Influence of mercury ore roasting sites from 16th and 17th century on the mercury dispersion in surroundings of Idrija

In the first decade of mercury mining in Idrija the ore was roasted in piles. After that the ore was roasted for 150 years, until 1652, in earthen vessels at various sites in the woods around Idrija. Up to present 21 localities of ancient roasting sites were established. From the roasting areas Frbej‘ene trate, lying on a wide dolomitic terrace on the left side of the road from Idrija to ^ekovnik, 3 soil profiles are discussed. In all three profiles in the upper, organic matter rich soil horizon very high mercury contents (from 3 to 4,000 mg/kg) were found. In two profiles the contents rapidly decrease with depth, to about 10times lower values already at 0.5 m. Below that, the mercury contents decrease slowly, to reach at the 1.3 m depth a few mg/kg metal. In the third profile the upper humic layer is followed downward by an additional humic layer containing very abundant pottery fragments. In this layer the maximum mercury contents were determined, 7.474 mg/kg Hg. The underlying loamy soil contains between 1000 and 2000 mg/kg mercury. P{enk is one of the larger localities of roasting vessels fragments. It is located at La~na voda brook below Hlev{e, above its confluence with the Padar ravine. The most abundant pottery remains are found in the upper western margin of the area, just below the way to Hlevi{e. The considered geochemical profile P{enk contains at the top a 45 cm thick humic layer with 4,000 to 5,000 mg/kg mercury. Deeper the contents fall to around 100 mg/kg mercury. The calculations result in an estimated amount of 1.4 t mercury still present at the P{enk locality, and in about 40 t of mercury on all roasting sites described up to present. The determined mercury contents in soils at old roasting sites are very high, and they surpass all hitherto described localities at Idrija and in the surroundings.