The Mississippi Valley-type (MVT) Pb-Zn ore district at Mežica is hosted by Middle to Upper Triassic platform carbonate rocks in the Northern Karavanke/Drau Range geotectonic units of the Eastern Alps, northeastern Slovenia. The mineralization at Mežica covers an area of 64 km 2 with more than 350 orebodies and numerous galena and sphalerite occurrences, which formed epigenetically, both conformable and discordant to bedding. While knowledge on the style of mineralization has grown considerably, the origin of discordant mineralization is still debated. Sulfur stable isotope analyses of 149 sulfide samples from the different types of orebodies provide new insights on the genesis of these mineralizations and their relationship. Over the whole mining district, sphalerite and galena have δ 34 S values in the range of-24.7 to-1.5‰ VCDT (-13.5±5.0‰) and-24.7 to-1.4‰ (-10.7±5.9‰), respectively. These values are in the range of the main MVT deposits of the Drau Range. All sulfide δ 34 S values are negative within a broad range, with δ 34 S pyrite <δ 34 S sphalerite <δ 34 S galena for both conformable and discordant orebodies, indicating isotopically heterogeneous H 2 S in the ore-forming fluids and precipitation of the sulfides at thermodynamic disequilibrium. This clearly supports that the main sulfide sulfur originates from bacterially mediated reduction (BSR) of Middle to Upper Triassic seawater sulfate or evaporite sulfate. Thermochemical sulfate reduction (TSR) by organic compounds contributed a minor amount of 34 S-enriched H 2 S to the ore fluid. The variations of δ 34 S values of galena and coarse-grained sphalerite at orefield scale are generally larger than the differences observed in single hand specimens. The progressively more negative δ 34 S values with time along the different sphalerite generations are consistent with mixing of different H 2 S sources, with a decreasing contribution of H 2 S from regional TSR, and an increase from a local H 2 S reservoir produced by BSR (i.e., sedimentary biogenic pyrite, organo-sulfur compounds). Galena in discordant ore (-11.9 to-1.7‰;-7.0±2.7‰, n=12) tends to be depleted in 34 S compared with conformable ore (-24.7 to-2.8‰,-11.7± 6.2‰, n=39). A similar trend is observed from finecrystalline sphalerite I to coarse open-space filling sphalerite II. Some variation of the sulfide δ 34 S values is attributed to the inherent variability of bacterial sulfate reduction, including metabolic recycling in a locally partially closed system and contribution of H 2 S from hydrolysis of biogenic pyrite and thermal cracking of organo-sulfur compounds. The results suggest that the conformable orebodies originated by mixing of hydrothermal saline metal-rich fluid with H 2 Srich pore waters during late burial diagenesis, while the Editorial handling: B. Lehmann Electronic supplementary material The online version of this article

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The methods used in geology to determine colour and colour coverage are expensive, time consuming, and/ or subjective. Estimates of colour coverage can only be approximate since they are based on rough comparisonbased measuring etalons and subjective estimation, which is dependent upon the skill and experience of the person performing the estimation. We present a method which accelerates, simplifies, and objectifies these tasks using a computer application. It automatically calibrates the colours of a digital photo, and enables the user to read colour values and coverage, even after returning from field work. Colour identification is based on the Munsell colour system. For the purposes of colour calibration we use the X-Rite ColorChecker Passport colour chart placed onto the photographed scene. Our computer application detects the ColorChecker colour chart, and finds a colour space transformation to calibrate the colour in the photo. The user can then use the application to read colours within selected points or regions of the photo.The results of the computerised colour calibration were compared to the reference values of the ColorChecker chart. The values slightly deviate from the exact values, but the deviation is around the limit of human capability for visual comparison. We have devised an experiment, which compares the precision of the computerised colour analysis and manual colour analysis performed on a variety of rock samples with the help of geology students using Munsell Rock-color Chart. The analysis showed that the precision of manual comparative identification on multicoloured samples is somewhat problematic, since the choice of representative colours and observation points for a certain part of a sample are subjective. The computer based method has the edge in verifiability and repeatability of the analysis since the application the original photo to be saved with colour calibration, and tagging of colouranalysed points and regions. IzvlečekMetode, ki se v geologiji uporabljajo za določanje barv in barvne pokritosti, so drage, zamudne in/ali subjektivne. Ocena barvne zastopanosti ali pokritosti je lahko le zelo približna, saj temelji na grobih primerjalnih etalonih in subjektivni oceni, ki je odvisna od izurjenosti in izkušenj ocenjevalca. Predstavljamo metodo, ki te naloge pospeši, poenostavi in objektivizira s pomočjo računalniške aplikacije, ki na zajeti digitalni fotografiji z uporabo računalniškega vida samodejno umeri barve in uporabniku tudi kasneje, po terenskem delu, omogoča odčitavanje barvnih odtenkov. Barvna identifikacija temelji na barvnem sistemu Munsell. Za barvno umerjanje uporabljamo umerjevalno barvno lestvico X-Rite ColorChecker Passport, ki jo uporabnik postavi v območje zajema fotografije kamnine. Računalniška aplikacija, ki smo jo razvili, na zajeti fotografiji zazna barvno lestvico ColorChecker in poišče transformacijo barvnega prostora, s katero fotografijo barvno umerimo. Uporabnik lahko nato s pomočjo aplikacije po barvnem sistemu Munsell odčita barvo v izbranih ...

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