GC_2-2013_KB.indd Geologia CroaticaGeologia Croatica Geologia Croatica 66/2 129–142 4 Figs. 4 Tabs. Zagreb 2013 AB STRA CT This paper presents the results of sampling surveys carried out in order to evaluate the environmental impact of the Rude and the Sv. Jakob historical mining sites, NW Croatia. The studied polymetallic ore deposits differ in their min- eralogical and geochemical features as well as in the host rock lithology. The Rude Fe-Cu-Pb-Zn-Ba deposit is host- ed by Permian siliciclastic sediments. Siderite, haematite, galena, sphalerite, chalcopyrite, pyrite, barite and gypsum are the major ore minerals. The Sv. Jakob Pb-Zn deposit occurs in the Middle Triassic dolostone. The most abundant ore minerals are galena, sphalerite and pyrite. Although the deposits represent potential sources of numerous toxic metals, no pollution of the drainage streams and associated stream sediments was recorded. The studied mining sites are characterized by high carbonate/sulfi de ratios responsible for the alkaline character of the drainage streams (pH=7.3–8.7). Consequently, the mining sites have very low potential for both generation of acid mine drainage and for leaching of heavy metals into the drainage systems. Furthermore, the study revealed that the populated areas (stream waters with decreased redox potential, increased organic matter content, high NO3 –, NH4 + and PO4 3– con- centrations; stream sediments enriched in exchangeable Pb and Zn) and the Sava river alluvium (overfl owing streams enriched in Hg) represent a greater environmental threat than the investigated polymetallic ore deposits. Keywords: polymetallic ore deposits, exchangeable metals, stream water, stream sediments, Samoborska Gora Mts., Medvednica Mts., NW Croatia. Environmental geochemistry of the polymetallic ore deposits: Case studies from the Rude and the Sv. Jakob historical mining sites, NW Croatia  Sabina Strmić Palinkaš1, Dragana Dogančić2, Ladislav A. Palinkaš1, Jasmina Obhođaš3, Štefi ca Kampić1, Maja Kuzmanović1 and Maša Martinić1 1 Faculty of Science, University of Zagreb, Horvatovac 95, HR-10000 Zagreb, Croatia; (sabina.strmic@inet.hr; phone: +385-1-4605-971; fax: +385-1-4605-998) 2 Geotechnical Faculty, University of Zagreb, Hallerova aleja 7, HR-42000 Varaždin, Croatia; (dragana.dogancic@gfv.hr; phone: +385-42-408-947) 3 Department of Experimental Physics, Ruđer Bošković Institute, Bijenička c. 54, HR-10000 Zagreb, Croatia; (jasmina.obhodjas@irb.hr; phone: +385-1-4571-311) doi: 10.4154/gc.2013.10 1. INTRODUCTION The polymetallic ore deposits represent the geochemical anomalies of numerous potentially toxic metals such as lead, copper, cadmium, mercury, arsenic and barium. Although the primary minerals of these elements (mostly sulfi des) do not represent a signifi cant environmental threat, their weath- ering under surface conditions may mobilize heavy metals making them biologically available. The environmental be- haviour of the polymetallic ore deposits varies according to the ore and gangue mineralogy, major and trace element geo- chemistry and the host rock lithology (e.g. MASCARO et al., 2001; FOLEY, 2002; HUANG et al., 2010; KIRSCH- BAUM et al., 2012). The presented study focused on the two polymetallic ore deposits, at Rude, in the Samoborska Gora Mts., and Sv. Ja- kob, (Medvednica Mts.), in the vicinity of Zagreb, NW Croatia. The deposits differ in their mineralogical and geo- Geologia Croatica 66/2Geologia Croatica 130 chemical features as well as in the host rock lithology. The Rude Fe-Cu-Pb-Zn-Ba deposit is hosted by Permian silici- clastic sediments. Siderite, haematite, galena, sphalerite, chalcopyrite, pyrite, barite and gypsum are the principal ore minerals (PALINKAŠ et al., 2010). The Sv. Jakob Pb-Zn deposit occurs in the Middle Triassic dolostone. The most abundant ore minerals are galena, sphalerite and pyrite (ŠINKOVEC et al., 1988). Both deposits are drained