Year

1988

Degree Name

Master of Science

Department

Department of Geology

Abstract

The Gunung Liinbung base metal mineralization is one' of several such deposits located in western Java, Indonesia. The geology of the Gunung Limbung area corprises a sequence of argillite, tuf faceous sandstone and volcanic breccia and lava v ^ c h has been intruded by diorite v^ch was derived frcm an andesitic calc-alkaline parent magma ^lich forrted in an island arc volcanic zone. Mineragraphic studies show that the ores at Gunung Limbung, can be divided into four types - massive ore, quartz vein ore, brecciated ore and disseninated ore. The mineralogy of the the four types is a sinple assemblage corprising dominantly sphalerite, galena, chalcopyrite, and pyrite with minor gold. The ores have textures vtoch are typical of those filling open spaces with crustification and banding conmon. Petrograi^c and geochemical studies indicate that the host rocks are porf^iyritic diorites v ^ c h have been considerably altered during or after the mineralizing ftese. Phenocrysts of plagioclase, orthoclase, clinopyroxene and hornblende occur in a matrix of quartz, feldspars, epidote, sericite and chlorite (the latter three forned as a result of the alteration). The host rocks are characterized by veins and microveinlets of quartz and less connonly quartz and pyrite. Geochemical studies indicate the the host rocks, coipared to unaltered calc-alkaline island arc andesites, are enriched in quartz, potassium, barium and rubidium but deficient in sodium and calcium.

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