Reference Work Entry


Part of the series Encyclopedia of Earth Science pp 331-333

Hydrothermal alteration

  • Byron R. Berger

Hydrothermal alteration, also referred to as wallrock alteration, is a general term that encompasses many processes by which rock-forming minerals are altered due to reactions accompanying the flow of heated aqueous fluids along fractures and grain boundaries (Meyer and Hemley, 1967; Rose and Burt, 1979; Lentz, 1994; Reed, 1997). Alteration may occur through dissolution, ion exchange, replacement, precipitation and (or) recrystallization processes. The most important factors in alteration include temperature, pressure, chemical composition of the fluid, water-rock ratio, and the chemical and physical nature of the wallrocks. Time, or the duration of rock-water interaction, is also important (Schwartz, 1950). Alteration minerals that form a chemically stable group make up an assemblage, and the volume of rock affected by an assemblage is an alteration zone, halo, envelope, or selvage (Guilbert and Park, 1986). Alteration assemblages may be interpreted as ...

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