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View of Mining Geological Exploration of the Uranium Ore Deposit Žirovski Vrh

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522 E. Lukacs UDK 553.495:622.013.34

Geološko rudarske raziskave uranovega rudišča Žirovski vrh Egon Lukacs

Geološki zavod, Ljubljana, Dimičeva 16

Naloga vsebuje določitev rudnih rezerv urana v ležišču Žirovski vrh ter proučevanje geološke zgradbe nahajališča in njegovega nastanka. Ve- lik del rudnih rezerv na Žirovskem vrhu je kategorije C2. Ker rudne rezerve te kategorije niso zadostna osnova za odpiranje rudnika, je treba prekategorizirati del teh rezerv v kategorije A + B Ci.

Pred dobrimi desetimi leti je bilo v srednjepermskih grodenskih plasteh najdeno nahajališče urana Žirovski vrh. Na območju Slovenije pa so bili regi- strirani še številni drugi uranski pojavi.

Grodenske plasti sestoje iz peščenjaka, meljevca, skrilavca in konglomerata.

Kamenine so povečini rdeče, posamezni horizonti, zlasti v spodnjem delu za- poredja, pa so zelenkasto sivi. Uran je vezan izključno samo na te zelenkasto- sive plasti. Prvi pojavi urana so bili najdeni na izdankih s sekundarnimi mine- rali. Neoksidirano, primarno- rudo so- odkrili kasneje z vrtinami in rudarskimi deli.

V spodnjem, zelenkasto- sivem delu grodenskih plasti na Žirovskem vrhu razlikujemo tri sedimentacijske- makrc-ritme, ki imajo obliko dvojne polegle gube, o-ziro-ma tako- imenovane strukture »S«. Rudni horizont, debel 30 do 60 m, leži približno v sredini tretjega ritma. V rudnem horizontu so trije do pet rudnih pasov, od katerih sta dva ekonomsko' pomembna in sta običajno- ločena z diskontinuiranimi vložki rdečega skrilavega peščenjaka. Tudi v krovnini in talnini rudnega pasu ležijo prekinjeni vložki rdečega peščenjaka. Ruda je torej v tesni zvezi s spremembo faciesa. Na podlagi novejših raziskav smo- prišli do sklepa, da je bil uran v ležišče prinesen že med sedimentacijo-, a je bil kasneje na novo razvrščen. Mineraloške raziskave pa kažejo-, da je uranova svetlica naj- važnejši mineral v ležišču.

Rudne rezerve so računane po- statističnih metodah, pri katerih so izhodišče podatki o debelini orudenih intervalov in poprečne vsebnosti urana v teh inter- valih. Zaradi velikega števila vrtin je tako narejen račun dovolj natančen in so rudne rezerve v določenem prostoru ocenjene z zadostno sigurnostjo-. Ni pa do-- volj natančno določeno prostorsko- razprostiranje posameznih rudnih teles.

Zato bodo pred pričetkom odkopavanja potrebna dodatna vrtanja in druge spremljajoče raziskave.

Raziskave smo- razširili tudi na okolico- rudišča, da bi ugotovili raztezanje rudnega pasu proti severozahodu in s tem možnost povečanja rudnih rezerv.

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Mining Geological Exploration of the Uranium Ore Deposit Žirovski Vrh 523 Mining Geological Exploration of the Uranium Ore Deposit

Žirovski Vrh Egon hukacs

Geološki zavod, Ljubljana, Dimičeva 16

The aims of the exploration were to determine the uranium resources of the Žirovski Vrh ore deposit, and to study the geological structure of the deposit as well as its origin. A large part of the Uranium Re- sources are of the Estimated Additional category (inferred, C2 according to Yugoslav classification). As resources of this category are no satis- factory basis for opening the mine, additional exploration had to be carried out that would allow their transfer into Reasonably Assured ca- tegory (measured and indicated, A -j- B + Ci). The exploration was also expanded outwards the limits of the known deposit, to determine the extension of the mineralized zone in north-western direction.

The uranium resources have been calculated by statistical methods that are based on data about the thickness of the ore bearing intervals and their average uranium ore content. The dense grid of exploratory bore holes guarantees a sufficiently accurate calculation, and therefore the ore reserves in the ex- plored area are determined in an adequately accurate degree. On the other hand, the extensions of the individual ore bodies are not exactly determined, and therefore, before starting mining operations, additional driling and (similar auxiliary exploration) will be necessary.

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