Chemical composition of groundwater in the zone of slow water exchange of the Upper Pontian aquifer, Northwestern Bulgaria

The Upper Pontian aquifer occupies the central part of the Lom Depression. The geological position determines its gradual dipping from the periphery to the central parts. It is one of the most water-abundant aquifers in Northwestern Bulgaria and is associated with the sands of the Archar Formation. The chemical composition of the waters is of interest and is important for the water supply in the area. The analysis of the data shows that there are regularities in the change of the water quality with aquifer depth. Significant differences in some of the hydrochemical parameters are found in the zone of slow water exchange and geological and hydrogeological explanations have been sought.

Exotic rock block from the Koshava gypsum mine, Northwest Bulgaria: Petrography, geochemistry, mineralogy and melting phenomena

The described exotic rock block (60×80×13–15 cm) was found at 290 m depth in a lower–middle Badenian gypsum layer in the Koshava mine, NW Bulgaria, near the Danube River. It is greyish-black, granular, with layered structure and layers composed of α-quartz rosettes covered with organic matter (kerogen-like type with high contents of Ge, Mo and B), wood relicts with chalcedony replacement, and porous lenses with compact accumulation of organic matter. The block is coated with quartz crust, up to 2 cm thick, with regmaglypt-like forms, also replaced by quartz. Aside from the surface, melting phenomena were also observed inside the quartz rosettes and especially in the wood relicts and porous lenses. The melted drops are actually crystallized chalcedony. The organic matter accumulations contain Si-organic zoned micrometre-sized spherules. Fe silicides were found in the organic matter of all parts of the block, in which hapkeite was determined by X-ray analysis. Other detected minerals include graphite, cristobalite, coesite, skeletal and framboidal pyrite, moassanite, magnetite, suessite, sphalerite and minerals formed in the gypsum lagoon (gypsum, celestine, barite, calcite, halite and clays). The geological position of the block in the gypsum without any other sediments, the extensive melting phenomena with melted spherules, crushed quartz, its enrichment in 18O isotope and the presence of coesite suggest that it is shock ejecta, in certain aspects resembling the large Muong Nong-type tektites, but its characteristics could be the basis for distinguishing it as a new tektite type. The fact that it was found in a gypsum layer of early–middle Badenian age points to its probable association with the Ries-Steinheim impact event, despite the long distance between them (~1100 km).

Trace element geochemistry and isotopy (Sm, Nd) of lamproites of the Aldan Shield

<p>Lamproites of the Aldan Shield were found (Vladykin 1985) at the beginning of 80-es (for the first time in the USSR), being mainly the intrusive varieties of lamproites, though there occur among them some dyke and volcanic varieties. The general geological and geochemical features of lamproites of the Aldan shield were reported at the VI International Kimberlite Conference at Novosibirsk in 1995 (Vladykin 19971).</p><p>In  Aldan Shield there are known 14 locations of lamproites mostly referred to the Mesozoic rifting. This zone stretches out over all Aldan Shield, from the Murun massif in the Western part of the shield up to the Konder massif in the Eastern part of the shield. These occurrences of lamproites are of Jurassic age (120-150 m.a.). Only lamproites of Khani massif in the SW part of the Aldan Shield are more ancient. At first (according to the data of V.V.Arkhangelskaya) the Khani massif was considered to be Paleozoic, then using K-Ar method (VSEGEI) it was established Proterozoic age of biotite pyroxenites of the massif 1800 m.a. We found the dyke of olivine lamproites of the massif that crosses the biotite pyroxenites. We obtained even more ancient age – 2700 m.a. by zircons from these lamproites with a device SHRIMP (VSEGEI) (Vladykin, Lepekhina - 2005).</p><p>New data on Sr-Nd – systematization of the lamproites of the Aldan Shield have been obtained. The ratios 87Sr/86Sr in lamproites of Aldan vary from 0.703 to 0.708, whereas έ Nd – from -6 to -25. The source of Aldan Shield lamproites is enriched mantle ЕМ-1 (рис.1), that is consistent with their geological position (Vladykin -1997). They are situated between the Aldan Shield and the Siberian platform, where did not occur subduction. The North American lamproites (Leucite Hills, Smoky Bewt, Prery Creak ecc) have a similar position between the Canadian shield and the North-American platform and the same mantle source.</p><p>Compared to the Australian lamproites, the lamproites of the Aldan Shield have lower concentrations of rare-earth elements. The TR spectra for the Aldan lamproites (fig. 2) are rather uniform. A slight slope of the spectrum curves and slight Eu-anomaly are typical. For the earlier olivine lamproites lower TR concentrations are typical as compared with more differentiated leucite and sanidine lamproites.</p><p>The lamproites of the Aldan Shield originated from the enriched mantle source ЕМ-1, the age of that, according to Pb isotopic data, obtained for the rocks of the Murun massif (Vladykin 19972) is estimated as 3200 m.a. The dykes of the olivine lamproites of the Khani massif are the oldest lamproites in the world (2700 m.a.). The TR spectrum of the same type is indicative of similar genesis of the lamproites from various massifs of the Aldan Shield. In spite of the deep mantle source of the Aldan lamproites, they don’t bear diamonds actually, since the diamonds were likely burnt during their crystallization (at t- 1200-1000o C).</p><p><img src="https://contentmanager.copernicus.org/fileStorageProxy.php?f=gepj.68d9d1da710063179070161/sdaolpUECMynit/12UGE&app=m&a=0&c=833cbfbac13f62c9a0cf1376ced7de51&ct=x&pn=gepj.elif&d=1" alt=""></p><p><img src="https://contentmanager.copernicus.org/fileStorageProxy.php?f=gnp.52e855ea710063379070161/sdaolpUECMynit/12UGE&app=m&a=0&c=1874a7ee7bd883faf28c1a71fad727e1&ct=x&pn=gnp.elif&d=1" alt=""></p><p>RFBR 09-05-00116, 08-05-9000.</p><p>References:</p><p>Vladykin N.V. First occurence of lamproites in the USSR.//Doklady Academii Nauk SSSR, 1985, Vol..208, N 3, p.718-722. (in Russia).</p>

