The euclase mines of Colombia are situated in the Central part of the Eastern Cordillera, specifically in the Guavio region. These Be-mineralizations of Tertiary age (?) are found in lower Cretaceous marine sedimentary rocks and belong to the stratigraphic unit Calizas del Guavio. The field ocurrence and geology of these mines imply a tectonic influence of large fault systems. The euclasa occurs in voids and nodules, very often accompanied by veins of calcite and fault breccia in carbonaceous argillites and carbonates. To unravel the conditions of formation, fluid and solid inclusions have been investigated by microthermometric studies, IR and micro-Raman spectroscopy, X-ray diffraction and electron microscopy. The fluids were defined as hot solutions (>360°C), of relative high density and salinity (40-50 weigh % NaCI equiv.). The CO 2 content is 0,75 mole % and nitrogen content is even lower.