Subordinate Amounts Research Articles

Pegmatites As Decorative and Dimensional Stone Occurring in South-Central Rajasthan, India

The Precambrian formations of south-central Rajasthan host the unique deposits of pegmatite popularly known as ‘Alaska white’. These deposits are located mainly in Jawaja and Rajgarh areas of Ajmer, Gangapur and Jahazpur areas of Bhilwara and Amet and Deogarh areas of Rajsamand districts, Rajasthan. Field and the mineralogical study indicate that these deposits represent a compact and massive-type of pegmatite composed mainly of microcline, quartz and muscovite with subordinate amounts of albite and tourmaline. These pegmatite deposits occur as rounded to sub-rounded lenticular bodies emplaced concordantly within the rock formations of Bhilwara and Delhi Supergroups. These deposits are being developed and utilized by open-cast, fully-mechanized block-benching methods of mining for their extensive use as decorative and dimensional stones. Nearly 90% of the recovered resource is being exported mainly to U.S.A. and China in the form of well-dressed blocks of suitable sizes.

Aeolian transportation mechanics and mass movement of surficial beach sands – a case study on Bendi-BaruvaMineral Sand Deposit, Srikakulam District, Andhra Pradesh

Surficial sediment transportation studies carried out in the beach zone of Bendi-Baruva mineral sand deposit show that sand grains are transported by wind (saltation and suspension) beyond the high water line. The sand population of the study area contains heavy mineral sands (~20%) like ilmenite, garnet and sillimanite which covers 95% of the heavy mineral distribution with subordinate amounts of monazite, rutile, and zircon whereas light mineral sands (~80%) contain mostly quartz. Due to the sorted nature of these beach and dune sands the whole spectra falls within a specific range of grain size which shows a bi-modal distribution, primary mode at 0.025cm and secondary at 0.015cm. Due to this variation in density and grain size, mass of these sand particles vary resulting in differential transportation in any energy regime. In the study area, on the beach near the frontal dunes, surficial concentration of garnet grains are observed in patches having an average thickness 0.2cm i.e. around ten times of the dominant grain diameter. This surficial enrichment of garnet grains resting on a semi-uniform sand surface is the result of differential transportation of the dominant mineral grains. As more than 80% of the grain size population show a dominant grain size of 0.025cm, the wind flow parameters for the whole population is standardized with mean grain diameter (D) of 0.025cm. Mass of dominant individual minerals arrived from the grain counting technique was tallied with the theoretical mass considering spherical shape of the grains indicates a difference of mass to be within 5%. For ease of calculation and generalization the grains were considered to be spherical and their theoretical masses were taken into consideration in calculations. Considering the whole spectra of mineralogical distribution, a theoretical mass group distribution for dominant different minerals of different dominant grain sizes were formulated and total six mass groups were identified. Because quartz (~80%), ilmenite, sillimanite and garnet (together ~20%) are the most abundant, their positions were identified specifically in the theoretical mass groups and only these are considered for further discussion. To analyse wind velocity and pressure at different heights from the surface, a sediment trap was fabricated using piezo-electric sensors. A tail was attached to orient the device parallel to the wind flow so that the piezo surfaces always face the wind flow at 900 angle. The device records pressure data and converts those into voltage. Using the velocity data, macroscopic physical quantities of aeolian transportation were calculated for the study area, which empirically show the effect of mass in differential transportation of the dominant minerals that gives rise to these surficial garnet patches.

Beyond Beauty. Byzantine steatite icon from Chełm. Archaeology, Petrography and Traceology

Abstract A fragmentarily preserved Byzantine icon made of steatite was discovered in 2015 during regular excavations in Chełm, eastern Poland. Identified as the left wing of a diptych illustrating the Twelve Great Feasts and created at the close of the 12th century, the find is one of the most important and beautiful Byzantine artefacts to have been found in Poland. The icon was uncovered within the confines of the palace complex which was created by Daniel (Danylo) Romanovych († 1264) in Chełm in the second quarter of 13th century. The icon, even though it was found within the borders of what is now Poland, is material evidence of contact between Byzantium and the social elite of the Galicia-Volhynia lands, rather than with the Polish Piasts. In this paper we concentrated on the presentation of the archaeological context of the find, which made it possible to establish that the icon arrived Chełm before the middle of the 13th century (terminus ante quem 1253), and especially on petrographic and traceological analyses of the icon. Assuming that greenish plaques were indeed the most characteristic steatite icon type, a decision was made to examine, apart from the Chełm artefact made from white rock, a greenish icon from the National Museum in Krakow as well. Petrographic analyses were based on optical microscopy, scanning electron microscopy with energy dispersive spectrometry (SEM-EDS) and X-ray powder diffraction (XRPD). Both icons were carved in steatite i. e. talc rich rock but their chemical compositions indicate the presence of other components. Artifact from Chełm is white. Porous, enriched in potassium (K) and locally blistering outer rim of the icon from Chełm was formed probably during the fire event. Presence of forsterite and subordinate amount of leucite also indicate high temperature influence. Local enrichment in calcium (Ca) is related to exchange reactions with ground compounds. Accumulation of different components on the surface of the icon’s surface was noted. The icon from the National Museum in Krakow is greenish probably because of the presence of chlorite. The results of the traceological analysis (icon from National Museum in Krakow was not analysed) indicate that the icon found in Chełm was created most likely by a skilled and experienced carver with access to the high-quality magnifying glass and specialist tools required for rendering minuscule objects and their details. The production of the icon also involved the use of a “mechanical” tool, probably a kind of a miller with a rotating polishing head, which also seems to point to a specialist workshop. The use-wear traces observed on artefact are limited to polish resulting from prolonged contact with human hands or storing the icon in a leather case. Most of the extant Byzantine icons are unprovenanced objects held in museum collections or church treasuries. Therefore, as the icon presented in this paper was discovered during archaeological excavations, it ranks among the few Byzantine artefacts to have been found outside of this realm. The petrographic and traceological analyses conducted are the first published natural science contributions to the study of Byzantine steatite icons and we hope they will provide the impetus for undertaking such research on other Byzantine finds, helping to develop Byzantine archaeology further.

