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Epigenetic-Hydrothermal Fluorite Veins in a Phosphorite Deposit from Balaton Highland (Pannonian Basin, Hungary): Signatures of a Regional Fluid Flow System in an Alpine Triassic Platform

DOI:10.3390/min11060640
Authors:
Zsuzsa Molnár at Eötvös Loránd University
Zsuzsa Molnár
Gabriella B. Kiss at Eötvös Loránd University
Gabriella B. Kiss
Ferenc Molnar at Eötvös Loránd University
Ferenc Molnar
Tamás Váczi at Hungarian Academy of Sciences
Tamás Váczi
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Abstract and Figures

The middle Anisian extensional tectonics of the Neotethyan realm developed a small, isolated carbonate platform in the middle part of the Balaton Highland (western Hungary), resulted in the deposition of uranium-bearing seamount phosphorite on the top of the drowned platform and produced some epigenetic fluorite veins in the Middle Triassic sequence. The stable C-O isotope data of carbonates are shifted from the typical Triassic carbonate ranges, confirming the epigenetic-hydrothermal origin of veining. Primary fluid inclusions in fluorite indicate that these veins were formed from low temperature (85–169 °C) and high salinity NaCl + CaCl2 + H2O type (apparent total salinity: 15.91–22.46 NaCl wt%) hydrothermal fluids, similar to parent fluids of the Alpine-type Pb-Zn deposits. These findings indicate that the Triassic regional fluid circulation systems in the Alpine platform carbonates also affected the area of the Balaton Highland. This is also in agreement with the previously established palinspatic tectonic reconstructions indicating that the Triassic carbonate and basement units in the Balaton Highland area were a part of the Southern Alpine. Similar fluorite veining in phosphorite deposits is also known in the Southern Alpine areas (e.g., Monte San Giorgi, Italy). Raman spectroscopic analyses detected H2 gas in the vapor phase of the fluid inclusions and a defect-rich fluorite structure in violet to black colored growth zones. This unique phenomenon is assumed to be the result of interaction between the uranium-rich phosphorite and the parent fluids of the epigenetic fluorite veins.
Location and geological structure of the study area. (a) Major structural units of the Eastern Alps-Pannonian Basin region (modified after [18]) with the positions of major Pb-Zn deposits; (b) facies arrangement of Middle Triassic Formations along the strike of the Balaton Highland [16]. The formations found in the area of Pécsely are marked with a yellow rectangle; (c) schematic geological section of the Pécsely-11 exploration trench (modified after [1]).
Location and geological structure of the study area. (a) Major structural units of the Eastern Alps-Pannonian Basin region (modified after [18]) with the positions of major Pb-Zn deposits; (b) facies arrangement of Middle Triassic Formations along the strike of the Balaton Highland [16]. The formations found in the area of Pécsely are marked with a yellow rectangle; (c) schematic geological section of the Pécsely-11 exploration trench (modified after [1]).
… 
Post Archean Australian Shale normalized REE distribution patterns of fluorite samples from Pécsely.
Post Archean Australian Shale normalized REE distribution patterns of fluorite samples from Pécsely.
… 
Fluid inclusions in fluorite. (a) Two-phased P inclusion near an S1 inclusion plane; (b) two-phased P inclusion close to a grain boundary near an S1 inclusion plane; (c) S2 two-phased inclusion generation; (d) one-phased S3 inclusion generation; (e) the behavior of an S1 inclusion during freezing. Abbreviations used: P, primary inclusion; S, secondary inclusion; L, liquid phase; V, vapor phase; HH, hydrohalite (NaCl•2H2O); AA, antarticite (CaCl2•6H2O); I, ice. The homogenization temperatures (Th(L-V)L) of primary fluid inclusions of the vein filling fluorite crystals are between 85 °C and 169 °C (average = 112 °C, standard deviation = 20.7 °C, number of analyses = 55) (Figure 5a). The average eutectic melting temperature (Teut) of the primary inclusions is −49.8 °C, corresponding to NaCl-CaCl2-H2O type model composition (Figure 5c-e). Melting of hydrohalite (NaCl•2H2O) occurred between −26.5 °C and −21.5 °C and the melting point of ice from −21 to −12 °C, corresponding to 0.64-
Fluid inclusions in fluorite. (a) Two-phased P inclusion near an S1 inclusion plane; (b) two-phased P inclusion close to a grain boundary near an S1 inclusion plane; (c) S2 two-phased inclusion generation; (d) one-phased S3 inclusion generation; (e) the behavior of an S1 inclusion during freezing. Abbreviations used: P, primary inclusion; S, secondary inclusion; L, liquid phase; V, vapor phase; HH, hydrohalite (NaCl•2H2O); AA, antarticite (CaCl2•6H2O); I, ice. The homogenization temperatures (Th(L-V)L) of primary fluid inclusions of the vein filling fluorite crystals are between 85 °C and 169 °C (average = 112 °C, standard deviation = 20.7 °C, number of analyses = 55) (Figure 5a). The average eutectic melting temperature (Teut) of the primary inclusions is −49.8 °C, corresponding to NaCl-CaCl2-H2O type model composition (Figure 5c-e). Melting of hydrohalite (NaCl•2H2O) occurred between −26.5 °C and −21.5 °C and the melting point of ice from −21 to −12 °C, corresponding to 0.64-
… 
Results of the microthermometry study of primary (P) and S1 (secondary) fluid inclusions. (a) Frequency distribution diagram of the homogenization temperature of P inclusions; (b) frequency distribution diagram of the homogenization temperature of S1 inclusions; (c) homogenization temperature vs. total salinity diagram of P and S1 inclusions; (d) vapor-saturated liquidus phase relations in the H2O-NaCl-CaCl2 system [28,29]; (e) salinity compositions of aqueous inclusions trapped in fluorite from Pécsely.
Results of the microthermometry study of primary (P) and S1 (secondary) fluid inclusions. (a) Frequency distribution diagram of the homogenization temperature of P inclusions; (b) frequency distribution diagram of the homogenization temperature of S1 inclusions; (c) homogenization temperature vs. total salinity diagram of P and S1 inclusions; (d) vapor-saturated liquidus phase relations in the H2O-NaCl-CaCl2 system [28,29]; (e) salinity compositions of aqueous inclusions trapped in fluorite from Pécsely.
… 
Results of a Raman line scan. (a) In the colorless or pale purple zones, only a sharp fluorite band appears in the spectrum; (b) in the medium purple zone, the fluorite band and the structural damage are also visible; (c) the intensive Raman feature from dark purple zones obscures the fluorite band.
+3
Results of a Raman line scan. (a) In the colorless or pale purple zones, only a sharp fluorite band appears in the spectrum; (b) in the medium purple zone, the fluorite band and the structural damage are also visible; (c) the intensive Raman feature from dark purple zones obscures the fluorite band.
… 
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Minerals2021,11,640.https://doi.org/10.3390/min11060640www.mdpi.com/journal/minerals
Article
Epigenetic‐HydrothermalFluoriteVeinsinaPhosphorite
DepositfromBalatonHighland(PannonianBasin,Hungary):
SignaturesofaRegionalFluidFlowSysteminanAlpine
TriassicPlatform
ZsuzsaMolnár
1,
*,GabriellaB.Kiss
1,
*,FerencMolnár
2
,TamásVáczi
1,3
,GyörgyCzuppon
4
,IstvánDunkl
5
,
FedericaZaccarini
6
andIstvánDódony
1
1
DepartmentofMineralogy,EötvösLorándUniversity,PázmányP.Street1/C,H‐1117Budapest,Hungary;
vaczi.tamas@wigner.mta.hu(T.V.);dodony@t‐online.hu(I.D.)
