• Revision of the World Species of Megaphragma Timberlake (Hymenoptera: Trichogrammatidae)

      Polaszek, Andrew; Fusu, Lucian; Viggiani, Gennaro; Hall, Andie; Hanson, Paul; Polilov, Alexey A (MDPI AG, 2022-06-20)
      Megaphragma species are important models for basic organismal research, and many are potential biological control agents. We present the first extensive revision of species of the genus Megaphragma based on morphological and molecular data. Our revision includes all previously described species, 6 of which are synonymized, and 22 of which are described here as new. We also provide the first key to all species of the genus and reconstruct their phylogeny based on 28S and CO1 molecular markers. The following species are synonymized with M. longiciliatum Subba Rao: M. aligarhensis Yousuf and Shafee syn. nov.; M. amalphitanum Viggiani syn. nov.; M. decochaetum Lin syn. nov.; M. magniclava Yousuf and Shafee syn. nov.; M. shimalianum Hayat syn. nov. M. anomalifuniculi Yuan and Lou syn. nov. is synonymized with M. polychaetum Lin. The following species are described as new: M. antecessor Polaszek and Fusu sp. nov.; M. breviclavum Polaszek and Fusu sp. nov.; M. chienleei Polaszek and Fusu sp. nov.; M. cockerilli Polaszek and Fusu sp. nov.; M. digitatum Polaszek and Fusu sp. nov.; M. fanenitrakely Polaszek and Fusu sp. nov.; M. funiculatum Fusu, Polaszek, and Viggiani sp. nov.; M. giraulti Viggiani, Fusu, and Polaszek sp. nov.; M. hansoni Polaszek, Fusu, and Viggiani sp. nov.; M. kinuthiae Polaszek, Fusu, and Viggiani sp. nov.; M. liui Polaszek and Fusu sp. nov.; M. momookherjeeae Polaszek and Fusu sp. nov.; M. nowickii Polaszek, Fusu, and Viggiani sp. nov.; M. noyesi Polaszek and Fusu sp. nov.; M. pintoi Viggiani sp. nov.; M. polilovi Polaszek, Fusu, and Viggiani sp. nov.; M. rivelloi Viggiani sp. nov.; M. tamoi Polaszek, Fusu, and Viggiani sp. nov.; M. tridens Fusu, and Polaszek sp. nov.; M. uniclavum Polaszek and Fusu sp. nov.; M. vanlentereni Polaszek and Fusu sp. nov.; M. viggianii Fusu, Polaszek, and Polilov sp. nov.
    • Crystal structure and investigation of Bi2TeO6·nH2O (0 ≤ n ≤ 2/3): natural and synthetic montanite

      Missen, Owen P; Mills, Stuart J; Rumsey, Michael S; Weil, Matthias; Artner, Werner; Spratt, J; Najorka, J (Springer Science and Business Media LLC, 2022-06-09)
      The crystal structure of montanite has been determined using single-crystal X-ray diffraction on a synthetic sample, supported by powder X-ray diffraction (PXRD), electron microprobe analysis (EPMA) and thermogravimetric analyses (TGA). Montanite was first described in 1868 as Bi2TeO6·nH2O (0 ≤ n ≤ 2/3). The determination of the crystal structure of synthetic montanite (refined composition Bi2TeO6·0.22H2O has led to the reassignment of the formula to Bi2TeO6·0.22H2O where 0 ≤ n ≤ 2∕3 rather than the commonly reported Bi2TeO6·2H2O. This change has been accepted by the IMA–CNMNC, Proposal 22-A. The PXRD pattern simulated from the crystal structure of synthetic montanite is a satisfactory match for PXRD scans collected on both historical and recent natural samples, showing their equivalence. Two specimens attributed to the original discoverer of montanite (Frederick A. Genth) from the cotype localities (Highland Mining District, Montana and David Beck’s mine, North Carolina, USA) have been designated as neotypes. Montanite crystallises in space group P6, with the unit-cell parameters a = 9.1195(14) Å, c = 5.5694(8) Å, V = 401.13(14) Å3, and three formula units in the unit cell. The crystal structure of montanite is formed from a framework of BiOn and TeO6 polyhedra. Half of the Bi3+ and all of the Te+ cations are coordinated by six oxygen atoms in trigonal-prismatic arrangements (the first example of this configuration reported for Te6+, while the remaining Bi3+ cations are coordinated by seven O sites. The H2O groups in montanite are structurally incorporated into the network of cavities formed by the three-dimensional framework, with other cavity space occupied by the stereoactive 6s2 lone pair of Bi3+ cations. While evidence for a supercell was observed in synthetic montanite, the subcell refinement of montanite adequately indexes all reflections in the PXRD patterns observed in all natural montanite samples analysed in this study, verifying the identity of montanite as a mineral.
    • Petrological and geochemical characterisation of the sarsen stones at Stonehenge

