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1
Bazylev, B. A., G. V. Ledneva, Ya V. Bychkova, N. N. Kononkova, T. G. Kuz’mina und T. V. Romashova. „Estimation of the content and composition of trapped melt in dunite“. Геохимия 64, Nr. 5 (23.05.2019): 471–85. http://dx.doi.org/10.31857/s0016-7525645471-485.
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A method was developed for the quantitative estimation of the content of trapped melt in various dunite types and the composition of this melt on the basis of the major- and trace-element characteristics of the dunites and compositions of their chrome spinels. Our approach is advantageous over the method based on clinopyroxene geochemistry and clinopyroxene–melt partition coefficients for the contents of the light REE and more incompatible elements in melt, comparable with it for the middle REE, and possibly less accurate for the heavy REE and Sr. The estimated mean contents of trapped melt in dunites from ophiolite and concentrically zoned complexes are 1.0–1.5 wt %, which is probably typical of various dunite types, including cumulate dunites from layered complexes. These values are an order of magnitude higher than previous estimates. The correspondence between the compositions of calculated trapped melts in dunites and real natural melts indicates that the estimated contents of trapped melt in dunites are realistic, and the mineral–melt partition coefficients that were used in our calculations are valid for the complexes considered in this paper. In general, the proposed method is suitable for serpentinized dunites, including dunitic serpentinites.
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Malafosse, Maxime, Amandine Pascal und Serge Amabile. „Commoning with blockchain. The Ğ1 libre currency/Duniter case“. Systèmes d'information & management Volume 27, Nr. 2 (18.11.2022): 7–34. http://dx.doi.org/10.3917/sim.222.0007.
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Çina, A. „MINERALOGY OF CHROMITITE, BULQIZA ULTRAMAFIC MASSIF, ALBANIAN OPHIOLITIC COMPLEX“. Bulletin of the Geological Society of Greece 43, Nr. 5 (31.07.2017): 2577. http://dx.doi.org/10.12681/bgsg.11665.
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Ultramafic massif of Bulqiza belongs to Eastern Jurassic Albanian ophiolite belt of IAT-BSV- type. This massif is the most important chromite-bearing ore. The mantle ultramafics have extremely refractory nature. This is due to the high partial fusion of upper mantle which is depleted in CaO and Al2 O3 . The chromitite is situated to different parts of ultramafic pile, from bottom Cpx harzburgites up to massive dunites and cumulate ultramafic but the mainly chromite potential belongs to mantle harzburgite –dunite level and to transition dunites partly. The chromite is chiefly of Cr-rich metallurgical type. The atomic ratios of chromite , Fo of olivine and some physical properties of them vary according to the chromitite setting and reflects the evolution of Ol-Sp equilibrium process depended of the chromite concentration, from baren dunitic lenses towards dunite envelops of the ore bodies and the interstitial and inclusions of olivine within chromite grains. Two particular chromite deposits are the Bulqiza- Batra tabular folded ore body and Shkalla, pencil –like ore body.
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Akizawa, Norikatsu, Asuka Yamaguchi, Kenichiro Tani, Akira Ishikawa, Ryo Fujita und Sung Hi Choi. „Highly refractory dunite formation at Gibbs Island and Bruce Bank, and its role in the evolution of the circum-Antarctic continent“. Canadian Mineralogist 59, Nr. 6 (01.11.2021): 1731–53. http://dx.doi.org/10.3749/canmin.2100030.
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ABSTRACT The continental margin is of profound importance as it records continental growth by accretion of orogenic magmas and following continental rifting. A high degree of mantle melting due to hydrous fluid input is expected to simultaneously stimulate continental growth and lower the intrinsic density of the mantle than more fertile mantle, which in turn isolates the continental lithosphere from the convective mantle. The mantle peridotites from Gibbs Island (South Shetland Islands) and Bruce Bank in the Drake Passage provide us an insight into the tectonic history in the circum-Antarctic region. To elucidate the continental growth of Antarctica, we present geochemical data of eight dunites from Gibbs Island and one dunite from Bruce Bank, including Re–Os isotope and highly siderophile element compositions. The dunites are severely affected by serpentinization as evidenced by antigorite + brucite or lizardite (loss on ignition = LOI ranging from 3 to 34 wt.%) but contain primary euhedral to subhedral chromites with or without spherical inclusions. The chromites rarely form lens-shaped aggregates. A dunite from Gibbs Island contains fresh olivine grains filling a fracture in the chromite with low LOI (3 wt.%), indicating a deserpentinization origin from a precursor serpentinized dunite. The dunites show highly depleted bulk-rock major element compositions (Mg/Si = 1.4–1.6 and Al/Si = 0.004–0.01 for Gibbs Island dunites, Mg/Si = 0.66 and Al/Si = 0.008 for Bruce Bank dunite), overlapping a compositional field defined by forearc peridotites. The positive correlation in Re/Ir–LOI space corroborates Re input during the later serpentinization process. The 187Os/188Os ratios of the dunites range from 0.11907 to 0.14493. Phanerozoic Re-depletion (melt depletion) ages of ca. 535–129 Ma are recorded in the Gibbs Island dunites, except for one with a Mesoproterozoic Re-depletion age of ca. 1.2 Ga. Since there exists serpentinization-related perturbation of Re, the ages provide minimum time estimates for melt depletion events. The early Paleozoic melt depletion is inferred to have occurred at a very early stage of Antarctic Peninsula formation in response to plate convergence along the margin of Gondwana, whereas the Mesoproterozoic Re-depletion age reflects convecting mantle heterogeneity unrelated to any nearby crust-forming events. The petrographic characteristics of the chromites and highly depleted nature of the dunites are attributed to melt–peridotite reaction in a subduction zone setting. A feasible interpretation for the dunite formation is that the mantle had experienced two stages of melting with the final stage occurring along the Gondwana continental margin in the subduction zone setting. Resultant highly refractory lithospheric mantle was later displaced and dispersed during the Gondwana breakup. Widespread existence of the dunite may be attributed to multi-stage melt depletion along the continental margin.
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Motov, Andrey, Yury Malakh und Ilya Voropaev. „Nickel anomalies and gold-quartz mineralization in dunite-harzburgite massifs of the Pervomaisko-Verkhoturinskaya area, Central Urals“. Ores and metals, Nr. 2 (16.08.2021): 90–98. http://dx.doi.org/10.47765/0869-5997-2021-10012.
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Along with some gold-quartz deposits hosted by dunite-harzburgite massifs elsewhere in the Urals, elevated Ni concentrations were revealed within the ore field of the Anna gold-(sulfide)-quartz deposit localized in weathered oxidized dunites and harzburgites of the Pervomaisky complex (συO2p) in the Pervomaisko-Verkhoturie district of the Central Urals. The spatial association of Au and Ni concentrations in dunites-harzburgites may be attributed to a partial inheritance of Ni-controlling tectonic dislocations by those hosting gold mineralization. Therefore, the combination of halos of Ni and Au concentrations in dunite-harzburgite massifs is a favorable indicator of areas prospective for discovery of goldquartz mineralization.
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Ishimaru, S., und S. Arai. „Possibility of titanium transportation within a mantle wedge: formation process of titanoclinohumite in Fujiwara dunite in Sanbagawa belt, Japan“. Solid Earth Discussions 4, Nr. 1 (27.01.2012): 203–39. http://dx.doi.org/10.5194/sed-4-203-2012.
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Abstract. Titinoclinohumite-bearing dunites from Fujiwara, the Sanbagawa metamorphic belt of high-pressure type, Japan, were described to examine the possibility of Ti mobility during metasomatism within the mantle wedge. The Fujiwara dunite body and surrounding high-pressure Sanbagawa schists possibly form a subduction complex, and the dunites are a good analogue to the mantle wedge overlying the slab. The Fujiwara dunites are of deserpentinization origin; the deserpentinized olivine is high in Fo (up to 96) and low in NiO (0.2 to 0.3 wt %), and contains magnetite inclusions. Titanoclinohumites are associated with the deserpentinized olivine, as lamellar intergrowth or veinlets, up to 1 cm in width. Other metamorphic minerals include antigorite, brucite, chlorite, ilmenite, perovskite, Ti-rich ludwigite, and carbonates. The protolith of the Fujiwara dunite was partially serpentinized cumulative dunites from intra-plate magma, containing relatively low-Fo (85 to 86) olivines and TiO2-rich (up to 3 wt %) chromian spinels. The metamorphic olivines and titanoclinohumites contain micro-inclusions of methane (CH4) with or without serpentine and brucite. The source of Ti for titanoclinohumite was possibly the Ti-rich chromian spinel, but Ti was mobile through hydrocarbon-rich fluids, which were activated during the metamorphism. The hydrocarbons, of which remnants are carbonates and methane micro-inclusions, were derived from carbonaceous materials or bitumen, possibly incorporated in the precursory serpentinized and brecciated peridotite (= the protolith for the Fujiwara dunites) before subduction. Ti can be mobile in the mantle wedge if hydrocarbons are available from the subducted slab.
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Stepanov, S. Yu, R. S. Palamarchuk, D. A. Khanin, D. A. Varlamov und A. V. Antonov. „Character of the distribution and the form of finding platinum group elements in the chromitites of the Svetloborsky, Veresovoborsky and Kamenushensky clinopyroxenite-dunite intrusions (Middle Urals)“. Moscow University Bulletin. Series 4. Geology, Nr. 5 (28.10.2018): 60–69. http://dx.doi.org/10.33623/0579-9406-2018-5-60-69.
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The note describes the mineralogical and geochemical features of platinum-bearing vein-disseminated and massive chromitite from the dunites of the Svetloborsky, Veresovoborsky and Kamenushensky clinopyroxenite-dunite intrusions located in the Middle Urals. It was found that platinum in chromitites has an extremely uneven distribution and is concentrated in the form of Pt-Fe intermetallides. The texture-structural features of the chromitites studied, the distribution of platinum group elements and the composition of chromoshpinelides in them are similar to the detailed study of the chromitites of the zonal clinopyroxenite-dunite intrusions of the Urals (Nizhnetagilsky) and Koryakia (Gal’moenan).
