Abstract

FORERO, Jhon; ZULUAGA, Carlos  and  MOJICA, Jaime. ALTERATION RELATED TO HYDROTHERMAL ACTIVITY OF THE NEVADO DEL RUIZ VOLCANO (NRV), COLOMBIA. bol.geol. [online]. 2011, vol.33, n.1, pp.59-67. ISSN 0120-0283.

The hydrothermal activity in the NRV generates alteration characterized by mineral associations depending on a number of physic-chemical factors of the hydrothermal system. Petrography of unaltered rocks was used to establish the mineral assemblage prior to rock-fluid interaction. XRD was used in altered rocks, where it was not possible to recognize the alteration products. The observed mineral assemblages indicate advanced and intermediate argillic alterations, this and the observation of very low modal proportion of sulphates, sulphides and native sulphur in some areas could point to a low sulphidation zone. However, the proximity to the volcano and the presence of acid thermal waters and steam pose an apparent contradiction with an expected high sulphidation zone which is explained by climatic conditions, where excess water has dissolved and leached sulfides, sulphur and sulphates close to the volcano. Fault zones serve as conducts for fluid transport and have acid-sulphate mineral associations produced by atmospheric oxidation at the water table in a steam-heated environment of H₂S released by deeper, boiling fluids or by the disproportionation of magmatic SO₂ to H₂S and H₂SO₄ during condensation of magmatic vapor plume at intermedia depths in magmatic hydrothermal environment in andesitic volcanic terrain characteristic of high sulphidation zones.

Keywords : Hydrothermal Alteration; Nevado del Ruiz; Volcano.

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