2
GeologicalSurveyofFinland,Vuorimiehentie5,P.O.Box96,FI‐02151Espoo,Finland;ferenc.molnar@gtk.fi
3
WignerResearchCentreforPhysics,EötvösLorándResearchNetwork,Konkoly‐ThegeMiklósStreet29–33,
H‐1124Budapest,Hungary
4
ResearchCentreforAstronomyandEarthSciences,InstituteforGeologicalandGeochemicalResearch,
EötvösLorándResearchNetwork,BudaörsiStreet45,H‐1112Budapest,Hungary;czuppon@geochem.hu
5
GeoscienceCenter,DepartmentofSedimentologyandEnvironmentalGeology,UniversityofGöttingen,
Goldschmidtstrasse3,D‐37077Göttingen,Germany;istvan.dunkl@geo.uni‐goettingen.de
6
DepartmentofAppliedGeosciencesandGeophysics,UniversityofLeoben,PeterTunnerStreet5,
A‐8700Leoben,Austria;federica.zaccarini@unileoben.ac.at
*Correspondence:molnarzsuzsa89@gmail.com(Z.M.);gabriella.b.kiss@ttk.elte.hu(G.B.K.)
Abstract:ThemiddleAnisianextensionaltectonicsoftheNeotethyanrealmdevelopedasmall,iso‐
latedcarbonateplatforminthemiddlepartoftheBalatonHighland(westernHungary),resultedin
thedepositionofuranium‐bearingseamountphosphoriteonthetopofthedrownedplatformand
producedsomeepigeneticfluoriteveinsintheMiddleTriassicsequence.ThestableC‐Oisotope
dataofcarbonatesareshiftedfromthetypicalTriassiccarbonateranges,confirmingtheepigenetic‐
hydrothermaloriginofveining.Primaryfluidinclusionsinfluoriteindicatethattheseveinswere
formedfromlowtemperature(85–169°C)andhighsalinityNaCl+CaCl
2
+H
2
Otype(apparenttotal
salinity:15.91–22.46NaClwt%)hydrothermalfluids,similartoparentfluidsoftheAlpine‐typePb‐
Zndeposits.ThesefindingsindicatethattheTriassicregionalfluidcirculationsystemsintheAlpine
platformcarbonatesalsoaffectedtheareaoftheBalatonHighland.Thisisalsoinagreementwith
thepreviouslyestablishedpalinspatictectonicreconstructionsindicatingthattheTriassiccarbonate
andbasementunitsintheBalatonHighlandareawereapartoftheSouthernAlpine.Similarfluorite
veininginphosphoritedepositsisalsoknownintheSouthernAlpineareas(e.g.,MonteSanGiorgi,
Italy).RamanspectroscopicanalysesdetectedH
2
gasinthevaporphaseofthefluidinclusionsand
adefect‐richfluoritestructureinviolettoblackcoloredgrowthzones.Thisuniquephenomenonis
assumedtobetheresultofinteractionbetweentheuranium‐richphosphoriteandtheparentfluids
oftheepigeneticfluoriteveins.
Keywords:fluidinclusions;H
2
gas;Ramanspectroscopy;C‐Oisotopesincarbonate;structurally
disorderedzonesinfluoritecrystals;AlpinetypePb‐Znindication
Citation:Molnár,Z.;Kiss,G.B.;
Molnár,F.;Váczi,T.;Czuppon,G.;
Dunkl,I.;Zaccarini,F.;Dódony,I.
Epigenetic‐HydrothermalFluorite
VeinsinaPhosphoriteDepositfrom
BalatonHighland(PannonianBasin,
Hungary):SignaturesofaRegional
FluidFlowSysteminanAlpine
TriassicPlatform.Minerals2021,11,
640.https://doi.org/10.3390/min
11060640
AcademicEditor:JoelE.Gagnon
Received:19April2021
Accepted:12June2021
Published:16June2021
Publisher’sNote:MDPIstaysneu‐
tralwithregardtojurisdictional
claimsinpublishedmapsandinstitu‐
tionalaffiliations.
Copyright:©2021bytheauthors.Li‐
censeeMDPI,Basel,Switzerland.
Thisarticleisanopenaccessarticle
distributedunderthetermsandcon‐
ditionsoftheCreativeCommonsAt‐
tribution(CCBY)license(https://cre‐
ativecommons.org/licenses/by/4.0/).
Minerals2021,11,6402of21
1.Introduction
TheregularlyrevisedrawmaterialpolicyoftheEuropeanUnioncallsattentionto
theimportanceofcertainmetalsandminerals(e.g.,criticalrawmaterials)forthesustain‐
abledevelopmentofEuropeanindustry.Severalmineralandoreoccurrencesthathave
notbeenpreviouslystudiedindetailhavesignificantpotentialforsomecriticalelements
throughouttheCircum‐PannonianBasin.Re‐evaluationofhistoricallyknownmineraloc‐
currencesmayleadtorecognitionoftheirpreviouslyignoredrawmaterialcontentaswell
astore‐considerationofthemineralpotentialintheregion.Developmentofneworede‐
positmodelsbyre‐investigationofthoseoccurrencesbyapplicationofmodernconcepts
andresearchmethodsmayrevealpreviouslyhiddenexplorationpossibilities.
Thepresentstudyfocusesonapreviouslyknownuranium‐bearingphosphoriteoc‐
currenceatPécselyvillage[1,2],whichislocatedintheBalatonHighlandarea,inwestern
Hungary.ThismineraloccurrenceislocatedintheNorthernTransdanubiumUnit,which
isanallochthonousunitoriginatedfromtheSouthernAlps[3–5].Thephosphorite‐bear‐
ingsedimentaryhorizonsarecutbyepigeneticfluoriteveins.Fluoriteandfluorite‐base
metalveinsystemswitheconomicsignificanceinthepastalsooccurinotherpartsofthe
Transdanubianterrain[6].Therefore,theoccurrenceofthefluoriteveinsatPécselymay
havesignificanceinaregionalmetallogeneticcontext.Thislocalityalsooffersaunique
opportunitytoinvestigatethemineralogicalandgeochemicalconsequencesoftheinter‐
actionbetweenthephosphoriteandthesuperimposinghydrothermalprocessesrespon‐
siblefortheformationofthefluoriteveins.
Resultsofresearchpresentedinthispaperandcomparisonofresultswithsimilar
occurrencesoffluorite‐bearingveinsintheregionprovideanewbackgroundfortheeval‐
uationofthemetallogeneticcontextofthepeculiarmineralizationatPécselyandhighlight
thepotentialroleoftheoverprintingregionalscaleAlpinefluidflowsystemsonolder
mineraldepositsinformationofunusualmetalassociationsandenrichments.Thispaper
alsopresentsanddiscussessomeunusualfeaturesobservedatthislocality,suchasthe
presenceofstructurallydisorderedzonesinfluoritecrystalsandtheoccurrenceofhydro‐
gengasinfluidinclusionsoffluorite.
2.GeologicalBackground
2.1.RegionalGeology
ThestudyareaislocatedinthesouthernpartoftheALCAPA(Alpine,Carpathian,
Pannonian)Megaunit[4,7]alongthenorthernsideofthePeriadriaticBalatonLineament
System(PABL)inwesternHungary(Figure1a).TheALCAPAMegaunitiscomposedof
metamorphosedProterozoictoMesozoicblocksoftheEasternAlpsandofPaleozoiclow‐
grademetamorphicandSouthernAlpine‐typeMesozoiccarbonaceoussequencesofthe
TransdanubianMountainRange(TDMR),theBükkMountains,aswellasthecrystalline
blocksoftheInnerWesternCarpathians[5,7,8].ThecurrentlocationoftheALCAPA
MegaunitwithintheAlp‐Carpathianrealmistheresultofitsnortheastwarddirectedlat‐
eralescapementfromtheEasternAlpinecollisionzone[4,5,7–9].Thetotal350–400km
presentdayoffsetcanbeattributedtothePaleogenetoMid‐LateMioceneextension,lat‐
eralextrusion,andcounter‐clockwiserotationoftheALCAPAMegaunit[9–11].There‐
fore,thePaleozoic,Mesozoic,andPaleogeneunitsalongthePABLcanberegardedas
allochthonousblocksinatectonicmega‐mélange,betweentheALCAPAandZagorje‐
Mid‐TransdanubianZone[12,13].