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Krasnobaev, A. A., P. M. Valizer und A. L. Perchuk. „ORDOVICIAN AGE OF DUNITE-WEHRLITE-CLINOPYROXENITE BENDED COMPLEX OF NURALI MASSIF (SOUTHERN URALS, RUSSIA): SHRIMP U-PB ZIRCON DATING“. Moscow University Bulletin. Series 4. Geology, Nr. 1 (28.02.2018): 60–70. http://dx.doi.org/10.33623/0579-9406-2018-1-60-70.
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We present the data of geochemistry and geochronology of zircons from wehrlites and clinopyroxenites from dunite-wehrlite-clinopyroxenite bended complex of the base of crustal section of ophiolite Nurali massif. The U-Pb age of the bended complex is 450±4 Ma which is different from the previous data. Zircons from the studied rocks have complimentary REE patterns and similar U-Pb ages to lherzolites and dunites from mantle section of the Nurali massif.
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Kuzmin, I. A., R. S. Palamarchuk, V. M. Kalugin, A. V. Kozlov und D. A. Varlamov. „Chromite-platinum mineralization of clinopyroxenite-dunite massif Zheltaya Sopka, North Ural“. МИНЕРАЛОГИЯ (MINERALOGY), Nr. 3 (Dezember 2020): 46–59. http://dx.doi.org/10.35597/2313-545x-2020-6-4-3.
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The paper presents the new data on platinum group minerals (PGM) and chromite from the Zheltaya Sopka massif, North Urals. Few chromite bodies along with specifc composition of chromite indicate weak ore-forming processes developed in this massif. Minakawaite (RhSb) and chengdeite (Ir3Fe) are found for the frst time in the Uralian Platinum Belt. The PGM assemblage of the Zheltaya Sopka massif is compared with that of the Iov, Yuda, and Sosnovsky dunite massifs of the northern part of the Uralian Platinum Belt. As a result, similar PGM assemblages with domi¬nant minerals of late assemblages are established in dunites of the Zheltaya Sopka massif. Chromites of the massif show no evident chromite-magnetite trend typical of clinopyroxenite-dunite massifs of the Urals and are relatively enriched in Cr2O3 and Al2O3 in comparison with chromite of other UPB massifs.
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Yang, Sai-Hong, Ben-Xun Su, Xiao-Wen Huang, Dong-Mei Tang, Ke-Zhang Qin, Yang Bai, Patrick Sakyi und Melesse Alemayehu. „Platinum-Group Mineral Occurrences and Platinum-Group Elemental Geochemistry of the Xiadong Alaskan-Type Complex in the Southern Central Asian Orogenic Belt“. Minerals 8, Nr. 11 (01.11.2018): 494. http://dx.doi.org/10.3390/min8110494.
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Alaskan-type complexes commonly contain primary platinum-group element (PGE) alloys and lack base-metal sulfides in their dunite and chromite-bearing rocks. They could therefore host PGE deposits with rare sulfide mineralization. A detailed scanning electron microscope investigation on dunites from the Xiadong Alaskan-type complex in the southern Central Asian Orogenic Belt revealed: various occurrences of platinum-group minerals (PGMs) that are dominated by inclusions in chromite grains containing abundant Ru, Os, S and a small amount of Pd and Te, indicating that they mainly formed prior to or simultaneously with the crystallization of the host minerals; A few Os–Ir–Rurich phases with iridium/platinum-group element (IPGE) alloy, anduoite (Ru,Ir,Ni)(As,S)2−x and irarsite (IrAsS) were observed in chromite fractures, and as laurite (RuS2) in clinopyroxene, which was likely related to late-stage hydrothermal alteration. The rocks in the Xiadong complex display large PGE variations with ∑PGE of 0.38–112 ppb. The dunite has the highest PGE concentrations (8.69–112 ppb), which is consistent with the presence of PGMs. Hornblende clinopyroxenite, hornblendite and hornblende gabbro were all depleted in PGEs, indicating that PGMs were likely already present at an early phase of magma and were mostly collected afterward in dunites during magma differentiation. Compared with the regional mafic–ultramafic intrusions in Eastern Tianshan, the Xiadong complex show overall higher average PGE concentration. This is consistent with the positive PGE anomalies revealed by regional geochemical surveys. The Xiadong complex, therefore, has potential for PGE exploration.
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Cocomazzi, Grieco, Tartarotti, Bussolesi, Zaccarini, Crispini und Science Team. „The Formation of Dunite Channels within Harzburgite in the Wadi Tayin Massif, Oman Ophiolite: Insights from Compositional Variability of Cr-Spinel and Olivine in Holes BA1B and BA3A, Oman Drilling Project“. Minerals 10, Nr. 2 (13.02.2020): 167. http://dx.doi.org/10.3390/min10020167.
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Holes BA1B and BA3A were drilled into the Wadi Tayin Massif, southern ophiolite complex of Oman, a fragment of the Tethyan oceanic lithosphere obducted onto the Arabian continent. Within the sequence, we have studied a portion of the shallow mantle, composed mainly of strongly serpentinised harzburgite that embeds dunitic levels, the biggest being over 150 m thick. The formation of thick dunitic channels, already approached via published structural and mathematical models, is here investigated with a mineral chemistry approach. We focused on Cr-spinel, the only widespread phase preserved during serpentinization, whose TiO2 content displays a wide variability from low in harzburgite, (TiO2 < 0.25 wt. %), typical of non-metasomatised ophiolite mantle, to moderately high in dunite (TiO2 < 1.10 wt. %) characterizing a rock/melt interactions. The high variability of TiO2, accompanied by similar patterns of Cr# and Mg# is observed, in a fractal pattern, at all scales of investigation, from the whole channel scale to the single thin section, where it affects even single grain zonings. Our results suggest that the over 150 m thick dunite channel here investigated was formed by coalescence of different scale melt channels and reaction zones with different sizes, confirming the published structural model.
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Ashchepkov, Igor, Nikolay Medvedev, Nikolay Vladykin, Alexander Ivanov und Hilary Downes. „Thermobarometry and Geochemistry of Mantle Xenoliths from Zapolyarnaya Pipe, Upper Muna Field, Yakutia: Implications for Mantle Layering, Interaction with Plume Melts and Diamond Grade“. Minerals 10, Nr. 9 (26.08.2020): 755. http://dx.doi.org/10.3390/min10090755.
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Minerals from mantle xenoliths in the Zapolyarnaya pipe in the Upper Muna field, Russia and from mineral separates from other large diamondiferous kimberlite pipes in this field (Deimos, Novinka and Komsomolskaya-Magnitnaya) were studied with EPMA and LA-ICP-MS. All pipes contain very high proportions of sub-calcic garnets. Zapolyarnaya contains mainly dunitic xenoliths with veinlets of garnets, phlogopites and Fe-rich pyroxenes similar in composition to those from sheared peridotites. PT estimates for the clinopyroxenes trace the convective inflection of the geotherm (40–45 mW·m−2) to 8 GPa, inflected at 6 GPa and overlapping with PT estimates for ilmenites derived from protokimberlites. The Upper Muna mantle lithosphere includes dunite channels from 8 to 2 GPa, which were favorable for melt movement. The primary layering deduced from the fluctuations of CaO in garnets was smoothed by the refertilization events, which formed additional pyroxenes. Clinopyroxenes from the Novinka and Komsomolskaya-Magnitnaya pipes show a more linear geotherm and three branches in the P-Fe# plot from the lithosphere base to the Moho, suggesting several episodes of pervasive melt percolation. Clinopyroxenes from Zapolyarnaya are divided into four groups according to thermobarometry and trace element patterns, which show a stepwise increase of REE and incompatible elements. Lower pressure groups including dunitic garnets have elevated REE with peaks in Rb, Th, Nb, Sr, Zr, and U, suggesting mixing of the parental protokimberlitic melts with partially melted metasomatic veins of ancient subduction origin. At least two stages of melt percolation formed the inclined PT paths: (1) an ancient garnet semi-advective geotherm (35–45 mW·m−2) formed by volatile-rich melts during the major late Archean event of lithosphere growth; and (2) a hotter megacrystic PT path (Cpx-Ilm) formed by feeding systems for kimberlite eruptions (40–45 mW·m−2). Ilmenite PT estimates trace three separate PT trajectories, suggesting a multistage process associated with metasomatism and formation of the Cpx-Phl veinlets in dunites. Heating associated with intrusions of protokimberlite caused reactivation of the mantle metasomatites rich in H2O and alkali metals and possibly favored the growth of large megacrystalline diamonds.
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Lloyd, F. E., A. D. Edgar, D. M. Forsyth und R. L. Barnett. „The paragenesis of upper-mantle xenoliths from the Quaternary volcanics south-east of Gees, West Eifel, Germany“. Mineralogical Magazine 55, Nr. 378 (März 1991): 95–112. http://dx.doi.org/10.1180/minmag.1991.055.378.08.
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AbstractGroup I xenoliths, orthopyroxene-rich and orthopyroxene-free, contain Cr-spinel and clinopyroxene ± phlogopite, and occur together with Group II clinopyroxenites ± Ti-spinel ± phlogopite in K-mafic pyroclastics southeast of Gees. The petrography and clinopyroxene chemistry of orthopyroxene-rich (opx-rich sub-group) Group I xenoliths is consistent with an ‘original’ harzburgitic mantle that has been transformed to lherzolite by the addition of endiopside. In harzburgites, orthopyroxenes are reacting to diopside + olivine + alkali-silicate melt, and, by inference, the orthopyroxene-free (opx-free subgroup) Group I, dunite-wehrlite series can be linked to the opx-rich sub-group via this reaction. Progressive enrichment of dunitic material in endiopside-diopside has resulted in the formation of wehrlite. Phlogopite is titaniferous and occurs as a trace mineral in opx-rich, Group I xenoliths, whereas substantial phlogopite vein-networks are confined to the opx-free sub-group (dunite-wehrlite series). Interstitial, alkali-felsic glass occurs are veins within, and as extensions of, the phlogopite networks. Clinopyroxenes in phlogopite-veined xenoliths are decreased in Mg/(Mg + FeTotal) (mg) and Cr and increased in Ti, Al and Ca, compared with clinopyroxenes in xenoliths which have trace phlogopite. It is proposed that harzburgitic and dunitic mantle has been infiltrated by a Ca- and alkalirich, hydrous silicate melt rather than an ephemeral carbonatite melt. Dunite has been transformed to phlogopite wehrlite by the invasion of a Ca-, Al-, Ti- and K-rich, hydrous silicate melt. Ca-activity was high initially in the melt and was reduced by clinopyroxene precipitation. This resulted in enhanced K-activity which led to phlogopite veining of clinopyroxene-rich mantle. Group II phlogopite clinopyroxenites contain Ti-spinel and salites that are distinct in their Ti, Al and Cr contents from endiopsides and diopsides in Group I xenoliths. It is unlikely that these Group II xenoliths represent the culmination of the infiltration processes that have transformed dunite to wehrlite, nor can they be related to the host melt. These xenoliths may have crystallised from Ca- and K-bearing, hydrous silicate melts in mantle channelways buffered by previously precipitated clinopyroxene and phlogopite. Gees lherzolites contain pyroxenes and spinel with distinctly lower Al contents than these same minerals in lherzolites described previously from other West Eifel localities, which may reflect a distinctive lithology and/or processes of modification for the Gees mantle.
