UREGIONAL TRIASSIC FLUID FLOW IN THE GRANITE: GENETIC MODEL AND STRUCTURAL CONTROLU

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35BHydrothermal processes related to the igneous activity of the Palaeogene age

The hydrothermal mineralization and the alteration of the Palaeogene diorite intrusion and the stratovolcanic sequence were discussed in the last decades by several authors (FÖLDVÁRINÉ 1947; JANTSKY 1957; KOCH 1985; DARIDA-TICHY 1987; MOLNÁR 1996, 2003, 2004; BAJNÓCZI et al. 2002, BAJNÓCZI 2003, PROHÁSZKA, 2004).
In the diorite intrusion, propilitic (actinolite, albite, epidote, chlorite, magnetite, ilmenite) and K-metasomatic (flogopite, biotite, sericite, pirite) alterations together with copper-sulphides are known. The general features of mineralization correspond to a Cu-porphyry type ore forming system. The K-metasomatic alteration and the sporadic occurrences of the K-feldspar-quartz veins are accompanied by quartz-pyrite-chalcopyrite-sphalerite stockwork mineralization that was superimposed by a late carbonate-zeolite vein system. At 670 m depth (in a few meters thick intercept in the Pd-2 drillhole), skarn minerlization also occur. Characteristic minerals of the skarn are andradite, epidote, quartz and pyrite.
Studies by MOLNÁR (1996) and PROHÁSZKA (2004) indicate that the potassic alteration took place at high temperature (>350 ºC), and the composition of the high salinity (>40 NaCl equiv. wt%; Table 1) hydrothermal fluids were rather complex. The hydrothermal fluids have undergone phase separation at relatively low pressure and trapped between lithostatic and hydrostatic conditions at about 1100 m depth. In a later hydrothermal phase, possibly related to the collapse of the magmatic-hydrothermal system, lower temperature (180-200°C) and low salinity (<<20 NaCl equiv. wt.%) epithermal fluids circulated in both of the diorite intrusion and in the stratovolcanic series.

36BHydrothermal mineralization of Palaeogene age in the Variscan granite

West of the Nadap-line, andesite dikes and small stocks intruded the Paleozoic granite and slate. Brecciation and hydrothermal alteration along these intrusions and in the dikes and stocks themselves are also present. Most of these small intrusions have weak chloritic alteration only butthere are also some dikes with intense argillic alteration. Fluorite, calcite, quartz, pyrite, epidote, hematite, sphalerite, galena, tetraedrite, and laumontite appear in small nests and veins of these dikes, as well (MAURITZ 1908a, b; SCHAFARZIK 1908; ERDÉLYI 1939; KOCH 1985). FÖLDVÁRINÉ VOGL (1947) recognised Mo anomalies in the andesite dikes. Mo-anomalies are characteristics to the the whole Palaeogene volcanic unit of the Velence Mts.
Enargite-grey ore and chalcopyrite bearing siliceous breccias and silica rich pods are known along the brecciated contact of the granite and the slate on the Meleg Hill, in the eastern part of the granite intrusion (KUBOVICS 1958, MOLNÁR 1996; Figure 2). JANTSKY (1957) and GASZTONYI & SZABÓ (1978) have also observed occurrences of alunite and pyrophyllite in the brecciated zone of the granite. Trace elements (Mo, Ag, Pb, Cu, Sb, As Te) have also elevated concentrations in this zone. Next to Sukoró in the St-4 drillcore (Figure 3) quartz-chalcopyrite veins have been identified: the host granite has silicic-sericitic alteration. Studies by MOLNÁR (1996) showed that petrographyic and microthermometric properties of fluid inclusions from this breccia-realted mineralization carry many similarities with the fluid inclusions found in the Cuporphyry type mineralization, east from the Nadap-line (Table 1). The phase separation of high and low salinity fluids happened at 370-460°C, which corresponds to 200-400 bar pressure under hydrostatic conditions.
On the Antónia-hill, in the vicinity of the breccia zone of the Meleg Hill another hydrothermal mineralization containing spahalerite, galenite, grey ore, chalcopyrite, molybdenite and native gold in quartz veinlets surrounded by kaolinite and alunite alteration has been found in the slate (BÖJTÖSNÉ VARRÓK, 1967), HORVÁTH et al. (1987) considers Palaeogene age of this mineralization. The granite below the slate shows chloritic, argillic, silicic and pyritic alteration with geochemical anomalies of Sn, Ag, As, and Bi.