Gender Variation in the Writings of Ghanaian Colleges of Education Students: A Study of Syntactic Complexity

This study explored the differences in the writings produced by both male and female students in colleges of education in Ghana with respect to syntactic complexity. The study was based on a corpus of two hundred examination essays which were collected from two hundred students in Assin Fosu, Wesley and Presbyterian colleges of education who took the English language Studies course (FDC 211) in 2018/2019 academic year. The study adopted a descriptive design, involving qualitative and quantitative methods. The analysis showed that the male students were more syntactically complex than the female students in their writings. The study established clear variations in the areas of length of production unit, sentence complexity, amount of subordination and coordination and particular structures. It has therefore upheld the difference version of gender and language theory as compared to the discursive theory. Implications and areas for further research are also discussed.

Syntactic complexity in translated and non-translated texts: A corpus-based study of simplification.

This study approaches the investigation of the simplification hypotheses in corpus-based translation studies from a syntactic complexity perspective. The research is based on two comparable corpora, the English monolingual part of COCE (Corpus of Chinese-English) and the native English corpus of FLOB (Freiburg-LOB Corpus of British English). Using the 13 syntactic complexity measures falling into five subconstructs (i.e. length of production unit, amount of subordination, amount of coordination, phrasal complexity and overall sentence complexity), our results show that translation as a whole is less complex compared to non-translation, reflected most prominently in the amount of subordination and overall sentence complexity. Further pairwise comparison of the four subgenres of the corpora shows mixed results. Specifically, the translated news is homogenous to native news as evidenced by the complexity measures; the translated genres of general prose and academic writing are less complex compared to their native counterparts while translated fiction is more complex than non-translated fiction. It was found that mean sentence length always produced a significant effect on syntactic complexity, with higher syntactic complexity for longer sentence lengths in both corpora. ANOVA test shows a highly significant main effect of translation status, with higher syntactic complexity in the non-translated texts (FLOB) than the translated texts (COCE), which provides support for the simplification hypothesis in translation. It is also found that, apart from translation status, genre is an important variable in affecting the complexity level of translated texts. Our study offers new insights into the investigation of simplification hypothesis from the perspective of translation from English into Chinese.

Mineralogical and Geochemiccal Assessment of Edda Clays for Possible Use in the Ceramics Industry,Afikpo Sub-Basin,Nigeria

Clay samples from selected part of Edda were analyzed to identify the clay mineral types present, their chemical and physical properties with a view to appraising their industrial suitability as ceramic materials. The mineralogical and geochemical analyses were done using the principles of X-Ray diffraction and X-ray fluorescence respectively. A total of seven clay samples were used for the study, other tests such as plasticity, bulk density, shrinkage, loss on ignition (LOI) and water absorption capacity was carried out to determine the amount of water absorbed under specified conditions. The basic industrial properties assessment showed that more than 70% of the clays are fine-grained. The clays exhibited low to moderate plasticity, moderate shrinkage and bulk density, low to moderate values of both loss on ignition and water absorption capacity. The clays are buff to yellowish in colour. The results of x-ray fluorescence revealed that the mean concentration of major oxide in the clays is shown as follows: SiO2 (62.78%), Al2O3 (20.25%), total Fe (6.09%), CaO (0.56%), MgO (3.21%), Na2O (0.47%), K2O, (1.44%) and TiO2 (0.52%). The samples have high silica content, low alumina and low oxide content. The results of x-ray diffraction revealed that kaolinite is the dominant clay mineral with illite and montmorillonite occurring in subordinate amounts, while quartz and feldspar are the non-clay components present. The characteristics of the clays for each parameter were compared with industrial standards. These properties are appropriate for the Afikpo clays to be useful in the manufacturing of ceramics. However, since the silica content of the clays is high further beneficiation is recommended.

