GEOLOGI DAN MINERALOGI ALTERASI HIDROTERMAL DESA SERANGPANJANG DAN SEKITARNYA, KAB. SUBANG, JAWA BARAT

Abstract

This study is about the geological condition of Serangpanjang and its surroundings as well as the study of hydrothermal alteration mineralogy in the research area. Administratively, the research area belongs to Subang regency, West Java. The area of geological study is located at 6°38'2.67" S & 107°36'10.10" E to 6°41'42.23" S & 107°40'56.34" E with an area of ±60.17 Km2. The research methods used are literature studies, primary data retrieval (data in the field), calculation of petrography incision composition using point counting method and using Fiji software (ImageJ Win-64), and XRD analysis using MAUD software v.2.94. The geomorphology of the research area is divided into five units namely the Lava Flow Ridge Unit, the Lava Flow Plain Subang Unit, the Lava Flow Hill Subang Unit, the Pyroclastic Flow Ridge Subang Unit, and the Pyroclastic Flow Plain Subang Unit. The stratigraphy of the research area is divided into five unofficial units, namely from the oldest to youngest: Andesite Hornblende Lava Unit (Lah), Pyroclastic Flow Rock Unit (Ap), Basalt Ortho-pyroxene Lava Unit (Lbo), Basalt pyroxene Lava Unit (Lbp), and Basalt Olivine Lava Unit (Lbol). The value of plagioclase anorthite decreased as lava units resulted from Tangkuban Parahu and Malang/Palasari volcanoes indicating magma differentiation. The history of volcanism in research area began with Sunda volcanism which resulted in Andesite hornblende Lava Unit and Pyroclastic Flow Rock Unit. Sunda Volcanism caused caldera collapse and resulted normal fault in the west – north part of the research area. Then, there was Tangkuban Parahu volcanism which produced the Basalt Pyroxene Lava Unit and the Basalt Ortho-pyroxene Lava Unit. After that, there was Malang and/or Palasari volcanism which produced Basalt Olivine Lava Unit. The research area has one type of alteration zone, namely the Silica-Illite/Muscovite/Kaolinite Alteration Zone. The hydrothermal fluid that formed the alteration mineralogy is acidic (pH 4-6) with temperature about 250oC. Keywords: Geology, Subang, Serangpanjang, petrography, alteration mineralogy.