Evidence from the Mesta half-graben, SW Bulgaria, for the Late Eocene beginning of Aegean extension in the Central Balkan Peninsula

The ENE-tilted Mesta half-graben contains a 3-km-thick section of Priabonian (Late Eocene) to Oligocene sedimentary and volcanic rocks that rest unconformably on basement metamorphic rocks along its west side. Basal strata dip 50–60° E and dip at progressively lower angles upward, indicating synrotational deposition. The southern part of the half-graben contains nested volcanic caldera complexes, formed during the deposition of the middle part of the sedimentary sequence, which have been rotated by about half the total rotation of the sedimentary succession. The half-graben is bounded on the east by a fault that steepens from more deeply exposed structural levels in the south (8–18° W) to shallower exposed structural levels in the north (70° W) and together with the rotation of Paleogene strata during deposition indicate the Mesta half-graben is underlain by a listric detachment fault, the Mesta detachment. Subhorizontal Middle Miocene strata that unconformably overlie tilted Paleogene strata yield an upper age limit to the extension. West and northwest of the Mesta half-graben are many other NNW-trending NE-tilted Paleogene half-grabens which we suggest are part of an important extended area in SW Bulgaria and eastern Macedonia that lies above one or more west-dipping detachment faults and date the beginning of Aegean extension in the southern Balkan region as at least as old as Priabonian. The Mesta detachment is oblique to the trend of a contemporaneous Paleogene magmatic arc in the southern Balkans and the origin of the detachment is probably related to gravitationally induced spreading of thickened hot arc crust and Hellenic trench roll back.     

Timing and tectonic significance of Paleozoic magmatism in the Sakar unit of the Sakar-Strandzha Zone,SE Bulgaria

ABSTRACT

Palaeozoic granitoids and meta-granitoids dominate the metamorphic basement of the Sakar unit of the Sakar-Strandzha Zone (SASTZ) in southeast Bulgaria. In this article, we present new whole-rock geochemical data and U–Pb zircon geochronology for the Sakar unit granitoids. The igneous minerals and textures are preserved, except the meta-granitoids that experienced a weak amphibolite-facies overprint. Geochemistry reveals compositions of peraluminous high-K calc-alkaline I- to S-type granitoids of volcanic arc origin. A major group of LILE-LREE-enriched granitoids and meta-granitoids and a single HFSE-HREE-enriched meta-granitoid are distinguished. U–Pb geochronology has yielded crystallization ages between 305 and 295 Ma for the major group granitoids and a ca. 462 Ma crystallization age of HFSE-HREE-enriched meta-granitoid. Late Palaeozoic granitoids of the Sakar unit show similar compositions and a similar tectonic setting when compared to other granitoids of the SASTZ, confirming a uniform region-wide tectono-magmatic event. As the Late Carboniferous-Permian magmatic arc components extend across the SASTZ, they trace the time-correspondent active continental margin along the Eurasian plate during subduction of the Palaeotethys oceanic lithosphere. The late Palaeozoic Eurasian active continental margin magmatic arc evolution of the SASTZ can be extended into the Serbo-Macedonian-Rhodope zones to the west, where time equivalent meta-granitoids support the same geodynamic context.     

Heavy mineral characteristics of the Neogene–Quaternary sediments from the southern part of the Blagoevgrad Basin, SW Bulgaria

