002.4.Idrija

Idrija Mercury Heritage Management Centre, Bazoviška 2, SI-5280 Idrija

Public

Republic of Slovenia

Geological profile 5, part 4644 Idrija ore deposit

Ore deposit

In the decline I/20–I/19 of Kropáč MF, on the left and right side, a normal, gradual transition between Skonca beds and tuffites is visible. As typical for the entire upper pit, the layers lie in the inverted position (inverse), therefore the black Skonca beds are on the top and smaller tuffites on the bottom. In the highest part of cross section (inverse position) we can observe the strong bituminous fine-grained sandstone Skonca beds. The sandstone is layered, with rare pyrite lenses in dimension 2 × 5 cm also lying in it. In the lower part of the profile, the sandstone passes (upwards) into mudstones and claystones. Skonca beds are richly mineralised with mercury drops and mould superficial layers of crystal of cinnabar.

The tunnel intersection is approx. 1 × 1 m.

Skonca beds, tuffites

Approximately 238 million years ago, in the Mid-Triassic tectonic stage, in the Ladinian.

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Skonca beds are undoubtedly the most important rocks of the Idrija ore deposit. They were extremely richly mineralised. From a total of 107,829 tons of obtained mercury, around 30,000 to 40,000 Hg was obtained from Skonca beds, which is 30 to 40% of all mercury in Idrija. Skonca beds consist of different rocks. The prevailing ones are claystones, mudstones and sandstones. Due to the fact that the rocks were formed in the wetlands surroundings, they are rich with organic residue and therefore almost black. Simultaneously with the mentioned stones, the very rich cinnabar sedimentary ore (syngenetic mineralisation) was also deposited, and was later additionally saturated with crystal of cinnabar and native mercury (epigenetic mineralisation). Its disposal was sharply interrupted with large layers of volcanic ash.

The Idrija ore deposit and Anthony's Main Road gained the status of a geological natural value of national importance in 2004. In the Anthony's Main Road area, eight geological profiles of the utmost importance are registered, which represent an important part of the European naturalistic heritage. In these geological profiles, the development elements, which were involved in the creation and formation of mercury ore deposit, are preserved and at the same time, also the numerous tectonic events, which transformed the original Mid-Triassic mine structure into the current condition. Geological profiles are on display for visitors of Anthony's Main Road, geology students and professional groups. The rich Skonca beds had an especially important position in mining history of Idrija. This is the only location in the open part of the pits, where the mineralised Skonca beds are visible in their primary position.

Idrija ore deposit, decline I/20–I/19 Kropáč MF

Anthony’s Main Road (top pit building, south mine unit, decline I/20–I/19 of Kropáč MF), Kosovelova 3, 5280 Idrija

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Performing regular maintenance services by the programme, including status control and preservation, security and presentation of the heritage.

- Official Gazette of the Republic of Slovenia no. 111/2004 of 14/10/2004 4623. Rules on the designation and protection of natural values, p. 13173–13175; https://www.uradni-list.si/glasilo-uradni-list-rs/vsebina/51517. See: Annex 1: Seznam naravnih vrednot in njihova razvrstitev na vrednote državnega in lokalnega pomena;
- Čar, Jože. Opis najpomembnejših geoloških profilov v odprtem delu idrijske jame. Tipkopis, 9 strani, 4 priloge, 35 fotografij s komentarjem in 6 jamskih kart. CUDHg, Idrija, 2017.

Mestni muzej Idrija

Miha Kosmač

27. 2. 2018

Never