Petrographic Varieties Research Articles

Association of Fe–Ti oxides in subalkaline dolerites of the Rai-Iz massif (Polar Urals)

The relevance of the research. Subalkaline dolerites, Fe–Ti oxides of which were studied in this work, occur within the largest deposits of chromium ores of the Rai-Iz massif. The study of the material composition and age of these rocks was carried out by the authors for the first time. The purpose of the research is to reveal the patterns of changes in the chemical composition of the main accessory minerals of rocks – titanomagnetite and ilmenite, and on the basis of the obtained data to evaluate the conditions for the formation of subalkaline dolerites of the massif. Research methodology. The chemical compositions of minerals were determined using microprobe analysis on a CAMECA SX 100 and scanning electron microscopy on a Jeol JSM-6390LV setup with an INCA Energy 450 X-Max 80 energy dispersive attachment. Raman spectra were obtained on a LabRam HR 800 Evolution spectrometer equipped with an Olimpus BX-FM microscope. The studies were carried out at the “Geoanalyst” сenter for the collective use of scientific equipment of the IGG, UB RAS. Results. The typomorphism of the chemical composition of titanomagnetite and ilmenite has been established for petrographic varieties of dolerites allocated on the massif. The T–fO2 parameters of dolerite formation were estimated and compared with metaultramafites. It is shown that titanomagnetite in amphibole dolerites undergoes maghemitization. The highest temperatures (1076–1126 °C) are recorded in pyroxene dolerites. The oxygen fugacity in these rocks is FMQ +0.6–+1 units. Hyalodolerite from the chilled margin of the pyroxene dolerite dike gives a temperature of 811–818 °C and an oxygen fugacity of 1.8 units above FMQ. The compositions of the associated ilmenite and titanomagnetite from amphibole dolerites correspond to fO2 = –2–0 units relative to FMQ and temperature 580–720 °C. The trend of change in T–fO2 parameters shows that the injection of the mafic melt occurred under conditions of metamorphism of ore-bearing ultramafic rocks. Conclusions. The formation of dolerite veins occurred under conditions of ultramafic rock metamorphism. The increased fugacity of oxygen at a relatively low temperature led to the maghemitization of titanomagnetite, rather than to the redistribution of components in the magnetite-ilmenite paragenesis.

Study of the Impact of Coals and Claystones on Wear-Resistant Steels

This paper discusses the impact of coal abrasive materials of varied petrographic composition and claystones containing admixtures of coal matter on the surface wear of wear-resistant martensitic steels. Wear tests were conducted at a test stand for three petrographic varieties of hard coal: vitrinite, clarinite, and durinite, and five samples of claystone. These tests revealed no significant effect of the type of coal abrasive used on the value of mass loss from the surface of the wear-resistant steel samples. The reason behind the foregoing is the observed tendency of coal abrasives, irrespective of their petrographic variety, to penetrate surface irregularities, especially those attributable to previous surface treatment of the samples and the impact of wear products. The dominant forms of surface damage were surface fatigue chipping and scratches caused by the particles which detached themselves from the surface of the steel samples, as observed for all the analysed coal variants. On the surfaces of the samples seasoned in the presence of claystones, highly varied forms of damage were observed: microcutting, scaly surface cracks, delamination, and deep cracks. In these cases, it was possible that the abrasive grains had been pressed into the steel surface irregularities, but no layered forms of the pressed-in abrasive material were observed to have developed. The paper also presents a model for the formation of coal films and discusses their possible effect on wear minimisation.

Properties of Fine-Grained Rock Waste from the Pilawa Gorna Amphibolite and Migmatite Aggregates Production Plant

In the course of mining and processing of almost all petrographic varieties of rock raw materials for the production of building and materials, aggregates for road and railway construction, waste is generated. These are usually fine-grained fractions of these rocks that are difficult to manage and are deposited at dumps. The article presents and describes the results of the physical, chemical, and mineralogical properties of fine-grained waste from the production of amphibolite aggregate from Pilawa Gorna in Lower Silesia (S-W Poland). Such studies have not been carried out on this waste before. The tested waste is a very fine-grained dusty material (<0.100 mm) originating from the dedusting of the crushing and classification operations during the production of aggregates. Preliminary studies of the separation of the tested material using collector-less flotation and gravity separation are also presented. Detailed chemical analysis shows that most of the elements in the studied rock dust occur in abundance close to the average in the Earth’s crust. The collector-free flotation of the investigated sample allows effective separation of graphite and the part of sulfide minerals Cu, Ni, and Mo. The presented results may be the basis for further research and development of the concept of their economic use.

