Quantifying natural source mercury emissions from the Ivanhoe Mining District, north-central Nevada, USA

In order to assess the importance of mercury emissions from naturally enric hed sources relative to anthropogenic point sources, data must be collected that characterizes mercury emissions from representative areas and quantif ies the influence of various environmental parameters that control emission s. With this information, we will be able to scale up natural source emissi ons to regional areas. In this study in situ mercury emission measurements were used, along with data from laboratory studies and statistical analysis , to scale up mercury emissions for the naturally enriched Ivanhoe Mining D istrict, Nevada. Results from stepwise multi-variate regression analysis in dicated that lithology, soil mercury concentration, and distance from the n earest fault were the most important factors controlling mercury flux. Fiel d and lab experiments demonstrated that light and precipitation enhanced me rcury emissions from alluvium with background mercury concentrations. Diel mercury emissions followed a Gaussian distribution. The Gaussian distributi on was used to calculate an average daily emission for each lithologic unit , which were then used to calculate an average flux for the entire area of 17.1 ng Hg m(-2) h(-1). An annual emission of similar to8.7 x 10(4) g of me rcury to the atmosphere was calculated for the 586 km(2) area. The bulk of the Hg released into the atmosphere from the district (similar to 89%) is f rom naturally enriched non-point sources and similar to 11% is emitted from areas of anthropogenic disturbance where mercury was mined. Mercury emissi ons from this area exceed the natural emission factor applied to mercury ri ch belts of the world (1.5 ng m(-2) h(-1)) by an order of magnitude. (C) 20 01 Elsevier Science Ltd. All rights reserved.