      Nash, David J; Ciborowski, T Jake R; Darvill, Timothy; Parker Pearson, Mike; Ullyott, J Stewart; Damaschke, Magret; Evans, Jane A; Goderis, Steven; Greaney, Susan; Huggett, Jennifer M; et al. (Public Library of Science (PLoS), 2021-08-04)
      Little is known of the properties of the sarsen stones (or silcretes) that comprise the main architecture of Stonehenge. The only studies of rock struck from the monument date from the 19th century, while 20th century investigations have focussed on excavated debris without demonstrating a link to specific megaliths. Here, we present the first comprehensive analysis of sarsen samples taken directly from a Stonehenge megalith (Stone 58, in the centrally placed trilithon horseshoe). We apply state-of-the-art petrographic, mineralogical and geochemical techniques to two cores drilled from the stone during conservation work in 1958. Petrographic analyses demonstrate that Stone 58 is a highly indurated, grain-supported, structureless and texturally mature groundwater silcrete, comprising fine-to-medium grained quartz sand cemented by optically-continuous syntaxial quartz overgrowths. In addition to detrital quartz, trace quantities of silica-rich rock fragments, Fe-oxides/hydroxides and other minerals are present. Cathodoluminescence analyses show that the quartz cement developed as an initial <10 μm thick zone of non-luminescing quartz followed by ~16 separate quartz cement growth zones. Late-stage Fe-oxides/hydroxides and Ti-oxides line and/or infill some pores. Automated mineralogical analyses indicate that the sarsen preserves 7.2 to 9.2 area % porosity as a moderately-connected intergranular network. Geochemical data show that the sarsen is chemically pure, comprising 99.7 wt. % SiO2. The major and trace element chemistry is highly consistent within the stone, with the only magnitude variations being observed in Fe content. Non-quartz accessory minerals within the silcrete host sediments impart a trace element signature distinct from standard sedimentary and other crustal materials. 143Nd/144Nd isotope analyses suggest that these host sediments were likely derived from eroded Mesozoic rocks, and that these Mesozoic rocks incorporated much older Mesoproterozoic material. The chemistry of Stone 58 has been identified recently as representative of 50 of the 52 remaining sarsens at Stonehenge. These results are therefore representative of the main stone type used to build what is arguably the most important Late Neolithic monument in Europe.
    • Petrographic and chemical studies of the Cretaceous-Paleogene boundary sequence at El Guayal, Tabasco, Mexico: Implications for ejecta plume evolution from the Chicxulub impact crater

      Salge, T; Tagle, Roald; Schmitt, Ralf-Thomas; Hecht, Lutz; Wolf Uwe, Reimold; Chris, Koeberl (Geological Society of America, 2021-06-30)
      A combined petrographic and chemical study of ejecta particles from the Cretaceous-Paleogene boundary sequence of El Guayal, Tabasco, Mexico (520 km SW of Chicxulub crater), was carried out to assess their formation conditions and genetic relation during the impact process. The reaction of silicate ejecta particles with hot volatiles during atmospheric transport may have induced alteration processes, e.g., silicification and cementation, observed in the ejecta deposits. The various microstructures of calcite ejecta particles are interpreted to reflect different thermal histories at postshock conditions. Spherulitic calcite particles may represent carbonate melts that were quenched during ejection. A recrystallized microstructure may indicate short, intense thermal stress. Various aggregates document particle-particle interactions and intermixing of components from lower silicate and upper sedimentary target lithologies. Aggregates of recrystallized calcite with silicate melt indicate the consolidation of a hot suevitic component with sediments at ≳750 °C. Accretionary lapilli formed in a turbulent, steam-condensing environment at ~100 °C by aggregation of solid, ash-sized particles. Concentric zones with smaller grain sizes of accreted particles indicate a recurring exchange with a hotter environment. Our results suggest that during partial ejecta plume collapse, hot silicate components were mixed with the fine fraction of local surface-derived sediments, the latter of which were displaced by the preceding ejecta curtain. These processes sustained a hot, gas-driven, lateral basal transport that was accompanied by a turbulent plume at a higher level. The exothermic back-reaction of CaO from decomposed carbonates and sulfates with CO2 to form CaCO3 may have been responsible for a prolonged release of thermal energy at a late stage of plume evolution.
    • An overlooked contributor to palaeontology—the preparator Richard Hall (b. 1839) and his work on an armoured dinosaur and a giant sea dragon