Theuranium‐bearingphosphoriteoccurrenceatPécselyislocatedinthemiddlepart
oftheBalatonHighland,onthesoutheasternflankoftheNE–SWtrendingsynformof
TDMR.IntheMiddleTriassicsequenceofthisareathePelsonianhemipelagicbasinal
strataoftheFelsőörsLimestonearereplacedherebycoevalplatformcarbonatesofthe
TagyonFormation[14](Figure1b).Thislateralfacieschangeisexplainedbysynsedimen‐
taryextensionaltectonismthathasformedhalf‐grabentypehemipelagicbasinsandiso‐
latedcarbonateplatforms[15].Astheresultofarelativesea‐levelrise,thePelsonian
Minerals2021,11,6403of21
TagyonPlatformwasdrownedandtransformedtoasubmarinemount(theTagyon
High);thefirstoverlyinglayersaboveitbelongtotheupperIllyrianCamunumSubzone
[16].ThiseventwasfollowedbydepositionoftheupperAnisian–Ladiniansequencewith
phosphoritehorizonsandradiolaritelayersonthetopofthesubmarinemount.Phospho‐
ritesareknownonlyatthenortheasternmarginoftheTagyonHigh,atÖregHill,near
thevillageofVászoly[17].Incontrast,radiolaritesandradiolarian‐richcarbonatesoccur
morewidely:inadditiontotheareaoftheTagyonHigh,theyarealsoknownfromthe
easternpartoftheFelsőörsBasinlocatedintheproximityofthehighatAszófő.Theoc‐
currenceofanupperLadinianammonoidassemblageinaneptuniandykecutting
throughtheMiddleTriassicplatformcarbonatesinthenortheasternpartoftheBalaton
Highland[16]indicatestheprolongationoftheextensionaltectonicregimeatleastuntil
theendoftheMiddleTriassic.
Minerals2021,11,6404of21
Figure1.Locationandgeologicalstructureofthestudyarea.(a)MajorstructuralunitsoftheEasternAlps—Pannonian
Basinregion(modifiedafter[18])withthepositionsofmajorPb‐Zndeposits;(b)faciesarrangementofMiddleTriassic
FormationsalongthestrikeoftheBalatonHighland[16].TheformationsfoundintheareaofPécselyaremarkedwitha
yellowrectangle;(c)schematicgeologicalsectionofthePécsely‐11explorationtrench(modifiedafter[1]).
Minerals2021,11,6405of21
2.2.GeologyofthePécselyLocality
ThephosphoritedepositislocatedatÖregHill,betweenthevillagesofPécsely,
Vászoly,andÖrvényes(Figure1b);GPScoordinatesofthesamplingsiteinWGS’84(DM):
N46°55.764′E17°47.147′).Thisdepositwasstudiedindetailduringthe1950s[1]dueto
theobservedradioactiveanomalycausedbytheuraniumcontentofthesedimentary
phosphoriteoccurrence.
Thephosphoritelayers,togetherwiththecross‐cuttingfluoriteveins,arelocatedin
Triassiclimestoneanddolostone(Figure1c).ThehostrockofthephosphoriteistheLadin‐
ianpelagicVászolyLimestoneFormation[17].Thisformationisunconformablyoverlying
theAnisianplatformcarbonateTagyonLimestoneFormationdepositedinalocalbasin
andintercalatedwithfelsictuffintheupperAnisian[14,16].
Thebrownish‐greyU‐bearingphosphoritelayersinthesedimentarysequenceofthe
ÖregHillappearinthreehorizons[2]inalessthan1km2area.Thelowermostandthickest
(max.1.2m)horizonoccursatthedrowningsurfaceoftheTagyonFormationandthe
overlyingtuffaceouscarbonatebedsoftheVászolyFormation.Themiddlesectionwith
varyingthickness(5–20cm)depositedaftertheformationoforganic‐richlimestoneofthe
lowermemberoftheVászolyFormation.Theuppermostthinnestphosphoritehorizon
(max5cm)formsadark,greenish‐greycrustonthebeddingsurfaceoftheVászolyFor‐
mation.Asdescribedby[1],fluorite‐calciteveinsappearalongnormalfaultsandcut
acrossthephosphorite‐richcarbonatesequence(Figure1c).
Thedetailedmineralogicalandgeochemicalcharacteristicsofthephosphoritelayers
arepresentedin[2].Thedominantmineralassemblageinthephosphoriticlayersconsists
ofcarbonate‐bearingfluorapatite(CFA)andcalcite,buthematite,pyrite,andzirconare
alsopresentrarely.TheCFAcontains137–612ppmUand113–261ppmtotalREE+Y.The
UenrichmentisrelatedtotheCFA;individualuranium‐mineralswerenotidentified.The
carbonandoxygenisotopiccompositionsofthehostlimestone(δ18OPDB=from−2.18‰to
−1.54‰;δ13CPDB=from1.86‰to1.99‰)overlapwiththestableisotopefieldofthetypical
MiddleTriassicmarinecarbonates[19],whilethestableisotopevaluesofcarbonatesfrom
veinsaregenerallycharacterizedbydifferentvalues(δ18OPDB=from−8.12‰to−6.42‰;
δ13CPDB=from–5.50‰to1.55‰)suggestingepigenetic‐hydrothermalorigin[2].
Earlierstudies[1]suggestedanepigeneticoriginforthefluoriteveins;however,they
haveleftseveralopenquestionsregardingtheformationprocessesoftheseveins,thein‐
teractionbetweenthephosphoritelayers,andthesuperimpositionofhydrothermalpro‐
cessesaswellastheregionalcorrelationwithsimilarveinsintheTransdanubianUnit.
3.MaterialsandMethods
Inordertoachievetheobjectivessetupduringtheresearchwork,hostrock,phos‐
phorite,andfluoriteveinsampleswerecollectedfromtheareaofÖregHillatPécsely
(Figure1b).Petrographyofsampleswascarriedoutonstandardpolishedthinsections
usingNikonAlphaphotandZeissAxioplanpolarizingmicroscopes.QualitativeSEM‐
EDSanalysesofmineralswerecompletedbyanAMRAY1830Iscanningelectronmicro‐
scope.Theobservationswereperformedwith20kVacceleratingvoltageand1nAbeam
current.Cathodoluminescence(CL)imagingoffluoritewasperformedwiththesame
equipmentusingaGatanMiniCLdetector,with10kVacceleratingvoltageand3nAbeam
current.Quantitativeelectronmicroprobeanalysesofthefluoritegrainswerecompleted
bymeansofaJEOLSuperprobeJXA8200‐typeelectronmicroprobe.Wavelengthdisper‐
sivemodewasused,with15kVacceleratingvoltageand10nAbeamcurrent.Thedetec‐
tionlimitsforeachelementareshownintherelatedtables.
Fluidinclusionpetrographyandmicrothermometrywerecarriedouton100–120μm
thick,double‐polishedsectionsofhydrothermalfluoriteandcalcite,usingaLinkamFT‐
IR600typeheating–freezingstagemountedonanOlympusBX‐51typepolarizingmicro‐
scopeprovidingupto1000timesopticalmagnification.Thecalibrationofthestagewas
donebyanalysesofCO2andpurewatersyntheticfluidinclusions.Theprecisionofthe
Minerals2021,11,6406of21
microthermometricmeasurementswas±0.1°Cbelow0°C,and±1°Cathighertempera‐
tures.Interpretationofthemicrothermometricdatawascarriedoutbyamacroprogram
inMSExcel,developedinaVisualBasicenvironmentbyG.B.Kiss,usingthecalculation
methodsofsalinitiesandisochorsin[20–23].
Ramanmicroanalysesoffluoritestructureandfluidinclusionsinfluoritewerecom‐
pletedusingaHoribaJobinYvonLabRAMHR800UVedgefilterbasedconfocaldisper‐
siveRamanspectrometercoupledwithanOlympusBXFMtypemicroscope.Duringthe
measurements,the532nmemissionofafrequency‐doubledNd:YAGlaser,a600
grooves/mmgrating,50μmconfocalaperture,and50xlongworkingdistanceobjective
wereused.
