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

Kawah Putih is a summit crater of Patuha volcano, West Java, Indonesia, whi ch 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 deg rees C, pH = <0.5-1.3, S-tot = 2500-4600 ppm and Cl = 5300-12 600 ppm, and floating sulfur globules with sulfide inclusions are common. Sulfur oxyanio n concentrations are unusually high, with S4O62- + S5O62- + S6O62- = 2400 - 4200 ppm. Subaerial fumaroles (<93 degrees C) on the lake shore have low m olar SO2/H2S ratios (<2), which is a favorable condition to produce the obs erved distribution of sulfur oxyanion species. Sulfur isotope data of disso lved sulfate and native sulfur show a significant S-34 fractionation (Delta SO4-S-e of greater than or equal to 20 parts per thousand), probably the r esult of SO2 disproportionation in or below the lake. The lake waters show strong enrichments in O-18 and D relative to local meteoric waters, a resul t of the combined effects of mixing between isotopically heavy fluids of de ep origin and meteoric water, and evaporation-induced fractionation at the lake surface. The stable-isotope systematics combined with energy-balance c onsiderations support very rapid fluid cycling through the lake system. Lak e levels and element concentrations show strong seasonal fluctuations, indi cative 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 p redicted by the model calculations are consistent with the bulk chemistry o f the sulfur-rich bottom sediments and their identified mineral phases. Muc h of the lake water chemistry can be explained by congruent rock dissolutio n in combination with preferential enrichments from entering fumarolic gase s or brines and element removal by precipitating mineral phases, as indicat ed 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 pa- dependent element mobility. Discharges of warm sulfate- and chloride-rich w ater 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 p rocesses at Patuha have led to the accumulation of elements that are common ly 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. (C) 20 00 Elsevier Science B.V. All rights reserved.