ALTERATION AND MINERALIZATION OF ANCIENT CALDERA

IN CUPUNAGARA, SUBANG, WEST JAVA

H. Utoyo

Geological Survey Centre; Jl. Diponegoro 57 Bandung, Indonesia, Phone (022) 7203205

A B S T R A C T

The study area which is an ancient caldera of Cupunagara, northern part of Bandung, belong to Subang
district, West Java Province. This area coverages arround 60 km2, between 650 to 1200 m above sea
level. The morfology of this area is an ancient caldera, with steep wall, young degree of erotion and
subtrellis drainage pattern of northeast to southwest direction. The area is covered by volcanic rocks,
which consist of pyroxene andesite. K/Ar age results yielded between 58,99 ± 1,94 Ma (Upper Paleocene)
and 36,88 ± 3,96 Ma (Upper Eocene).

The altered on rocks consist of 5 zones, i.e: Argilite Silica, Argilite, Propylite Pyrite, Propylite and
Cloritize Andesite. The results of XRD analysis of the altered rocks show various minerals i.e: quartz,
calcite, albite, haloysite, feldspar, pyrite, kaolinite, crystobalite and mica, which were formed in the low
temperature and pH. Mineralization is known by the present of pyrite, which is formed in the epitermal
condition. Consist of disseminated of pyrite and calcopyrite, spotted, veinlets, vuggy and replacement of
primary minerals.

Keywords: Alteration, mineralization, Cupunagara, Subang.