Along-dip variations of subduction fluids: The 30–80 km depth traverse of the Schistes Lustrés complex (Queyras-Monviso, W. Alps)

The Queyras-Monviso traverse of the Schistes Lustrés complex, is a stack of underplated nappes of oceanic rocks subducted from blueschist- to eclogite-facies conditions.This study reports on salinities and gas contents of primary fluid inclusions trapped in high pressure veins from metasediments and metamafic rocks (445 fluid inclusions in 22 samples). These data provide snapshots of the compositions of fluids present at peak burial conditions, varying from ~30 to 80 km depth and illustrate the evolution of fluid composition with burial along a cold subduction zone.Fluid inclusions trapped in lawsonite- and carpholite-bearing veins in metasediments contain moderately saline aqueous fluids (average salinity of 4.6 wt% NaCl eq.) with subordinate amounts of CO2 and CH4 in the vapor phase. The observed salinity decrease with increasing grade is interpreted as reflecting progressive dilution of initial seawater-like pore fluid by low-salinity fluids released locally by dehydration reactions. Less-frequently measured higher salinities in the uppermost metasedimentary-dominated tectonic unit suggest brine infiltration from embedded blocks of margin units containing evaporites. CO2 and CH4 (and scarce potential hydrocarbons) appear to be locally released from fluid interaction with carbonates and carbonaceous matter-rich pelitic horizons, respectively.Fluid inclusions in high pressure omphacite veins in metagabbros record higher salinities (mean salinity about 17 wt% NaCl eq.) with small amounts of N2 in eclogitic veins only, and a variety of minerals (calcite, white mica, salts) indicative of complex chemical systems. These high salinities are interpreted as partly inherited from seafloor high-temperature hydrothermal alteration of gabbros, resulting in phase separation and brine formation. Progressive breakdown of hydrothermal Cl-rich amphibole to glaucophane (blueschist-facies) and then omphacite (eclogite-facies) and release of brines trapped in fluid inclusions could account for the high salinity fluids. Therefore, in metagabbros, fluid inclusions record progressive release of Cl in the fluid phase with increasing grade.Fluid signatures of metasediments and metamafics appear characteristic of each rock type. Local fluid signatures and redox conditions were preserved within units, possibly due to restricted and transient fluid circulation (at the hm-scale at most).Fluid inclusions in Alpine metasediments show salinities and gas contents comparable with other subducted fragments of oceanic lithosphere worldwide, whereas fluid salinities of Alpine metagabbros are higher than salinities recorded elsewhere, either due to (1) higher-temperature hydrothermal alteration and brine formation in Alpine metagabbros (compared to metavolcanics) or (2) more restricted infiltration by sediment-derived fluids compared to block-in-mélange subduction complexes.

Mineralogy of the 2019 Aguas Zarcas (CM2) carbonaceous chondrite meteorite fall

AbstractThe 2019 Aguas Zarcas CM2 meteorite is the most significant carbonaceous chondrite CM2 fall since Murchison in 1969. Samples collected immediately following the fall and studied here provide the rare opportunity to analyze the bulk mineralogy of a CM2 largely free of terrestrial contamination. Bulk samples were analyzed by powder X-ray diffraction (XRD), thermal gravimetric (TG) analysis, evolved gas analysis (EGA), and scanning electron microscopy (SEM) with an electron-probe micro-analyzer (EPMA). Water-extracted salts were analyzed by XRD. In hand specimen, the stones are brecciated and dominated by chondrule-rich and chondrule-poor lithologies, and locally, a matrix-rich lithology. Powder XRD patterns from multiple stones are dominated by reflections from serpentine group minerals, on which are superimposed reflections for ferrotochilinite, 1:1 regularly interstratified ferrotochilinite/cronstedtite, anhydrous silicates, calcite, pentlandite, pyrrhotite, and minor phases. Reflections for magnetite are present only from a metal-rich breccia clast. The serpentine XRD reflections from the chondrule-rich and chondrule-poor lithologies match those from 1T cronstedtite, whereas those from the matrix-rich lithology match the 1M polytype. Patterns with the 1M polytype also show a distinct low-angle scattering to the serpentine basal reflection centered near 8.6 Å, the origin of which is obscure. Further matching of the known serpentines to the Aguas Zarcas data shows that cronstedtite accounts for a subordinate amount of the clays, and at least three other chemically and structurally distinct serpentines are likely present. A typical fragment of Aguas Zarcas yielded 0.6 wt% water-extractable salts. The powder XRD pattern of the dried water extract shows reflections for halite = NaCl; chlorartinite = Mg2(CO3)(OH)Cl·2H2O; thenardite = Na2SO4; and sodium chlorate = NaClO4. The TG mass losses of 11.4 to 14.7 wt% are consistent with other CM2 chondrites. The gases detected by EGA are dominated by H2O and CO2, largely derived from the dehydroxylation and decomposition of serpentine and calcite, respectively. Also detected are gases with masses matching SO2/S2 and H2S, which are primarily released below 480 °C, and a mass of 30, which matches the molecular weight of formaldehyde and ethane, shows a maximum at 376 °C. These organic gases likely derive from the pyrolysis of indigenous organic matter. Taken together, the millimeter-scale mineralogical study of Aguas Zarcas reveals a complex breccia dominated by CM2-like clasts. The detailed study of this meteorite, together with similar studies from a range of carbonaceous chondrites, provides the foundations for studying and interpreting the samples returned from the NASA OSIRIS-REx and JAXA Hayabusa2 missions.

