Gál, Á.
1*, Kovács, I.J.
2, Szabó, Cs.
3, Berkesi, M.
3, Szakács, A.
4& Ionescu, C.
1,51Department of Geology, Babeş-Bolyai University Cluj-Napoca, Romania; 2Kövesligethy Radó Seismological Observatory, Geodetic and Geophysical Institute, Research Centre for Astronomy and Earth Sciences, Hungarian Academy of Sciences, Hungary; 3Lithosphere Fluid Research Lab, Institute of Geography and Earth Sciences, Eötvös Loránd University Budapest, Hungary; 4Institute of Geodynamics, Romanian Academy, Romania;
5Archeotechnologies and Archeological Material Sciences Laboratory, Institute of International Relations, History and Oriental Studies, Kazan (Volga Region) Federal University, Russia; *agi.gal@ubbcluj.ro
The Certej low sulphidation epithermal Au deposit, one of the most important ones in Romania, occurs at the south-eastern part of the Apuseni Mts. within the well-known “Gold quadrangle”, related to Miocene (14.7-7.4 Ma) calc-alkaline volcanics and intrusives. The disseminated Au mineralisation is hosted by andesites and Cretaceous and Neogene breccias.
Our research focuses on fluid inclusions in hydrothermal quartz crystals aiming to obtain information on the ore-forming hydrothermal fluids, which will provide a better understanding of the paleoenvironment and the chemical and thermodynamic conditions in which the Au deposit was formed. The fluid inclusion studies were performed using a heating/cooling stage. The investigation methodology was completed by Raman spectroscopy applied to the fluid inclusions and by Fourier Transform Infrared Spectroscopy on selected quartz crystals.
The quartz crystals show heterogeneity in their infrared spectra. Both structural hydroxyl and molecular water contents vary not only among different specimens but also within a single crystal.
The most important substitutions of structural hydroxyl are related to the linked substitutions: Li+ + OH- in interstitial positions (band at 3480 cm-1) or Al3+ + OH- into a vacant Si4+ site (triplet of bands at 3420, 3380 and 3320 cm-1). There are also indications for the trace presence of B3+ + OH -substitution into vacant Si4+ sites (band at 3600 cm
-1). The broad band of molecular water in the 3400 – 3300 cm-1 range is usually present with extremely variable intensities. The structural hydroxyl content is usually below 5 ppm wt. (expressed in molecular water equivalent) but varies considerably within and among crystals. The molecular water content in sub-microscopic inclusions is low (~10–15 ppm).
The structural hydroxyl and molecular water content is at the lower end of the array defined by quartz grains from various igneous and metamorphic assemblages. The various substitution mechanisms of structural hydroxyl and the strong heterogeneity in water concentrations may be in line with the complex nature of shallow hydrothermal systems as manifested in their strongly time-dependant chemical and physical properties. Such complexity at Certej might be the result of boiling in the deeper part of the hydrothermal system, input of meteoric water to the
fluids of prevalently magmatic origin and resulting variations in fluid temperatures and concentrations, and interaction with the host rocks of various composition (e.g. organic-rich shales).
The determined eutectic temperatures of the fluid inclusion brines range between -19.3 and -24.4 °C (corresponding to a KCl-bearing H2O-NaCl system), whereas the freezing point depressions range from -4.1 to -0.1 °C. The final melting temperature occurred between -0.1 and -3.3 °C.
The fluid inclusion salinity is between 0.18 and 5.41 wt% NaCl. These data allowed for pressure calculations and determination of the corresponding depths of the paleo-watertable (100-300 m) at the time of the mineralisation processes. Vapour-rich fluid inclusions consist of H2O=67.0–99.9 vol%, N2=0.0–7.2 vol%, and CO2=0.0–29.7 vol%, as the main components.
Insight into Miocene seawater composition from fluid inclusions in halite, Praid, Transylvanian Basin Romania
Gelencsér, O.
1,2*, Berkesi, M.
1, Palcsu, L.
2, Futó, I.
2, Aradi, L.E.
1& Szabó, Cs.
