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The Sheahan Diamond Literature Reference Compilation - Technical, Media and Corporate Articles based on Major Region - Other Europe
The Sheahan Diamond Literature Reference Compilation is compiled by Patricia Sheahan who publishes on a monthly basis a list of new scientific articles related to diamonds as well as media coverage and corporate announcements called the Sheahan Diamond Literature Service that is distributed as a free pdf to a list of followers. Pat has kindly agreed to allow her work to be made available as an online digital resource at Kaiser Research Online so that a broader community interested in diamonds and related geology can benefit. The references are for personal use information purposes only; when available a link is provided to an online location where the full article can be accessed or purchased directly. Reproduction of this compilation in part or in whole without permission from the Sheahan Diamond Literature Service is strictly prohibited. Return to Diamond Region Index
Sheahan Diamond Literature Reference Compilation - Scientific Articles by Author for all years
Each article reference in the SDLRC is tagged with one or more key words assigned by Pat Sheahan to highlight the main topics of the article. In addition most references have been tagged with one or more region words. In an effort to make it easier for users to track down articles related to a specific region, KRO has extracted these region words and developed a list of major region words presented in the Major Region Index to which individual region words used in the article reference have been assigned. Each individual Region Report contains in chronological order all the references with a region word associated with the Major Region word. Depending on the total for each reference type - technical, media and corporate - the references will be either in their own technical, media or corporate Region Report, or combined in a single report. Where there is a significant number of technical references there will be a technical report dedicated to the technical articles while the media and corporate references are combined in a separate region report. References that were added in the most recent monthly update are highlighted in yellow within the Region Report. The Major Region words have been defined by a scale system of "general", "continent", "country", "state or province" and "regional". Major Region words at the smaller scales have been created only when there are enough references to make isolating them worthwhile. References not tagged with a Region are excluded, and articles with a region word not matched with a Major Region show up in the "Unknown" report.
Kimberlite - diamondiferous
Lamproite - diamondiferous
Lamprophyre - diamondiferous
Other - diamondiferous
Kimberlite - non diamondiferous
Lamproite - non diamondiferous
Lamprophyre - non diamondiferous
Other - non diamondiferous
Kimberlite - unknown
Lamproite - unknown
Lamprophyre - unknown
Other - unknown
Future Mine
Current Mine
Former Mine
Click on icon for details about each occurrence. Works best with Google Chrome.
CITATION: Faure, S, 2010, World Kimberlites CONSOREM Database (Version 3), Consortium de Recherche en Exploration Minérale CONSOREM, Université du Québec à Montréal, Numerical Database on consorem.ca. NOTE: This publicly available database results of a compilation of other public databases, scientific and governmental publications and maps, and various data from exploration companies reports or Web sites, If you notice errors, have additional kimberlite localizations that should be included in this database, or have any comments and suggestions, please contact the author specifying the ID of the kimberlite: [email protected]
Shoshonitic and alkaline lamprophyres with elevated gold (Au) and platinum group elements (PGE) concentrations from the Kreuzeck Mountains, eastern Alps, Austria
Mineralogy and Petrology, Vol. 46, No. 1, pp. 23-42
Perraki, M., Proyer, A., Mposkos, E., Kaindl, R., Hoinkes, G.
Raman micro spectroscopy on diamond, graphite and other carbon polymorphs from the ultrahigh pressure metamorphic Kimi Complex of the Rhodope metamorphic province.
Earth and Planetary Science Letters, Vol. 241, 3-4, pp. 672-685.
Guzmics, T., Zajacz, Z., Kodoenyi, J., Halter, W., Szabo, C.
LA ICP MS study of apatite and K feldspar hosted primary carbonatite melt inclusions in clinopyroxenite xenoliths from lamprophyres, Hungary: implications
Geochimica et Cosmochimica Acta, Vol. 72, 7, pp. 1864-1886.
Sand, K.K., Nielsen, T.F.D., Secher, K., Steenfelt, A.
Kimberlite and carbonatite exploration in southern West Greenland: summary of previous activities and recent work by the kimberlite research group at the Geological Survey of Denmark and Greenland.
Ackerman, L., Walker, R.J., Puchtel, I.S., Pitcher, L., Jelinek, E., Strnad, L.
Effects of melt percolation on highly siderophile elements and Os isotopes in subcontinental lithospheric mantle: a study of upper mantle profile central Europe
Geochimica et Cosmochimica Acta, Vol. 73, 8, pp. 2400-2414.
Perraki, M., Korsakov, A.V., Smith, D.C., Mposkos, E.
Raman spectroscopic and microscopic criteria for the distinction of microdiamonds in ultrahigh-pressure metamorphic rocks from diamonds in sample preparation materials.
Mineral variations from Mediterranean lamproites: major element compositions and first indications from trace elements in phlogopites, olivines and clinopyroxenes.
Journal of Metamorphic Geology, in press available, 44p.
Europe, Bulgaria
Gneiss - diamonds
Abstract: Evidence for ultrahigh-pressure metamorphism (UHPM) in the Rhodope Metamorphic Complex comes from occurrence of diamond in pelitic gneisses, variably overprinted by granulite facies metamorphism, known from several areas of the Rhodopes. However, tectonic setting and timing of UHPM are not interpreted unanimously. Linking age to metamorphic stage is a prerequisite for reconstruction of these processes. Here we use monazite in diamond-bearing gneiss from Chepelare (Bulgaria) to date the diamond-forming UHPM event in the Central Rhodopes. The diamond-bearing gneiss comes from a strongly deformed, lithologically heterogeneous zone (Chepelare Mélange) sandwiched between two migmatized orthogneiss units, known as Arda-I and Arda-II. Diamond, identified by Raman micro-spectroscopy, shows the characteristic band mostly centred between 1332 and 1330 cm?1. The microdiamond occurs as single grains or polyphase diamond + carbonate inclusions, rarely with CO2. Thermodynamic modelling shows that garnet was stable at UHP conditions of 3.5-4.6 GPa and 700-800 °C, in the stability field of diamond, and was re-equilibrated at granulite facies/partial melting conditions of 0.8-1.2 GPa and 750-800 °C. The texture of monazite shows older central parts and extensive younger domains which formed due to metasomatic replacement in solid residue and/or overgrowth in melt domains. The monazite core compositions, with distinctly lower Y, Th and U contents, suggest its formation in equilibrium with garnet. The U-Th-Pb dating of monazite using electron microprobe analysis yielded a c. 200 Ma age for the older cores with low Th, Y, U and high La/Nd ratio, and a c. 160 Ma age for the dominant younger monazite enriched in Th, Y, U and HREE. The older age of around 200 Ma is interpreted as the timing of UHPM whereas the younger age of around 160 Ma as granulite facies/partial melting overprint. Our results suggest that UHPM occurred in Late Triassic to Early Jurassic time, in the framework of collision and subduction of continental crust after the closure of Palaeotethys.
Petrik, I., Janak, M., Froitzheim, N., Georgiev, N., Yoshida, K., Sasinkova, V., Konecny, P., Milovska, S.
Triassic to Early Jurassic ( c. 200Ma) UHP metamorphism in the Central Rhodopes: evidence from U-Pb dating of monazite in diamond bearing gneiss from Chepelare ( Bulgaria).
Journal of Metamorphic Geology, Vol. 34, 3, pp. 265-291.
