Annual Report 8

Project No 2 is financially supported in part by the Bulgarian National Science Fund of the Ministry of Education and Science. Project No 14 is financially supported by NATO's Lincage Grant.

INTRODUCTION

This annual report presents the activities of the Central Laboratory of Mineralogy and Crystallography during the 8th year of its existence.The topics developed were in accordance with the preliminary specified scientific and applied priorities.

The most significant scientific results, published or reported at conferences can be grouped as follows:

A common geo-genetic model is developed for the Fluorite Formation deposits in Bulgaria allowing their prognosing; on the basis of new data on the isotope composition of barite, siderite, and dolomite from Kremikovtsi deposit the geo-genetical model is specified further with respect to ore bearing source solutions, the mechanism of ore deposition, and the ore potential of the region; the phase-mineralogical transformation and the chemical interactions in the inorganic matter are established for the combustion products of coals from the main Bulgarian deposits.
The reguliarities in the hydrothermal syntesis of titanosilicate phases in a kinetic regime are studied and the sequence of the phase transformation of the more stable products is established; a new layered titanosilicate is synthesized as well as new materials of the type Synroc are designed with simulative additions of Sr, Sm, and Nd aiming at stable and irreversible inclusion of radioactive wastes inthere; the mass-transport processes in basaltic melts in an external electric field are studied.
The local structure and the dynamics of the phase transition is investigated in to relaxor materials and the atomic mechanism of the formation of ferroelectric state therein are determined; the distribution of cations in the structure of metal-containing boron-carbide ceramics is studied; the structural position of tungsten in tungsten-bearing goethites is established as well as the structural state of opals from Eastern Rhodopes is discussed and two crystal structure are refined.

Among the most important achievements of practical character are:

Geological maps of the heavy mineral concentrates are prepared aiming at prospecting gold, tin, tungsten, mercury, and other mineralizations in particular regions in Bulgaria.
Solid-phase synthesis of pyro- and polyphosphates is performed by mechanochemical activation and thermal treatment of mixtures of natural phosphorites and ammonium sulfates and the possibility is proved for obtaining fertilizer components and sorbents from low-grade raw materials and waste products.
New poly-oxy-ethylene phosphonates are synthesized suitable for obtaining effective radio-protective druggs.
Combined filters are constructed based on the minerals vermiculite, montmorillonite, and clinoptilolite, suitable for clean-up of waste waters.

The most important results obtained in the framework of the interantional collaboration of CLMC are:

According to a mutual scientific project with the University of Ghent, Belgium, financed in the framework of the Scientific Program of NATO, gold catalyst systems are synthesized on micro- and mesoporous titanosilicates. They are effective for oxydation of aliphatic hydrocarbons under very soft conditions. The method is cheap and ecologically pure as compared with the methods used nowadays in industry.
In the frame of a mutual project with the Institute of Isotope Geology and mineral resources, ETH Zurich, Switzerland, and Sofia University "St. Kliment Ohridski" the work on dating and isotopic geochemical characterization of the ore-bearing magmatism in the deposit Elatsite is completed (92 ± 10.3 Ma - 91.84 ± 0.3 Ma - U-Pb age after zircons); Upper Cretaceous age (79-86 Ma - U-Pb age after zircons) of a number of plutons cropping out in the south part of Central Srednogorie zone is determined; Early Paleozoic age (451+18/-9 Ma - 459.9 ± 7.6 Ma - U-Pb age after zircons) of intrusion of metagranites croping out in Ograzden and Maleshevska mountains is determined.
In the framework of a mutual project with the Institute of Geology of the Ural Branch of the Russian Academy of Science, Syktyvkar, Russia, Middle-Upper Jurassic age of granitoides near Skrit village in Belasitsa mountain is determined (167 ± 9.9 Ma - Rb/Sr data).

During 2002 the work in the new building of CLMC was in general put under normal conditions and this made it possible the optimal usage of the scientific equipment and stuff activity.

Nikola Zidarov
Sofia, January, 2003

RESEARCH TOPICS:

I. MINERAL SYSTEMS:

1. Magmatic and metamorphic minerals and mineral associacions in Serbo-Macedonian Massif (N. Zidarov, I. Peytcheva, R. Titorenkova, L. Macheva)

Metagranites from the most SE part of Serbo-Macedonian Massif (Ograzhden and Maleshevska mountains, SW Bulgaria) were investigated using petrologic-geochemical analyses, zircon typology, isotope U-Pb (TIMS) and Hf zircon data [26].

Two facial varieties of metagranitoids are distinguished: equigranular and porphyritic. They are deformed, metamorphosed (amphibolite facies formed at 650 ^OC and 7-8 kbar) and uneven migmatized with augen, augenlayered or layered structure. Less deformed parts reveal magmatic peculiarities: micro-granular enclaves, zonally arranged plagioclase inclusions in potassium feldspar porphyroclasts and foliated aplitic and pegmatitic dikes. Petrochemical and geochemical features point to a predominantly crustal origin (ASI 1.02-1.48). Discriminant diagrams are controversal and argue for VAG and post-collisional geodynamic environment.

The typology distribution of zircons from equigranular metagranites and their typology trends confirm that they originate predominantly from a crustal magma source and point to an anatectic origin. The zircon population include mainly S₁, S₆, L₁subtypes. The most abundant zircon subtypes from porphyritic metagranite variety are S₃, S₆ and S₁, but curved and resorbed surfaces dominate due to the higher degree of migmatization and metamorphic overgrowths.


Fig. 1. U-Pb concordia diagram for zircons of the equigranular metagranites from Serbo-Macedonian Massif.	Fig. 2. U-Pb concordia diagram for zircons of the porphyritic metagranites from Serbo-Macedonian Massif

Longprismatic to needle-shaped violet-pinkie crystals of the small fractions are separated for U-Pb single zircon analyses, with the purpose to avoid inherited cores. Some of the grains are additionally abraded to remove the outer parts, which are usually disturbed by the overprinted metamorphism. Zircons of the equigranular metagranites yield a discordia (Fig. 1) with an upper intercept age of 459.9 ± 7.6 Ma (MSWD 1.17), interpreted to reflect the time of intrusion. Zircons of the porphyritic varieties point to an upper intercept age of 451 +18/-9 Ma (MSWD 0.24) (Fig. 2). Both types of metagranites contain also zircons with older cores (spatially in shorter crystals and in fractions of greater size) and lead inheritance and lead losses are observed.

Lu-Hf ratios are measured by MS-ICPMS in the same zircons, that are used for age determination. Calculated e-Hf values range from -0.14 to - 2.97 (Fig. 1 and 2) and give evidence for mixed but crustal dominated origin of the magma. These data are in good agreement with the discriminant ratios of the main and rare elements and argue for VAG affinity of the granitic magma.The presented new data suggest widespread Neoproterozoic to Early Paleozoic magmatic activity in the tectonic units of West Bulgaria, ranging in time from 568±7.5 Ma (gabbro, Ossogovo-Lisets) and 563±3 Ma (gabbro, Tcherny vrach) to 460±9 Ma (metagranites in Ograzhden and Maleshevska mountains).

2. Accessory zircon in orthogneisses from the Ograzdenian block of Serbo-Macedonian Massif (R. Titorenkova)

The chemical composition of zircon from equigranular metagranites, porphyritic metagranites, and melanocratic enclaves from Ograzden and Maleshevska Mountains is studied on the base of back-scattered electrons (BSE) patterns and cathodoluminescence (CL) images (Ann. Report 7/2001).

Zircons from equigranular metagranites. Magmatic zircon from these rocks is characterized with highest contents of Y, U, and Th and of trace elements. The highest contents (wt. %) of Y₂O₃ (up to 2), HfO₂ (up to 2.5), P₂O₅ (up to 1.9), and of all the other analyzed trace elements were registered in dark CL areas [85].

The content of trace elements typically increases in the low temperature morphotypes - P, G, and L. The inherited cores reveal a significantly low content of all the analyzed elements (wt. %): Y₂O₃ (0.1-0.4), HfO₂ (1.2-1.6), P₂O₅ (0.3), UO₂ (up to 0.1).

Zircon crystals from porphyritic metagranites. Cores and overgrowths have the same chemical characteristics. The content (wt. %) of P₂O₅ is in the range from 0.1 to 0.49 and that of Y₂O₃ - from 0.05 to 0.6.

The main difference with respect to equigranular metagranites is in the distribution of UO₂ (up to 0.37 wt. %) and ThO₂ (below the detection limit).

Zircons from microgranular enclaves in equigranular metagranites. The zircons from microgranular enclaves are of nearly constant content of HfO₂ (1.13-1.8 wt. %) while the content (wt. %) of Y₂O₃ (0.04 and 0.2) and P₂O₅ (up to 0.15) is lower than in zircon from metagranites. The concentrations of Al, Fe, Yb, Er, and Dy are below the detection limit, which is also sometimes the case with that of UO₂ and ThO_2.

The external morphology, the inner structure and chemical features of zircons allow one to propose the following geological evolution of the studied rocks: 1) The crystallization of evolved igneous protoliths gives rise to the formation of idiomorphic oscillatory-zoned magmatic zircon or unzoned one (dark in CL). During this stage the magmatic dissolution and the partial resorbtion of the magmatic crystals is possible. The BSE images are usually of a low contrast, which is due to insufficient differences in the chemical composition; 2) Prograde metamorphic stage leading to the formation of metamorphic zircon overgrowths and to smoothing of the fine oscillatory zones in the areas most strongly affected by the migmatic event. The metamorphic process causes homogenisation in different degree and erasing of the primary grown structures, as well as migration of U in the crystals, which leads to chemical homogenisation; 3) Retrograde metamorphic stage leading to partial recrystallization (surface- or cracks-controlled), related to fluids. This process is related to migration and uranium leaching out of the crystal.

The results indicate a complex zircon structure when primary geochemical characteristics cannot be separated from the secondary imposed variations. For isotopic U-Pb single crystal thermal evaporation we used long prismatic zircon crystals not containing inherited cores and often with well-preserved primary zoning.

3. Accessory epidote-group minerals from the Kolarovo metaplagiogranites, Belassitza Mountain, Ograzdenian block of Serbo-Macedonian Massif (E. Tarassova)

Accessory minerals of the epidote group in granitoid rocks are well known as indicators for the type of primary magma and its crystallization history, for the postmagmatic and deformation processes. Based on these findings, we studied the minerals of epidote group from metaplagiogranites cropping out south of Kolarovo village (Belassitza Mountain, Ograzdenian block of Serbo-Macedonian Massif). The metaplagiogranites described for the first time by Zidarov et al. (1966 unpublished data) are distributed on a small scale in the district, being presented by one large and several smaller bodies. The rocks are leucocratic, of a weak schistosity and consist of a stable magmatic association of plagioclase, quartz, and biotite. Three types of the epidote group minerals are established in Kolarovo metaplagiogranites: (1) allanite (reported here for the first time), (2) magmatic epidote (epidote-I), and (3) postmagmatic epidote (epidote-II). Allanite is the earliest and rarely occurring mineral of the group, being entirely embedded in part of the epidote-I grains. The allanite cores in epidote grains are isometric or euhedral crystals and demonstrate markedly the dissolution in the melt and the replacement by magmatic epidote. According to its chemical composition (wt.%) (Ce₂O₃ - up to 9.3; La₂O₃ -up to 4.2; Nd₂O₃ - up to 4.7; Y₂O₃ - up to 1.2; ThO₂ - up to 0.9; UO₂ - up to 0.4) the mineral may be classified as Ce-type allanite. Epidote-I occurs as euhedral to hemihedral crystals with and without allanite cores.

The mineral had been formed before and simultaneously with biotite. Epidote crystals are euhedral and are entirely embedded in biotite. At the contacts with plagioclase a significant deterioration of the morphology of epidote crystals is observed. According to literature data, the observed relationships of epidote with biotite and plagioclase are typical and indicative for the magmatic origin of epidote. Epidote-II replaces plagioclase and is related with a process of deformation. The replacement occurs most intensively along the boundaries between the plagioclase grains.

The chemical compositions of the epidote type minerals studied are plotted in the figure in terms of (REE+Y+Th+U) against the total Al (p.f.u.) (Fig. 1.). As seen, the points corresponding to the allanite under study lies between the regions of I- and S-type granitoids (according to Broska et al., 2000), thus suggesting that the primary magma had been mixed (S- + I-types). Epidote-I is of an intermediate epidote-clinozoisite-allanite composition corresponding well to the composition trend observed for allanite. At the same time, the composition of postmagmatic epidote (epidote-II) is close to that of proper epidote, containing about 25 mol.% of clinozoisite.

Fig. 1. Compositions of allanite, magmatic epidote and metamorphic epidote plotted in terms of (REE+Y+Th+U) vs. total Al (cations per 23.5 oxygen atoms). Shaded fields are related to the allanite compositions for I-, S- and A-type granitoids, respectively.

4. Main elements of the common geogenetic model for deposits of the Fluorite Formation (B. Zidarova, N. Zidarov).

The industrial deposits of fluorite in Bulgaria - Slavyanka, Mikhalkovo, and Chiprovci-East originate from hydrothermal systems with similar characteristics. Based on published local geologic-genetic models concerning these deposits (see Ann. Reports 1/1995, and 6/2000) the following main elements of the common geo-genetic model of the deposits of the Fluorite Formation are specified.

1. The Fluorite formation is a mineral type of ore formation including fluorite deposits of simple mineralogical composition - fluorite, quartz, calcite±clay minerals, ±barite, and small amounts of sulfide minerals.

2. Geodynamic environment of formation - a magmatic arc formed on the active continental margin. The hydrothermal system is connected with acid magmatism (volcanism), appearing in tectonic units framed by first-order disslocations reaching the Upper Mantle.

3. Spatial development - controlled by the local structure-deformation scheme and lithology, which determines the morphogenetic type of the deposits: vein type in silicate rocks and stratiform type in carbonate rocks.

4. Temporal development - determined by pulsed supply of hydrothermal solutions resulting from temporary closure of their paths due to still deposited mineral products or to contracting tectonic strains.

5. Hydrothermal activity - organized in a hierarchical system of convective cells of several orders: I - connected with magma generating system; II - circulation of hydrothermal solutions in the deposit or in ore locus of the deposits; III - circulation of the hydrothermal solutions in separate parts of the deposit (fluorite bodies).

6. Source of substance - fluorine is most probably resulting from degasification of the Upper Mantle, while the remaining components (Ca, Si, Al, and others) coming from the embedding rocks.

7. Heat mass transport - realized through migration of the solutions, which depends on the thermal gradient, the direction of the heat flow, heterogeneity in the local thermal fields, the degree of openness of the hydrothermal system.

8. Temperature of the hydrothermal solutions depositing fluorite - it varies between 300-100 °C, the industrially important concentrations being in the range 230-179 °C (Chiprovtsi - East); 210-120 °C (Slavyanka); and 175-120 °C (Mikhalkovo).

9. Physical-chemical characteristics of the hydrothermal solutions (according to data on gas-liquid inclusions) - low salinity (? 1% NaCl eq), pH=6 (Slavyanka) and pH=4.90 to 5.52 (Mikhalkovo); P_eq=3.7 to 13.0 MPa (Mikhalkovo) and P_eq=1.0 to 20.0 MPa (Slavyanka); transport of fluorine in the form of fluorine ions (F^-), silicon-fluorine (SiF₆^2-); aluminum fluorine (AlF_n^3-n); and other complex ions, which in decomposing, aside of fluorite, form quartz and clay minerals.

10. Mechanism of fluorite deposition:

10.1. On macro-level - it depends on the local peculiarities of the system (degree of openness) and on the concentration of Ca²⁺ and F^- ions on the crystallization front, when the ratio between their activities and the product of dissolution the crystallization starts. In the open spaces fluorite aggregates and crystals are formed, while in replacement of carbonate rocks are formed infiltration metasomatic columns characterized by well-developed zoning in the distribution of fluorite, quartz, and calcite.

