SECONDARY MINERAL PARAGENESIS IN THE MAFIC EXTRUSIVE ROCKS FROM THE MT. MEDVEDNICA OPHIOLITE MÉLANGE (CROATIA)

Uzorci djelomično ili potpuno izmijenjenih bazaltnih ekstruzivnih stijena iz ofiolitnog melanža Medvednice analizirani su primjenom optičke mikroskopije i rendgenske difrakcije u prahu. Kemijski sastav minerala u različitim paragenezama određen je pomoću elektronske mikrosonde, a strukture analiziranih mikrodomena su dokumentirane slikama unatrag raspršenih elektrona. Glavni alteracijski procesi uključuju albitizaciju, kloritizaciju, epidotizaciju, prehnitizaciju, pumpellyitizaciju, zeolitizaciju i titanitizaciju. Sporedni procesi su limonitizacija, kalcitizacija, zoisitizacija, sideritizacija, hematitizacija, manganizacija, piritizacija i silicifikacija koji nisu detaljno razmatrani. Albitizacija plagioklasa je dominantni alteracijski proces čije je postupno napredovanje jasno vidljivo na slikama unatrag raspršenih elektrona. Komponente izlužene alteracijom plagioklasa i klinopiroksena, moguće i uz komponente izlužene iz sekundarnih minerala prve generacije, omogućuju stvaranje klorita, epidota, pumpellyita i kalcita. U izvorno vitričnim uzorcima dio klorita i pumpellyita je nastao devitrifikacijom vulkanskog stakla. Alteracijom plagioklasa također nastaju i prehnit i laumontit. Obilato zastupljene nakupine leukoksena u svim uzorcima stijena predstavljaju guste agregate nanokristalnog titanita. Titan za stvaranje leukoksena potječe iz ilmenita odnosno titanom bogatog magnetita. Parageneze s epidotom bilježe komparativno najviši stupanj hidrotermalne alteracije koji odgovara srednjem odjeljku facijesa zelenih škriljavaca.The samples of partly or completely altered basaltic extrusive rocks from Mt. Medvednica ophiolite mélange were analysed by the optical microscopy and by X-ray powder diffraction (XRD). The chemical composition of minerals from different paragenetic assembleges were determinated by electron probe microanalysis (EPMA) and the measured microdomains were documented by back-scattered electrons (BSE) imagery. The most widespread alteration processes that affected analysed rocks are albitization, chloritization, epidotization, prehnitization, pumpellyitization, zeolitization and titanitization. Subordinate processes that include formation of limonite, calcite, zoisite, siderite, hematite, Mn-oxydes, pyrite and SiO2-phases were not constrained in this paper. Albitization is fairly dominant alteration process in all rock and its progradation throughout a plagioclase grain is clearly documented by BSE microphotographs and microprobe chemical analysis. Prehnite and laumontite are sporadic alteration products of plagioclases. The chemical components released during the alterations of plagioclases and/or clinopyroxenes along with components from circulating and percolating heated see water and fluids enable formation of chlorites, epidote and pumpellyite. Chlorites and pumpellyite formed also by devitrification of volcanic glass in vitric rim of pillow lavas. Small patches of leucoxene, that is abundant in all samples, represent dense aggregates of titanite nanocrystals replacing ilmenite and/or Ti-magnetite. Epidote-bearing paragenesis in the analyzed rocks record comparatively the highest alterations grade that correspond to the middle grade of greenschist facies metamorphism typical of upper sequence of a see floor crust

Analyse der Keramik aus der frühmittelalterlichen Siedlung am Standort Ledine bei Torčec

