NON POINT SOURCE MERCURY RELEASES TO THE AIR FROM TWO NEVADA GOLD MINES

Mercury is an element that is naturally associated with economic concentrations of precious metals. As a result gold mines have been found to have significant point source releases associated with their processing facilities. Some mines collect Hg in the gold recovery process and sell it as a by-product. Because Hg is associated with rock materials that are disturbed during the mining process it has been suggested that in addition to the point source releases fugitive emissions could be significant. Diffuse non-point sources releases could occur from a variety of materials including waste rock, low grade ore that is heap leached, ore stockpiles, and tailings resulting from the higher grade ore processing. To address this concern, non-point source emissions of Hg were measured from two gold mines in Nevada (Twin Creeks Mine-Newmont Corporation and Cortez/Pipeline-Barrick Corporation). Hg flux was measured in the field and laboratory from representative materials on a seasonal time step using dynamic flux chambers. To contextualize the magnitude of the mine emissions with respect to undisturbed areas, concomitant fluxes were measured from areas near the mines that were of similar geologic composition. Algorithms were generated that related the Hg flux to environmental parameters allowing for the release of Hg to be scaled over space and time. Factors found to be best correlated with flux include substrate Hg concentration, soil moisture and incident radiation.