ThetraceelementcontentoffluoritesampleswasdeterminedbyICP‐MS.Twenty‐
eightelementswereanalyzedusingexternalcalibrationandUandThbyisotopedilution
[24].Singlecrystalsof0.5–2mmsizeweregentlycrushedand0.1–0.2mm(ca.100–200
μg),inclusionfreefragmentswithdifferentcolorswerecarefullyselectedanddissolved
inhot,ultrapureHCl.Thus,thesensitivityandspatialresolutionofthistechniquewas
betweentheclassicalwetchemicalanalysisperformedonpulverizedandhomogenized
samplesofseveralhundredsofmginmassandthelaserablationtechniquethatrepre‐
sentsasmallervolume,butwithconsiderablyhigheruncertainty.Additionally,laserab‐
lationistypicallynotviableonfluoritebecauseofthelowabsorptionofUVlightandthe
frequentfragmentationandsmallexplosionsduringablation.TheREEdistributionpat‐
ternsoffluoritewerecomparedwithCIcarbonaceouschondrite(CI)andPostArchean
AustralianShale(PAAS)[25,26].
Carbonandoxygenisotopeanalysesofcarbonatemineralsassociatedwithfluorite
werecarriedoutbyinsitusamplingofcarbonatesusinganelectricmicrodrillwithabit
diameterof0.6mm.Theresulting150–200μgsamplesweredissolvedbycarbonate‐or‐
thophosphoricacidreactionat72°C[27],andthealiquotswereanalyzedusinganauto‐
matedGASBENCHIIsamplepreparationdeviceattachedtoaThermoFinniganDelta
PlusXPmassspectrometer.Theisotopecompositionsareexpressedasδ13Candδ18Oin
‰relativetoV‐PDB(ViennaPeeDeeBelemnite),accordingtotheequation:δ=
(Rsample/Rstandard−1)×1000,whereRisthe13C/12Cor18O/16Oratiointhesampleorinthe
internationalstandard.Theprecisionwasbetterthan0.15‰forCandOisotopedata,
basedonreplicatemeasurementsofinternationalstandards(NBS‐19;NBS‐18)andin‐
housereferencematerials.
4.Results
4.1.FieldDescription,Mineralogy,andPetrographyoftheFluoriteVeinsandtheirHostRock
Duringthefieldwork,fluorite–dolomite–calciteveinsweresampledinanaban‐
donedpitaswellasinthewastedumpofthatpitintheareaofÖregHillatPécsely(Figure
1b).ThelocationofveinsiscontrolledbyNW–SEorientednormalfaultsdippingby70°
totheNEinwhitepinkishandwhiteyellowishlimestone,dolomitizedlimestone,and
dolomite.Theveinscanbefollowedinaseveralmeterslong,~10cmwidezonesalong
thefaults.Thehostrocksarebrecciatedalongthefaults(Figure2c).Thethicknessofthe
faultbrecciais~5cm.Theclastsinthemonomictbrecciaaretypicallyangular,rarely
rounded,elongatedinshape,2mmto3cminsize,whichindicatesmovementwithina
shortdistance.Theratiooffragmenttocementis4to1.Thecrystalsoffluorite,dolomite,
andcalcitearelocatedaroundtheclastsofthebrecciaaswellasinsatelliteveins(Figure
2a,b).Fluoriteanddolomiteinthematrixofthebrecciaalsoappearinnestsandcavities,
inwhichtheamountofdolomiteishigher(Figure2a,b).Thefluoritegrainsarecharacter‐
izedby0.1–2mmsizeanddarkpurplecolor,andthezonationofthecrystalscanoftenbe
observedmacroscopically.Thesaddledolomiteinthesebrecciaveinsisoftentranslucent
andcolorlessorwhite,butinthenests,itisalwaysnottransparent,withwhiteorpale
rosecolor.Texturalfeaturesindicatethatdepositionofdolomiteandcalciteoutlastedthe
crystallizationoffluoriteinthebrecciamatrixandalsointheconnectedveinlets.
Minerals2021,11,6407of21
Observationsinthepolarizingmicroscopeconfirmedthatthelightpinkishcolorof
thehostrockcanberelatedtothepresenceofdisseminationofsmallflakes(2–5μm)of
hematitecrystals(Figure2a).Theindividualhematiteflakesarerectangularandhexago‐
nalinshapewithcherryredcolor.Dolomiteprismsarecommonlycorrodedbyhematite
flakes(Figure2b,d,e)andshowunduloseextinction.Microscopicobservationsonfluorite
anddolomiteshowedthattheoutlinesofthesecrystalsareoftencorroded,andthegrains
aremostlycrushedorfragmented.Individualfluoritecrystalsshowfromdarkpurpleto
colorlessgrowthzoneswithallshadesofpurple.TheSEM‐CLimagesoffluoritealso
showaveryfineandcomplicatedzonation(Figure2i,j).
Themacroscopicallyvisibledarkbandsconsistofseveralthin(10–100μm)darkpur‐
plezones(Figure2d,e).Undercrossedpolarizers(+N),incontrasttothenormalisotropic
behavior,thesecrystalsdonotshowfullextinction,andzoningindarkgreycolorisstill
visible(Figure2e).
ObservationsintheSEMrevealedthatthehostrocklimestoneofphosphoritehori‐
zonsandfluoriteveins(VászolyLimestoneFm.)ispartlyorentirelydolomitized.Inthe
partlydolomitizedrockbodies,variousfabric‐selectivedolomitetypeswereobserved.In
thebeds,scattered,irregularaggregatesofveryfinelycrystallinedolomiteand/or15to
200μmsizedeuhedral,subhedral,andanhedraldolomitecrystalsorcrystalclustersoccur
inthemicriticfabricelements,testifyingtomicrite‐selectivedolomitization(Figure2c).
Coarselycrystallinemosaicofcalciteand/orcoarselycrystallinedolomiteoccursinthe
centralpartofvugs(Figure2f).Intheentirelydolomitizedintervals,fabric‐destructive
dolomiteprevails,althoughghostsofsomecalcitegrainsarelocallyrecognizable.This
dolomiteistypicallyfine‐to‐mediumcrystalline,exhibitingplanar‐subhedralandnon‐
planar‐anhedraltexturewithcoarselycrystallinedolomitecementinvugs.Saddledolo‐
miteoccurslocallyasthelastcementphaseinthesevugs.Thecarbonatemineralsinthe
matrixofthebrecciahavealsosufferedcomplicateddolomitization/dedolomitizationpro‐
cess(Figure2g),wherethesaddledolomiteisdedolomitized.Furthermore,thepresence
offine‐grainedcalcitewasalsoobservedamongthefluoritegrainsaswellasinhealed
microfracturesoffluorite(Figure2g,h).
Resultsofpetrographysuggestthatthesequenceofprecipitationofthemineralswas
asfollows:fluoriteanddolomitewerecrystallizedtogetherattheearlystagesofveining,
buttheformationofdolomitelastedlonger,andthentheresidualspaceandcrackswere
filledupbycalcite,whichalsoresultedindedolomizationofthesaddledolomite.The
veinfillingmineralsprecipitatedfromthesamefluid,whichcontributedtothecomplex
dolomitization–dedolomitizationhistoryofthepartlydolomitizedhostrocklimestone.
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Figure2.Mineralogyandpetrographyofthefluoriteveinsandtheirhostrock.(a)Macroscopicpictureofthecontactof
thefluorite–calcite–dolomiteveinsandhostrock;(b)Microscopicpictureofthefluorite–calcite–dolomiteveins.Theveins
containfluorite,dolomite,calcite,andhematitegrains.Thepurplezonationofthefluoritegrainsisalsovisible.(c)Micro‐
scopicpictureofthedolomitizedlimestonehostrock;(d)microscopicimageoftheareaindicatedbyanorangesquarein
thepictureb;(e)magnifiedmicroscopicimageoftheareaindicatedbyanorangesquareinpictureb.Theisotropicfluorite
crystalsshowopticalanomaly(e.g.,lackoffullextinction)undercrossedpolarizers(+N)ofthemicroscope;therefore,the
zonationisvisible;(f)BSEimageofthehostrock;(g)BSEimageoffluoriteanditsenvironment.Thecomplexdolomitiza‐
tionhistoryoftheveinisalsovisible.Thefluoritegrainsareoftenfragmented,andcalcitefillsinthespacebetweenthem;
(h)BSEimageofthevein‐fillingminerals;(i)SEM‐cathodoluminescence(CL)pictureofthefluoritegrainsandfragments;
(j)BSE,elementmappingandSEM‐CLimagesofthesamearea.Abbreviationsused:cal,calcite;dol,dolomite;fl,fluorite;
hem,hematite.