U članku je obrađen keramički materijal iz istraživanja ranosrednjovjekovnog naselja Torčec-Ledine 2002. g. Uz arheološku tipološko-kronološku obradu nalaza, potvrđenu i rezultatima radiokarbonske analize ugljena iz zatvorenih arheoloških cjelina, provedena su i mineraloškopetrografska ispitivanja karakterističnih keramičkih uzoraka. Na osnovi oblika posuda, njihovih osnovnih oblikovnih dijelova, tehnoloških obilježja i načina ukrašavanja kao i njihovih analogija na stratigrafski istraživanim nalazištima širega srednjoeuropskoga i istočnoeuropskog prostora, posude s Ledina datirane su u drugu polovicu 10. i u 11. st. Život se u tom razdoblju u naselju odvijao tijekom nekoliko generacija, odnosno kraćeg odsječka unutar tog vremenskog okvira.Der Artikel befasst sich mit Keramikbeständen, die in der frühmittelalterlichen Siedlung Torčec–Ledine im Jahr 2002 ausgegraben wurden. Neben der archäologischen typologisch-chronologischen Bearbeitung der Funde, deren Ergebnisse auch durch diejenigen der Radiokarbonanalyse von Kohle aus geschlossenen archäologischen Komplexen bestätigt wurden, wurden auch mineralogisch-petrographische Untersuchungen an charakteristischen Keramikexemplaren vorgenommen. Aufgrund der Gefäßformen, ihrer grundlegenden Formteile, technologischer Merkmale und Verzierungsmethoden sowie ihrer Analogien an den stratigraphisch untersuchten Fundorten des weiteren Gebiets Mittel- und Osteuropas wurden die Gefäße von Ledine in die zweite Hälfte des 10. und in das 11. Jahrhundert datiert. In dieser Zeitspanne war die Siedlung während mehrerer Generationen beziehungsweise kürzerer Abschnitte innerhalb dieses zeitlichen Rahmens bewohnt

SEDIMENTNA LEŽIŠTA HEMATITA S MALIM UDJELOM MANGANA NA PODRUČJU BUKOVICE U SJEVERNOZAPADNOM DIJELU PLANINE PETROVA GORA, SREDIŠNJA HRVATSKA