Abstract: We report on the Lu-Hf and Re-Os isotope systematics of a well-characterized suite of spinel and garnet pyroxenites from the Gföhl Unit of the Bohemian Massif (Czech Republic, Austria). Lu-Hf mineral isochrons of three pyroxenites yield undistinguishable values in the range of 336-338 Ma. Similarly, the slope of Re-Os regression for most samples yields an age of 327 ± 31 Ma. These values overlap previously reported Sm-Nd ages on pyroxenites, eclogites and associated peridotites from the Gföhl Unit, suggesting contemporaneous evolution of all these HT-HP rocks. The whole-rock Hf isotopic compositions are highly variable with initial ?Hf values ranging from ? 6.4 to + 66. Most samples show a negative correlation between bulk rock Sm/Hf and ?Hf and, when taking into account other characteristics (e.g., high 87Sr/86Sr), this may be explained by the presence of recycled oceanic sediments in the source of the pyroxenite parental melts. A pyroxenite from Horní Kounice has decoupled Hf-Nd systematics with highly radiogenic initial ?Hf of + 66 for a given ?Nd of + 7.8. This decoupling is consistent with the presence of a melt derived from a depleted mantle component with high Lu/Hf. Finally, one sample from Be?váry plots close to the MORB field in Hf-Nd isotope space consistent with its previously proposed origin as metamorphosed oceanic gabbro. Some of the websterites and thin-layered pyroxenites have variable, but high Os concentrations paralleled by low initial ?Os. This reflects the interaction of the parental pyroxenitic melts with a depleted peridotite wall rock. In turn, the radiogenic Os isotope compositions observed in most pyroxenite samples is best explained by mixing between unradiogenic Os derived from peridotites and a low-Os sedimentary precursor with highly radiogenic 187Os/188Os. Steep increase of 187Os/188Os at nearly uniform 187Re/188Os found in a few pyroxenites may be connected with the absence of primary sulfides, but the presence of minor late stage sulfide-bearing veinlets likely associated with HT-HP metamorphism at crustal conditions.
Petrik, I., Janak, M., Froitzheim, N., Georgiev, N., Yoshida, K., Sasinkova, V., Konecny, P., Milovska, S.
Triassic to Early Jurassic ( c. 200Ma) UHP metamorphism in the central Rhodopes: evidence from U-Pb-Th dating of monazite in diamond bearing gneiss from Chepelare Bulgaria.
Journal of Metamorphic Geology, Vol. 34, 3, pp. 265-291.
Miner's in Russia's Pomorie area produced 2.6 million carats of diamonds in first half of 2016. Severalmaz Alrosa 0.9 million and Archangel LUKOIL 1.7 million
Earth and Planetary Science Letters, Vol. 454, pp. 121-131.
Europe, Czech Republic
Bohemian Massif
Abstract: Carbonatites are peculiar magmatic rocks with mantle-related genesis, commonly interpreted as the products of melting of CO2-bearing peridotites, or resulting from the chemical evolution of mantle-derived magmas, either through extreme differentiation or secondary immiscibility. Here we report the first finding of anatectic carbonatites of crustal origin, preserved as calcite-rich polycrystalline inclusions in garnet from low-to-medium pressure migmatites of the Oberpfalz area, SW Bohemian Massif (Central Europe). These inclusions originally trapped a melt of calciocarbonatitic composition with a characteristic enrichment in Ba, Sr and LREE. This interpretation is supported by the results of a detailed microstructural and microchemical investigation, as well as re-melting experiments using a piston cylinder apparatus. Carbonatitic inclusions coexist in the same cluster with crystallized silicate melt inclusions (nanogranites) and COH fluid inclusions, suggesting conditions of primary immiscibility between two melts and a fluid during anatexis. The production of both carbonatitic and granitic melts during the same anatectic event requires a suitable heterogeneous protolith. This may be represented by a sedimentary sequence containing marble lenses of limited extension, similar to the one still visible in the adjacent central Moldanubian Zone. The presence of CO2-rich fluid inclusions suggests furthermore that high CO2 activity during anatexis may be required to stabilize a carbonate-rich melt in a silica-dominated system. This natural occurrence displays a remarkable similarity with experiments on carbonate-silicate melt immiscibility, where CO2 saturation is a condition commonly imposed.
Abstract: The generation of strongly potassic melts in the mantle is generally thought to require the presence of phlogopite in the melting assemblage. In the Mediterranean region, trace element and isotope compositions indicate that continental crustal material is involved in the generation of many potassium-rich lavas. This is clearest in ultrapotassic rocks like lamproites and shoshonites, for which the relevant chemical signals are less diluted by extensive melting of peridotite. Furthermore, melting occurs here in young lithosphere, so the continental crust was not stored for a long period of time in the mantle before reactivation. We have undertaken two types of experiments to investigate the reaction between crust and mantle at 1000-1100 °C and 2-3 GPa. In the first, continental crustal metasediment (phyllite) and depleted peridotite (dunite) were juxtaposed as separate blocks, whereas in the second, the same rock powders were intimately mixed. In the first series, a clear reaction zone dominated by orthopyroxene was formed between dunite and phyllite but no hybridized melt could be found, whereas analyzable pools of hybridized melt occurred throughout the charges in the second series. Melt compositions show high abundances of Rb (100-220 ppm) and Ba (400-870 ppm), and consistent ratios of Nb/Ta (10-12), Zr/Hf (34-42), and Rb/Cs (28-34), similar to bulk continental crust. These experiments demonstrate that melts with as much as 5 wt% K2O may result from reaction between melts of continent-derived sediment and depleted peridotite at shallow mantle depths without the need for phlogopite or any other potassic phase in the residue.
Abstract: The Carboniferous sub-platform Tajno alkaline-carbonatite intrusion is located within a narrow alkaline magmatic belt, which trends E–W from SW Lithuania to NE Poland, along the southern rim of the Mesoproterozoic A–type Mazury Complex. The Tajno pluto–volcanic massif comprises clinopyroxenite cumulates and syenites that are crosscut by carbonatite veins of variable thickness. An emplacement age for the carbonatite has been obtained based on zircon U–Pb and pyrrhotite Re–Os from albitites crosscut by the intrusion. Both ages cluster at 354–345Ma, which corresponds to the Tournaisian Epoch of the Early Carboniferous Period. The carbonatite is 5 to 20Ma younger than the Kola Province, Russian Federation [1]. The current Tajno pluto-volcanic massif lies under ~600m of a Meso–Cenozoic cover. Carbonatite igneous systems are formed by processes of partial melting in metasomatised lithospheric mantle, and are associated with mantle plumes. This implies that a specific geochemical footprint may be spread throughout the host rocks and overlying sedimentary cover by post–emplacement processes. This is of key importance for carbonatite mineral exploration under cover. The Tajno carbonatitic veins do not contain typical accessory minerals (e.g. pyrochlore, perovskite, zirconolite, baddeleyite) that are classically found in other carbonatites. Instead, REE-bearing minerals such as burbankite, parisite, synchysite and bastnaesite are common. This explains its low Nb content. By contrast, fluorite is abundant as cement in the carbonatite breccia.This new study of alkaline-carbonatite rock assemblages is focused on: (1) characterise Tajno's isotopic, REE and HFSE footprint based on petrographic and geochemical observations of apatite and titanite; and (2) increase the understanding of Tajno–type carbonatitic intrusions in the region, and determine if such intrusions can be detected under the sedimentary cover by geochemical techniques. [1] Demaiffe et al.,(2013) The Journal of Geology 12, (1), 91–104
Central European carbonatites under cover: insights for mineral exploration from the Tajno alkaline intrusions, NE Poland.
