Geochemical characteristics of diff erent iron ore types from the Southern Tomašica deposit , Ljubija , NW Bosnia

Pulverized limonite ore from a Pleistocene–Quaternary lake deposit and compact limonite ore from the Olistostrome member of the Javorik fl ysch formation, in the Southern Tomašica iron ore deposit, were investigated and compared with different types of siderite and ankerite, limestone and carbonate shale from the same location in order to determine their possible protolith. Two limonite types display a notably distinct REE pattern, REE fractionations, Eu anomalies and other trace element and main oxide content. The REE pattern of compact limonite is characterized by relatively low light ((La/Sm)N = 2.87), heavy ((Gd/Yb)N = 0.98) and total ((La/Yb)N = 3.19) REE fractionations, a strong positive Eu anomaly (Eu/Eu* = 2.11) and weakly expressed negative Ce anomaly (Ce/Ce* = 0.82). The compact limonite and siderite REE patterns almost overlap suggesting a common REE source. The same is valid for their Zr/TiO2 ratios (0.040 in the compact limonite, 0.033–0.053 in the siderites). Pulverized limonite shows remarkably different REE patterns and the highest REE concentrations, (up to 6 to 13 times higher relatively to the other samples). Its REE fractionation pattern ((La/Sm)N = 3.68, (Gd/Yb)N = 1.58, (La/Yb)N = 9.41, Eu/Eu* = 1.10 and Ce/Ce* = 0.81) is very similar to those in the carbonate shale, identifying it as the possible protolith of pulverized limonite. The same is valid for the Zr/TiO2 ratios (0.025 in pulverized limonite and 0.017 in carbonate shale). The REE pattern of fi ne grained ankerite ((La/Yb)N = 2.15, Eu/Eu* = 1.95, Ce/Ce* = 0.78) and its Zr/TiO2 ratio (0.030) are similar to those in siderite, and could, assuming extensive contamination of pulverized limonite, also represent its protolith. However, the REE patterns of coarse grained ankerite exhibit remarkable depletion of LREE over HREE and a strong reverse LREE pattern ((La/Yb)N =0.05–0.20, (La/Sm)N = 0.04–0.10, (Gd/Yb)N = 1.77–1.91). They have (similar to the other studied samples), a positive Eu anomaly (Eu/Eu* = 2.16–2.75) and negative Ce anomaly (Ce/Ce* = 0.32–0.83). Their Zr/TiO2 ratio (0.004–0.010) excludes coarse grained ankerite as the possible protolith of pulverized limonite.


INTRODUCTION
Southern Tomašica is one of the four opencast mines (Adamuša, Vidrenjak, Tomašica and Omarska) in the Ljubija iron ore fi eld, situated approximately 200 km northwest of Sarajevo, in Bosnia and Herzegovina.Southern Tomašica is a large deposit of siderite, ankerite, compact limonite and pulverized limonite laying 18 km southeast of Prijedor.It is located on the northern side of the mountain system of Ljepovica (+678 m) and Mačkovac (+474 m) and bordered to the west by the Velika Gradina plateau (Fig. 1).
The origin and time of formation of the iron deposits in the Ljubija iron ore fi eld are matters of considerable debate.GRUBIĆ & PROTIĆ (2003) clearly distinguishes an older siderite-limonite formation and a younger ankerite-limonite formation.According to them, siderite occurring as lenses and alternating with black argillaceous schist in the sideritelimonite formation, originated as primary non-magmatic hydrothermal marine sediment in the Lower to Middle Carboniferous.The fi rst evidence of the synsedimentary origin of this siderite was provided by JURKOVIĆ (1961).JURIĆ (1971) shared the same opinion.GRUBIĆ & PROTIĆ (2003) discovered fi ssures fi lled with iron and manganese minerals in Upper Flysch, Permian and Werfenian sediments of Southern Tomašica.Therefore they concluded that ankerite replacing carbonate rock fragments in fl ysch and small siderite bodies, associated with the carbonate olistoliths in the Olistostrome Member of the Javorik fl ysch formation, was precipitated from hydrothermal solutions partly associated with porphyrite volcanism in the Middle Triassic.STRMIĆ PA-LINKAŠ et al. (2009) regarded iron deposits within the Ljubija fi eld as stratabound Fe carbonate ore bodies, hosted by marine limestones, and as siderite-sulfi de veins within Carboniferous shales.They concluded that Fe mineralization occured through hydrothermal-metasomatic processes in the Permian, in accordance with the earlier opinions of PA LIN-KAŠ (1988, 1990), PALINKAŠ et al. (2003) and BORO JE-VIĆ ŠOŠTARIĆ (2004).Later in geological time, siderite and ankerite ore bodies were partly oxidized and hydrated to various types of limonite ore (JURKOVIĆ, 1961;JURIĆ, 1971;GRUBIĆ & PROTIĆ, 2003).Although the mineralogy and major element chemistry of different limonite ore types from the Southern Tomašica mine have been described earlier (JUR-KOVIĆ, 1961;ŠARAC, 1981), their REE patterns are still unknown.
The aims of this study are to present the results of more detailed geochemical analyses for two different limonite ore types and compare them with the REE distribution patterns of ankerite, siderite, host limestone and carbonate shale, from the Olistostrome Member of the Javorik fl ysch formation, in order to establish their possible genetic relationships.

