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Geologic and geochemical investigation in Mount Taftan indicates a viable
geothermal resource probably centered and upflowing beneath the volcano. This
volcanic region in SE Iran has a very high potential for generation of
geothermal energy. The presence of volcanos is intimately related to the
subduction of Neotethys oceanic lithosphere under the Central Iranian
continental plate. Magmatism in Mt. Taftan is represented by subalkaline
volcanics that vary from basaltic through andesitic to dacitic composition.
Springs with temperatures ranging from 10 to 35 °C are located in the prospect
area, fed by the sedimentary aquifers. Based on geochemical and hydrological
data, the thermal Cl-Ca-SO4 waters rise toward the surface from reservoirs made
up of a volcano-sedimentary sequence through faults and fractures. Fumerolic
and thermal discharges from this volcanic region contain deeply derived H2S
with subsequent oxidation to SO4 -2 in the system. Based on Na-K-Mg ternary
diagram, none of the discharge waters could be representative of deep fluids in
“full equilibrium” with the reservoir rocks. The acid alteration in the shallow
parts of Mt. Taftan results from the oxidation of H2S. Steam, accompanied by
H2S rises from depth and produces acid sulfate fluids, which react with the
surficial rocks to generate alteration mineral assemblages. The temperature
range established from alteration mineralogy, overlaps with that determined
from chemical geothermometers. The occurrence of hydrothermal alteration
minerals at the surface indicates a low to moderate geothermal system. Clay
mineral alteration assemblage encountered in Taftan geothermal system might
have been superimposed on older and higher-temperature stages. The
geothermal energy produced in the system is from the cooling magma, which is
heating circulating groundwater. The magma-heated water, which emerges at
the surface as fumerolic discharges and heats up the descending cold meteoric
water, signals the presence of the shallow heat source beneath Mt. Taftan