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Epithermal Gold Mineralization in the T renggalek District, E ast J ava, I ndonesia
Author(s) -
Takahashi Ryohei,
Shingo Yuki,
Imai Akira,
Watanabe Koichiro,
Harijoko Agung,
Warmada I Wayan,
Idrus Arifudin,
Setijadji Lucas Donny,
Phoumephone Phouvang,
Scherstén Anders,
Page Laurence
Publication year - 2014
Publication title -
resource geology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.597
H-Index - 43
eISSN - 1751-3928
pISSN - 1344-1698
DOI - 10.1111/rge.12034
Subject(s) - geology , geochemistry , pyroclastic rock , andesite , quartz , pyrite , volcanic rock , mineralogy , breccia , porphyritic , volcano , paleontology
Gold‐mineralized quartz veins at the T renggalek district of the S outhern M ountains R ange in E ast J ava, I ndonesia, are hosted by O ligo‐ M iocene volcaniclastic and volcanic rocks, and are distributed close to andesitic plugs in the northern prospects ( D alangturu, S uruh, J ati, G regah, J ombok, S alak, and K ojan) and the southern prospects ( S entul and B uluroto). The plugs are subalkaline tholeiitic basaltic‐andesite to calc‐alkaline andesite in composition. 40 A r– 39 A r dating of a quartz‐adularia vein at the D alangturu prospect yielded an age of 16.29 ± 0.56 Ma (2σ), and a crystal tuff of a limestone‐pyroclastic rock sequence at the southwest of the Dalangturu prospect was determined as 15.6 ± 0.5 Ma (2σ). Statistic overlap of ages suggests that the gold mineralization in the northern prospects took place in a shallow marine to subaerial transitional environment. Hydrothermal alteration of the host rocks is characterized by the replacement of quartz, illite and adularia. Quartz veins in surface outcrops are up to 50 cm wide in the northern prospects and up to 3 m wide in the southern prospects, showing a banded or brecciated texture, and are composed of quartz, adularia, carbonates with pyrite, electrum, sphalerite, galena, and polybasite. Gold contents of quartz veins are positively correlated with Ag , Zn , Pb , and Cu contents in both the northern and southern prospects. The quartz veins at the J ati, G regah, and S entul prospects have relatively lower gold‐silver ratios ( Ag / Au = 23.2) compared to those at the K ojan, D alangturu, S alak, and S uruh prospects ( Ag / Au = 66.8). The quartz veins at the D alangturu prospect are relatively rich in base metal sulfides. Ag /( Au + Ag ) ratios of electrum in the D alangturu prospect range from 45.2 to 65.0 at%, and FeS contents of sphalerite range from 1.2 to 6.4 mol%. Fluid inclusion microthermometry indicates ore‐forming temperatures of 190–200°C and 220–230°C at the S entul and K ojan prospects, respectively. Widely variable vapor/liquid ratio of fluid inclusions indicates that fluid boiling took place within the hydrothermal system at the Sentul prospect. Salinities of ore‐fluids range from 0 to 0.7 wt% (av. 0.4 wt% NaCl equiv.) and from 0.5 to 1.4 wt% (av. 0.9 wt%) for the S entul and K ojan prospects, respectively. The boiling of hydrothermal fluid was one of the gold deposition mechanisms in the S entul prospect.