Heavy metals, radionuclides activity and mineralogy of soil samples from an artisanal gold mining site in Ile-Ife, Nigeria: implications on human and environmental health

The Ife-Ilesha schist belt of the Nigerian Basement Complex is renowned for artisanal gold mining activities owing to the occurrence of gold-bearing eluvial deposits within and around the belt. However, gold mining operations in Ile-Ijesha axis are carried out haphazardly without consideration of probable health risks that might be posed to the miners and local community by heavy metals and naturally occurring radionuclides materials (NORMs) contents in the soil. This study was therefore conducted to determine the mineralogy, heavy metals contents and radionuclide activity of soil samples collected from a gold mining site in Ile-Ife with a view to assessing the consequential health and radiological risks. Thirty-five (35) soil samples were collected from abandoned and active excavating pits over the entire area using stainless-steel spade. The heavy metals and radionuclides concentrations and mineralogical compositions of the samples were obtained by Atomic Absorption Spectroscopic (AAS), gamma ray spectrometry and X-ray diffraction (XRD) methods, respectively. The contamination indices consisting of Enrichment Factor (EF) and Index of geoaccumulation (Igeo) were calculated from heavy metals concentrations. The sequence of the average concentrations of heavy metals in the soil samples decreases as follows: Pb (72.93 ± 4.60) > Cd (58.26 ± 3.25) > Cr (42.81 ± 3.00) > Zn (33.66 ± 2.71) > Mn (24.60 ± 1.80) > Ni (23.93 ± 2.51). The mean EF values of the measured heavy metals occurred in the order of Cr > Pb > Zn > Cd > Ni. The Igeo values of the measured heavy metals (except Pb) were less than one (< 1) revealing practically uncontaminated condition of the studied soil. The radiation dose and radiological hazard risks were estimated by employing absorbed dose, effective dose, radium equivalent, gamma index, external hazard index, excess life cancer risk and representative level. The hazard index values of all the measured heavy metals were < 1 indicating no significant non-carcinogenic effects. The average activity concentrations of 40 K, 238U and 232Th are 259.23 ± 84.20 Bqkg−1, 185.48 ± 73.31 Bqkg−1, 11.93 ± 4.68 Bqkg−1, respectively. All the radiological indices were below the world average values stipulated by the radiation monitoring bodies. The result of the XRD indicates the preponderance of quartz, and biotite, as well as subordinate amounts of plagioclase, kaolinite, ilmenite, andradite, actinolite and microcline in the soil samples, pointing to a schistose source rock, which is probably gold-bearing. The current study indicated practically low contamination of the Ile-Ife gold mining site soils by heavy metals, low radiological risk from NORMs and prospect of mineral exploration in the area if well-established procedure is followed.

Study of the Upper Paleocene-Lower Ypresian phosphate succession in El Guettar out crop (Gafsa area, central Tunisia)

This research work corresponds to a sedimentological and geochemical investigation applied on the phosphate series cropping out in Oued Tarfa section in El Guettar area (eastern Gafsa) leading to the characterization of the phosphate deposits, as well as the reconstruction of the phosphatogenesis environment.It is worth mentioning that the phosphatic series in El Guettar area is elaborated and described for the first time in the present work. It corresponds to the Chouabine Formation (Upper Paleocene-Lower Eocene) which is underlain by Selja Formation (Lower Paleocene) and is overlain by Kef Eddour formation (Lower Eocene). The studied series includes nine phosphate layers alternating with limestones and marls. The latter intercalations are themselves interbedded with 5–10 cm-thick phosphate horizons. The deposit facies analysis discloses that the Chouabine formation includes an alternation of fossiliferous phosphates that developed within a relatively deep-water open-marine circatidal environment and sandy phosphates which developed within a relatively shollow-water infratidal environment. The total rock major element distribution reveals that the fossiliferous phosphates are in particular relatively rich in Na2O against low concentrations of SiO2, whereas the sandy phosphates are rather poor in Na2O against significant concentrations of SiO2.The deep-water phosphates are richer in P2O5 (30% in average) than the shallow-water phosphates (18% in average), which suggests that the phosphatogenesis in the El Guettar area was controlled by the depositional environment conditions.The chemical analysis reveals that The P2O5 contents of Guettar samples range from 11% to 31%; the ratio CaO/P2O5 varies between 1.58 and 2.16 for the studied layers with an average of 1.76. Samples contain high amounts of SiO2 with an average of 11.30% and may reach 34%. The amount of organic carbon ranges from 0.15% to 0.58%. The low Cd contents at El Guettar amounting to 8 ppm in the fossiliferous and 14 ppm in the sandy phosphates, probably suggest sedimentation in suboxic conditions. A Poor correlation is recorded between MgO and P2O5 (r2 = 0.382) indicating that Mg might not have been incorporated in the apatite structure. Likewise, a poor correlation is reported between MgO with K2O and Al2O3.The antipathetic relationship between P2O5 and Fe2O3 (r2 = 0.374) indicates the presence of absorbed phosphate onto Fe-oxy-hydroxides (Fig 9).XRD analysis confirms the presence of apatitic minerals (francolite), carbonates (Calcite, and dolomite), quartz, opal-CT and even sulphides as well as gypsum. Clay minerals in El Guettar deposits are dominated by smectite (48–80%) of the clay mineral assemblage, with subordinate quantities of palygorskite (typically 17–36%), kaolinite (about 18%) in the lowest beds only, and sepiolite (generally 10–15%).