The Blagoevgrad Basin, a graben filled with Neogene–Quaternary continental sedimentary successions, is one of the most prospective placer-gold bearing regions in southwestern Bulgaria. The Quaternary sediments have been well explored and economically prospective areas have been identified. Previous studies indicated very limited occurrences of placer gold in the Neogene sediments, the genesis of which is connected with resedimentation of Paleogene sediments from the adjacent Bobov dol Basin to the north. From these previous studies, a detailed allo- and lithostratigraphic scheme, and paleogeographic models were developed.The present study aimed to evaluate the plausibility of the existing stratigraphic schemes and paleogeographic models for the area, through detailed study of the heavy mineral fraction of the Neogene and part of the Quaternary sediments from the southern part of the Blagoevgrad Basin. Additional objectives were to determine the mode of occurrence and the stratigraphic position of the placer gold in the Neogene sediments, and to investigate possible source areas. Special attention was paid to the mineral composition and the structure of the opaque detrital Fe–Ti oxide minerals, and the typologic features of the zircons. The results obtained could be used as a provenance indicator and for determination of the nature of the source area and the processes that operated therein.A very important finding is the discovery of placer gold in an additional three Neogene units. The morphologic features of the gold grains indicate short transport or proximity to the primary source. This interpretation is inconsistent with existing hypotheses on the origin and presence of the gold in the sediments of the basin. The characteristics of the magnetic heavy mineral fraction, and the morphologic features of zircon grains in auriferous samples, indicate the diorites and gabbro-diorites from the Strouma Diorite Group, which outcrop along the eastern edge of the graben, as a possible source.The stratigraphic distribution of the heavy minerals fully supports the plausibility of the existing detailed allo- and lithostratigraphic subdivision, and the paleogeographic model for the development of the southern part of the basin. Also, the results provide support for the soundness of an allostratigraphic approach for the study and exploration of placer deposits in basins similar to the Blagoevgrad.     

Trace elements in the Goze Delchev coal deposit, Bulgaria

The geochemistry of trace elements in the underground and open-pit mine of the Goze Delchev subbituminous coal deposit have been studied. The coals in both mines are highly enriched in W, Ge and Be, and at less extent in As, Mn and Y as compared with the world-wide Clarkes for subbituminous coals. Ni and Ti are also enhanced in the underground coals, and Zr, Cr and Mo in the open-pit mine coals.Characteristic for the trace element contents in the deposit is a regular variation with depth. The following patterns were distinguished for profile I: a — the element content decreases from the bottom to the top of the bed paralleling ash distribution (Fe, Co, As, Sb, V, Y, Mo, Cs, REE, Hf, Ta, Th, P and Au); b — Ge and W are enriched in the near-bottom and near-top coals; c — in the middle part of the bed the content of K and Rb is maximal, while that of U is slightly enriched; d — Ba content decreases from the top to the bottom of the bed. In profile II, W and Be contents decrease from the bottom to the top. The near-bottom, and especially the near-roof samples of profile IV are highly enriched in Ge, while for W the highest is the content of the near-bottom sample.Ge, Be, As, Mn, Cl and Br are mainly organically associated. The organic affiliation is still strong for Co, B, Sr, Ba, Sb, U, Th, Mo, La, Ce, Sm, Tb and Yb in the underground coals, and Fe, Co, Na, W, Sr, Y and Ag in the coals from the open-pit mine. K, Rb, Ti, Zr, Hf and Ta are of dominant inorganic affinity. The chalcophile and siderophile elements correlate positively with Fe and each other and may be bound partly with pyrite or other sulphides and iron containing minerals.Compared statistically by the t-criteria, the elements Na, Li, Cu, Zn, Pb, Cr, Ni, Co, Mo, Fe and Be are of higher content in the open-pit mine. Tungsten is the only element of higher concentration in the underground mine. The contents of Ge, As, Sr, V, Mn, Y, Zr and P are not statistically different in both mines.It was supposed that there were multiple sources of the trace elements in the deposit. The source of the highly enriched elements (W, Ge, Be, and As) most probably were the thermal waters in the source area. The contemporary mineral springs are of high content of these elements. Another source were the hosting Mesta volcanic rocks, which are enriched in Sb, Mo, Hf, U, Th, As, Li and Rb. Some of the volcanics were hydrothermally altered and enriched or depleted of many elements. Thus, the hydrothermal solutions were also suppliers of elements for the coals. It is obvious that the contents, distribution and paragenesis, of the trace elements in both Goze Delchev coals reflect the geochemical specialization of the source area, including rocks, paleo- and contemporary thermal waters.     