GEOLOGICAL SETTING
The area of Southern Tomašica consists mainly of sedimentary rocks of Carboniferous, Permian, Werfenian and Quaternary age (Fig. 2), which were metamorphosed, folded and faulted during the Variscan and Alpine orogenies (Fig. 3).
Carboniferous rocks belong to the Javorik fl ysch formation, and the Permian rocks to the Tomašica clastite formation.The most detailed stratigraphic column of this area was drawn by GRUBIĆ et al. (2000) and GRUBIĆ & PROTIĆ (2003) on the basis of fi eld work (M 1:1000) and core descriptions from 520 wells (Fig. 4).According to GRUBIĆ & PROTIĆ (2003) the Javorik fl ysch formation consists of six members.The oldest member is the Lower Flysch characterized by dark green argillaceous schists, alternating with medium-grained sandstone.It is followed by the Siderite-Limonite member which is up to 30 m thick, becoming thinner at the margins.This member contains massive siderite alternating with black argillaceous schist.Siderite is partly transformed to limonite.The Wild Flysch member, (<50 m thick), overlies the Siderite-Limonite member.It consists of two black argillaceous phyllite packets and one sandstone packet.It exhibits characteristic spheroidal and tube-like olistolithes at the decimetre-level on the surface.The Wild Flysch member is overlain by the Middle Flysch member which is about 60 m in thickness, consisting of alternations of argillaceous schist, (subfl ysch), sandstone (argillaceous eufl ysch) and sandstone (coarse fl ysch).It contains variably sized olistostrome lenses with mineralized limestone fragments, sandstone banks and rare microconglomeratic sequences.The Middle Flysch member is overlain by an Olistostrome member, which is 800 m long and 50 to 150 m wide, consisting of fl ysch matrix in which carbonate olistolithe fragments, blocks and their mineralized parts are embedded.The Flysch groundmass of the Olistostrome member is mainly sandstone fl ysch, 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), dolomite limestones, dolomites, ankeritic limestone and ankerite.The occurrence of pulverized limonite, which in larger blocks represents the transition from ankerite and  The southern part of the Southern Tomašica opencast mine consists of marls, marl limestone, siltstones, sandstones and breccia-like intercalations of Werfenian age, which reach a thickness of around 70 m.
According to JURIĆ (1967) and PODUBSKI (1969), the rocks of the Javorik formations are metamorphosed at the highest grade of the greenschists facies.
During the Tertiary, after uplift of the Upper Palaeozoic complex, the oxidation processes of primary iron ore (siderite, ankerite and ankeritized carbonate rocks) in Ljubija had begun and limonite gossans had been formed "in situ".According to JURKOVIĆ (1961), gossans developed by weathering of siderite were compact and stable, while those derived from massive ankerite were more mobile.Later, due to erosion, gravity, mechanical and chemical leaching and solution, different aureoles of secondary limonite ore were developed.In the Pliocene-Quaternary period remarkable part of this limonites were further transported by rain, river or wind, and redeposited in palaeovalleys, palaeobasins and lakes, partly as detrital limonite, partly as pulverized limonite or "brand" (termed by Jurković in publications).On this occasion limonites became more or less contaminated.
The best description of reworked deposits of limonite and pulverized limonite in the area of Tomašica (Southern Tomašica, Northern Tomašica, Šiljezi, Stankovići, Dabića Brdo, Tevanovići, Bojići) was by CVIJIĆ (1986CVIJIĆ ( , 2001)).The ore bodies are mainly characterized by lense-like or conelike shapes, rarely irregular layers, reaching thicknesses of 10-30 m, locally up to 50 m, rarely more than this.The borders of ore bodies are not sharp.

