Skarn textures and a case study: the Ocna de Fier-Dognecea orefield, Banat, Romania

We address the question of the predictability of skarn textures and their role in understanding the evolution of a skarn system. Recent models of skarn formation show that skarns are ideal for application of self-organisation theory, with self-patterning the rule in fluid-rock interaction systems rather than the exception. Zonation in skarn deposits, a consequence of infiltration-driven metasomatism, can also be treated in terms of self-organisation. Other less commonly described features, such as scalloping, fingering and mineral banding, can be understood by application of reactive infiltration and hydrodynamics at the skarn front. Devolatilisation may trigger formation of back-flow fluxes that overprint previously formed skarn. The range of textures formed from such events can be used to discriminate between prograde and retrograde stages. Refractory minerals, such as garnet, magnetite and pyrite, readily retain overprinting events. Skarns are also composed largely of minerals from solid solution series (garnet, pyroxene, pyroxenoids, etc.) and therefore skarn mineralogy helps to establish trends of zonation and evolution. The same minerals can act as ‘chemical oscillators’ and record metasomatic trends.The Ocna de Fier-Dognecea deposit was formed in a 10 km deep skarn system. Zonation and evolution trends therefore represent only the result of interaction between magmatically derived fluids emerging at the source and limestone. From the same reason, the transition from prograde to retrograde regime is not influenced by interaction with external fluids. Thirdly, the mineralisation comprises Fe, Cu and Zn-Pb ores, thus facilitating comparison with skarn deposits that commonly are formed in shallower magmatic-hydrothermal environment. Copper-iron ores (magnetite+Cu-Fe sulphides), hosted by magnesian (forsterite+diopside) skarn, occur in the deepest and central part of the orefield, at Simon Iuda. Their petrological character allows interpretation as the core of the skarn system formed from a unique source of fluids emerging from the subjacent granodiorite. It formed first as a consequence of the local setting, where a limestone indented in the granodiorite permitted strong reaction at 650 °C and focussed the up-streaming, buoyant fluids. The first sharp front of reaction is seen at the boundary between the Cu-Fe core and Fe ores hosted by calcic skarn (Di_70-90-And_70-90), where Cu-Fe sulphides disappear, and forsterite gives way to garnet in the presence of diopside (Di₉₀). Following formation of forsterite, devolatilisation and transient plume collapse is interpreted from a range of piercing clusters and trails. We presume lateral flow to have been initiated at the source, as the emerging fluids are in excess to the fluids driven into reaction by the plume. Formation of the other orebodies, up to 5 km laterally downstream in both directions, is interpreted as skarn fingering at the limestone side. The metasomatic front is perpendicular to the flow along the channel of schists placed between the limestone base and the granodiorite.A metal zonation centred onto the source is defined, based on metal distribution: Cu-Fe/Fe/Zn-Pb. The second front of reaction, at the boundary between the Fe and Zn-Pb zone, has a sulphidation/oxidation character, with diopside giving way to a Fe-Mn-rich pyroxene, (HedJoh)_>60+pyroxmangite±bustamite; garnet is minor. Johannsenite-rich pyroxene (Di_20-40Hed_20-40Joh₄₀) is found in proximal skarn at the upper part of Simon Iuda, stable with Zn_0.95Fe_0.05S, at an inferred 570 °C. In distal skarn from Dognecea and Paulus, Mn-hedenbergite (Di_<10Hed₇₀Joh_20-30) formed at 400 °C is stable with Zn_0.84Fe_0.16S. Extensive compositional fields, eutectic decomposition and lamellar intergrowths characterise pyroxene in the Zn-Pb zone, formed at the magnetite-hematite buffer in the presence of pyrite. Distal skarn has a reducing character, in comparison with the proximal. A drop in both fS₂ and O₂, with the zoned system moving closer to the pyrite-pyrrhotite buffer, is induced from the temperature gradient. Based on pyroxene mineralogy and calculated fS₂, the metal zonation is confirmed as being formed upwards and outwards from the source.The Fe and Zn-Pb zones both have a patterned side coexisting with the unpatterned one. Patterning is seen at scales from macroscopic (rhythmic banding, nodular, spotted, orbicular, mossy, mottled textures) to microscopic scales (oscillatory zonation in garnet and silica-bearing magnetite). Following plume updraft, the path of decarbonation reaction controlled the motion of the skarn front until, towards the end of the prograde stage, a multiple steady state regime developed and produced rhythmic patterns on all scales. The activation of powerful patterning operators, represented by Liesegang banding alone, or coupled with competitive particle growth, show that the skarn front had the characteristics of an unstable coarsening front of reaction.A second retrograde event, carbofracturing, triggered by erratic decarbonation after cessation of infiltration, can be interpreted from overprinting textures in the Fe and Zn-Pb zone. A major drop in fO₂ is inferred from extensive, pseudomorphous replacement of hematite by magnetite. Textures show progressive destruction of prograde assemblages, i.e., piercing clusters, shock-induced, fluid-pressure assisted brecciation and deformation, followed by healing of the disrupted assemblages. Release of trace elements accompanies both retrograde events, with a Bi-Te-Au-Ag association common to both. The importance of shock-induced textures is emphasised in the context of Au enrichment, especially when the retrograde fluids cross the main buffers in fO₂-fS₂ space.The presence of Bi-sulphosalt polysomes in the Fe zone indicates that patterning extends down to the nanoscale. The key role played by polysomatism in stabilising compositional trends that cannot otherwise be formed at equilibrium is a fertile ground yet to be adequately explored.     