10.2. On a micro-level - it depends on the degree of openness and primarily on the equilibrium state in the system crystal-solution:

- in an open system secretional formation of fluorite is realized. Under conditions far from equilibrium synergetic effects appear leading to self-organization of the medium through dissipation. For a non-equilibrium system there is a cooperative effect of directed variation in concentration, temperature, pH of solutions, and partial pressure of the dissolved gases therein. Under conditions close to equilibrium - small changes in the concentration, temperature, and pH of solutions affect the process of crystallization and the formation of energetically profitable crystal faces.

- in a closed system (under stationary conditions in some caverns) local fluctuations occur in the concentration of hydrothermal solutions due to their gravitational stratification, which leads to appearance of aggregates with banded structures (montmorillonite-quartz-fluorite aggregates).

- metasomatic formation - the mechanism results from the cooperative action of four groups of factor: (1) lithologic composition of the medium (different degree of re-crystallization, breccia formation, and fissuring of carbonate rocks); (2) presence of dynamometamorphosed silicate rocks in contact with carbonate rocks and shielding the hydrothermal solutions; (3) tectonic activity; (4) the composition and the physical-chemical parameters of the incoming hydrothermal solutions - their aggressiveness to carbonate rocks is controlled by the activity of ions in the solution:

the configuration of bodies being different: sheet-like or tube-like if it follows the configuration and filling in hydrothermal paleokarst.

11. Practical application of the model - it makes possible prognosis and evaluation criteria for deposits of the Fluorite Formation in general, not only for Bulgaria.

5. Genetic model of the barite ore formation in Kremikovtsi deposit, Bulgaria (Z. Damyanov)

The aim of this study is the composition of Sr isotopes in representative barite samples and of C, O and Sr isotopes in ore siderites, ankerites and host dolomites from Kremikovtsi carbonate-hosted sedimentary exhalative iron(+Mn)-barite-sulfide deposit. The isotopic data for C and O in the host carbonates are indicative for Middle Triassic marine limestones and dolomites and differ from those for siderites from the iron carbonate ore bodies (Fig. 1). A correlation with a possitive slope of regression of about 0.4 between the amounts of d¹⁸O_smow and d¹³C_pdb is established for the siderites studied. This trend differs markedly from that of 0.25 regression trend expected for carbonate deposition in a system with variable temperatures (as in the conventional "evolutionary" hydrothermal ore formation according to the gradual temperature drop), which is close to the value for the host carbonates (0.22).

The obtained data for the ⁸⁷Sr/⁸⁶Sr ratio of barites vary slightly in the range 0.70917-0.71059. Similar values are characteristic of the studied siderites and ankerites, while the ratio for the host dolomite is lower (0.70857) and typical of the Middle Triassic seawater.The Sr and Rb contents in the samples studied show that the ⁸⁷Sr/⁸⁶Sr ratio is practically the same as that at the moment of the ore formation, i.e. they reflect an authentic picture of the source matter without considerable subsequent changes.

Fig. 1. Plot of d¹⁸O vs. d¹³C for siderites from different geological settings (compiled data). 1 - low-Mn diagenetic siderite from the upper marginal parts of Kremikovtsi deposit; 2 - bulk Mn-Mg siderites from Kremikovtsi SIF (the upper right values are from femicrite); 3 - coarse grained euhedral limpid Mn-Mg siderite, associated with barite and sulfides; 4 - diagenetically sideritized organic remnants (Middle Triassic mollusc fauna); 5 - oolithic siderite.

The analysis of the isotopic data for barites, siderites, ankerites and dolomites from Kremikovtsi deposit suggests several important conclusions about the genesis of the deposit, namely:

FLUID SOURCES: (1) host carbonates formed as a result of direct chemical precipitation from Middle Triassic seawater; (2) low-Mn siderites, located outside the ore bodies, formed also upon a chemical precipitation of Middle Triassic seawater, but with a slight thermal influence of a hydrothermal fluid (i.e. a fluid differing from the seawater); (3) ore siderites and barites formed from a hydrothermal fluid generated during a convective circulation of Middle Triassic seawater through rocks with a crustal origin, i.e. the hydrothermal fluid being actually modified as a result of fluid-rock exchange seawater; (4) common hydrothermal fluid for both the barite and siderite mineralizations evidencing the formation of primary ores in Kremikovtsi deposit as a result of Middle Triassic metallogenesis;

SOURCES OF ORE MATTER: the data obtained excludes the presence of Sr of a mantle origin and indicates a crustal well-homogenized source of ore matter most probably from Upper Paleozoic metasediments from the underlying basement;

MODEL OF ORE FORMATION: the obtained isotopic data provide important new evidences supporting the geological-genetic model of the recycling type proposed earlier. They indicate that due to the insufficient seawater bed pressure in an epicontinental setting, the deposition of the great part of the hydrothermal metal load (Pb, Cu, Zn, partly Ba) in the Middle Triassic paleohydrothermal ore-forming system was realized by a fluid boiling in the feeder channels (before exhalation onto the seafloor), proposed so far based on indirect indicators. This mechanism lies in the dualistic nature (the presence of time- and spatial related syn- and epigenetic ore bodies) of Kremikovtsi deposit and explains adequately its characteristic zoning. It is worth noting that the ore field metallogenic potential can be greatly enlarged as a starting point for prospecting new SEDEX-type deposits in the region.

6. Minerals of the platinum-group elements in the alluvial sediments of Samokov region, Western Bulgaria (Z. Tsintsov)

Individual grains of platinum-group minerals (PGM) in alluvial gold-bearing sediments in Samokov region are investigated which crop out in the upper parts of the Iskar river and its inflows (mainly the Palakaria river). The concentration of PGM in the sediments studied is much lower than 1 mg/m³ thus revealing the low concentration of these minerals in the their primary sources. They are represented in a quantitatively decreasing row by sperrylite, merthierite II, Pt-Fe alloys, and rustenburgite. All they are concentrated in grain fractions sized below 200 mm. Additionally, in individual grains of Pt-Fe alloys inclusions of Os-Ir-Ru alloy (osmium) and unnamed (Pt_0.42Rh_0.26Cu_0.22 Fe_0.12)_1.02S_0.98. Pyrite and quartz are observed in sperrylite, while quartz fills intersticies in Pt-Fe alloys.

The extremely small size of the studied PGM and the strong mechanical processing of the grains suggest that the grains have been subjected to a substantial alluvial transport under conditions of an actively developing placer. Grains of such sizes can hardly be separated by gravitational methods due to which one can suggest that the phase composition of the considered group of minerals from the placers studied is more diverse. Their low concentration in the placers results most probably from their low concentration in the primary sources placed far away (tens of kilometers) from the placers. The peculiarities of the studied Pt-Fe alloys and of inclusions of Os and unnamed (Pt_0.42Rh_0.26Cu_0.22 Fe_0.12)_1.02S_0.98 therein indicate that they are of high temperature magmatic origin. The sperrylite and merthierite II studied are probably formed from hydrothermal fluids in the process of serpentinization. The latter have probably provoked destruction of a part of the primary PGM. The paragenetic position of rustenburgite in this case is not well clarified, but some existing experimental data allow to suppose that it had not been formed in the process of serpentinization of ultrabasites [56].

7. Microstructural, mineralogical, and chemical transformations upon heterogeneous deformation of metamorphic rocks from Plana Mountain, Bulgaria (L. Macheva)

The heterogeneous character of the deformation of the high-grade metamorphic complex in Plana Mountain (Plana Formation of Ograzdenian Supergroup) allows one to determine their parent rocks, to trace the metamorphic evolution and to specify the nature of the boundary between high metamorphic complex and the Diabas-Phyllitoid Complex in this region. The rock-forming minerals from the high-grade metamorphic rocks are studied and the granitoid genesis of these rocks is proved. Their metamorphic evolution is marked by: 1) a regional heterogeneous deformation coupled with irregularly developed migmatization and 2) imposed low temperature metamorphic and deformational processess on the contact with the Prasinite Formation of Diabas-Phyllitoid Complex.

As a result of high temperature heterogeneous deformation granitoids are transformed into different structural types of gneisses - augen, augenlayered and layered ones affected as well by irregularly developed migmatization. K-feldspar porphyroclasts and poikilitic enclosed plagioclase and biotite crystals are among the primary mineral paragenesis preserved in the rocks. The high temperature metamorphic and deformational processes had brought to the following structural and mineral transformations: 1) recrystallization of the relict micropertitic orthoclase in crosshatched microcline, the later showing plentiful development of myrmekites on their rims; 2) recrystallization of the magmatic plagioclase into an acidic one, resulting in the formation of high temperature clear in appearance patch antiperthite of crosshatched microcline; 3) the magmatic biotite, is recrystallized to the association Bt _II+ Mu + Ep +Sp. With increasing the intensity of deformation and migmatization, muscovite rimmed by fine-grained biotite becomes dominant mica species; 4) Quartz is totally recrystallized in low- as well as in intensely-deformed areas, forming short, elongated high temperature polycrystalline ribbons parallel to the foliation.

Feldspar and quartz deformation is accomplished by high temperature deformational mechanisms: 1) grain boundary migration with forming a typical "core - mantle" structure; 2) large subgrains and neoblasts, rotated at more than 5⁰ to each other, displaying probably the recrystallization by sub-grain rotation; 3) regeneration. Quartz shows deformation bands and recrystallization by sub-grain rotation and grain boundary migration.

Near the contact with the rocks of Diabas-Phyllitoid Complex orthogneisses undergo a later intense low temperature brittle deformation. As a result they are transformed into cataclasites and ultracataclasites, containing pseudotachylitic lenses and bands. The most important changes in high-grade rocks are mainly of a microstructural character. The rocks consist of mechanically broken and rotated quartz and feldspar grains as well as of polymineral particles, "floating" in an ultra-fine-grained matrix. Opaque ore material is concentrated parallelly to the foliation and around porphyroclasts.

The high temperature rock deformation and migmatization is realized under approximately isochemical conditions. The imposed low temperature deformation is accompanied by a significantly greater mobility of the chemical components, thus resulting in an increase in the content of Ti₂O, Al₂O₃, Fe₂O_3(t), MgO and decrease in a the concentration of Si₂O and CaO with increasing the deformation. These geochemical tendencies correspond with the established microstructural and mineralogical transformations leading to disappearance of micas and feldspars and to preserving of quartz and the resistant ore minerals.

8. Isotope-geochemical and geochronological investigation of magmatism and ore formation evolution in Srednogorie zone (I. Peytcheva, A. v. Quadt, B. Kamenov)

Rigorous geochemical investigation and radiometric dating are powerful tools to unravel the processes of magma-related hydrothermal ore formation. The timing of ore-forming processes requires the simultaneous use of several isotope methods to define the time-span of geological events in one deposit in the broader tectonic framework, including magmatism, metamorphism and hydrothermal metal precipitation. The Cu-Au deposits of the Srednogorie zone in Bulgaria provides a good opportunity for studying the genetic relationships between magmatism, alteration and ore formations, as well as the lifespan of porphyry systems. In the frame of GEODE project of ESF (Geodynamic and Ore Deposit Evolution; European Science Foundation) an investigation was started, concentrated on above problems. Currently the investigation of the Elatsite porphyry copper deposit in Central Srednogorie is almost finished and the results are published [20, 81].

The following main methods used in this study are: (a) dating of distinct magmatic bodies, with clear age relationships in the field (cross-cutting relations f.e.); (b) dating of alteration and hydrothermal minerals; (c) isotope tracing of minerals and rocks, informative for magma- and element sources.

Single zircons from several porphyry dykes bracketing the formation of the Elatsite porphyry Cu-Au-deposit were dated by high-precision U-Pb isotope analysis, using thermal ionizing mass spectrometry (TIMS). On the basis of mapped crosscutting relationships, and the mineralogy and geochemistry of igneous and altered rocks, five dyke units are distinguished. The earliest and the latest porphyry dyke is associated with and overprinted by the main stage of ore-related veining and potassic alteration. U-Pb analyses of zircons yield a mean ²⁰⁶Pb/²³⁸U age of 92.1 ± 0.3 Ma, interpreted to reflect the time of intrusion. Zircons of the latest ore-forming dyke, crosscutting the main stage veins but still associated with minor potassic alteration and veining, give an intrusion age of 91.84 ± 0.3 Ma (Fig. 1). Thus, ore mineralization is confined by individually dated igneous events, indicating that the entire time span for the ore-forming magmatism and hydrothermal activity extend over a maximum duration of 1.1 Ma, but probably much less. Zircon analyses of a post ore dyke cutting all ore veins and hosting pyrite as the only sulphide mineral give a concordant ²⁰⁶Pb/²³⁸U age of 91.42 ± 0.15 Ma.

Geochemical discrimination ratios suggest a mixed mantle and crustal source of the Cretaceous magma. Isotope Sr - Nd - Hf analyses confirm the conclusion that all porphyry rocks within and around the Elatsite deposit reflect an enriched mantle source at Cretaceous times.

Apart of the isotope investigation in distinct magmatic and metallogenic centers (Elatsite-Chelopech; Elshitsa-Vlaykov Vruh etc.), concentrated on problems of the link porphyry copper - epithermal deposits and source and transportation of the ore forming elements, a wide isotope-geochronologica and geochemical information is provided, which allows reasonable geodynamic reconstructions. In the Etropole-Panagyurishte-Pazardjik strip of Central Srednogorie the magmatic activity starts at the northern border at 92.1 Ma with the intrusion of the unit 1 dykes in Elatsite, shifted to the south and finished at the border to the Rhodope Massif at 78 Ma with the intrusion of the Capitan-Dimitrievo pluton. The total duration of the magmatism of the strip includes a time of about 14 Ma. Sr-tracing of most studied magmatic rocks gives ⁸⁷Sr/⁸⁶Sr ratios ~ 0.704-0.706, suggesting derivation of the rocks from melts generated in a mantle source modified by the addition of crustal materials. The e-Hf values of the zircons range from + 5 (T~92Ma) in the north and up to +9.4 (T~80 Ma) in the south. The subduction roll-back model is used to explain the trenchword migration of magmatic activity along the transect in Upper Cretaceous time based on these data.

Fig. 1. U-Pb concordia diagram for zircons of a diorite-porphyry dyke (LF-025) of Elatsite deposit

9. Lead phosphate minerals from Brussevtzi deposit, Eastern Rhodopes: SEM, IR and DTA studies (Y. Tzvetanova)

Pyromorphite, plumbogummite and corkite occur as secondary minerals in the weathering zone of the sulfide ore deposit Brussevtzi, which is a part of the Madjarovo ore field, East Rhodope massif, associated with plumbojarosite and limonite in quartz-adularia type metasomatic rocks. They form fine-granular crystals, up to 700 mm in size, filling cracks and cavities or occur as pseudomorphs after quartz (Fig. 1). The sequence in the formation of these lead phosphates is as follows: pyromorphite ® plumbogummite ® corkite. The observed range of crystallization suggests a decrease of concentrations of Pb and P and a change of pH from acidic to alkaline during the formation process.



Fig. 1. SEM-micrographs: a - corkite pseudomorphs after quartz (x 500); b - replacement of pyromorphite by plumbogummite (x 1000); c - plummbogummite (x 1200).

The lead phosphates are studied by applying XRD, SEM, DTA, and IR spectroscopy [57]. The chemical analyses of corkite and plumbogummite were recalculated to formula contents on the basis of 2 mol of (XO₄) per formula unit. The number of (OH)^- radicals present is that required to achieve electrostatic neutrality in the formula.Corkite.The microprobe analysis confirmed two types of corkite with the following crystal structural formulae:

I) Pb_1.03(Fe_2.32Cu_0.21 Al_0.28)_2.81(PO₄)_1.22(SO₄)_0.71(OH)_5.04

and

II) Pb_1.10(Fe_2.25Cu_0.64 Al_0.11)_3.00(SO₄)_1.23(PO₄)_0.77(OH)_5.79.

