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Title: Prostorski razvoj sivega dela Grödenske formacije na Žirovskem vrhu Authors: ID Čadež, Franc (Author) ID Gantar, Ivan (Author) Files: PDF - Presentation file, download (2,73 MB) MD5: 2E1B8F349A7F32EE7901B4C9CE4EF64C   Language: Slovenian Typology: 1.01 - Original Scientific Article Organization: GeoZS - Geological Survey of Slovenia Abstract: Raziskave in odkopavanje se je na Rudniku urana Žirovski vrh opravljalo med leti 1960 in 1990. Ivan Mlakar (2000) je razdelil celotno Grödensko formacijo na 6 členov in poimenoval najstarejši Brebovniški člen v katerem je poznano orudenje z uranom. Že pred tem je Tomaž Budkovič (1980) ta sivi del Grödenske formacije razčlenil na 10 horizontov na osnovi barve, zrnavosti in prodniških združb in sicer po podatkih kartiranja podkopa P-10 in njegovega nadaljevanja. V tem članku smo prikazali razvoj Brebovniškega člena na celotnem prostoru rudišča, tako jame kot tudi njenega nadaljevanja proti JV in SZ. Prvotno razdelitev Budkoviča smo spremenili tako, da smo zgornji del 3. horizonta z intraformacijskimi konglomerati in nekdanji 4. peščeni horizont združili v enoten 5. konglomeratni horizont. Dragomir Skaberne je namreč v svojem doktoratu (1995) Brebovniški člen razdelil na 2 megaritma pri čemer se vsak pričenja s konglomerati, zaključi pa z drobnozrnatimi sedimentnimi kamninami. Zato je ustrezneje, da se 3. horizont zaključi z drobnozrnatimi sedimenti in je hkrati zaključek 1. megaritma, intraformacijski konglomerati, ki so bili prej še zgornji del 3. horizonta pa so po novem že del enotnega konglomeratnega horizonta, ki podrejeno vsebujejo še peščenjake. Debelina celotnega Brebovniškega člena je največja v osrednjem delu odprte jame, kjer znaša 410 m in se proti robovom bazena zmanjšuje. Na območju Golega vrha proti JV, do kamor sežejo pojavi orudenja, se njegova debelina zmanjša na 50 m. Debelina posameznih horizontov pa se, razen 2. in 5. horizonta, zmanjša z nekaj 10 metrov le na nekaj metrov oziroma se posamezni horizonti celo izklinjajo. V SZ smeri od nekdanjih jamskih del ni več ekonomsko pomembnih orudenj z uranom. V to smer se izklinjajo pisani konglomerati, spreminja se tudi značaj peščenih horizontov, ki so bili v jami glavni nosilci orudenja. Njihova barva se spreminja iz sive in temnosive v zelenosivo, v njih je manj drobcev antracitizirane organske snovi, ki je pogojevala nastanek redukcijskih sredin, kjer se je lahko izločal uran. V pisanih konglomeratih je pomembna prisotnost prodnikov kislih magmatskih predornin, ki imajo povišan clark urana glede na druge skupine kamnin. Z njihovo erozijo so se površinske vode ter podtalnica obogatile z uranom že na površju, dodatno pa še pri precejanju skozi plasti pisanega konglomerata. V oksidacijskih pogojih se je uran raztapljal, v redukcijskih pa izločal v vezivu peščenih klastitov. Od celotne dolžine pojavljanja plasti sivega Brebovniškega člena, ki meri po geološki karti 18 km, znaša območje s pogojno ekonomskim orudenjem le dobrih 5,5 km in približno na ta del je omejeno tudi pojavljanje pisanih konglomeratov. Keywords: sedimentacijski razvoj, orudenje, grödenske klastične kamnine, Žirovski vrh Publication status: Published Publication version: Version of Record Publication date: 10.12.2025 Publisher: Geološki zavod Slovenije Year of publishing: 2025 Number of pages: str. 251-267 Numbering: vol. 68, no. 2 PID: 20.500.12556/DiRROS-24868  UDC: 551.1/.4 ISSN on article: 0016-7789 DOI: 10.5474/geologija.2025.011  COBISS.SI-ID: 262058499  Publication date in DiRROS: 24.12.2025 Views: 21 Downloads: 6 Metadata:    Cite this work Plain text BibTeX EndNote XML EndNote/Refer RIS ABNT ACM Ref AMA APA Chicago 17th Author-Date Harvard IEEE ISO 690 MLA Vancouver : Copy citation

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Record is a part of a journal

Title:	Geologija
Shortened title:	Geologija
Publisher:	Geološki zavod Slovenije
ISSN:	0016-7789
COBISS.SI-ID:	5636866

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License:	CC BY 4.0, Creative Commons Attribution 4.0 International
Link:	http://creativecommons.org/licenses/by/4.0/
Description:	This is the standard Creative Commons license that gives others maximum freedom to do what they want with the work as long as they credit the author.

Secondary language

Language:	English
Title:	Spatial development of the grey part of the Val Gardena Formation on Žirovski vrh
Abstract:	The Uranium Mine Žirovski vrh was actively being researched and excavations took place between 1960 and 1990. Ivan Mlakar (2000) divided the entire Val Gardena Formation into 6 members and named the oldest one the Brebovnica member. This is the only member with uranium ore mineralization. Previously, Tomaž Budkovič (1980) subdivided the gray part of the Val Gardena formation into ten horizons based on colour, grain size, and pebble associations. He did that by mapping of undercut P-10 and its continuation. In this article, we have shown the development of the Brebovnica member in the entire area of the ore deposit, both the mining area and its continuations to the SE and NW. We have modified Budkovič's original division by combining the upper part of the 3rd horizon with intraformational conglomerates and the former 4th sandy horizon into a single 5th conglomerate horizon. In his doctoral thesis (1995), Dragomir Skaberne divided the Brebovnica member into 2 megarhythms, each of which begins with conglomerates and ends with fine-grained sediments. Therefore, it is more appropriate that the 3rd horizon ends with fine-grained sediments and is at the same time the end of the 1st megarhythm, while the intraformational conglomerates, which were previously the upper part of the 3rd horizon, are now part of a single conglomerate horizon, which sometimes also contains sandstones. The total thickness of the Brebovnica member is greatest in the central part of the mine area, where it reaches 410 meters and decreases towards the edges of the basin. Towards Goli vrh in the southeast, where the last uranium mineralization occurs, its thickness decreases to 50 meters. The thickness of individual horizons, except the second and fifth, decreases from tens of meters to only a few meters, and some horizons even wedge out. To the northwest from the former mining area there are no economically significant uranium ores. In that direction, the colorful conglomerates wedge out, and the nature of sandy horizons, which were the main carriers of uranium mineralization in the mining area, changes. Their colour changes from gray and dark gray to greenish gray, with fewer fragments of anthracitized organic matter that created reducing environments necessary for uranium precipitation. The colourful conglomerates contain important pebbles of acidic magmatic rocks with higher uranium contents compared to other rock groups. Their erosion enriched surface and groundwater with uranium already at the surface and additionally during percolation through the layers of colorful conglomerate. Uranium dissolved under oxidizing conditions, while under reducing conditions it precipitated in the binder of sandy grains. Of the entire 18 km length of the gray Brebovnica member as shown on the geological map, only 5.5 km show conditionally economic uranium mineralization, which approximately corresponds to the area where colorful conglomerates occur.
Keywords:	sedimentary horizons, mineralization, Val Gardena clastic rocks, Žirovski vrh

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