Sulphur Isotopic Studies of Pyrite from Gogi Uranium Deposit, Bhima Basin, Karnataka

Abstract Uranium deposit at Gogi area is located along the E-W Gundahalli-Gogi-Kurlegere (GK) fault, in the brecciated impure limestone of Shahabad Formation of the Bhima Group of sediments and the basement granite in the central part of the Meso-Neoproterozoic Bhima basin. Uranium mineralisation is associated mainly with sulphide bearing minerals and secondary calcite. Ore microscopic studies indicate that among the sulphide minerals pyrite is predominant (about 98%) with subordinate amounts of chalcopyrite, chalcocite, marcasite, arsenopyrite and galena. Megascopically, three different varieties of pyrite viz., euhedral, lumpy and vein types are identified in the limestone and siltstone. Ore microscopic studies reveal that vein type pyrite and lumpy pyrite are fractured and crushed. Euhedral pyrite is idiomorphic and devoid of any fractures. The pyrite samples were analysed for δ34S sulphur isotopes. The δ34S values show a wide range from −30.51 to +20.77‰ (Canyon Diablo Troilite, CDT). δ34S values of pyrite can be classified into three groups depending on the values. High values of +17.73 to +20.77 ‰ (CDT) of euhedral pyrite (Py-I) indicate sedimentary pyrite formed due to bacterial reduction of sea water sulphate in relatively closed system, while pyrite (Py-II) having negative values of δ34S imply bacterial reduction of sea water sulphate in open system. The third group (Py-III) of pyrite have δ34S values of −0.51‰ (CDT) and 7.38‰(CDT), indicating their magmatic/ hydrothermal origin. Sulphides in the deformed sediments acted as reducing agent for uranium precipitation.

Host rock peculiarities and influence of major structures on gold and base metal sulfide mineralization in northern Pakistan

For decades, the streams and rivers in northern areas of Pakistan are being explored for gold but the source rock for primary gold is yet to be located. Recent geological surveys have identified several areas for follow-up study for Cu-Au mineralization in Chitral and Gilgit-Baltistan regions. The rocks exposed at various localities are variably altered and/ or mineralized and intensely deformed, which mostly include diorite, granodiorite, greenschists, limestones and undeformed volcanic rocks and granitoids of the Kohistan island arc. The results of petrographic and X-ray diffraction (XRD) analyses of a variety of representative rock samples from a number sites have revealed that mineralization in the Chitral and Gilgit-Baltistan regions is dominantly in the form of pyrite, tetrahedrite, chalcopyrite and galena with subordinate amounts of magnetite, malachite and azurite. The associated/ gangue minerals include albite, quartz, actinolite, biotite, chlorite, epidote, calcite, garnet, illite and titanite (sphene). Diffraction patterns of glycolated samples did not show the existence of swelling clay (e.g., smectite). Sericitic, chloritic and carbonatic alterations have been observed in the studied altered rocks. Mass balance calculations indicate that most of the sulfide-bearing samples are enriched in Cu, Au, Sb, As and Pb and depleted in the rest of the metals reflecting differences in elements mobility during the ore-forming processes. Some of the mineralized rocks especially limestone have experienced a significant volume change due to mobilization of some of the major element oxides e.g. CaO, Fe2O3, SiO2 and ore-forming components e.g. Cu and Pb. The mineralization is of epithermal type in most of the investigated sites, however a few areas show ore formation though orogenic processes and very rarely the ore deposit displays features of the volcanogenic massive sulfide type. Some of the areas are quite promising with respect to their ore element contents and the highly mineralized zones lie in close proximity to major structures in the region. Besides, results from the current study indicate that the mineralization shows close spatial association and hence a strong genetic link with strike slip faults especially where they bend and merge together.

