The Mangani mine in West Sumatra is historically one of the most important precious metal mines in Indonesia, although the past production by World standards is small, totall- ing 5.66 tonnes gold and 242 tonnes silver. The geology is dominated by a distinctive NW-SE graben structure formed by dextral splay faults from the Sumatran Fault System. Quartz- rhodochrosite-rhodonite-Ag-Au veins are hosted by Tertiary pyroxene andesite volcanics and quartz-phyllite conglomerates, on N-S tensional fractures which intersect the Mangani graben._x000D_
Intrusive rocks include andesitic dykes, pyroxene microdiorite, and hornblende granodiorite. Quartz-epidote-pyrrhotite alteration is related to concealed intrusions._x000D_
Precious metal vein mineralization is characterized by: high Ag/Au ratio (>25); complex sulphide mineralogy of Fe, Mn, Ag, Cu, Pb, Zn, As, Se and the occurrence of Sn as stannite; low total sulphide content (<5%); mn carbonate, silicate and chalcedonic quartz gangue assemblages; multistage vein textures, including diffusion banding, encrustation, dilational infilling and brecciation; a probable vertical zonation of precious metal distribution, gangue mineralogy and wallrock alteration; rapid upward termination of vein systems; lensoid development and relatively wide veins compared to strike length. the mineralization is interpreted as a low sulphur type epithermal system, characterized by boiling and vertical zonation.>