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4.2.MineralChemistry
Thefluoriteischaracterizedby15–20ppmREE+Yconcentrations.AllsixPAAS
normalizedfluoriteanalysesshowsimilarREEpatterns(Figure3)thatarestronglyde‐
pletedinlightandheavyREEcomparedwiththemiddleREE.TheycharacterizedlowLa
andCevalues.Allanalyzedgrainscontainedseveralpurplezones;therefore,nocorrela‐
tioncouldbeestablishedbetweenthecolorofthezonesandtheconcentrationsofana‐
lyzedelements.
Figure3.PostArcheanAustralianShalenormalizedREEdistributionpatternsoffluoritesamplesfromPécsely.
4.3.CarbonandOxygenIsotopesinVein‐FillingCarbonates
Theδ18OPDBvaluesrangefrom−7.79‰to−6.76‰,whiletheδ13CPDBvaluesrangefrom
−7.16‰to2.12‰inthehydrothermalsaddledolomiteassociatedwithfluoriteinthe
veins(Table1).Bycomparingtheobtainedresultswiththestableisotopiccompositionof
sedimentarycarbonatesprecipitatedinequilibriumwithDIC(dissolvedinorganiccar‐
bon)inTriassicseawater[19],mostofthevaluesplotoutsideofthemarinecarbonatefield
(δ18OPDBvaluesrangefrom−2.18‰to−1.54‰;δ13CPDBvaluesrangefrom1.86‰to1.99‰).
Table1.StableisotopedataofveinfillingsaddledolomitefromPécsely.
Numberδ
13CPDB(‰)δ
18OPDB(‰)Numberδ
13CPDB(‰)δ
18OPDB(‰)
11.92−7.4613−4.12−7.36
21.62−7.6314−3.78−7.41
31.66−7.6615−4.07−7.39
41.57−7.6916−3.05−7.45
51.57−7.5817−7.11−6.93
6−6.91−7.1218−6.79−6.78
7−7.16−7.1519−7.15−6.92
8−1.63−7.5420−5.78−7.36
9−3.08−7.50211.85−7.17
10−5.60−7.51221.91−6.76
11−4.71−7.79232.12−7.58
12−4.24−7.44242.09−7.53
4.4.FluidInclusionPetrographyandMicrothermometry
Accordingtothepetrographicobservations,fourfluidinclusionassemblagescanbe
distinguishedinfluorite:oneofthemconsistsofprimaryandthreeotherassemblages
consistofsecondaryfluidinclusions(Table2,Figure4a–d).
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The5–30μmlargerectangular(negativecrystal)shaped,aqueous,two‐phase,liquid
andvapor(L+V)primaryinclusions(P)occurinisolationorinclustersof2–3smallin‐
clusionsapartfromthehealedmicrocracks,alongthegrowthzonesoffluorite(Figure
4a,b).Theratioofthevaportoliquidphaseisconstantlyaround0.15atroomtemperature,
indicatingthattheseinclusionswereentrappedfromahomogenousparentfluid(Figure
4a,b).
Table2.Resultsofthefluidinclusionmicrothermometry.
PrimarySecondary
S1S2S3
Numberofmeasure‐
ments5521829‐
Size5–30μm5–15μm5–30μm5–10μm
Shaperectangular(nega‐
tivecrystalshape)angular irregularroundish
Phases85%L+15%V95%L+5%V95%L+5%V100%L
Th85–169°C42–121°C45–65°C‐
Teut−57.7to−44.0°C−58.0to−46.0°C‐ ‐
TmeltHydrohalyte−26.5to−21.5°C−25.0to−21.2°C‐ ‐
TmeltIce−21.0to−12.0°C−20.8to−13.7°C‐ ‐
Apparenttotalsalin‐
ity
15.91–22.46NaCl
wt%17.35–22.93wt%‐ ‐
Calculatedsalinity
0.64–9.98CaCl2
wt%+
9.59–20.64NaCl
wt%
0–8.47CaCl2wt%
+
12.4–20.01NaCl
wt%
‐ ‐
Figure4.Fluidinclusionsinfluorite.(a)Two‐phasedPinclusionnearanS1inclusionplane;(b)two‐phasedPinclusion
closetoagrainboundarynearanS1inclusionplane;(c)S2two‐phasedinclusiongeneration;(d)one‐phasedS3inclusion
generation;(e)thebehaviorofanS1inclusionduringfreezing.Abbreviationsused:P,primaryinclusion;S,secondary
inclusion;L,liquidphase;V,vaporphase;HH,hydrohalite(NaCl∙2H2O);AA,antarticite(CaCl2∙6H2O);I,ice.
Thehomogenizationtemperatures(Th(L‐V)L)ofprimaryfluidinclusionsofthevein
fillingfluoritecrystalsarebetween85°Cand169°C(average=112°C,standarddeviation
=20.7°C,numberofanalyses=55)(Figure5a).Theaverageeutecticmeltingtemperature
(Teut)oftheprimaryinclusionsis−49.8°C,correspondingtoNaCl–CaCl2–H2Otypemodel
composition(Figure5c–e).Meltingofhydrohalite(NaCl∙2H2O)occurredbetween−26.5
°Cand−21.5°Candthemeltingpointoficefrom−21to−12°C,correspondingto0.64–
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9.98CaCl2+9.59–20.64NaClwt%(n=8)salinity(Figure5e).Theapparenttotalsalinities,
calculatedfromtheicemeltingtemperaturesusingNaCl–H2Omodelcompositionand
expressedinNaClequivalentweight%,arefrom15.91to22.46(Figure5c).
Thefracture/cleavageplanehostedS1inclusionsoffluoritealsohaveanangular
shapewithabout5–15μmsizes(Figure4a,b),andtheratioofthevaportoliquidphaseis
around0.05.Theseobservationsindicateentrapmentfromahomogenousparentfluid.
Theirhomogenizationtemperature(Th(L‐V)L)isbetween42–121°C(average=71°C,
standarddeviation=11°C,numberofmeasurements=218)(Figure5b).Theaverageeu‐
tecticmeltingtemperature(Teut)ofS1inclusionswas−51.4°C,sotheircompositioncan
alsobemodelledintheNaCl–CaCl2–H2Osystem(Figure4e,Figure5c–e).Themelting
temperatureofhydrohaliteisfrom−25°Cto−21.2°C,andthemeltingtemperatureofice
isfrom−20.8°Cto−13.7°C.ThesedataindicatethattheCaCl2contentoftheseinclusions
isbetween0–8.47wt%,whereastheNaClcontentisbetween12.4–20.01wt%(Figure5e).
Theapparenttotalsalinitycalculatedfrommeltingtemperatureoficeandexpressedin
NaClequivalentweight%usingtheNaCl–H2Omodelsystemis17.35–22.93(Figure5c).
Figure5.Resultsofthemicrothermometrystudyofprimary(P)andS1(secondary)fluidinclusions.(a)Frequencydistri‐
butiondiagramofthehomogenizationtemperatureofPinclusions;(b)frequencydistributiondiagramofthehomogeni‐
zationtemperatureofS1inclusions;(c)homogenizationtemperaturevs.totalsalinitydiagramofPandS1inclusions;(d)
vapor‐saturatedliquidusphaserelationsintheH2O–NaCl–CaCl2system[28,29];(e)salinitycompositionsofaqueousin‐
clusionstrappedinfluoritefromPécsely.
