Geochemistry and Isotopic Composition of H2S Rich Water in Flooded
Underground Mine Workings, Butte Montana
Principal Investigator: Dr. Chris Gammons
cgammons@mtech.edu
This field study involved collecting a suite of ground water samples
from the West Camp Extraction Well (WCEW) for chemical and isotopic
analysis in an effort to better understand the processes which control
the geochemistry of the flooded underground mine complex in Butte,
Montana. This study was one of the first comprehensive geochemical
and stable isotope investigations of a hydrogen sulfide rich mine
water. Water emanating from the West Camp mine workings is elevated
in hydrogen sulfide, has a circum-neutral pH, has elevated arsenic
concentrations, but otherwise low metal concentrations. Chemistry
and isotopic composition of the WCEW water remains fairly constant
throughout the year. Isotopic analysis of coexisting aqueous sulfide
and sulfate validates that the H2S is produced by sulfate-reducing
bacteria (SRB). It is suspected that the SRB are present as biofilms
attached to the flooded mine walls. Geochemical modeling suggests
that the West Camp waters are close to equilibrium saturation with
amorphous iron sulfide, amorphous zinc sulfide, siderite, rhodochrosite,
barite, and calcite, but are under saturated with orpiment.
MWTP Activity IV, Project 32
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