Naslov
The Ljubija siderite deposit, NW Bosnia: Fluid inclusions, stable isotopes, inorganic and organic geochemical constraints

Autori
Strmić, Sabina ; Spangenberg, Jorge E. ; Palinkaš, Ladislav A. ; Borojević, Sibila

Vrsta, podvrsta i kategorija rada
Sažeci sa skupova, sažetak, znanstveni

Izvornik
Swiss Geoscience Meeting 2003, Abstract Volume / Bousquet, R. ; Dresmann, H. ; Groger, H. - Basel : University of Basel, 2003, 106-106

Skup
Swiss Geoscience Meeting 2003

Mjesto i datum
Basel, Švicarska, 28.11.2003. - 29.11.2003

Vrsta sudjelovanja
Predavanje

Vrsta recenzije
Nije recenziran

Ključne riječi
siderite; fluid inclusions; stable isotope; organic matter

Sažetak
The siderite-barite-polysulfides mineralization at Ljubija (500 Mt of ore with 45 wt% Fe) in northwestern Bosnia (44°33'N, 16°18'E) is hosted by the Paleozoic organic-rich sediments at the border of the Adriatic-Dinaridic carbonate platform. This deposit is part of the Fe-Ba metallogenic province in Bosnia, Croatia and Hungary, which is related to Permian-Scythian intracontinental rifting during the opening of Tethys. The siderite ore occurs as replacement in dolostones and limestones, and as open space-filling (veins) with rare chalcopyrite and pyrite in slates. The replacement ore has occasionally a zebra texture, with rhytmic succesion of dark fine-grained and light sparry siderite, and galena, sphalerite and quartz as open space- filling. Large accumulations of limonite occur as secondary ore. The genesis of the deposit has been explained as syngenetic sedimentary-exhalative mineralization of Carboniferous age, or as epigenetic replacement of Permian or Middle Triassic age (see Palinkas 1998). An extensive geochemical investigation of the ore, host rocks, and associated organic matter aims to a better understanding of the genesis of Ljubija. A study of fluid inclusions in quartz points to a moderately hot (Th = 100 to 250°C) and low to highly saline (5 to 30 wt% NaCl equiv.) H2O-NaCl-CaCl2 fluids (Palinkas et al. 2003). The fluid inclusions leached from siderites and quartz plot along the "evaporation line" in the Cl/Br vs. Na/Br scatterplot (Palinkas et al. 2003). The C and O isotopic compositions of host carbonates range from -0.5 to +1.9&#8240; V-PDB and +20.0 to +27.3&#8240; V-SMOW, respectively, and for siderites from -2.2 to +0.3&#8240; and +20.7 to +22.8&#8240; . Overall, the carbonates have a marine isotopic signature. The isotopic fractionation of siderite (precipitation) and limestone (recrystallization) gives a mineralization temperature of about 295°C. The 34S values of barite samples (+9.2 &plusmn ; ; 0.2&#8240; V-CDT) fall within the range of latest Permian marine evaporites. The 34S values of the ore sulfides cover a relatively narrow range between -2.3 and 8.5 &#8240; , increasing in the order galena (-2.3 to +3.0 &#8240; ) < chalcopyrite (-0.8 to +2.3&#8240; ) < sphalerite (+0.4 to +4.4&#8240; ) < pyrite (+5.4 to +8.5&#8240; ), reflecting isotopic equilibrium and high-temperature formation. Isotopic fractionation temperature of sphalerite-galena pairs are generally around 240°C. Thermochemical reduction of evaporitic and contemporaneous seawater sulfates (TSR) was the main source of reduced sulfur. The Rock Eval analyses indicate highly mature organic matter. The results of molecular (GC-MSD) and isotopic (GC-C-IRMS) analyses of the hydrocarbons (HC) extracted from ore and host rock samples give further insights into the ore fluid composition and ore deposition. The GC of the saturated HC of all samples are dominated by few low molecular-weight homologous series, including n-alkanes from C12 to C19, maximizing at C13-C16, isoprenoids i-C15, i-C18, i-C19 and i-C20 (farnesane, norpristane, pristane = Pr, phytane = Ph), with i-Cx/n-Cx+2 > 1, and Pr/Ph > 1, alkylcyclohexanes and methyl-alkenes. The barren samples plot in the Pr/n-C17 vs. Ph/n-C18 field of hydrocarbons from algal kerogen deposited in carbonate sequences. The high Pr/C17 and Ph/C18 ratios, combined with the high concentration of short-chain n-alkanes, reflect chromatographic migration effects. The biomarker HC hopanes (m/z 191) and steranes (m/z 217) were not detected. In barren and mineralized samples the individual n-alkanes have uniform &#61540; 13C values (-29.2 to -27.5&#8240; ) across the C-number range, which indicates their common marine phytoplanktonic origin.

Izvorni jezik
Engleski

Znanstvena područja
Geologija

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