Middle-Permian Gröden deposits crop out on the surface of 0.8 km in the Bukovica area and on the surface of 0.8 km2 in the Mt. Loskun-jska gora in the NW part of the Petrova gora Mountain. One half of the Bukovica Gröden deposits contains in its lowest parts 1 to 5 m (in average 2.5 m) thick hematite bed cutted in blocks by NE-SW stretch¬ing vertical, normal and reverse faults. The hematite bed is unconfor-mably underlain by Lower Permian quartz-wackes (subgraywackes) intercalated with shales intercalations. Ore deposit is explored by 308 boreholes (10509 m) and by numerous adits, inclines and crosscuts on the underground surface of 0.4 km2 . From 1936 to 1941 and from 1953 to 1969 has been exploited 183000 t of ore with (in wt %): 34.0 Si02, 2.9 Al2O3; 59.0 Fe203; 0.15 MnO; 0.7 CaO; 0.4 MgO; 0.1 P, 0.37 S; 1.25 l.o. ign. Proven remaining ore reserves are 250.000 t. Paragenesis is investigated by microscopy of thin and polished sections, XRD, DTA, AAS analyses and by sedimentological analyses. Paragenesis major minerals are of hematite and quartz, with subordinate stable litho-clasts, muscovite (sericite) and scarce kaolinite, calcite, dolomite, and barite. Accessories are zircon, rutile, tourmaline, amphibole, garnet, apatite. Epigenetic veinlets and small nests are built up of quartz or calcite as the main neominerals associated with siderite, barite, kaolinite, pyrite, gypsum. Iron from the Bukovica hematite ore origi¬nated by land weathering during hot climate and transported by rivers and underground waters deposited in river beds, in flood plains and in shallow sea. Precipitation of the Bukovica iron ores took place after the Saalic orogenetic phase. At Hrastno (SE Slovenia) and at Rude nearby Samobor (Croatia), similar hematite deposits were found.Srednjopermski Gröden sedimenti pokrivaju površinu od 0.8 km u području Bukovice i 0.8 km u planini Loskunja u SZ dijelu Petrove gore. Oko polovine Gröden naslaga u Bukovici sadrži u svojim najdon-jim dijelovima 1-5 m (u prosjeku 2,5 m) debeo sloj hematita rasjedan u blokove vertikalnim, normalnim i reversnim rasjedima pružanja NE-SW. Sloj hematita leži nesukladno na donjopermskim kvarcnim grejvakama (subgrejvakama) s interkalacijama šejlova. Rudno je ležište istraženo sa 308 bušotina (10509 m) i brojnim potkopima, galerijama, prečnicima i niskopima na podzemnoj površini od 0,4 km2 . Od 1936. do 1941. te od 1953. do 1969. izvađeno je 183000 t rude sa (u mas %) 34,0 Si02; 2,9 Al2O3; 59,0 Fe203; 0,15 MnO; 0,7 CaO; 0,4 MgO; 0,1 P; 0,37 S i 1,25 g.ž. Dokazane preostale rezerve iznose 250 000 t. Parageneza je istražena mikroskopski u providnim i rudnim preparatima, s XRD, DTA, AAS analizama te sedimentološkim anali¬zama. Glavni minerali su kvare i hematit s podređenim stabilnim litoklastima, muskovitom (sericitom), oskudnim kaolinitom, kalcitom, dolomitom i baritom. Akcesorije su cirkon, rutil, turmalin, amfibol, granat, apatit. Epigenetske žilice i mala gnjezdašca izgrađena su od kvarca ili kalcita kao glavnih neominerala asociranih sa sideritom, baritom, kaolinitom, piritom i gipsom. Željezo hematitnog ležišta Bukovica potječe iz kore trošenja na kopnu za vrijeme vruće klime i transportirano je rijekama i podzemnim vodama te taloženo u koritima rijeka, naplavnim ravnicama i u plitkim unutarnjim morima. Taloženje željezne rude u području Bukovice nastalo je nakon salske orogene faze. Kod Hrastnog (JI Slovenija) i kod Ruda blizu Samobora (Hrvat¬ska) nađena su slična hematitska ležišta

The origin and composition of flysch deposits as an attribute to the excessive erosion of the Slani Potok valley („Salty Creek“), Croatia