PREVIOUS STUDIES OF LIMONITES IN TOMAŠICA
Laboratory and commercial studies by LOGOMERAC (1960) have shown that pulverized limonite is a suitable oregrade raw material for sintering, pelletizing and bricketizing in the production of raw iron.The granulometric composition of pulverized limonite was characterized by 26.8 wt.% of particles fi ner than 60 μm, 46.8 wt.% of particles ranging between 60 and 100 μm, 16.3 wt.% of particles laying between 100 and 400 μm and 10.0 wt.% of particles from 400 to 1500 μm diameter.The specifi c and volume weights were 3.3 g/cm 3 , and 1.38 g/cm 3 , respectively.The LOI was equal to 8.15% and H 2 O -to 6.8%.
The fi rst laboratory, physico-chemical and optical studies of limonite samples from the Southern Tomašica ore district (Točak, Gradina, Stojančići and Klimenta localities) were performed by JURKOVIĆ (1961).The XRD analyses of pulverized limonite (brand) from Stojančići show mostly the presence of micro-cryptocrystallized goethite (70 wt.%), and some amorphous clay, having no peaks on the Debye diagram.DTA has given endothermic effects, which were strong at +200°C (goethite) and 350°C (partly amorphous limonite) and weak at temperatures from +550°C to +650°C (clay).TGA shows weight loss of 8% in the range between +100°C and +400°C (goethite-limonite), and 4 % between +550°C and +650°C (illite clay).The results of XRD, DTA and TG analyses reveal that the brand consists of a mixture of cryptocrystalline and partly amorphous goethite and allophanoid amorphous clay (68.25 and 8.65 wt.% respectively).The studied sample was prepared in Plexiglas and investigated under refl ected light microscopy (Fig. 5).Pulverized limonite (brand) consists of pizoliths having diameters in the range of 30 and 300 μm, on average between 100 and 200 μm.Pizoliths are spheroidal, rarely oval and consist of an intimate mixture of cryptocrystalline goethite and amor phous or cryptocrystalline clay masses.In refl ected light they have considerably lower lustre than goethite, are isotropic, and in crossed polars show diffusely scattered brown inner refl ections.ŠARAC (1981) analyzed pulverised limonite samples, discovering a very high content of SiO 2 (15.56%) and Al 2 O 3 (3.40%)compared to compact limonite.
Studies in the Boris Kidrič Institute in Ljubljana and in Firma Bayer have shown that ore deposits of pulverised limonite in Tomašica represent a natural mineral pigment with a high content of natural chromofore (up to 80 %) which is applicable to the colour and varnish industry and in the industry of anticorrosive coating and coloured building materials.On the basis of these studies, a natural pigments factory was built in Tomašica using pulverised limonite raw material from the Southern Tomašica deposit and the Blatnjak deposit.
Detailed petrological characteristics of compact limonite have been described by JURKOVIĆ (1961).Using XRD analyses, he identifi ed goethite as the main mineral intimately intergrown with illite which has sheets up to 10, and rarely up to 30 μm or more and with quartz crystals, occurring in bipyramidal prisms, with diameters in the range between 30 and 300 μm, or in alotriomorphic masses.There are oxidized pyrite relics and minor lepidocrocite in massive goethite.Additionally, fi ne microscopic tiny veinlets of cryptocrystalline pyrolusite and microcrystalline pyrolusite in pores are also present in goethite.Cryptocrystalline or fibrous psilomelane also occur replacing goethite or being transformed into pyrolusite.The manganese minerals were most likely formed as a weathering product of siderite, which contains up to 2.55 wt.% of MnO.Elemental silver was observed in the goethite pores.Mineral intergrowths are frequent and fi ne-grained, or rare and coarse-grained.

