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Ljubija

Bosnia Herzegovina

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The Ljubija siderite deposits are located 180 km NW of Sarajevo, in north-western Bosnia-Herzegovina, and 100 km SSE of Zagreb (#Location: 44° 33'N, 16° 18'E).

The history of mining in this district dates back to the sixth century BC, although industrial scale production only commenced in 1916. In addition to iron, zinc, lead, barite and fluorite have also been exploited. The Ljubija ore field includes four open pit mines (Adamuša, Tomašica, Omarska and Vidrenjak) distributed over an area of ~200 km2. The iron ore occurs as stratabound siderite and ankerite replacement-type bodies in limestones and as siderite-sulphide veins within shales. In the eastern part of the Ljubija district economically significant galena, tetrahedrite, chalcopyrite and sphalerite were historicaly exploited, while barite and fluorite veins that crosscut dolostones at the Vidrenjak mine (Palinkaš 1988).

The deposits are hosted exclusively within a Carboniferous sedimentary complex of the Inner Dinarides, located within the Palaeozoic Sana-Una River nappe, that has been thrust to the SW over the margin of the Mesozoic Adriatic-Dinaric carbonate platform to the west. The Sana-Una River terrain comprises Devonian to Quaternary sedimentary rocks (Jurić 1971).

The Dinarides were developed during the Alpine evolution of the Dinaridic part of the Neotethys. Despite their complex fold, thrust and imbricate structure, the Dinarides of the Balkan Peninsula are characterised by a regular zonal pattern of Mesozoic-Palaeogene tectonostratigraphic units. From SW to NE, the following NW-SE trending tectonostratigraphic units are recognised: i). the Adriatic-Dinaridic carbonate platform, a 100 to 150 km wide belt along the NE Adriatic coast of the Balkan Peninsula; ii). carbonate-clastic sedimentary rocks with local flysch signature, corresponding to the passive continental margin of the Dinaridic Tethys ocean, comprising the bulk of the Sana-Una River nappe; iii). ophiolites and genetically related sedimentary formations from the Tethyan open-ocean realm, obductyed to the east during the collision with the Eurasian plate; and iv). sedimentary, igneous and metamorphic units of the Eurasian active continental margin (Pamić 1993).

The Ljubija deposits were emplaced within the Javorik flysch formation, the Carboniferous member of the Sana-Una River terrain, which is well exposed within the Adamuša and the Tomašica open pit mines (Grubić et al., 2000; Grubić and Cvijić, 2003). According to Grubić and Protić (2003) and Garašić and Ivan Jurković (2012) the Javorik flysch formation is composed of six members:
The Lower Flysch, the oldest member, is characterised by dark green argillaceous schists, alternating with medium-grained sandstone, followed by
The Siderite-Limonite member, which is up to 30 m thick, thinning to the margins, and contains massive siderite alternating with black argillaceous schist. This member contains dark-grey massive to yellowish coarse-grained siderite and a gossan made of porous limonite from the oxidation of siderite.
The Wild Flysch member, which is <50 m thick, comprising two black argillaceous phyllite and one sandstone units, with characteristic spheroidal and tube-like olistolithes that are tens of cms across in outcrop.
The Middle Flysch member is ~60 m thick, consisting of alternations of argillaceous schist (sub-flysch), sandstone (argillaceous flysch) and sandstone (coarse flysch), containing variably sized olistostrome lenses with mineralised limestone fragments, sandstone banks and rare micro-conglomeratic sequences.
The Olistostrome member is 800 m long and 50 to 150 m wide, consisting of a flysch matrix in which carbonate olistolithic fragments, blocks and their mineralised sections are embedded. The flysch groundmass of the Olistostrome member is mainly sandstone flysch, the lower and upper parts of which are composed of grey and dark grey medium-grained sandstones, and black laminated siltstones, respectively. Carbonate fragments and blocks of the Olistostrome member include black micrites, dark grey organogenic sparites (rich in fossils), dolomitic limestones, ankeritic limestone and ankerite. The occurrence of pulverised limonite in larger blocks represents the transition from ankerite and dolomitic limestones into fossiliferous limestones. Typically, large (up to 3 to 4 m across) isolated, spherical and irregular bodies of partly comb-textured ankerite and dolomitic limestones occur in this member, completely enclosed by pulverised limonite, and appear in groups of several bodies over a thickness of several tens of metres. The olistostrome horizon comprises a wide variety of carbonates including dark massive limestones, dolomitic limestones, dolostones, Fe-enriched limestones, dark massive ankerite, and dark massive siderite locally weathered to porous limonite.
The Upper Flysch, the uppermost member, which is 700 m long, 140 m wide and 70 m thick is located on the northern side of the Tomašica pit (Grubić and Protić, 2003). The lower part of this member is particularly black due to Mn oxides and hydroxides, and is mostly composed of sandstone-siltstone flysch.

