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,

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.