HYDROTHERMAL MINERALIZATION AT GOMBONG AREA KEBUMEN REGENCY - CENTRAL JAVA']JAVA

Circular (Polygonal) and linear features in LANDSAT imagery of Gombong area, Central Java, express magma activities and faults. Their formation is presumed followed by mineralization processes, which is initiated by magmatic and tectonic activities in Pliocene, shown by a close relationship between mineralized and fault zones. Propylitic alteration assemblages, veins (mainly carbonate), and ore minerals consist of very fine grains of Fe, Cu, Pb, and Zn sulphides characterize mineralization in the studied area, hosted by Late Oligocene rock units of Gabon Formation. Latticed quartz vein from Lodeng River indicates that boiling hydrothermal fluid has formed it. Unfortunately, there is no fluid inclusion found in the samples for micro-thermometric studies; however, the sulphide mineral assemblage indicate that the temperature of the hydrothermal fluids in the studied area had cooled down from between 300 -350 degrees C to below 300 degrees C.