Sphalerite Oxidation in Seawater with Covellite: Implications for Seafloor Massive Sulfide Deposits and Mine Waste

Metal
sulfide minerals exist in several marine environments and
are in thermodynamic disequilibrium with oxygenated seawater from
the time of their formation. Oxidation is both ubiquitous and heterogeneous,
as observational and experimental evidence demonstrates that sulfide
minerals may oxidize completely on decadal timescales (hydrothermal
plumes) or incompletely in billions of years (mineral deposits); however,
the processes, rates, and interactions among minerals as oxidative
dissolution occurs are not well understood. Added impetus to understanding
these processes exists due to the potential for mining of seafloor
massive sulfide deposits and potential environmental impacts of that
activity. Here, we present a laboratory-based experimental study on
the galvanic oxidation of sphalerite and synthesized zinc sulfide
and coupled to covellite. We find that, in contrast to single-mineral
reactions, coupled mineral reactions are at least 2 orders of magnitude
more rapid, light independent, and have a lower apparent activation
energy for oxidation. These results begin to provide insight into
observed differences between laboratory and environmentally observed
oxidation rates and are a step in the direction of more accurately
predicting environmental rates as well as any changes to those rates
from anthropogenic disturbances.