12BHYDROTHERMAL MINERALIZATION OF THE SZABADBATTYÁN AREA

Hydrothermal formations of the Szabadbattyán area consist of epigenetic, Pb-(Zn) mineralizations in metamorphosed carbonates (KISS, 2003). The main mineral phase is galena which occurs typically in fractures and along the contacts to the Polgárdi Limestone Formation, as well as in small nests, pods and metasomatic replacements in the silicified limestone (Figure 4). Galena is associated with bournonite, sphalerite, chalcopyrite, tetraedrite and native silver are the dominant mineral phases (MOLNÁR & SZAKÁLL 2003). The epigenetic-metasomatic base metal mineralization has been exploited by the Romans and small scale mining was also conducted during the World War II and following years (KISS, 2003).
The Paleozoic carbonate rocks are intruded by andesitic dikes of Triassic age (DUNKL et al. 2003). Exo-skarn (diopside, predazzite, calcite) and endoskarn (garnet-epidote, clinopyroxenprehnite and vesuvianite) surround these dikes in narrow zones, however, there is no obvious genetic relationship between the skarn formation and the base metal mineralization. In analogy with the the Velence Mts., several hypotheses have been formulated about the origin of the epigenetic mineralization at Szabadbattyán. VENDL (1928), KOCH (1943), FÖLDVÁRI (1952) and KISS (1951) suggested relationships to the Variscan granite intrusion of the Velence Mts. KISS (1951) also considered a remobilization effect induced by the Triassic andesite dikes. VENDL (1928) and JANTSKY (1960) suggested an Eocene age for the mineralization. KISS (2003) completed a whole revision of available geological, mineralogical and geochemical data and suggested tha the mineralization at Szabadbattyán is a Mississipy-Valley type epigenetichydrothermal Pb-Zn ore deposit.

14BFLUID INCLUSION STUDIES: PRINCIPLES AND METHODS

The first and very important part of the fluid inclusion studies is the fluid inclusion petrography. During the fluid inclusion study two characters of fluid inclusions are observed; their origin and assemblage.
Fluid inclusions can be primary or secondary of origin. Primary inclusions are entrapped during the crystallization of the mineral and therefore the fluid in the inclusions represents the composition of the hydrothermal fluid from which the mineral crystallized. They mostly occur along growth zones or as individual inclusions or clouds. Secondary inclusions are captured along fractures in the mineral, and thus they may form FIP. Their formation could happen any time after the crystallization of the mineral. They can form the same fluid from which the mineral crystallized but can be related to any younger hydrothermal fluid migration event with different composition.
Since the recognition of petrographic characteristics is fundamental during the microthermometric work, single fluid inclusions were never analysed during this work. Microthermometric analyses were always performed on fluid inclusion assemblages (FIA), e.g. on assemblages of fluid inclusions which were in the same FIP. This principle was also used for primary inclusions of vein filling minerals.
Regarding the phase state of the hydrothermal system and the type of the entrapment different possibilities are distinguished:
􀂃 If the hydrothermal fluid is homogeneous, the trapping in inclusions is homogeneous. In this case the phase ratios observed on room temperature are equivocal in the inclusions in the same assemblage.
􀂃 If the hydrothermal fluid is in heterogeneous phase state (boiling), two possibilities are distinguished:
• Homogeneous trapping from the heterogeneous system (only liquid or only vapour in individual fluid inclusions).
• Inhomogeneous trapping from a heterogeneous system (trapping of liquid+vapour±solid phase or trapping of two non-mixing, different type of fluids (e.g.aqueous and carbonic phases)).
Petrographically, in a set of fluid inclusions which trapped from a boiling (heterogeneous) fluid the phase ratios (the ratio of the aqueous vapour: Vaq and aqueous liquid: Laq phase) observed on room temperature are always highly variable.

