KARAKTERISTIK DISTRIBUSI MINERAL UBAHAN: JEJAK EPISODE KEGIATAN HIDROTERMAL DI DAERAH CUPUNAGARA, SUBANG, JAWA BARAT

Abstract

Cupunagara Area, lies in the North-Northeastern of the Sunda Volcanic Complex, occupied by rough mountainous  area consisting of two calderas and surrounded by several volcanic cones. The lithology of the studied area consists of intrusive rocks unit, andesitic – basaltic lava and pyroclastic, mostly had been altered into prophylitic and argillic zones. The prophylitic zone is distributed widely in the central part of the calderas, whilst the argillic zone is distributed confined to the Northwest-Southeast trending fault zones overprints the prophylitic zone and contains the remnants of quartz veins. Structural geology pattern of the studied area is affected by its position as the meeting area of the Cimandiri and the Baribis Fault Systems. Two main strike slip faults are recognized consist of the Northeast-Southwest trending sinistral fault and the Northwest-Southeast trending dextral fault. Two episodes of hydrothermal activities occurred in the studied area, in the first episode the hydrothermal fluid was relatively hot (temperature between >100 to 250^oC) and neutral (pH 5-6), whilst in the second its temperature was <100^oC and acid. The first episode was triggered by the Oligo-Miocene tectonic activity (the formation of the Northeast-Southwest fault zone), the controlling factor of the hydrothermal alteration distribution were the permeability of the host rocks and fault zones, altered the mineralogy of the host rocks into the prophylitic alteration assemblage and formed quartz veins. The second episode was triggered by the Plio-Pleistocene tectonic activity (the formation of the Northwest-Southeast fault zone), altered (overprinted) the wall rocks into the argillic alteration assemblage, the controlling factor was the fault zones.