Samples and analytical methods
All samples were collected within the Olistostrome member of the Javorik fl ysch formation excluding pulverized limonite (TBRA) which was found on an ancient mine heap at Stojančići representing relics of one Pleistocene-Quaternary lake limonite deposit.
Levels of the quarry containing the Siderite-limonite member have been submerged some years ago since mining operations ceased and it was impossible to collect samples from this part of the Javorik fl ysch formation.
The sample of compact limonite (TLIM) represents a gossan formed "in situ" on siderite.It occurs in the form of black and shiny, kidney shaped concretions, and glassy needles (Fig. 6).Microscopic investigations show that the concretions have an internal radiating structure (Fig. 7) and the main mineral is goethite.Other minerals in the paragenesis are quartz, clay minerals and muscovite.This is in accord-  ance with the former more specifi c petrographic investigations of compact limonites performed by JURKOVIĆ (1961).
Pulverized limonite or "brand" (TBRA) from the Stojančići locality (Fig. 8) have also been studied in detail by JURKOVIĆ (1961) and therefore no new microscopic investigations of this sample have been made.
Common characteristics of the limestone sample (TVAP1) are veins bearing brown siderite, pale yellow ankerite, and tiny white calcite veinlets (Fig. 9).Macroscopic and microscopic structural relationships suggest that the siderite was partly replaced by ankerite, whereas calcite represents the youngest occurrence (Fig. 10).The limestone is dark gray micrite containing rare quartz grains, (up to 0.12 mm) and muscovite, (up to 0.06 mm).Only vein and veinlet free parts of the limestone were taken for chemical analysis.
The studied sample of carbonate shale (TVAP2) is composed of clay-sized grains, and is a dark, fi ssile, and laminated rock (Fig. 11).Microscopic study revealed that it consists of clay minerals, detrital quartz, muscovite and variously sized spherical and oval-shaped calcispheres, which are characteristically 60 to 300 µm in diameter (Fig. 12).
The sample of white-gray coloured ankerite (TMIX) shown in Figure 13 consists of an intimately associated white area of coarse grained ankerite crystals, with regular grain boundaries and a gray area of fi ne to medium grained ankerite with black lobate grain boundaries, and interstitial places fi lled with a clayey-carbonaceous substance and quartz ag-     gregates (Fig. 14).Relics of fi ne grained ankerite with lobate black grain boundaries have been observed within the white coarse grained ankerite.Ankerites of both, white and gray areas are characterized by undulose extinction.Due to the intimate association of the white and gray areas of this sample, one chemical analysis of a mixed area was made.
White coarse grained ankerite (sample TANK), occurs in the form of an irregular nest (Fig. 15) in the matrix of dark fi ne grained ankerite (sample TANK 1).White coarse grained ankerite is characterized by regular grain boundaries and grains free of inclusions.In contrast, grain boundaries of dark fi ne grained ankerite are highly irregular, and the interstitial space is fi lled with a clayey-carbonaceous substance containing usually small quartz grains and rarely muscovite (Fig. 16).Dark fi ne ankerite grains show locally tiny quartz inclusions.The undulose extinction is typical for both coarse and fi ne grained ankerite.Different parts of this non-homogeneous rock sample were carefully separated from each other for chemical analysis.
White coarse grained ankerite (sample TANMIC) also occurs in the form of an irregular nest, but this time in a matrix of reddish coarse grained siderite (sample TCOR), which     is surrounded by dark fi ne grained siderite (sample TMIC) as shown in Fig. 17.Various parts of this non-homogeneous rock sample were carefully separated for chemical analysis.interstitial spaces fi lled with a clayey-carbonaceous substance and disseminated quartz grains.Partial breakdown of both types of siderite results in the occurrence of haematite along grain boundaries, cleavage and cracks in the siderite (Fig. 18).Ankerite and both type of siderite are characterized by undulose extinction.
The sample of yellow coarse grained siderite (sample AD-2) irregularly embedded in a matrix of reddish fi ne grained siderite was collected in the Adamuša opencast mine (Fig. 19).Again, fi ne grained mineral is characterized by irregular boundaries and interstitial spaces fi lled with a clayeycarbonaceous substance and disseminated quartz grains, whe reas the coarse grained mineral consists of polygonal grains.Chemical analysis of yellow coarse grained siderite was undertaken, although due to the intimate association of yellow and reddish siderite it is possible that a minor quantity of reddish siderite was included in the analysis.
Careful examination of mineral thin-sections using trans mitted polarized light enabled separation of the fresh and weathered samples, and the different parts of non-homogeneous samples to be distinguished.Selected samples were crushed, hand-picked under binocular microscope and powdered in an agate mortar for chemical analysis.
Major, minor and trace element contents were determined by inductively coupled plasma mass spectrometry (ICP-MS) in the Acme Analytical Laboratories (Vancouver) Ltd in Canada.In the same laboratory the total organic carbon (TOT/C) and total sulphure (TOT/S) of all six samples were measured too.