Bottled natural mineral waters in Romania

Different from drinking water supplied by the municipal network or from other bottled waters, all of which undergo some kind of prior treatment in order to become potable, the natural mineral water is an ecologically pure product, that by virtue of its composition may induce beneficial health effects. According to the EC Directive 80/777, the main criteria used for defining the natural mineral water refer to its original purity and its adequate protection against any pollution hazard. In Romania, mineral water consumption is an old tradition. The geological setting and the existence of unpolluted areas favored the development of mineral water sources of an outstanding quality, many of which include also carbon dioxide in natural state. The present work presents the main sources of bottled mineral water in Romania, classified as a function of total mineral content, ionic composition and carbon dioxide content. There are also forwarded forecasts concerning the medium term evolution of the structure of the bottled mineral water market in Romania.     

罗马尼亚东南部康斯坦萨高岭土矿床的矿物学研究

本文对罗马尼亚东南部康斯坦萨高岭土矿床进行矿物学研究,该矿床在白垩系古海纳组地层中．经化学分析、Ｘ射线衍射分析、红外光谱分析、差热和电子显微镜扫描等研究,其矿物组成主要为结晶度差的高岭石、少量蒙脱石、伊利石及其混层矿物。铁和钛的有害组份较高。它的成因是由中酸性火成岩受风化作用,经剥蚀、搬运、在较稳定的沉积环境中．经过几次海浸沉积形成的。在沉积后,粘土矿物随着埋藏深度的加大,致使粘土矿物发生转化。     

Three Dimensional Plate Kinematics in Romania

Since 1996 the Collaborative Research Center (CRC) 461``Strong Earthquakes: A Challenge for Geosciences andCivil Engineering' is funded by the DeutscheForschungsgemeinschaft (German Research Foundation) asa German contribution to the UN initiative``International Decade of Disaster Reduction' (IDNDR).A central project of this CRC is the subproject B1``Three Dimensional Plate Kinematics in Romania', whichis installed to detect borders of the geotectonicplates in Romania, to quantify their three-dimensionalmovement rates and to determine in detail thedeformation of each geotectonic unit in the VranceaRegion as a contribution to the research of thetectonic cause of the intermediate depth earthquakesin this region. These aims shall be accomplished byrepeated GPS-measurements in a network which has beeninstalled in 1997 and measured until now in 1997 and1998. This network is consisting of 26 stations,covering an area of 250 km × 380 km with the Vranceaarea as the centre. The geodetic frame is given by sixstations of the CEGRN (Central European GeodynamicRegional Network) of the CEI-initiative CERGOP, forwhich coordinates and velocities in a global tectonicscenario are available. The paper gives informationabout the tectonic background, the geodetic network,the GPS-measurements and the achieved accuracies andfirst results of deformation analyses. It is shownthat until now no significant deformations could bedetected. But the extension of the GPS network andremeasurements with time intervals of two years willallow statements about the recent crustal movementswithin the lifetime of the CRC 461.     