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Edwards, Stephen J. „Boninitic and tholeiitic dykes in the Lewis Hills mantle section of the Bay of Islands ophiolite: implications for magmatism adjacent to a fracture zone in a back-arc spreading environment“. Canadian Journal of Earth Sciences 32, Nr. 12 (01.12.1995): 2128–46. http://dx.doi.org/10.1139/e95-166.
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A detailed, integrated field, petrographic, and geochemical study of the Springers Hill area of the Bay of Islands ophiolite exposed in the Lewis Hills was undertaken to explain the anomalously high abundance of veins and dykes of chromitite, orthopyroxenite, and clinopyroxenite, and their associated dunites, hosted by a refractory harzburgite–dunite mixture. A geodynamic situation is presented, which is constrained by previous studies requiring formation of the Springers Hill mantle section at a ridge–fracture zone intersection, and the whole of the Bay of Islands ophiolite within a back-arc spreading environment. The veins and dykes formed during magmatism at the ridge–fracture zone intersection and along the fracture zone, as progressively hotter, more fertile (richer in clinopyroxene) asthenosphere ascended and was channelled up and along the fracture zone wall. Shallow melting of refractory harzburgite in the presence of subduction-derived hydrous fluids produced light rare earth element (LREE)-enriched boninitic magma from which crystallized chromitites, some of their associated dunites, and orthopyroxenites. This melting event dehydrated much of the mantle in and around the zone of partial melting. Continued rise and shallow partial melting of hotter, more fertile mantle under conditions of variable hydration generated LREE-depleted, low-Ti tholeiitic magma. This magma crystallized olivine clinopyroxenite, some associated dunite, and clinopyroxenite. The final magmatic event may have involved partial melting of mid-ocean-ridge basalt-bearing mantle at depth, ascent of the magma, and formation of massive wehrlite–lherzolite bodies at the ridge–fracture zone intersection and along the fracture zone. Ridge–fracture zone intersections in suprasubduction-zone environments are sites of boninitic and tholeiitic magmatism because refractory asthenospheric mantle may melt as it is channelled with subduction-derived fluids to shallow depths by the old, cold lithospheric wall of the fracture zone. Heat for melting is provided by the ascent of hotter, more fertile mantle. Extremely refractory magmas do not occur along "normal" oceanic fracture zones because volumes of highly refractory mantle are much less, subduction-derived hydrous fluids are not present, and fracture zone walls extend to shallower depths.
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Abbou-Kebir, Khadidja, Shoji Arai, Ahmed Hassan Ahmed und Georges Ceuleneer. „Spinel-free and spinel-poor dunite veins crosscutting the Wadi Rajmi ophiolite chromitite (northern Oman ophiolite)“. Bulletin de la Société Géologique de France 184, Nr. 3 (01.03.2013): 261–66. http://dx.doi.org/10.2113/gssgfbull.184.3.261.
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Abstract Peculiar dunitic veins almost or totally free of spinels crosscut a podiform chromitite ore body in the Wadi Rajmi, northern Oman ophiolite. They probably originated from a komatiitic melt which was oversaturated in Fo≤94 olivines and which evolved to precipitate simultaneously both chromian spinels, with Cr# ranging from 0.6 to 0.8, and Fo91-93 olivines. The absence or the low modal amounts of spinels are possibly governed by a Cr-undersaturation state of the involved melt which crystallized under relatively low cooling rates to generate the spinel-free and the spinel-poor dunites. A shallow and highly depleted mantle source for this komatiitic melt was envisaged during a converging tectonic regime, initiated earlier in the dynamic history of the Oman ophiolite.
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Chayka, Ivan F., Nikolay I. Baykov, Vadim S. Kamenetsky, Anton V. Kutyrev, Evgenii V. Pushkarev, Adam Abersteiner und Vasily D. Shcherbakov. „Volcano–Plutonic Complex of the Tumrok Range (Eastern Kamchatka): An Example of the Ural-Alaskan Type Intrusion and Related Volcanic Series“. Minerals 13, Nr. 1 (15.01.2023): 126. http://dx.doi.org/10.3390/min13010126.
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Zoned plutons, composed of dunites, pyroxenites, and gabbroic rocks, have been referred to as the Ural-Alaskan type complexes (UA-complexes) and occur in numerous paleo-arc settings worldwide. Many of these complexes are source rocks for economic placers of platinum-group metals. Thus, it is important to understand how UA-complexes form and the origin and behavior of platinum-group elements (PGEs). It is widely assumed that the UA-complexes result from differentiation of supra-subduction high-Ca high-Mg sub-alkaline magmas. However, there is a lack of direct evidence for the existence and differentiation of such magmas, mainly because cases of UA-complexes being spatially and temporally linked to co-genetic volcanics are unknown. We studied an UA-complex from the Tumrok range (Eastern Kamchatka) where a dunite-clinopyroxenite-gabbro assemblage is spatially and temporary related to high-Ca volcanics (i.e., picrites and basalts). Based on the mineral and chemical composition of the rocks, mineral chemistry, and composition of melt inclusions hosted within rock-forming minerals, we conclude that the intrusive assemblage and the volcanics are co-genetic and share the same parental magma of ankaramitic composition. Furthermore, the compositions of the plutonic rocks are typical of UA-complexes worldwide. Finally, the rocks studied exhibit a full differentiation sequence from olivine-only liquidus in picrites and dunites to eutectic crystallization of diopside or hornblende, plagioclase, and K-Na feldspar in plagio-wehrlites and gabbroic rocks. All these results make the considered volcano–plutonic complex a promising case for petrological studies and modelling of UA-complex formation.
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Antonicelli, Marta, Riccardo Tribuzio, Tong Liu und Fu-Yuan Wu. „Contaminating melt flow in magmatic peridotites from the lower continental crust (Rocca d'Argimonia sequence, Ivrea–Verbano Zone)“. European Journal of Mineralogy 32, Nr. 6 (04.11.2020): 587–612. http://dx.doi.org/10.5194/ejm-32-587-2020.
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Abstract. The lower continental crust section of the Ivrea–Verbano Zone (Italian Alps) was intruded by a ∼ 8 km thick gabbroic–dioritic body (Ivrea Mafic Complex) in the Upper Carboniferous–Lower Permian, in conjunction with the post-collisional transtensional regime related to the Variscan orogeny. In the deepest levels of the Ivrea Mafic Complex, several peridotite–pyroxenite sequences considered of magmatic origin are exposed. We present here a petrological–geochemical investigation of the peridotites from the largest magmatic ultramafic sequence of the Ivrea Mafic Complex, locally called Rocca d'Argimonia. In spite of the widespread subsolidus re-equilibration under granulite facies conditions, most likely reflecting a slow cooling evolution in the lower continental crust, the Rocca d'Argimonia peridotites (dunites to harzburgites and minor clinopyroxene-poor lherzolites) typically retain structures and microstructures of magmatic origin. In particular, the harzburgites and the lherzolites typically show poikilitic orthopyroxenes enclosing partially dissolved olivine and minor spinel. Olivine has forsterite proportion diminishing from the dunites to the harzburgites and the lherzolites (90 mol % to 85 mol %) and negatively correlating with δ18O (+5.8 ‰ to +6.6 ‰). Gabbronorite dykes locally crosscut the peridotites and show millimetre-scale thick, orthopyroxenite to websterite reaction zones along the contact with host rocks. We propose that the Rocca d'Argimonia peridotites record a process of reactive melt flow through a melt-poor olivine-rich crystal mush or a pre-existing dunite. This process was most likely responsible for the olivine dissolution shown by the poikilitic orthopyroxenes in the harzburgites–lherzolites. We infer that the reactively migrating melts possessed a substantial crustal component and operated at least at the scale of ∼ 100 m.
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Surin, T. N. „Late-devonian sakhara dunite-clinopiroxenite-gabbro complex (East Magnitogorsk zone, South Urals): petrological-mineralogical features and geodynamic setting“. МИНЕРАЛОГИЯ (MINERALOGY) 7 (April 2021): 40–53. http://dx.doi.org/10.35597/2313-545x-2021-7-1-3.
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The relevance of the work is caused by necessary regional analysis of magmatic evolution of the East Magnitogorsk belt and refnement of ideas on geodynamics of the South Urals. The geology and petrochemical-mineralogical features of the Sakhara dunite-clinopyroxenite-gabbro complex in the South Urals are characterized in the paper. Its late Frasnian age is substantiated. The composition of olivine, clinopyroxene and chromite in rocks of the complex are determined. The restite nature of dunites is proved. It is shown that rocks of the complex are similar to those of the Urals platinum belt and belong to Ural-Alaskan type. It is concluded that the complex formed in island-arc geodynamic setting and in the beginning of the formation of a mature island arc. The location of massifs of the complex is an additional argument in favor of a western dip (in the present-day coordinates) of a subduction paleozone at the moment of its formation. Crystallization diferentiation was a leading mechanism of petrogenesis of rocks of the complex.
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Appel, C. C., P. W. U. Appel und H. R. Rollinson. „Complex chromite textures reveal the history of an early Archaean layered ultramafic body in West Greenland“. Mineralogical Magazine 66, Nr. 6 (Dezember 2002): 1029–41. http://dx.doi.org/10.1180/0026461026660075.