Mineralogical and geochemical characteristics of the Sedemte Prestola potassic alkaline pluton

The Sedemte Prestola pluton is an intermediate to acid plutonic body of Variscan age (308.7 ± 9.1 Ma). Despite its small size, several petrographic varieties are present: syenites, quartzsyentes and granites. It is composed of potassium feldspar, quartz, sodic-calcic amphibole; biotite, when present, is often rimmed by amphibole or strongly altered; zircon, titanite, apatite and ilmenite are the accessory phases. The rocks display pronounced potassic character with up to 10.4 wt% K2O, peralkaline tendency, and significant trace element enrichment for REE, Zr, Th, U, and Ba. The rocks also show enriched isotopic characteristic with 87/86Sri between 0.7107 and 0.7111, and 143/144Ndi between 0.51193 and 0.51182. The geochemical features of the Sedemte Prestola pluton imply orogenic geodynamic setting of formation as a product of more primitive magma fractionation. Isotopic characteristics and high LILE, Th and U contents support the derivation from enriched mantle source – phlogopite-bearing peridotites in the spinel stability field.

Magnetic petrology of the Neoarchean granitoids in the Vila Jussara Suite, Carajás Province, Amazonian Craton

The Vila Jussara Suite (VJS) is formed by Neoarchean (~ 2.75 Ga) granites that are located in the Sapucaia Domain of the Carajás Province (CP), Amazonian Craton. Four petrographic varieties were identified in the VJS: biotite-hornblende monzogranite (BHMzG); biotite-hornblende tonalite (BHTnl); biotite monzogranite (BMzG); and hornblende-biotite granodiorite (HBGd). In terms of magnetic signature, BHMzG has two subgroups: the first subgroup has low magnetic susceptibility (MS) values (0.16 × 10-3 to 0.81 × 10-3) and more commonly contains ilmenite with titanite rims; the second subgroup shows moderate to high MS (1.91 × 10-3 to 6.02 × 10-3) and magnetite dominant over ilmenite. BHTnl has moderate MS (0.85 × 10-3 to 1.36 × 10-3) and dominance of pyrite followed by magnetite. BMzG and HBGd have comparatively high MS (3.35 × 10-3 to 19.3 × 10-3 and 2.14 × 10-3 to 25.0 × 10-3, respectively), with magnetite dominant over pyrite. The granite varieties of the VJS were formed under different oxygen fugacity (fO2) conditions, varying from reducing (< fayalite-magnetite-quartz (FMQ)) to oxidizing conditions (nickel-nickel oxide (NNO) to NNO+1). In addition, biotite-hornblende syenogranite occurs subordinately and shows high MS values and extremely high FeOt/(FeOt + MgO) ratios, both in whole-rock and amphibole and biotite. The granites of the VJS are similar to other Neoarchean granites of the Carajás province. The reduced VJS granites are akin to the ferroan granites of Planalto suite, Estrela Complex and Vila União area and the magnesian granites of VJS approach the magnesian granites of Vila União area.

Evolution of ultrapotassic volcanism on the Kaapvaal craton: deepening the orangeite versus lamproite debate

