Hypogene advanced argillic alteration, typically quartz-alunite with halos of kaolinite ± dickite and roots of pyrophyllite ± diaspore, forms in the epithermal environment from condensates of magmatic vapor that contain SO2 and HCl, all of which exsolved from an underlying intrusive source. The most aggressive, nearly isochemical leaching of host rock by acidic condensate, commonly pH~1, leaves residual silica that recrystallizes to quartz close to the flow channel, forming the core of alteration. The alteration flares upward along feeder structures, and if a lithologic unit is intersected and condensate flows laterally, a subhorizontal blanket of alteration is formed, termed a lithocap; the residual quartz can host subsequently formed Au-Cu ore with high-sulfidation state sulfides. The leached rock lacks the wall-rock buffer, resulting in high-sulfidation state minerals (enargite, etc.) forming by a cooling magmatic fluid. Eventual interaction with less altered rock that has some buffer control causes these mineralizing fluids to evolve to subsequent intermediate sulfidation states, accompanying late-stage gold mineralization. The same trends are evident from active hydrothermal systems.