Hydrothermal alteration refers to the chemical alteration of minerals in rocks by hot, mineral-rich fluids, typically associated with volcanic activity or deep-seated geothermal systems. This process can lead to the formation of economically important ore deposits, such as gold, copper, and silver. Hydrothermal alteration is key in understanding mineralization processes and the evolution of hydrothermal systems. 

Reference: Guilbert, J. M., & Park, C. F. (1986). The Geology of Ore Deposits. Waveland Press.