The Bystrinskii gabbro massif: the first data concerning composition, age and formation affiliation

Research subject. The research covered the geological position, material composition and rock age of a comparatively small (about 32 km2) Bystrinskii gabbro massif. This massif underlies a tectonic plate package consisting of serpentinized dunits and harzburgites of the ophiolite association in the Eastern boundary of the Middle Urals. Methods. The content of petrogenic elements was measured by the Х-ray fluorescence method using an Х-ray multichannel spectrometer CPM-35. The analysis of rare-earth element contents was conducted using a NexION 300S mass-spectrometer. The composition of rock-forming minerals was studied using an Х-ray microanalyzer CamecaSX100. The age of the massif was determined by the 147Sm-143Nd method of isotope dating. Amphibole geobaometers were used to determine the depth of the rock formation. Results. According to the petro- and geochemical features and composition of the rock-forming minerals, the 147Sm-143Nd isotope age of the rocks was found to be 587 Ma. It was shown that gabbroids in the massif are represented by two petrographic varieties. The predominant type of the rocks is gabbrodolerites, which are similar to the isotropic gabbros of undisturbed ophiolite sections in terms of mineral composition, structure, geochemical features and the depth of formation (not more than 2–3 km). The mapping results showed the massif under study to be the largest among those described thus far. The medium grained gabbroids, which are present in lesser quantities, differ sharply from gabbrodolerites in terms of lower contents of Fe, Ti, both rockforming (K, Na) and rare (Li, Rb, Cs) alkalis, Ba, V, Y, Nb, Zr, Hf and elements of rare-earth group, as well as by significantly higher quantities of Ca, Mg and Cr. The depth of their formation is 10–12 km, which corresponds to the upper mantle. Conclusions. The obtained information demonstrates that fragments of two levels of the ophiolite section are tectonically aligned in the Bystrinskii massif: relatively shallow isotropic gabbros of the upper part of the ophiolite section and deep gabbros of the mantle part of the ophiolite section.

First Finding of the Orbicular Gabbroids in the Ukrainian Antarctic Station Area (Wilhelm Archipelago, West Antarctica)

A new occurrence of igneous rocks with an orbicular structure was discovered by the authors in West Antarctica. The place of finding is Hovgaard Island in the Wilhelm Archipelago located near the Graham Coast of the Antarctic Peninsula. Until now, not a single manifestation of these rare rocks was known in this region. Usually orbicular rocks are formed under the condition of local "coincidence" of many geological and petrogenetic factors. The study of the geological position, texture features and mineral composition of the orbicular rocks on Hovgaard Island was carried out in order to create their primary petrographic description. It was found that orbiculites are exposed in a small area, about 200 m2, in the field of amphibolized gabbroids and their intrusive breccias. The occurrence and textures of the orbiculites indicate that their crystallization occurred at the hypabyssal depth. Probably, this occurrence is a marginal facies of a small gabbroid intrusion, some parts of which are exposed on the adjacent coastal areas of Hovgaard Island. The studies performed have shown that the orbiculites of Hovgaard Island belong to the rarest petrographic representatives of these rocks namely orbicular gabbroids. In their petrographic feature, they differ markedly from the famous French napoleonites (corsites) exposed on the Corsica Island. The mineral composition of the orbicules is represented by calcium plagioclase (An88-97), hornblende (#Mg = 0.77-0.81), clinopyroxene (Wo48-50En43-47Fs5-8), spinel (Sp62-72Hrc14-20Mt12-17), actinolite, phlogopite, chlorite, magnetite and apatite. The interorbicular matrix has a gabbroid composition and a porphyritic texture. It differs from orbicules in somewhat less calcium plagioclase and less magnesian hornblende, as well as in the absence of spinel. In view of the rarity of orbicular gabbroids and the specificity of the described manifestation, it is proposed that the orbicular gabbro on Hovgaard Island be considered as a new petrographic variety of the gabbroid family. The name "hovgaardite" is recommended for the name of this variety of orbicular gabbro.