Abstract Orangeites are a significant source of diamonds, yet ambiguity surrounds their status among groups of mantle-derived potassic rocks. This study reports mineralogical and geochemical data for a c. 140 Ma orangeite dyke swarm that intersects the Bushveld Complex on the Kaapvaal craton in South Africa. The dykes comprise distinctive petrographic varieties that are linked principally by olivine fractionation, with the most evolved members containing minor amounts of primary carbonate, sanidine and andradite garnet in the groundmass. Although abundant groundmass phlogopite and clinopyroxene have compositions that are similar to those of cratonic lamproites, these phases show notable Ti-depletion, which we consider a hallmark feature of type orangeites from the Kaapvaal craton. Ti-depletion is also characteristic of bulk rock compositions and is associated with strongly depleted Th–U–Nb–Ta contents at high Cs–Rb–Ba–K concentrations. The resultant high large ion lithophile element/high field strength element ratios of orangeites suggest that mantle source enrichment occurred by metasomatic processes in the proximity of ancient subduction zones. The Bushveld-intersecting orangeite dykes have strongly enriched Sr–Nd–Hf isotopic compositions (initial 87 Sr/ 86 Sr = 0.70701–0.70741; ε Nd = −10.6 to −5.8; ε Hf = −14.4 to −2.5), similar to those of other orangeites from across South Africa. Combined with the strong Ti–Nb–Ta depletion, this ubiquitous isotopic feature points to the involvement of ancient metasomatized mantle lithosphere in the origin of Kaapvaal craton orangeites, where K-rich metasomes imparted a ‘fossil’ subduction geochemical signature. Previous geochronology studies identified ancient K-enrichment events within the Kaapvaal cratonic mantle lithosphere, possibly associated with collisional tectonics during the 1.2–1.1 Ga Namaqua–Natal orogeny of the Rodinia supercontinent cycle. It therefore seems permissible that the cratonic mantle root was preconditioned for ultrapotassic magma production by tectonomagmatic events that occurred along convergent plate margins during the Proterozoic. However, reactivation of the K-rich metasomes had to await establishment of an extensional tectonic regime, such as that during the Mesozoic breakup of Gondwana, which was accompanied by widespread (1000 × 750 km) small-volume orangeite volcanism between 200 and 110 Ma. Although similarities exist between orangeites and lamproites, these and other potassic rocks are sufficiently distinct in their compositions such that different magma formation processes must be considered. In addition to new investigations of the geodynamic triggers of K-rich ultramafic magmatism, future research should more stringently evaluate the relative roles of redox effects and volatile components such as H 2 O–CO 2 –F in the petrogeneses of these potentially diamondiferous alkaline rocks.

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

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

Potential possibility of using terrestrial laser scanning in petrography

Terrestrial laser scanning is a wide spectrum tool, applied at present both in engineering and medicine. This work presents the results of a laboratory test that was aimed at assessing the potential of using this measurement technique for the identification of petrographic varieties. Rock samples were measured with the application of a Leica ScanStation C10 scanner. Values of the intensity index obtained from point cloud data were subject to statistical analysis. The main focus was posed on comparative analyses of samples from the same petrographic varieties collected from different localities, as well as on the influence of colour and surface humidity of the samples on the change of intensity index values.

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

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

Mikrobiološki diverzitet slanih lekovitih voda Slankamen banje - Srbija

In 2017, the microbiological and biochemical diversity of saline healing water at Slankamen Banja was assessed for the presence of targeted physiological groups of bacteria, using a system of six biological activity reaction tests (BART): IRB, SRB, HAB, DN, SLYM and FLOR. The water samples originated from a karst-fractured aquifer, represented by petrographic varieties of Pliocene and Miocene litho-tamian, ceritic and sandy limestones, which discordantly overlie Anisian and Ladinian limestone and serpentinite. Prior to using the BART biodetectors for detailed observations, the physical and chemical composition of the saline healing water was defined, indicating that it is of the Na+- Cl- type, with a high mineral content. The water is also cold and low alkaline, exhibiting elevated concentrations of significant balneotherapeutic elements: Sr2+, J- and B3+. The detected biochemical activity of anaerobic fermentation bacteria and aerobic iron oxidants was high. It is 2,200 potentially active cells per ml of water, approximately by day of reaction. Sulphate-reducing bacteria of medium biochemical activity were also detected, while the presence of denitrifying and slime forming bacteria was characterized by low biochemical activity. BART-Soft v-6 software was used to assess the risk of biocorrosion and biofouling processes developing in well B-1 ('Slanjača'), as well as the potential health risk. The study indicates that the development of these processes is possible, that the health risk of using the saline mineral water for balneotherapy is minimal, and that the BART FLOR biodetector did not reveal any Pseudomonas (fluorescences and aeruginosa) bacteria, which cause waterborne diseases.

