Geokemične in mineralne značilnosti izbranih slovenskih boksitov : magistrsko delo

Mencinger, Lara (author), Zupančič, Nina (mentor), Teran, Klemen (comentor)

Raziskovani boksiti pripadajo kraškemu tipu boksita in spadajo v del Mediteranskega pasu. Nahajajo se v paleokraškem reliefu, razvitem v različnih karbonatnih kamninah. Namen magistrskega dela je mineraloška in geokemična karakterizacija izbranih boksitov s poudarkom na vsebnosti elementov redkih zemelj (REE) in določitev ali so boksiti in situ ali presedimentirani. Vzorčili smo triasne boksite iz Podlipe, jurske boksite iz Logatca, kredne boksite iz Hrušice in oligocenske boksite iz Kamniške Bistrice. Vzorce smo makroskopsko in mikroskopsko pregledali, analizirali z rentgensko praškovno difrakcijo (XRD), masno sprektrometrijo z induktivno sklopljeno plazmo (ICP-MS) in vrstičnim elektronskim mikroskopom z energijsko disperzijsko spektroskopijo (SEM/EDS) ter podatke statistično obdelali. Izdelani so bili vertikalni geokemični profili. Boksiti so oolitni, sestavljeni iz böhmita, gibbsita, diasporja, kaolinita, kremena, muskovita, anataza, hematita in pirita. Vzorci povprečno vsebujejo 38 % Al2O3, 24 % SiO2, 12 % Fe2O3, 1045 mg/kg LREE in 459 mg/kg HREE. S SEM analizo smo ugotovili, da je ena izmed nosilk REE skupina fosfatnih mineralov (monacit in ksenotim). Statistične analize povezave med REE in P2O5 niso potrdile. Domnevamo, da se REE v vzorcih pojavljajo večinoma razpršeno, vezane na različne minerale. Na podlagi mineralne sestave, normaliziranih vsebnosti REE na hondrite in Zr–Ga–Cr diagrama, smo poskusili določiti izvorno kamnino boksitnih vzorcev. Točnega izvornega materiala nismo uspeli določiti, vendar je najverjetneje izvorni material predstavljal material granitne do vmesne sestave. Geokemični profili nakazujejo na enakomerno razporeditev Al2O3, Fe2O3, SiO2, K2O in TiO2 v boksitih iz Hrušice, Logatca in Kamniške Bistrice, medtem ko se v boksitih iz Podlipe pojavljajo naključno porazdeljeni po globini. Vsebnost REE v profilih je enakomerna v boksitih iz Hrušice in Kamniške Bistrice, v boksitih iz Podlipe se pojavljajo razpršeno, medtem ko v boksitih iz Logatca opazimo nizko vsebnost REE v zgornjem delu profila in višje vsebnosti na dnu profila. Normalizirane vsebnosti REE so pokazale drugačen nastanek boksitov iz Logatca od preostalih preiskovanih boksitov.

• Language: Slovenian
• Keywords: boksit, geokemija, kritične mineralne surovine, REE, vertikalni geokemični profili
• Work type: Master's thesis/paper
• Typology: 2.09 - Master's Thesis
• Organization: NTF - Faculty of Natural Sciences and Engineering
• Place of publishing: Ljubljana
• Publisher: L. Mencinger
• Year: 2023
• Number of pages: XVI, 57 f., h
• PID: 20.500.12556/RUL-150743
• UDC: 55
• COBISS.SI-ID: 167929603
• Publication date in RUL: 22.09.2023

Secondary language

• Language: English
• Title: Geochemical and mineralogical properties of selected Slovenian bauxites : master's thesis

Abstract

All investigated bauxites belong to the karst type of bauxite and are part of the Mediterranean belt. Bauxites are found in the paleokarst relief developed in various carbonate rocks. We have collected samples of bauxites of different ages from different locations. The purpose of the master thesis is mineralogical and geochemical characterization of selected bauxites with emphasis on the content of rare earth elements (REE). We sampled Triassic bauxites from Podlipa, Jurassic bauxites from Logatac, Cretaceous bauxites from Hrušica and Oligocene bauxites from Kamniška Bistrica. Statistical analysis, XRD analysis, ICP-MS analysis, SEM/EDS analysis and macroscopic and microscopic examinations of the samples were performed on 39 samples. Vertical geochemical profiles were prepared. The bauxites are oolitic and consist of mineral assemblage of böhemite, gibbsite, diaspore, kaolinite, quartz, muscovite, anatase, hematite and pyrite. The samples contain an average of 38 % Al2O3, 24 % SiO2, 12 % Fe2O3, 1045 mg/kg LREE and 459 mg/kg HREE. With SEM analysis, we found that one of the REE carriers is represented by a group of phosphate minerals (monazite and xenotime), but with statistical analysis, we found that they are not the main carriers of REE. REEs are assumed to occur dispersed in the samples, bound to different minerals. Based on the mineralogical composition, the content of normalized REE normalized to chondrite, the Cr/Ni ratio and Zr–Ga–Cr ratio, we tried to determine the source rock of the bauxite samples. We were unable to determine the exact source material using the given methods. According to the results of most methods, this indicates a material of granitic to intermediate composition. The geochemical profiles show a uniform distribution of elements in the bauxites from Logatec, Hrušica and Kamniška Bistrica, while in bauxites from Podlipa they appear scattered throughout the profile. The content of REE in the profiles is uniform in the bauxites from Hrušica and Kamniška Bistrica, in the bauxites from Podlipa they appear scattered, while in the bauxites from Logatec we observe a lower content of REE in the upper part of the profile and higher concentrations in the lower part of the profile. The normalized REE contents show that the bauxites from Logatec formed differently from the other investigated bauxites.

• Keywords: critical raw materials, geochemistry, REE, vertical geochemical profiles