General features of the geometry of Los Azufres reservoir have been defined through the mapping of hydrothermal mineral alteration zones. Hydrothermal alteration has been studied in cuttings and drill cores from most of the active wells. X-ray diffraction micro-probe analysis and classical optical methods have been employed for the identification of primary and authigenic minerals in fresh and altered samples. Observed patterns of alteration have been correlated with temperature and patterns of fluid circulation. The res u l t in g model depicts a body of geothermal fluid at depth, which ascends and discharges through two main fracture systems. These two c i r c u l at i o n zones are characterized by conc e n t r i c aureoles of increasing hydrothermal alteration towards quasi vertical axes. The overall pattern could be described as a dome structure produced by the abnormal thermal gradient, distorted by the effects of active upward circulation of the fluids .

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