Petrographic and structural analysis of exposed rocks of Musawa Sheet 56, Northwestern Nigeria

This work is among the few studies conducted in Musawa sheet 56 NE, which is part of the basement complex rocks of TudunWulli - Kankia area. The study area lies between Latitude 12º 19ʹ 00ʹʹ to 12º 23ʹ 00ʹʹN and longitude 7º 42ʹ 00ʹʹ to 7º 46ʹ 00ʹʹN. Due to the continuous play of geologic processes on the earth, there is the need to continuously update the geology of the Nigeria basement complex as this has a very important economic implication especially in areas like mineral and groundwater exploration. Equally, less attention has been given to this sheet unlike other sheets within the zone. The study done in this area has revealed the various rock types and their geological characteristics: field relation, macroscopic and microscopic features as well as structural elements. Results from the study shows that the area consists of granite, migmatite- gneiss and quartzite which all display a variety of colors, textures and mineralogy. Careful analysis of the distinctive mineralogy, textures, optical and structural characteristics led to the nomenclature of the rocks. The migmatite-gneiss display two petrographic varieties base on their foliation: one with linear foliation of alternating light and dark color minerals, and the other with wave like foliation. While granite is generally fine to medium grained in texture. The dominant structural trend of joints and faults in the study area are NNE-SSW and NW-SE. All these trends are consistent with the general trends of the Nigeria basement rocks. A study of thin sections of the rocks under a petrological microscope reveals optical properties peculiar to each rock type. The type and nature of structural elements associated with the rocks together with their geometry reveal that the rocks have undergone more than one deformational event. The occurrence of numerous brittle and ductile structures shows that the area has a great potential for groundwater and mineralization. But the area still experience shortage of water for domestic purposes.Keywords: basement complex, brittle structures, foliation, petrographic varieties, thin sections

Petrography and mineralogy of the white marble and black stone of Göktepe (Muğla, Turkey) used in antiquity: New data for provenance determination

The discovery near Göktepe (Muğla province, Western Turkey) of an ancient quarrying site of white marbles and black stones has recently been reported by some authors. Assigning the provenance of stone from ancient artifacts to Göktepe is currently possible mainly thanks to chemical, EPR and MGS data. Petrographic description, which many researchers use to characterize ancient marbles, is still incomplete. Several thin sections of both types of stone were thus examined in this study, and also used for cathodoluminescence analysis. As the rock is >99% calcite, trace minerals could only be detected in some samples by XRD analysis of insoluble residues after acetic acid attack. Data on strontium and manganese contents and carbon and oxygen isotopes were also recorded, for better understanding of some petrographic features.A new method of grain size characterization was tentatively introduced to improve the description of grain size variability in the white marble. Microstructure and grain size measurements on thin sections of this marble identify two petrographic varieties: the first is extremely fine with signs of dynamic recrystallization, and the second exhibits texture and MGS similar to those of Carrara marble.Statuary samples of white marble from Villa Adriana (Tivoli, Rome), preliminarily assigned in a previous study partly to Carrara and partly to Göktepe quarry, are reconsidered here.A certain degree of variability was found in the structures and textures in the thin sections of the Göktepe black stone. It may have undergone transformations at an advanced stage of diagenesis. One important source of this variability seems to be a fluid alteration event, revealed by both isotopic and chemical data and trace mineral assemblages.

The polycyclic Lausche Volcano (Lausitz Volcanic Field) and its message concerning landscape evolution in the Lausitz Mountains (northern Bohemian Massif, Central Europe)

The Tertiary Lausitz Volcanic Field covers a broad area encompassing parts of Eastern Saxony (Germany), Lower Silesia (Poland) and North Bohemia (Czech Republic). Volcanism was predominantly controlled by the volcano-tectonic evolution of the Ohře Rift and culminated in the Lower Oligocene. This paper deals with the highest volcano of this area, the Lausche Hill (792.6m a.s.l.) situated in the Lausitz Mountains. We offer a reconstruction of the volcanic edifice and its eruptive history. Its complex genesis is reflected by six different eruption styles and an associated petrographic variety. Furthermore, the Lausche Volcano provides valuable information concerning the morphological evolution of its broader environs. The remnant of an alluvial fan marking a Middle Paleocene–Lower Eocene (62–50Ma) palaeo-surface is preserved at the base of the volcano. The deposition of this fan can be attributed to a period of erosion of its nearby source area, the Lausitz Block that has undergone intermittent uplift at the Lausitz Overthrust since the Upper Cretaceous. The Lausche Hill is one of at least six volcanoes in the Lausitz Mountains which show an eminent low level of erosion despite their Oligocene age and position on elevated terrain. These volcanoes are exposed in their superficial level which clearly contradicts their former interpretation as subvolcanoes. Among further indications, this implies that the final morphotectonic uplift of the Lausitz Mountains started in the upper Lower Pleistocene (~1.3Ma) due to revived subsidence of the nearby Zittau Basin. It is likely that this neotectonic activity culminated between the Elsterian and Saalian Glaciation (~320ka). The formation of the low mountain range was substantially controlled by the intersection of the Lausitz Overthrust and the Ohře Rift.