Primary reduction technology in the Sukhaya Mechetka site assemblage

The Sukhaya Mechetka site in the Lower Volga region being widely known due to the unique preservation of cultural remains, their clear geological position and a rich set of tools has long become a kind of icon of the Middle Paleolithic of Eastern Europe. Improtantly the site was excavated over a wide area (about 650 square meters). During the excavation an assemblage of stone items including more than 350 tools, cores and about 10,000 flint and quartzite flakes of various types was collected. The neogene flint and the paleogene quartzite were used as raw materials approximately equally. According to our observations almost all available and suitable for processing stone rocks that were carried to the site as nodules, blocks, fragments and flakes were intensively used. Raw materials were collected in the immediate vicinity of the site. The signals of raw materials shortage and significant depth of its processing were detected. The distribution of the products of flint and quartzite raw materials on the site is irregular. Primary knapping was carried out according to typical Middle Paleolithic technologies. A small series of stone hammers display specific patterns of their use-wear. The cores and the flakes produced with these hammers were found. The complete sequence of preparation and flaking from the pre-cores to the residual forms has been documented. The shortage of high-quality raw material resulted in extremely complete usage of the most cores. Additionally many residual forms have been used for making tools. The cores can be divided into radial, cuboid and Levallois samples.

Mineralogy of the Vorontsovskoe gold deposit (Northern Urals). Part 1: history of study, mineral assemblages, list of minerals

This work is the frst paper in a series of publications dedicated to mineralogy of the Vorontsovskoe gold deposit in the Northern Urals. The deposit is unique for both Russia and world with regard to the diversity and originality of Tl–Hg–Mn–As–Sb–S mineralization. Based on available literature and our data, we compiled an exhaustive list of 209 mineral species of the deposit, including eight new minerals found by the authors: vorontsovite, ferrovorontsovite, tsygankoite, gladkovskyite, luborzakite, pokhodyashinite, gungerite and auerbakhite. In addition, 40 and 89 minerals are found for the frst time in Russia and the deposit, respectively. Systematic studies of ores revealed nine main mineral assemblages, seven of which are confned to carbonate breccias. They contain more than 70 rare sulfdes, tellurides and sulfosalts including 30, 12 and 9 minerals, where Tl, Hg and Mn are species-defning elements, respectively. In this paper, we characterize the history of study of the deposit, its geological position and structure, ore types, mineral assemblages, and analytical methods.

Mineral-geochemical characteristics Cu-U-Au-manifestations in the Kon Ra region of the Kon Tum province, Vietnam

Background. Complex Au-Cu-U mineralization is found in the metamorphic rocks of central Vietnam in the zones of their contact with Triassic granite intrusions. It is localized in tectonic breccias and cataclasites, which affected Triassic granitoids and Precambrian metaskarn rocks. The greatest differentiation is observed for tectonically disturbed granites of the Hai Van complex and the metasomatically reworked zones of contacts of this complex with metacarbonate and metaultramafic rocks of the Kham Duc complex.Aim. To determine the mineral and elemental composition of complex occurrences of Cu, U and Au in Proterozoic rocks of the Kon Tum province of central Vietnam.Materials and methods. The work was based on the authors’ data obtained during fieldwork and analytical laboratory studies in the 2016–2019 period. The diagnostics of ore mineral composition was carried out using 60 polished sections. The chemical composition of ores was determined for 214 samples by ICP MS and for 374 samples by atomic absorption spectrometry at the Vietnamese Centre for Geological and Experimental Analysis in the city of Hanoi. The geochemical relationships of ore components were established by the method of multivariate statistical correlations.Results. The mineral composition includes pyrrhotite, pyrite, chalcopyrite, molybdenite, magnetite, martite, hematite, cubanite, marcasite, gold, xenotime, sphalerite, uraninite, chalcocite, covellite, goethite, malachite and limonite. According to the petrographic and petrochemical composition, the geological position and the data on isotopic age, the metamorphic formations of the Kham Duc complex can be considered as Neoproterozoic-Cambrian formations having experienced metamorphism in the Ordovician.Conclusion. A scheme of the sequence of mineral formation was outlined. ICP MS results of primary ores showed that, in addition to Cu, the formations under study contain concentrations of Co, Mo, U, Au, Zn, Ni, V, Y, La, and As. A positive correlation was found between Cu, U and Au. A model of hydrothermal ore formation was proposed.