Abstract: Various combinations of diamond, moissanite, zircon, corundum, rutile and titanitehave been recovered from the Bulqiza chromitites. More than 10 grains of diamond have been recovered, most of which are pale yellow to reddish–orange to colorless. The grains are all 100–300 ?m in size and mostly anhedral, but with a range of morphologies including elongated, octahedral and subhedral varieties. Their identification was confirmed by a characteristic shift in the Raman spectra between 1325 cm?1 and 1333 cm?1, mostly at 1331.51 cm?1 or 1326.96 cm?1. This investigation extends the occurrence of diamond and moissanite to the Bulqiza chromitites in the Eastern Mirdita Ophiolite. Integration of the mineralogical, petrological and geochemical data of the Bulqiza chromitites suggests their multi–stage formation. Magnesiochromite grains and perhaps small bodies of chromitite formed at various depths in the upper mantle, and encapsulated the ultra–high pressure, highly reduced and crustal minerals. Some oceanic crustal slabs containing the magnesiochromite and their inclusion were later trapped in suprasubduction zones, where they were modified by tholeiitic and boninitic arc magmas, thus changing the magnesiochromite compositions and depositing chromitite ores in melt channels.
Abstract: The Cameca 1280-HR large geometry SIMS instrument is a highly versatile analytical tool which can support a broad range of geochemical applications. Research using the Potsdam 1280 instrument focuses primarily on isotope ratio determinations in geomaterials. Optimized measurement protocols have already been established for ?18O determinations in zircon, and we are also working towards routine oxygen isotope determinations for quartz, calcite, mica, apatite and titanite. The primary challenge in developing such measurement systems are the identification and characterization of suitable reference materials (RMs), and this is made particularly challenging due to the matrix dependent ion yields of the SIMS ion source. Here we wish to report our progress towards establishing new analytical protocols for the determination of ?13C in both diamond and moissanite. In the case of diamond, our facility possesses three natural RMs with which we are able to produce data with a typical analytical repeatability of ?0.15 ‰ (1sd). An inter-comparison of our three diamond RMs demonstrates an overall data quality of better than 0.5‰ in terms of systematic offset between the various materials characterized using gas source mass spectrometry (Palot et al., 2012). A single such ?13C determination in diamond requires 80 s of data acquisition and involves a test portion mass of ?400 pg of material. In-house diamond reference materials for ?15N calibration allow us to measure this isotopic system to a total analytical uncertainty of ± 1.6 ‰ (1sd) at nitrogen concentrations reaching down to 250 ?g/g. Due to the relatively low abundance of nitrogen in diamonds, such isotope ratio determinations require around 9 minutes of data collection. With respect to ?13C determinations in moissanite, we use a kimberlitic SiC as calibrant (Mathez et al., 1995), on which we achieve a repeatability of ?0.2 ‰ (1sd) on a ?350 pg test portion mass. Total data acquisition time for such measurements is 80 s. We are currently in the process of developing a second moissanite RM based on a synthetic, coarse-grained powder. We will also investigate this new material for its ?30Si characteristics.
Abstract: In recent years diamonds and other unusual minerals (carbides, nitrides, metal alloys and native elements) have been recovered from mantle peridotites and chromitites (both high-Cr chromitites and high-Al chromitites) from a number of ophiolites of different ages and tectonic settings. Here we report a similar assemblage of minerals from the Skenderbeu massif of the Mirdita zone ophiolite, west Albania. So far, more than 20 grains of microdiamonds and 30 grains of moissanites (SiC) have been separated from the podiform chromitite. The diamonds are mostly light yellow, transparent, euhedral crystals, 200-300 ?m across, with a range of morphologies; some are octahedral and cuboctahedron and others are elongate and irregular. Secondary electron images show that some grains have well-developed striations. All the diamond grains have been analyzed and yielded typical Raman spectra with a shift at ?1325 cm?1. The moissanite grains recovered from the Skenderbeu chromitites are mainly light blue to dark blue, but some are yellow to light yellow. All the analyzed grains have typical Raman spectra with shifts at 766 cm?1, 787 cm?1, and 967 cm?1. The energy spectrums of the moissanites confirm that the grains are composed entirely of silicon and carbon. This investigation expands the occurrence of diamonds and moissanites to Mesozoic ophiolites in the Neo-Tethys. Our new findings suggest that diamonds and moissanites are present, and probably ubiquitous in the oceanic mantle and can provide new perspectives and avenues for research on the origin of ophiolites and podiform chromitites.
Earth and Planetary Science Letters, Vol. 498, pp. 387-396.
Europe, Bulgaria
moissanite
Abstract: Terrestrial moissanite (SiC) is widely reported as an ultra-high pressure mineral occurring in kimberlites, diamonds and ultramafic/mafic rocks of mantle origin. However, the conditions of crystallization remain largely unknown. Moreover, dozens of SiC occurrences have been reported from continental crust sources such as granitoids, andesite-dacite volcanic rocks and their breccia, metasomatic and metamorphic rocks, and even limestones. The validity of many of these reports is still debated primarily due to possible contaminations from the widespread use of synthetic SiC abrasives in samples preparation. Indeed, reports of well-documented in-situ occurrences of moissanite in association with co-existing minerals are still scarce. The only condition of moissanite formation that is agreed upon is that extremely reducing media are required (e.g. 4.5-6 log units below the iron-wustite buffer). Here, we report the new occurrence of moissanite that was found in-situ within the garnet-staurolite-mica schists of Topolovgrad metamorphic group of Triassic age in Southern Bulgaria. The 10-300 ?m moissanite crystals are situated within 0.1-1.2 mm isolated clusters, filled with amorphous carbon and nanocrystalline graphite. Most of moissanite crystals are 15R (rhombohedral) and 6H (hexagonal) polytypes, and one prismatic crystal, found within them, exhibits unusual concentric polytypical zoning with core (15R), intermediate zone (6H) and rim (3C-cubic). Experimental data show that this type of polytypical zonation is likely due to a decrease in temperature (or/and pressure?) and changes in Si/C ratio. Indeed, amphibolite facies metamorphism (500-580?°C - garnet-staurolite zone) followed by a subsequent cooling during the retrograde stage of green schist facies metamorphism (?400-500?°C) could have provided a change in temperature. The SiC containing clusters exhibit evidence that they are pre-metamorphic, and we hypothesize that their protolith was a "lack shale" material likely rich in carbon, hydrocarbon and terrigenous silica. The latter served as a source of isolated chemically-reduced media, which is required for SiC formation. Other concepts to explain moissanite occurrences in metasedimentary rocks are also discussed. Importantly, our findings show that the formation conditions of moissanite are likely more variable than previously recognized.
Mineralogy and Petrology, Vol. 112, 5, pp. 603-616.
Europe, Austria
subduction
Abstract: Mafic layers displaying transition between clinopyroxenite and eclogite within peridotite from felsic granulite in the Bohemian Massif (Lower Austria) have been investigated. The mafic-ultramafic bodies shared a common granulite facies metamorphism with its hosting felsic rocks, but they still preserve evidence of eclogite facies metamorphism. The selected mafic layer for this study is represented by garnet with omphacite in the core of coarse-grained clinopyroxene, while fine-grained clinopyroxene in the matrix is diopside. In addition, garnet contains inclusions of omphacite, alkali feldspars, hydrous and other phases with halogens and/or CO2. Textural relations along with compositional zoning in garnet from the clinopyroxenite-eclogite layers favour solid-state recrystallization of the precursor minerals in the inclusions and formation of garnet and omphacite during subduction. Textures and major and trace element distribution in garnet indicate two stages of garnet growth that record eclogite facies and subsequent granulite facies overprint. The possible model explaining the textural and compositional changes of minerals is that the granulite facies overprint occurred after formation and exhumation of the eclogite facies rocks.