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Abstract Massive chromitite, banded chromitite and disseminated chromite grains are found in a ˜3800 Ma layered ultrabasic body in West Greenland. The major part of the ultrabasite is dominated by dunite. In the upper exposed part, harzburgite and sheets of gabbro-anorthosite occur. Chromite grains in dunites, and in massive and banded chromitites are homogeneous, with increasing Fe contents upwards in the intrusion. In harzburgites chromites show unusual and very complex textural relationships, with two generations ofchromites one replacing the other, and both exhibiting exsolution textures. In harzburgites, an Fe-rich chromite crystallized first. This first chromite exsolved two spinel phases in a very fine-scale pattern and ilmenite lamellae in a trellis pattern. The Fe-rich chromite was later partly replaced by Al-rich chromite, which crystallized contemporaneously with formation of a late gabbro-anorthositic melt. Subsequently, the Al-rich chromite exsolved a very fine-scale magnetite-rich phase. The exsolutions in the first generation chromite were formed under magmatic conditions. Exsolution of ilmenite lamellae in Fe-rich spinel was caused by oxidation under magmatic conditions.
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Mues-Schumacher, U., J. Keller, V. A. Kononova und P. J. Suddaby. „Mineral chemistry and geochronology of the potassic alkaline ultramafic Inagli complex, Aldan Shield, eastern Siberia“. Mineralogical Magazine 60, Nr. 402 (Oktober 1996): 711–30. http://dx.doi.org/10.1180/minmag.1996.060.402.02.
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AbstractThe Inagli complex, one of several Mesozoic intrusive complexes of the Aldan Shield (Siberian Platform), exhibits a concentric structure comprising several alkaline ultramafic rock-types. A central dunite body is surrounded by olivine- and phlogopite-clinopyroxenites forming an inner rim. The outer rim consists of different shonkinitic and malignitic rocks. The K-Ar ages obtained for the whole complex vary around 132 Ma.The dunites and clinopyroxenites are characterized by cumulate textures. With increasing modal abundances of clinopyroxene and subordinate phlogopite, the rocks develop to olivine-clinopyroxenite, shonkinite, and malignite with intercumulus potassium feldspar. Mineralogical characterization of the rocks suggests they evolved by fractional crystallization. The highly forsteritic olivines (Fo up to 95) require a melt as magnesian as mg# 87.1, representing ±26 wt.% MgO. The parental melt is likely to be an olivine-, H2O- and K2O-rich picritic liquid of shoshonitic character. Major and trace element systematics show high LILE/LREE and LREE/HFSE ratios indicating the involvement of a subduction zone component in the genesis of these rocks.
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Bazylev, B. A., M. V. Portnyagin, D. P. Savelyev, G. V. Ledneva und N. N. Kononkova. „Subduction and Oceanic Magmatism Records in Plutonic Rocks of the Kamchatsky Mys Ophiolite, Eastern Kamchatka“. Петрология 31, Nr. 3 (01.05.2023): 300–320. http://dx.doi.org/10.31857/s0869590323030020.
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The paper presents petrographic, mineralogical, and geochemical data on dunites, pyroxenites, peridotites, and gabbroids of the Kamchatsky Mys ophiolite. These data were acquired to distinguish cogenetic assemblages of igneous rocks, gain an insight into their geodynamic settings, and test various criteria of genetic links between the different magmatic rocks of ophiolites. The ultramafic and mafic rocks are shown to belong to two series, which differ in the compositions of the primary minerals, bulk rocks, and estimated trapped melts. The rocks of these series are found out to have been produced by geochemically different melts in different geodynamic settings, and during different episodes of mantle magmatism. The rocks of the high-Ti series (gabbro of the Olenegorsk massif, dunite and melanogabbro xenoliths in them, and vein gabbro in these xenoliths) crystallized from N-MORB melts in an oceanic spreading center. The rocks of the low-Ti series (dunite, pyroxenite, and gabbro veins in the residual spinel peridotites of the Mount Soldatskaya massif, as well as pyroxenite, peridotite, and gabbro alluvium and diluvium in the central and western parts of the peninsula) crystallized from water-rich boninite melts in relation to initial subduction magmatism. Taken into account the absence of boninite lavas from the Kamchatsky Mys ophiolite, the plutonic ultramafic rocks (including the rocks of the veins) might be the only evidence of subduction boninitic magmatism in the ophiolites. It was demonstrated that conclusions about the geodynamic settings of plutonic ultramafic and mafic rocks and recognition of cogenetic relations of these rocks with spatially associated basalts are more reliable when derived from the compositions of the trapped melts, which are estimated from their bulk geochemistry and primary mineral compositions, than when they are based on the mineral compositions only.
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Rashid, Muhammad Imran, Emad Benhelal, Faezeh Farhang, Michael Stockenhuber und Eric M. Kennedy. „Magnesium Leachability of Mg-Silicate Peridotites: The Effect on Magnesite Yield of a Mineral Carbonation Process“. Minerals 10, Nr. 12 (05.12.2020): 1091. http://dx.doi.org/10.3390/min10121091.
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The aim of this study was to increase feedstock availability for mineral carbonation. Acid dissolution and carbonic acid dissolution approaches were used to achieve higher Mg extractions from peridotites. Acid dissolution studies of raw dunite, heat-activated dunite, heat-transformed dunite, and twin sister dunite have not been reported in the literature. Heat-activated dunite is more reactive as compared to heat-transformed dunite, raw dunite, and twin sister dunite. The fraction of magnesium extracted from heat-activated dunite was 57% as compared to 18% from heat-transformed dunite, 14% from raw dunite, and 11% from twin sister dunite. Similarly, silicon and iron extractions were higher for heat-activated dunite compared to that of heat-transformed dunite, raw dunite, and twin sister dunite. Materials rich in forsterite (twin sister dunite and heat-transformed dunite) showed preferential Mg release and exhibited incongruent dissolution similar to that of forsterite. Heat-activated dunite (amorphous magnesium silicate rich) on the other hand behaved differently and showed congruent dissolution. Olivine did not dissolve under carbonic acid dissolution (with concurrent grinding) and acidic conditions. Under carbonic acid dissolution with concurrent grinding conditions, olivine was partially converted into nanometer sized particles (d10 = 0.08 µm) but still provided 16% Mg extraction during 4 h of dissolution.
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Serov, Pavel A., Tamara B. Bayanova, Ekaterina N. Steshenko, Evgeniy L. Kunakkuzin und Elena S. Borisenko. „Metallogenic Setting and Evolution of the Pados-Tundra Cr-Bearing Ultramafic Complex, Kola Peninsula: Evidence from Sm–Nd and U–Pb Isotopes“. Minerals 10, Nr. 2 (19.02.2020): 186. http://dx.doi.org/10.3390/min10020186.
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The article presents new Sm–Nd and U–Pb geochronological data on rocks of the poorly studied Pados-Tundra Cr-bearing complex. It is part of the Notozero mafic–ultramafic complex (western Kola Peninsula) and occurs at the border of the Paleoproterozoic Lapland Granulite Belt and the Archean Belomorian composite terrain. The Pados-Tundra complex hosts two major zones, the Dunite and Orthopyroxenite Blocks. Dunites are associated with four levels of chromite mineralization. Isotope Sm–Nd studies of dunites, harzburgites, and orthopyroxenites from the central part of the complex have been carried out. The isochron Sm–Nd age on 11 whole-rock samples from a rhythmically layered series of the complex is 2485 ± 38 Ma; the mineral Sm–Nd isochron for harzburgites shows the age of 2475 ± 38 Ma. It corresponds with the time of large-scale rifting that originated in the Fennoscandian Shield. When the rhythmically layered series of the intrusion and its chromite mineralization were formed, hornblendite dykes intruded. The U–Pb and Sm–Nd research has estimated their age at ca. 2080 Ma, which is likely to correspond with the occurrence of the Lapland–Kola Ocean. According to isotope Sm–Nd dating on metamorphic minerals (rutile, amphibole), the age of postmetamorphic cooling of rocks in the complex to 650–600 °C is 1872 ± 76 Ma. The U–Pb age on rutile from a hornblendite dyke (1804 ± 10 Ma) indicates further cooling to 450–400 °C. The conducted research has determined the early Proterozoic age of rocks in the rhythmically layered series in the Pados-Tundra complex. It is close to the age of the Paleoproterozoic ore magmatic system in the Fennoscandian Shield that developed 2.53–2.40 Ga ago. Later episodes of alterations in rocks are directly related to main metamorphic episodes in the region at the turn of 1.9 Ga. Results of the current study expand the geography of the vast Paleoproterozoic East Scandinavian Large Igneous Province and can be applied for further studies of similar mafic–ultramafic complexes.
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Mochalov, A. G., N. V. Berdnikov, O. L. Galankina, P. K. Kepezhinskas, Liu Jinlong und V. O. Krutikova. „MINERALOGY OF PLATINUM GROUP ELEMENTS IN EXPLOSIVE BRECCIAS OF THE POPERECHNOE DEPOSIT (MALYI KHINGAN, RUSSIA)“. Tikhookeanskaya Geologiya 42, Nr. 2 (2023): 88–104. http://dx.doi.org/10.30911/0207-4028-2023-42-2-88-104.