The type I is with a lower content of CuO and a higher content of P₂O₅, while the type II reveals the opposite content relation. The isomorphic substitution of Fe³⁺ on Cu²⁺ in corkite is accompanied by an exchange of (PO₄)^3- on (SO₄)^2- to retain the charge balance. The IR absorption of corkite (Fig. 2, curve C) is very complex.

Fig. 2. IR curves of pyromorphite (A);
plumbogummite (B), and corkite (C)

Fig. 3. DTA curves of plumbogummite, corkite,
and pyromorphite from Brussevtzi deposit

The bands at 510 and 580 cm^-1 correspond probably to n₄ vibrational mode of the (PO₄)^3- group. Due to the overlapping of the n₃ and n₁ regions for (SO₄)^2- and (PO₄)^3- groups, multiple absorption bands between 900 and 1200 cm^-1 are observed in the IR spectrum corresponding to these modes. The bands at 911 cm^-1 and at 1160 cm^-1 could be ascribed to the n₁ and n₃ modes for the (SO₄)^2- group, respectively. The DTA-curve of corkite (Fig. 3) is characterized by one dehydration step at 530 °C. The exothermic peaks in DTA curves for corkite at 650 and 680 °C are indicators of the recrystallization process. The final mass losses are 8 wt. %.

Pyromorphite. The obtained data show the presence of two varieties of pyromorphite: 1) with Ca²⁺ in the position of Pb²⁺ and 2) - pure pyromorphite. The crystal chemical formulae are:I) (Pb_3.68Ca_1.32)(PO₄ )₃Cl_1.10 and
II) Pb_5.05(PO₄)₃Cl_1.12.

The unit cell parameters of these two types, refined from powder XRD data, are respectively a = 9.886(2), c = 7.236(1) and a = 9.987, c = 7.330. The IR spectrum of pyromorphite (Fig. 2, curve A) shows the absorption bands, which correspond to the vibrational frequencies of n₁, n₃ and n₄ modes of the (PO₄)^3- group. Analysis of the spectrum reveals that both n₄ and n₃ modes have two-component bands, respectively at 520 and 570 cm^-1 for n₄, and 960 and 1020 cm^-1 for n₃. The n₁ mode of (PO₄)^3- occurs at 922 cm^-1. The DTA study of pyromorphite shows that the mineral is thermally stable (Fig. 3). The final mass loss is about 4 wt.% and could be interpreted as a result of the solid-state decomposition.

Plumbogummite. The mean chemical composition of plumbogummite from Brussevtzi deposit is:

Pb_1.10(Al_2.93Fe_0.01 )_2.94 [(PO₄)_1.96(SO₄)_0.04]_2.00(OH)_5.05.H₂O.

The IR absorption frequency data for plumbogummite (Fig. 2, curve B), by analogy with the IR spectra of other phosphate minerals, show two bands for n₄ mode of the (PO₄)^3- group at 520 and 560 cm^-1. The bands at 1020 and 1080 cm^-1 could be ascribed to the n₃ vibrational mode of the (PO₄)^3- group and that at 911 cm^-1 to n₁. The DTA curve (Fig. 3) of the mineral demonstrates two-step dehydration, indicated by a shoulder at 400-420 °C. Two-step dehydration should be expected as water can be released from two lattice positions - H₂O{Al(OH)_4/2O_2/2}^- -octahedra and H₂O from O3PO^..H^..OPO3-hydrogen bonds. The endothermic effect of plumbogummite at 250 °C could be explained by dehydration of H₃O⁺ incorporated in the structure of the mineral, as known for the alunite-jarosite family. The exothermic peak in DTA curve for plumbogummite at 740 °C is indicator of the recrystallization process. The final mass losses are 13 wt.%.

10. Mineral composition and origin of the amethyst mineralization in agates from Eastern Rhodopes (Z. Tsintzov, B. Banushev)

Characterized are the mineralogical and structural peculiarities of agates including violet varieties of SiO₂ (mainly amethyst and damsonite) and partially morion type of quartz from the region of Krumovgrad and Potochnitsa areas (Kurdjali district). Isolated are vein- and geode-type morphologies, with dense and chamber-like varieties built mainly of chalcedony distinguished according to microcrystalline features into: fibrous length-fast (CH_LF); parabolic fibrous (CH-W_LF); horizontal strata and spherulitic fibrous radiating spherulites (CH-H_LF) and micrograined (massy) (CH_M). Their phase composition includes in addition quartz (milky-white amethyst, morion), opal (opal-CT and opal-C), quartzine, calcite, zeolites, Fe-hydroxides, pumpellyite, and barite. Amethyst crystals and/or damsonite represent the violet varieties of SiO₂. The crystals have a short prismatic habit and cover the chambers or have grown radial around chalcedony pseudocrystallites with one or several nuclei, thus forming a structure of a type "amethyst sun". Agates are imbedded in volcanites (andesites and latites) and pyroclastites (lapili tuffs and agglomerates) from the second medium acid volcanism. Andesites are black in color, fine porphyric with a massive structure. They are built up of fresh zonal plagioclases, An_33-46 (with inclusions of pyroxene and isotropic volcanic glass zonally displaced and following the crystallite contours), orthopyroxene, clinopyroxene, and individual crystals of entirely serpentinized olivine. The main mass consists of plagioclase, pyroxene microlites and isometric magnetite grains. Latites are dark-gray colored, fine porphiric with massy structure. Phenocrysts are composed of fresh zonal plagioclases (An_46-50) and rare augite crystals. The main mass pylotaxitic structure is built up of plagioclase microlites with subparallel orientation as well as of magnetite grains. Volcanites are with calcium alkaline and high potassium-calcium alkaline character.

The formation of amethyst agates from the region of Krumovgrad is related to post-volcanic activity in the region, their specific features being probably predetermined by the presence of specific cations ("catalysts") in the crystallization medium (especially Fe³⁺) having been played the role of chromophor agents [28, 29].

11. Mineralogical map of the heavy mineral concentrates in Bulgaria scaled 1:25 000 (O. Vitov)

The possibilities for creating a database for prognosis and prospecting of raw materials (gold, tin, bismuth, tungsten, mercury, and other ores) based on heavy mineral concentrates data are considered and mapping is performed on a small scale (M 1:1 000 000 and M 1:2 000 000).

The data concern prognosis and survey of cassiterite [36], gold [38, 86, 88, 89], bismuth (Fig. 1), scheelite (Fig.2), cinnabar (Fig. 3) [37], and other ore formations in Bulgaria [86, 87].

Fig. 1. Prognosis map for survey of bismuth ore mineralization in Bulgaria.

Fig. 2. Prognosis map for survey of tungsten ore mineralization in Bulgaria.

Fig. 3. Prognosis map for survey of mercury ore mineralization in Bulgaria.

Specific areas for prospecting of a complex of raw materials are given (for example the region of Kazanluk town with expressed complex anomaly in respect to gold, cassiterite, bismuthite, and others) as well as unknown tendencies in the arrangement of minerals in stripes directed along NW-SE and SE-NW [36, 38, 86, 87, 88, 89].Mineralogical and geochemical prognosis for prospecting mercury ore formation scaled 1:200 000 are prepared for the region western of Struma river, Kyustendil district [37].

A summary of data on the mineral diversity is given for the heavy mineral concentrates in Bulgaria [87].

Performed are 61 geomorphological "water shed/catchment areas" maps scaled 1:25 000 in order to make detailed prognoses and mapping projects in the same scale.

II. ENVIROMENTAL MINERALOGY

12. Mineralogy and geochemistry of coals and coal products (S. Vassilev, Chr. Vassileva)

Phase-mineral and chemical composition of 6 types of coals and their waste products (fly ashes) derived from coal burning at 4 Spanish thermo-electric power stations (TPSs) were characterized. A combination of conventional procedures (flotation, leaching, vaporization and crystallization) was applied to separate ceramic microspheres and water-soluble salts from 5 types fly ashes produced from coal combustion at 4 Spanish TPSs for a multicomponent, wasteless and environmentally friendly utilization of such fly ashes. The phase and chemical composition, as well as some properties of useful and/or potentially hazardous products were characterized.

Spanish coal, char and activated char doped with model V components (V₂O₅ and NH₄VO₃) and petroleum coke ash (enriched in V, Fe and Ni) were prepared and characterized as potential catalytic sorbents for NO_x reduction [31]. The phase-mineral and chemical composition, the content and behaviour (capture, retention, distribution and redistribution) of transition metals, as well as morphogenesis, surface area, acid-base properties, surface active sites and oxidation-reduction transformations of the catalytic sorbents were characterized. It was found that minerals and phases such as anhydrite, calcite, clay minerals, pyrite, pyrrhotite, magnetite and fusinoid-type ingredients play a leading role for the behaviour of loaded transition metals. Some original (pyrite, jarosite, shcherbinaite, coulsonite, trevorite, Ni oxide) and newly formed Fe, V and Ni minerals (pyrrhotite, magnetite, wuestite, hematite, paramontroseite, karelianite) in the catalytic sorbents are perspective redox indicators for the physicochemical conditions in such complex system. The data indicate that the V-Fe-Ni containing minerals dispersed onto and into the carbon support may be the most active catalytic sites. The preparation procedure that could provide the most favorable conditions for the production of effective and low cost catalytic sorbents for NO_x reduction is described. The sorbents prepared were tested for reduction of NO - gases [50]. They are active for reduction of NO at temperatures above 350 ^oC, the most efficient sorbents being those obtained from inactivated chars and doped with model V compounds or petroleum coke ash. Despite of the slightly higher NO conversions for the samples loaded with pure V components as compared to those impregnated with petroleum coke ash, the latter are perspective for producing low-cost and effective catalyst doped activated carbons.

The phase-mineral transformations and the chemical interactions in inorganic matter during combustion of 6 types of Bulgarian lignites, subbituminous and bituminous coals (Maritza East, Maritza West, Sofia, Pernik, Bobov Dol and Balkan) were characterized [32]. The relationships between ash-fusion temperatures and the chemical and mineral composition of these coals were established and described [33]. The major phase-mineral transformations in the inorganic matter of the above listed coals during their gradual heating up to 1600 °? in air were generalized [34].

13. Synthesis, composition, structure, and properties of crystal matrices of Synroc type (I. Donchev, F. Dipchikov, O. Petrov, N. Zidarov, M. Tarassov)

Following previous studies in this field new experiments were performed for synthesizing Synroc matrices. Used are mixtures of oxide precursors Al₂O₃, TiO₂, ZrO₂, CaO, BaCO₃, SrCO₃, Nd₂O₃, and Sm₂O₃ dosed by recalculation for directed crystallization, well preliminary homogenized in alcohol and pelleted upon various pressures.

Batches were melted in a corundum crucible covered with corundum in an electric oven with "Superkantal" heaters for 11 hours (with a time delay of 2 hours at 1320 ^oC).

Samples of Sinroc crystalline materials are obtained in that way, which are studied using powder XRD, SEM, and EPMA. X-ray microanalyses (EPMA) are given in the table. A part of the samples are only precursors typical of Sinroc B (the first six analyses in the table) while one sample (analyses 10-1, 10-3) is with additions of Sr, Nd, and Sm.

As seen in the table in the Synroc B samples (the first six analyses) phase analogues of zirconolite, hollandite-like phase, perovskite, and non-reacted baddeleite and rutile have crystallized. This fact is also established on the basis of powder XRD data, as previously reported [1]. The microstructure and morphology of Synroc B crystals are as those as established previous studies, which reveal a good reproducibility of the experiments for obtaining this type of a matrices. The last two microanalyses in the table (10-2 and 10-3) are of zirconolite with additions of Sr, Nd, and Sm, while 10-1 of perovskite-like mineral in which a great part of the positions of Ti and Ca are occupied by Sr and rare earth elements.

14. Adsorption of NO_x on gold-titanosilicate catalysts (Yu. Kalvachev)

The increasing requirements of the environmental protection provoke many efforts to improve available and to develop new DeNOx catalytic technologies. In searching effective DeNOx techniques, it is necessary to know in detail the mechanism of the processes. One step of this mechanism is the adsorption of NO on the surface of catalysts.

Adsorption of NO on Au/ETS-10 was performed. By using in-situ infrared spectroscopy, various adsorbed species were observed. The effects of the temperature against time on the infrared species were studied. It is noteworthy to mention that the bands due to monomeric Au-nitrosyl complexes at 1880 and 1800 cm^-1 are seen only at 100 ^oC. Therefore, NO did not completely dissociate at this temperature. These bands conceivably could be assigned to adsorbed NO in Au-NO complexes by analogy with NO band on CuZSM-5. From the observed gradual peak shift to lower frequency with time, namely, from 1890 to 1880 cm^-1, it is concluded that the NO bond order is weakened due to charge transfer from Au to NO. The charge donation from Au to NO is almost complete as the observed IR frequency is slightly higher than that of free NO at 1876 cm^-1. The 1800 cm^-1 band can be assigned to NO^- or to dinitrosyl complexes. It is difficult for NO to accept an electron, because the latter would occupy an antibonding orbital. Therefore, most probably the observed band at 1800 cm^-1 is due to dinitrosyl complexes.

When the temperature was raised to 200 ^oC, the spectra obtained resembled those collected over the catalyst at 100 ^oC except that the bands at 1800 and 1880 cm^-1 have completely vanished. Thus, the slightly upscale shift of the band at 1880 cm^-1 from that of gaseous NO (1876 cm^-1) indicates that the structure contributing this bond is weakly attached on the surface and is rapidly removed by increasing the temperature. Because of this fact, it appears more reasonable to propose that the band at 1800 cm^-1 is due to Au-dinitrosyl complexes.

The band at 1645 cm^-1 is in the region typical of NO₂/NO₃ species, but is also characteristic for water. Water can be formed from hydroxyl groups from zeolite.

The band at 1440 cm^-1 is attributed to NO₂^- species, adsorbed on Ti centers. In the literature this band is described as nitro-nitrito species and was observed on TiO₂ and microporous TS-1 and there are stable as in our case. The possible ways of bonding of NO₂^- to catalyst surfaces are via O atom, called nitrito-species and via N atom, called nitro-species. The adsorption can be via 2 metals atoms - bridging species or via 1 metal atom.

IR spectroscopy provides direct information on the nature and stability of the different adsorbed species.

15. Thermal analysis of new soil sorption regulators (V. Ivanova, V. Petkova, Y. Pelovski)

Complex fertilizers NPKS with high water capacity are obtained upon mechanochemical treatment of multicomponent mixtures. Some solid wastes and ammonia and potassium sulfates are used as raw materials. New solid phases are formed using various ratios of components in the mixtures and are specified by studying the stages and the changes in the weight changes and enthalpy changes at different temperatures as well as using powder X-ray diffraction (Fig. 1).

On the basis of the obtained data the mechanism of chemical transformations is considered. It was found that the kinetics of decomposition of the mechanically activated mixtures is significantly influenced by the treatment duration, proceeding in several stages (Fig. 2).

Fig. 1. XRD patterns of the studied mixtures

Fig. 2. TG-DTA-DTG curves of the studied mixtures

The results obtained confirm that the activation of the complex systems of selected raw materials could be used for synthesizing new products suitable for fertilization and for improvement of the soil structure, water capacity and, finally, of the soil productivity. The selected system does not require high temperature or continuous mechanical treatment. The control of the ratio between the initial raw materials makes it possible to obtain final products with properties within the EU standards for fertilizers. The optimal content of the initial mixture lies is in the range 35-39% ammonium sulfate, 27-35% phosphorous solid waste, 11-16% potassium sulfate, and 16-20% ash.

16. Effect of natural sorbents during clean-up of polluted water: vermiculite - clinoptilolite filter (B. Vassileva, B. Shadova, O. Petrov)

The purpose of this study is to further evaluate the ability of natural filtering materials widely spread in Bulgarian deposits to purify waste waters from different productions.