Abstract: Lamprophyres represent hydrous alkaline mantle melts that are a unique source of information about the composition of continental lithosphere. Throughout southwest Britain, post-Variscan lamprophyres are (ultra)potassic with strong incompatible element enrichments. Here we show that they form two distinct groups in terms of their Sr and Nd isotopic compositions, occurring on either side of a postulated, hitherto unrecognized terrane boundary. Lamprophyres emplaced north of the boundary fall on the mantle array with ?Nd ?1 to +1.6. Those south of the boundary are enriched in radiogenic Sr, have initial ?Nd values of ?0.3 to ?3.5, and are isotopically indistinguishable from similar-aged lamprophyres in Armorican massifs in Europe. We conclude that an Armorican terrane was juxtaposed against Avalonia well before the closure of the Variscan oceans and the formation of Pangea. The giant Cornubian Tin-Tungsten Ore Province and associated batholith can be accounted for by the fertility of Armorican lower crust and mantle lithosphere.
Abstract: Our discovery of moissanite grains in a peralkaline syenite from the Água de Pau Volcano (São Miguel, Azores Islands, Portugal) represents the first report of this mineral in present day oceanic geodynamic settings. Raman spectroscopy and single-crystal X-ray diffraction show the presence of both the 6H and 4H polytypes with the predominance of the first one. The distribution of trace elements is homogeneous, except for Al and V. Azorean moissanite often hosts rounded inclusions of metallic Si and other not yet identified metallic alloys. A process involving a flushing of CH4-H2 ultra-reducing fluids in the alkaline melts might be considered as a possible mechanism leading to the formation of natural SiC, thus calling for strongly reducing conditions that were locally met in the crust-mantle beneath the São Miguel Island.
Abstract: LakeDiamond, a Swiss-based company that grows ultra pure diamonds and transforms them for high-tech applications, is currently developing a system that could revolutionize the use of civilian drones. According to a story in phys.org, the Swiss company is testing the use of small lab-grown diamond in recharging drones mid-flight through a laser beam. The laser beam, guided by a tracking system, can recharge photovoltaic cells on the drones’ surface. Recently, LakeDiamond’s project was included among ten projects supported for two years by the Swiss Space Office. Currently, batteries of drones - especially propeller drones - can keep the drones in flight for up to 15 minutes at a time. Using a high-power laser that cannot damage human skin or eyes, LakeDiamond’s technology is built around lab-grown diamonds used as as the optical component on a booster, which is also composed of reflective material and a small metal plate to absorb the heat. According to the pice, “the diamonds are able to transfer heat to a small metal plate that dissipates it, while at the same time reflecting light in such a way as to create a laser beam”. The new diamond-based system could have other potential applications, such as charging and transmitting data to satellites. Although the future for LakeDiamond’s project looks bright, its remote recharging system works in the lab “but will require further development and refinement before it’s ready for field use”. The company also has to work out how to recharge large drones, and how to deal with some expected problems - such as the drone flying behind an obstacle and being cut off from its laser energy source.
Abstract: Garnet chemistry provides a well-established tool in the discrimination and interpretation of sediment provenance. Current discrimination approaches, however, (i) suffer from using less variables than available, (ii) subjective determination of discrimination fields with strict boundaries suggesting clear separations where in fact probabilities are converging, and (iii) significant overlap of compositional fields of garnet from different host-rock groups. The new multivariate discrimination scheme is based on a large database, a hierarchical discrimination approach involving three steps, linear discriminant analysis at each step, and the five major host-rock groups to be discriminated: eclogite- (A), amphibolite- (B) and granulite- (C) facies metamorphic rocks as well as ultramafic (D) and igneous rocks (E). The successful application of statistical discrimination approaches requires consideration of the a priori knowledge of the respective geologic setting. This is accounted for by the use of prior probabilities. Three sets of prior probabilities (priors) are introduced and their advantages and disadvantages are discussed. The user is free to choose among these priors, which can be further modified according to the specific geologic problem and the level of a priori knowledge. The discrimination results are provided as integrated probabilities of belonging to the five major host-rock groups. For performing calculations and results a supplementary Excel® spreadsheet is provided. The discrimination scheme has been tested for a large variety of examples of crystalline rocks covering all of the five major groups and several subgroups from various geologic settings. In most cases, garnets are assigned correctly to the respective group. Exceptions typically reflect the peculiarities of the regional geologic situation. Evaluation of detrital garnets from modern and ancient sedimentary settings of the Western Gneiss Region (Norway), Eastern Alps (Austria) and Albertine Rift (Uganda) demonstrates the power to reflect the respective geologic situations and corroborates previous results. As most garnet is derived from metamorphic rocks and many provenance studies aim at reconstructing the tectonic and geodynamic evolution in the source area, the approach and the examples emphasize discrimination of metamorphic facies (i.e., temperature-pressure conditions) rather than protolith composition.
Abstract: Our discovery of moissanite grains in a peralkaline syenite from the Água de Pau Volcano (São Miguel, Azores Islands, Portugal) represents the first report of this mineral in present day oceanic geodynamic settings. Raman spectroscopy and single-crystal X-ray diffraction show the presence of both the 6H and 4H polytypes with the predominance of the first one. The distribution of trace elements is homogeneous, except for Al and V. Azorean moissanite often hosts rounded inclusions of metallic Si and other not yet identified metallic alloys. A process involving a flushing of CH4-H2 ultra-reducing fluids in the alkaline melts might be considered as a possible mechanism leading to the formation of natural SiC, thus calling for strongly reducing conditions that were locally met in the crust-mantle beneath the São Miguel Island.
Abstract: Geophysical investigations and laboratory experiments provide strong evidence for subduction of ancient oceanic crust, and geological and mineralogical observations suggest that subducted oceanic crust is recycled into the upper mantle. This model is supported by some direct petrologic and miner-alogical evidence, principally the recovery of super-deep diamonds from kimberlites and the presence of crustal materials in ophiolitic chromitites and peridotites, but many details are still unclear. Here we report the discovery of ophiolite-hosted diamonds in the podiform chromitites of the Skenderbeu massif of the Mirdita ophiolite in the western part of Neo-Tethys. The diamonds are characterized by exceedingly light C isotopes (?13CPDB ~ -25‰), which we interpret as evidence for subduction of organic carbon from Earth's surface. They are also characterized by an exceptionally large range in ? 15Nair (-12.9‰ to +25.5‰), accompanied by a low N aggregation state. Materials sparsely included in diamonds include amorphous material, Ni-Mn-Co alloy, nanocrystals (20 × 20 nm) of calcium silicate with an orthorhombic perovskite structure (Ca-Pv), and fluids. The fluids coexisting with the alloy and Ca-Pv provide clear evidence that the diamonds are natural rather than synthetic. We suggest that the Skenderbeu diamonds nucleated and grew from a C-saturated, NiMnCo-rich melt derived from a subducted slab of ocean crust and lithosphere in the deep mantle, at least in the diamond stability field, perhaps near the top of the mantle transition zone. The subsequent rapid upward transport in channeled networks related to slab rollback during subduction initiation may explain the formation and preservation of Skenderbeu diamonds. The discovery of diamonds from the Mirdita ophiolite not only provides new evidence of diamonds in these settings but also provides a valuable opportunity to understand deep cycling of subducted oceanic crust and mantle composition.
