Geochemistry of the acid Kawah Putih lake, Patuha Volcano, West Java, Indonesia

• Published in: Journal of volcanology and geothermal research Vol. 97; no. 1-4; pp. 77 - 104
• Main Authors: SRIWANA, T, VAN BERGEN, M. J, VAREKAMP, J. C, SUMARTI, S, TAKANO, B, VAN OS, B. J. H, LENG, M. J
• Format: Conference Proceeding Journal Article
• Language: English
• Published: Lausanne Elsevier 01.04.2000; Amsterdam; New York, NY
• Subjects: Crystalline rocks; Earth sciences; Earth, ocean, space; Exact sciences and technology; Freshwater; Geochemistry; Igneous and metamorphic rocks petrology, volcanic processes, magmas; Indonesia, Java, Patuha Mt; Mineralogy; Silicates; Water geochemistry; Far East; Java; Indonesia; hydrogen sulfide gas; epithermal deposits; springs; mixing; thermodynamics; energy balance; crater lakes; sulfates; fumaroles; precipitation; hydrochemistry; fluctuations; isotopes; pH; temperature; sulfur; sulfides; chlorides; sulfur dioxide; models; dissolution; halides; chlorine; mineralization; acidity; Asia; isotope fractionation; residence time; evaporation; S-34; seasonal variations
• ISSN: 0377-0273; 1872-6097
• DOI: 10.1016/S0377-0273(99)00178-X

Kawah Putih is a summit crater of Patuha volcano, West Java, Indonesia, which contains a shallow, similar to 300 m-wide lake with strongly mineralized acid-sulfate-chloride water. The lake water has a temperature of 26-34 degree C, pH=<0.5-1.3, S super(tot)=2500-4600 ppm and Cl=5300-12600 ppm, and floating sulfur globules with sulfide inclusions are common. Sulfur oxyanion concentrations are unusually high, with S sub(4)O sub(6) super(2-)+S sub(5)O sub(6) super(2-)+S sub(6)O sub(6) super(2-)=2400-4200 ppm. Subaerial fumaroles (<93 degree C) on the lake shore have low molar SO sub(2)/H sub(2)S ratios (<2), which is a favorable condition to produce the observed distribution of sulfur oxyanion species. Sulfur isotope data of dissolved sulfate and native sulfur show a significant super(34)S fractionation ( Delta SO sub(4)-S sub(e) of 20ppt), probably the result of SO sub(2) disproportionation in or below the lake. The lake waters show strong enrichments in super(18)O and D relative to local meteoric waters, a result of the combined effects of mixing between isotopically heavy fluids of deep origin and meteoric water, and evaporation-induced fractionation at the lake surface. The stable-isotope systematics combined with energy-balance considerations support very rapid fluid cycling through the lake system. Lake levels and element concentrations show strong seasonal fluctuations, indicative of a short water residence time in the lake as well. Thermodynamic modeling of the lake fluids indicates that the lake water is saturated with silica phases, barite, pyrite and various Pb, Sb, Cu, As, Bi-bearing sulfides when sulfur saturation is assumed. Precipitating phases predicted by the model calculations are consistent with the bulk chemistry of the sulfur-rich bottom sediments and their identified mineral phases. Much of the lake water chemistry can be explained by congruent rock dissolution in combination with preferential enrichments from entering fumarolic gases or brines and element removal by precipitating mineral phases, as indicated by a comparison of the fluids, volcanic rocks and lake bed sediment. Flank springs on the mountain at different elevations vary in composition, and are consistent with local rock dissolution as a dominant factor and pH-dependent element mobility. Discharges of warm sulfate- and chloride-rich water at the highest elevation and a near-neutral spring at lower level may contain a small contribution of crater-lake water. The acid fluid-induced processes at Patuha have led to the accumulation of elements that are commonly associated with volcano-hosted epithermal ore deposits. The dispersal of heavy metals and other potentially toxic elements from the volcano via the local drainage system is a matter of serious environmental concern.