      Graham, M; Radley, Jonathan; Lomax, Dean; Brewer, Pip (Geological Curator, 2020-11-12)
      The work of Richard Hall, a fossil preparator at the British Museum (Natural History) in the late 19th century, has been largely unrecorded. It included the excavation, preparation and restoration of two important specimens: the dinosaur Polacanthus foxii and the ichthyosaur Temnodontosaurus platyodon. The painstaking reconstruction of the dorsal shield of Polacanthus took seven years to complete and enabled a supplemental note redescribing the specimen to be published in 1887. The significance of the discovery in 1898 of the Temnodontosaurus to the town of Stockton in Warwickshire was such that it featured in an article in Nature. It has entered the local folklore and remains celebrated on the town’s road signage and features as the logo of Stockton Primary School.
    • “Hope” is the thing with feathers: how useful are cyclomethicones when cleaning taxidermy?

      Allington-Jones, L (NatSCA, 2020-10-01)
      Silicone solvents have extreme hydrophobicity so they can be used as a temporary barrier to aqueous cleaning solutions. They are characterised as having low odour, moderately low toxicity, low polarity and surface tension. They are 100% volatile so will leave no trace behind. Silicone solvents could potentially be used to flood the skin of taxidermy specimens, to provide a barrier whilst fur or feathers are cleaned, and even permit the use of heat treatments without causing damage to the skin. They will not cause drying or swelling and will not dissolve or mobilise any skin components such as dyes or fats, which would normally be adversely affected by water or other solvents. They are also, in theory, safe to use on skin which has suffered so much deterioration that the shrinkage temperature is close to room temperature. Different classes of silicone solvents have different working times and this article explores 3 of these, and their practical applicability when cleaning taxidermy.
    • Preparing detailed morphological features of fossil brittle stars (Ophiuroidea, Echinodermata) for scanning electron microscopy using a combination of mechanical preparation techniques.

      Graham, M; Ewin, Timothy; Brewer, P (Geological Curators Group, 2020-01-27)
      In order to facilitate detailed SEM analysis of recently available, undescribed fossil ophiuroid material from the Aptian, Lower Cretaceous, Atherfield Clay Formation of the Isle of Wight, Hampshire, UK a combination of careful mechanical preparation techniques was employed to great effect. Specimens were initially exposed using standard air abrasive techniques, but the final few millimetres of matrix were removed using pins. To get individual arm pieces exceptionally clear of matrix, they were removed from the blocks using a mini pedestalling technique and then further cleaned using an ultrasonic pen. This combination of techniques fully exposed all the elements required for full taxonomic study without causing severe damage to the plate surfaces and greatly improved the overall aesthetic of the specimens. These techniques could be more widely applied in fossil preparation.
    • Zircon-hosted apatite inclusions: A powerful tool for reconstruction of Cl contents in melts