Facies and provenance analysis of Paleogene‐age alluvial conglomerates from the northern part of the Mesta Basin,SW Bulgaria

The Mesta Basin in southwest Bulgaria is a graben that contains a Paleogene‐age siliciclastic and volcaniclastic succession deposited in alluvial and fluvial settings. A sedimentological analysis has shed light on conglomerate provenance, and the links between deposition and tectonic setting. Petrographical and chemical analysis of conglomerate clasts and matrix from the Dobrinishka, Gradinishka, Osikovo (or Osenovo) and Zlataritsa formations reveal both local, and more distal source provenance ages. The basal conglomerates are subdivided into three types, a lower and upper polymictic and a middle granitic conglomerate type. Petrographical and chemical analysis reveals granite, gneiss and amphibolite clasts that were sourced from the Sidironero–Mesta Unit of the Middle Allochthon of the Rhodope Metamorphic Complex, and the Rila–Rhodope Batholith to the east of the basin. Cathodoluminescence analysis of quartz sand grains reveals an increased input of red‐ and violet‐luminescent volcanic grains. Volcanic quartz in the oldest conglomerates indicates a hitherto unknown early (pre‐Oligocene) phase of volcanic activity in the vicinity of the Mesta Basin. The conglomerates were deposited in association with movement on the Ribnovo low‐angle normal fault during the Late Eocene, creating subsidence and the development of considerable accommodation space. The establishment of a fluvial environment followed subsequent Oligocene‐age volcanic activity. Copyright © 2012 John Wiley & Sons, Ltd.     

Mineral and inorganic chemical composition of the Pernik coal, Bulgaria

The mineral and inorganic chemical composition of five types of samples from the Pernik subbituminous coals and their products generated from the Pernik preparation plant were studied. They include feed coal, low-grade coal, high-grade coal, coal slime, and host rock. The mineral matter of the coals contains 44 species that belong mainly to silicates, carbonates, sulphates, sulphides, and oxides/hydroxides, and to a lesser extent, chlorides, biogenic minerals, and organic minerals. The detrital minerals are quartz, kaolinite, micas, feldspars, magnetite, cristobalite, spessartine, and amphibole. The authigenic minerals include various sulphides, silicates, oxihydroxides, sulphates, and carbonates. Several stages and substages of formation were identified during the syngenetic and epigenetic mineral precipitations of these coals. The authigenic minerals show the greatest diversity of mineral species as the epigenetic mineralization (mostly sulphides, carbonates, and sulphates) dominates qualitatively and quantitatively. The epigenetic mineralization was a result of complex processes occurring mostly during the late development of the Pernik basin. These processes indicate intensive tectonic, hydrothermal and volcanic activities accompanied by a change from fresh to marine sedimentation environment. Thermally altered organic matter due to some of the above processes was also identified in the basin. Most of the trace elements in the Pernik coals (Mo, Be, S, Zr, Y, Cl, Ba, Sc, Ga, Ag, V, P, Br, Ni, Co, Pb, Ca, and Ti) show an affinity to OM and phases intimately associated with OM. Some of the trace elements (Sr, Ti, Mn, Ba, Pb, Cu, Zn, Co, Cr, Ni, As, Ag, Yb, Sn, Ga, Ge, etc.) are impurities in authigenic and accessory minerals, while other trace elements (La, Ba, Cu, Ce, Sb, Bi, Zn, Pb, Cd, Nd, etc.) occur as discrete phases. Elements such as Sc, Be, Y, Ba, V, Zr, S, Mo, Ti, and Ga exceed Clarke concentrations in all of the coal types studied. It was also found that a number of elements in the Pernik coals (F, V, As, Pb, Mo, Li, Sr, Ti, Ga, Ni, Ge, Cr, Mn, etc.) reveal mobility in water and could have some environmental concerns.     