Flysch deposits that crop out in the elongated coastal area of the Vinodol Valley (External Dinarides), and particularly in the Slani Potok (&lsquo;Salty Creek&rsquo;) catchment, are characterized by excessive erosion. Formation of badlands, creeping and sliding processes have been related to crystallization of thenardite. Unusually intense erosion is caused by the dispersive effect of sodium on clay particles (derived from pelitic flysch intervals) in solution, as well as by expansion of thenardite during transformation into a deckahydrate (with a four fold increase in volume). The search for a sodium source required for thenardite crystallization has focused on a particular composition of Slani Potok Eocene fl ysch rock types. Slani Potok flysch is predominantly composed of pelitic intervals, with subordinate sandstones and biocalcirudites. Sandstones and biocalcirudites contain appreciable amounts of siliciclastic detritus. Lithic fragments are represented by volcanic rocks revealing porphyry structures - possibly andesite or altered volcanic glass fragments, quartzite, schists, shales, and carbonate grains. High amounts of sodium and barium (0.93&ndash;1.09 % and 267&ndash;276 mg/kg respectively), in marls and sandstones, is essentially ascribed to a particular composition of flysch, refl ecting its area of provenance. A Palaeozoic clastic complex with barite mineralization, (black shales, sandstones and conglomerates), as well as a Mesozoic hornblende andesite located near Fužinski Benkovac in the Gorski Kotar region, are interpreted as flysch source rocks. Sodium at least could be partly leached from the lithic and feldspar grains in clastic rocks, due to circulation of pore fluids. An increased amount of sulphur, barium and strontium in flysch can be related to that of a barite ore complex in the source area of the Gorski Kotar region. Transportation and deposition of material eroded from the hinterland (North of Slani Potok), suggests turbidity current flow was transverse to the main axis of the Eocene foreland basin striking NW-SE.Abstract. Flysch deposits that crop out in the elongated coastal area of Vinodol Valley (External Dinarides) and particularly in the Slani Potok (&lsquo;Salty creek&rsquo;) catchment area have particular composition. Sandstones and biocalcrudites from the flysch in Slani Potok contain appreciable amount of siliciclastic material opposite to the other flysch domains in the External Dinarides where carbonate detritic material prevails. Siliciclastic component of sandstones and biocalcrudites contains ca 50% quartz, 30% lithic and 20% feldspar grains. Lithic fragments are represented by volcanic rocks revealing porphyric structures (possibly andesite) or altered volcanic glass fragments. The differences in flysch composition, also documented by high amount of sodium and barium measuring 0.93-1.09 % and 267- 276 mg/kg, respectively, is essentially ascribed to the different rocks in the provenance area of the Gorski Kotar region located in the hinterland of the Vinodol Valley. Occurrence of andesite near Fužinski Benkovac and Palaeozoic complex with barite mineralization in the Gorski Kotar, are considered as source. Proximity of the source area and its position straight north of Slani Potok imply that the direction of turbidity currents that deposited the flysch sediments in Slani Potok were transverse to the main axis of the Eocene foreland basin striking NW-SE.A particular composition of sandstones and biocalcrudites in the Slani Potok area attributed the formation of thenardite mineral. Source of sodium and sulphur for formation of thenardit is volcanic particles found in the flysch. Unusually intense erosion, having a varied character to the landscape, is caused by dispersive effect of sodium in solutions to clay particles derived from pelitic flysch rocks, as well as by expanding of thenardite while transforming into a deckahydrate (enlarging its volume at least 4 times). </p

SEDIMENTARY LOW-MANGANESE HEMATITE DEPOSITS OF THE BUKOVICA AREA IN THE NORTHWESTERN MT. PETROVA GORA, CENTRAL CROATIA

Middle-Permian Gröden deposits crop out on the surface of 0.8 km in the Bukovica area and on the surface of 0.8 km2 in the Mt. Loskun-jska gora in the NW part of the Petrova gora Mountain. One half of the Bukovica Gröden deposits contains in its lowest parts 1 to 5 m (in average 2.5 m) thick hematite bed cutted in blocks by NE-SW stretch¬ing vertical, normal and reverse faults. The hematite bed is unconfor-mably underlain by Lower Permian quartz-wackes (subgraywackes) intercalated with shales intercalations. Ore deposit is explored by 308 boreholes (10509 m) and by numerous adits, inclines and crosscuts on the underground surface of 0.4 km2 . From 1936 to 1941 and from 1953 to 1969 has been exploited 183000 t of ore with (in wt %): 34.0 Si02, 2.9 Al2O3; 59.0 Fe203; 0.15 MnO; 0.7 CaO; 0.4 MgO; 0.1 P, 0.37 S; 1.25 l.o. ign. Proven remaining ore reserves are 250.000 t. Paragenesis is investigated by microscopy of thin and polished sections, XRD, DTA, AAS analyses and by sedimentological analyses. Paragenesis major minerals are of hematite and quartz, with subordinate stable litho-clasts, muscovite (sericite) and scarce kaolinite, calcite, dolomite, and barite. Accessories are zircon, rutile, tourmaline, amphibole, garnet, apatite. Epigenetic veinlets and small nests are built up of quartz or calcite as the main neominerals associated with siderite, barite, kaolinite, pyrite, gypsum. Iron from the Bukovica hematite ore origi¬nated by land weathering during hot climate and transported by rivers and underground waters deposited in river beds, in flood plains and in shallow sea. Precipitation of the Bukovica iron ores took place after the Saalic orogenetic phase. At Hrastno (SE Slovenia) and at Rude nearby Samobor (Croatia), similar hematite deposits were found