      Tuffield, L; Buret, Y; Large, S; Spratt, J; Wilkinson, JJ (Mineral Deposits Studies Group, 2020-01)
      Chlorine in the exsolved volatile phase plays an important role in complexing with metals in the extraction and concentration of metals in magmatic-hydrothermal ore deposits. Therefore, tracking the concentration and evolution of Cl in the parent melt is of particular importance in understanding how such deposits form. In theory, the incorporation of Cl into apatite could be used to track the volatile content of melts; however, low closure temperatures and the rapid diffusion of halogens in apatite make it susceptible to sub-solidus re-equilibration by later thermal events and hydrothermal fluids. This susceptibility compromises its ability to retain the primary halogen signature. However, the common occurrence of apatite as an inclusion phase in zircon crystals, together with the refractory nature of zircon, open up the possibility that such inclusions may preserve primary Clmelt compositions [1]. The Rio-Blanco-Los Bronces porphyry copper district is located in central Chile and hosts several world class porphyry copper deposits as well as barren intrusions [2]. This makes it an excellent area for an investigation of the role of Clmelt in the formation of porphyry copper deposits, as well as the effect of sub-solidus re-equilibration of Cl in apatite. For this study we analysed apatite crystals that occur both in the groundmass and as inclusions in zircons in four samples from the Los Bronces porphyry copper district using EPMA for halogen and major elements and LA-ICP-MS for trace elements. These samples include a barren intrusion unrelated to mineralisation that precedes mineralisation by around 10 Ma, and pre-, syn- and post-mineralisation porphyries. Apatite inclusions hosted in zircon crystals typically exhibit a large range in Cl concentrations (<0.5 –2.5 wt.% Cl), with all inclusion data exhibiting polymodal distributions of Cl concentrations. By contrast, groundmass apatites from all samples are characterised by uniformly low Cl concentrations (<0.5 wt.% Cl). These results are consistent with the apatite crystals in the groundmass having experienced sub-solidus re-equilibration related to the pervasive hydrothermal alteration in the district. The wide range in Cl concentrations recorded by the apatite inclusions is interpreted to reflect changing Clmelt for the duration of apatite and zircon crystallisation, perhaps linked to volatile saturation and preferential partitioning of Cl into the aqueous phase. Additionally, the apatites hosted in zircon crystals show significant inter-sample variations, evolving from low Cl concentration (<0.5 wt. % Cl) in the barren intrusion, to higher Cl concentrations (0.5 – 2.5 wt.% Cl) in the samples closely temporally associated with porphyry Cu mineralisation. These data suggest that Clmelt was significantly higher (0.05 – 0.40 wt.% Clmelt) in the melts associated with porphyry copper mineralisation compared with the precursor barren magmatism (~0.04 wt.% Clmelt) [3]. We conclude that due to the rapid diffusion of halogens in apatite in the presence of melt or hydrothermal fluid, the study of apatite inclusions hosted in zircon crystals is required to reconstruct primary melt compositions and to track the evolution of Cl concentrations in porphyry-forming magmas. This study reveals high Clmelt concentrations in the magmas related to mineralisation in the Los Bronces district, a property that would have facilitated the efficient extraction and concentration of metals. References: [1] Brugge, E. et al. (2019). Proc. 15th SGA Biennial Meeting, Vol. 2, 983-986. [2] Toro, J.C. et al. (2012). SEG Special Publication 16:105-126. [3] Li, H. and Hermann, J. (2017) Am. Mineral. 102:580-594.
    • Classification and characterisation of magmatic-hydrothermal tourmaline by combining field observations and microanalytical techniques

      Drivenes, K; Brownscombe, W; Larsen, RB; Seltmann, Reimar; Spratt, J; Sørensen, BE (IOP Publishing, 2020)
      Tourmaline from the St. Byron lobe of the Land’s End granite, SW England, was assessed by macroscopic, optical and quantitative microanalytical methods. In total, seven types of tourmaline were distinguished. The seven types reflect different crystallisation environments and stages in the magmatic-hydrothermal transition. Types 1-3 are interpreted to represent a gradual transition from tourmaline crystallising from a silicate melt to precipitation from magmatic aqueous fluids. Types 5-7 crystallised at subsolidus conditions from a different fluid generation than types 1-3. These fluids may be magmatic or mixed with other fluids (e.g., meteoric or formation waters). The Sn-mineralisation in the area is mostly related to the latter fluid generation, and the mineralising potential is reflected by the tourmaline composition.
    • Mechanisms for the generation of HREE mineralization in carbonatites: Evidence from Huanglongpu, China.

      Smith, M; Cangelosi, D; Yardley, B; Wenlei Song, CX; Spratt, J (The Society for Geology Applied to Mineral Deposits, 2019-12-30)
      The Hunaglongpu carbonatites, Qinling Mountains, China, are exceptional as they form both an economic Mo resource, and are enriched in the HREE compared to typical carbonatites, giving a metal profile that may closely match projected future demand. The carbonatites at the level currently exposed appear to be transitional between magmatic and hydrothermal processes. The multistage dykes and veins are cored by quartz which hosts a fluid inclusion assemblage with a high proportion of sulphate daughter or trapped minerals, and later stage, cross-cutting veins are rich in barite-celestine. The REE mineral paragenesis evolves from monazite, through apatite and bastnäsite to Ca-REE fluorcabonates, with an increase in HREE enrichment at every stage. Radio-isotope ratios are typical of enriched mantle sources and sulphur stable isotopes are consistent with magmatic S sources. However, Mg stable isotopes are consistent with a component of recycled subducted marine carbonate in the source region, The HREE enrichment is a function of both unusual mantle source for the primary magmas and REE mobility and concentration during post-magmatic modification in a sulphate-rich hydrothermal system. Aqueous sulphate is a none specific ligand for the REE, and this coupled with crystal fraction lead to HREE enrichment during subsolidus alteration.
    • Professional fossil preparators at the British Museum (Natural History), 1843-1990*