Thetwo‐phase(L+V)S2inclusionsoccurinfracturesthathavedifferentorientations
comparedtothehealedfractureswiththeS1typeofinclusions.OccurrenceofS2type
inclusionsistypicalinfan‐likeinclusionplanes.InclusionsinS2fractureshaveirregular
shapeswith5–30μmsizes(Figure4c).Thevaportoliquidratioisalwayslessthan0.05;
thissuggeststhattheseinclusionsalsoentrappedahomogeneousparentfluid.Theho‐
mogenizationtemperatureoftheS2inclusionassemblageisfrom45to65°C(average=
55°C,standarddeviation=5.24°C)(n=29).Duetotheobservedmetastabilityduringthe
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microthermometrystudies(e.g.,disappearanceofthevaporphaseduringfreezingand
meltingofice/hydrohaliteintheabsenceofvaporphase),compositionandsalinitiesfor
theseinclusionscannotbedetermined.
TheS3inclusionsarefilledupbyaliquidphaseatroomtemperatureandtheirsizes
areabout5–10μm(Figure4d)withroundishshapes.Thisgenerationofinclusionsap‐
pearsalonglarge,intersectingfractureplanes.Nomicrothermometrymeasurementswere
performedontheseinclusions.
4.5.RamanSpectroscopyofFluidInclusionsandFluorite
ThefluidinclusionmicrothermometrystudywascompletedbyRamanspectros‐
copy.ThismethodhelpedtocheckthecalculatedsalinityvaluesofthePandS1inclusions
(incaseswhereonlyalowamountofmicrothermometrydatawasavailableduetometa‐
stability)aswellasaimedtodeterminethegascontentofthevaporphase.
Basedon[30,31],theO‐Hstretchingregion(2800–3800cm−1)inRamanspectraof
aqueoussolutionsissensitivetochangesinthesaltconcentration.Thispermitsdetermi‐
nationofthesalinityintheaqueousphaseoffluidinclusions(atroomtemperature)by
calculatingskewingparametersfromRamanmicroprobespectra.Inthisstudy,theOH
RamansignalisfittedusingtwoGaussiansub‐bands,theconcentrationequilibriumcon‐
stantwasdetermined,thenthecalibrationequationofCl−molaritywasdetermined[31].
ThecalculatedtotalsalinityofthePinclusionswas13.9and19.0NaClequivalentwt%,
andtheS1inclusionswere13.0and17.2NaClequivalentwt%.Theseresultsareingood
agreementwiththemicrothermometrydata.
AccordingtotheRamanspectraoftheVphaseofPandS1inclusions,theycontain
H2gas.ThecharacteristicbandsofH2gasareat355,588,816,and1037cm−1(Figure6),
whicharerelatedtotherotationaltransitionsofthegasmolecule.
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Figure6.ResultsofRamanspectroscopyoffluidinclusionsandfluorite.(a)Ramanspectrumoforderedfluorite;(b)Ra‐
manspectrumoftheliquidphaseinaPinclusioninfluorite;(c)RamanspectrumofthevaporphaseofaPinclusion
showingthecomplexrotationalbandstructureofH2.TheRamanbandoforderedfluoriteisstillpresent,whilefourother
intensitiesindicatestructurallydisorderedfluorite(indicatedbyredarrows);(d)Ramanspectrumofthevaporphaseof
anS1inclusion.TheH2rotationalbandsarealsoobservable.
UsingRamanspectroscopy,wealsoaimedtoinvestigatetherelationshipsbetween
finecolorzoning,aswellastheanomalousopticalbehaviorandthestructuralstateofthe
fluoritecrystals.Colorlesstransparentfluoriteischaracterizedbyasingle,sharpbandat
318cm−1.Inthedarkvioletzones,whichalsoshowanomalousopticalbehavior,broad
bandsappearbetween80–480cm−1,andthebaselineofthespectraisalsoelevated.This
phenomenonmaybeexplainedbythechangesinthestructureoffluorite:thedarker
zonesoffluoritearepartlyorextensivelydisordered,whereasthecolorlessandclear
zoneshaveanorderedstructure(Figure7).Thisphenomenonsystematicallyoccurs
withinthefluoritecrystals.Thesamephenomenonwaspreviouslydescribedforpurple
fluoriteusedashistoricpigments[32].Thecauseofthedisorderwasnotidentifiedduring
therecentinvestigation.Note,however,thatthewidthofindividualcoloredzonesisin
casesverysmall,approachingorpossiblybelowthelateralopticalresolution(<1μm)of
theRamanmicroscope.Spectrashowingmixedcrystallineanddisorderedfluoritesigna‐
turesmaythereforearisefromthepresenceofdamagedandorderedstructuresinthe
excitationvolume.TheFWHM(FullWidthatHalfMaximum)offluoritebandswasalso
examined.Thereisnoobservablebandbroadeningnearthedisorderedzones;hence,
thereisasharpboundarybetweentheorderedandthedisorderedstructures.
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Figure7.ResultsofaRamanlinescan.(a)Inthecolorlessorpalepurplezones,onlyasharpfluoritebandappearsinthe
spectrum;(b)inthemediumpurplezone,thefluoritebandandthestructuraldamagearealsovisible;(c)theintensive
Ramanfeaturefromdarkpurplezonesobscuresthefluoriteband.
5.Discussion
5.1.FormationConditionsoftheFluoriteVeins
Fieldandpetrographicobservationssupportthatthefluoriteveinscuttingthephos‐
phoritelayerswereformedduringlowtemperatureepigenetichydrothermalprocesses.
Theresultsoffluidinclusionpetrographyandmicrothermometryindicatethatthepri‐
maryandtheS1generationofsecondaryfluidinclusionsoffluoritehaveasimilarap‐
pearance(size,shape,phaseratio),andtheirentrapmenttookplacefromahomogeneous
fluid.Therefore,thehomogenizationtemperaturesfortheprimaryfluidinclusionsof
fluoritecanbeevaluatedasminimumformationtemperatureofveins,e.g.,theminimum
temperatureofveinformationwasmostprobablybetween90and130°C(Figure5).Much
highertemperaturesforveinformationaregeologicallyunreasonable,astheisochorsof
thesesalinefluidinclusionsarefairlysteep,andthehostrockisnon‐metamorphosed.The
scatteringofdatatowardhighertemperaturesmayreflectsomeunrecognized“necking
down”[33]processes,ortemperaturefluctuationduringthegrowthofzonedcrystals.
However,thecorrodedcontourandfragmentationofthefluorite(anddolomite)crystals
maysuggestthatthedeformationeventsresultingintheopeningoftheveinscontinued
alsoaftertheformationoffluorite.
TheΣREEcontentsarelowinthefluoritesamplesofthestudyarea.Fluoriteswith
lowΣREEarebelievedtobederivedfromasedimentaryenvironment[34].ThelowCe
valuesinthestudiedfluoritesindicatethatthehighoxygenfugacityinthesourceofthe
hydrothermalfluidshasledtotheCe3+oxidationandCe4+immobilization[35].Addition‐
ally,thenegativeCeanomalycanbeinheritedfromseawater[36].Thisisbecausemarine
carbonatesshownegativeCeanomaly[37].InadditiontolowCevalues,thesamples
showlowREEconcentrations.Accordingly,itcanbeconcludedthatREEpatternsof
Minerals2021,11,64015of21
Pécselyfluoritesshowthatthehydrothermalfluidinteractswithmarinecarbonates,i.e.,
wemayassumethatbasinalbrinesarethemainsourceofthemineralizationfluids.
TherelativelylowhomogenizationtemperatureswithCa‐enriched,highsalinity
compositionsaresimilartofluidinclusioncharacteristicsofsalinebasinalfluidsandes‐
peciallytoMississippiValleyorIrishTypesediment‐hostedepigeneticPb‐Znoredeposits
[38](Figure8).
Figure8.Salinityvs.Thillustratingtypicalrangesforinclusionsfromdifferenttypesofdeposits
[38].Forcomparisonpurposes,fluidinclusiondatafortwoAlpine‐typeepigeneticlead‐zincdepos‐
itsintheDrauRange(Bleiberg,Mežica)[39],thePb‐Zn‐fluoritemineralizationoftheVelenceMts.
[6],andtheprimaryfluidinclusionsfromPécsely(greendots)arealsoshown.Fluidinclusionsfrom
PécselyplotwithintheMVTfieldandoverlapwithdatafromMežica,Bleiberg,andVelenceMts.