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The results of detailed study of the platinum-group minerals (PGM) from explosive breccias of the Poperechnoe Fe-Mn deposit (the Lesser Khingan Range, Russian Far East) are presented. Native PGMs are dominated by isoferroplatinum; rutheniridosmine, native iridium, platinum, and osmium are less com-mon. Micron-sized segregations of laurite, bowieite, сuproiridsite, cuprorhodsite, hollingworthite, as well as new mineral phases of (Ir,Rh,Os)7 (S,As)13 , (Rh,Ir,Ru) 7(S,As) 13, and Pd 3(Sb,As) were recognized as micro-inclusions in isoferroplatinum and on the surface of its grains. It is shown that the studied PGMs are derived from rocks of ultramafic formations: (1) vein pyroxenites, harzburgites, and dunites of metamorphic and cumulative complexes of the most depleted peridotite varieties of the suprasubduction wedge of island-arc ophiolites and (2) vein pyroxenites of cumulative high-pressure ultramafic complexes of the basement of the ensialic island arc and products of evolution of suprasubduction mantle melts. In terms of PGE contents, the compositions of isoferroplatinum from explosive breccias are divided into four groups: group I: isoferroplatinum of fluid-metamorphogenic genesis from harzburgite, group II: isoferroplatinum of fluid-metamorphogenic genesis from dunites and magmatogenic-fluid-metasomatic genesis from vein pyrox-enites; group III: isoferroplatinum of magmatogenic genesis from chromitites of dunites of the cumulative complex; and group IV: isoferroplatinum with an elevated Pd content, which is likely derived from the melt formed by explosive breccias. Three scenarios of PGM occurrence in the fluid-saturated andesite-dacite melt of explosive breccias at the Poperechnoe deposit are discussed: (1) directly from early ultramafic com-plexes in suprasubduction settings; (2) from the reservoir of ancient platinum placer deposits; and (3) from a mantle wedge above the Mesozoic subduction zone during the generation of initial island-arc melts. The first two petrogenetic models suggest «rejuvenation» of the 190Pt-4He age of isoferroplatinum grains as a result of the thermal effect of the andesite-dacite melt to the age of 125 ± 21 Ma. The third geodynamic scenario suggests that the Lower Cretaceous age of isoferroplatinum marks the processes of metamorphogenic-metasomatic transformation of the dunite-harzburgite mantle wedge and probably corresponds to the age of the subduction magmatism at the Poperechnoe Deposit in particular and within the Lesser Khingan terrane as a whole. PGM associations in andesite-dacite breccias of the Poperechnoe Deposit are a new type of potentially commercial noble-metal mineralization in the Russian Far East, while explosive breccias (fluidoliths) can be used as an exploration guide to discover PGE lode and placer deposits of volcanogenic-explosive genesis in the Russian Federation.
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Bussolesi, Micol, Giovanni Grieco und Evangelos Tzamos. „Olivine–Spinel Diffusivity Patterns in Chromitites and Dunites from the Finero Phlogopite-Peridotite (Ivrea-Verbano Zone, Southern Alps): Implications for the Thermal History of the Massif“. Minerals 9, Nr. 2 (27.01.2019): 75. http://dx.doi.org/10.3390/min9020075.
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The study of Mg–Fe2+ subsolidus exchange between olivine and spinel is a powerful tool to unravel the thermal history of ultramafic rocks. We have implemented such a study using olivine–spinel diffusivity patterns in fresh mineralogical samples from the Finero mafic-ultramafic Complex in the Ivrea-Verbano zone of Northern Italy. Our analytical suite includes chromitites and dunites of the Phlogopite-Peridotite Unit from the core of the Complex. Primary and re-equilibrated olivine and spinel compositions were derived from diffusivity curves calculated by fitting data via an exponential function. Resulting XMg (Mg/(Mg + Fe2+) values were then used for geothermometry. Samples are found to demonstrate a maximum temperature of 849 °C and a minimum temperature of 656 °C; these temperatures coincide with the limits of elemental exchange in this mineralogic system. We were unable to identify primary olivine/spinel compositions related to the original formation of the dunite–chromitite suite during Early Permian metasomatic activity. Temperature of 849 °C is ascribed to the Late Triassic re-heating event dated at 208 ± 2 Ma. Continuous cooling followed this event at rates of 10−4 and 10−2 °C/yr until cessation of elemental exchange activity at ~656 °C. A rapid cooling rate is associated with the uplift and subsequent decrease of geothermal gradient during the early stages of the opening of the Piemont ocean basin.
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Barkov, Andrei Y., Vladimir N. Korolyuk, Larisa P. Barkova und Robert F. Martin. „Double-Front Crystallization in the Chapesvara Ultramafic Subvolcanic Complex, Serpentinite Belt, Kola Peninsula, Russia“. Minerals 10, Nr. 1 (23.12.2019): 14. http://dx.doi.org/10.3390/min10010014.
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Dunite–harzburgite–olivine-bearing orthopyroxenite successions in the subvolcanic Chapesvara-I and Chapesvara-II intrusions in the Serpentinite Belt, western Kola Peninsula, are notably magnesian. The mean Mg# value (whole-rock) is 86.6, and the olivine is Fo84−89. The upper contact facies (UCF) displays a lower Mg# (81.6). It consists of grains of Fo92 and abundant chromian spinel, implying rapid crystallization of an almost unfractionated melt. On average, the whole-rock Al2O3/TiO2 value is 22.45, close to 22.9 (UCF) and to the primitive mantle, ~22. The rise of primitive ultramafic magma presumably occurred in a special tectonic setting at the boundary of the Paleoproterozoic Lapland Granulite Terrane and the Belomorian Composite Terrane of Archean age. The Chapesvara suite resembles examples of the Al-undepleted komatiites in the Barberton Belt, South Africa, with magmas of up to 30–35% MgO. The UCF rock yields an anomalously low molar MgO/SiO2 value, close to that of dunitic rocks located at the center of the Chapesvara-II body. This rock is the most primitive, as indicated by the maximum Fo content of olivine, the lowest value of (Gd/Yb)N, 0.52, and the lowest abundances of middle to heavy rare-earth elements (REE) in the chondrite-normalized spectrum. The crystallization of the Chapesvara-II sill-like intrusion likely proceeded in two stages, which are evident from the olivine compositions varying from the maximum Fo92 (UCF) to Fo≤89.5 (the central dunite zone). At Stage 1, the UCF rock (Fo92) crystallized first, close to the upper contact. The area of crystallization then shifted to a central portion of the Chapesvara-II body, in which the dunitic zone (Fo89.5) formed in situ (Stage 2). The compositional variations in chromian spinel are consistent with this suggestion. Two crystallization trends were recognized. The type-1 trend displays a relative maximum or minimum close to the center, and then diverges into two linear subtrends directed upward and downward. This pattern is manifested in the variations of Mg# in olivine and chromian spinel, the whole-rock contents of Al and Ca, and in levels of incompatible elements: Ti, V, Zr, Y, and Hf. The type-2 trend decreases or increases uniformly from top to bottom. Variations in amount of Ni in olivine, the Fe3+# index in chromian spinel, and in values of Mg# (rocks), follow a type-2 trend. Variations in total amounts of REE, Nb, and Th, which gradually increase downward, are also related to a type-2 trend. Thus, a contrasting development and possible interference of the two types of evolutionary trends were observed in the crystallization history of the Chapesvara-II sill-like body. A double-front crystallization, hitherto unreported, involved two fronts moving upward and downward, respectively. The upward subtrend appeared to be of subordinate importance, whereas the extent of fractional crystallization of the downward front was much greater. Crystallization proceeded from the top to the bottom, presumably because of the preferential loss of heat at the roof. Variations in the Fe3+# index indicate that the level of fO2 also increased downward with progressive crystallization. Convection cells were presumably the key mechanism of accumulation of the crystallizing olivine grains to form the central dunite zone close to the center of the sill-like intrusion. The observed characteristics of the Chapesvara complex indicate the existence of a primitive-mantle source and imply a highly magnesian composition of intruding magma not only for Chapesvara, but also for the Pados-Tundra layered complex and associated suites of the Serpentinite Belt in the Kola Peninsula.
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Stepanov, Sergey, Roman Palamarchuk, Aleksandr Kozlov, Dmitry Khanin, Dmitry Varlamov und Daria Kiseleva. „Platinum-Group Minerals of Pt-Placer Deposits Associated with the Svetloborsky Ural-Alaskan Type Massif, Middle Urals, Russia“. Minerals 9, Nr. 2 (28.01.2019): 77. http://dx.doi.org/10.3390/min9020077.
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The alteration of platinum group minerals (PGM) of eluval, proximal, and distal placers associated with the Ural-Alaskan type clinopyroxenite-dunite massifs were studied. The Isovsko-Turinskaya placer system is unique regarding its size, and was chosen as research object as it is PGM-bearing for more than 70 km from its lode source, the Ural-Alaskan type Svetloborsky massif, Middle Urals. Lode chromite-platinum ore zones located in the Southern part of the dunite “core” of the Svetloborsky massif are considered as the PGM lode source. For the studies, PGM concentrates were prepared from the heavy concentrates which were sampled at different distances from the lode source. Eluvial placers are situated directly above the ore zones, and the PGM transport distance does not exceed 10 m. Travyanistyi proximal placer is considered as an example of alluvial ravine placer with the PGM transport distance from 0.5 to 2.5 km. The Glubokinskoe distal placer located in the vicinity of the Is settlement are chosen as the object with the longest PGM transport distance (30–35 km from the lode source). Pt-Fe alloys, and in particular, isoferroplatinum prevail in the lode ores and placers with different PGM transport distance. In some cases, isoferroplatinum is substituted by tetraferroplatinum and tulameenite in the grain marginal parts. Os-Ir-(Ru) alloys, erlichmanite, laurite, kashinite, bowieite, and Ir-Rh thiospinels are found as inclusions in Pt-Fe minerals. As a result of the study, it was found that the greatest contribution to the formation of the placer objects is made by the erosion of chromite-platinum mineralized zones in dunites. At a distance of more than 10 km, the degree of PGM mechanical attrition becomes significant, and the morphological features, characteristic of lode platinum, are practically not preserved. One of the signs of the significant PGM transport distance in the placers is the absence of rims composed of the tetraferroplatinum group minerals around primary Pt-Fez alloys. The sie of the nuggets decreases with the increasing transport distance. The composition of isoferroplatinum from the placers and lode chromite-platinum ore zones are geochemically similar.
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Xiong, Fahui, Jingsui Yang, Hans-Peter Schertl, Zhao Liu und Xiangzhen Xu. „Multistage origin of dunite in the Purang ophiolite, southern Tibet, documented by composition, exsolution and Li isotope characteristics of constituent minerals“. European Journal of Mineralogy 32, Nr. 1 (17.02.2020): 187–207. http://dx.doi.org/10.5194/ejm-32-187-2020.