      Graham, M; Reichenbach, H (Edinburgh University Press, 2019-10-01)
      Since the inception of the British Museum (Natural History) in 1881 (now the Natural History Museum, London), the collection, development and mounting of fossils for scientific study and public exhibition have been undertaken by fossil preparators. Originally known as masons, because of their rock-working skills, their roles expanded in the late nineteenth and early twentieth centuries, when, at the forefront of the developing science of palaeontology, the Museum was actively obtaining fossil material from the UK and abroad to build the collections. As greater numbers of more impressive specimens were put on public display, these preparators developed new and better methods to recover and transport fossils from the field, and technical improvements, in the form of powered tools, enabled more detailed mechanical preparation to be undertaken. A recurring theme in the history of palaeontological preparation has been that sons often followed in their fathers’ footsteps in earth sciences. William and Thomas Davies, Caleb and Frank Barlow, and Louis and Robert Parsons were all father-and-son geologists and preparators.
    • Porphyry Cu(Mo) deposits of the Urals: insights from molybdenite trace element geochemistry

      Plotinskya, OP; Abramova, VD; Bondar, D; Seltmann, Reimar; Spratt, J (The Society for Geology Applied to Mineral Deposits, 2019-10-01)
      The first data on EMPA and LA-ICPMS study of molybdenite from four porphyry deposits of the South and Middle Urals (Tomino, Mikheevskoe and Benkala porphyry Cu and Talitsa porphyry Mo deposits) are presented. It is shown that most trace elements form mineral inclusions within molybdenite in all the deposits studied; only Re and W are most likely to be incorporated into the molybdenite lattice. Porphyry Cu deposits (Tomino and Mikheevskoe) formed within oceanic arc settings are featured by high contents of Re (mostly over 400 ppm) and low contents of W (<10 ppm) in molybdenite; porphyry Cu deposits from Andean-type geotectonic environment (Benkala) are featured by lower Re content (hundreds ppm) and high contents of W (tens ppm) in molybdenite. Molybdenite from porphyry deposits from collisional setting (Talitsa) has low content of Re and elevated W contents (tens ppm). It is demonstrated that trace element geochemistry of molybdenite is a useful tool to define the source of metal components and the geotectonic environment for porphyry Cu(Mo) deposits.
    • A unique CO-like micrometeorite hosting an exotic Al-Cu-Fe-bearing assemblage – close affinities with the Khatyrka meteorite

      Suttle, MD; Twegar, K; Nava, J; Spiess, R; Spratt, J; Campanale, F; Folco, L (Springer Science and Business Media LLC, 2019-08-27)
      We report the discovery of a unique micrometeorite, containing an exotic Al-Cu-Fe alloy composed of two intermixed phases: khatyrkite (CuAl2) and stolperite (CuAl) and both containing minor Fe (<1.4 wt%). These phases are dendritic and rapidly co-crystallized at the binary system’s peritectic (~550 °C). The host micrometeorite is an otherwise typical S-type micro-porphyritic cosmic spherule containing relict olivine (Fo76–90, Cr2O3: 0.01–0.56 wt%, MnO: 0.03–0.32 wt% and CaO: 0.09–0.22 wt%) and a cumulate layered texture. These properties suggest the micrometeorite is derived from a carbonaceous chondrite (best matched to a CO chondrite) and entered the atmosphere a high speed (~16 kms−1), implying an origin from a highly eccentric orbit. This particle represents the second independent discovery of naturally occurring intermetallic Al-Cu-Fe alloys and is thus similar to the previously reported Khatyrka meteorite - a CV chondrite containing near-identical alloys and the only known natural quasicrystals. We did not observe quasicrystalline phases in this micrometeorite, likely due to the low amounts of Fe in the alloy, insufficient to stabilize quasicrystals. Our discovery confirms the existence of Al-Cu-Fe intermetallic alloys on chondritic parent bodies. These unusual phases require a currently unexplained formation process, we tentatively suggest this could represent the delivery of exotic interstellar material to the inner solar system via impact.
    • Perforocycloides nathalieae new genus and species, an unusual Silurian cyclocystoid (Echinodermata) from Anticosti Island, Québec, Canada