ThemicrothermometricresultsoftheS1inclusiongenerationsuggestthatthefor‐
mationoffluorite‐containingveinswasoverprintedbyasubsequent,lowertemperature
fluidflow.ThecompositionofS1fluidinclusionsisalmostidenticaltothoseofthepri‐
maryinclusions,whilethehomogenizationtemperaturesareslightlylower(with70–
80°Casthemostcommonvalues)withalmostidealandrelativelynarrownormaldistri‐
bution(Figure5).ThesepropertiessuggestthatS1inclusionswereformedduringthe
waning,lowertemperaturestageofthesamehydrothermalactivity,whentheinfiltrations
ofanewpulseofthesametypeoffluidwasgeneratedbyfracturingoftherocks.
Althoughthecarbonandoxygenisotopedataobtainedfromthecarbonatesassoci‐
atedwithfluoriteveinsaredifferentfromthesedimentarycarbonateofthehostrock(Fig‐
ure9),itisassumedthatthefluidultimatelyoriginatedfromPermianorTriassicburied
seawater(δ18OSMOW≈0‰,[19]),asnodirectmagmaticactivityhasbeenidentifiedinthis
period[2,40].Evenduringtheformationofphosphorite‐bearinglayers,whichpreceded
thedevelopmentofthefluoriteveinsandwerecontemporarywithvolcanicactivity[2],
themagmaticcontributionwasinsignificanttotheparentfluid[2].Nevertheless,thesta‐
bleisotopecompositionsofthedolomitesassociatedwithfluoriteveinsoverlapwiththe
datafromthefracturefillingandbrecciacementingcarbonateofthephosphoritedeposit
[2](Figure9).Thenegativeδ18Ovaluesmightindicatearelativelyelevatedformationtem‐
perature,asutilizingthedolomite–wateroxygenfractionequationby[41]andassuming
seawateroxygenisotopecomposition(δ18OSMOW≈0‰,[19])fortheparentfluid,thefor‐
mationtemperatureisabout70–75°C.Thisobservationfitswellwiththeassumedevolu‐
tionofthishydrothermalsystembecausethecarbonatesrepresentalaterstageinthemin‐
eralparagenesis.Inaddition,thegeneralmorphologyofthecrystalalsosuggestsslightly
Minerals2021,11,64016of21
elevatedtemperature,assaddledolomiteisbelievedtoformabove60°C[27].Alterna‐
tively,itshouldbeassumedanexoticfluidcharacterizedbynegativeoxygenisotopecom‐
position.However,thislaterscenarioisnotsupportedbyanyevidence.
Incontrasttotheoxygenisotopecomposition,theδ13Cvaluescoveraverywide
rangefrom+2.12‰to−7.16‰.Thenegativevaluemightberelatedtoorganicderived
carbon,whichcanhavemultiplesources.Thefirstsourcecouldbetheorganicrichphos‐
phoritelayers(theirTOC—totalorganiccarbon—are0.58–0.77%[42]),whicharecutby
thefluoriteveins.AnothersourcecouldbetheunderlyingPermianredsandstone,which
isinterpretedasapotentialsourceofvein‐formingfluid,containingburiedplantresiduals
inaddition.Theinteractionofthefluorite‐formingfluidwiththeseformations(Figure1c)
islikelytoberesponsiblefortheobservednegativeδ13Cvalues.Inaddition,theobserved
variabilityincarbonisotopecompositionisprobablyassociatedwiththedegreeofthis
interaction.
Figure9.Stableisotopedataofcalcitegrainsfromfluoriteveinsaresimilartothecarbonandoxygen
isotopiccompositionsoftheepigeneticcalcitecrystalsfoundinphosphorite,suggestingtheircom‐
mon,hydrothermalorigin[2].InthefiguretherangeofMiddleTriassiccarbonatesisalsoshown
[19].
5.2.TheOriginofH2inFluidInclusionsofFluorite
FluoritecrystalsfromtheareaofPécselyhaveauniquecharacteristic:thepresence
ofH2gasinthevaporphaseofPandS1fluidinclusions.Theauthorsof[43,44]examined
fluidinclusionsinquartzanddolomitegrainsfromPrecambrianuraniumdepositsby
Ramanspectroscopy,wheretheinclusionscontainedH2withorwithoutO2.Concerning
theoriginofthegas,ithasbeenconcludedthatchemicalreactionsofwaterororganic
matter,nuclearreactions,andindirectchemicalreactionsofradiolysisprocessesleadto
theenrichmentofH2andothergasesinhydrothermalfluids.
IntheBalatonHighlandarea,thePermian–Triassicsandstonelayersinthebasement
containtracesofredox‐frontcontrolleduraniumenrichments[18,45],andthephosphorite
layersatPécselyarealsoenrichedinuranium.Therefore,itisplausibletoestimatethat
thehydrothermalfluidsresponsibleforthefluoritemineralizationwerealsointeracting
withthoseuraniumrichzonesandwereenrichedinhydrogen.However,amodelfavor‐
inglocalconditionswouldbemoreacceptableregardingtheoriginofthegascontentof
theinclusionsbecausefluidinclusionswithsimilargascontentwerenotdescribedfrom
thePb‐ZndepositsalongthePABL(seee.g.,[6]).FluoriteandthehostrocksatPécsely
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haveelevateduraniumcontent;therefore,thepresenceofhydrogeninfluidinclusions
couldmoreprobablyberelatedtotheinsitu(withininclusion)radiolysisofwater.
Presumably,thephosphoritestrataareresponsibleforthehydrogengasinfluidin‐
clusionsoffluoriteandthestructuraldegradationofthecrystals,whichweredetected
duringRamanspectroscopicinvestigation.Duetothedirectstratigraphicrelationshipbe‐
tweenfluoriteandphosphorite,theradiolysisoffluoritefluidinclusionshasbeencontin‐
uousfor~235millionyears,whichallowedthedetectionofH2despitepossiblediffusion.
5.3.MetallogenicImplications
TheAlpine‐Balkan‐Carpathian‐Dinaride(ABCD)metallogenicandgeodynamic
provincesincludephasesofearlyintracontinentalrifting,advancedrifting,oceanization,
subduction,andemplacementofophiolites;collisionalandpostcollisionaldeformation
eventswithsynkinematicgraniteplutonismandvolcanism;andpost‐collisionaligneous
activity[46].Theoccurrenceofphosphoritelayersandfluoriteveinsarelocatedinthe
TransdanubianMountainRange,whichisboundedbythePeriadriaticBalatonLineament
System(PABL),themostsignificantshearzoneoftheABCDregion.Thestructurallyde‐
formedzoneofthePABLhasbeenthemainchannelformagmaandfluidflowsinvarious
geotectonicenvironmentsduringandsincetheMesozoicera.TheformationofCretaceous
lamprophyricmagmatism(e.g.,Eisenkappel),PaleogeneandNeogeneintermediatemag‐
matism(e.g.,Recsk,VelenceMts.),dioriteintrusionsandstratovolcanoes(e.g.,Adamello,
Bergerplutons,Pohorjeintrusions)aswellasvarioustypesofmineralization(Cu‐
porphyry,epithermal,epigeneticPb‐Zn)areclearlyorapparentlycontrolledbythere‐
peatedreactivationofthisfaultsystem[6,13,46].TheTriassicriftingandoceanization—
associatingintensivesubmarinevolcanism—processestookplacealmostsynchronously
withintheABCDregion,creatingcarbonateplatformsonthepassivecontinentalmargin.
AlongthePABL,anumberofepigenetic‐hydrothermalPb‐Znoredepositsoccurinthe
TriassicsedimentaryrocksoftheNorthernandSouthernCalcareousAlps(e.g.,Bleiberg,
Mežica,Topla,Raibl,Salafossa)(Figure10a,b),andapartfromthe“majors”,thereare
morethan200smallerbutsimilarPb‐Znoccurrencesknownintheregion[46].Theore
formingfluidsofthesedepositsarecharacterizedby122–200°Candhighsalinity(7–
25NaClequivalentwt%)(Figure8)wherethemetalswereleachedandtransportedbyCl‐
richfluids[39,47].Theauthorof[48]hadrecognizedlow‐temperatureandhighsalinity
calcium‐chloride‐enrichedsecondaryfluidinclusionsinregional‐scaledistributioninthe
rockformingquartzofgraniteintheVelenceMts.,whicharelocatedabout50kmtothe
eastofthecurrentstudyarea(Figure1a).Parentfluidsofthoseinclusionswereinter‐
pretedas“basinalfluids”,andlaterresearchby[6]showedthattheyrecordaregional
fluidflowsystemofTriassicage,whichalsoproducedPb‐ZnmineralizationintheVar‐
iscangraniteoftheVelenceMts.Fluoriteisalsoacommonmineralinthosebase‐metal
richveins[6]alsoemphasizingthesimilaritiesbetweenthosefluidsandoreformingflu‐
idsofthecarbonatehostedlead–zincmineralizationsintheAlps(Figure8)[39].