The test samples used in the study are: vermiculite from Parapandovtsi deposit near Belitsa village, Ihtiman region and clinoptilolite from Beli plast deposit, Kurdjali region.

According to data from the geological survey the content of vermiculite in the sample is about 16 wt.% and major exchangeable cations are Ca, Mg, and Na. The ion-exchange capacity of the vermiculite sample was determined through an experiment in a glass where to the dry powder sample there was added a solution of NH₄Cl with known concentration (1M) under continuous homogenization with electromagnetic mixer (250 rpm). The ratio dry-to-liquid phase is 1:10 and the contact between the phases is 30 min. After the end of the contact the liquid phase is decanted and analyzed for contents of NH₄⁺, Na⁺, Ca²⁺, and Mg²⁺. Then a fresh quantity of NH₄Cl solution is added again to the sample. The procedure is repeated up to the moment when the concentration of the examined ions remains unchanged or with very close values. The analysis of the water extractions was performed by potentiometric method with ion-selective electrodes.

The used clinoptilolite tuff sample contains above 70 wt.% clinoptilolite, which is a calcium-potassium variety and has ion-exchange capacity (CEC) in the range 110-140 mg/g.

Model waste water with known chemical composition is used as an object of study (tested in our previous studies).

Four combinations of clinoptilolite (cpt) and vermiculite (vmc) were used to study the purification effect, namely: 1:1, 2:1, 3:1, and 4:1 (cpt/vmc). The experiment was performed in a column with dimensions: H=450 mm, d=18 mm, h(bed)=45 mm. The quantity of the used sorbent was 10 g. Model waste water of a volume of 2000 ml was passed through the column with a speed of 5 ml/s. Water samples for analysis were taken from the initial quantity and after 100, 200, 300, 500, 600, 800, 1000, 1100, 1300, 1500, 1800, and 2000 ml have passed through the column and then are analyzed for ion content.

Atomic absorption spectroscopy (AAS) was used for analysis of the water extraction samples. The used apparatus was Perkin-Elmer 3030.

Fig. 1. Sorption effect of combinations of natural sorbents

As a result of the study it was found that most effective purifying ability in respect to anions of chlorine is displayed by the filter cpt:vmc=1:1 (Fig. 1). As concerns the cations (K, Ca, Cu, and NH₄) best performing is the combination cpt:vmc=2:1.The performed experiments give reason to believe that the investigated natural sorbents can be used during creation of waste deposits in the form of barriers through which the passing waste waters are of safe quality for the underground waters and the soils.

III. MODELING AND MODIFICATION OF MINERAL SYSTEM

17. Geometrization of the language of mineralogy (V. Penev, N. Zidarov, B. Zidarova)

The relationship between the common for all natural sciences categorical and notional (i.e., epistemologycal) basis and the language of mineralogy is studied. Analyzed is the already "defined" [14] triade of cognitive categories structure, composition, and construction. Logically correct are "defined" the categories material objects (matter), solids, liquids, and gasses.

It is shown that from a logical point of view:

The notion mineral is a concretization of the cognitive categories structure, matter, volume, and order.
Each material object (including each mineralogical object) is a chemical structure (i. e. a unity of chemical composition and construction in the ordinary physical space V_M(3). So, in the language of mineralogy for the first time originates the necessity of a constitutional union of both main approaches for describing objects - the geometric one used for describing crystal morphology of minerals and the substantial one used for describing the chemical composition of minerals.
Each chemical structure (including each mineralogical object) can be represented entirely mathematically and uniquely in the space of chemical structures V_S(6) (the definition of V_S(6) is given in Ann. Report 3/1997 through a corresponding simple discrete function defined in the ordinary physical space V_E(3) and having values in the Mendeleev's space V_M(3).

All chemical structures (and consequently all mineralogical objects) which are of a periodic construction can be represented entirely mathematically and uniquely in V_S(6) through the corresponding periodic discrete simple inreversible functions.It becomes clear from the last two statements that from a mathematical point of view:

Mineralogy, just as chemistry, is dealing with the description and study of one exactly defined subset of the set all possible functions in V_S(6). This is the subset of these simple discrete irreversible functions, which describe the various chemical structures (both totally ordered and partially or totally disordered).
Descriptive mineralogy is concerned with the description and study of one exactly specified subset of the set of all discrete simple and irreversible functions. This is the subset of the periodic discrete simple irreversible functions in V_S(6), which represent entirely mathematically and uniquely the corresponding entirely ordered mineralogical objects.
The classification of minerals is in fact a classification of such periodic discrete simple irreversible functions in V_S(6), which are of a mineralogical meaning.

18. Successive phase transformations of hydrothermally prepared titanosilicates (V. Kostov-Kytin, S. Ferdov, O. Petrov)

Aiming at further optimization of the synthesis conditions for preparation of already known or new titanosilicates we have explored the system Na₂O-K₂O-TiO₂-SiO₂-H₂O without using organics as templates, chemical sources or additives [8, 68]. Ten crystalline titanosilicate phases have been synthesized, namely: the microporous ETS-10 - (Na,K)₂Si₅TiO₁₃; ETS-4 - Na₉Si₁₂Ti₅O₃₈ (OH).12H₂O; STS - K₂TiSi₃O₉.H₂ O; GTS-1 - Na₂Ti₂O₃(SiO₄ )₂.2H₂O; and Na₃HTi₄O₄(SiO₄)₃.4H₂O); the layered AM-4 - Na₃(Na,H)Ti₂O₂[Si₂O₆]₂.2H₂O and JDF-L1 - Na₄Ti₂Si₈O₂₂ .4H₂O, and three dense titanosilicate phases, which are analogous to the minerals natisite - Na₂TiSiO₅; paranatisite - Na₈Ti_3.5O₂(OH)₂[SiO₄]₄; and davanite - K₂TiSi₆O₁₅.

Kinetic investigations provided evidence on the validity of Ostwald's rule of successive phase transformations in the systems Na₂O-TiO₂-SiO₂-H₂O [4, 8, 61, 68]. The phases appear and are replaced in the following sequence: JDF-L1 - ETS-4 - GTS-1 - AM-4 - Na₃HTi₄O₄(SiO₄)₃.4H₂O - paranatisite - natisite (Fig. 1, Fig. 2).


Fig. 1. Powder XRD patterns depicting the successive transformation of JDF-L1 into ETS-4	Fig. 2. Powder XRD patterns depicting the successive transformation of GTS-1 through AM-4 and to natisite

As the size of the pores decreases the Ti content in the run products increases. The suggested mechanism for such successive transformations is closely related with the pH values of the reaction medium. In general, the parameter pH plays a leading role in the formation of various titanosilicate structure types by influencing the configuration of the primary and secondary building units (PBU and SBU) in the precursor gel. The values of Ph depend on the ratios NaOH/TiCl₄ and NaOH/H₂O in the initial gel batches. This allows a precise tuning and control in the preparation of phases with desired crystal chemical features [8, 68]. The transformations from microporous and layered titanosilicates to dense synthetic analogues of the minerals paranatisite, natisite and davanite are indicative for the evolution of the PBU, SBU and the resulting titanosilicate structures in the nature. This explains the possibilities for the occurrence of mineral counterparts in terms of the degree of alkalinity in the mineral-forming environment.

19. Precise characterization of hydrothermally prepared titanosilicate phases (V. Kostov-Kytin, S. Ferdov, O. Petrov)

Some members of the potentially large class of titanosilicates with zeolite-type structure, e.g. ETS-10 and ETS-4, have already found application in catalysis, ion exchange and separation processes. Others are not yet sufficiently studied. The comprehensive characterization of these materials would significantly contribute to our understanding of their nature and properties.

Ten pure hydrothermally prepared crystalline titanosilicate phases and two more kindred compounds have been investigated by means of powder X-ray diffraction, X-ray fluorescence analysis, Raman and IR spectroscopy, SEM, BET-surface analysis, TG and DTA. Despite their comprehensive diagnosis, improved values of some characteristics used as standards for phase identification, have been obtained. Improved indexing and unit cell parameters refinement are achieved for the dense titanosilicates paranatisite, natisite, narsarsukite and for the layered titanosilicate JDF-L1 (see table).

For the first time Raman spectroscopy is used to verify the presence of five-coordinated Ti polyhedra in the structure of JDF-L1 through the observation of strong scattering at 880 cm^-1.

20. Thermal evolution and sorption properties of hydrotalcite compounds (N. Petrova, Ts. Stanimirova)

The process of thermal decomposition of hydrotalcite, Mg_4+xAl₂(OH)_12+2xCO₃ x 3-4H₂O (0 < x <4), includes dehydration, dehydroxylation and decarbonization of the materials and leads to the formation of series of hydrotalcite methaphases. The correlation between the HT metaphases and their behavior in dehydration/hydration process is shown on the scheme, where HT-D is dehydrated HT; HT-B is partially dehydroxylated HT with bidentant bonded CO₃^2-; HT-B-r is hydrated HT-B; HT-P is periclase-like mixed (Mg, Al) oxide; Sp is spinel and Per is periclase.

Two reversing hydration/dehydration processes are found in a relatively low-temperature region: HT « HT-D and HT-B-r « HT-B.

Several synthetic hydrotalcites with ratios Mg/Al = 2:1, 3:1 and 3.7:1, prepared at 90 or 20 ^oC temperature of aging as well as natural hydrotalcite are studied. Aimed at the relating thermal data on the chemical, structural and morphological evolution of hydrotalcite samples, a variety of methods are used: differential thermal analysis (DTA), thermo-gravimetric analysis (TG), evolved gas analysis (EGA), scanning electron microscopy (SEM), infrared spectroscopy (IR), and X-ray powder diffraction (XRPD).

The thermal decomposition of hydrotalcite is accompanied by evolution of discrete number of water molecules, as each separate evolved portion causes the appearance of new metaphase and individual endothermic peak on the DTA-curves.

Carbonate groups play different roles in the individual hydrotalcite metaphases. The evolution of CO₂ during the thermal decomposition of CO₃ proceeds specifically for differing samples in the high-temperature region, as the synthetic samples with a high aluminum content retain a part of CO₃ groups up to high temperatures.

The heat of hydration of the compounds of the low-temperature hydrotalcite metaphases (HT-B) is measured via an adiabatic water-vapor absorption calorimeter. Several factors are studied as determining the nature of HT-B as a heat sorbent, namely: (1) the ratio Mg/Al; (2) CO₃^2- or SO₄^2- as interlayer anions; and (3) the temperature of aging of the initial samples. The temperature of the transformation HT ® HT-B (from 200 to 250 ^oC) is found to vary with the factors mentioned above. The dehydration temperature before the calorimetric measurement is in the range 50-140 ^oC. Due to the large surface area of the dehydrated state and the low temperature of dehydration, HT-B is a very suitable heat exchanger [19]. The absolute hydration heat values were found to be largest for the samples aged at 90 ^oC with CO₃^2- used as an interlayer anion. The sorption ability of CO₃-samples is slightly influenced by the ratio Mg/Al at higher dehydration temperatures, while at 70 ^oC the sample with Mg/Al = 3.7:1 gains a greater priority as heat exchanger (an absolute hydration heat of 450 Jg^-1).

21. Electrochemically induced transport processes in basaltic melts (N. Zidarov, J. Mouchovski, M. Tarassov)

Previous data on a mass-transport in anhydrous basaltic melts imposed to a constant electric field under open-system conditions have been presented in Ann. Report 7/2001. It has been assumed that upon dissociation and reduction of molecular oxygen on the cathode, the formed oxide ions O^2-participate in several reversible chemical reactions including couples Me^Z+/Me^O (z = 2, 1) and leading to a shift of the electrode potential in negative direction and to a depolymerization of the silicate structure. Despite the significance of such considerations to clarify the complex transport processes in the melts, some questions remain without answer: 1) What is the mechanism of nucleation in the melt and the type of crystallization? 2) How the cathode passivation affects the character of the mass-transport phenomena for iron ions as main network modifiers? 3) What is the contribution of the ion-migration in the total current throughout the electrochemical cell at different intensities (E) of the imposed electric field? 4) Do the up-hill diffusion effects influence the distribution of elements in the basaltic melts? 5) What conclusions could be drawn from the geological point of view? To answer these questions we performed additional precise microprobe analyses of samples, obtained by quenching basaltic melts via the technique described in Ann. Report 7/2001. The profiles on Fig. 1 cover a higher number of points very close to each other, especially nearby the cathode.

The primary data are fitted using differential equations describing the one-dimensional mass transport caused by chemical diffusion and the ionic migration in multicomponent molten ionic systems.

The results obtained suggest that the mass-transport is determined by interfering effects of the preceding and following chemical reactions upon the cations reduction, local distortion of the applied electric field, and the partial crystallization near to the walls and to the bottom of the cell at constant concentration of the dissolved oxygen. It is shown that the content of the crystallized spinel phases in the melt depends on the concentration of Al-ions diffused from the ceramic walls of the cell to the adjacent melt layer, as well as on the Fe²⁺/Fe³⁺ ratio in this layer. At E > 1.4 V/cm the cathode potential is controlled by diffusion-kinetic transport limitations arisen during a two-stage electroreduction of the ferric iron ions. Such a character of limitation is provoked by the deep passivation of the Pt cathode due to an active chemisorption of iron atoms onto the cathode surface and to their much slower diffusion into the Pt plate.

This phenomenon may be considered as the reason for a significant shifting of the cathode potential in negative direction. It is also estimated that the contribution of the ion-migration to the mass transport becomes perceptible (up to 31%) at low values of E. However, the increase in E > 1.5 V/cm leads only to a slight decrease in the ion-migration contribution to the limiting value of 10.5 %. Other important results concern the chemical diffusion: 1) its dominant role as a mass transport mechanism does not dependent on E; 2) its multicomponent character is revealed through the inverse diffusion of iron ions affected by all the concentration gradients in the melt.

Fig. 1. Longitudinal element distribution in the middle part of the quenched basaltic sample (S10) imposed 24 hours to an electric field of E = 1.84 V/cm. The points cover the gradient region near to the cathode.

In conclusion, it is possible conditions similar to the experimentally studied by us, to take place on the peripheries of large magmatic chambers that with their cooler surrounding rocks represent thermogradient systems. In this case the mass transport of some magmatic constituents can be determined by multicomponent chemical diffusion accelerated significantly by ion-migration in the induced electric field. As a consequence, in a time scale of the order of 10² years (very short from the geological point of view), heterogeneities in the melt should arise and spread within the magmatic chamber in a spatial region of several hundred meters.

22. Thermal analysis of mechanically activated mixtures of Tunisian phosphorite and ammonium sulfate (V. Petkova, A. Toneva, Y. Pelovski, I. Dombalov, S. Stefanova, P. Kostadinova, V. Stoyanov)

Combination of thermal and tribochemical methods is perspective to utilize low phosphate containing raw materials and sub-products or industrial wastes for obtaining new types of ecologically pure complex NPS and NPKS fertilizers.

The changes in the system phosphorite-ammonium sulphate are interesting due to the possibility to dope the mixture with additional nutritious sulfur. The experiments concern preliminary triboactivation of mixtures of Tunisian phosphorite and ammonium sulfate in a mass ratio 1:1 in a planetary mill triboreactor Pulverisette-5 (Fritsch, Germany) with iron, chromium, nickel, and agate milling bodies for activation times from 10 min to 50 h. To claryfy the structural and phase changes when treating the mixtures thermal and powder X-ray diffraction (XRD) methods were used.

