Secondary mineralogy in the 1912 vent region at Novarupta illustrates an alteration history that evolved from high-temperature degassing of ejecta through surficial argillic alteration to near-neutral, wet-steam alteration as the post-eruptive volcanic system cooled. The localized distribution of surficial argillization appears to have been controlled mainly by fractures related to slumping and compaction in the near-surface fallback ejecta. The fractures guiding the surviving warm, near-neutral fumarolic fluids, however, must be connected with deeper vent structures that reach a subsurface heat source, perhaps the boiling zone of a hydrothermal system. Trace metals, including Mo, Pb, Cu, Cd, and Zn, concentrated by high-temperature, vapor-phase mobilization, have subsequently been partly removed by argillization processes; in contrast, Hg, Sb, Tl, Bi, and As remain high even though the fumaroles now emit only low-temperature, near-neutral wet steam.