Dichotomy of The Messada Pluton, Serbo-Macedonian Massif, Greece: From Rifting to Subduction

The Messada pluton is a mafic intrusion that is located about 12 km SW of Serres town, (Macedonia Greece) that intrudes the two mica, biotite and the augen gneisses of the Vertiskos formation (Serbo-Macedonian massif). The aim of this study is to investigate, define and evaluate the geochemical characteristics of the pluton in order to determine the geotectonic environment in which the parental magma has been formed. The Mesada pluton is a mid to coarse grained intrusion presenting petrographic variety from diorite and quartz diorite to tonalite and granodiorite. The variety in petrography reflects its chemical inhomogeneity in major and trace elements. It is suggested that parts of pluton have been formed by distinctly different types of magmas originated in diverse geotectonic settings. Those parts of quartz diorite and tonalite composition, present similar geochemical characteristics, LILE/HFSE ratios and negative Nb, but no Ti anomalies in their primitive mantle normalized trace elements spider grams. They exhibit higher HFS values than those of granodioritic composition. Moreover, their ORG normalized spider grams not only suggest that they have been evolved by a common parental magma, but also present the typical characteristics of a “crust dominated” within plate pluton that may have been formed in an early stage during rifting, prior to a subsequent subduction episode. This interpretation may be in accordance with the suggestion for the Gondwanian origin of the more silicic Triassic rift related meta-granites (e.g. Arnea plutonic complex) of the Serbo-Macedonian massif. In contrary; the parts of Mesada pluton of granodioritic composition, exhibit a calc-alkaline to high K calc-alkaline magmatic suite and present higher LILE/HFSE and LREE/HREE ratios, related to a higher crustal component contribution for the magma genesis. Furthermore, their primitive mantle normalized spider grams’ present negative anomalies at Nb and Ti. These characteristics indicate that those granodioritic parts have been formed by the crystallization of a calk-alkaline magma, produced by the partial melting of lower crust, lithospheric mantle and asthenospheric mantle components, in a volcanic arc geo-tectonic setting. Their geochemical characteristics have close similarities to those of the collision related granitoids that have intruded the Serbo- Macedonian during Tertiary.

U–Pb dating and composition of inclusions in zircon from ophiolitic gabbro of the Klyuchevsk massif (Middle Urals): Results and geological interpretation

The U–Pb (SHRIMP) dating of zircon from the layered complex of ophiolitic gabbro in the Klyuchevsk massif yielded an age of 456 ± 6 Ma corresponding within the limits of error to zircon dates obtained for other petrographic varieties from this massif. The investigation of the composition of silicate inclusions in dated zircon grains revealed that they are represented by typical metamorphic minerals: albite, zoisite, and secondary amphiboles. The data indicate that zircon was crystallized during metamorphic transformations of gabbroids and its U–Pb age (Late Ordovician–Silurian) is characteristic of all rocks in the ophiolite association of the Klyuchevsk massif indicating the age of metamorphism, not their formation time.

The Rudnik Mts. volcano-intrusive complex (central Serbia): An example of how magmatism controls metallogeny

This study reports and discusses new radiometric ages, petrographical and volcanological observations and whole rock geochemical data of the rocks of the Rudnik Mts. volcano-intrusive complex. The complex hosts a Pb-Zn-Ag deposit and belongs to the Serbo-Macedonian metallogenetic belt. Two distinct igneous events are distignuished. The first occurred >30 Ma and was mainly characterized by extrusive and shallow intrusive dacites and andesites and was unrelated to mineralization. The second igneous event occurred <23 Ma and was highly heterogeneous in terms of volcanic products and petrographic varieties, but with predominance of quartzlatites. The dacite-andesites (first event) and the quartzlatites (second event) are geochemically similar and display a calc-alkaline affinity and highly incompatible element enriched patterns on spider diagrams, but the younger quartzlatites are richer in K2O, Rb and Ba and poorer in Sr. This is taken as evidence that mixing between an ultrapotassic lamprophyre/lamproite magma and an acid calc-alkaline (dacite-like) magma was essential petrogenetic processes during the second event. The proposed simplified volcanological model suggests that this mixing was responsible for triggering strongly explosive volcanic activity as well as for providing conditions for active hydrothermal and mineralization processes. The observed link between a specific magmatic phase and ore deposit formation can be a general phennomenon in the Balkans, and must be addressed by further and more advanced studies.