Main oxides
The concentrations of many main oxides (SiO 2 , Al 2 O 3 , TiO 2 , Na 2 O, K 2 O) in compact limonite are slightly higher but very similar to those in siderite, limestone and dark fi ne grained ankerite (Table 1).Slightly lower concentrations of these oxides, (but still similar to those in siderite and limestone) are displayed in the white coarse grained ankerite.Pulverized limonite on the other hand differs signifi cantly, relative to compact limonite.The SiO 2 component in pulverized limonite is enriched by 3 times, Al    White coarse grained ankerite and reddish coarse grained siderite are characterized by regular grain boundaries, whereas those of dark fi ne grained siderite are irregular with shows lower MnO values (0.88 to1.10 wt%) and limestone has the lowest MnO value (0.10 wt%).The highest CaO content in siderite is found in the red coarse grained TCOR sample (3.98 wt%) in the immediate vicinity of the ankerite nests.The CaO content of the other two siderite samples varies from 1.34 to 1.63 wt%.Ankerite is characterized by a CaO content varying between 26.87 and 28.59 wt%.The greatest chemical differences between pulverized limonite and carbonate shale is visible in the content of Fe 2 O 3 (3.27wt% in carbonate shale and 53.87 wt% in pulverized limonite) and CaO (31.60 wt% in carbonate shale and 0.23 wt% in pulverized limonite).

REE content
The REE content of ankerite, limestone, siderite and compact limonite is low (up to 22.49 ppm), in contrast to pulverized limonite (118.45 ppm) and carbonate shale (72.99 ppm), as reported in Table 2.There is a clear positive correlation between the weight percent of the main oxides SiO 2 and Al 2 O 3 and REE (Table 1, Table 2) in compact limonite, pulverized limonite and carbonate shale.This suggests REE concentration dependence of the clay component in the samples.However, the same correlation is not so obvious for carbonates.

Other trace elements
The content of Rb, Cs, Ba and Ga are characterized by a positive correlation with K 2 O and Al 2 O 3 values, pointing to the aluminosilicate fraction of the samples.Consequently, the pulverized limonite contains the highest values of Rb (74.2 ppm), Cs (14.8 ppm), Ba (227 ppm) and Ga (14.1 ppm).It is also characterized by the highest concentrations of V (104 ppm), Zr (115.2 ppm) and Y (19.3 ppm).The compact limonite contains elevated concentrations of many trace elements (Cs, Ga, Hf, Rb, Th, V, Zr,Y, Cu, Zn, Ni and Sb) relative to siderite, ankerite and limestone (Table 3).In the same comparison the highest contents of Co (5.60 ppm) and As (4.60 ppm) are found in siderite, of Hg (0.14 ppm) in ankerite and of U (1.60 ppm) and Pb (11.1 ppm) in the limestone.
In comparison with compact limonite, siderite, ankerite and limestone the concentrations of Ni, Co, Cs, Ga, Hf, Nb, Rb, Ta, Th, U, V, W. Zr, Y, Mo, Cu, Pb, Zn, As, Sb and Hg are even more elevated in the pulverized limonite and carbonate shale (Table 3).The only elements having higher concentrations in the carbonate shale than in pulverized limonite are Co, Bi, Ag, Hg and Se (Table 3).

DISCUSSION
Geochemical investigations of two limonite ore types show considerable differences in the content of their main elements, REE and other trace elements.In order to constrain their possible lithotype sources, the geochemical characteristics of studied siderite, ankerite, host limestone and carbonate shale are further discussed.