Abstract: Diamonds have been discovered in mantle peridotites and chromitites of six ophiolitic massifs along the 1300 km?long Yarlung?Zangbo suture (Bai et al., 1993; Yang et al., 2014; Xu et al., 2015), and in the Dongqiao and Dingqing mantle peridotites of the Bangong?Nujiang suture in the eastern Tethyan zone (Robinson et al., 2004; Xiong et al., 2018). Recently, in?situ diamond, coesite and other UHP mineral have also been reported in the Nidar ophiolite of the western Yarlung?Zangbo suture (Das et al., 2015, 2017). The above?mentioned diamond?bearing ophiolites represent remnants of the eastern Mesozoic Tethyan oceanic lithosphere. New publications show that diamonds also occur in chromitites in the Pozanti?Karsanti ophiolite of Turkey, and in the Mirdita ophiolite of Albania in the western Tethyan zone (Lian et al., 2017; Xiong et al., 2017; Wu et al., 2018). Similar diamonds and associated minerals have also reported from Paleozoic ophiolitic chromitites of Central Asian Orogenic Belt of China and the Ray?Iz ophiolite in the Polar Urals, Russia (Yang et al., 2015a, b; Tian et al., 2015; Huang et al, 2015). Importantly, in?situ diamonds have been recovered in chromitites of both the Luobusa ophiolite in Tbet and the Ray?Iz ophiolite in Russia (Yang et al., 2014, 2015a). The extensive occurrences of such ultra?high pressure (UHP) minerals in many ophiolites suggest formation by similar geological events in different oceans and orogenic belts of different ages. Compared to diamonds from kimberlites and UHP metamorphic belts, micro?diamonds from ophiolites present a new occurrence of diamond that requires significantly different physical and chemical conditions of formation in Earth's mantle. The forms of chromite and qingsongites (BN) indicate that ophiolitic chromitite may form at depths of >150?380 km or even deeper in the mantle (Yang et al., 2007; Dobrthinetskaya et al., 2009). The very light C isotope composition (?13C ?18 to ?28‰) of these ophiolitic diamonds and their Mn?bearing mineral inclusions, as well as coesite and clinopyroxene lamallae in chromite grains all indicate recycling of ancient continental or oceanic crustal materials into the deep mantle (>300 km) or down to the mantle transition zone via subduction (Yang et al., 2014, 2015a; Robinson et al., 2015; Moe et al., 2018). These new observations and new data strongly suggest that micro?diamonds and their host podiform chromitite may have formed near the transition zone in the deep mantle, and that they were then transported upward into shallow mantle depths by convection processes. The in?situ occurrence of micro?diamonds has been well?demonstrated by different groups of international researchers, along with other UHP minerals in podiform chromitites and ophiolitic peridotites clearly indicate their deep mantle origin and effectively address questions of possible contamination during sample processing and analytical work. The widespread occurrence of ophiolite?hosted diamonds and associated UHP mineral groups suggests that they may be a common feature of in?situ oceanic mantle. The fundamental scientific question to address here is how and where these micro?diamonds and UHP minerals first crystallized, how they were incorporated into ophiolitic chromitites and peridotites and how they were preserved during transport to the surface. Thus, diamonds and UHP minerals in ophiolites have raised new scientific problems and opened a new window for geologists to study recycling from crust to deep mantle and back to the surface.
Chemical Geology, doi: 10.1016/ j.chemgeo .2019.119290 46p. Pdf
Europe, Czech Republic, Germany, Poland, Austria
lamproites
Abstract: Orogenic lamproites represent a group of peralkaline, ultrapotassic and perpotassic mantle-derived igneous rocks that hold the potential to sample components with extreme compositions from highly heterogeneous orogenic mantle. In our pilot study, we present highly siderophile element (HSE) and ReOs isotope systematics of Variscan orogenic lamproites sampled in the territories of the Czech Republic, Austria and Poland, i.e., from the termination of the Moldanubian and Saxo-Thuringian zones of the Bohemian Massif. Orogenic lamproites of the Bohemian Massif are distinguished by variably high contents of SiO2, high Mg# and predominant mineral associations of K-rich amphibole and Fe-rich microcline. The HSE show (i) consistently very low contents in all investigated orogenic lamproites compared to the estimated concentrations in majority of mid-ocean ridge basalts, hotspot-related volcanic rocks (e.g., ocean island basalts, continental flood basalts, komatiites, some intraplate alkaline volcanic rocks such as kimberlites and anorogenic lamproites) and arc lavas, and (ii) marked differences in relative and absolute HSE abundances between the samples from the Moldanubian and Saxo-Thuringian Zone. Such a regional dependence in HSE from mantle-derived melts is exceptional. Orogenic lamproites have highly variable and high initial suprachondritic 187Os/188Os values (up to 0.631) compared with rather chondritic to subchondritic Os isotope values of the young lithospheric mantle below the Bohemian Massif. The highly radiogenic Os isotope component in orogenic lamproites may be derived from preferential melting of metasomatised vein assemblages sitting in depleted peridotite mantle. This process appears to be valid generally in the petrogenesis of orogenic lamproites both from the Bohemian Massif and from the Mediterranean area. As a specific feature of the orogenic lamproites from the Bohemian Massif, originally ultra-depleted mantle component correlative with remnants of the Rheic Ocean lithosphere in the Moldanubian Zone was metasomatised by a mixture of evolved and juvenile material, whereas the lithospheric mantle in the Saxo-Thuringian Zone was enriched through the subduction of evolved crustal material with highly radiogenic Sr isotope signature. As a result, this led to observed unique regionally dependent coupled HSE, RbSr and ReOs isotope systematics.
Abstract: Orogenic lamproites represent a group of peralkaline, ultrapotassic and perpotassic mantle-derived igneous rocks that hold the potential to sample components with extreme compositions from highly heterogeneous orogenic mantle. In our pilot study, we present highly siderophile element (HSE) and ReOs isotope systematics of Variscan orogenic lamproites sampled in the territories of the Czech Republic, Austria and Poland, i.e., from the termination of the Moldanubian and Saxo-Thuringian zones of the Bohemian Massif. Orogenic lamproites of the Bohemian Massif are distinguished by variably high contents of SiO2, high Mg# and predominant mineral associations of K-rich amphibole and Fe-rich microcline. The HSE show (i) consistently very low contents in all investigated orogenic lamproites compared to the estimated concentrations in majority of mid-ocean ridge basalts, hotspot-related volcanic rocks (e.g., ocean island basalts, continental flood basalts, komatiites, some intraplate alkaline volcanic rocks such as kimberlites and anorogenic lamproites) and arc lavas, and (ii) marked differences in relative and absolute HSE abundances between the samples from the Moldanubian and Saxo-Thuringian Zone. Such a regional dependence in HSE from mantle-derived melts is exceptional. Orogenic lamproites have highly variable and high initial suprachondritic 187Os/188Os values (up to 0.631) compared with rather chondritic to subchondritic Os isotope values of the young lithospheric mantle below the Bohemian Massif. The highly radiogenic Os isotope component in orogenic lamproites may be derived from preferential melting of metasomatised vein assemblages sitting in depleted peridotite mantle. This process appears to be valid generally in the petrogenesis of orogenic lamproites both from the Bohemian Massif and from the Mediterranean area. As a specific feature of the orogenic lamproites from the Bohemian Massif, originally ultra-depleted mantle component correlative with remnants of the Rheic Ocean lithosphere in the Moldanubian Zone was metasomatised by a mixture of evolved and juvenile material, whereas the lithospheric mantle in the Saxo-Thuringian Zone was enriched through the subduction of evolved crustal material with highly radiogenic Sr isotope signature. As a result, this led to observed unique regionally dependent coupled HSE, RbSr and ReOs isotope systematics.