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Abstract. The Purang ophiolite, which crops out over an area of about 650 km2 in the western Yarlung–Zangbo suture zone, consists chiefly of mantle peridotite, pyroxenite and gabbro. The mantle peridotite is comprised mainly harzburgite and minor dunite. Locally, the latter contains small pods of chromitite. Pyroxenite and gabbro occur as veins of variable size within the peridotite; most of them strike northwest, parallel to the main structure of the ophiolite. Three types of dunite occur in the Purang ophiolite: dunite that envelopes podiform chromitite (1) and lenses of dunite with either Cr-rich spinel (2) or Cr-poor spinel (3) in a harzburgite host. The constituent minerals of dunite envelopes around podiform chromitite are similar in composition to those of transition-zone dunite (Fo91.01−91.87 in olivine; Cr/(Cr+Al) (Cr#) =41.5–47.0 and Mg/(Mg+Fe2+) (Mg#) =58.9–63.0 in Cr-spinel). Forsterite contents in olivine decrease from type 2 lenses with Cr-rich spinel (91.9–93.0) to type 1 dunite enveloping chromitite (91.7–93.7) to type 3 lenses with Cr-poor spinel (95.3–96.0). Similarly, Cr# in spinel decreases from type 2 (66.9–67.9) to type 1 (41.5–47.0) to type 3 (19.8–20.6). In addition, Al2O3 in clinopyroxene is highest in type 2 (3.48–5.24 wt %) and decreases to type 1 (1.56–3.29 wt %) and type 3 (0.78–0.86 wt %). Olivine in type 1 dunite enveloping podiform chromitite has Li concentrations and δ7Li values of 1.48–1.71 ppm and 6.19 ‰–7.98 ‰, respectively. Type 2 dunite lenses with Cr-rich spinel contain olivine with Li =0.98–1.64 ppm and δ7Li =6.77 ‰–10.99 ‰. The type 3 dunite lenses with Cr-poor spinel show the highest values of Li =0.94–1.40 ppm and δ7Li =10.25 ‰–14.20 ‰. Exsolution lamellae of clinopyroxene and magnetite occur as oriented intergrowths in olivine of type 3 dunite lenses with Cr-poor spinel. We suggest that the Purang ophiolite developed during two main stages of formation. In the first stage, abyssal peridotites formed in a mid-ocean-ridge environment. During the second stage, hydrous high-Mg boninitic melts were produced by high degrees of partial melting in a supra-subduction zone mantle wedge, which reacted with peridotite to form type 2 dunite pods with high-Cr# spinel. At lower degrees of partial melting in the same mantle wedge, Al-rich melts were produced, which reacted with peridotite to form type 3 dunite pods that contain low-Cr# spinel. These Al-rich melts were also relatively rich in Ti4+, Ca2+ and Fe3+, which were incorporated into the olivine structure by appropriate substitutions. During cooling, these elements exsolved as lamellae of magnetite and clinopyroxene.
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ALEKSEEV, Aleksandr Valer’evich, und Tat’yana Andreevna SHERENDO. „Composition, structure and magnetic properties of ore chrome spinels of the Klyuchevsky massif (Middle Urals)“. NEWS of the Ural State Mining University 1, Nr. 1 (23.03.2020): 73–85. http://dx.doi.org/10.21440/2307-2091-2020-1-73-85.
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The overall objective was to create a geological and geophysical field test site for chromite mineralization and detailed works in order to determine and test the main search criteria for disseminated mineralization. To create a field test site, an area was selected in the southern part of the Klyuchevsky massif characterized by abundant development of disseminated mineralization in the banded dunite-clinopyroxenite complex and strong processes of superimposed metamorphism. This paper gives a piece of research on the composition of chrome spinel from disseminated ores that underwent metamorphism of different stages. The composition of chrome spinelide, the evolution of its metamorphism and the related changes in its magnetic properties are examined in detail. It was established that all chrome spinels are of a high-chromium type, to one degree or another, they were subject to secondary changes, leading to the appearance of magnetic phases. The degree and nature of the change in chrome spinels in dunites directly depends on the degree of metamorphism of the rocks. The formation of the magnetic phase begins with the formation of nuclei consisting of single magnetic dipoles, groups of 2-3 dipoles or chains of magnetic dipoles, which was first discovered by us in chrome spinel grains. Then there is an increase in the number of such phases, the appearance of optically diagnosed secondary changes in chrome spinelide. A comparison of the degree of variation of chrome spinel and its reflection in the pattern of recorded anomalies of geomagnetic fields allows us to identify some criteria for the search for disseminated chromite ores of this type.
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Bussolesi, Micol, Giovanni Grieco, Alessandro Cavallo und Federica Zaccarini. „Different Tectonic Evolution of Fast Cooling Ophiolite Mantles Recorded by Olivine-Spinel Geothermometry: Case Studies from Iballe (Albania) and Nea Roda (Greece)“. Minerals 12, Nr. 1 (04.01.2022): 64. http://dx.doi.org/10.3390/min12010064.
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Mg-Fe2+ diffusion patterns in olivine and chromite are useful tools for the study of the thermal history of ultramafic massifs. In the present contribution, we applied the exponential modeling of diffusion patterns to geothermometry and geospeedometry of chromitite ores from two different ophiolite contexts. The Iballe ophiolite (Northern Albania) hosts several chromitite pods within dunites. Primary and re-equilibrated Mg#, estimated by using an exponential function, provided re-equilibration and primary temperatures ranging between 677 and 996 °C for chromitites and between 527 and 806 °C for dunites. Cooling rates for chromitites are higher than for dunites, suggesting a different genesis for the two lithologies, confirmed also by spinel mineral chemistry. Chromitites with MORB affinity formed in a SSZ setting at a proto-forearc early stage, explaining the higher cooling rates, while dunites, with boninitic affinity, were formed deeper in the mantle in a more mature subduction setting. At the Nea Roda ophiolite (Northern Greece) olivine in chromitites do not show Mg-Fe variations, and transformation into ferrian chromite produced “fake” diffusion patterns within chromite. The absence of diffusion patterns and the low estimated temperatures (550–656 °C) suggest that Nea Roda chromitites were completely re-equilibrated during an amphibolite-facies metamorphic event that obliterated all primary features.
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Karaseva, E. S., A. Yu Kissin und V. V. Murzin. „The Poldnevskoye deposit of demantoid (Middle Urals): Geology and mineralogy“. LITHOSPHERE (Russia) 21, Nr. 5 (31.10.2021): 683–98. http://dx.doi.org/10.24930/1681-9004-2021-21-5-683-698.
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Research subject. The results of studying the geology and mineralogy of the Poldnevskoye deposit of demantoid are presented. Material and methods. The factual material was collected during feld research. Demantoid samples were pro vided by mine owners. Rock and vein minerals were studied in hand specimens, polished specimens and thin sections; the chemical composition was determined by X-ray fluorescence spectroscopy, scanning electron microscopy, electron probe X-ray spectral microanalysis, inductively coupled plasma mass spectrometry with laser sampling (LA-ICP-MS).Results. The Korkodinsky ultrabasic massif containing the deposit experienced strong decompression and syndecompression mineral formation during the ascent. At an early stage, veins of clinopyroxenite formed in dunite, which also experienced decompression cracking. Then the rocks underwent antigoritization and the appearance of vein antigorite, which was replaced by veins of clinochrysotile (+ magnetite ± carbonate ± demantoid). This was followed by the formation of lizardite (+ magnetite ± carbonate ± demantoid), which also developed along the earlier vein serpentines. Demantoid is represented by rounded grains and rounded grain aggregates with the signs of growth under the conditions of allround extension. The predominant color is brownish-green, yellow-green, rarely green and dark green. Green and dark green demantoids contain Cr2O3 0.52–2.3 wt %. In the central part of some grains and demantoid aggregates, a brown color is observed, which binds to TiO2, the content of which reaches 1 wt %. The demantoids of the Poldnevskoye deposit bear typomorphic features of the Ural-type demantoids (inclusions of the “horse’s tail” type). The distribution of demantoid is nested. The length of the veins with demantoid is frst meters. Their pillar-like shape is assumed. Conclusion.Demantoids from nests in serpentinized massive or brecciform dunites are more intact; demantoid nests in strongly serpentinized rocks were tectonic crushed and contain little gemstone.
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Divya, K. „Strengthening of AR Glass Fibre Concrete by Using Dunite Powder“. International Journal for Research in Applied Science and Engineering Technology 11, Nr. 5 (31.05.2023): 2022–25. http://dx.doi.org/10.22214/ijraset.2023.51942.
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Abstract: In the contemporary era. Concrete, the most significant and frequently used material, frequently needs to have a very high strength and acceptable workability. Research on glass fibre reinforced concrete led to the development of alkali resistant fibres with a high capacity for dispersion, increasing long-term durability. When dunite is utilised as a cement alternative rather of regular cement, concrete is discovered to become up to 40% stronger. Studies based on periodic cement rate data show that, on average, dunite powder is less expensive than cement. Future cement usage will be dominated by the replacement of dunite powder. In the current experimental investigation, alkali resistant glass fibres have been employed to investigate the effect on compressive and split tensile strength on M30 grade of concrete can be determined for 28,56 and 90 days
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Grieco, Giovanni, Alessandro Cavallo, Pietro Marescotti, Laura Crispini, Evangelos Tzamos und Micol Bussolesi. „The Formation of Magnesite Ores by Reactivation of Dunite Channels as a Key to Their Spatial Association to Chromite Ores in Ophiolites: An Example from Northern Evia, Greece“. Minerals 13, Nr. 2 (21.01.2023): 159. http://dx.doi.org/10.3390/min13020159.
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Ophiolite magnesite deposits are among the main sources of magnesite, a raw material critical for the EU. The present work focuses on magnesite occurrences at Kymasi (Evia Island, Greece), in close spatial association with chromitite within the same peridotite massif, and on the relationship between ultramafic rocks and late magnesite veins. Chromitite lenses are hosted within dunite, in contact with a partially serpentinized peridotite cut by magnesite veins. Close to the veins, the peridotite shows evidence of carbonation (forming dolomitized peridotite) and brecciation (forming a serpentinite–magnesite hydraulic breccia, in contact with the magnesite veins). Spinel mineral chemistry proved to be crucial for understanding the relationships between different lithologies. Spinels within partially serpentinized peridotite (Cr# 0.55–0.62) are similar to spinels within dolomitized peridotite (Cr# 0.58–0.66). Spinels within serpentinite–magnesite hydraulic breccia (Cr# 0.83–0.86) are comparable to spinels within dunite and chromitite (Cr# 0.79–0.84). This suggests that older weak zones, such as dunite channels, were reactivated as fluid pathways for the precipitation of magnesite. Magnesite stable isotope composition, moreover, points towards a meteoric origin of the oxygen, and to an organic source of carbon. The acquired data suggest the following evolution of Kymasi ultramafic rocks: (i) percolation of Cr-bearing melts in a supra-subduction mantle wedge within dunite channels; (ii) obduction of the ophiolitic sequence and peridotite serpentinization; (iii) uplift and erosion of mantle rocks to a shallow crustal level; (iv) percolation of carbon-rich meteoric waters rich at shallow depth, reactivating the dunite channels as preferential weak zones; and (v) precipitation of magnesite in veins and partial brecciation and carbonation of the peridotite host rock.
