Hydrothermal alteration is a complex dynamic process involving mineralogical, textural, and chemical changes, resulting from the interaction of hot aqueous fluids with the rocks through which they pass, under changing physico-chemical conditions. Alteration is a geological open system process that constitutes chemical reactions between the fluid and the constituent minerals in the rocks, involving heat and mass transfer. However, alteration is commonly observed with or without the ore body. This is because while formation of an ore deposit demands many pre-conditions to be simultaneously fulfilled, alteration is imminent, even in barren rocks since the hot aqueous fluid and the cold rocks are alien entities, in terms of temperature and chemical composition. Thus, the job of ore geologists is to link the nature of alteration with specific types of hydrothermal ore deposits. Such linking is achieved by quantifying alteration with the help of various approaches such as: (i) mineral-chemical (alteration indices), and (ii) chemical mass balance calculations (Mathieu, 2018). In addition, hydrothermal alteration concerns with conversion of the original mineral assemblage to a new set of assemblage, thermodynamically stable at the imposed hydrothermal conditions of pressure, temperature, and fluid composition. Accordingly, the thermodynamic method for quantification of alteration involves construction of various phase diagrams involving temperature, activities/fugacities of dissolved gases/fluid species, and fluid pH (Henley et al., 1984; Reed, 1997; Wood, 1998).