Abstract: The emerald mineralization in the Habachtal (Austria) is geologically and tectonically complex, and previous investigators have identified fluid inclusion evidence for a hydrothermal/metamorphic origin for the emeralds. In this paper we report the discovery of emeralds with a distinctly different inclusion population including melt inclusions, which demonstrates that at least some and probably most of the emerald mineralization in the Habachtal occurred from an extremely fluid-rich pegmatite-like aluminosilicate melt under supercritical conditions, at high temperatures and moderate pressures (~700 °C, 5 kbar). This conclusion is based on the presence of very highly-ordered graphite, and extremely water-rich melt inclusions in emerald. The Lorentz distribution of MgCO3 against the water concentration is a very robust proof for the supercritical state. We suggest that the purely metamorphic model, based on the extrapolation of fluid inclusion data to the regional metamorphic conditions (550 °C and 5 kbar) by some previous investigators are inconsistent with our finding of high-temperature indications (well-ordered graphite, high-temperature fluid inclusions and melt inclusions). This apparent conflict suggests a more complex situation and requires a re-investigation of the emerald genesis in the Habachtal deposit.
Earth and Planetary Science Letters, Vol. 543, 116328 14p. Pdf
Europe, Switzerland, Alps
boron diamonds
Abstract: Understanding the volatile cycles at convergent margins is fundamental to unravel the Earth's evolution from primordial time to present. The assessment of fluid-mobile and incompatible element uptake in serpentinites via interaction with seawater and subduction-zone fluids is central to evaluate the global cycling of the above elements in the Earth's mantle. Here, we focus on the carbon (C), nitrogen (N) and C isotope compositions of chlorite harzburgites and garnet peridotites deriving from subduction-zone dehydration of former oceanic dehydration of serpentinite - i.e., metaperidotites (Cima di Gagnone, Swiss Central Alps) with the aim of evaluating the contribution of these rocks to the global C-N cycling. These ultramafic rocks, enclosed as lenses in a metasedimentary mélange, represent the destabilization of antigorite and chlorite at high-pressure/temperature (P/T) along a slab-mantle interface. Chlorite- and garnet-bearing rocks have similar ranges in C concentration ([C] = 210 - 2465 ppm and 304 - 659 ppm, respectively), with one magnesite-bearing chlorite harzburgite hosting 11000 ppm C. The average N concentrations ([N]) of the garnet peridotites (54 ± 15 ppm, one standard deviation indicated) are higher than those of the chlorite harzburgites (29 ± 6 ppm). The C of total C (TC) and total organic C (TOC) values of the Gagnone metaperidotites range from -12.2 to -17.8‰ and from -27.8 to -26.8‰, respectively, excluding the magnesite-bearing chlorite harzburgites with higher values of -7.2‰ (TC) and -21.2‰ (TOC). The [C] of these rocks are comparable to those of serpentinites form modern and ancient oceanic environments and with [C] of high-P serpentinites. However, the lack of preserved serpentinite precursors makes it difficult to determine whether release of H2O during high-P breakdown of antigorite and chlorite is coupled with significant C release to fluids. The C values appear to reflect mixing between seawater-derived carbonate and a reduced C source and a contribution from the host metasedimentary rocks ([C] = 301 ppm; [N] = 33 ppm; TC C = -24.4‰; TOC C = -27.0‰) cannot be completely excluded. The C-O isotope composition of the carbonate in magnesite-bearing chlorite harzburgites is compatible with progressive devolatilization at oxidized conditions, whereas the signatures of the majority of the other Gagnone samples appear to reflect different degree of interaction with sedimentary fluids. The [N] of the Gagnone metaperidotites are higher than those of oceanic and subducted serpentinites and show a range similar to that of high-P antigorite-serpentinites from mantle wedges. This enrichment is compatible with fluid-mediated chemical exchange with the surrounding metasedimentary rocks leading to strong modification of the Gagnone metaperidotites' geochemistry during prograde subduction along the slab-mantle interface. Comparing the C data reported in this study with published C values for diamonds, we suggest that the volatile recycling via Gagnone-like metaperidotites in subduction zones could contribute to deep-Earth diamond genesis and in particular to the formation of blue boron (B)-bearing diamonds. Our results highlight that the subduction of secondary peridotites evolved along the slab-mantle interface is a viable mechanism to inject volatiles into the deep mantle, particularly in hotter geothermal regimes such as the ones active during the early Earth's history.
Abstract: Variscan orogenic lamproites in the Bohemian Massif predominantly occur as 1 to 2?m wide and petrographically uniform dykes along the eastern borders of the Moldanubian and Saxo-Thuringian zones. Variscan orogenic lamproites were derived by preferential melting of subduction-related olivine-free metasomatic vein assemblages stabilised in the lithospheric mantle. These lamproitic melts may subsequently undergo extensive differentiation. In this study, we present the first combined petrographic and Sr-Nd-Pb-Li isotope characteristics of a complex lamproite exposed at ca 100?m long profile near Horní Rokytnice (Czech Republic) in the Saxo-Thuringian Zone. This lamproite is characterised by the primary mineral assemblage of K-amphibole + K-feldspar ± aegirine and quartz that petrographically varies from relatively primitive (fine-grained, mafic) to more differentiated (medium- to coarse-grained, felsic) pegmatitic lamproite domains. These domains may represent the product of crystallisation of immiscible liquids that had separated from the mafic melt. The primitive lamproite zone is characterised by the typomorphic minerals - baotite, benitoite, and henrymeyerite. The more differentiated pegmatitic domains are free of aegirine and show replacement of primary red-luminescent (Fe3+-rich) K-feldspar by blue-luminescent (Fe-poor) K-feldspar. Residual fluids rich in Ca, Ti, and HFSE in combination with the decreasing peralkalinity of the lamproite system resulted in the local formation of secondary zircon, titanite and quartz at the expense of the primary Ti-Ba-Zr-K lamproitic mineral assemblages. Lamproites from the Moldanubian and Saxo-Thuringian zones fall on separate mixing trends in the 87Sr/86Sr(t) - ?Nd(t) diagram, which indicates that the mantle beneath these two zones had been metasomatised by different crustal material. The scatter in the peralkalinity index vs. ?7Li diagram indicates that the Li isotope composition is not controlled by mixing of two end members metasome and ambient depleted mantle alone, but may also be affected by late-stage magmatic and hydrothermal processes. The compositionally zoned Horní Rokytnice dyke is special as the petrographically different types show a variation of about 4 ?-units in ?7Li due to dyke-internal processes, such as fractionation, which increases ?7Li in late-stage lamproitic melts, and post-emplacement interaction with fluids that reduced ?7Li in samples that have lost Li. Post-emplacement alteration also led to the disturbance in the Pb isotope systematics of the differentiated orogenic lamproite as indicated by variable over-correction of in situ radiogenic Pb ingrowth.
Abstract: This Tajno alkaline massif (together with the nearby E?k and Pisz intrusions) occurs beneath a thick Mesozoic- Cenozoic sedimentary cover. It has first been recognized by geophysical (magnetic and gravity) investigations, then directly by deep drilling (12 boreholes down to 1800 m). The main rock types identified as clinopyroxenites, syenites, carbonatites, have been cut by later multiphase volcanic /subvolcanic dykes. This massif was characterized as a differentiated ultramafic, alkaline and carbonatite complex, quite comparable to the numerous massifs of the Late Devonian Kola Province of NW Russia [1,2]. Recent geochronological data (U-Pb on zircon from an albitite and Re-Os on pyrrhotite from a carbonatite) indicate that the massif was emplaced at ca. 348 Ma (Early Carboniferous). All the rocks, but more specifically the carbonatites, are enriched in Sr, Ba and LREE, like many carbonatites worldwide but depleted in high field strength elements (Ti, Nb, Ta, Zr). The initial 87Sr/86Sr (0.70370 to 0.70380) and ?Nd(t) (+3.3 to +0.7) isotopic compositions of carbonatites plot in the depleted quadrant of the Nd-Sr diagram, close to “FOcal ZOne” (FOZO) deep mantle domain [1]. The Pb isotopic data (206Pb/204Pb <18.50) do not point to an HIMU (high U/Pb) source. The ranges of C and O stable isotopic compositions of the carbonatites are quite large; some data plot in (or close to) the “Primary Igneous Carbonatite” box while others extend to much higher, typically crustal ?18O and ?13C values.
