Studi awal inklusi fluida pada fenokris kuarsa di Hargorojo, Bagelen, Purworejo, Jawa Tengah

okki verdiansyah

okki verdiansyah Institut Teknologi Nasional Yogyakarta

Keywords: Eksplorasi, tembaga, emas, Kulon Progo

Abstract

The research focuses on dacite intrusion, in the Hargerejo area in the southern Kulonprogo Mountains and administratively in the Begelen District, Purworejo Regency, Central Java Province. The presence of a hydrothermal system in the Kulon Progo area is in the form of low-medium sulfidation epithermal in Kokap, Epithermal - Lithocap in Bagelen, and high-sulfidation epithermal in Menoreh (Magelang). In the case of the Bagelen intrusion, it is suspected that it is part of the hydrothermal system that forms the Au-Ag hydrothermal system. The research uses geological mapping methods and surface sampling on dacite rocks and laboratory observations with polarization and ore microscopy. This study focuses on the character of quartz and the presence of fluid inclusions by using the qualitative concept of fluid inclusion petrography. The lithology of the Bagelen area consists of volcanic breccias, andesite intrusions, dacites, and alluvial deposits. Petrographic analysis of dacite samples showed a porphyritic texture with 55-76% phenocrysts in the form of quartz (8-22%), hornblenda (3-11%), plagioclase (40-55%), surrounded by a bottom mass of volcanic glass and feldspar microlites. , as well as opaque minerals in the form of pyrite and residual magnetite as much as 2-5% and the base mass undergoes diagenesis and is changed to silica. Quartz is divided into types 1 and 2, indicating the presence of primary and pseudosecondary inclusion types. Quartz type 1 (qz-1) shows an irregular distribution and pseudosecondary trail with Type I, II, III inclusions. In type 2 quartz, it is seen that the inclusions are dominated by type II & III or L<V and L>V biphase, with low to high vapor densities. Inclusions in type 2 quartz show a primary pattern and are similar to the general epithermal vein fluid on the surface. The presence of fluid inclusions in the magmatic quartz at Bagelen, indicates the existence of a hydrothermal system formed due to changes in silicate character, and affects the fluid character from magmatic to hydrothermal. Epithermal or related mineralization is more influenced by the presence of type 2 quartz, and subsequent hydrothermal processes. The type of mineralization affected is intermediate sulfidation with a characteristic presence of disseminated pyrite-chalcopyrite in dacite. The fluid that affects mineralization is dominated by the epithermal system.

Keyword : Exploration, Fluid, Copper, Gold, Kulon Progo

References

1. Setijadji LD, Maryono A. Geology and Arc Magmatism of the Eastern Sunda Arc, Indonesia. In: Proceeding of Banda and Eastern Sunda Arcs 2012 MGEI Annual Convention. 2012. hal. 26â€“7.
2. Soeria-Atmadja R, Maury RC, Bellon H, Pringgoprawiro H, Polve M, Priadi B. Tertiary magmatic belts in Java. J Southeast Asian Earth Sci. 1994;9(1â€“2):13â€“27.
3. Hartono HG. Peran Paleovolkanisme Dalam Tataan Produk Batuan Gunung Api Tersier di Gunung Gajahmungkur, Wonogiri, Jawa Tengah. University Padjadjaran; 2010.
4. Rahardjo W, Sukandarrumidi, Rosidi H. Yogyakarta Sheet Geological Map scale 1:100.000. Bandung: Geological Research and Development Center; 1995.
5. Widagdo A, Pramumijoyo S, Harijoko A. The Morphotectono-Volcanic of Menoreh-Gajah-Ijo Volcanic Rock In Western Side of Yogyakarta-Indonesia. J Geosci Eng Environ Technol [Internet]. 2018;3(3):155. Tersedia pada: http://journal.uir.ac.id/index.php/JGEET/article/view/1715
6. Sugarbo O. Tinjauan Awal Hubungan Vulkanostratigrafi Dengan Tipe Mineralisasi Daerah Kokap, Kulon Progo, Yogyakarta. Pros Nas Rekayasa Teknol Ind dan Inf XIV Tahun 2019. 2019;2019(November):338â€“46.
7. Fadlin F, Hajar Sulystiawan I, Adi Prasetyo L. Studi Alterasi, Mineralisasi Dan Inklusi Fluida Prospek Hidrotermal (Pb-Zn-CuÂ±Au-Ag) Kubah Kulonprogo Bagian Selatan, Jawa Tengah. J Geol dan Sumberd Miner. 2019;20(4):211.
8. Pintea I, Iatan LE. the Magmatic-Hydrothermal History of the Î’ -Quartz Polymorphs From Rosia Montana Dacite ... Miner Depos. 2017;90(December):41â€“61.
9. Shepherd TJ, Rankin AH, Alderton DHM. A Practical Guide to Fluid Inclusion Studies. Vol. 50, Mineralogical Magazine. Glasgow and London (Blackie); 1985. 239 hal.
10. Pirajno F. Hydrothermal processes and mineral systems. Springer Science & Business Media; 2008.
11. Pirajno F. Hydrothermal Processes and Mineral Systems [Internet]. Dordrecht: Springer Netherlands; 2009. 1â€“1250 hal. Tersedia pada: http://link.springer.com/10.1007/978-1-4020-8613-7