Properties and depositional environment of the Neogene Elhovo Lignite, Bulgaria

Several Mio-Pliocene aged lignite seams occur as part of a non-marine transgressive sequence in the Elhovo graben in south-eastern Bulgaria. The present study is focused on 45 samples collected from three boreholes in the eastern part of the basin. Petrographic data along with ash and sulphur contents were used in order to determine the lateral and vertical variations of the coal facies and depositional environment of the Elhovo lignite.The lignite seams accumulated in a rheotrophic, low-lying mire with high pH value and are characterized by high ash yields and sulphur contents. Despite of the neutral to weakly alkaline environment the bacterial activity was limited and the tissue preservation and gelification were mainly controlled by the redox conditions.Vegetation rich in decay resistant conifers dominated in the Elhovo basin together with mesophytic angiosperm species. The absence of algal remains and sapropelic coal indicated that open water areas were not present during peat accumulation. The latter processed in an environment, characterized by low subsidence rate, in which prior to the burial the woods were subjected to severe mechanical destruction. According to our interpretation, the enhanced impregnation of the tissues bacteria and fungi played only a secondary role in the process of humification. The lignite from borehole 122 and partly from BH 145 deposited in an environment characterized by relatively low (ground)water table, whereas to the south an area dominated by a flooded forest swamp (BH 104) formed. This is suggested by the better tissue preservation and gelification of the organic matter in BH 104. The vertical variation of the maceral composition in the studied lignite is interpreted as a consequence of vegetational changes, rather than to changes in the depositional environment. The low contents of inertinite macerals indicate that despite of the low water level the environment was relatively wet and the thermal and oxidative destruction of the tissues was limited.Peat accumulation was terminated by a major flooding event and a short term establishment of a lake. In contrast to the West Maritsa basin, no seam formed in the Elhovo basin during the filling stage of the lake.     

Rural diversification in Bulgaria

Agriculture has always been very important for the Bulgarian economy, but during the socialist period there was considerable progress made in the diversification of employment opportunities in rural areas. While many people commuted to non-agricultural jobs in the townships (and there was a large permanent transfer from rural to urban areas), there were additional opportunities in small factories and local services in the villages themselves. The transition has seen these opportunities much reduced, at precisely the time when full-time paid work in agriculture has declined due to market restructuring while complex problems have emerged associated with liquidating the state-run cooperatives and establishing a viable alternative. The paper discusses the general issues and presents a case study from the north-central part of the country. The rebuilding of a cooperative farming system (along with other forms of consolidation) is a positive trend which could increase spending power in the villages and help in the growth of employment in rural industries and services. This revised version was published online in July 2006 with corrections to the Cover Date.     

Stable isotope study of carbonate-cemented rocks from the Pobitite Kamani area,north-eastern Bulgaria

The Precipitation of carbonate cements in the Pobitite Kamani area (Lower Eocene) began during early diagenesis of sediments. There is evidence, however, that calcite is still forming today.The negative ¹³C values to –29.2 suggest that the carbonate formed during degradation of ¹²C-enriched organic matter (perhaps partly from oxidation of methane). The ¹⁸O values of –0.9 to –1.6 reflect the marine origin of the early diagenetic carbonate cements. Most of the carbonates, however, formed during late diagenesis (at approximately 1300 m burial depth) and/or recently (after uplift) from percolating groundwaters. These carbonates have an isotopic composition characteristic of carbonates which precipitated from meteoric waters under normal sedimentary temperatures in isotopic equilibrium with ¹²C-enriched soil carbon dioxide.     

Organic petrology, mineralogy and depositional environment of the Kipra lignite seam, Maritza-West basin, Bulgaria