REE chemistry of carbonate phases
Generally, many factors may infl uence the REE content of carbonate minerals.The most important include the size of sites occupied by REE ions in the crystal lattice, REE chemistry of mineralizing fl uids and REE partitioning between the precipitating mineral and mineralizing fl uid (MÖLLER, 1983).In addition, according to MÖLLER et al. (2004), REE abundances are higher in hydrothermal than in cold fl uids and increase with decreasing pH (MICHARD, 1989).In acid solutions LREEs are enriched relative to HREEs,  MARKL, 2005).
In the context of crystal chemistry, calcite should be characterized by enrichment of LREE over HREE in contrast to siderite that should display depletion of LREE over HREE.
Ankerite should show intermediate characteristics between these two patterns.The larger Ca ion site in calcite incorporates larger LREEs more easily, whereas the smaller Fe ion site in siderite easily incorporates smaller HREEs.
Thus the LREE enrichment in siderite (Fig. 20), and its overall greater REE content (ΣREE = 13.71-18.17ppm) in comparison with limestone (ΣREE = 9.15 ppm), could not be solely attributed to crystallographic control, but indicates the precipitation of siderite from an LREE enriched parent fl uid.Strong depletion of LREE over HREE ((La/Yb) N = 0.05-0.20) in the two white coarse grained ankerites on the other hand reveals that they were precipitated either from a colder and more alkaline mineralizing fl uid, or from a fl uid with a different source relative to siderite and fi ne grained ankerite.
The negative Ce anomaly, being the result of the oxidation of Ce 3+ to Ce 4+ and its consequent removal from the solution as CeO 2 , is typical for marine limestones (HU et al., 1988).The studied limestone exhibits a pronounced negative Ce anomaly (0.68) and weak positive Eu anomaly (1.13).The negative Ce anomaly, although weaker, is present in siderite (0.78-0.87), fi ne grained ankerite (0.78), and also in one coarse grained ankerite (0.83).Its lower values relative to limestone could be explained by lower pH or a lower pO 2 of mineralizing fl uids from which siderite and ankerite samples precipitated.The presence of a signifi cant negative Ce anomaly (0.32) in the TANMIC sample (coarse grained ankerite) indicates more oxygenated conditions for its precipitation.
The additional noticeable feature in the studied carbonate REE patterns is a pronounced positive Eu anomaly in siderite (2.24-3.40)and coarse grained ankerite (2.16-2.75).It is weaker in the fi ne grained ankerite (1.95) and weakest in the limestone (1.13).Numerous analyses of REE concentrations in hydrothermal fl uids along oceanic ridges (MI-CHARD & ALBAREDE, 1986;CAMPBELL et al., 1988) revealed that hydrothermal fl uids are enriched in ΣREE (10-10 4 times relative to seawater concentrations), and are characterized by a signifi cant positive Eu anomaly (OLIVAREZ & OWEN, 1991).Furthermore, textural evidence (the occurrence of veins and nests) in the studied siderite and ankerite samples from the Olistostrome member in Javorik Formation support the hydrothermal origin.The interaction between some Eu-rich mineralizing fl uid and limestone could be refl ected in the LREE depletion of ankerite, due to effective HREE complexion.Additionally, the strong similarity in the content and the fractionation of HREE in fi ne grained ankerite and limestone (Fig. 20) might also indicate the possible involvement of limestone in the origin of ankerite.The analytical results obtained are in accordance with those published by STRMIĆ PALINKAŠ et al. (2009) who suggested a hydrothermal-metasomatic origin of the Fe mineralization.However, it should be emphasized that there was more than one hydrothermal stage.This is refl ected in ore texture (fi ne grained, coarse grained, veins, nests), colour (white, gray, red) and chemical features.Signifi cantly lower Al 2 O 3 values occur in white coarse grained ankerite (0.05 wt.%) when compared to those in fi ne grained ankerite (0.57 wt%) and siderite (0.27-0.49wt%).However, due to the lack of a clear positive correlation between wt% Al 2 O 3 and ΣREE (see Table 1 and 2) it seems that the REEs are not hosted in detrital phases of carbonate samples.