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Baragaño, Diego, Rubén Forján, Juan María Menéndez Aguado, Marcos Covián Martino, Pamela Díaz García, Javier Martínez Rubio, Juan José Álvarez Rueda und José Luis R. Gallego. „Reuse of Dunite Mining Waste and Subproducts for the Stabilization of Metal(oid)s in Polluted Soils“. Minerals 9, Nr. 8 (08.08.2019): 481. http://dx.doi.org/10.3390/min9080481.
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The circular economy seeks to minimize the use of raw materials and waste generation. In this context, here we addressed the use of dunite mining tailings and subproducts to stabilize metal(oid)s in polluted soils. We first characterized the dunite mining tailings and subproducts, and a paradigmatic polluted soil in depth to determine their chemical and mineralogical properties. Experimental trials using Brassica juncea L. were performed to evaluate the impact of the two materials on vegetation growth, edaphic properties and pollutant stabilization yields. To this end, the plants were grown over 75 days in 1 kg pots containing the polluted soil amended with the dunite materials. Notably, both amendments caused a dramatic decrease in the available Zn and a moderate reduction in available Cu, Cd and Pb. In contrast, the concentration of available As was not modified. The cation exchange capacity (CEC) was improved by treatment with the amendments, allowing an increase in the biomass harvested. The immobilization mechanism achieved was probably due to an increase in pH and CEC. In conclusion, the dunite tailings and subproducts could be effective amendments for stabilizing polluted soil. This work paves the way for additional studies with distinct types of soils and conditions.
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Sahera, Sk. „Mechanical Properties AR Glass Fibre Concrete by Using Dunite Powder“. International Journal for Research in Applied Science and Engineering Technology 11, Nr. 5 (31.05.2023): 2012–14. http://dx.doi.org/10.22214/ijraset.2023.51938.
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Abstract: In the modern world. The most significant and commonly utilised material, concrete, must frequently have a very high strength and appropriate workability.Alkali resistant fibres with a high capacity for dispersion were created as a consequence of research in glass fibre reinforced concrete, which increased long-term durability.Alkali resistant glass fibres have been used in the current experimental examination to explore the impact on compressive and split tensile strength on M30 grade of concrete.Concrete is found to become up to 40% stronger when dunite is used as a cement substitute rather than conventional cement.Test can be carried for 7 and 28 days. Studies based on periodic cement rate records indicate that the dunite powder is less expensive than cement, on average. The substitution of dunite powder will predominate in cement consumption in the future. It enhances, among other things, Split tensile strength, compressive strength.
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Ishimaru, Satoko, Yuji Saikawa, Makoto Miura, Osman Parlak und Shoji Arai. „Decoding of Mantle Processes in the Mersin Ophiolite, Turkey, of End-Member Arc Type: Location of the Boninite Magma Generation“. Minerals 8, Nr. 10 (18.10.2018): 464. http://dx.doi.org/10.3390/min8100464.
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The Mersin ophiolite, Turkey, is of typical arc type based on geochemistry of crustal rocks without any signs of mid-ocean ridge (MOR) affinity. We examined its ultramafic rocks to reveal sub-arc mantle processes. Mantle peridotites, poor in clinopyroxene (<1.0 vol.%), show high Fo content of olivine (90–92) and Cr# [=Cr/(Cr + Al) atomic ratio] (=0.62–0.77) of chromian spinel. NiO content of olivine is occasionally high (up to 0.5 wt.%) in the harzburgite. Moho-transition zone (MTZ) dunite is also highly depleted, i.e., spinel is high Cr# (0.78–0.89), clinopyroxene is poor in HREE, and olivine is high Fo (up to 92), but relatively low in NiO (0.1–0.4 wt.%). The harzburgite is residue after high-degree mantle melting, possibly assisted by slab-derived fluid. The high-Ni character of olivine suggests secondary metasomatic formation of olivine-replacing orthopyroxene although replacement textures are unclear. The MTZ dunite is of replacive origin, resulted from interaction between Mg-rich melt released from harzburgite diapir and another harzburgite at the diapir roof. The MTZ dunite is the very place that produced the boninitic and replacive dunite. The MTZ is thicker (>1 km) in Mersin than in MOR-related ophiolite (mostly < 500 m), and this is one of the features of arc-type ophiolite.
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Krasnobaev, A. A., und V. N. Anfilogov. „Zircons: Implication for dunite genesis“. Doklady Earth Sciences 456, Nr. 1 (Mai 2014): 535–38. http://dx.doi.org/10.1134/s1028334x1405033x.
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Braun, Michael G., und Peter B. Kelemen. „Dunite distribution in the Oman Ophiolite: Implications for melt flux through porous dunite conduits“. Geochemistry, Geophysics, Geosystems 3, Nr. 11 (November 2002): 1–21. http://dx.doi.org/10.1029/2001gc000289.
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Álvarez Agudelo, Jairo, und Raúl H. Muñoz Arango. „Distribución de cromo, níquel y cobalto en la saprolita y en los concentrados de sedimentos fluviales derivados de las dunitas de Medellín“. Boletín Geológico 28, Nr. 3 (01.10.1987): 45–71. http://dx.doi.org/10.32685/0120-1425/bolgeol28.3.1987.308.
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En el cuerpo de dunitas de Medellín, se presentan varios depósitos podiformes de cromita. En una zona restringida de dicho cuerpo, alrededor de una ocurrencia de cromita, se hizo un estudio geoquímico sobre la distribución de Ni, Co y Cr en la saprolita y en los concentrados en batea procedentes de la ultramafita, con el fin de conocer la utilidad de estos elementos como indicadores de mineralizaciones. Los análisis fueron realizados por espectrografía semicuantitativa. El níquel y el cobalto en la saprolita son afectados notoriamente por la meteorización química siendo redistribuidos y lixiviados y no son útiles como indicadores de ocurrencias. de cromita. Ambos elementos tienen una coherencia geoquímica más alta con el hierro que con el manganeso. El cromo, en cambio, se encuentra principalmente en los minerales resistatos (cromita y magnetita), e indica la distribución primaria del mismo en la dunita. La zona al oeste del depósito de Patio Bonito, tiene valores altos en cromo, lo cual sugiere una mayor concentración de cromita y mejores posibilidades para cuerpos de cromita. La prospección geoquimica usando concentrados en batea, demostró ser útil y mediante esta herramienta se encontraron dos áreas anómalas, en la cuenca de captación de la quebrada Las Palmas.
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Liu, Jianguo, Jian Wang, Keiko Hattori und Zeli Wang. „Petrogenesis of Garnet Clinopyroxenite and Associated Dunite in Hujialin, Sulu Orogenic Belt, Eastern China“. Minerals 12, Nr. 2 (28.01.2022): 162. http://dx.doi.org/10.3390/min12020162.
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The origin of ultramafic rocks, especially those in suture zones, has been a focus because they are not only important mantle sources of magma, but also provide substantial information on metamorphism and melt/fluid–peridotite interaction. Ultramafic rocks in Hujialin, in the central part of the Sulu orogen, include peridotite and pyroxenite. Although many papers on their origin and tectonic evolution have been published in the past few decades, these questions are still highly debated. Here, we present mineralogy, mineral composition, and bulk-rocks of these ultramafic rocks to evaluate their origin and tectonic evolution. The garnet clinopyroxenite is low in heavy rare-earth elements (HREE, 5.97–10.6 ppm) and has convex spoon-shaped chondrite-normalized REE patterns, suggesting the garnet formed later, and its precursor is clinopyroxenite. It is high in incompatible elements (i.e., Cs, Rb, Ba) and shows negative to positive U, Nb, and Ta anomalies, without pronounced positive Sr or Eu anomalies. Clinopyroxene in garnet clinopyroxenite contains high MgO (Mg# 0.90–0.97). The mineral chemistry and bulk-rock compositions are similar to those of reactive clinopyroxenite, suggesting that it originally formed via peridotite–melt interaction, and that such silicic and calcic melt might derive from the subducted Yangtze continent (YZC). Dunite contains olivine with high Fo (93.0–94.1), low NiO (0.11–0.29 wt.%) and MnO (≤0.1 wt.%), chromite with high Cr# (0.75–0.96), TiO2 (up to 0.88 wt.%), and Na2O (0.01–0.10 wt.%). It has negatively sloped chondrite-normalized REE patterns. Mineral chemistry and bulk rocks suggest dunite likely represent residual ancient lithosperic mantle peridotite beneath the North China Craton (NCC) that was overprinted by aqueous fluids. The lack of prograde and retrograde metamorphic minerals in dunite and irregular shaped mineral inclusions in chromite suggest dunite did not subduct to deep levels. Dunite mingled with garnet clinopyroxenite during exhumation of the latter at shallow depths. These ultramafic rocks, especially hydrated peridotite, may be important sources of Au for the Jiaodong gold province in the NCC.
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Simonov, V. A., A. V. Kotlyarov, V. V. Sharygin und Yu R. Vasiliev. „Crystallization conditions of olivine in dunites the Guli massif, Siberian platform“. МИНЕРАЛОГИЯ (MINERALOGY) 10, Nr. 1 (04.04.2024): 16–31. http://dx.doi.org/10.35597/2313-545x-2024-10-1-2.
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Crystallization conditions of olivine in dunites of the Guli massif (Siberian Platform) are established using petrological, geochemical, mineralogical and thermobarogeochemical methods. The formation of olivine and chromite from picrite-meimechite ultramafc magmas was followed by the fractionation of clinopyroxenes from basaltic systems with the formation of residual high-alkaline melts. The calculations in PETROLOG and COMAGMAT programs based on the compositions of inclusions and minerals, as well as using olivine-spinel geothermometer, showed that a magmatic system, which was responsible for the formation of dunites of the Guli massif, evolved during the crystallization of olivine in a wide temperature range of 1520–1250 °C in a magma chamber at a depth of about 17 km.
