How can chemical reactions between hydrothermal fluids and rocks create mineral deposits?

Chemical reactions between hydrothermal fluids and surrounding rocks are a primary mechanism for the formation of hydrothermal mineral deposits. These deposits occur when hot, mineral-laden brines interact with reactive host rocks, triggering the precipitation of dissolved metals.12

This process often involves metasomatism, where chemical components diffuse across boundaries between dissimilar rocks. For example, when a mineral-rich solution encounters a reactive host, such as limestone, the resulting chemical exchange can force the minerals out of the solution and into the rock structure. A specific instance of this is the formation of scheelite ($CaW{O}_4$), which occurs when tungstate in a hydrothermal solution reacts with calcium carbonate ($CaC{O}_3$) in limestone:13

$$CaC{O}_3+W{O}_3\text{ (solution)}\to CaW{O}_4+C{O}_2\text{ (gas)}$$

By altering the chemical environment of the fluid, these reactions effectively strip the solution of its dissolved load, concentrating metallic minerals within specific zones of the crust.13