REE chemistry of compact limonite
The REE pattern of compact limonite ((La/Sm) N = 2.87, (Gd/Yb) N = 0.98, (La/Yb) N = 3.19, Eu/Eu* = 2.11, Ce/Ce* = 0.82) and its other trace element content (Table 3), exhibits the closest genetic relationship with siderite.Chemical wea thering of siderite most probably resulted in its extensive supergene modifi cation and the origin of compact limonite.Textural relationships and fi eld occurrences of siderites and compact limonite support such a concept.It is also in accordance with the opinions of earlier investigators in this area (JURKOVIĆ, 1961;GRUBIĆ & PROTIĆ, 2003).The formation of limonite due to siderite weathering is observed and documented in many other geological environments (MORRIS, 1980).described comb-textured ankerite and dolomite limestone being completely enclosed by pulverized limonite.Therefore they concluded that the weathering of ankerite led to the formation of pulverized limonite.The REE pattern of pulverized limonite analysed in this study differs strongly from the REE patterns of any ankerite types analysed here and hence would contradict such a conclusion.However, it has to be emphasized that the analysed sample of pulverized limonite (TBRA) was not taken in its original place of formation, but in the Pleistocene-Quaternary lake limonite deposit (Sto jan čići location).During transportation by rain, river or wind, pulverized limonite could become more or less contamina ted.The enhanced overall REE content in pulverized limo ni te (ΣREE = 118.45ppm) relative to compact limonite (18.78 ppm), may be explained by such crustal rock contamination.
Trace elements are in general depleted in compact limonite relative to pulverized limonite.The high values of Zr (115.2 ppm) in pulverized limonite indicate the possible presence of a clastic component of igneous origin, whereas high values of Rb (74.2 ppm), Sr (42.4 ppm), Th (8.9 ppm) indicate components derived by weathering from crustal felsic rocks.The enhanced concentrations of Cu (52.4 pppm), Pb (112 ppm), Zn (345 ppm) and As (382.8 ppm) may be attributed to the presence of components arising from the weathering of sulphide minerals.
The ratios of some immobile trace elements such as Zr/TiO 2 and Nb/Y are regarded as very useful for protolith determination (WINCHESTER & FLOYD, 1977) because they don't change during weathering processes.The values of the Zr/TiO 2 ratio in compact limonite (0.040) and siderite (between 0.033 and 0.053), are in concordance with the postulated origin of compact limonite from siderite.In the fi ne grained ankerite (sample TANK1), the Zr/TiO 2 ratio is 0.030, whereas in the coarse grained ankerite it varies between 0.004 and 0.010.As pulverized limonite has a Zr/TiO 2 ratio of 0.025, only fine grained ankerite or carbonate shale (0.017) might be regarded as its possible protolith.Similar conclusions could be drawn on the basis of the Zr/Nb ratio which in siderite varies from 11 to 22 and in compact limonite is 20.In the pulverized limonite, the Zr/Nb ratio is 11.29, in carbonate shale 7.78, in the fi ne grained ankerite 11.8, and in the coarse grained ankerite it ranges between 4 and 10.However, the values of the Nb/Y ratios in pulverized limonite (0.53), carbonate shale (0.29), compact limonite (0.13), siderites (0.05-0.08), fi ne grained ankerite (0.06) and coarse grained ankerite (0.01-0.02) do not support the possibility of the origin of pulverized limonite through the weathering processes of ankerites.

Field relationships and geochemical data
The fi eld relationship between siderite and compact limonite, is consistent with the conclusion based on REE geochemistry, that compact limonite most probably originated by the alteration of siderite.Compact limonite occurs as gossan formed in situ on siderite.
Pulverized limonite occurs in the fi eld as bedded and lensoid shape deposits in palaeolakes, but also enclosing ankerite relics and ankeritic limestone in the Olistostrome member.The analyzed sample of pulverized limonite from a limonite deposit from the palaeolake exhibits signifi cantly distinct REE patterns relative to any ankerite types studied in this paper.
Carbonate shale is part of a fl ysch groundmass of the Olistostrome member in which carbonate olistolith fragments, blocks and their mineralized parts are embedded.The remarkable resemblance of its REE pattern with that of pulverized limonite indicates the possibility that pulverized limonite may generally originate by the alteration of a carbonate shale or fl ysch groundmass.