The analysis of TG-DTG-DTA data of the decomposition of non-activated mixture indicates that the mechanism of reactions, which proceed between the Tunisian phosphorite and ammonium sulfate is determined by the behavior of (NH₄)₂SO₄, which is thermally more unstable. As a result of the chemical interactions between the reagents in the temperature range 250-370 ^?? new compounds are formed, (NH₄)₂SO₄.2CaSO₄ and CaHPO₄. The compounds CaHPO₄ and NH₄HSO₄, formed in the course of the reactions, interact with Ca₅F(PO₄)₃ in the temperature range 360-400 ^oC, resulting in the formation of H₄CaP₃O₉, CaSO₄, and a-Ca₂P₂O₇. In the temperature range 610-765 ^oC the reaction between phosphorite and NH₄CaP₃O₉ leads to the formation of additional amounts of a-Ca₂P₂O₇. During the next stage (760 - 900 ^oC) together with the decarbonation of Ca?O₃, an interaction between a-Ca₂P₂O₇ and the accumulated CaSO₄in the system results in the formation of Ca₃(PO₄)₂.

XRD patterns indicate that for the mechanically activated samples the intensity of the peaks decreases and broaden with increasing the time of treatment from 10 min to 50 h [15, 16, 17, 18, 52, 74]. Additional peaks of newly formed compounds are identified together with the peaks of the main reagents Ca₅F(PO₄)₃ and (NH₄)₂SO₄, namely Ca₃(PO₄)₂.H₂ O; (NH₄)₂SO₄.2CaSO₄; NH₄Ca(PO₃)₃;(NH₄)₂H₂P₂O₇; CaH₂P₂O₇; a-Ca₂P₂O₇ (chromium nickel and agate milling bodies) [15, 16, 17, 52, 74], as well as such belonging to (NH₄)₂CaH₄(P₂ O₇)₂ and (NH₄)₂Ca₃(P₂ O₇)₂.6H₂O when using iron milling bodies [18]. The newly formed phases such as ammonium-calcium piro and polyphosphates, point that solid-state reactions are taking place between the components of the system during triboactivation. The presence of (NH₄)₂SO₄.2CaSO₄ and a-Ca₂P₂O₇ (products of thermal decomposition of the non-activated mixture) indicates similar character of transformations upon thermal and mechanical treatment. Probably, during triboactivation the temperature in some local regions becomes so high that the formation of the same products is possible.

The formation of new compounds during the mechanochemical activation results from a partial decomposition of (NH₄)₂SO₄with the release of NH₃ and SO₃. These gaseous products are connected with active centers and as a result of these interactions (NH₄)₂SO₄.2CaSO₄, NH₄CaP₃O₉, Ca₃(PO₄)₂, (NH₄)₂H₂P₂ O₇, CaH₂P₂O₇, and a-Ca₂P₂O₇ are formed according to the reactions [15, 16, 17, 74]:

XRD data prove that the formation of ammonium-calcium trimeta- and pirophosphates result from a direct synthesis (reactions 1-5) confirmed also by the fact that peaks of other ammonium-calcium hydrogenortho- or hydrogenphosphates, used usually as precursors for obtaining polyphosphates, are not observed.

(NH₄)₂SO₄ = NH₄HSO₄ + NH₃ (1)

2Ca₅F(PO₄)₃ + 4NH₄HSO₄ = (NH₄)₂SO₄.2CaSO₄ + CaH₂P₂O₇ + CaSO₄+2Ca₃(PO₄)₂ + 2HF + 2NH₃ + H₂O (2)

Ca₅F(PO₄)₃ + 6NH₄HSO₄ = 2(NH₄)₂SO₄.2CaSO₄ + NH₄CaP₃O₉ + HF + NH₃ + 3H₂O (3)

Ca₅F(PO₄)₃ + 6NH₄HSO₄ = 2(NH₄)₂SO₄.2CaSO₄ + (NH₄)₂H₂P₂ O₇ + 2Ca₃(PO₄)₂ + 2HF + H₂O (4)

2Ca₅F(PO₄)₃ + 3NH₄HSO₄ = (NH₄)₂SO₄.2CaSO₄ + Ca₂P₂O₇ + 2Ca₃(PO₄)₂ + 2HF + NH₃ + H₂O (5)

Thermal analysis data point at further complication of the process of thermal decomposition of activated mixtures compared to the non-activated ones expressed in superposition of the effects of decomposition of the products formed upon triboactivation. Comparing TG-DTA data of activated mixtures with non-activated ones the presence of new endoeffects in the temperature ranges 35-120 ^oC and 150-240 ^oC is found as well as two additional exoeffects superimposed with the endothermal peak in the temperature range 600-670 ^oC [15, 16, 17, 52, 74].

The exothermal effect originates probably from the triboactivation of the samples, since a similar effect is absent in the DTA spectrum of the non-activated mixture. As a result of the mechanochemical impact the crystal structure of phosphorite is deformed and accumulates mechanical energy. The accumulated energy is relaxing initiating the complex of chemical reactions connected with the formation of ammonium-calcium phosphates and with reduction of the temperature regions of the transformations. The exothermal effect markedly seen for the mixture activated for 10 h probably results from the spontaneous restructuring of the solid phase in the relaxation of the accumulated energy, when the transformation of CaH₂P₂O₇ into a-Ca₂P₂O₇ proceeds.

It is found that the thermo-triboactivation of mixtures of Tunisian phosphorite and ammonium sulphate in the temperature range 20-1100^oC for 10 min to 50 h leads to a solid-phase synthesis between the components of the system and to the formation of ammonium-calcium metaphosphates and pyrophosphates - NH₄Ca(PO₃)₃;(NH₄)₂CaH₄(P₂O₇)₂; (NH₄)₂Ca₃(P₂ O₇)₂.6H₂O; (NH₄)₂H₂P₂ O₇; CaH₂P₂O₇, which gains priority over the simple thermal treatment of the system studied. Although the chemical reactions involved are complex and multi-variant the formation of compounds containing P₂O₇^4--groups turn out to be energetically most probable. It is proved that one can substantially reduce the temperatures of the transformation as compared with those for the non-activated mixture and a possible mechanism of thermal decomposition is proposed.

IV. SYNTHESIS, COMPOSITION, STRUCTURE, AND PROPERTIES OF MINERALS AND NEW MATERIALS

23. Phonon anomalies and local structure in crystals with defects. Lead-based relaxors. (B. Mihailova, L.Konstantinov, R. Petrova)

Lead-based complex perovkite-type materials of general formula Pb(B'_1-xB"_x)O₃ are a subject of both theoretical and practical interest. Relaxors form a special class of ferroelectric materials, which possess extremely high dielectric constant. They differ from the normal ferroelectrics by a broad, diffuse phase transition near the dielectric constant maximum, T_m, and a strong frequency dependence of e(T). Due to their extraordinary dielectric properties relaxors are of great technological importance and have found various applications in room-temeparture pyroelectric detectors, multilayer ceramic capacitors, electromechanical devices, ultrasonic and modern medical imaging devices etc. Although relaxors have extensively been investigated by different methods the understanding of the relation between their nanoscale structure and their unique properties remains a challenging problem. Because of the compatible coherent length of the inelastic light scattering event in oxides, Raman spectroscopy is fairly appropriate method for studying the nanoscale structural features in relaxors. However, the rather complex character of the Raman spectra hampers their precise analysis.

Using Raman spectroscopy we studied the local structure and dynamics in two relaxors of equal stoichiometry and equal B"-cation ionic radius, PbSc_0.5Nb_0.5O₃ and PbSc_0.5Ta_0.5O₃[11, 71]. The samples are single crystals, entirely B-site disordered as determined by the standard procedure based on powder x-ray diffraction. By comparing the polarised spectra of the two compounds, measured at temperatures higher than T_m, we determined the symmetry of the phonon modes giving rise to the Raman scattering of the paraelectric state. Hence, by performing normal mode calculations the observed Raman peaks were unambiguously assigned to definite atomic vibrations (Fig.1).

Fig.1. Structural unit used in modeling the Raman spectra of PbSc_0.5B"_0.5O₃ (a), the atom vector displacements of the normal modes in the paraelectric state (b) and the peak assignment (c).

Further, we investigated the dependence of the atomic vibrations on different structural deviations by calculating the modes of structural units with varied atomic positions. This allowed us to analyse the phonon anomalies in the spectra measured at different temperatures near the Curie range and to gain more information about the formation of precursor ferroic species. It is shown that on a local scale of a few unit cells doubling of the structural unit exists in both materials. The presence of two Raman peaks originating from the silent F_2u mode reveals the occurrence of electron-phonon coupling in PbSc_0.5B"_0.5O₃ , which leads to dynamical off-centre-symmetrical structural fluctuations. The structural perturbation consists of a non-coplanarity of Pb and O atoms in planes perpendicular to the body diagonal and deviations of B cations from the centre of BO₆ octahedra [51]. The intensity ratio of the two peaks is sensitive to the degree of orientational ordering of the stereoactive electron lone pairs of Pb atoms within the P-b-O planes, which is related to the degree of compositional B'/B" ordering existing in nanoscale regions. The temperature dependence of the polarised Raman spectra shows that on cooling different structural changes are preferential in the two materials studied. In PbSc_0.5Nb_0.5O₃ the lowering of the temperature favours the off-centre deviations of the B cations. In PbSc_0.5Ta_0.5O₃ the temperature decrease stabilises the non-coplanarity of the Pb and O atoms in the planes perpendicular to the body diagonal and enhances the correlation between the electronic lone pairs of Pb. Thus, different mechanisms of formation of the ferroelectric state should dominate in the two compounds. The spontaneous polarisation in PbSc_0.5Nb_0.5O₃ is most probably related to deformation of individual Pb-BO₃ entities and the system behaves rather as isotropic glassy-like matter, while the spontaneous polarisation in PbSc_0.5Ta_0.5O₃ is mainly related to lead-oxygen non-coplanarity and the system behaves as composed of anisotropic incipient domains.

24. Crystal structure of aminoguanidinium hydrogen carbonate (Tz. Kolev, R. Petrova)

It is found that the commercial product with the formula C₂H₈N₄O₃ aminoguanidinium hydrogene carbonate (AGHC) exists as a betaine of aminoguanidinium monohydrate. It crystallizes in the monoclinic space group P2₁/c with a=9.1929(8)Å, b=4.8380(5)Å, c=13.2467(11)Å,b=93.073(7)^o.

The vibrational spectra of AGHC differ significantly from the expected, although that compound produces aminoguanidinium cations and this is unambiguously pointed out by the crystal structure of aminoguanidinium squarate. In IR spectra of AGHC there are no characteristic bands for hydrogen carbonate anion and, in addition, two strong bands at 1688 and 1634 cm^-1 appear. We compared our spectra with that of the aminoguanidinium chloride, which could be used as a model system for IR study of aminoguanidinium cation. There are seven h(N-H) bands in the IR spectrum of aminoguanidinium chloride and only five in the spectrum of AGHC. These discrepancies motivated us to calculate the theoretical spectrum of the aminoguanidinium cation on ab initio RHF 6-31G* and DFT B3LYP 6-31G* levels. The obtained theoretical frequencies proved our assumption that the commercial product is not AGHC. product is better than the literature data for different betaines.

There is no data in literature for the compound studied (CSD, Beilstein and Chemical Abstracts ). That is the reason to undertake the present determination of molecular and crystal structure of AGHC. The molecule of the investigated compound could be regarded as a derivative of aminoguanidinium, where the positive charge is delocalized over the guanidinium moiety and the negative one over the NHCO₂. This is confirmed by the IR spectrum of the solid sample (KBr pellet). The guanidile and NHCO₂ groups are planar and nearly perpendicular to each other, with a dihedral angle of 83.26^o. An extensive hydrogen-bonding network holds the structural units together (Fig.1).

Fig. 1. Three dimensional packing of the
structure. The hydrogen bonds are denoted
with doted lines.

The inner guanidile hydrogen atoms form N-H...O bonds through which the organic molecules are connected to form zig-zag chains parallel to c-axis. The chains are linked along the b-axis and thus, a layer perpendicular to a-axis is formed. The water molecule is donor of two and acceptor of two hydrogen bonds, which hold the layers along a-axis. The crystal structure can be thought as a layered one, where layers of organic molecules alternate with that formed by water molecules [47].

25. Crystal structure of NaAl(WO₄)₂ single crystals (U. Kolb, D. Nihtianova, I. Nikolov, D. Kovacheva)

Single crystals of NaAl(WO₄)₂ are suitable as a material for tunable lasers. The chemical compound NaAl(WO₄)₂ is new for the system Na₂O - Al₂O₃ - WO₃. It is an incongruently melting compound with temperature of decomposition 775 ^oC.

Single crystals of NaAl(WO₄)₂ are grown for the first time by spontaneous crystallization (T_cryst. = 715 ± 2 ^oC) by using solutions with the following concentration: Na₂O 28.0 - 28.5 mol %; Al₂O₃ 6.2 - 6.5 mol %; and WO₃ 65.5 - 66.0 mol %.

The crystal stucture of NaAl(WO₄)₂ is studied by transmission electron microscopy and X-ray powder diffraction. The unit cell parameters of NaAl(WO₄)₂ are obtained by tilt series method in TEM using EM 420 Philips (tilt - rotation holder, 120 kV) and Tecnai F30 (double tilt - rotation holder, 300 kV). Tilts are performed from an initial zone [100] around axis c*: [110], [210], [-210], [310], [-310]. The zone axes [101], [201], [301] are registered from an initial zone [001] around axis b*. The following data are obtained: a = 9.652Å, b = 5.392Å, c = 13.018Å, b = 89.88^o, space group C2/c. These data are used to index the experimental X-ray powder diffraction spectrum of this compound (CuK_a radiation).

A reasonable structural model of NaAl(WO₄)₂ is created. It is shown that this compound is isostructural with the known NaFe(MoO₄)₂.

Using the initial structural model the theoretical SAED patterns are calculated by the program CERIUS 4.0 and are compared with the experimental transmission electron diffraction data and a good correspondence between both set of data is found. The calculated electron diffraction patterns and the simulated powder X-ray diffraction spectrum both compared with experimental data show that the structural model of NaAl(WO₄)₂ is correct.

26. Fe₂O₃.nH₂O-nanophases formed in tungsten-polyanion-assisted sol-gel processes (M. Tarassov, B. Mihailova, E. Tarassova, L. Konstantinov)

Several samples of Fe₂O₃.xWO₃.nH₂O are synthesized via a sol-gel process in solution with the following parameters: 0.1 g.mol/l Fe³⁺, W/Fe=0.1, pH=4-10. The samples are studied by powder XRD and micro-Raman spectroscopy to clarify the influence of tungsten and of the pH of the solution on the formation of ferric iron oxides. It is shown that: (1) goethite (a-FeOOH) with nanometric size (<30 nm) is the only crystalline phase formed in tungsten-assisted sol-gel processes; (2) the increase in pH and in the content of W leads to an increase in the disorder of the formed gel; (3) W is predominantly present in the form of self-assembled particles with metatungstate-like atom arrangement, while in natural ferric oxides it exists both as an admixture in the goethite/hematite structure and as self-assembled clusters in goethite-like Fe-O network [55].

27. Chemical composition and vibrational spectra of tungsten-bearing goethite and hematite from Western Rhodopes, Bulgaria (M. Tarassov, B. Mihailova, E. Tarassova, L. Konstantinov)

The incorporation of tungsten in goethite and hematite as well as the relationships between the two minerals in W-containing exogene media are considered on the basis of a representative sample from Grantcharitza deposit (Western Rhodopes, Bulgaria), studied by scanning electron microscopy, electron probe microanalysis, X-ray powder diffraction and micro-Raman spectroscopy [24, 84]. The sample is a colloform black material consisting predominantly of goethite (G-I) with 6.83-10.85 wt.% WO₃ and of several products of its alteration, including W-poor goethite (G-II) with 1.35-5.72 wt.% WO₃, W-rich ferric iron oxide phase (F_w) with 22.19-25.12 wt.% WO₃, and hematite (H-I) with 1.21-1.72 wt.% WO₃. It is shown that G-I is an aggregate of proper goethite and of a W-rich ferric iron oxide phase (S_w). The alteration of G-I aggregates includes: (1) selective dissolution of S_w which either re-precipitates, thus forming a separate W-rich phase (F_w), or which is almost entirely removed from the aggregate; (2) replacement of the residual goethite G-II by hematite H-I. An atomic ratio W/Fe of about 0.006 is supposed corresponding to the isomorphic (Fe³⁺« W⁶⁺) incorporation of tungsten into goethite and hematite in the sample studied. The Raman spectrum of G-II resembles the already published spectroscopic data on goethite, whereas H-I shows spectral features typical of a highly disordered hematite structure. The presence of W atoms in the structures of hematite H-I and goethite G-II causes the appearance of a low-frequency shoulder of the Raman peak near 400 cm^-1. According to the Raman spectroscopy data, the W-rich constituent S_w in G-I aggregates as well as its re-precipitated variety F_w both have a Fe-O network similar to that of goethite. In both materials only a small amount of W atoms occupies Fe-positions, while the major part of tungsten forms W-O self-assembled clusters generating a broad band between 580 and 750 cm^-1 in the Raman spectra. As shown by model calculations, tungsten is organised in chain-like clusters of corner-sharing WO₆ octahedra with an average W-O-W bond angle of about 150^o. In addition, F_w contains isolated WO₆ octahedra or corner-sharing-WO₆ clusters with an average W-O-W angle of about 180^o.