11Lithosphere Fluid Research Lab, Institute of Geography and Earth Sciences, Eötvös Loránd University, Hungary;
2Laboratory of Climatology and Environmental Physics, Institute for Nuclear Research, Hungarian Academy of Sciences, Hungary; *gecso@caesar.elte.hu
The middle Miocene Badenian Salinity Crisis (BSC) event during the closing of the Paratethys ca. 13.8 Ma ago (Peryt, 2006), resulted in the deposition of massive amounts of marine salt rocks in the eastern margin of the Transylvanian Basin (Romania). Fluid inclusions in halite, collected from the locality of Praid, offer insights into the properties and history of marine fluids and paleoenvironment in this region.
The halite trapped both primary (p) and secondary (s) fluid inclusions (FI) The negative crystal shaped pFI (50-100 μm in diametre) are distributed along growth zones of halite and represent droplets of the paleo seawater from which halite precipitated. These FI appear only as single-phase liquid inclusions at room temperature, and are possibly in a metastable state. Therefore, the bubble nucleation was induced by cooling the inclusions to -20 °C to overcome the metastable barrier. The pFI show homogenisation temperatures (Th) to liquid ranging from 10 °C to 24
°C, values typical for a marine formation environment. The measured eutectic temperatures (Te) during low-temperature microthermometry range from -55 °C to -42 °C, indicating the potential presence of Ca and Mg besides Na in the fluids.
Cryogenic Raman spectroscopy was performed on the pFI to better determine their chemical composition. Raman spectra were collected following the secondary freezing method of Ni et al.
(2006) to avoid the formation of disequilibrium solid assemblages, and to observe the series of all bands of various salt hydrates. Initial freezing to -190 °C indicates only the peak for water ice (Fig.
1). A heating of the inclusions to -70 – -50 °C followed by re-freezing causes recrystallisation in the FI, and the appearance of characteristic bands of salt-hydrates on the Raman spectra of these inclusions. Several salt phases such as Na-, Ca- and Mg-hydrates can be distinguished on the spectra (Fig. 1), in agreement with the observed low Te values. The collected spectra show fairly consistent peak positions with sharp/narrow bands.
Typical wavenumbers are at 3404, 3422, 3436, 3538 cm-1, only the presence of Mg-hydrate (~3513 cm-1) is varying in the measured samples. The pFI also contain SO4- besides H2O, as confirmed by the Raman band at 983 cm-1.
The sFI appear along healed microfractures and halite grain boundaries, containing gas-rich fluids.
Based on Raman spectroscopy at room temperature the gas phase contains low density N2
and CH4. These later fluids may be originated from organic matter trapped during later burial.
The examined fluid inclusions in halite at Praid suggest a complex fluid evolution beginning at the precipitation of the halite and through to deformation during burial. The pFI are proxy to paleo-seawater and show its complex salinity during salt deposition, while the sFI are witnesses of a possible fluid migration event potentially related to the halokinetic deformation of halite.
Acknowledgement
This work was supported by the ELTE Excellence Program (1783-3/2018/FEKUTSTRAT) supported by the Hungarian Ministry of Human Capacities and by the European Union and the State of Hungary, co-financed by the European Regional Development Fund in the project of GINOP-2.3.2-15-2016-00009 ’ICER’.
References
Ni P. et al. (2006) Chin. Sci. Bull. 51:108-114.
Peryt T.M. (2006) Sediment. Geol. 188-189:379-396.
Fig. 1. Characteristic Raman spectra of P-type fluid inclusions on -190 °C after first (hairline) and second (thick black) freezing in the stretching regions of structural H2O.
Fluid inclusion in apatite of the Sorkhe-Dizaj magnetite deposit (Tarom, NW Iran) Ghahramani, S.
1*, Tarantola, A.
2, Whitechurch, H.
1& Jannessary, M.R.