Climatic implications of cirque distribution in the Romanian Carpathians: palaeowind directions during glacial periods

The many glacial cirques in the mountains of Romania indicate the distribution of former glacier sources, related to former climates as well as to topography. In the Transylvanian Alps (Southern Carpathians) cirque floors rise eastward at 0.714 m km⁻¹, and cirque aspects tend ENE, confirming the importance of winds from some westerly direction. There is a contrast between two neighbouring ranges: the Făgăraş, where the favoured aspect of cirques is ENE, and the Iezer, where the tendency is stronger and to NNE. This can be explained by the Iezer Mountains being sheltered by the Făgăraş, which implies precipitation‐bearing winds from north of west at times of mountain glaciation. Palaeoglaciation levels also suggest winds from north of west, which is consistent with aeolian evidence from Pleistocene dunes, yardangs and loess features in the plains of Hungary and southwestern Romania. In northern Romania (including Ukrainian Maramureş) the influence of west winds was important, but sufficient only to give a northeastward tendency in cirque aspects. This gave stronger asymmetry than in the Transylvanian Alps, as the northward (solar radiation incidence) tendency in these marginally glaciated mountains was less diluted by wind effects. Cirque floors in northern Romania are lower also in northeast‐facing cirques. In general, cirque aspects result from several factors and the mean tendency is not downwind, but is displaced from poleward by wind and by minor effects. Copyright © 2010 John Wiley & Sons, Ltd.     

Solution lakes on gypsum evaporites: Lake Inva^rtita (Nucs¸oara), Romania

The distribution of solution lakes on gypsum evaporites isconsidered. Details are given of Lake Inva^rtita (Nucs¸oara), aRomanian lake of this type, in the Arges¸ district.     

Seasonal trends in Romanian streamflow

Mean daily streamflow records from 44 river basins in Romania with an undisturbed runoff regime have been analyzed for trends with the nonparametric Mann‐Kendall test for two periods of study: 1961–2009 (25 stations) and 1975–2009 (44 stations). The statistical significance of trends was tested for each station on an annual and seasonal basis, for different streamflow quantiles. In order to account for the presence of serial correlation that might lead to an erroneous rejection of the null hypothesis, a trend‐free prewhitening was applied to the original data series. The regional field significance of trends is tested by a bootstrap procedure. Changes in the streamflow regime in Romania are demonstrated. The main identified trends are an increase in winter and autumn streamflow since 1961 and a decrease in summer flow since 1975. The streamflow trends are well explained by recent changes in temperature and precipitation that occurred in the last 50 years. Copyright © 2013 John Wiley & Sons, Ltd.     

Connexion porphyre cuprifère–épithermaux de type low-sulfidation : analyse structurale et représentation 3D du secteur de Bolcana,monts Apuseni,Roumanie

The AuPbZn low-sulfidation epithermal ore deposits of Troita, Trestia, and Magura (Apuseni Mountains, Romania) are spatially related to the Bolcana Cu-porphyry. In an attempt to demonstrate the connection between these mineralizations, a geometric study was made based on structural measurements and GOCAD^© geomodeller 3D representation of deposits. This study indicates that a specific spatial distribution of the different Au and PbZn veins of the epithermal deposits occurs around the Cu-porphyry, which cannot result from telescoped systems. To cite this article: O. Cardon et al., C. R. Geoscience 337 (2005).     

Identification of blasting sources in the Dobrogea seismogenic region,Romania using seismo-acoustic signals

In order to discriminate between quarry blasts and earthquakes observed in the Dobrogea seismogenic region, a seismo-acoustic analysis was performed on 520 events listed in the updated Romanian seismic catalogue from January 2011 to December 2012. During this time interval, 104 seismo-acoustic events observed from a distance between 110 and 230 km and backazimuth interval of 110–160° from the IPLOR infrasound array were identified as explosions by associating with infrasonic signals. WinPMCC software for interactive analysis was applied to detect and characterize infrasonic signals in terms of backazimuth, speed and frequency content. The measured and expected values of both backazimuths and arrival times for the study events were compared in order to identify the sources of infrasound. Two predominant directions for seismo-acoustic sources’ aligning were observed, corresponding to the northern and central parts of Dobrogea, and these directions are further considered as references in the process of discriminating explosions from earthquakes. A predominance of high-frequency detections (above 1 Hz) is also observed in the infrasound data. The strong influence of seasonally dependent stratospheric winds on the IPLOR detection capability limits the efficiency of the discrimination procedure, as proposed by this study.