The aim of the present study is to provide additional information about the properties and depositional environment of the Kipra lignite seam, which was deposited during the regressive stage of development of the Maritza-West basin. Petrographical and mineralogical data, along with ash yields and sulphur contents of 24 samples from a seam profile, have been used to study the vertical variation of the depositional settings during peat accumulation and subsequent coalification.The Kipra lignite is characterized by high ash yields and sulphur contents. It formed in a rheotrophic, low-lying mire with alkaline pH value. Vegetation with low preservation potential dominated within the palaeomire. During peat formation, frequent changes of the water level controlled the depositional environment. During the deposition of units 1 and 2, high water energy caused the transportation of high amounts of inorganic material into the mire, resulting in the formation of weakly gelified mineral-rich lignite. The organic matter from units 3 and 4 is characterized by enhanced gelification, which probably reflects the decreasing energy of the system. Good positive correlation between sulphur contents and the GI values was established in units 4, indicating that the gelification of the tissues was probably mainly controlled by the bacterial activity. In contrast, the gelification of the samples from unit 3 of the Kipra seam was probably governed by the redox conditions. The organic matter deposited under relatively wet conditions, in which the thermal and oxidative destruction of the tissues, was limited.A variety of major, minor and accessory minerals are present in Maritza-West lignite. The mineral composition is dominated mainly by pyrite, gypsum and calcite, and to a lesser extent limonite, quartz, kaolinite, montmorillonite, illite, chlorite and plagioclase. Jarosite, hematite, halloysite, mica, K-feldspar, aragonite, siderite, and dolomite were also determined in very low concentrations. These minerals formed syngenetically and epigenetically. The syngenetic stage is characterized mainly by the formation of pyrite, carbonates, silicates and sulphates, whereas the Fe-oxyhydroxides, partially the carbonates and almost all silicates are of detrital origin. During the epigenetic stage, carbonates, sulphates, clay minerals, pyrite, and Fe-oxyhydroxides were formed. Alteration products like gypsum, jarosite, limonite, chlorite, kaolinite, illite, mica, and calcite were generated due to the transformation of detrital and authigenic minerals.     

FLAC3D在边坡数值分析及位移监测中应用

以辽宁省岫岩县某山头边坡为例,通过槽探、钻探、大型剪切试验等多种手段,找出合理潜在滑动面。利用FLAC3D软件对该边坡进行三维数值模拟,分析应力应变关系,得出变形较大及应力集中区域,同时利用强度折减法得出边坡的安全系数,评价其稳定性。将从边坡后缘张拉裂隙上布设的位移监测点采集到的数据,与数值模拟结果进行对比分析,验证数值模拟的可靠性,为边坡抗滑设计提供依据。     

Archaeological evidence for tectonic activity in the region of the Haifa-Qishon Graben, Israel

Thirty-five archaeological sites between Lebanon and Gaza on the Mediterranean shore of Israel were surveyed for evidence of relative changes of sea level; and published and unpublished data were compiled on a further 23 sites. Remains of occupation levels were classified into 13 archaeological periods from Neolithic to Crusader, giving a good dating scale over the last 9000 years. The Bronze Age shoreline (4000 years B.P.) is shown to be very close to the present shore along most of the coast, with vertical changes of less than 1.0 m at most sites. For later periods the accuracy of measurement of relative changes of level was improved to a root sum square error of 28 cm.The mean and modal sea levels derived from all sites of the same archaeological period were plotted against time to indicate the most probable “eustatic” sea-level curve, though it is accepted that hydro-isostatic adjustment and broad-scale slow earth movements cannot be separated statistically from eustatic changes on a 200-km stretch of coast. The relative sea level is shown to have been between −70 cm and present sea level for the last 4000 years, with no evidence for oscillations of amplitude more than ±30 cm at periodicities longer than 400 years, and no high sea level still stands.Relative vertical displacement between sites of the same archaeological age is attributed to tectonism. The sites on the alluvium of the Haifa—Qish on graben show no signs of vertical displacement, but there is maximum activity to north and south. Acco, on the north margin, shows submergence of nearly 2.0 m since A.D. 1300, with probable uplift preceding that date. Mount Carmel, south of the graben, shows signs of only very slight relative change, possibly attributable to eustatic change, in the immediate vicinity of the graben. But the southern flank of the mountain, 20–80 km south of the southern fault of the Graben, shows active vertical movements on the whole coast. Dor and Caesarea indicate multiple vertical movements ranging from 1.0 to 5.0 m in the last 2000 years, and a slump or fault has intersected the harbour area of Caesarea about 150 m offshore.These observations are related briefly to recent geodetic levelling of the coast and graben area; observations on the Dead Sea Rift, and hypotheses of fault control of the linearity of the Israel Mediterranean coastline.     