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15BMETHODS OF ANALYSIS OF HYDROTHERMAL VEIN NETWORKS, JOINTS,  FRACTURES

Hydrothermal veins – similar to the FIP – usually form perpendicular to the minimum stress field axis in homogeneous rocks (TOSDAL & RICHARDS 2001). In a deformed rock body rich in fractures, the fluid mobilization is constrained by the pre-existing faults and joints.
Formation of hydrothermal vein network fundamentally influences the character of the mineralization therefore the geometrical analysis of hydrothermal vein systems yields important additional information on the understanding of the formation of economically important mineral deposits. In a well-developed, broad and well-connected fracture system, huge amounts of hydrothermal fluids may be transported. The physical-chemical conditions of the fluid (composition, pressure, temperature) may change in short distances but the fluid/rock interaction has a less important role (because of sealing of veins’ walls by the early mineral precipitation in the vein). Rapid physical changes – fluid mixing, phase separation, pH, redox, saturation etc. – within the fracture is the principal factor in mineral deposition. If the system is characterised by few but well connected fractures, the possibility of formation of high grade deposits increase because this kind of system provides focussed fluid flow (COX et al. 2001).
If the mineralizing fluids migrate along cleavages, microfractures or along grain boundaries (e.g. failing any main fluid flow channel), the fluid/rock interaction will play a major role in the formation alteration of host rock and formation of an ore deposit. Depending on the composition of the fluids (e.g. cation ratios, pH, oxygene and sulphur fugacities etc.) and mineralogy of the wall rock, the geochemically sensitive elements will precipitate and disseminated or stockworck type mineralization will form.

Table of contents :

