Sulfur melt in Golovnin Caldera, Kunashir Island, Russia

Abstract

The paper considers the formation of native sulfur and sulfides in the bottom sediments of volcanic lakes in the Golovnin Caldera. Our observations and microstructure studies indicate the presence of sulfur melt at the bottom of Kipyaschee Lake. Drops of this melt are carried to the surface of the lake as part of a light gray foam. The significant differences of sulfur spherules in the concentration of sulfide mineralization, in its composition, as well as in the presence or absence of numerous opal inclusions are most simply explained by the capture of droplets in various parts of the sulfur melt and their subsequent movement by a gas stream passing through the melt. The effusions of sulfur melt in 1979 are direct evidence of its existence. Molecular chemical modeling shows that the stability of sulfur condensate in the bottom sediments is controlled by two thermobaric surfaces. The upper is controlled by the beginning of water condensation and a wave of acidity, the lower by the beginning of sulfur condensation. Both surfaces are a consequence of the cooling effect of lake water, and when bottom sediments accumulate, they move following changes in the surface of the lake bottom. Elemental sulfur condensate is formed between these surfaces as a result of forced cooling of endogenous gas flows. This process is most active in crater depressions at the bottom of Golovnin Caldera lakes, where sulfidization of the sulfur melt occurs simultaneously with the condensation of sulfur itself. Gravitational deposition of sulfides in the sulfur melt leads to their enrichment of the root parts of crater depressions, where pyrite ore bodies are formed in real time.