Monitoring the tectonic plate movements in Turkey based on the national continuous GNSS network

In recent decades, the space geodesy has been applied to the areas such as transportation, infrastructure planning, navigation, etc. Among them, the precise positioning at the Global Navigation Satellite System (GNSS) stations yields better view in the understanding of the crustal deformation that requires global-scale measurements. There have been numerous studies examining the data process of continuous GNSS observations in the field of earth monitoring. More recently, GNSS stations established for continuously operating reference station networks have been beneficial resources in the tectonic plate-monitoring studies in lieu of campaign-type observations. However, this requires that the Continuously Operating Reference Station (CORS) should be established on stable structures acting like foundations and requires investigation of the long-term repeatability time series. This study aims to introduce recently established national CORS network, named CORS-TR, covering the entire Turkey and Northern Cyprus, and to explain the process of the long-term data obtained from the network on the characteristics of the tectonic plate movement within the area. The results of the CORS-TR data process present a great potential of using continuously operating reference stations not only in real-time kinematic applications of conventional geodesy studies but also in detecting and monitoring the crustal deformations of those that are crucial in earthquake-prone areas like Turkey. Since the findings are computed from the results of the all permanent stations of CORS-TR network, this study also examines the GNSS observation quality of the network for the given time interval. One of the major conclusions of the data process conducted in the study displays that the CORS-TR stations established on the carefully selected large and low-rise existing building had been more stable than the stations on the ground which have been subjected to soil settlement since the construction.     

Water resource impacts of climate change in southwestern Bulgaria

This study assesses the regional impact of climate change on runoff in a mountainous region of southwestern Bulgaria. A GIS-based distributed hydrologic model and two climate change scenarios – HadCM2 and CCC – were employed for years around 2025 and 2085. Results from both scenarios demonstrate the basin's sensitivity of runoff to climate change, which produce significant spatial and temporal changes in the basin's water yield with maximum runoff shift into early spring and further decreases in summer runoff. There could be no reduction in mean annual runoff, except under the Hadley scenario by 2085. Changes in the magnitude of mean monthly and peak flow are associated with early snowmelt and a reduction in snow cover in spring. Increases in spatial variability of runoff reflect the basin's complex physiographic characteristics. The increase of spatial and temporal variability in runoff points to different strategies for future water resource management. This revised version was published online in July 2006 with corrections to the Cover Date.     

Gated communities in Bulgaria: interpreting a new trend in post-communist urban development

Private residential neighbourhoods encircled by a wall or fence and cut off from the public by a remote-controlled or guarded gate are not entirely new in Bulgaria. Both ‘dacha’ and leisure settlements of the communist rulers existed in such enclosed developments on the outskirts of Sofia, in mountain resorts, and on the coast of the Black Sea until the end of the 1980s. After the political change in 1989, new types of walled settlements, similar to gated communities in the U.S., began to spring up in Bulgaria, a result of the dramatic and decisive changes in Bulgarian society that are still very much underway today. Seven gated communities, comprising 78 housing units and six projects that are not yet fully completed create an entirely new social context and a residential landscape in the Sofia metropolitan area, which may indicate future residential desires. Ivanyane, situated on the western periphery of Sofia, and Mountain View Village to the southeast, exemplify the two main types of gated communities which are either self-organized by residents or developer-organized. The reasons why these gated communities were built appear to be very similar to those in other places. It can be expected that the demand for this new type of residential living will continue to increase in Sofia’s urban periphery, but it would be unwise to assume that these developments will necessarily provide a positive context for building a new society. The research for this paper was made possible through a project on post-communist urban development approved and financed by the Austrian Ministry of Education, Science and Culture and the Austrian Institute for East and Southeast Europe (Liaison Office in Sofia).     