28. Investigation of the structure of porous silicon obtained by electrochemical etching (V. Dimov)

Porous silicon plates with thickness down to 100 nm obtained by electrochemical etching are of a great interest in micro- and optoelectronics and micromechanics. Their optical, electrical and physical properties depend on the structure of the porous layers.

Fig. 1. Bright-field (a) and dark-field (b) images of porous and non-treated silicon plate
and electron diffraction pattern (c) of the porous layer.

The porous structure obtained from silicon plates via standard electrochemical etching are studied by transmission electron microscopy (TEM). Bright-field (BF) (Fig. 1a) and dark-field (DF) (Fig. 1b) TEM patterns were obtained for a cut perpendicular to the treated surface {100} of a sample thinned in a wedge-like way to thickness from 0 to 100 nm by ion etching. On the BF pattern one can see the pores non-periodically disposed as bright columns perpendicular to the surface of dissolution {100} and sized up to 10 nm. All pores are opened and merge themselves in a region of dissolution of the surface layer of the silicon plate. The DF pattern visualizes the crystal columns of the silicon skeleton in the form of differently sized bright stripes of a smaller area than that of the amorphous silicon of the porous. The boundary between the porous and primary silicon is observed as a region of intermediate contrast, which is parallel to the surface of the plate {100}. A diffraction pattern of a selected region (Fig. 1c) is obtained, which demonstrates the preservation of the single crystalline character of the pores. A deviation from the spherical form of the diffraction spots is observed, which indicates changes in the crystal structure. They result from de-orientation of the columns to each other and from torsion of the structure along the length of the columns. According to the measured arc of torsion of the spots the angle of de-orientation is evaluated approximately to 3^o.

The results obtained show that the porous silicon structure was formed by non-dissolved columns and pores positioned perpendicularly to the surface of etching in three regions: boundary, porous, and intermediate, which are parallel to the plate surface.

29. Temperature dependence of crystallization in Fe₇₈Si₉B₁₃ and Co₇₅Si₁₅B₁₀ amorphous alloys using positron-anihilation lifetime spectroscopy and powder X-ray diffraction (I. Minkov, V. Ganev, T. Troev, B.Shivachev)

During the last years the amorphous alloys containing Fe, Co, Ni, and REE gain a large interest for application in device design due to their specific ferro-magnetic properties preserved in a relatively large temperature range.

Positron-anihilation lifetime spectroscopy and powder X-ray diffraction analysis (XRD) are applied to metallic glasses with composition Fe₇₈Si₉B₁₃ and Co₇₅Si₁₅B₁₀ treated at different temperatures. Samples of Fe₇₈Si₉B₁₃ and Co₇₅Si₁₅B₁₀ are heated and annealed from room temperature to 650 ^oC and 700 ^oC, respectively. Several samples with the same compositions are heated to 625 ^oC and 700 ^oC for Co-Si-B and quenched in liquid nitrogen. Three positron lifetimes are established. The phase composition is determined by XRD. The positron trapping rates in defect-like formations in amorphous and crystalline states are calculated, as well as the vacancy formation enthalpy. The values are 0.23 eV for Fe₇₈Si₉B_13, 0.063 eV for the amorphous phase and 0.2 eV for the crystalline Co₇₅Si₁₅B₁₀ phase.

Fig. 1. XRD patterns and phase identification of Fe-Si-B amorphous alloy heated
at temperature: (a) 560 ^oC, (b) 525 ^oC, (c) 475 ^oC, and (d) 325 ^oC

It is established that the crystallization of Fe₇₈Si₉B₁₃ amorphous alloy (Fig.1) is accomplished by the formation of composite crystals of Fe₂B (PDF 39-1314) surrounded by a-Fe (PDF 06-0696) and Fe₃Si (PDF 35-0519). The crystallization temperature is between 500 ^oC and 525 ^oC. In both samples (Fe₇₈Si₉B₁₃ and Co₇₅Si₁₅B₁₀) three lifetime components were observed: (1) t₁, related to positron annihilation in composite crystals; (2) t₂, due to annihilation in the amorphous phase; and (3) t₃, resulting from annihilation around the grain boundaries. All the three positron lifetimes have intensities corresponding to the crystallization stages of the investigated alloys. The main difference between Co₇₅Si₁₅B₁₀ metallic glass and Fe₇₈Si₉B₁₃consissts in the absence of the first lifetime component during the annealing the temperature range 100 ? 350 ^oC, which is due to a stronger recovery of the amorphous structure at low temperatures. The crystallization point for Co₇₅Si₁₅B₁₀ is around 525 ^oC.

Fig. 2. XRD patterns and phase identification of Co-Si-B amorphous alloy heated to 650 ^oC.

The final phase composition for Co₇₅Si₁₅B₁₀ at 650 ^oC, determined by XRD (Fig.2) includes Co₂Si (PDF 04-0847), Co₂B (PDF 03-0278), a-Co (PDF 15-0806) and b-Co (PDF 05-0727) phases. XRD patterns of both glasses being annealed, but not quenched show a distinct peak splitting, which indicates the formation of structural defects in crystallites due to re-amorphisation. The Fe-Si-B amorphous alloy can be used as a standard for investigating Fe-valence states in oxides and silicates minerals.

30. Thermal and structural analysis of FeSO₄.H₂O-BaO₂ mixtures (V. Petkova, Y. Pelovski)

The thermal decomposition of mixtures of molar ratio n=FeSO₄.H₂O/BaO₂, where n is 4, 2, and 1 are studied under isothermal conditions of heating in the temperature range 553 - 673 K and in gaseous environment of 1% H₂ and 99 % Ar using a solid-electrolite oxygen analyzer. New data are obtained for the thermal interactions taking place in the system FeSO₄.H₂O - BaO₂. The reactions are intense and proceed evolution of oxygen in the gas phase (Fig. 1).

On the basis of Mossbauer spectroscopy and powder X-ray diffraction data it is shown that these recations are connected with destruction of Ba-peroxide, formation of barium ferrites of the type BaFe₂O₄ and BaFe₁₂O₁₉. In contrast to previous results, the present studies in the low temperature region (T=623 K) and in gaseous environment of 1% H₂ and 99% Ar there is no BaFeO₃ detected, but BaFe₁₂O₁₉, obtained so far only in the high temperature region. According to the new data presented, small amounts of BaFe₁₂O₁₉ are obtained for the first time at 623 K. These results prove once again the essential effect of the partial pressures of the gaseous components in the system on the phase composition of solid products from the thermal decomposition of mixtures of FeSO₄.H₂O - BaO₂ in various molar ratios.

Fig. 1. Plots of lgP_O2 versus time T=623 K for mixtures of FeSO₄.H₂O - BaO₂with:
a) n = 4; b) n = 2; c) n = 1

On the basis of the experimental results obtained and on the data of physical methods of analysis the following most probable scheme is proposed for the reactions in mixtures of FeSO₄.H₂O and BaO₂ in molar ratios 4 and 1 at T=623 K in gaseous environment of 1% H₂ and 99% Ar:

(1) BaO₂ = BaO + 1/2O₂; (2) 2FeSO₄.H₂O + 1/2O₂ = 2FeOHSO₄ + H₂O; (4) FeSO₄.H₂O = FeSO₄ + H₂O;
(5) 2FeSO₄ + 3BaO₂ = BaFe₂O₄ + 2BaSO₄ + O₂ and/or (6) 2FeOHSO₄ + 3BaO₂ = BaFe₂O₄ + 2BaSO₄ + H₂O + 3/2O₂ ;
(7) 12FeOHSO₄ + 3BaO₂ = BaFe₁₂O₁₉ + BaSO₄ + 11SO₃ + 6H₂O + O₂ ; (8) BaO + SO₃ = BaSO₄

31. Oxidation of aliphatic hydrocarbons on gold catalysts (Yu. Kalvachev)

It is possible to perform one-step vapor phase oxidation of aliphatic hydrocarbons on nanosized gold catalysts using oxygen. An attempt was made to oxidize selectively propylene to propylene oxide, propane to acetone, and isobutene to t-butanol with hydrogen-oxygen mixture in flow conditions. The reaction occurs at the interface perimeter of the support around the gold particles. The activity of these catalysts can be attributed to synergetic effects between gold and titanium.

Since dodecyl trimethyl ammonium chloride was used as a template during the synthesis of Ti-MCM, the pore diameters of the samples being about 2.0-2.5 nm. Before reaction, gold particles are homogeneously dispersed on the support with an average diameter of about 2 nm. The particle size distribution shows that about 30 % of the gold particles are of a diameter above 2.5 nm. This suggests that a fraction of gold particles are not incorporated in the pores of the support. Thee particles located outside the pores are coagulated during the reaction. However, the majority of gold particles are encapsulated in the channels of the support and they are prevented from coagulation and from irreversible deactivation.

The best catalytic performance in these reactions was obtained with the sample of 1.2 % gold loading and a ratio Ti/Si of 2.8/100. The partial oxidation products, propylene oxide from propylene, acetone from propane, and t-butanol from isobutene, have been obtained with a selectivity of 95, 48, and 85 % at hydrocarbon conversion of 1.8, 0.3, and 2.2 %, respectively.

The products are similar to those obtained in oxidation of hydrocarbons by H₂O₂ on Ti-MCM. The active species are most probably similar to hydroperoxo-species, located at the boundary between gold and titanium.

In the oxidation of propylene on Au/Ti-MCM catalyst, a relatively long induction period of about 1.5 h is observed in propylene conversion at 100 ^oC, whereas a selectivity to propylene oxide and hydrogen consumption reach steady state much earlier. The induction period at 50 ^oC becomes longer. The consumption of hydrogen is about twice that on Au/TiO₂/SiO₂ for similar conversion of propylene, suggesting that the selective oxygen species formed by the reaction of oxygen with hydrogen may have a smaller chance to react with propylene. Since Ti atoms are isolated from each other in Ti-MCM, the long induction period can be regarded as a period necessary to accumulate selective oxygen species, probably H₂O₂, on the Ti-MCM surface and in the gas phase. Another alternative is that propylene oxide formed firstly remains on the surface until saturation has been reached and then tends to desorb from the surface.

Taking into account the experimental results, the following reaction pathways may be proposed: 1) Hydrocarbon covers partly the surface of Au particles, on which hydrogen reacts with oxygen to form H₂O₂; 2) The formed H₂O₂ is transmitted to free titanium sites on the surface of Ti-MCM and is transformed there to hydroperoxo-species; 3) The hydrocarbon adsorbed on the surface reacts with the hydroperoxo-species to yield oxygenates.

This method of oxidation of hydrocarbons is much more environmental friendly than the methods used nowadays in industry [46, 66].

32. Applying the methods of mutual co-sedimentation and tribo-chemical activation to synthesis of zinc stanate (I. Stambolova, A. Toneva, V. Bluskov,D. Radev, P. Peshev)

Zinc stanate Zn₂SnO₄ is a perspective material for application in sensors of humidity flamable gases, barrier coatings, electrically conducting layers, etc. The synthesis of Zn₂SnO₄ through conventional solid phase method proceeds at high temperatures, so that the reduction of the temperature of synthesis is of fundamental and practical interest.

From the known methods for reducing the temperature of solid phase synthesis of powder materials we have performed co-sedimentation and tribochemical activation. As precursors of the tribochemical synthesis compounds containing water and hydroxyl groups were chosen in order to obtain zinc stanate under softer conditions.

The performed experiments show that both methods, co-sedimentation and tribochemical activation, using the chosen compounds leads to synthesis of Zn₂SnO₄, the synthesis temperature being substantially lower that of the conventional methods. The use of the former method turns out to be more effective than the latter, which can be explained by the finer mixing and creation of conditions for a higher reactivity [23, 82].

33. Synthesis of new effective radioprotective drugs (K. Kosev)

The macromolecular approach to improving lowmolecular biologically active substances allowing the development of a new generation of drugs is of a wide applicability. The phisiologically active polymers form a new class of drugs with advantages in respect to the monomeric ones such as high effectiveness and stability and low toxicity and depot-effect.

Polyoxiethylene phosphonates form a new class of biodegradable polymers synthesized via the reaction of pre-esterification of diesters of the phosphonate acid with diols or polyethyleneglycol. The presence of the strongly reacting P-H group in these polymers allows their participation in various polymer-analogous reactions: attachment to double bonds (? = ? or N=C), carbonyl group, reaction of Atherton-Todd, and reaction of oxydation.

Synthesis of 1,2-epoxyalkylphosphonates. The interaction of dialkylphosphonates with a-challogenized ketones were studied under conditions of interphase catalysis:

Conditions were specified under which high yields of diapkyl-1,2-epoxyalkylphosphonates are obtained which are close structural analogues of Phosphomicin. Their alkalline, tiuronievi, and aluminium salts are interetsing as phitopharmaceutical compounds - analogues of the alluminium tricetylphosphonate. It is possible this kind of reactions, under specific conditions (interphase catalysis), to be effective for producing polyalalkyl phosphonates.

Synthesis of polyalkylenephosphonates and polyalkylenephosphates. Polyalkylenephosphonates were synthesized following the scheme of pre-esterification of dialkylphosphonate (dimethyl or diethyl) with polyethyleneglycol, as described in the literature. We used polyethylene glycols of molecular masses between 200-800, which are the maximum values corresponding to the conditions for obtaining phosphonates with the required biocompatibility and stability. The applied two-step scheme of pressure variations makes it possible to obtain a controllable narrow molecular mass distribution and molecular masses of the order of 10 000.

The obtained polyalkyl phosphonates are semi-products from the synthesis of carriers and polymerically bound druggs. One of the interesting possibilities is their transformation into polyalkyl phosphates when interacting with methanol [48, 49].

The potential in synthesizing the polymer drugs is studied on the basis of their bonding with 1-amino-2-etantiol. When as a reagent a free amino base is used the interaction proceeds through metyliration of the amino group of tiol, whereas for hydrochloride and hydrobromide it prceeds with separation of metylchalogenide and bounding of 1-amin-2-entantiola in the form of hydrophosphate [5].

The obtained polymer drugs possess radio-protecting properties. Some of the substances studied are of a substantially higher activity as compared with their low molecular analogue, it being combined with a reduced toxicity and depot effect.

The modification of polyalkilenephosphonates by interaction with a-chalogenated carbonyl compounds was also studied. By including Cl-acetone a polyoxyethylenephosphonate was obtained, carrying a-hydroxy-groups and/or epoxy-groups. For the purpose conditions for inter-phase catalysis were used. Their choice allows to carry out interaction following the scheme, which leads to a product of prevailing presence of epoxy- or hydroxy-groups [7, 49]:

The obtained polyphosphonates are perspective as carriers for bonding drugs, which contain amino, hydroxy-, tio-, or other functional groups. They are characterized by a high biocompatibility and a low toxicity.