      Graham, M; Ewin, TAM; Reich, Mike; Cournoyer, ME; Klug, C (Springer, 2019-08-22)
      Cyclocystoids are a poorly known, rare, extinct class of bi-facially flattened, disc shaped echinoderms, ranging from the Middle Ordovician to the Early Carboniferous. Articulated cyclocystoids are relatively common in the Ordovician but are rarer in younger strata. Here we describe Perforocycloides nathaliae new genus and species, from the early Silurian of Anticosti Island, Québec, Canada, the first articulated cyclocystoid from the Silurian of North America. This taxon is distinguished from other cyclocystoids by the number of variably sized marginal ossicles, the lack of interseptal plates, and the novelty of pores located in the distal part of the sutures between adjacent marginals on the dorsal surface. These dorsal intermarginal sutural pores led to canals which penetrated the contiguous area of the lateral surface of the marginals and emerged on the ventral surface between the cupules of adjacent marginals. These dorsal intermarginal sutural pores/canals appear to be unique to Perforocycloides and whilst their function is speculative, they provided some form of communication between the dorsal disc and the distal side of the ventral marginals/cupules. Perforocycloides most closely resembles the Ordovician–Silurian genus Zygocycloides, suggesting that this genus may have diversified more widely during the Silurian than previously reported. A review of global Silurian cyclocystoid distribution suggests taxa were geographically confined and that greatest diversity appears to have been located within Baltica. However, it also demonstrates our current limited knowledge. No specimens have been recorded from Gondwana (e.g. Africa, Australia, South America), Siberia, and North and South China, nor are any specimens known confidently anywhere from Přidolí strata.
    • Deep-sea anthropogenic macrodebris harbours rich and diverse communities of bacteria and archaea

      Woodall, LC; Jungblut, AD; Hopkins, K; Hall, A; Robinson, LF; Gwinnett, C; Paterson, GLJ (PLOS, 2018-11-28)
      The deep sea is the largest biome on earth, and microbes dominate in biomass and abundance. Anthropogenic litter is now almost ubiquitous in this biome, and its deposition creates new habitats and environments, including for microbial assemblages. With the ever increasing accumulation of this debris, it is timely to identify and describe the bacterial and archaeal communities that are able to form biofilms on macrodebris in the deep sea. Using 16S rRNA gene high throughput sequencing, we show for the first time the composition of bacteria and archaea on macrodebris collected from the deep sea. Our data suggest differences in the microbial assemblage composition across litter of different materials including metal, rubber, glass, fabric and plastic. These results imply that anthropogenic macrodebris provide diverse habitats for bacterial and archaeal biofilms and each may harbour distinct microbial communities.
    • The mineralogy of the effusive silicate rocks from the Mosonik volcano, Northern Tanzania.