Mineralogical and technological properties of the Konya clays, Central Turkey

Konya clay occurrence is the biggest clay mine of Turkey, except for the Şile region (Istanbul, Turkey) clays, and crop out near the Doganhisar (Konya, Central Turkey). It was formed by alteration of the Na- and K-feldspars, and muscovitic micas; additionally, direct transportation of the sericitic/illitic clays from the metapelitic rocks of metamorphic basement into the Neogene depositional basin. X-ray diffraction (XRD) studies revealed that major constituents of the Konya clays are the quartz, kaolinite and illite with the subordinate amount of paragonitic mica, pyrite, rutile and the organic materials (lignite, peat). The main purpose of this study is to determine the ceramic properties of Konya clays fired at various temperatures. For this aim, the chemical and mineralogical composition of clays was determined by X-ray fluorescence (XRF) and XRD. Thermal analysis techniques are used to measure the physical changes on heating, namely differential thermal analysis (DTA) and thermo-gravimetric analysis (TG). Test samples have been prepared by pressing and firing in the range of 900–1200 °C. Linear shrinkage, water absorption, flexural strength and color values were done in order to characterize clays after firing. Particularly between 1150 and 1200 °C, a significant decrease was observed in water absorption values. All studied samples seem to be easily adaptable for dry pressing ceramic process. In particular, kaolinite and illite rich samples show the best technological behaviors. The addition of Konya clays could have been used in wall, floor and porcelain stoneware tiles and sanitaryware ceramic products.

Formation of clinohumite ± spinel in dolomitic marbles from the Makrohar Granulite Belt, Central India: Evidence for Ti mobility during regional metamorphism

Abstract The mobility of Ti, a member of high field strength elements, in metamorphic fluids is crucial to understand the recycling of commonly perceived nominally soluble elements and for mass-flux calculations during crustal processes. In this study, we present evidence for large-scale Ti mobility from a suite of clinohumite±spinel-bearing dolomitic marbles from the Makrohar area in central India. The studied rocks mostly contain dolomite and calcite (in subequal proportions) and a subordinate amount of forsterite. It commonly develops 1–5 cm thick, laterally continuous, mostly parallel, sometimes anastomosing, brown-colored clinohumite rich bands with variable spinel. Clinohumite has moderate Ti and F (TiO2 = 0.55–2.88 wt%; F = 0.94–1.88 wt%; n = 32). Textural and phase equilibria modeling indicate that clinohumite grew at the expense of forsterite + dolomite under static conditions due to infiltration of F- and Ti-bearing extremely H2O-rich fluids (XCO2 &amp;lt; 0.03), at ~5–6 kbar pressure and ~650–700 °C temperature. The Ti and F were most likely supplied by highly channelized aqueous fluids restricted within the centimeter-thick bands. The negative volume change of the reactions further facilitated fluid ingress. The lateral continuity of the bands over several meters across multiple out-crops indicates that Ti was mobile at the meter to kilometer scale. The results are in accordance with experimental studies that solubility of Ti increases in the presence of halides and imply that Ti may be much more mobile in metamorphic fluids during regional metamorphism than previously anticipated.

Metallogeny of a base metal sulfide-bearing magnetitite body from the Eretria mine, East Othris massif, Greece: Insights into an ancient seafloor hydrothermal system

Magnetite deposits comprise a very small volume of a serpentinized peridotite body that constitutes the Eretria chrome mine of the East Othris ophiolite in central Greece. Magnetite deposits have been examined to aid determination of their mode of occurrence, mineralogy and origin. Research attention has been focused on an ore body that consists of a ~30 cm-thick pod of semi-massive to massive magnetite (~75%–85% modal) hosted in a serpentinite shear zone. The silicate matrix of magnetitite (~10%–15% modal) is composed of unstrained serpentine, chlorite and subordinate amounts of andradite and actinolite. Base metal sulfides (BMS; ~5%–10% modal) and phosphates are dispersed between the magnetite grains. Variably altered Cr-spinel crystals are poikilitically enclosed within magnetite. The investigated ore samples show great variations in the Cu (890–9530 ppm), Ni (190–3260 ppm), Co (120–2180 ppm) and Zn (20–1240 ppm) contents. The δ18ΟSMOW value for magnetite from a magnetitite sample is −2.2‰.The undeformed nature of the silicate minerals in magnetitite points toward crystal growth from a post-magmatic fluid. The low Ni, Mn, Mg and high Si contents in magnetite suggest that it was not derived from fluids produced concurrent to serpentinization. The presence of phosphates, BMS and hydrosilicates suggest that the ore forming fluids were acidic and halogen-bearing. Our preferred hypothesis for the formation of magnetitite is that mixing of upwelling, metal-rich brines along the dilational segments of the host shear zone caused saturation of the ensuing fluids with Fe, which eventually prompted magnetite precipitation. The T estimates deduced from mineralogy, with an uppermost limit of ~460 °C required, and cessation of mineralization at ~150–100 °C, are consistent with the ambient T present within a cooling oceanic lithospheric slab. In analogy with some modern serpentinite-hosted BMS deposits at rifted settings, the BMS-bearing magnetitite of Eretria may represent part of an ancient seafloor hydrothermal system. Our study provides important insights into the initiation and episodicity of hydrothermal activity in oceanic settings.