by sur- face streams which could transport potentially toxic metals downstream. The Rude deposit is drained by the Rudarska Gradna creek. The geochemical and mineralogical study undertaken by ČOVIĆ (2003) to evaluate heavy metal levels in overbank sediments of the Žumberak and Samoborsko Gorje Mts., re- vealed an increased content of numerous metals (Hg, Cu, Pb, Ba, As, Cr and Fe) in samples from the Rudarska Gradna catchment. Soils developed above the Sv. Jakob historic mining site were found to contain increased concentrations of Pb, Zn and Cd, related to the oxidation of primary sulfi des in the near-surface weathering environment (DURN et al., 1998). The deposit is located only 300 m north from the Veliki po- tok creek headwater, and there is a strong possibility that the creek might transport signifi cant concentrations of heavy metals downstream. The primary objective of this study was to determine the environmental impact of the historical mining sites on the surrounding ecosystems, including the streams that drain them. Stream water chemistry and stream sediment compo- sition are discussed, as well as the geochemical behaviour of metals during the weathering processes in the two differ- ent types of polymetallic ore deposits. 2. GEOLOGICAL SETTING The Rude, Samoborska Gora Mts., and the Sv. Jakob, Med- vednica Mts., polymetallic ore deposits are located within the westernmost part of the Zagorje Mid-Transdanubian zone (ZMTZ); PAMIĆ, & TOMLJENOVIĆ, 1998; TOM- LJENOVIĆ, 2002). The Samoborska Gora and Medvednica Mts. consist of Palaeozoic, Mesozoic-Palaeogene and Neogene formations (Fig. 1). The Autochthon of Samoborska Gora Mts. com- prises: 1) Palaeozoic unit, composed of Late Carboniferous dark gray schists, shales and sandstones. Shallowing of the sedimentary basin evolved into a dry-land phase, followed Figure 1: Simplifi ed geological setting of the investigated areas with marked sampling sites along a) the Rude ore deposit and marked sampling sites along the Rudarska Gradna creek (RG-1 – RG-12); b) the Sv. Jakob ore and marked sampling sites along the Veliki Potok creek (VP-1 – VP-12). Strmić Palinkaš et al.: Environmental geochemistry of the polymetallic ore deposits: Case studies... Geologia Croatica 131 by deposition of fi ne to coarse-grained sandstones, interlay- ered with conglomerates, dolostones and evaporites (HERAK, 1956). These deposits are unconformably overlain by an Early Triassic clastic-carbonate unit, followed by Middle and Late Triassic carbonate-marl sediments, with occasional appear- ances of cherts, and 2) Cretaceous mélange predominantly composed of basalts and diabases within shales, graywackes, conglomerates, radiolarites and limestones of dif ferent Meso- zoic ages, covered by Neogene sediments. The volcanics, often as basalt-spilite pillow lavas, are probably products of a Triassic rifting stage. The Allochthon is represented by Mesozoic carbonate platform lithotypes (ŠIKIĆ et al., 1979; TOMLJENOVIĆ, 2000; PALINKAŠ et al., 2010). Tectonostratigraphic units of the Medvednica Mts. are grouped into four main units (Fig. 1). Autochthon: 1) Tec- tonized ophiolite mélange, including all lithological members, from sediments, to mafi c and ultramafi c igneous components, 2) Palaeozoic-Triassic magmatic-sedimentary complex over- printed by Early Cretaceous metamorphism, 3) Late Creta- ceous-Paleocene flysch, and Allochthon: 4) Triassic and younger sequences belonging mainly to carbonate platform facies (ŠIKIĆ et al., 1978; ŠIKIĆ et al., 1979; ŠIKIĆ, 1995; PALINKAŠ et al., 2010). 