CONCLUSION
Two studied types of limonite ore from the Southern To mašica mine display a notably distinct REE pattern, REE fractionations, Eu anomalies and contents of other trace elements and main oxides.The compact limonite formed in situ on siderite is characterized by remarkable lower overall REE abundances, lower LREE fractionation, lower and opposite HREE fractionation, a more strongly expressed positive Eu anomaly and far lower overall content of other trace elements compared to pulverized limonite.This supports the hypothesis of different protolith material for the two different limonite ore types.
The REE pattern of compact limonite and siderite almost overlap, supporting the interpretation of former investigators (JURKOVIĆ, 1961;GRUBIĆ & PROTIĆ, 2003) who concluded that compact limonite originated by the alteration of siderite.
The REE pattern of pulverized limonite on the other hand clearly differs from that of ankerite, which GRUBIĆ & PROTIĆ (2003) regarded as the protolith of pulverized limonite.On the basis of the similarity of their REE patterns, other trace element contents and Zr/TiO 2 ratios, carbonate shale might be regarded as a potential protolith of pulverized limonite.Alternatively, assuming that the analysed samples of pulverized limonite, collected in the Pleistocene-Quaternary lake limonite deposit, were contaminated during transportation by rain, river or wind, fi ne grained ankerite might also, on the basis of its Zr/TiO 2 ratio and Eu and Ce anomaly, be a potential protolith of pulverized limonite.
In order to develop full understanding of the formation of all limonite types in this area, the REE pattern and con-tent of other trace elements in siderite occuring as lenses in the lowest parts of the geological column of Southern Tomašica, and in the superposed limonite (Siderite-limonite member) and in pulverized limonite enclosing ankerite relicts (Olistostrome member) remain to be investigated.

Figure 1 :
Figure 1: The location of the studied area.

Figure 5 :
Figure 5: Spheroidal pizoliths consist of a mixture of cryptocrystalline goethite and amorphous or cryptocrystalline clay.White thin intergranular fi lms of crypto-to microcrystalline goethite surround the pizolites.The black area is a hole.Magnifi cation: x55 (after JURKOVIĆ, 1961).

Figure 6 :
Figure 6: Black and shiny kidney shaped concretions and glassy needles in compact limonite (sample TLIM).

Figure 9 :
Figure 9: Brown siderite and pale yellow ankerite veins and tiny white calcite veinlets that cut the studied limestone (sample TVAP1) .

Figure 13 :
Figure 13: Intimately associated white coarse grained area and gray fi ne to medium grained area of ankerite (sample TMIX).

Figure 14 :
Figure 14: Photomicrograph of the fi ne to medium part of an ankerite sample TMIX with quartz aggregates fi lling interstitial places between ankerite grains having lobate grain boundaries (N+).

Figure 15 :
Figure 15: White coarse grained ankerite (sample TANK) occurs in form of an irregular nest in the matrix of dark fi ne grained ankerite (sample TANK1).

Figure 16 :
Figure16: Photomicrograph of the boundary area between coarse grained ankerite (sample TANK) and fi ne grained ankerite (sample TANK 1).Grain boundaries of fi ne grained ankerite are highly irregular, the interstitial space is fi lled with a clayey-carbonaceous substance (N + ).
2 O 3 component by 10 times, Na 2 O component by 7 times, K 2 O component by 4 times and the P 2 O 5 component by 20 times compared to compact limonite (Table1).These elevated values are mostly comparable to carbonate shale which is even more enriched in the SiO 2 component (27.10 wt % compared to 16.73 wt % of pulverized limonite), but depleted in Al 2 O 3 (only 4.99 wt % in comparison with 11.78 wt% of pulverized limonite).There are positive correlations between the Al 2 O 3 , K 2 O and TiO 2 contents and the aluminosilicate fraction of the samples.The Fe 2 O 3 and MgO contents in siderite vary from 3.09 and 5.11 wt%, to 51.66 and 58.34 wt% respectively.In ankerite, the Fe 2 O 3 content ranges from 13.94 to 21.35 wt%.Its MgO content is between 9.29 and 10.41 wt%.MnO values are positively correlated with Fe 2 O 3 in all samples.The highest MnO content is present in siderite (2.15 to 2.55 wt%).Ankerite

Figure 17 :
Figure 17: White coarse grained ankerite (sample TANMIC) occurs in the form of an irregular nest in a matrix of reddish coarse grained siderite (sample TCOR) which is surrounded by dark fi ne grained siderite (sample TMIC).

Figure 18 :
Figure 18: Photomicrograph of fi ne grained siderite (sample TMIC) with ir regular grain boundaries and interstitial spaces fi lled with a clayey-carbonaceous substance and disseminated quartz grains.Red haematite occurs along cracks and cleavage of siderite because of weathering processes (N).

Figure 19 :
Figure 19: Yellow coarse grained siderite (sample AD-2) irregularly embedded in a matrix of reddish fi ne grained siderite from the Adamuša opencast mine.

Table 1 :
The main element content of the studied samples.

Table 2 :
Rare earth element composition of the studied samples.

Table 3 :
Trace element content of the studied samples.