COMPARATIVE STUDY OF ACTIVE AND ANCIENT HIGH-SULFIDATION EPITHERMAL SYSTEMS AT KAWAH IJEN AND TUMPANG PITU, EAST JAVA, INDONESIA

KRY, REAKSMEY, Dr. Lucas Donny Setijadji,S.T.,M.Sc; Dr.Ir.I Wayan Warmada

2019 | Tesis | MAGISTER TEKNIK GEOLOGI

Kawah Ijen and Tumpang Pitu are located in East Java Province, Indonesia. Kawah Ijen is considered as an active high-sulfidation system, while Tumpang Pitu is an ancient or fossil high-sulfidation epithermal deposit. In this research, researcher would like to compare similarities and differences of hydrothermal alteration types from both locations by using remote sensing analysis. There are two types of satellite images used here, which are Landsat 8-OLI and ASTER scenes. Each location uses both satellite images, in which Band Ratio is the main method used for image processing. Landsat 8 images can be used to detect clay and iron oxide mineral, while ASTER images can detect siliceous rock, alunite, kaolinite, illite-smectite and iron oxide.

For ASTER band ratio, there are (b5+b7)/b6 for illite-smectite, (b4+b6)/b5 for alunite, b2/b1 for iron oxide and b7/b5 for kaolinite. For Landsat 8 images, b6/b7 is used for clay mineral while b2/b4 is for iron oxide. After band ratio, there are several other steps to process the results, such as: set null, convert raster to point and buffer the point. The intersection of 'clay' and 'alunite merge with kaolinite' is used to define advance argillic alteration, while intersection of 'clay' with 'illite-smectite' is used to define argillic alteration, and intersection of 'iron oxide' from both images defines 'iron oxide'. Then image analysis results are confirmed using ground checking samples, in which there are nine samples taken from Kawah Ijen analyzed using X-ray Diffraction, and five samples are taken from Tumpang Pitu analyzed using Analytical Spectral Device to define mineral contents. Most of the samples are well correlated with image analysis results. Kawah Ijen contains siliceous rock and advance argillic alteration at the center, then iron oxide zone located at outer part of advance argillic zone, while argillic zone seems to distribute far from the center of research location. At Tumpang Pitu, near the mining site is covered by advance argillic and little siliceous rock, while argillic zone is located far from the advance argillic zone. Iron oxide appears a little near the mining site, but it is abundant on the northern part of mining site. Landsat 8 images can detect iron oxide better than ASTER images.

Kata Kunci : High-sulfidation epithermal system, remote sensing, ASTER, Landsat 8, color composite and band ratio