Item talk:Q137973
Environmental geochemical study of Red Mountain--an undisturbed volcanogenic massive sulfide deposit in the Bonnifield District, Alaska range, east-central Alaska: Chapter I in Recent U.S. Geological Survey studies in the Tintina Gold Province, Alaska, United States, and Yukon, Canada--results of a 5-year project
The Red Mountain volcanogenic massive sulfide (VMS) deposit exhibits well-constrained examples of acid-generating, metal-leaching, metal-precipitation, and self-mitigation (via co-precipitation, dilution, and neutralization) processes that occur in an undisturbed natural setting, a rare occurrence in North America. The unmined pyrite-rich deposit displays a remarkable environmental footprint of natural acid generation, high metal concentrations, and exceedingly high rare-earth-element (REE) concentrations in surface waters. Dissolution of pyrite and associated secondary reactions under near-surface, oxidizing conditions are the primary causes for the acid generation and metal leaching. The deposit is hosted in Devonian to Mississippian felsic metavolcanic rocks of the Mystic Creek Member of the Totatlanika Schist. Water samples with the lowest pH values, highest specific conductances, and highest major- and trace-element concentrations are from springs and streams within the quartz-sericite-pyrite alteration zone. Aluminum, As, Cd, Co, Cu, Fe, Mn, Ni, Pb, Y, and particularly Zn and the REEs are all found in high concentrations, ranging across four orders of magnitude. Waters collected upstream from the alteration zone have near-neutral pH values, lower specific conductances, lower metal concentrations, and measurable alkalinities. Water samples collected downstream of the alteration zone have pH values and metal concentrations intermediate between these two extremes. Stream sediments are anomalous in Zn, Pb, S, Fe, Cu, As, Co, Sb, and Cd relative to local and regional background abundances. Red Mountain Creek and its tributaries do not support, and probably never have supported, significant megascopic faunal aquatic life.