Peri-Gondwanan Ordovician crustal fragments in the high-grade basement of the Eastern Rhodope Massif,Bulgaria: evidence from U-Pb LA-ICP-MS zircon geochronology and geochemistry

Field, geochemical, and geochronologic data of high-grade basement metamafic and evolved rocks are used to identify the nature and timing of pre-Alpine crustal growth of the Rhodope Massif. These rocks occur intrusive into clastic-carbonate metasedimentary succession. Petrography and mineral chemistry show compositions consistent with Alpine amphibolite-facies metamorphism that obliterated the original igneous textures of the protoliths. Bulk-rock geochemistry identifies low-Ti tholeiitic to calc-alkaline gabbroic-basaltic and plagiogranite precursors, with MORB-IAT supra-subduction zone signature and trace elements comparable to modern back-arc basalts. The U-Pb zircon dating revealed a mean age of 455 Ma for the magmatic crystallization of the protoliths that contain inherited Cambrian (528–534 Ma) zircons. Carboniferous, Jurassic, and Eocene metamorphic events overprinted the Ordovician protoliths. The radiometric results of the metamorphic rocks demonstrate that Ordovician oceanic crust was involved in the build-up of the Rhodope high-grade basement. Dating of Eocene-Oligocene volcanic rocks overlying or cross-cutting the metamorphic rocks supplied Neoproterozoic, Ordovician and Permo-Carboniferous xenocrystic zircons that were sampled en route to the surface from the basement. The volcanic rocks thus confirm sub-regionally present Neoproterozoic and Paleozoic igneous and metamorphic basement. We interpret the origin of the Middle-Late Ordovician oceanic magmatism in a back-arc rift-spreading center propagating along peri-Gondwanan Cadomian basement terrane related to the Rheic Ocean widening. The results highlight the presence of elements of Cadomian northern Gondwana margin in the high-grade basement and record of Rheic Ocean evolution. The eastern Rhodope Massif high-grade basement compared to adjacent terranes with Neoproterozoic and Cambro-Ordovician evolution shares analogous tectono-magmatic record providing a linkage among basement terranes incorporated in the Alpine belt of the north Aegean region.     

Constraints of stable isotopes on the origin of alunite from advanced argillic alteration systems in Bulgaria

Voluminous areas of advanced argillic alteration (AAA) constitute major exploration targets for surficial Cu–Au epithermal and potentially underlying porphyry-type deposits. In Bulgaria, more than 30 alunite occurrences are recognised, few of them being associated with a mineralised system. A mineralogical study combined with a stable isotopic (O, H, S) study has been carried out on nine alunite occurrences of advanced argillic zones hosted by volcanic rocks of Late Cretaceous age in the Srednogorie belt and of Oligocene age in the Rhodopes belt. This work was realised in order to constrain the origin of alunite and to define criteria to discriminate alunite from ore deposits and alunite from large barren alteration systems.Mineralogy of the nine occurrences consists of alunite + quartz + minor alumino-phospho-sulphates, associated with more or less kaolinite, dickite, pyrophyllite, diaspore and zunyite, depending on formation temperature. Alunite generally occurs as tabular crystals but is also present as fine-crystalline pseudocubic phases at Boukovo and Sarnitsa, in Eastern Rhodopes. In the advanced argillic alterations associated with economic ore, the presence of zunyite in the deeper parts indicates acid–fluorine–sulphate hydrothermal systems, whereas it is absent in uneconomic and barren advanced argillic alteration. All occurrences are formed at temperatures between 200 and 300 °C.(H, O, S) isotopic signatures of alunite combined with mineralogical features from all the studied occurrences, whatever their type, show characteristics of magmatic-hydrothermal systems. Sulphur data indicate essentially a magmatic origin for sulphur. Oxygen and hydrogen data suggest that hydrothermal fluids result from a mixing between magmatic fluids and an external component, which is identified as seawater-derived fluids or meteoric water in the vicinity of a sea. In most of the alunite occurrences, magmatic fluids are dominant and H₂S/SO₄ ratios are estimated to be higher than 2. Two exceptions exist in the Rhodopes. At Boukovo and Sarnitsa, where the estimated formation temperatures of alunite are the lowest, the external fluids are dominant and H₂S/SO₄ratios are estimated to be lower than or close to 1.At this stage of the work, the mineralogical and isotopic criteria do not enable a clear distinction between economic and uneconomic systems. However, some features are common in the economic ore deposits: the presence of zunyite in the deeper part of the system, the relatively high temperatures suggested by the zunyite + pyrophyllite + alunite + diaspore assemblages, the (O, H, S) signature of alunite, which is characteristic of dominant magmatic–hydrothermal acid–sulphate–fluorine systems.     

