THE CHLORITE TOURMALINE TRANSFORMATION IN NATURAL AND EXPERIMENTAL HYDROTHERMAL ENVIRONMENTS

Alterations leading to borosilicate formation in hydrothermal systems evolve together with aluminous alterations with the assemblage chlorit e + calcium-borosilicate in the periphery, then phengite + tourmaline and, in the core of the hydrothermal system, (pyrophylite, andalousite ) + dumortierite. The circulation of a boron-rich fluid induces the tr ansformation of chlorite into tourmaline. This reaction was reproduced using a mixture of chlorite, alkali-feldspar and H3BO3 in sealed gold tubes introduced into pressure vessels at temperatures from 400 to 70 0-degrees-C. It seems to be a general reaction in such an environment.