2, BTG-A_3, BTG-A_4.1, BTG-A_4.2, BTG-A_5, BTG-A_6, BTG-A_7.1, BTG-A_7.2, respectively from top to bottom) surround Sibanteng crater were collected based on its discoloration. The alteration minerals of 9-layer samples were examined through XRD. A few selected samples were then analyzed to observe the presence and behavior of its alteration minerals through SEM-EDS. In understanding magmatic-hydrothermal interaction and identifying the acid sources, sulfur isotope analysis of sulfur-bearing minerals is conducted. The XRD and SEM-EDS analysis shows aluminosilicate (kaolinite + pyrophyllite) and silicate minerals as the majority of alteration minerals produced with TiO2 as mineral accessories. Alunite appears mostly as a vug filling, and other sulfur-bearing minerals are also present such as native sulfur, and pyrite. The sulfur mineral appears in layers BTG-A2, 4.2, and 5 located near solfatara manifestation. These mineral assemblages reflect an advanced argillic alteration in an acid environment with medium temperature and pH ± <2.5. This study may provide some clues about the origin of acid fluid in Sikidang-Merdada, as a fundamental guide to expand geothermal energy production from subvolcanic hydrothermal systems.