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Saveliev, D. E. „Morphological and Compositional Features of Chromian Spinel from Mantle Ultramafic Rocks of The Nurali Massif (South Urals)“. МИНЕРАЛОГИЯ (MINERALOGY) 5 (27.12.2019): 3–18. http://dx.doi.org/10.35597/2313-545x-2019-5-4-1.
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Accessory chromian spinels of lherzolites and dunites from a mantle section of the Nurali ophiolite massif are described in the paper. Lherzolites typically host anhedral chromian spinel grains associated with olivine, pyroxenes and plagioclase. The compositions of silicates and chromian spinels are typical of those from ophiolite mantle sections. Olivine and orthopyroxene are characterized by high Mg content (forsterite and enstatite); clinopyroxene is diopside. The compositions of chromian spinel on the Al–Cr–Fe+3 plot occur close to the Al–Cr side. The #Cr and #Mg values of chromian spinels increase from lherzolites to dunites. Both vermicular spinels trapping olivine and orthopyroxene fragments (type I) and symplectite-like intergrowths of chromian spinel and plagioclase (type II) are most genetically interesting. Type I formed during synkinematic growth in deformed silicate matrix. Type II possibly formed as a result of decompression breakdown of a high-P mineral phase enriched in Cr, Al and Ca (a knorringite-type garnet?). In dunites, numerous tiny chromian spinel rods (type IV) in plastic deformed olivine are observed along with typical euhedral chromian spinel (type III) with inclusions of olivine and pargasite. Latter ones locally occur closely to fne pargasite grains. The formation of chromian spinel rods is explained as a result deformation-induced segregation of trace elements on the structural defects of the olivine lattice. Figures 7. Tables 4. References 48.
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Hu, Wen-Jun, Mei-Fu Zhou, Marina A. Yudovskaya, Ilya V. Vikentyev, John Malpas und Peng-Fei Zhang. „Trace Elements in Chromite as Indicators of the Origin of the Giant Podiform Chromite Deposit at Kempirsai, Kazakhstan“. Economic Geology 117, Nr. 7 (01.11.2022): 1629–55. http://dx.doi.org/10.5382/econgeo.4955.
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Abstract This study presents a complete trace element data set of chromite from the world’s largest podiform chromite deposit at Kempirsai, Kazakhstan, together with platinum group element (PGE) and Re-Os isotope compositions, to explore the potential of trace elements in the study of podiform chromite deposits. Chromite orebodies in the Karaagash area of the Kempirsai Main ore field are hosted by dunites in the mantle sequence of the ophiolite. Dunites slightly distal to the orebodies are composed of olivine (forsterite content = 91.5–93.4) and minor euhedral chromite with variable Cr# (0.73–0.83). These dunites have primitive mantle-normalized Pt-Pd–poor PGE patterns and subchondritic 187Os/188Os ratios (0.12174–0.12220). Negative correlations between Cr# and incompatible trace elements (Sc and Ti) of the chromite are consistent with melt-rock reaction, whereas positive correlations between Cr# and compatible trace elements (V and Ga) reflect the role of fractional crystallization. It is therefore proposed that chromite in the distal dunites was crystallized from magmas after reaction with mantle peridotites. In comparison, chromite grains in the ores and adjacent dunites exhibit relatively uniform Cr# numbers (0.81–0.86) and higher 187Os/188Os values (0.12319–0.12414). Both compatible and incompatible trace elements of chromite exhibit negative correlations with Cr#, which are best explained by mixing between the modified magma after melt-rock reaction and a later injected magma from a more depleted source. After the ore formation, subsolidus reequilibration between olivine and chromite reduced Mg# and modified divalent trace elements of chromite in the order of Zn > Co = Mn > Ni but did not affect distribution of nondivalent trace elements, except V and Fe3+. The decoupling of redox-sensitive and redox-insensitive trace elements suggests that the redox states have been modified during subsolidus reequilibration. The existing iron equilibrium between olivine and chromite records high fO2 values (quartz-fayalite-magnetite buffer [∆QFM] 0.8–2.4), whereas correction of subsolidus reequilibration results in a decrease of the fO2 values toward the QFM buffer (∆QFM 0.1–0.6), indicating that increase in fO2 was not a critical factor in the ore formation. Principal component analysis and factor analysis were further carried out to identify differences in trace elements between high-Cr and high-Al podiform chromite deposits worldwide. High-Cr chromite deposits have variable divalent trace element compositions and show complex distributions of nondivalent trace elements. The former reflects longer and slower cooling histories of the high-Cr chromite deposits with respect to the high-Al chromite deposits, whereas the latter indicates more variable magma compositions and complex processes during the formation of the high-Cr chromite deposits.
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Demetriou, Antri, und Ioannis Pashalidis. „Adsorption of hexavalent chromium on dunite“. Water Science and Technology 63, Nr. 4 (01.02.2011): 818–24. http://dx.doi.org/10.2166/wst.2011.118.
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The paper presents and discusses the effect of various physicochemical parameters (e.g. pH, ionic strength, Cr(VI) initial concentration, amount of the adsorbent, temperature and contact time between metal ion and adsorbent) on the adsorption efficiency of Cr(VI) on dunite in aqueous solutions under atmospheric conditions. Evaluation of the experimental data shows that dunite presents increased affinity for Cr(VI) over a wide pH range and Cr(VI) concentration, and the experimental data are well fitted by the Kd adsorption model. The relative adsorption is pH dependent and decreases slightly (about 10%) with increasing pH, because of changes in the surface charge of the solid. The effect of the ionic strength is significant (particularly at low pH), indicating the predominance of outer-sphere complexes. Moreover, adsorption experiments at various temperatures, two different pH values (pH 3 and pH 8) and three different ionic strengths (0.0, 0.1 and 1.0 M NaClO4), indicate an endothermic but spontaneous entropy-driven processes.
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Demetriou, Antri, Michaela Lysandrou, Antonios Charalambides und Ioannis Pashalidis. „Acid mine drainage treatment with dunite“. Desalination and Water Treatment 16, Nr. 1-3 (April 2010): 129–33. http://dx.doi.org/10.5004/dwt.2010.1049.
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Kislov, E. V. „Dunite of the Ioko-Dovyrensk massif“. Refractories 36, Nr. 12 (Dezember 1995): 399–404. http://dx.doi.org/10.1007/bf02227138.
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Agrawal, Amit Kumar, und Anurag Mehra. „Dunite carbonation in batch-tubular reactor“. Environmental Science and Pollution Research 27, Nr. 25 (02.06.2020): 31439–45. http://dx.doi.org/10.1007/s11356-020-09426-4.
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Madeddu, Silvia, Michael Priestnall, Erik Godoy, R. Vasant Kumar, Sugat Raymahasay, Michael Evans, Ruofan Wang, Seabelo Manenye und Hajime Kinoshita. „Extraction of Mg(OH)2 from Mg silicate minerals with NaOH assisted with H2O: implications for CO2 capture from exhaust flue gas“. Faraday Discussions 183 (2015): 369–87. http://dx.doi.org/10.1039/c5fd00047e.
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The utilisation of Mg(OH)2 to capture exhaust CO2 has been hindered by the limited availability of brucite, the Mg(OH)2 mineral in natural deposits. Our previous study demonstrated that Mg(OH)2 can be obtained from dunite, an ultramafic rock composed of Mg silicate minerals, in highly concentrated NaOH aqueous systems. However, the large quantity of NaOH consumed was considered an obstacle for the implementation of the technology. In the present study, Mg(OH)2 was extracted from dunite reacted in solid systems with NaOH assisted with H2O. The consumption of NaOH was reduced by 97% with respect to the NaOH aqueous systems, maintaining a comparable yield of Mg(OH)2 extraction, i.e. 64.8–66%. The capture of CO2 from a CO2–N2 gas mixture was tested at ambient conditions using a Mg(OH)2 aqueous slurry. Mg(OH)2 almost fully dissolved and reacted with dissolved CO2 by forming Mg(HCO3)2 which remained in equilibrium storing the CO2 in the aqueous solution. The CO2 balance of the process was assessed from the emissions derived from the power consumption for NaOH production and Mg(OH)2 extraction together with the CO2 captured by Mg(OH)2 derived from dunite. The process resulted as carbon neutral when dunite is reacted at 250 °C for durations of 1 and 3 hours and CO2 is captured as Mg(HCO3)2.
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Dvornik, Gennadiy Petrovich. „Distribution platinum content in chromite and dunite type ores Nizhny Tagil massif (Middle Ural)“. NEWS of the Ural State Mining University, Nr. 2 (15.06.2023): 62–71. http://dx.doi.org/10.21440/2307-2091-2023-2-62-71.
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The relevance of the work is due to the importance industrial meaning native and placer platinum deposits in basic-hiperbasic complexes. Methods of research included separation industrial type of ores for valuation quality platinum ore chute, use probabilistic-statistic, geometric-statistic and geostatistic model for description amplitude and frequency changeability in distribution platinum content in ore Nizhny Tagil massif. Result research. In chromite ores Nizhny Tagil massif platinum content vary in wide limits by predominance among theirs rich and ordinary ores and extremely uneven distribution platinum and other elements platinum group (palladium, rhodium, iridium, osmium, ruthenium) concentration in ores. In difference from ores chromite type in distribution platinum content in dunite ores massif in limits prospected Alexandrovsky area among industrial type ores prevail more low on quality poor and wretched ores by amplitude changeability platinum concentration in ores on data theirs ordinary sampling in prospect hole-from uneven to extremely, by gross sampling more deep mine working (half-pit and pit) – from even to very uneven. The largest frequency changeability in distribution platinum concentration in ores dunite type be distinguished ores widespread in north part Alexandrovsky area, differ and more low quality. Contemporary level development technology dressing platinum-bearing chromite and dunite type ores allowed consider theirs in quality perspective ores for joint processing.
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Karklit, A. K., L. E. Kademina und L. M. Myznikova. „Properties of dunites from the Inaglinsk deposits“. Refractories 29, Nr. 3-4 (März 1988): 231–34. http://dx.doi.org/10.1007/bf01389565.
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