Archean Metaterrigenous Rocks of the Karelian Province: Geological Position, Geochemistry, Sediment Provenance

The geology and composition of Archean terrigenous sedimentary rocks of the Karelian province (Baltic Shield) are studied in order to establish their positions in the structures of greenstone belts and their role in the provenance composition. It is shown that metaterrigenous rocks from the greenstone belts of the youngest Central Karelian domain, together with intermediate-to-felsic volcanic rocks, compose the main part of the sections, occurring at their bases, and are about 2745 Ma in age. In the belts of the West Karelian domain, metaterrigenous rocks compose the upper parts of the sections, and their age is 2745–2750 Ma. Geological data on the position of metaterrigenous rocks in the belts of the oldest Vodlozero domain also suggest their Neoarchean age. On this basis, it is concluded that metaterrigenous rocks mark the beginning of the Neoarchean stage of crust formation in the Karelian province. According to geochemical data, metagreywackes are predominant among the Archean metaterrigenous rocks of all three domains. At the bases of the sections of some structures, polymictic conglomerates are present with the predominance of tonalite, trondhjemite, and, less often, granodiorite pebbles and with a subordinate amount of igneous rocks of different compositions. Low CaO and Na2O contents and CIA < 55 indicate an insignificant degree of weathering. The Th, Co, Sc, Hf, and La contents indicate a leading role of the TTG-association rocks in the compositions of the sources for all the studied structures. The influence of the basic source was small and affected exclusively Ti, Y, and heavy REE contents in metaterrigenous rocks. The role of komatiites as a source of detrital material was insignificant.

Is postgraduate English academic writing more clausal or phrasal? Syntactic complexification at the crossroads of genre, proficiency, and statistical modelling

This study uses a novel approach to describe modern English academic texts in terms of the amount and distribution of syntactic subordination, coordination and phrasal structures. Inconsistent results have been reported in previous scholarship regarding the trajectory of syntactic complexification based on English language backgrounds and linguistic proficiency of writers. For the first time, a combination of two predictive statistical modelling methods of mixed-effects modelling and supervised machine learning modelling with random forest is used to examine the extent to which the type, amount, and distribution of these syntactic structures can be attributed to a text-intrinsic feature (sub-genres or rhetorical sections of academic register) and a text-extrinsic factor (English language background based on academic context) in a corpus of master’s dissertations. To revisit the theories of English L1 vs. L2 texts, strong predictors of syntactic complexity across academic writings of EFL, ESL, and English L1 postgraduate students were identified. The findings show that EFL texts are dominantly subordinate in nature, English L1’s dominantly phrasal, and the ESL dissertations exhibited similar amounts of subordination and phrasal structures. Distinct syntactic structures also characterise rhetorical sections: abstracts are predominantly phrasal, literature reviews distinctly subordinate, and conclusion sections have noticeable amounts of verb phrases.

Contrasting platinum-group mineral assemblages of the Kondyor massif (Russia): Implications for the sources of HSE in zoned-type ultramafic massifs

This study presents the first highly siderophile element (HSE: Re, Os, Ir, Ru, Rh, Pt, Pd, Au) abundance and Re–Os isotopic data for primary Pt–Fe minerals and Os-rich alloys from the Kondyor zoned-type ultramafic massif located in the southeastern part of the Siberian Craton, Russia. The Kondyor massif is composed of three zones: (A) the oldest dunite core with associated chromitites, with an age of emplacement of ~250 Ma, (B) a younger rim represented by metadunite, wehrlite, clinopyroxenite, and melanocratic gabbro that has transitional contacts with the dunite core, and (C) the youngest apatite-phlogopite-magnetite-rich clinopyroxenite stockwork exposed in the southwestern part of the massif. It has intrusive contacts with the dunite core and formed at ~125 Ma. Chromitites from zone (A) and clinopyroxenites from zone (C) analyzed in this study are characterized by distinct platinum-group mineral (PGM) assemblages dominated by Pt–Fe alloys in the former and cooperite with sperrylite and Pt–Fe alloys in the latter, with subordinate amounts of Os–Ir alloys present in both assemblages. The Re–Os isotope results identify a narrow range of initial 187Os/188Os values for Os–Ir alloys from the zone A chromitites (0.1249–0.1254) and the chromitites themselves (0.12466 ± 0.00005). Such chondritic initial 187Os/188Os values (γ187Os(T =250 Ma) ranging between −0.5 and + 0.1) indicate that the HSE budget of the chromitites and PGM from zone (A) was largely controlled by that of the mantle domain that evolved with long-term near-chondritic Re/Os, a notion that is also supported by the recent data of Luguet et al. (2019). In contrast, Os alloys from the zone C clinopyroxenites have initial 187Os/188Os values ranging between 0.1302 and 0.1308 (initial γ187Os(T =125 Ma) = +3.2 to +3.7), indicative of a suprachondritic time-integrated Re/Os in the source of these rocks. The mineralogical and isotope-geochemical data point to a high-temperature origin of the studied PGM and at least two distinct sources of HSE in the ultramafic rocks of the Kondyor massif.