3. MINERALIZATION The Rude Fe-Cu-Pb-Zn-Ba deposit consists of two ore types, an epigenetic, hydrothermal vein-type beneath a stratiform, SEDEX type. Epigenetic, epi-mesothermal, quartz-siderite veins with chalcopyrite, galena, sphalerite and barite, cross- cut the Middle-Upper Permian clastic rocks. The epigenetic part of the deposit represents a feeder zone of the SEDEX, stratiform ore lenses formed in an evaporitic pond-lagoon by sedimentation of gypsum-anhydrite, haematite, siderite and barite. Laterally, epigenetic, epithermal barite-galena veins intersect Upper Permian coarse-grained sandstones. The deposit is covered by Lower Triassic variegated clastics (PALINKAŠ et al., 2008; ŠINKOVEC, 1971). Mining ac- tivities in the area began in the early 13th century with the exploitation of copper. The production of iron ore from sid- erite started in 1850 and lasted less than 10 years. According to PALINKAŠ et al. (2010) the Rude deposit is declared as a prototype of the Permian siderite-polysulphide-barite de- posits produced during the early stage of intracontinental rifting. The deposit is drained by the Rudarska Gradna creek (Fig. 1), which originates approximately 1.8 km southwest of the deposit. Generally, it runs southwest-northeastwards for about 16 km. In the upper part of the course, the creek fl ows through a rural area and it is fed by several small streams. After its confl uence with the Lipovečka Gradna creek, it fl ows through the town of Samobor. The Gradna creek joins the Sava River in the vicinity of Gradna village. After its headwater in the Middle Triassic carbonates, the Rudarska Gradna creek fl ows over the Permian unmeta- morphosed siliciclastic complex, the Lower Triassic clastic rocks, Middle to Upper Triassic carbonates, Cretaceous lime- stones, proluvial and alluvial sediments (Fig. 1; ŠIKIĆ et al., 1978; ŠIKIĆ et al., 1979). The Sv. Jakob Pb-Zn deposit is hosted by non-metamor- phosed Middle Triassic dolostone (PALINKAŠ et al., 2008), with the ore occurring in the form of veinlets and lenses. Ga- lena is the principal ore mineral, and it is coarse grained. The vein-type mineralization, beside galena, comprises minor sphalerite, pyrite, quartz and calcite (ŠINKOVEC et al., 1988), and was actively mined during the 17th century. Ac- cording to the epigenetic character of the ore mineralization, a simple ore paragenesis without copper minerals, and the fl uid inclusions and sulfur isotope data, the deposit is clas- sifi ed as a Mississippi Valley type of Pb-Zn deposits formed during the stage of advanced intracontinental rifting in the Middle Triassic (PALINKAŠ et al., 2008; ŠINKOVEC et al., 1988; DURN et al., 1999; BOROJEVIĆ ŠOŠTARIĆ, 2004). The deposit is located at 830 m above sea level, approx- imately 300 m north of the Veliki Potok creek headwater. The Veliki Potok creek runs north-south for about 12 km, and is fed in its upper part by the Mali Potok creek and sev- eral small streams. The central and lower part of the creek fl ows through the urban area of Zagreb. In the lowermost part of the course, about 500 m upstream from its entry point into the Sava River; the Veliki Potok has its confl uence with the Vrapčak creek (Fig. 1). The Veliki Potok originates in the Palaeozoic parametamorphic complex (Fig. 1) composed of greywackes, siltstones, limestones, dolostones, muscovite- chlorite and muscovite-quartz schists (ŠIKIĆ et al., 1978; ŠIKIĆ et al., 1979). According to several authors (ĐURĐANOVIĆ, 1973; BELAK et al., 1995) some proto- liths from the parametamorphic complex are of Triassic age. Continuing downstream, the creek is entrenched in the Cre- taceous sedimentary rocks predominantly represented by fi ne-grained clastics. The orthometamorphic complex, pre- dominantly composed of greenschist and metamorphosed gabbro and diabase, is referred to as being of Devonian-Car- boniferous age. Further, the creek fl ows through the Neogene sediments represented mostly by sandstones, marls and lime- stones. The lowermost part of the creek dissects the Sava river alluvial sediments (ŠIKIĆ et al., 1978; ŠIKIĆ et al., 1979). 