Petrographic and mineral variability of the rocks accompanying selected coal seams of the Poruba beds and their influence of the trace elements content / Zróżnicowanie Petrograficzno-Mineralogiczne Skał Współ Występujacych Z Wybranymi Pokładami Węgla Z Warstw Porębskich I Jego W Pływ Na Zawartość Pierwiastków Śladowych

Streszczenie Skały współwystępujące z węglem w wybranych pokładach warstw porębskich (610, 620, 630) reprezentowane są najczęściej przez iłowce oraz iłowce syderytyczne, a rzadziej przez mułowce i mułowce syderytyczmne. Sporadycznie występują piaskowce. Stwierdzono także występowanie przerostu z tonsteinem. Zależnie od odmiany petrograficznej skał stwierdzono w nich zróżnicowanie zawartości pierwiastków śladowych (Ba, Zn, Mn, V, Cr, Cu, Ni. Pb, As, Ga, B, Co, Ge, Be, Li, Cd, Ag, Sr - w kolejności malejącego udziału). Znaczna część pierwiastków wykazała wysoki i często dominujący udział w iłowcach. Stwierdzono także regionalne zróżnicowanie zawartości pierwiast- ków śladowych w skałach. Badania korelacji pomiędzy zawartością pierwiastków śladowych a zawartością głównych mine- rałów w skałach potwierdziły powinowactwo wielu pierwiastków śladowych z substancją organiczną, minerałami ilastymi i węglanami. Zwraca uwagę występowanie korelacji licznych pierwiastków śladowych z substancją organiczną (węglem) przy stosunkowo niewielkiej liczbie pierwiastków korelujących z minerałami ilastymi.

Petrographic and Structural Analysis of Exposed Rocks of Bishini Sheet (Block 2), North Central Nigeria

This study is the second of a series of work to be done on Bishini Sheet 165 SW, which is part of the basement complex of the Kushiriki-Minna area. The area lies between latitudes 9°34? N and 9°40? N and longitudes 7°00? E and 7°08? E. Due to the continuous play of geologic processes on the earth, there is the need to continuously update the geology of the Nigeria basement complex as this has a very important economic implication in areas like mineral and water exploration. Equally, less attention has been given to this sheet unlike other sheets within the zone. The study of the block has revealed the various rock types and their geological characteristics: field relation, macroscopic and microscopic features and structural elements. Results from the field shows that the block consists of migmatites, gneisses, schists and granites which all show a variety of colours, textures and mineralogy. The displacement of distinctive mineralogy, textures, optical and structural characteristics led to the nomenclature of the rocks. The granitic rocks displayed two petrographic varieties based on their textures. These are the fine-medium grained and coarse porphyritic varieties. The granitic rocks have greatly intruded other rocks and this is thought to be responsible for gold mineralization in the area, The NNE-SSW and the NNW-SSE are the major structural trends determined for the joints and faults while the minor ones are the NE-SW and NW-SE. All these trends are consistent with the general trends of the Nigeria basement rocks. A study of thin sections of the rocks under a petrological microscope reveals characteristic optical properties peculiar to each rock type. The type and nature of the minerals the rocks contain together with their geometry reveal that the rocks have undergone more than one deformational event since the time of their formation. The occurrence of numerous fractures (joints and faults) shows that the area has a great potential for water and mineral exploration.