The structure of the compounds studied is proved through a combination of ¹H-, ¹³C- and ³¹P-NMR spectroscopy as well as data from IR spectroscopy. The molecular mass and its distribution is determined by GPH or a by combination with NMR spectral data.

34. Comparison between SMT procedure for consecutive extraction and single extractions to study the distribution of metals in coal ashes (N. Lihareva)

The conventional SMT procedure for sequential extraction, developed by the European Community Bureau of References in 1993, is compared with a procedure of single extractions using reagents and conditions identical with the different stages of the SMT procedure in studying coal ashes. The analyses of the initial samples and of the extractions are performed using ICP-AES and flame and non-flame atomic absorption spectrometry (AAS). The separation of elements is performed in five fractions: 1) water soluble and adsorbed; 2) bonded with carbonates of Ca, Mg, and Fe; 3) bonded with oxides of Fe and Mn; 4) bonded with sulfides and organic matter; 5) bonded with silicates and other hardly dissolvable minerals. The obtained results show that the usage of the conventional SMT procedure leads to higher concentrations of extraction for all the elements and on all stages. For the major elements, Ca and Fe, the total extracted amounts for both procedures are in good agreement (the ratio of the sums of the extracted elements in the simple extractions procedure to their sum in the consecutive extraction is equal to 90%). For trace elements this ratio is higher than 90% for Zn, Ni, while it is between 80-90% for Cr, Cu, and Pb. The difference between the results from both procedures is high for Cd (67%), resulting from the low initial concentration of this element in the samples. The reproducibility of the determinations, expressed in terms of the relative standard deviation (RSD, %) varies in a wide range depending on the element and on the stage of extraction. A good reproducibility (up to 15 %) is obtained for the majority of the elements studied. The values of RSD are higher when using the SMT procedure. There is a tendency for increasing the values of RSD for all the elements studied in the later stages of each procedure. The replacement of the sequential SMT extraction by single extractions leads to a remarcable reduction of the time for analysis and facilitates the sample treatment. The simple extractions can be applied for fast scanning in order to evaluate the mobility and biological availability of metals in the ashes to the environment.

V. Ph. D. THESISES

35. Phase-mineral transformations and chemical interactions in the inorganic matter during combustion of Bulgarian coals (Chr. Vassileva)

The purpose of the work is to characterize and systematize the phase-mineral transformations and chemical interactions in the inorganic matter during combustion of Bulgarian coals from 6 coal basins - Sofia (S), Maritza West (MW), Maritza East (ME), Bobov Dol (BD), Balkan (B) and Pernik (P) [32]. The methodological approach used includes a parallel investigation of coals and their products obtained during coal heating from 100 to 1600 °C using a temperature step of 100 °C in air and for a fixed holding time of 0.5 h. A complex of analytical methods and procedures (separation, thermal treatment, optical microscopy, SEM, TEM, X-ray powder diffraction, DTA-TGA, various chemical analyses, ash-fusion test, etc.) was used. The most important results achieved can be grouped as follows: 1) Phase-mineral and chemical classification of the coals and coal ashes are studied. It was found that the coals have low (S, MW, ME) or high (BD, B, P) detrital abundance and carbonate (S, BD), sulphide-sulphate (MW, ME, B) or mixed (P) authigenic mineralization. The coal ashes belong to 4 chemical types, namely: calferrisialic (S, MW), sialoferric (ME), sialoferricalcic (BD, B) and sialic (P); while the phase composition of these ashes are of a low (S, MW, ME) or high (BD, B, P) silicate concentration and oxyhydroxide (S, BD, B, P) or sulphate (MW, ME) tendency. 2) The behavior of organic and inorganic matter during heating is discussed. The behavior of 39 major and minor minerals and phases of primary and secondary origin in the products obtained during oxidation and combustion of the coals studied was characterized up to 1600 °C. 3) The phase-mineral transformations and chemical interactions are studied. The processes of oxidation and burning of the organic matter, transformation of minerals and solid phases, and the interactions between them, as well as the processes taking place in solutions and melts that induce the formation of solid products during oxidation and combustion of the coals are systemized. The temperature intervals for such processes were described. The coal ashes studied have low (S, MW, ME), medium (BD, B) and high melting (P) ash-fusion temperatures. The phase transformations responsible for these ash-fusion temperatures were identified. 4) An attempt is made for additional explanation and prediction of some technological (fouling, slagging, abrasion, corrosion and less effective combustion of coals in power plants) and environmental (stack emissions of sulphur and trace elements, and contaminated waters that transport the waste products from power stations) problems related to the combustion of Bulgarian coals.

INTERINSTITUTES PROGRAMS:

Gold based catalysts for environmental important reactions. Interinstitute project with University of Ghent, Belgium (Collaborative linkage grant, NATO Scientific Affairs Division).
Geochronology of the magmatism and metamorphism of the Bulgarian part of the Serbo-Macedonian Massif. Interinstitute project with the Institute of Geology of the Ural Branch of the Russian Academy of Science, Syktyvkar, Russia.

POSTDOCTORAL FELLOWS AND VISITING SCIENTISTS

Dr. Boriana Mihailova – Hamburg University (Humboldt’s Grant), Germany
Dr. Yuri Kalvachev – Leipzig University (Humboldt’s Grand), Germany
Dr. Diana Nihtianova – Johannes Gutenberg University, Mainz, Germany

LECTURING ON INTERNATIONAL EVENTS

Banjesevic, M., V. Cvetcovic, D. Kozelj, I. Peytcheva, A. v. Quadt 2002. Timok magmatic complex and Rifanj-Krepoljin belt: geodynamic evolution. - Conference "100 years copper institute of Bor", October 22-25, Bor, Yugoslavia.
Mihailova, B. 2002. Local structure and related phonon anomalies in complex oxide materials. - 1^st ANKA users meeting, September 16-17, Karlsruhe, Germany.
Ovtcharova, M., A. v. Quadt, M. Rohrmeier, Ch. Heinrich, M. Frank, R. Handler, F. Neubauer, I. Peytcheva. 2002. Relationship between formation of extensional Central Rhodopian Core Complex (Bulgaria) and magmatism and mineralization - isotope-geochronological study. - GEODE study center - final workshop, October 25-27, Grenoble, France.
Peytcheva, I., A. v. Quadt, Ch. Heinrich, Zh. Ivanov, B. Kamenov, K. Kouzmanov, St. Stoykov, A. Zartova. 2002. Evolution of magmatism and related ore formation in Central Srednogorie, Bulgaria: new insight from high precision U-Pb zircon and rutile geochronology and isotope tracing. - GEODE study center - final workshop, October 25-27, Grenoble, France.
Quadt, A. v., I. Peytcheva. 2002. Geochronology, geochemistry and isotope tracing of the Cretaceous magmatism of East Serbia as part of the Apuseni-Timok-Srednogorie metallogenic belt. - GEODE study center - final workshop, October 25-27, Grenoble, France.

PUBLICATIONS AND REPORTS AT CONFERENCES AND LOCAL MEETINGS

PUBLISHED ARTICLES AND REPORTS:

1. Donchev, I., F. Dipchikov, O. Petrov, N. Zidarov, M. Tarassov. 2002. Synthesis of artificial rocks (Synroc type). - Compt. rend. Acad. bul. Sci., 55, 12, 53-56.

2. Donchev, I. 2002. 40 years mineralogical-technological research in "NIPRORUDA". - Mining and Geology, 5, 32-35. (in Bulgarian with English abstracts)

3. Ferdov, S., V. Kostiv-Kytin, O. Petrov. 2002. A rapid method for synthesizing the layered titanosolicate JDF-L1. - Chemical Communication, 16 (issue), 1786-1787.

4. Ferdov, S., V. Kostiv-Kytin, O. Petrov. 2002. Improved powder diffraction patterns for synthetic paranatisite and natisite. - Powder Diffraction, 17, 3, 234-237.

5. Georgieva, R, R. Tsevi, K. Kossev, M. Balgjiska, R. Petrova, V. Tenchova, I. Gitsov, K. Troev. 2002. Immobilization of aminothiols on poly(ethylene phosphates). Formation of poly(ethylene phosphates)/cysteamine complexes and their radioprotective efficiency. - Journal of Medicinal Chemistry, 45, 5797-5801.

6. Ilieva, A., B. Mihailova. 2002. Structural state of opal siliceous rocks, Eastern Rhodopes. - Compt. rend. Acad. bulg. Sci., 55, 2, 65-70.

7. Kossev, K., N. Koseva, K. Troev. 2002. Preparation of 4-hydroxy-methyl-1.3-dioxolan-2-one under phase transfer catalysis conditions. - Reaction Kinetics and Catalysis Letters, 77, 1, 155-163.

8. Kostiv-Kytin, V., S. Ferdov, O. Petrov. 2002. Hydrothermal synthesis and successive transformation of paranatisite into natisite. - Compt. rend. Acad. bulg. Sci., 55, 2, 61-64.

9. Lenchev, A., J. Ninov, I. Donchev, S. Magaeva. 2002. Study on the properties of fly ashes from Bulgarian thermal power stations. - In: Proceedings of ISWA world environment congress&exhibition, Istanbul, Turkey, v. 5, 2699-2704.

10. Maleev, M., N. Zidarov. 2002. "Preservation of the diversity of minerals" - the Sofia initiative. - In: Proceeding of International scientific and technical conference "Mineral resources and man", v. I - Mineral resources and sustainable development of society, Varna, 113-122. (in Russian with English abstracts)

11. Mihailova, B.,U. Bismayer, B. Guttler, M. Gospodinov, L. Konstantinov. 2002.Local structure and dynamics in relaxor-ferroelectric PbSc_1/2Nb_1/2O₃ and PbSc_1/2Ta_1/2O₃ single crystals. - Journal of Physics: Condensed Matter, 14, 1091-1105.

12. Mihailova, B., L. Konstantinov. 2002. Raman spectroscopy as a method for nanoscaled structural investigations. - Nanoscience&Nanotechnology'02 (eds. E. Balabanova, I. Dragieva), Heron Press, Sofia, 60-63.

13. Pelovski, Y., V. Petkova, P. Kostadinova, V. Stoyanov, I. Dombalov. 2002. The effect of the conditions of triboactivation on the solid phase synthesis in the system natural phosphate and ammonium sulphate. - In: Proceeding of the X Jubilee science-technical session "Tribology and interdisciplinarity" CONTACT 2002, Sofia, 128-137. (in Bulgarian)

14. Penev, V., N. Zidarov, B. Zidarova. 2002. Geometrization of the language of mineralogy: Formulation of the problem and outlining the way of its solution. - Compt. rend. Acad. bulg. Sci., 55, 5, 47-50.

15. Petkova, V., A. Toneva, P. Kostadinova, S. Stefanova, Y. Pelovski, I. Dombalov. 2002. Effect of mechanochemical activation in phase formation in system of natural phosphate - ammonium sulphate. - In: Proceeding of the X Jubilee science-technical session "Tribology and interdisciplinarity" CONTACT 2002, Sofia, 110-119. (in Bulgarian)

16. Petkova, V., P. Kostadinova, V. Stoyanov, A. Toneva, Y. Pelovski, I. Dombalov. 2002. Possibility for solid phase synthesis in the system Tunisian phosphorite - ammonium phosphate upon tribochemical activation. - In: Proceeding of the X Jubilee science-technical session "Tribology and interdisciplinarity" CONTACT 2002, Sofia, 138-145. (in Bulgarian)

17. Petkova, V., A. Toneva, P. Kostadinova, Y. Pelovski, I. Dombalov. 2002. Investigation of the thermal decomposition of tribo-activated mixtures of Tunisian phosphorite and ammonium sulphate. - In: Proceeding of the X Jubilee science-technical session "Tribology and interdisciplinarity" CONTACT 2002, Sofia, 120-127. (in Bulgarian)

18. Petkova, V., S. Stephanov a, A. Toneva, I. Dombalov, Y. Pelovski. 2002. Investigation of the influence of SiO₂ on the phase-formation in the system natural phosphate and ammonium sulphate. - In: Proceeding of the Second Balkan conference on glass science and technology, 14^th conference on glass and ceramics,

19. Petrova, N., T. Mizota, Ts. Stanimirova, G. Kirov. 2002. Hydration enthalpy of hydrotalcite low-temperature methaphases. - Journal of Mineralogy and Petrology Science, 97, 1-6.

20. Quadt, A.v., I. Peytcheva, B. K. Kamenov, L. Fanger, C. A. Heinrich, M. Frank. 2002.The Elatsite porphyry copper deposit in the Panagyurishte ore district, Srednogorie zone, Bulgaria: U-Pb zircon geochronology and isotope-geochemical investigations of magmatism and ore genesis. - In: The timing and location of major ore deposits in an evolving orogen. Blundell, D.J., F. Neubauer, A. von Quadt (eds), Geological Society, London, special publications, 204, 119-135.

21. Quadt, A. v., I. Peytcheva, V. Cvetcovic, M. Banjesevic, D. Kozelj. 2002. Geochronology, geochemistry and isotope tracing of the Cretaceous magmatism of East Serbia as part of the Apuseni-Timok-Srednogorie metallogenic belt. - Geologica Carparthia, v. 53 (special issue), 175-177.

22. Radev, D., B. Mihailova, L. Konstantinov. 2002. Raman spectroscopic study of metal-containing boron carbide-based ceramics. - Solid State Sciences, 4, 37-41.

23. Stambolova, I., A. Toneva, V. Blaskov, D. Padev, P. Peshev. 2002. Applying the methods of co-sedimentation and tribochemical activation for synthesining zinc-stanate. - In: Proceeding of the X Jubilee science-technical session "Tribology and interdisciplinarity" CONTACT 2002, Sofia, 146-154. (in Bulgarian)

24. Tarassov, M., B. Mihailova, E. Tarassova, L. Konstantinov. 2002. Chemical composition and vibrational spectra of tungsten-bearing goethite and hematite from Western Rhodopes, Bulgaria. - European Journal of Mineralogy, 14, 977-986.

25. Tarassov, M., E., Tarassova. 2002. Forms of tungsten presence in hardly dressing ores in oxidizing zone of the Grincharitza deposit, Western Rhodopes. - In: Proceeding of International scientific and technical conference "Mineral resources and man", v.II - Complex utilization of mineral resources, Varna, 301-307. (in Bulgarian with Russian abstracts)

26. Titorenkova R., L. Macheva, N. Zidarov. 2002. Zircon typology of metagranites from Maleshevska and Ograzhden Mountains, SW Bulgaria. - Compt. rend. Acad. bulg. Sci., 55, 9, 61-66.

27. Tsanov, T., K. Kossev.2002. Practical application of modified poly(ethylene oxide) networks. - Polymer, 50, 242-255.

28. Tsintsov Z., B. Banushev. 2002. Characteristics of amethyst agates from Krumovgrad region. - Mining and Geology, 1, 23-27. (in Bulgarian with English abstracts)

29. Tsintsov, Z., B. Banushev. 2002. "Amethyst sun" - type agate structure from the region of Potochnitsa village, Krumovgrad district (Bulgaria). - Compt. rend. Acad. bulg. Sci., 55, 6, 67-72.

30. Tzvetanova, Y. 2002. Garnet-pyroxene skarns from Zvezdel pluton (East Rhodopes, Bulgaria). - Compt. rend. Acad. bulg. Sci., 55, 5, 51-56.

31. Vassilev, S., C. Braekman-Danheux, R. Moliner, I. Suelves, M. J. Lazaro, T. Thiemann. 2002. Low cost catalytic sorbents for NOx reduction: 1. Preparation and characterization of coal char impregnated with model vanadium components and petroleum coke ash. - Fuel, 81, 1281-1996.

32. Vassileva, C. 2002. Phase-mineral transformations and chemical interactions in the inorganic matter during combustion of Bulgarian coals. (PhD thesis) (in Bulgarian)

33. Vassileva, C., S. Vassilev. 2002. General observations on the phase-mineral transformations in inorganic matter of some Bulgarian coals during heating. - Compt. rend. Acad. bulg. Sci., 55, 7, 47-50.

