Žune Ba-F epitermalno ležište : mineraloške i geokemijske karakteristike : diplomski rad

The Žune Ba-F epithermal deposit is located in Ljubija ore field (NW Bosnia and Herzegovina) within the Upper Paleozoic dolostone. Dolostone is fresh to partly limonitized and has massive, homogenous structure. Geochemical composition exhibits high CaO (30.24–32.38 mass. %), MgO (16.47–17.35 mass. %) and LOI (44.60–45.58 mass. %) while having low SiO2 (1.33–3.65 mass. %), Al2O3 (0.27–0.74 mass. %) and BaO (0.02–0.83 mass. %) contents. Contact zone between dolostone and ore mineralization is characterized with primary accessory minerals tremolite magnesiochloritoid, topaz (pyknite), epidote, pyrite and rutile which point to forming temperatures generally above 300°C and pressure up to 2 kbars. The ore body of Žune deposit is predominantly vein-type of mineralization, whereas breccia-type is less common with barite and fluorite as main ore minerals. These two main ore minerals are deposited first in veinlets, alongside quartz but relationship with sulphides could indicate their near-simultaneous crystallization. Mineralized samples are characterized by high CaO (6.30–66.03 mass. %) and BaO (3.92–50.23 mass. %) contents, and increased concentrations of SO3 (2.05–26.22 mass. %) and fluor (2.01–22.88 mass. %). The rare earth element (REE) spectra (5.73 to 166.01 ppm) are dominated by enrichment of light lanthanides. Elevated Sr (> 1 mass. %), Sm (up to 118 ppm) and Eu (up to 44 ppm) contents follow trend of higher amount of barite in samples while fluorite-rich samples are characterized by enrichment of Y (up to 41 ppm) and HREE, and depletion of LREE. XRD analysis conducted on four ore samples confirmed presence of dolomite, barite and fluorite, respectively. From primary accessory minerals chloritoid was detected. Based on variable REE concentrations, negative Ce and Yb anomaly, Žune deposit geochemically belongs to category of fluorite deposits associated with carbonate sedimentary rocks.Žune Ba-F epitermalno ležište dio je Ljubijskog rudnosnog bazena (SZ Bosna i Hercegovina), smješteno u gornjo paleozojskim dolomitima kao stijenama domaćinima. Dolomit je uglavnom svjež do mjestimično limonitiziran, te ima masivnu, homogenu teksturu. Geokemijska analiza otkriva prisutnost viših koncentracija CaO (30.24–32.38 mass. %), MgO (16.47–17.35 mas. %) i LOI (44.6–45.58 mas. %), ali isto tako i niske koncentracije SiO2 (1.33–3.65 mas. %), Al2O3 (0.27–0.74 mas. %) i BaO (0.02–0.83 mas. %). Kontaktna zona između dolomita i mineralizacije u ležištu karakterizirana je primarnim akcesornim mineralima tremolitom, magneziokloritoidom, topazom (piknitom), epidotom, piritom i rutilom koji upućuju na temperature iznad 300°C i tlakove oko 2 kbar-a, kao uvjete formiranja. Rudno tijelo, s baritom i fluoritom kao glavnim rudnim mineralima, dominantno je žilnog, te u manjoj mjeri brečastog tipa. Barit i fluorit kristalizirali su prvi, uz kvarc u žilama, ali odnos sa sulfidima mogao bi upućivati na njihovu gotovo istovremenu kristalizaciju. Uzorci u kojima se javlja mineralizacija karakterizirani su visokim koncentracijama CaO (6.30–66.03 mas. %) i BaO (3.92–50.23 mas. %) te relativno nižim koncentracijama SO3 (2.05–26.22 mas. %) i fluora (2.01–22.88 mass. %). Od elemenata rijetkih zemalja (ERZ) dominiraju lake rijetke zemlje. Povišena koncentracija Sr (> 1 mas. %), Sm (do 118 ppm) i Eu (do 44 ppm) prati povećan sadržaj barita u uzorcima, dok su fluoritom bogati uzroci karakterizirani povišenim koncentracijama Y (do 41 ppm), elemenata teških rijetkih zemalja, te osiromašeni na elementima lakih rijetkih zemalja. XRD analiza provedena na četiri uzorka potvrdila je prisutnost dolomita, barita i fluorita, dok je od primarnih akcesornih minerala kloritoid detektiran. Na temelju varijabilnog sadržaja ERZ-a i negativne Ce i Yb anomalije, Žune kao ležište geokemijski pripada svjetskim ležištima fluorita vezanim za karbonatne sedimentne stijene