Theauthorsof[49,50]investigatedtheREEgeochemistryoffluoritefromtheAlpine
Pb‐Zndeposits.ComparingtheREEcontentoffluoritefromPécselywiththeirresults,it
canbestatedthatthefluoritegrainscontainrareearthelementstoasimilarextentand
distributionastheAlpinespecimens(Figure10c).
ThephosphoriteoccurrenceandfluoriteveinsatPécselyalsoshowsimilaritiestothe
MonteSanGiorgo(~70kmfromMilanototheNNW)occurrenceintheSouthernAlps.
Thetwoareasshowsimilaritynotonlyinthestratigraphicpositionandformationageof
phosphoritehorizonsbutalsointhepresenceofhydrothermalfluorite(‐galena‐barite)
veinmineralization.Galena,barite,andfluoriteoccurinMonteSanGiorgioalongfaults
anddykes,embeddedinthevolcanicrocksofthePermianandintheoverlyingLower
andMiddleTriassicsediments.ThedepositswereenrichedduringtheMiddleTriassicby
hydrothermalfluidsmovingalongtectonicfaults[51].
Minerals2021,11,64018of21
Figure10.(a)SimplifiedgeologicalmapoftheDrauRangeafter[18,52]showingthepositionsofthemajorAlpine‐type
Pb‐Zndeposits;(b)schematicprofileshowingthepositionsoftheore‐horizons(redlines)inthedifferentstratigraphic
niveous(modifiedafter[53]);(c)comparisonoftheREEcontentoffluoritefromPécselywithAlpineoccurrences[49,50].
TheTransdanubianMountainRangeescaped450–500kmeastfromtheAlpinecolli‐
sionzoneduringtheLatePaleogene–EarlyNeogene[9].Accordingly,itsoriginalposition
waslocatedbetweentheSouthAlpineandUpperEastAlpinerealmintheTriassic,asa
segmentoftheAdriaticmarginoftheNeotethysOcean[54–56].Ourresultsareconsistent
withthepaleogeographicandgeologicalreconstructions[7,56]too.Therearestrikingsim‐
ilaritiesbetweenthefluoriteveinsofPécselyandcertainepigeneticPb‐Zndepositsinthe
AlpsalongthePABL,especiallyregardingfluidinclusionsignatures.Allthisopensup
thepossibilitythatasimilartypeofAlpine‐typePb‐Zndepositsmaybeconcealedinthe
carboniferoussequenceoftheTransdanubianMountainRange.However,byfarinthe
absenceofawell‐establishedmodel,thisrawmaterialexplorationopportunityhasnot
beenstudiedbefore.
6.Conclusions
Epigenetic‐hydrothermalfluorite–carbonateveinsandbrecciascutacrosssedimen‐
taryphosphoritelayersatPécselyintheTransdanubianMountainRangeUnitofSouth
AlpineaffiliationinwesternHungary.Theresultsofthisstudyoftheseveinssupportthe
followingconclusions:
Theδ18OPDBandδ13CPDBvaluesofcarbonatemineralsfromveinsconfirmtheirepige‐
netic‐hydrothermalorigin.
Minerals2021,11,64019of21
FluoritefromtheveinscontainsREEsinsub‐ppmconcentration.Thislowcontentof
REEandtheirrelativeconcentrationsshowagoodmatchwiththepropertiesof
fluoriteintheAlpine‐typePb‐Znoredeposits.
Colorzoningoffluoriteisassociatedwithdefectsinthecrystalstructure.
TheresultsoffluidinclusionstudiesindicatethattheprimaryandtheS1generation
ofsecondaryfluidinclusionsoffluoritehaveasimilarappearance(size,shape,phase
ratio),andtheirentrapmenttookplacefromahomogeneousfluid.Therelativelylow
homogenizationtemperatureswithCa‐enriched,highsalinitycompositionsaresim‐
ilartofluidinclusioncharacteristicsofsalinebasinalfluidsthatwerealsorecorded
inotherareasofthePannonianBasinandintheAlpine‐typePb‐Zndepositsalong
thePeriadriatic‐BalatonLineament
Fluidinclusionsoffluoritecontainhydrogengas;thisratheruniquefeaturecanbe
relatedtotheinteractionoftheparentfluidsofthefluorite‐bearingveinswiththe
interactionbetweenthefluoritevein‐formingepigeneticprocessandtheuranium‐
bearingphosphoritelayersofthehoststrataanduraniumenrichmentsinthebase‐
mentrocksandalsotothepossiblyinsituradiolysisofwaterwithinthefluidinclu‐
sions.
AuthorContributions:Conceptualization,Z.M.,G.B.K.,F.M.,andI.D.(IstvánDódony);methodol‐
ogy,T.V.,I.D.(IstvánDunkl),F.Z.,G.C.,andG.B.K.;formalanalysis,Z.M.,T.V.,I.D.(IstvánDunkl),
F.Z.,andG.C.;investigation,Z.M.,T.V.,I.D.(IstvánDunkl),F.Z.,G.C.,andG.B.K.;writing—original
draftpreparation,Z.M.andG.B.K.;writing—reviewandediting,F.M,T.V.,I.D.(IstvánDunkl),F.Z.,
G.C.,andI.D.(IstvánDódony);visualization,Z.M.,I.D.(IstvánDunkl),F.M.,G.B.K.,T.V.,F.Z.,and
G.C.;supervision,G.B.K.,I.D.(IstvánDódony)andF.M.;fundingacquisition,G.B.K.,Z.M.,andF.M.
Allauthorshavereadandagreedtothepublishedversionofthemanuscript.
Funding:ThisstudywaspartlysupportedbyTÁMOP‐3.3.21‐15/1researchgrantno.NTP‐NFTÖ‐
16‐1032.FinalizationandpublicationofthisresearchissupportedbytheENeRAGproject,which
hasreceivedfundingfromtheEuropeanUnion’sHorizon2020researchandinnovationprogram
undergrantagreementNo810980.
DataAvailabilityStatement:Thedatapresentedinthisstudyareavailablewithinthisarticle.
Acknowledgments:Wewishtosaythankstoallcolleagueswhocontributedtothiswork:Zsolt
Bendő,ÁgnesTakács,andSándorKlaj.Theauthorsaregratefultothreeanonymousreviewersfor
thecarefulandcriticalreviewofthemanuscriptandfortheirusefulsuggestions.TheUniversity
CentrumofAppliedGeosciences(UCAG)isthankedfortheaccesstotheE.F.StumpflElectron
MicroprobeLaboratory,Leoben.TheELTEFacultyofScienceResearchInstrumentCoreFacilityis
thankedfortheaccesstotheRamanlaboratory.TheLA‐ICP‐MSmeasurementswereperformedat
theUniversityofGöttingen.TheInstituteforGeologicalandGeochemicalResearchCentreforAs‐
tronomyandEarthSciences,whichispartoftheEötvösLorándResearchNetwork,isthankedfor
thestableisotopeanalyses.TheSEM‐CLimagingwasavailablethankstotheKMOP‐4.2.1/B‐10‐
2011‐0002grantbytheEuropeanUnion,co‐financedbytheEuropeanSocialFund.
ConflictsofInterest:Theauthorsdeclarenoconflictofinterest.Thefundershadnoroleinthe
designofthestudy;inthecollection,analyses,orinterpretationofdata;inthewritingofthemanu‐
script,orinthedecisiontopublishtheresults.
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