MERCURY FATE AND TRANSPORT IN HUNZA AND GILGIT RIVERS, NORTHERN AREAS, PAKISTAN – A NUMERICAL MODELING APPROACH
Using mercury in pan amalgamation for the extraction of gold from stream deposits along Indus and Gilgit Rivers in Pakistan is being practiced for many decades. Pan amalgamation in the small-scale gold panning and extraction (GPE) activities are considered to be releasing considerable amount of mercury to the environment due to inappropriate smelting practices.
1372 stream sediments along Indus, Gilgit and Hunza Rivers were analyzed as part of Gold Exploration and Mineral Analysis Project conducted in 1999. Results showed that riverbank sediments upstream of Hunza and Gilgit Rivers are highly contaminated with mercury. From a data range of 4 to 2200 ppb, a total of 24 anomalous sites (having a concentration of more than 100 ppb) have been identified. Furthermore, no strong correlation between gold and mercury concentrations suggests that GPE is being employed in the northern parts -mostly in winter- where stream flow is lessened due to glaciations. As a result, panning becomes favorable.
An adaptive sampling of surface waters from Hunza and Gilgit Rivers was performed in June 2011. A total of 37 samples were collected. Sampling was done as per EPA Method 1631, Revision E: Mercury in Water by Oxidation, Purge and Trap, and Cold Vapor Atomic Fluorescence Spectrometry. Samples are being analyzed in terms of dissolved and suspended mercury content in the water column. During the field trip, many GPE sites were observed. Panning, amalgamation and roasting processes are being done at workers huts where large amount of mercury is released to environment particularly due to no mercury recycling in the smelting process. The goal of this research study is to understand the source, fate and transport of mercury by creating a hydrologic model and by using this model, develop scenarios to decrease mercury concentrations to allowable limits.