      Sedova, AM; Zaitsev, AN; Spratt, J (Vernadsky Institute of Geochemistry and Anlytical Chemistry of Russian Academy of Sciences (GEOKHI RAS), 2018-10-01)
      International Conference on Magmatism of the Earth and Related Strategic Metal Deposits 3-7 September, 2018 Vernadsky Institute of Geochemistry and Analytical Chemistry of Russian Academу of Sciences, Moscow, Russia. The mineralogy of the effusive silicate rocks from the Mosonik volcano, Northern Tanzania Sedova А.М.1, Zaitsev A.N.1,2, J. Spratt2 1 Department of Mineralogy, St. Petersburg State University, Saint-Petersburg, Russia, e-mail: a.sedova@spbu.ru 2Department of Core Research Laboratories, Natural History Museum, London, UK The Mosonik volcano belongs to the Neogene-Resent volcanics of the Natron-Engaruka region of the East African Rift system. It is one of several stratovolcanoes located on the northeastern tip of the Gregory Rift Valley. Mosonik is attributed as having the earliest phase of eruptions in this province (Dawson, 2008) and is dated in the range 3.18-1.28 Ma (Isaac & Curtis, 1974; Dawson, 2008). In 1961, it was mapped by the Tanganyika Geological Survey (Guest et al., 1961), with published data (Paslick et al., 1996) on the composition of minerals from basanites, nephelinites and phonolites. According to the results of this study the compositions of melilite and nephelinite, Zaitsev et al. (2015) have indicated that the Mosonik volcano could be a potential source for the Upper Laetolil Footprint Tuff 7. According to our data the main effusive rocks of Mosonic are various nephelinites and phonolites, quite often they contain xenoliths of plutonic rocks: melteigites, foyaites, ijolites, and rocks of the enclosing stratum (andesites). Carbonatites mostly occur as boulders of various sizes within creek deposits. Among nephelinites there are nephelinites s.s., phonolitic nephelinites, calcite-phonolite nephelinites and melilite nephelinites. Microphenocrysts are represented by nepheline (45-60%), pyroxenes of diopside-hedenbergite solid solution, in some cases with aegirine edging (15-30%), apatite (3-10%) and titanite (3-10%). Calcite content reaches 10% within the calcite varieties of nephelinites; sanidine up to 10% in phonolitic nephelinites, which are strongly altered. Melilite nephelinites are also characterized by the following coposition: melilite (20%), perovskite (5%), sherlomite (3%). In rare cases within the nephelinites there are microphenocrysts of nepheline. Phonolites are represented by the following species: phonolites, sodalite phonolites and calcite phonolites. Phenocrysts are represented by nepheline (40-65%), pyroxenes of the diopside-hedenbergite series, rarely with aegirine edging (10-50%), sanidine (15-40%), Mg-Fe mica (0-5%), titanite (1-10%), and apatite (0-8%). In these rocks a large number of macrophenic crystals of nepheline, pyroxene, and often sanidine are observed. The work is supported by Russian Foundation of Basic Research (grant 18-05-00835) and St. Petersburg State University (Geomodel Resource Center) References Dawson J. B. The Gregory Rift Valley and Neogene-Recent Volcanoes of Northern Tanzania. London. 2008. 112 pp. Guest N. J., James, T. C Pickering R., and Dawson J. B. Angata salei. Geol. Surv. Tanganyika. Quarter degree sheet 39. 1961 Isaac, G. L. & Curtis, G. H. Age of the Acheulian industries from the Peninj Group, Tanzania // Nature. 1974. p.249. Paslick, C., Halliday, A. N., Lange, R. A., James, D. & Dawson, J. B. Indirect crustal contamination: evidence from isotopic and chemical disequilibria in minerals from alkali basalts and nephelinites from northern Tanzania // Contributions to Mineralogy and Petrology. Vol. 125. 1996. 277–292. Zaitsev A.N., Spratt J., Sharygin V.V., Wenzel T., Zaitseva O.A., Markl G. Mineralogy of the Laetolil Footprint Tuff: A comparison with possible volcanic sources from the Crater Highlands and Gregory Rift // Journal of African Earth Sciences. Vol. 111. 2015. pp. 214–221.
    • Alkali-rich replacement zones in evolved NYF pegmatites: metasomatic fluids or immiscible melts?