Geologica Carpathica ** Eng, Vol. 71, 4, pp. 343-360. pdf
Europe, Czech Republic
alkaline rocks
Abstract: Sills of hydrothermally altered alkaline magmatic rock (teschenite) of Lower Cretaceous age at the ?er?ák and ?epišt? sites in the Silesian Unit (Flysch Belt of the Outer Western Carpathians, Czech Republic) host leucocratic dykes and nests which contain accessory minerals enriched in Zr, Nb and REE: Zr-, Nb-rich titanite, zircon, gittinsite, pyrochlore, monazite, REE-rich apatite, epidote, and vesuvianite. Titanite forms wedge-shaped crystals or irregular aggregates enclosed in the analcime groundmass or overgrowths on Zr-rich ferropargasite and taramite or Zr-rich aegirine-augite to aegirine. Titanite crystals show oscillatory or irregular patchy to sector zoning and contain up to 17.7 wt. % ZrO2 and 19.6 wt. % Nb2O5, and ?1.1 wt. % REE2O3. High-field-strength elements (HFSE) are incorporated into the structure of the studied titanite predominantly by substitutions: (i) [6]Ti4+???[6]Zr4+; (ii) [6]Ti4+?+?[6]Al3+???[6]Zr4+?+?[6]Fe3+; and (iii) [6]2Ti4+???[6]Nb5+?+?[6](Al, Fe)3+. Magmatic fractional crystallization, high-temperature hydrothermal autometasomatic overprint and low-temperature hydrothermal alterations resulted in the formation of the HFSE-rich mineral assemblages within the leucocratic teschenites. Autometamorphic processes caused by high-temperature hypersaline aqueous solutions (salinity ~50 wt. %, ~390-510 °C), which were released from the HFSE-enriched residual melt, played a major role in the crystallization of Zr-, Nb-, and REE-rich minerals. The mobilization of HFSE could have occurred either by their sequestration into a fluid phase exsolved from the crystallizing melt or by superimposed alteration processes. The distinctive positive Eu anomaly (EuCN/Eu*?=?1.85) of leucocratic dykes infers possible mixing of Eu2+-bearing magmatic fluids with more oxidized fluids.
Geologica Carpathica ** Eng, Vol. 65, 6, pp. 419-431. pdf doi: 10.15 /geoca-2015-0003
Europe, Czech Republic
alkaline rocks
Abstract: Hydrothermal mineralization hosted by the Lower Cretaceous igneous rock of the teschenite association at Jasenice (Silesian Unit, Flysch Belt, Outer Western Carpathians) occurs in two morphological types - irregular vein filled by granular calcite and regular composite vein formed by both fibrous and granular calcite and minor chlorite, quartz, and pyrite. Crosscutting evidence indicates that the granular veins are younger than the composite vein. The composite vein was formed by two mechanisms at different times. The arrangement of solid inclusions in the marginal fibrous zone suggests an episodic growth by the crack-seal mechanism during syntectonic deformation which was at least partially driven by tectonic suction pump during some stages of the Alpine Orogeny. Both the central part of the composite vein and monomineral veins developed in a brittle regime. In these cases, the textures of vein suggest the flow of fluids along an open fracture. The parent fluids of both types of vein are characterized by low temperatures (Th=66-163 °C), low salinities (0.4 to 3.4 wt. % NaCl eq.), low content of strong REE-complexing ligands, and ?18O and ?13C ranges of + 0.2/+12.5 %. SMOW and -11.8/-14.1 %. PDB, respectively. The parent fluids are interpreted as the results of mixing of residual seawater and diagenetic waters produced by dewatering of clay minerals in the associ-ated flysch sediments. The flow of fluids was controlled by tectonic deformation of the host rock.
Abstract: A review of the compositional features of Tunisia, Algeria, and Morocco phosphorites is proposed in order to assess and compare the paleoenvironmental conditions that promoted the deposit formation as well as provide information about their economic perspective in light of growing worldwide demand. Since these deposits share a very similar chemical and mineralogical composition, the attention was focused on the geochemistry of rare earth elements (REEs) and mostly on ?REEs, Ce and Eu anomalies, and (La/Yb) and (La/Gd) normalized ratios. The REEs distributions reveal several differences between deposits from different locations, suggesting mostly that the Tunisian and Algerian phosphorites probably were part of the same depositional system. There, sub-reducing to sub-oxic conditions and a major REEs adsorption by early diagenesis were recorded. Conversely, in the Moroccan basins, sub-oxic to oxic environments and a minor diagenetic alteration occurred, which was likely due to a different seawater supply. Moreover, the drastic environmental changes associated to the Paleocene-Eocene Thermal Maximum event probably influenced the composition of Northern African phosphorites that accumulated the highest REEs amounts during that span of time. Based on the REEs concentrations, and considering the outlook coefficient of REE composition (Koutl) and the percentage of critical elements in ?REEs (REEdef), the studied deposits can be considered as promising to highly promising REE ores and could represent a profitable alternative source for critical REEs.
Abstract: Geophysical investigations and laboratory experiments show evidence for possible subduction of ancient oceanic crust. Geological and mineralogical observations suggest that subducted oceanic crust is recycled into the upper mantle. The subduction is supported by the recovery of super?deep diamonds from kimberlites and the presence of crustal materials in ophiolitic chromitites and their host peridotites. What is the mechanism? Here we report the new discovery of ophiolite?hosted diamonds in the podiform chromitites within the Skenderbeu massif from the Mirdita ophiolite in the western part of Neo?Tethys (Fig. 1). The diamonds are characterized by exceedingly light C isotopes (?13CPDB ? ?25‰), which can be interpreted as evidence for subduction of organic carbon from Earth's surface. The diamonds are also characterized by an exceptionally large range in ?15Nair (?12.9‰ to +25.5‰), accompanied by a low N aggregation state (Fig. 2). On the other hand, materials sparsely included in diamonds include amorphous material, Ni?Mn?Co alloy, nanocrystals (20 nm×20 nm) of calcium silicate with an orthorhombic perovskite structure (Ca?Pv), and fluids (Fig. 3). We consider that the Skenderbeu diamonds nucleated and grew from a C?saturated, NiMnCo?rich melt derived from a subducted slab of ocean crust and lithosphere in the deep mantle environment. The environment is in the diamond stability field or near the top of the mantle transition zone. The new discovery of diamonds from the Mirdita ophiolite provides a valuable opportunity to understand deep cycling of subducted oceanic crust and mantle (i.e., composition and process).
Abstract: Farré?de?Pablo et al. (2018) report a new occurrence of in situ microdiamonds enclosed in chromite from ophiolitic chromitite pods hosted in the Tehuitzingo serpentinite of southern Mexico. The discovery enlarges the number of occurrence of the ophiolite?hosted microdiamonds to 7 countries in the world, including India (Das, 2015, 2017), Albania (Xiong et al., 2017; Wu et al., 2017), Turkey (Lian et al., 2017), Myanmar (Chen et al., 2018), Russia (Yang et al., 2015), and China (Bai et al., 1993; Xu et al., 2009). The microdiamonds occur in ophiolitic podiform chromitites and peridotites, and are generally interpreted as UHP phases formed at pressures > 4 GPa (Yang et al., 2014; Griffin et al., 2016; Das et al., 2017). However, Farré?de?Pablo et al. (2018) conclude that the Tehuitzingo diamonds were formed under low?temperature and low?pressure conditions during serpentinization, which challenges the current knowledge of diamond formation. Here, we discuss several lines of evidence that do not support the authors' conclusion.