Movement of the Shuping landslide in the first four years after the initial impoundment of the Three Gorges Dam Reservoir, China

The Shuping landslide was reactivated by the initial impoundment of the Three Gorges Dam Reservoir, China in June 2003. For purposes of landslide disaster mitigation in the reservoir area and identification of landslide movement and deformation caused by reservoir level changes, a monitoring system mainly consisting of drum-style extensometers was installed in the eastern part of the Shuping landslide. Systematic monitoring was started in August 2004 with installation of 13 extensometers above the waterline after the initial impoundment. In August 2006, 11 more drum-style extensometers were installed above the high waterline (175 m) and five flexible extensometers were installed along a longitudinal section in the elongation to low waterline. In this paper, the monitoring results from August 2004 to July 2007 are presented and the deforming of the Shuping landslide caused by both reservoir level changes and rainfall is examined.     

Ore petrology,hydrothermal alteration,fluid inclusions,and sulfur stable isotopes of the Milin Kamak intermediate sulfidation epithermal Au-Ag deposit in Western Srednogorie,Bulgaria

The Milin Kamak gold-silver deposit is located in Western Srednogorie zone, 50 km west of Sofia, Bulgaria. This zone belongs to the Late Cretaceous Apuseni-Banat-Timok-Srednogorie magmatic and metallogenic belt. The deposit is hosted by altered trachybasalt to andesitic trachybasalt volcanic and volcanoclastic rocks with Upper Cretaceous age, which are considered to be products of the Breznik paleovolcano. Milin Kamak is the first gold-silver intermediate sulfidation type epithermal deposit recognized in Srednogorie zone in Bulgaria. It consists of eight ore zones with lengths ranging from 400 to 1000 m, widths from several cm to 3–4 m, rarely to 10–15 m, an average of 80–90 m depth (a maximum of 200 m) and dip steeply to the south. The average content of gold is 5.04 g/t and silver – 13.01 g/t. The styles of alteration are propylitic, sericite, argillic, and advanced argillic. Ore mineralization consists of three stages. Quartz-pyrite stage I is dominated by quartz, euhedral to subhedral pyrite, trace pyrrhotite and hematite in the upper levels of the deposit. Quartz-polymetallic stage II is represented by major anhedral pyrite, galena, Fe-poor sphalerite; minor chalcopyrite, tennantite, bournonite, tellurides and electrum; and trace pyrrhotite, arsenopyrite, marcasite. Gangue minerals are quartz and carbonates. The carbonate-gold stage III is defined by deposition of carbonate minerals and barite with native gold and stibnite.Fluid inclusions in quartz are liquid H₂O-rich with homogenization temperature (T_h) ranging from 238 to 345 °C as the majority of the measurements are in the range 238–273 °C. Ice-melting temperatures (T_m) range from −2.2 to −4.1 °C, salinity – from 3.7 to 6.6 wt.% NaCl equiv. These measurements imply an epithermal environment and low- to moderate salinity of the ore-forming fluids.δ³⁴S values of pyrite range from −0.49 to +2.44‰. The average calculated δ³⁴S values are 1.35‰. The total range of δ³⁴S values for pyrite are close to zero suggesting a magmatic source for the sulfur.