Geophysical and structural pattern of the Knížecí Stolec pluton and its host rocks in the south-western part of the Moldanubian Zone, Bohemian Massif

*Corresponding author A detailed airborne magnetic and gamma-ray spectrometric as well as ground gravity survey in the south-western part of the Moldanubian Zone (Bohemian Massif) provided detailed geophysical characteristics of the principal geological units and large-scale tectonic features. The Knižeci Stolec durbachitic pluton with high contents of natural radioactive elements (Th, U and K) represents a body with no magnetically anomalous response but a pronounced positive gravity anomaly. The Křisťanov granulite massif, which is a host rock of the Knižeci Stolec pluton, exhibits low concentrations of Th and U, high abundances of K, slight magnetic and a negative gravity anomalies. The Plechý composite pluton is characterized by strikingly low gravity and an extremely monotonous magnetic field. One of its petrographic varieties (the Třistolicnik granite) is enriched in natural radioactive elements, especially in Th and U. Metamorphic complexes of the Monotonous and Varied groups contain multiple magnetic anomalies mostly related to the intercalated metabasic rocks; they also cause positive gravity anomalies. The Linsser density boundaries at a depth of 0.5 km clearly delimit the Plechý composite pluton and the Lhenice zone and indicate several structurally and/or lithologically different domains within the Křisťanov granulite massif and in the Knižeci Stolec pluton. The 2.5D gravity model indicates an asymmetric shape of the Knižeci Stolec pluton, which is deepest in its SE part (at least 4 km). The joint interpretation of the geophysical and structural data revealed that the maximum depth of the pluton is c. 4.5 km, with gently to moderately dipping intrusive contacts in the north and subvertical orientation in the south. The asymmetric shape of the pluton is consistent with its inferred syn-tectonic emplacement coeval with the regional subvertical contraction and development of regional flat-lying fabric. The gravity model combined with structural analyses also implies a considerable depth of the south Bohemian granulite massifs. This indicates their steep exhumation path and is at variance with the model of the Moldanubian Zone as a sequence of flat-lying nappes. The south-western part of the studied area is reworked by the NE-directed compression, referred to as the ‛Bavarian’ deformation phase.

Petrogenesis of syntectonic granites emplaced at the transition from thrusting to transcurrent tectonics in post-collisional setting: Whole-rock and Sr–Nd–Pb isotope geochemistry in the Neoproterozoic Quatro Ilhas and Mariscal Granites, Southern Brazil

The Neoproterozoic post-collisional period in southern Brazil (650–580Ma) is characterized by substantial volumes of magma emplaced along the active shear zones that compose the Southern Brazilian Shear Belt. The early-phase syntectonic magmatism (630–610Ma) is represented by the porphyritic, high-K, metaluminous to peraluminous Quatro Ilhas Granitoids and the younger heterogranular, slightly peraluminous Mariscal Granite. Quatro Ilhas Granitoids include three main petrographic varieties (muscovite–biotite granodiorite — mbg; biotite monzogranite — bmz; and leucogranite — lcg) that, although sharing some significant geochemical characteristics, are not strictly comagmatic, as shown by chemical and Sr–Nd–Pb isotope data. The most primitive muscovite–biotite granodiorite was produced by contamination of more mafic melts (possibly with some mantle component) with peraluminous crustal melts; the biotite monzogranite, although more felsic, has higher Ca, MgO, TiO2 and Ba, and lower K2O, FeOt, Sr and Rb contents, possibly reflecting some mixing with coeval mafic magmas of tholeiitic affinity; the leucogranite may be derived from pure crustal melts. The Mariscal Granite is formed by two main granite types which occur intimately associated in the same pluton, one with higher K (5–6.5wt.% K2O) high Rb and lower CaO, Na2O, Ba and Zr as compared to the other (3–5wt.% of K2O). The two Mariscal Granite varieties have compositional correspondence with fine-grained granites (fgg) that occur as tabular bodies which intruded the Quatro Ilhas Granoitoids before they were fully crystallized, and are inferred to correspond to the Mariscal Granite feeders, an interpretation that is reinforced by similar U–Pb zircon crystallization ages. The initial evolution of the post-collisional magmatism, marked by the emplacement of the Quatro Ilhas Granitoids varieties, activated sources that produced mantle and crustal magmas whose emplacement was controlled both by flat-lying and transcurrent structures. The transition from thrust to transcurrent-related tectonics coincides with the increase in the proportion of crustal-derived melts. The transcurrent tectonics seems to have played an essential role in the generation of mantle-derived magmas and may have facilitated their interaction with crustal melts which seem to be to a large extent the products of reworking of orthogneiss protoliths.