002.5.Idrija

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

Public

Republic of Slovenia

Geological profile 6, part 4644 Idrija ore deposit

Ore deposit

In the decline I/20–I/19 of Kropáč MF, on the left and right side and on the ceiling, a normal, gradual transition between Skonca beds and pyroclastic rocks is nicely visible. Pyroclasts begin with a 3 to 5 cm thick layer of chert. This layer is followed by different grey, grey-blue, green-grey tuffites and gradually granular tuffites with cherts. In the profile, on the left side, a normal gradual granularity from richly mineralised clay–radiolarial grains (1 to 5 cm thick) is visible (sedimentary ore with gradual granularity). Grains saturated in different amounts of mercury, have typical reddish-grey or reddish-green colour. The tuffites quickly decay, therefore they are covered with yellowish kaolinite coatings.

The area of protected profile is 0.3 m × 1.5 m.

Skonca beds, tuffites

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

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In this geological profile we can observe typical sedimentary ore in tuffites. In different parts of ore deposit, the cinnabar mineralisation occurs around 2.5 m in pyroclasts over the contact with Skonca beds. Grey to greenish-grey layered rocks were formed from different materials, especially of volcanic ashes, which was erupted by volcanoes in the Mid-Triassic period (Ladinian). They are the youngest rocks, which construct the ore-bearing zone of the Idrija ore deposit. The ore consists of mineralised particles (claystone minerals and planktonic radiolarians), brought by ocean currents. Larger mineralised parts deposited first, and smaller later. This is how the ore got its typical sedimentary inner structure of gradual granularity.

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 utmost importance are registered, which represent an important part of the European natural and technical heritage. In the described geological profiles, the most important 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. Syngenetic layered sedimentary ores are unique by creation and have not yet been found anywhere else on earth. The described geological profile is the only location described in the open part of the pit, where sedimentary ores with gradual granularity is visible. Geological profiles are on display for visitors of Anthony's Main Road, geology students and professional groups.

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