LIQUID SULFUR AT VOLCAN-AZUFRE, GALAPAGOS-ISLANDS

Volcan Azufre, located in the Sierra Negra caldera, is the most active fumarolic area in the Galapagos Islands. Large areas are covered with nearly one meter of deposits, and active vents are depositing crystalline sulfur and pervasively leaching and altering the basalt talus on which the fumaroles are located. Cones and ridges of crystalline sulfur are built over the vents at temperatures below 113°C; primary sulfur deposition at higher temperatures was not observed. Small pockets of liquid sulfur were observed near a few vents and sulfur stalactites occur within some of the cones. This liquid is formed by the melting of sublimated deposits. Several sulfur flows were found with the largest measuring 225 meters in length. The characteristics of the flows indicate that they are a recurring phenomenon at Azufre. Sand cones formed by sand fountaining sand pots occur over high temperature vents. (175-235°C), but liquid sulfur is notably deficient in these sand deposits. Field analyses of the gases show that they contain a large percentage of gases other than water and air; this is largely due to the dry climate and the collecting technique. C/S and SO2/H2S values indicate that the gases are closely related to a magmatic source. Thermal gradients show that solid sulfur could be stable only to very shallow depths and that the vaporization temperature of sulfur may be reached at depths of several meters. Equilibrium calculations are used to estimate the importance of various sulfur depositing mechanisms. The gases are not oxidized and may represent a partially quenched, high temperature composition. Below 170°C, sulfur could be deposited from SO2, H2S, and sulfur gas. Oxidizing reactions will cause sulfur deposition once the gases contact the atmosphere. Considering the field data, the oxidizing reactions prove to be the dominant and controlling mechanism for sulfur deposition; condensation of liquid sulfur from the gases is, at best, a minor process. Liquid sulfur, including the sulfur flows, is apparently formed by melting of the crystalline deposits during fluctuations in the thermal gradient. A cyclic sulfur budget is suggested, and the presence of liquid sulfur at greater depths is considered. © 1973 Society of Economic Geologists, Inc.