4. SAMPLES AND METHODS Stream water and sediment samples were simultaneously collected from the Rudarska Gradna creek (n=12), the Veliki potok creek (n=11) and the Sava River (n=1) during the sam- pling campaign in October 2010. The sampling sites are shown on Figure 1 and listed in Table 1. Collection and sample handling were conducted in ac- cordance to the standard methodology for the analysis of the selected parameters. Water samples were collected using two half-litre polyethylene (PET) bottles, one for the analysis of anions (SO4 2–, PO4 3–, Cl–, NO3 –) and ammonia, and other, which was pre-acid washed (10%, v/v, nitric acid 65%), for trace metal analysis. The bottles were rinsed three times with stream water prior to fi lling with the water sample. In the Geologia Croatica 66/2Geologia Croatica 132 laboratory, samples for trace metal analysis were fi ltered through 0.45 mm pore cellulose syringe fi lters, acidifi ed with HNO3 to pH<2 and stored at 4°C. Another bottle was frozen at –18°C for subsequent analyses of anions and ammonia. Stream sediment samples were collected and stored in double polyethylene bags. At the laboratory, samples were air dried, disaggregated in an agate mortar, homogenized, and fi nally dry-sieved through stainless-steel screens to the fraction of <125 μm. Water temperature, pH, redox potential, electrical con- ductivity and dissolved oxygen (DO) measurements were conducted in situ on unfi ltered water using a portable Hach Lange HQ40d Multimeasure Device. Nitrate was electrochemically measured using a low- level calibrated nitrate-sensitive electrode (Hach Platinum Series combination electrode, model 51920), connected to a volt meter (Hach SensIon 2). To avoid the interference ef- fects of bicarbonate ions, the pH of samples was adjusted to 3 by the addition of an acidic buffer (H2SO4). Ammonia content was determined using Hach Intelli- CAL™ ISENH3181 gas-sensing ammonia ion selective el- ectrode (ISE) with a replaceable membrane module, refi ll- able outer body, double junction reference and built-in temperature sensor. The measuring range is in the interval between 0.007 mg/L and 14,000 mg/L NH3–N. The sample preparation procedure required the addition of an alkaline buffer (LiOH) to ensure that the ammonia was essentially de-ionised prior to analysis. The chloride ion concentration was determined using a selective Radiometer Analytical chloride electrode ISE25Cl. Sulphate was determined by a titrimetric method. A 0.1 ml volume of methyl orange was added to 100 ml of each water sample. The sample was titrated against 0.1 M HCl to a permanent orange colour. An additional 1 ml of 0.1 M HCl and 25 ml of BaCl2 solution were then added. Samples were heated to boiling and cooled in tap water. After 30 minutes, 25 ml volume of potassium chromate, 1 drop of aluminum chloride and 1.6 ml 0.1 M KOH solutions were added. After 1 hour, any precipitate was removed by fi ltration and 100 ml of each fi ltrate was titrated against 10 ml 10% potassium io- dide solution and sodium thiosulphate using starch indicator. Total phosphates were analyzed by the ascorbic acid method (APHA Standard Method 4500-P; APHA, AWWA, Table 1: Description and location of the sample sites. Sample Gauss-Krüger coordinates Lithology Sample site description x y RG-1 5551315 5068279 Middle Triassic limestone The Rudarska Gradna headwater RG-2 5551349 5068151 Middle Triassic limestone The Rudarska Gradna creek, upstream from the Rude deposit RG-3 5551311 5068284 Middle Triassic limestone The Rudarska Gradna creek, upstream from the Rude deposit RG-4 5551315 5068279 Middle Triassic limestone The Rudarska Gradna creek, upstream from the Rude deposit RG-5 5551823 5068293 Permian unmetamorphosed siliciclastic rocks Right confl uent of the Rudarska Gradna creek RG-6 5551820 5068295 Permian unmetamorphosed siliciclastic rocks The Rudarska Gradna creek, upstream from the Rude deposit RG-7 5552531 5069116 Permian unmetamorphosed siliciclastic rocks Right confl uent of the Rudarska Gradna creek, abandoned waste-rock dump RG-8 5553843 5070412 