Insights for the Angra do Heroísmo hydrothermal reservoir conceptual model

Onshore and offshore hydrothermal activity over the Azores mostly links to young active large volcanic polygenic edifices. The surface features of upflowing fluids from the hydrothermal reservoirs include fumaroles, water springs, and gas emissions, as in the case of Guilherme Moniz and Pico Alto stratovolcanoes on Terceira Island, Azores. Geology, tectonics, and pressure and temperature of fluid dynamics affect possible lateral and fluid downflow, giving rise to hidden hydrothermal reservoirs. The several hydrothermal features identified on water springs, well fluid production temperature, radon gas emissions, and alteration rock minerals on the vicinities of Angra do Heroismo clearly outline a low-seated hot reservoir, the Angra do Heroismo hydrothermal reservoir. The top reservoir feature, hot water, might result from the mixing of low mineralized meteoric freshwater with a deeper upward hydrothermal fluid component. Several sites of the upflowing hot fluid are unknown, but most probably are linked to the closer young active stratovolcanoes of Guilherme Moniz, Pico Alto, and Santa Bárbara. Taking into consideration the available data and interpretation, we estimate the range and probable distribution of the stored heat reserves using Monte Carlo stochastic analysis in the order of 12.99–46.90 MWe. The proximity to potential end users, namely the tourism industry, turns the probable resource into a plausible geothermal reserve. The exploration studies implementation here outlined would highly contribute to the conceptual model improvement.