The Leading Edge; December 2002; v. 21; no. 12;
p. 1199-1202; DOI: 10.1190/1.1536133
© 2002 Society of Exploration Geophysicists
Reinterpretation of a vintage 4.5-km resistivity line through Sulphur Springs, St. Lucia
Frank Dale Morgan,
Yervant Vichabian and
John Sogade
Massachusetts Institute of Technology, Cambridge, Massachusetts, U. S.
Corresponding author: yerv@erl.mit.edu
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Saint Lucia is part of the Lesser Antilles volcanic island arc in the eastern Caribbean (Figure 1). Volcanic activity has been concentrated in the southern half of the island for the last several million years (Wohletz et al., 1986). The Sulphur Springs geothermal area lies within what has been identified as the Qualibou Caldera. Geologic studies have shown that recent volcanic activity in the area has been of a type that is likely to emplace a magma heat source for high temperature geothermal systems to naturally develop. Any evidence for a supposed intrusion beneath Sulphur Springs comes from temperature measurements of the superheated steam and wells, and from microseismic data (GENZL, 1992). Aspinall et al. (1976) suggest two fluid bodies, one near Sulphur Springs at a depth between 0.5 and 2 km and a second on the northern caldera rim at depths greater than 1 km.
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Figure 1 Location of Saint Lucia, West Indies.
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Surface geothermal activity is evidenced by acidic mud pools and fumaroles. Shallow groundwater is heated by steam from depth and may be locally acidified by the presence of gases in the steam. A hot (200° C) brine aquifer, heated by steam from a deeper source, is present about 200–500 m below the area of surface manifestations. A deeper reservoir encountered by well SL-2 at 800–1300 m appears to be high temperature (285° C), steam-dominated, and with a liquid component possibly being low concentration brine. The reservoir lies in a zone of dacite lavas, which may be providing permeability. The lateral extent of this steam-dominated reservoir is unknown but the small size of the overlying brine and alteration layers, together with the low temperatures in well SL-1 at similar elevations, indicate that it may be confined to a small area. This reinforces the assumption that vertical permeability . . . [Full Text of this Article]
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