PETROGRAPHY AND MINERALIZATION AT THE VOLCANIC ROCK OF HULUSIMPANG FORMATION MEMBER, IN LEBONG TANDAI, NORTH BENGKULU REGION, BENGKULU PROVINCE, SUMATERA.

PETROGRAPHY AND MINERALIZATION AT THE VOLCANIC ROCK OF HULUSIMPANG FORMATION MEMBER, IN LEBONG TANDAI, NORTH BENGKULU REGION, BENGKULU PROVINCE, SUMATERA.

By : Sri Indarto, Iskandar Zulkarnain, Iwan Setiawan and Sudarsono

Research Centre for Geotechnology – Indonesian Institute of Sciences (LIPI),
Komplek LIPI, Jl. Sangkuriang, Bandung , telp. 022-2503654, fax. 022-2504593,
email : sri.indarto@geotek.lipi.go.id, iwan@geotek.lipi.go.id, sudarsono@geotek.lipi.go.id

Abstract

The volcanic rocks exposed in the Lebong Tandai area and its surroundings, the North of Bengkulu Region, Sumatera can divide into two types, that are as lavas and pyroclastic. The petrographic and major elements analyses result of lavas are suitable for andesite and basalt. Whereas the pyroclastic rock are consist of lithic crystal tuff and crystal vitric tuff which are as andesitic to rhyolitic composition. The two types of rocks above are hydrothermally altered and mineralized. Based on to the physics characters Lebong Tandai volcanic rocks are can be equally to a member of Hulusimpang Formation. Ande site – basalt lavas are altered into propylitic and characterized by chlorites, carbonates, epidotes. Whereas alter tuff characterized by chlorite, carbonate, sericite and silicic.

Mineralization both of the two are associate with disseminated fine grain pyrite, chalcopyrite, sphalerite, and some time founded a comb structure of quartz veins and adularia veinlets. The hydrothermal minerallization of these area classified into low sulphidation epithermal systems.

Keywords : Lebong Tandai, Hulusimpang Formation, petrography, volcanic rocks, low sulphidation epithermal.