geochemistry of mercury mineralization and its environmental influence in the tavreh area, west of khoy, nw iran

mercury mineralization has occurred in relation with a listwaenitic type hydrothermal alteration system in tavreh area located northwest of khoy. mercury-bearing alteration zone which has an area about 0.4 km2 is situated in one of aland river upstreams. the only mercury compound found in this district is mercury sulfide (cinnabar) deposited as vein and veinlet forms. geochemical investigations indicate that mercury distribution has variable values which vary between 0.36-10500 ppm. its average in alteration zone is 300 ppm, although its average reaches to 0.35 percent in the mineralized veins. considering the clarke amount of mercury, it has increased more than 3750 times in overall alteration zone and more than 46000 times in mineralized veins. based on the stream sediment heavy mineral geochemistry, distribution of cinnabar under physical weathering and transportation processes has occurred at least 7 km far away from the altered zone in downstream sediments. mercury concentrations in samples taken from surface and underground waters are less than 0.1µg/l. in comparison with mercury concentrations, data obtained from other world’s ore fields and considering the maximum permissible contaminant level in drinking waters, it can be concluded that the waters of this region have not been contaminated in mercury. therefore, despite the extent of anomalous zone in tavreh region, this zone cannot play a role as the contaminant source of environment. it is seemed that due to presence of mercury as stable mercury sulfide compound, the possibility of its leakage could not been obtained due to decomposition of this mineral.