The C, O, and Sr Isotope Chemostratigraphy of the Vendian (Ediacaran)–Cambrian Transition, Olekma River, Western Slope of the Aldan Shield

The Upper Neoproterozoic–Lower Cambrian section in the Olekma River basin is divided (from bottom to top) into the Dikimdia, Seralakh, Porokhtakh, and Pestrotsvetnaya formations, which are mainly composed of dolostones with a subordinate amount of sandstone, silty shales, gypsum, anhydrite, and native sulfur. The isotope data available allow one to substantially correct the stratigraphic units of the Olekma section, which is probably the most completed section on the Siberian Platform, including the transitional strata from the Vendian (Ediacaran) to the Cambrian. The Dikimdia Formation dolostones have typical Late Ediacaran values of 87Sr/86Sr = 0.70837–0.70843 and abnormally high δ13С values (up to 5.1‰), which gives reason to correlate this formation with the Ust’-Yudoma Formation (the stratotype area), the Dengying Formation in South China (548–550 Ma), the Uluntuy Formation of the Baikal Group, and the terminal Ediacaran sections in some other areas. The 87Sr/86Sr ratio decreases upward and reaches a minimum (0.70803–0.70818) near the Porokhtakh–Pestrotsvetnaya boundary. The lowermost part of the Porokhtakh Formation contains a negative carbon isotope excursion (δ13С = –4.4‰) marking the base of the Nemakit-Daldynian Stage, whereas ~8 m below the base of the Pestrotsvetnaya Formation the positive “pre-Tommotian” excursion (δ13С = 4.1‰) is located. There is a sharp decrease in Fe and Mn contents from ~3800 and ~300 ppm to ~2000 and ~130 ppm, respectively, in dolostones at the Ediacaran–Cambrian transition boundary which corresponds to the Seralakh–Porokhtakh boundary. High δ18О values (26.0 ± 1.2‰) do not provide reasons to associate the carbon isotope excursions, the 87Sr/86Sr trend, and variations of Fe and Mn contents with diagenetic alterations.

Clinopyroxene and Garnet Mantle Cargo in Kimberlites as Probes of Dharwar Craton Architecture and Geotherms, with Implications for Post-1·1 Ga Lithosphere Thinning Events Beneath Southern India

AbstractThe Wajrakarur Kimberlite Field (WKF) on the Eastern Dharwar Craton in southern India hosts several occurrences of Mesoproterozoic kimberlites, lamproites and ultramafic lamprophyres, for which mantle-derived xenoliths are rare and only poorly preserved. The general paucity of mantle cargo has hampered the investigation of the nature and evolution of the continental lithospheric mantle (CLM) beneath cratonic southern India. We present a comprehensive study of the major and trace element compositions of clinopyroxene and garnet xenocrysts recovered from heavy mineral concentrates for three c.1·1 Ga old WKF kimberlite pipes (P7, P9, P10), with the goal to improve our understanding of the cratonic mantle architecture and its evolution beneath southern India. The pressure-temperature conditions recorded by peridotitic clinopyroxene xenocrysts, estimated using single-pyroxene thermobarometry, suggest a relatively moderate cratonic mantle geotherm of 40 mW/m2 at 1·1 Ga. Reconstruction of the vertical distribution of clinopyroxene and garnet xenocrysts, combined with some rare mantle xenoliths data, reveals a compositionally layered CLM structure. Two main lithological horizons are identified and denoted as layer A (∼80–145 km depth) and layer B (∼160–190 km depth). Layer A is dominated by depleted lherzolite with subordinate amounts of pyroxenite, whereas layer B comprises mainly refertilised and Ti-metasomatized peridotite. Harzburgite occurs as a minor lithology in both layers. Eclogite stringers occur within the lower portion of layer A and at the bottom of layer B near the lithosphere–asthenosphere boundary at 1·1 Ga. Refertilisation of layer B is marked by garnet compositions with enrichment in Ca, Ti, Fe, Zr and LREE, although Y is depleted compared to garnet in layer A. Garnet trace element systematics such as Zr/Hf and Ti/Eu indicate that both kimberlitic and carbonatitic melts have interacted with and compositionally overprinted layer B. Progressive changes in the REE systematics of garnet grains with depth record an upward percolation of a continuously evolving metasomatic agent. The intervening zone between layers A and B at ∼145–160 km depth is characterized by a general paucity of garnet. This ‘garnet-paucity’ zone and an overlying type II clinopyroxene-bearing zone (∼115–145 km) appear to be rich in hydrous mineral assemblages of the MARID- or PIC kind. The composite horizon between ∼115–160 km depth may represent the product of intensive melt/rock interaction by which former garnet was largely reacted out and new metasomatic phases such as type II clinopyroxene and phlogopite plus amphibole were introduced. By analogy with better-studied cratons, this ‘metasomatic horizon’ may be a petrological manifestation of a former mid-lithospheric discontinuity at 1·1 Ga. Importantly, the depth interval of the present-day lithosphere–asthenosphere boundary beneath Peninsular India as detected in seismic surveys coincides with this heavily overprinted metasomatic horizon, which suggests that post-1·1 Ga delamination of cratonic mantle lithosphere progressed all the way to mid-lithospheric depth. This finding implies that strongly overprinted metasomatic layers, such as the ‘garnet-paucity’ zone beneath the Dharwar craton, present structural zones of weakness that aid lithosphere detachment and foundering in response to plate tectonic stresses.