The bulk of the resources are hosted by the Siderite-Limonite and Olistostrome members. Palinkaš (1988) recognised three main types of iron ore textures, attributed to physicochemical variations (e.g., changes in acidity, temperature, and/or salinity) of the mineralising fluids and to the succession and intensity of replacement of host limestone. These are:
i). dark (organic) massive siderite and ankerite, which occur as replacements within limestone and dolostone blocks, although the contacts between Fe and unreplaced host carbonates are obscure;
ii). zebra siderite composed of dark massive and light sparry siderite bands, characterised by alternation of dark massive and light sparry siderite bands, formed at ~245°C; and
iii). sparry siderite veins hosted by shale, interpreted to have formed by precipitation from hydrothermal fluids in the late stage of mineralisation at ~185°C, contain centimeter scale yellowish to brownish siderite, with sulphides, mainly chalcopyrite on the contact between siderite and shale.
In addition, cavities infilled with white sparry ankerite, quartz, sulphides, and secondary phyllosilicates are common.

The time and formation of the Ljubija iron deposits are matters of debate. Grubić and Protić (2003) demonstrated an older siderite-limonite and a younger ankerite-limonite phase, and considered siderite, which occurs as lenses alternating with black argillaceous schist in the Siderite-Limonite member, to have originated as a primary non-magmatic hydrothermal marine sediment in the Lower to Middle Carboniferous, as previously been suggested by Jurković (1961) and Jurić (1971). Grubić and Protić (2003) also encountered fissures filled with iron and manganese minerals in Upper Flysch, Permian and Werfenian sediments at southern Tomašica, and consequently concluded that ankerite replacing carbonate rock fragments in flysch and small siderite bodies, associated with the carbonate olistoliths in the Olistostrome Member of the Javorik flysch formation, were precipitated from hydrothermal solutions, possibly partially associated with porphyrite volcanism in the Middle Triassic. Strmić Palinkaš et al. (2009) regarded iron deposits within the Ljubija field as stratabound Fe carbonate ore bodies, hosted by marine limestones, and as siderite-sulphide veins within Carboniferous shales. They interpreted sulphur isotope ratios to suggest Permian seawater or Permian evaporites as the main sulphur source, while their fluid inclusion composition data, they suggest, confirmed a contribution from the Permian seawater to the mineralising fluids and are consistent with a Permian hydrothermal-metasomatic processes and mineralisation age. Siderite and ankerite masses subsequently partially oxidised and hydrated to various types of limonite ore (Jurković 1961; Jurić (1971); Grubić and Protić (2003).

The potential reserves of iron ore in the district have been estimated to 500 Mt @ 40 to 49 wt.% Fe (Grubić and Cvijić 2003).

The most recent source geological information used to prepare this summary was dated: 2012.    
This description is a summary from published sources, the chief of which are listed below.
© Copyright Porter GeoConsultancy Pty Ltd.   Unauthorised copying, reproduction, storage or dissemination prohibited.


  References & Additional Information
 References to this deposit in the PGC Literature Collection:
Garasici V and Jurkovic I,  2012 - Geochemical characteristics of diff erent iron ore types from the Southern Tomasica deposit, Ljubija, NW Bosnia: in    Geologia Croatica   v.65 pp 255-270
Palinkas S S, Spangenberg J E and Palinkas L A,  2009 - Organic and inorganic geochemistry of Ljubija siderite deposits, NW Bosnia and Herzegovina: in    Mineralium Deposita   v.44 pp. 893-913


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