34. Vassileva, C., S. Vassilev. 2002. Relations between ash-fusion temperatures and chemical and mineral composition of some Bulgarian coals. - Compt. rend. Acad. bulg. Sci., 55, 6, 61-66.

35. Vassileva, M., Z. Damyanov, V. Atanassov. 2002. Dolomite-group ferroan carbonates from Kremicovtsi deposit. - Annual of the University of Mining and Geology "St. Iv. Rilski", 45, part I - geology, 77-82. (in English with Bulgarian abstract)

36. Vitov, O. 2002. Indications for cassiterite mineralizations in Bulgaria. - Mining and Geology, 3-4, 34-37. (in Bulgarian with English abstract)

37. Vitov, O. 2002. New data on mercury in the Kyustendil Kraiste. - In: Proceeding of the Museum of history Kyustendil, v. VI, 335-350. (in Bulgarian with English abstracts)

38. Vitov, O. 2002. Placer mineralogical prognosis for gold prospecting in Bulgaria. - Geology and Mineral Resourses, 4, 41-44. (in Bulgarian with English abstract)

39. Vitov, O. 2002. Placer mineralogical mapping and prognosis for prospecting of mineral resources. - In: Proceeding of International scientific and technical conference "Mineral resources and man", v. II - Complex utilization of mineral resources, Varna, 227-237. (in Bulgarian with English abstracts)

40. Yordanov, M., O. Vitov. 2002. Ore production optimization. Part I. Short and long term planning. Basic concentrations and terms. - In: Proceeding of International conference "Corporate finance management in mining industry", Sofia, 64-76. (in Bulgarian)

41. Yordanov, M., O. Vitov. 2002. Ore production optimization. Part II. Short and long term planning by computer packages geolarian^TMand mixtores^TM. - In: Proceeding of International conference "Corporate finance management in mining industry", Sofia, 77-81. (in Bulgarian)

42. Zidarova, B., M. Marinov, N. Zidarov. 2002. Mathematical model for the growth of fluorite aggregates in caverns in Slavyanka deposit. - Compt. rend. Acad. bulg. Sci., 55, 3, 59-64.

PUBLICATIONS IN PRESS:

43. Eskenazy, G., S. Vassilev. Geochemistry of chlorine and bromine in Bulgarian coals. - Rev. Bulg. Geol. Soc.,

44. Georgieva, B., I. Podolesheva, D. Nihtianova, I. Konstantinov. Nanosized tin-oxide layers - new method of preparation and humidity sensing properties. - Nanoscience & Nanotechnology' 03, Heron Press, Sofia,

45. Ivanova, V, V. Petkova, Y. Pelovski. Thermal analysis of new soil sorption regulators. - Journal of Thermal Analysis and Calorimetry,

46. Kalvachev, Yu. Oxidation of hydrocarbons over nanosized gold catalysts. - Nanoscience & Nanotechnology' 03", Heron Press, Sofia,

47. Kolev, Tz., R. Petrova. Is the aminoguanidinium hydrogen carbonate salt or betaine? - Acta Crystallographica E,

48. Kossev, K., N. Koseva, K. Troev. Calcium chloride as co-catalyst of onium halides in the cycloaddition of carbon dioxide to oxiranes. - Journal of Molecular Catalysis A, 194, 1-2,

49. Kossev, K., A. Vassilev, Y. Popova, I. Ivanov, K. Troev. Functionalization of poly(oxyethylene phosphonate) under phase-transfer catalyst conditions. - Polymer, 44, 7,

50. Lazaro, M. J., I. Suelves, R. Moliner, S. Vassilev, C. Braekman-Danheux. Low cost catalytic sorbents for NOx reduction. 2. Tests with no reduction reactives. - Fuel,

51. Mihailova, B., U. Bismayer, B. G?ttler, L. Tosheva, J. Sterte. Raman scattering in locally inhomogeneous oxide crystals. - Phase Transitions,

52. Pelovski, Y., V. Petkova, I. Dombalov. Thermal analysis of mechanoactivated mixtures of Tunisian phosphorite and ammonium sulfate. - Journal of Thermal Analysis and Calorimetry,

53. Petkova, V., Y. Pelovski. Thermal analysis and solid electrolyte system study of FeSO₄.H₂O-BaO₂ mixtures. - Journal of Thermal Analysis and Calorimetry,

54. Stoyanov, D. Applied aspects of diversity of ornamental stones in Losen's Mountains. - In: "Mineral diversity", Sofia, (in Russian with English abstracts)

55. Tarassov, M., B. Mihailova, E. Tarassova, L. Konstantinov. Fe₂O₃.n H₂O nanophases formed in tungsten-polyanion-assisted sol-gel process. - Nanoscience & Nanotechnology' 03", Heron Press, Sofia,

56. Tsintsov, Z. Platinum-group minerals (PGM) from the alluvial sediments of Samokov region, West Bulgaria. - Rev. Bulg. Geol. Soc., 64, (in English with Bulgarian abstracts)

57. Tzvetanova, Y. Lead phosphate minerals from Brussevtzi deposit (Eastern Rhodopes, Bulgaria) - SEM, IR and DTA study. - Compt. rend. Acad. bulg. Sci.,

58. Vassilev, S.,J. Tascon. Methods for characterization of inorganic and mineral matter in coal: a critical overview. - Energy and Fuels,

59. Zidarov, N., B. Zidarova. The collection "Fluorite mineralization in the Slavyanka deposit, SW Bulgaria", of the Central Laboratory of Mineralogy and Crystallography, BAS - an example for ex-situ preservation of the mineral diversity. - In: "Mineral diversity", Sofia, (in English with Russian abstracts)

60. Zidarova B. REE in the fluorite as indicators of the mineral-forming environment. - Compt. rend. Acad. bulg. Sci.,

ABSTRACTS AND POSTERS AT SCIENTIFIC EVENTS:

61. Ferdov, S., V. Kostiv-Kytin, O. Petrov, Ch.Lengauer, E. Tillmans. 2002. Synthesis and kinetic investigation of microporous titanosilicates in the system Na₂O-TiO₂-SiO₂-H₂O. - Third International conference on inorganic materials, September 7-10, Konstanz, Germany, abstracts, p.178. poster

62. Cherneva, Z., M. Ovtcharova, A. v. Quadt, K. Kolcheva, E. Stancheva, S. Sarov, I. Peytcheva. 2002. Monazite and zircon U-Pb ages of migmatites from the Arda river valley, Central Rhodopian dome, Bulgaria. - XVI Congress of KGBA, special issue of Geologica Carpathica (CD), September 1-4, Bratislava, Slovakia, v. 53, abstracts, 20-22.

63. Georgieva, B., I. Podolesheva, D. Nihtianova, I. Konstantinov. 2002. Nanosized tin-oxide layers - new method of preparation and humidity sensing properties. - IV Workshop "Nanoscience and nanotechnology 2002", October 17-19, Sofia. poster.

64. Ivanova, T. N., P. T. Kostov, O. Petrov, I. I. Ilieva. 2002. Zeolite for space greenhouse experiments on the MIR orbital station. - 6^th International conference "Occurrence, properties and utilization of natural zeolites", Zeolite`02, P. Misaelides (Ed.), June 3-7, Thessaloniki, Greece, abstracts, 146-147.

65. Ivanova, V., V. Petkova, Y. Pelovski. 2002. Thermal analysis of new soil sorption regulators. - VIII^th International seminar on thermal analysis and calorimetry to the memory of prof. Bretsznajder, September 18-20, Plock, Poland.

66. Kalvachev, Yu. 2002. Oxidation of hydrocarbons over nanosized gold catalysts. - IV Workshop "Nanoscience and nanotechnology 2002", October 17-19, Sofia.

67. Kamenov, B., A. v. Quadt, I. Peytcheva. 2002. New insight into petrology, geochemistry and dating of the Vejen pluton. - Geochimica et Cosmochimica Acta, 12 Annual Goldschmidt conference, August 18-23, Davos, Switzerland, abstracts, p. A380. poster

68. Kostov-Kytin, V., S. Ferdov, O. Petrov. 2002.Regularities in the hydrothermal synthesis of titanosilicate phases. - 6^th International conference "Occurrence, properties and utilization of natural zeolites", Zeolite`02, P. Misaelides (Ed.), June 3-7, Thessaloniki, Greece, abstracts, 183-184. poster

69. Lenchev, A., J. Ninov, I. Donchev, S. Magaeva. 2002. Study on the properties of fly ashes from Bulgarian thermal power stations. - ISWA world environment congress&exhibition, July 8-12, Istanbul, Turkey.

70. Maleev, M., N. Zidarov. 2002. "Preservation of the mineral diversity" - the Sofia initiative. - International scientific and technical conference "Mineral resources and man", v. I - Mineral resources and sustainable development of society, September 17-19, Varna. (in Russian with English abstracts)

71. Mihailova, B., U. Bismayer, B. Guttler, M. Gospodinov, L. Konstantinov. 2002. Local phenomena in relaxor-ferroelectric PbSc_0.5B"_0.5O₃ (B"=Nb,Ta) single crystals studied by Raman spectroscopy. - Third International conference on inorganic materials, September 7-10, Konstanz, Germany. poster

72. Ovtcharova, M., Z. Cherneva, A. v. Quadt, I. Peytcheva. 2002. Magmatitic geochronology and geochemistry - a key to understanding the exhumation of the Madan dome (Bulgaria). - Geochimica and Cosmochimica Acta, 12 Annual Goldschmidt conference, August 18-23, Davos, Switzerland, abstracts, p. A573. poster

73. Pelovski, Y., V. Petkova, I. Dombalov. 2002. Thermal analysis of mechanoactivated mixtures of Tunisia phosphorite and ammonium sulfate. - VIII^th European symposium on thermal analysis and calorimetry, ESTAC'8, August 25-29, Barcelona, Spain.

74. Pelovski, Y., V. Petkova, P. Kostadinova, V. Stoyanov, I. Dombalov. 2002. The effect of the conditions of triboactivation on the solid phase synthesis in the system natural phosphate and ammonium sulphate. - X Jubilee science-technical session "Tribology and interdisciplinarity" CONTACT 2002, October 31-November 01, Sofia. (in Bulgarian)

75. Petkova, V., A. Toneva, P. Kostadinova, S. Stoyanov, Y. Pelovski, I. Dombalov. 2002. Effect of mechanochemical activation in phase formation in system of natural phosphate - ammonium sulphate. - X Jubilee science-technical session "Tribology and interdisciplinarity" CONTACT 2002, October 31-November 01, Sofia. (in Bulgarian)

76. Petkova, V., V., P. P. Kostadinova, V. St?yan?v, ?. ??n?v?, Y. Pelovski, I. Dombalov. 2002. Possibility for solid phase synthesis in the system Tunisian phosphorite - ammonium phosphate upon tribochemical activation. - X Jubilee science-technical session "Tribology and interdisciplinarity" CONTACT 2002, October 31-November 01, Sofia. (in Bulgarian)

77. Petkova, V., A Toneva, P. P. Kostadinova, Y. Pelovski, I. Dombalov. 2002. Investigation of the thermal decomposition of tribo-activated mixtures of Tunisian phosphorite and ammonium sulphate. - X Jubilee science-technical session "Tribology and interdisciplinarity" CONTACT 2002, October 31-November 01, Sofia. (in Bulgarian)

78. Petkova, V., S. Stephanova, A. Toneva, I. Dombalov, Y. Pelovski. 2002. Investigation of the influence of SiO₂ on the phase-formation in the system natural phosphate and ammonium sulphate. - Second Balkan conference on glass science and technology, 14^th Conference on glass and ceramics, September 24-28, Varna.

79. Petkova, V., Y. Pelovski. 2002. Thermal analysis and solid electrolyte system study of FeSO₄.H₂O-BaO₂ mixtures. - VIII^th European symposium on thermal analysis and calorimetry, ESTAC'8, August 25-29, Barcelona, Spain.

80. Peytcheva, I., A. v. Quadt, V. Cvetcovic, M. Banjesevich, D. Kozelj. 2002. Geochronology, geochemistry and isotope tracing of the Cretaceous magmatism of East Serbia as part of the Apuseni-Timok-Srednogorie metallogenic belt. - Annual scientific conference of the Bulgarian Geology Society "Modern problems of the Bulgarian geology", November 21-22, Sofia, 24-25.

81. Quadt, A. v., I. Peytcheva, Ch. Heinrich. 2002. Life span of a Cu-(Au-PGE) porphyry deposit using high-precise U-Pb single zircon dating, example: Elatsite, Bulgaria. - Geochimica et Cosmochimica Acta, 12 Annual Goldschmidt conference, August 18-23, Davos, Switzerland, abstracts, p. A811. poster

82. Stambolova, I., A. Toneva, V. Blaskov, D. Padev, P. Peshev. 2002. Applying the methods of co-sedimentation and tribochemical activation for synthesining zinc-stanate. - X Jubilee science-technical session "Tribology and interdisciplinarity" CONTACT 2002, October 31-November 01, Sofia. (in Bulgarian)

83. Tarassov, M., B. Mihailova, E. Tarassova, L. Konstantinov. 2002. Fe₂O₃.n H₂O - nanophases formed in tungsten-polyanion-assisted sol-gel process. - IV Workshop "Nanoscience and Nanotechnology 2002", October 17-19, Sofia. poster

84. Tarassov, M., E. Tarassova. 2002. Forms of tungsten presence in hardly dressing ores in oxidizing zone of the Grincharitza deposit, Western Rhodopes. - International scientific and technical conference "Mineral resources and man", v.II - Complex utilization of mineral resources, September 17-19, Varna. (in Bulgarian with Russian abstracts)

85. Titorenkova, R., L. Macheva. 2002. Chemistry and morphology of zircon in metagranites from Maleshevska and Ograzhden Mountains, SMM, SW Bulgaria. - XVI Congress of KGBA, September 1-4, abstracts (CD), Bratislava, Slovakia.

86. Vitov, O. 2002. Placer mineralogical mapping and prognosis for prospecting of mineral resources. - International scientific and technical conference "Mineral resources and man", v. II - Complex utilization of mineral resources, September 17-19, Varna. (in Bulgarian with English abstracts)

87. Vitov, O. 2002. Mineral diversity in heavy minerals concentrate samples from Bulgaria. - II International symposium "Mineral diversity - research and preservation", October 11-14, Earth and Man National museum, Sofia, abstracts, p.47. (in Russian)

88. Vitov, O. 2002. Placer mineralogical prognosis for gold prospecting in Bulgaria. - In: Proceeding of International conference "Corporate finance management in mining industry", Sofia, 23-30. (in Bulgarian).

89. Vitov, O. 2002. A themotransfusion model for the distribution of gold in Bulgaria. - National conference "Modern problems of the Bulgarian geology", November 21-22, Sofia, abstracts, 53-54.

90. Yordanov, M., O. Vitov. 2002. Ore production optimization. Part I. Short and long term planning. Basic conceptions and terms. - International conference "Corporate finance management in mining industry", October 7-11, Varna (in Bulgarian)

91. Yordanov, M., O. Vitov. 2002. Ore production optimization. Part II. Short and long term planning by computer packages GeoLariAn^TMand MixtOres^TM. - International conference "Corporate finance management in mining industry", October 7-11, Varna. (in Bulgarian)

92. Zidarov, N. 2002. Classification of the mineral diversity - range and contents. - II International symposium "Mineral diversity - research and preservation", October 11-14, Earth and Man National museum, Sofia, abstracts, p.14. (in Russian)

93. Zidarov, N., V. Andreichev, E. Tarassova. 2002. Rb-Sr data for Jurassic granitic bodies in Belassitza mountain, SW Bulgaria. - Annual of scientific conference of the Bulgarian Geology Society "Modern problems of the Bulgarian geology", November 21-22, Sofia, abstracts, p. 23. (in Bulgarian)