Alkaline sulphate fluids produced in a magmatic hydrothermal system

Acid hot springs also occur in the Crater Wall area, but in contrast to the alkaline sulphate
springs, the acid hot springs are destructive, and lie within cavities. These springs typically
have very low water discharges (on the order of 0.001–0.010 kg/s) although vigorous
bubbling indicates significant gas discharge rates. These springs were not persistent features
over the two sampling periods.
2.2.3 Reoka
The Reoka hydrothermal field is an area (approximately 50 m 2 ) of hot springs and fumaroles
on the flat ground in the lower reaches of the Reoka stream (Fig. 1). Ground and hot spring
temperatures are typically 100°C. At the surface, advanced argillic alteration (kaolinite with
minor alunite) is widespread, with grey pyrite-bearing mud found up to 30 cm below. In
2005, acid hot springs (pH 2–5) occurred as pools within depressions within the thermal area.
The springs were isolated from the stream, and had very low discharge rates (10 cm thick beds of travertine. No high
temperature thermal areas occur within the Tanginakulu catchment.
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