Lower Triassic clastic sediments The Rudarska Gradna creek, downstream from the Rude deposit RG-9 5554470 5073216 Upper Triassic limestones The Lipovečka Gradna creek RG-10 5554409 5072907 Upper Triassic limestones The Rudarska Gradna creek, downstream from the Rude deposit RG-11 5556019 5073652 Proluvium The Gradna creek, Samobor center RG-12 5556384 5074588 Proluvium The Gradna creek VP-1 5572129 5082230 Paleozoic/Triassic(?) parametamorphic rocks The Veliki Potok creek VP-2 5572251 5081745 Paleozoic/Triassic(?) parametamorphic rocks The Veliki Potok creek VP-3 5572316 5081344 Cretaceous clastic sediments The Veliki Potok creek VP-4 5572617 5080280 Paleozoic/Triassic(?) parametamorphic rocks The Veliki Potok creek VP-5 5572958 5079768 Paleozoic orthometamorphic rocks The Veliki Potok creek VP-6 5573059 5079758 Paleozoic orthometamorphic rocks The Mali Potok creek VP-7 5572994 5079604 Paleozoic orthometamorphic rocks The Veliki Potok creek VP-8 5572763 5077404 Pliocene clastic sediments The Veliki Potok creek, urban area VP-9 5572867 5076130 Pliocene clastic sediments The Veliki Potok creek, urban area VP-10 5573103 5073379 Alluvium The Veliki Potok creek, urban area VP-11 5573816 5071199 Alluvium The Veliki Potok creek, urban area VP-12 5574057 5071255 Alluvium The Sava River Strmić Palinkaš et al.: Environmental geochemistry of the polymetallic ore deposits: Case studies... Geologia Croatica 133 EFA, 1998). Absorbance was measured at 880 nm using a Hach DR4000 spectrophotometer. Acidifi ed sample solutions were used for heavy metal concentration measurements, using the fl ame atomic absorp- tion method for Fe, Mn, Pb, Cu, and Zn and the graphite fur- nace technique for Hg and Cd measurements (Perkin-Elmer AAnalyst 800). Exchangeable metals were extracted from the stream sediments (m = 10 g) using 250 ml of 1 M NH4OAc solution at pH =7.00. The sediment-solution slurry was shaken for 2 h, and the solution separated from the solid by fi ltration. The addition of NH4 + in excess to the soil displaces the rapid ex- changeable alkali and alkaline cations from the exchange sites of the soil particles. The concentrations of metals in the solution were measured with a Perkin-Elmer AAnalyst 800 Atomic Absorption Spectrometer. Bulk stream sediment composition was estimated using energy dispersive X-ray fl uorescence (EDXRF). Measure- ments were made with a W anode and Mo secondary target in orthogonal geometry, with measurement parameters of 40 kV and 35 mA. The irradiation time was 1000 s. X-ray spec- tra were collected with a Si(Li) detector (FWHM=170 eV at 5.9 keV) and were analyzed using QXAS program package- direct comparison method. IAEA “Lake Sediment” was used as a reference material. Highly oriented samples of the <2 μm fraction of se- lected stream sediment samples were prepared for clay min- eral identifi cation on air-dried, ethylene-glycol saturated, and heated (at 400 and 550 °C, respectively) samples according to the procedure described by Starkey et al. (1984). Instru- mental conditions were 40 kV, 40 mA and constant time 5 s, with step scanning (0.02°2θ). 5. RESULTS The chemical characteristics of the water samples from the Rudarska Gradna and Veliki Potok creeks are listed in Table 2. According to the Croatian water quality guidelines (OG 77/98), analyzed samples are classifi ed within Classes I and II, concerning the general physicochemical parameters (pH, conductivity and dissolved oxygen; Fig. 2). According to ni- trate and ammonium concentrations, the water samples be- long to Classes II and III and Classes I and II, respectively Table 2: Stream water analytical data for the Rudarska Gradna and Veliki Potok creeks. Sample pH Eh (mV) DO (mg/l) Conductivity (μS/cm) N-NO3 – (mg/l) N-NH4 + (mg/l) Cl– (mg/l) SO4 2– (mg/l) P-PO4 3– (mg/l) Fe (mg/l) Mn (mg/l) Pb (mg/l) Zn (mg/l) Cu (mg/l) Hg (μg/l) Cd (μg/l) RG-1 7.39 306.7 9.75 520 1.10 0.05 1.74 3.1