      Muller, A; Spratt, J; Thomas, R; Williamson, BJ; Seltmann, Reimar (International Mineralogical Association, 2018-08-13)
      IMA2018 Abstract submission Pegmatite mineralogy, geochemistry, classification and origins IMA2018-1337 Alkali-rich replacement zones in evolved NYF pegmatites: metasomatic fluids or immiscible melts? Axel Muller* 1, John Spratt2, Rainer Thomas3, Ben J. Williamson4, Reimar Seltmann2 1Natural History Museum, University of Oslo, Oslo, Norway, 2Department of Earth Sciences, Natural History Museum, London, United Kingdom, 3Chemistry and Physics of Earth Materials, German Research Centre for Geoscience GFZ, Potsdam, Germany, 4Camborne School of Mines, University of Exeter, Penryn, United Kingdom What is your preferred presentation method?: Oral or poster presentation : Replacement zones (RZ), which are a common feature of evolved granitic pegmatites, are irregular, commonly alkali-rich zones superimposing, cross-cutting and replacing the primary zonation in almost all consolidated pegmatite bodies. RZ are widely considered to result from late-stage metasomatism even though little is known about the melts and/or fluids involved in their formation. However, the observed textures and mineral paragenesis of RZ cannot be explained by metasomatism in a strict sense. In this study, the nature of the late stage silicate melt forming “cleavelandite” RZ is assessed from textural, mineralogical, chemical and melt inclusion studies of evolved, Proterozoic Niobium-Yttrium-Fluorine (NYF) rare metal pegmatites from Evje–Iveland, southern Norway. These were studied as they are mineralogically simple, compared with RZ in evolved Lithium-Caesium-Tantalum (LCT) pegmatites. Silicate melt inclusions in RZ-forming topaz and “cleavelandite” document high H2O contents of up to18 wt.% of the F-rich silicate melt from which the RZ crystallized. In addition, from mineral compositions (“cleavelandite”, “amazonite”, white mica, garnet, columbite group minerals, topaz, fluorite, and beryl), they must have also been strongly alkaline (Na-dominated) with enrichments in F (at least 4 wt.%), Cs, Rb, Ta, Nb, Mn, Ge, Bi, As, and in some cases also Li compared with host pegmatites. These elements are concentrated in a few RZ-forming minerals resulting in very distinctive mineral-trace element signatures. “Amazonite” is strongly enriched in Cs and Rb and often white mica and beryl in Li and Cs. To acquire these mineral compositions, the overall Li-Cs-Ta-poor Evje-Iveland original pegmatite melt must have undergone extreme internal chemical differentiation resulting in melt/melt immiscibility aiding rheology contrasts and resulting in RZ formation. The resulting RZ-forming H2O-F-rich silicate melt would have shown large differences in viscosity and density, and therefore physical flow/transport properties, to the host pegmatite melt resulting in discordant contacts. The mineralogy and melt inclusion data from the Evje-Iveland pegmatites document a gradient of crystallization temperatures within the investigated pegmatite bodies with highest temperatures at the pegmatite margin (during initial emplacement, ~680°C) and lowest temperatures within the RZ (<500°C). Considering the temperature and pressure conditions of the host rocks gneisses and amphibolites (~650°C, up to 5 kbar) at the time of pegmatite emplacement and the crystallization conditions of the RZ, the Evje- Iveland pegmatites and RZ likely formed over a period of 2.2 million years, assuming an exhumation rate of 1.5 mm per million years and a geothermal gradient of 45°C km-1. Such a long crystallization time contradicts the classical view that pegmatites represent strongly undercooled melts which crystallize relatively fast.
    • The air-abrasive technique: A re-evaluation of its use in fossil preparation

      Graham, M; Allington-Jones, L (Coquina Press, 2018-08-02)
      This paper outlines the history of air-abrasion (also known as airbrasion) as a paleontological preparation technique and evaluates various powders and their properties. It explores the rationale behind the selection of abrasive powders and presents, for the first time, trench-scatter experiments through Scanning Electron Microscope (SEM) photography and three-dimensional (3-D) profiling. This article also offers general practical advice and details the results of an international survey of practising fossil preparators.
    • The air-abrasive technique: a re-evaluation of its use in fossil preparation.

      Graham, M; Allington-Jones, L (Coquina Press, 2018-08)
      This paper outlines the history of air-abrasion (also known as airbrasion) as a palaeontological preparation technique and evaluates various powders and their properties. It explores the rationale behind the selection of abrasive powders and presents, for the first time, trench-scatter experiments through Scanning Electron Microscope (SEM) photography and three-dimensional (3-D) profiling. This article also offers general practical advice and details the results of an international survey of practising fossil preparators
    • Trace-element geochemistry of molybdenite from porphyry Cu deposits of the Birgilda-Tomino ore cluster (South Urals, Russia)

      Plotinskaya, OY; Abramova, VD; Groznova, EO; Tessalina, SG; Seltmann, Reimar; Spratt, J (Cambridge University Press, 2018-05)
      Mineralogical, electron microprobe analysis and laser ablation-inductively coupled plasma-mass spectrometry data from molybdenite within two porphyry copper deposits (Kalinovskoe and Birgilda) of the Birgilda-Tomino ore cluster (South Urals) are presented.† The results provide evidence that molybdenites from these two sites have similar trace-element chemistry. Most trace elements (Si, Fe, Co, Cu, Zn, Ag, Sb, Te, Pb, Bi, Au, As and Se) form mineral inclusions within molybdenite. The Re contents in molybdenite vary from 8.7 ppm to 1.13 wt.%. The Re distribution within single molybdenite flakes is always extremely heterogeneous. It is argued that a temperature decrease favours the formation of Re-rich molybdenite. The high Re content of molybdenite observed points to a mantle-derived source.