1.U UINTRODUCTIONU
U2.U UGEOLOGICAL SETTING OF THE VELENCE MOUNTAINSU
U2.1U UREGIONAL GEOLOGYU
U2.2U UMAJOR GEOLOGICAL FORMATIONS OF THE VELENCE MOUNTAINSU
U2.2.1U UVariscan granite (Velence Granite Formation)U
U2.2.2U UEarly Palaeozoic Slate (Lovas Slate Formation)U
U2.2.3U UCretaceous igneous rocks (Budakeszi Picrite Formation)U
U2.2.4U UPalaeogene igneous rocks (Nadap Andesite Formation)U
U2.3U UGENERAL GEOLOGY OF THE SZABADBATTYÁN AREAU
U2.4U UHYDROTHERMAL SYSTEMS IN THE VELENCE MTS.U
U2.4.1U UMineralization of the granite and the shaleU
U2.4.2U UHydrothermal processes related to the igneous activity of the Palaeogene ageU
U2.4.3U UHydrothermal mineralization of Palaeogene age in the Variscan graniteU
U2.5U UHYDROTHERMAL MINERALIZATION OF THE SZABADBATTYÁN AREAU
U3.U UTHEORETICAL BACKGROUND AND APPLIED METHODSU
U3.1U UFLUID INCLUSION PLANESU
U3.2U UFLUID INCLUSION STUDIES: PRINCIPLES AND METHODSU
U3.3U UMETHODS OF ANALYSIS OF HYDROTHERMAL VEIN NETWORKS, JOINTS, FRACTURESU .
U3.4U UFRACTAL ANALYSIS OF HYDROTHERMAL VEINSU
U3.5U UCLAY MINERAL STUDIES: SAMPLE PREPARATION, METHODOLOGYU
U3.6U URADIACTIVE AND STABLE ISOTOPE STUDIESU
U4.U URESULTSU
U4.1U UDELINEATION AND CHARACTERIZATION OF SUPERIMPOSING HYDROTHERMAL PROCESSES
ON THE BASIS OF CLAY MINERALOGY IN THE ARGILLIC ALTERATION ZONES OF THE VELENCE GRANITEU
U4.1.1U UThe aim of the clay mineral studies and previous studiesU
U4.1.2U UArgillic alteration in and around the andesite dikes of Palaeogene age and
hydrothermal breccias hosted by the granite around the quartz-barite hydrothermal veinsU
U4.1.3U UArgillic alteration around the quartz-fluorite-base metal veins and regional argillic alteration of graniteU
U4.1.4U UTemperature conditionsduring the formation of the clay mineral assemblagesU
U4.2U UAGE, ORIGIN AND TEMPERATURE OF HYDROTHERMAL FLUID FLOW EVENTS IN THE VELENCE MTS.U
UK-Ar analysesU
U4.2.1U UK-Ar analysesU
U4.2.1.1U UK-Ar ages for rock forming mineralsU
U4.2.1.2U UK-Ar ages measured on hydrothermal mineralsU
U4.2.1.3U UInterpretation of K-Ar radiometric age data from the aspect of the extent of superimposing hydrothermal events that affected the granite intrusionU
U4.2.2U UPb isotope studies: age and genetical relationships of the quartz-fluorite-base metal veins and their geotectonical connectionsU
U4.2.3U USulphur isotope analysis: temperature estimation for the formation of the quartzfluorite- base metal veinsU
U4.3U UFLUID INCLUSION STUDIESU
U4.3.1U UType I FIA: Carbonic-aqueous fluid inclusion assemblages trapped from an inhomogeneous fluid (Photoplate 1/A.)U
U4.3.2U UType II and Type III FIA: Aqueous fluid inclusion assemblages trapped from homogeneous parent fluidU
U4.3.3U UType IV FIA: Aqueous fluid inclusion assemblages, trapped from inhomogeneous fluidU
U4.3.4U UInterpretation of the fluid inclusion analysisU
U4.3.5U UProving vertical movements in the granite by means of fluid inclusion studiesU
U4.4U UANALYSIS OF THE STRUCTURAL ELEMENTS OF THE GRANITE AND THE ANDESITE DIKESU
U4.4.1U UThe Székesfehérvár areaU
U4.4.2U UPákozd areaU
U4.4.3U UThe Nadap-Sukoró areaU
U4.4.4U UThe Nadap areaU
U4.4.5U UPalaeogene Volcanic UnitU
U4.4.6U URelatinships between FIP orientations, fluid inclusion petrography and microthermometryU
U4.5U USTATISTICAL ANALYSIS OF PALAEOGENE HYDROTHERMAL VEIN ARRAYS: FRACTAL ANALYSIS AND PERMEABILITY CALCULATIONU
U4.5.1U UFractal analysisU
U4.5.2U UPermeabilities calculated from the geometrical data of the veinsU
U4.6U UFIP STATISTICAL PARAMETERS: AVERAGE LENGTH, LENGTH DENSITY, NUMBER DENSITYU
U4.6.1U UIso-Fracture density map of the Nadap area and comparison of statistical parametersU
U5.U UDISCUSSIONU
U5.1U UVARISCAN TECTONISM AND ITS CONSEQUENCES ON THE FORMATION OF THE INITIAL FRACTURE SYSTEM OF THE GRANITEU
U5.2U UREGIONAL TRIASSIC FLUID FLOW IN THE GRANITE: GENETIC MODEL AND STRUCTURAL CONTROLU
U5.2.1U URadiometric age constraintsU
U5.2.2U UModel for the Triassic fluid mobilization processes in the Velence Mts.U
U5.2.3U UGeotectonical considerationsU
U5.2.4U UStructural control of the Triassic fluid flow: uplift of the granite and its effect on the fracture evolution on the graniteU
U5.3U UEVOLUTION OF THE FRACTURE SYSTEM OF THE GRANITE RELATED TO THE PALAEOGENE MAGMATIC-HYDROTHERMAL PROCESSESU
U5.3.1U UReopening of FIP in the illitic Palaeogene alteration zones and thermal propagation of the fracture networkU
U5.3.2U UFracture formation and evolution: thermal reopening versus mechanical fracture formationU
U5.4U UPOST-PALAEOGENE STRUCTURAL EVENTSU
U5.5U USTATISTICAL ANALYSIS OF THE FRACTURE SYSTEMS AT DIFFERENT SCALES: PRACTICAL
APPLICABILITYU
U6.U USUMMARYU
U7.U UACKNOWLEDGEMENTU
U8.U UREFERENCESU

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