Geological Society, London Special Publication, doi.org/10.1144/SP513-2021-36 49p. Pdf
Europe, Italy, France, Spain, Serbia, Macedonia, Turkey
lamproites
Abstract: High-MgO lamproite and lamproite-like (i.e., lamprophyric) ultrapotassic rocks are recurrent in the Mediterranean and surrounding regions. They are associated in space and time with ultrapotassic shoshonites and high-K calc-alkaline rocks. This magmatism is linked with the geodynamic evolution of the westernmost sector of the Alpine-Himalaya collisional margin, which followed the closure of the Tethys ocean. Subduction-related lamproites, lamprophyres, shoshonites and high-K calc-alkaline suites were emplaced in the Mediterranean region in the form of shallow level intrusions (e.g., plugs, dykes, and laccoliths), and small volume lava flows, with very subordinate pyroclastic rocks, starting from the Oligocene, in the Western Alps (Northern Italy), through the Late Miocene in Corsica (Southern France) and in Murcia-Almeria (South-Eastern Spain), to the Plio-Pleistocene in Southern Tuscany and Northern Latium (Central Italy), in the Balkan peninsula (Serbia and Macedonia), and in the Western Anatolia (Turkey). The ultrapotassic rocks are mostly lamprophyric, but olivine latitic lavas with a clear lamproitic affinity are also found, as well as dacitic to trachytic differentiated products. Lamproite-like rocks range from slightly silica under-saturated to silica over-saturated composition, have relatively low Al2O3, CaO, and Na2O contents, resulting in plagioclase-free parageneses, and consist of abundant K-feldspar, phlogopite, diopsidic clinopyroxene and highly forsteritic olivine. Leucite is generally absent and it is rarely found only in the groudmasses of Spanish lamproites. Mediterranean lamproites and associated rocks share an extreme enrichment in many incompatible trace elements and depletion in High Field Strength Elements and high, and positively correlated Th/La and Sm/La ratios. They have radiogenic Sr and unradiogenic Nd isotope compositions, high 207Pb over 206Pb and high time integrated 232Th/238U. Their composition requires an originally depleted lithospheric mantle source metasomatised by at least two different agents: i) a high Th/La and Sm/La (i.e., SALATHO) component deriving from lawsonite-bearing, ancient crustal domains likely hosted in mélanges formed during the diachronous collision of the northward drifting continental slivers from Gondwana; ii) a K-rich component derived from a recent subduction and recycling of siliciclastic sediments. These metasomatic melts produced a lithospheric mantle source characterised by network of felsic and phlogopite-rich veins, respectively. Geothermal readjustment during post-collisional events induced progressive melting of the different types of veins and the surrounding peridotite generating the entire compositional spectrum of the observed magmas. In this complex scenario, orogenic Mediterranean lamproites represent rocks that characterise areas that were affected by multiple Wilson cycles, as observed in the the Alpine-Himalayan realm.
Abstract: This manuscript presents results of the newest petrographic, mineralogical and bulk chemical, as well as H, C and O stable isotope study of carbonatites and associated silicate rocks from the Tajno Massif (NE Poland). The Tajno Intrusion is a Tournaisian-Visean ultramafic-alkaline-carbonatite body emplaced within the Paleoproterozoic rocks of the East European Craton (EEC). Carbonatites of the Tajno Massif can be subdivided into the calciocarbonatite (calcite), ferrocarbonatite (ankerite), and breccias with an ankerite-fluorite matrix. Due to location at the cratonic margin and abundance in the REE, Tajno classifies (Hou et al., 2015) as the carbonatite-associated REE deposit (CARD), and more precisely as the Dalucao-Style orebody (the breccia-hosted orebody). High Fe2O3 (13.8 wt%), MnO (2.1 wt%), total REE (6582 ppm), Sr (43895 ppm), Ba (6426 ppm), F (greater than10000 ppm) and CO2 contents points for the involvement of the slab - including pelagic metalliferous sediments - in the carbonatites formation. Spatial relations and Sr isotope composition ((87Sr/86Sr)i = 0.7043-0.7048; Wiszniewska et al., 2020) of alkali clinopyroxenite and syenite suggest that these are products of differentiation of the magma, generated by the initial melting of the SCLM due to influx of F-rich fluids from subducted marine sediments. Carbonatites Sr isotope composition ((87Sr/86Sr)i = 0.7037-0.7038), and Ba/Th (16-20620) and Nb/Y (0.01-6.25) ratios, link their origin with a more advanced melting of the SCLM, triggered by CO2-rich fluids from the subducted AOC and melts from sediments. The Tajno Massif - and coeval mafic-alkaline intrusions - age, high potassic composition, and location along the craton margin nearly parallel the Variscan deformation front, are suggesting Variscan subduction beneath the EEC. The oxygen isotope compositions of clinopyroxene (?18O value = 5.2‰) and alkali feldspar (?18O value = 5.7‰), from alkali clinopyroxenite and foid syenite, respectively, are consistent with mantle-derived magmas. Isotopic compositions of carbonatites and breccias (carbonate ?18O = 8.7‰ to 10.7‰; ?13C = -4.8‰ to ?0.4‰) span from values of primary carbonatites to carbonatites affected by a fractionation or sedimentary contamination. The highest values (?18O = 10.7‰; ?13C = -0.4‰) were reported for breccia cut by numerous veins confirming post-magmatic hydrothermal alteration. The lowest carbonate ?18O (9.3‰ to 10.7‰) and ?13C (?5.0‰ to ?3.8‰) values are reported for veins in alkali clinopyroxenites, whereas the highest ?18O (11.2‰) and ?13C (?1.2‰ to ?1.1‰) values are for veins in syenites and trachytes. Isotopic composition of veins suggests hydrothermal origin, and interaction with host mantle-derived rocks, as well as country rocks. In silicate rocks of the Tajno Massif, fluid influx leads to the development of Pb, Zn, Cu, Ag, Au sulfide mineralization-bearing stockwork vein system, with carbonate, silicate and fluorite infilling the veins. Bulk-rock contents of molybdenum (925 ppm), rhenium (905 ppb) and palladium (29 ppb) are notable. The Re-rich molybdenite association with galena, pyrite and Th-rich bastnäsite in carbonate veins is similar as in Mo deposits associated with carbonatites, implying the mantle source of Mo and Re.
Abstract: The sources of emeralds used in Roman jewelry as well as jeweled pieces (including crowns and book covers) dating from antiquity to the Middle Ages and before the discovery of the Colombian emerald deposits in the sixteenth century remain an ongoing matter of controversy. Two potential localities dominate the discussion: the mines in the Eastern Desert of Egypt and the Habachtal deposit in Austria. The first published reference to the Habachtal emerald occurrence dates to 1797. The majority of publications from the nineteenth and twentieth centuries agree that Samuel Goldschmidt, a jeweler from Vienna, purchased the mountain area in which the Habachtal emerald occurrence is located and commenced mining soon thereafter, in the early 1860s. A later period from the mid-1890s to about 1914 is frequently mentioned, in which the mine was owned and worked by an English company. However, further details regarding both periods and the various transitions of ownership and further circumstances of emerald mining before World War I are rarely given and often are not consistent, and activities in the times before the 1860s and between 1870 and 1890 are obscure. Using a wide selection of materials from Austrian and German archives, largely unpublished, the author seeks to trace the history of the Habachtal mine through several centuries and to fill gaps left by existing publications.