31Université de Strasbourg CNRS, IPGS-EOST, France; 2Université de Lorraine, CNRS, GeoRessources, F-54506 Vandœuvre-lès-Nancy, France; 3Geological Survey of Iran; *sghahramani@unistra.fr
The Sorkhe-Dizaj magnetite-apatite deposit is located in the Alborz-Azarbaijan magmatic belt in the Tarom volcano-plutonic zone (NW Iran). Field, petrography and geochemistry investigations demonstrate that the quartz-monzodiorite to monzogranite pluton of Early Oligocene age (41 Ma) (Nabatian et al., 2014), intrudes Eocene volcanic rocks including high-K calc-alkaline pyroclastic and lava flows (Amand Member of Karaj Formation). The mineralisation of magnetite and apatite is associated with large lenticular bodies, stockwork, veins and dykes that crosscut intrusive plutonic rocks. The mines are currently, exploited for iron. However, geochemical studies indicate high concentrations of REE in the apatite and the associated accessory minerals (monazite and thorite). The aim of the present study is to (1) characterise the REE ore deposit, associated with the Kiruna–type Fe-deposit, (2) determine the temperature and depth of formation of the REE-bearing phases, (3) understand the fluid characteristics (T, composition, redox state) in equilibrium with the REE phases.
Through petrographic studies, fluid inclusions (FIs) of sub to euhedral apatite crystals (within magnetite) classified to the primary which most trapped during crystals growth, secondary FIs as transgranular and rare pseudosecondary. 7 types of primary FIs are recognised: Monophase Type A1 and A2, containing only liquid (L) and only vapour (V); two-phase Type B, subdivided into Type B1 (L+V), the most common liquid-rich, with 10 to 30 vol% vapour; type B2 (L+V) vapour-rich between 50 to 60 vol% and Type B3 (L+S), containing liquid and opaque daughter minerals;
multiphase Type C (L+V+S) liquid-vapour with halite and opaque daughter minerals subdivided into Type C1 (Fig. 1) the second most frequent type with 10 to 40 vol% vapour, and Type C2 multiphase solid vapour-rich with 50 to 60 vol% vapour;
Multisolid Type C3, containing saturated aqueous salt, more than 50 vol% salt crystals and opaque daughter minerals. 5 types of secondary FIs are classified into monophase A1, A2, two-phase B1, B3 and multiphase C1.
First primary FIs are trapped as heterogeneous saturated solution with suspended solids type C3, Microthermometry results show Type C3 have two ranges ThLV-L (340-401 °C) and (179-240 °C) contain the highest salt content (23-43 wt%
NaCl eq.); concurrence homogeneous saturation Type B2 and C2, high ThLV-L (304-406 °C); then, homogeneous shrinkage type B1 and C1, having low ThLV-L (150-274 °C), type B1 have lower salinity (0-13 wt%); at the end secondary FIs of types C1
and B1 show low ThLV-L, (137-234 °C) and (115-228 °C) salinity of 3-23 wt% were trapped in secondary healed fractures. Boiling solution results in type A1, A2 and B3. The low eutectic temperatures (-50 to -20 °C) suggest that NaCl and CaCl2 are present in the aqueous solution of the FIs. Phase ratios, compositions and Raman spectrometry indicate a series of FIs that have been trapped in different proportions of vapour and liquid-like density together with salt crystals. The daughter mineral phase was identified as magnetite. The vapour phase does not show any presence of CO2, CH4 or N2.
The geochemical results (REE patterns) suggest that the apatite crystallised from magmatic fluids.
The results of the present study of fluid inclusions in the apatite show that they have an elevated homogenisation temperature and high salinity.
These results suggest a magmatic origin high temperature and high salinity (type C3, B2 and C2) followed quickly by lower temperature and salinity hydrothermal fluids (type B1 and C1) during the crystallisation of the REE-bearing phases. These results corroborate those of Nabatian and Ghaderi (2013), but attribute a preponderant role to the magmatic-hydrothermal fluids of high temperature for the crystallisation of the first generation of REE-bearing phase.
References
Nabatian G. et al. (2014) Lithos 184-187:324-325.
Nabatian G. and Ghaderi M. (2013) Int. Geol. Rev.
55:397-410.
Fig. 1. Primary fluid inclusion (Type C1) containing vapour, liquid, a halite crystal and 2 opaque daughter minerals; doubly polished section visualised by PPL at room temperature.
(Sorkhe-dizej-Tarom)