Showing papers in "Mineralogy and Petrology in 2019"
TL;DR: In this paper, the authors re-examined chondrite-normalized rare earth element (REE) patterns of zircon and found that the Ce* can be estimated according to a logarithmic function curve without involvement of La and Pr contents.
Abstract: As a proxy of magmatic oxidation state, the accurate characterization of the Ce anomaly of zircon is of great significance since it can give important information for provenance studies of rocks as well as for exploration of intrusion-related mineral deposits. The magnitude of the zircon Ce anomaly has been traditionally described by Ce/Ce*, where Ce* is the theoretical Ce value derived from a chondrite-normalized rare earth element (REE) pattern. More recently, the Ce4+/Ce3+ method based on the lattice strain model has been proposed, since the latter method does not need La and Pr contents for zircon, both of which are commonly below the limit of detection and susceptible to contamination from melt/mineral inclusions. In this contribution we show that the Ce4+/Ce3+ method is confronted with some problems in practice and should be further improved. In contrast, by re-examining chondrite-normalized REE patterns of zircon, we find that Ce* can be estimated according to a logarithmic function curve without involvement of La and Pr contents. Application of this new method to zircon data from 11 giant to supergiant porphyry Cu deposits suggests this revised method as a more valid measure in evaluating magmatic oxidation state. The revised Ce/Ce* method is of particular importance for analyses where the provenance of the analyzed zircon is unknown or in question, since the method does not require knowledge of the melt composition.
63 citations
TL;DR: In this paper, a comprehensive overview of the mechanochemical treatment of natural clay minerals, aiming at their transformation into cementitious or pozzolanic materials, is presented, with a special focus on mechanochemically activated clay minerals and their use as cementitious binders.
Abstract: Mechanochemical activation can be defined as a process able to induce structural disorder through intensive grinding. In certain conditions, it may increase the chemical reactivity of the processed material. The process is extensively utilized in extractive metallurgy, synthesis of nanocomposites or pharmacology. It is also considered an environmentally friendly alternative to activate kaolinitic clay avoiding high calcination temperature. This paper aims to give a comprehensive overview of the process, its evolution, process parameters and applications. The paper focuses on the mechanochemical treatment of natural clay minerals, aiming at their transformation into cementitious or pozzolanic materials. It provides a summarized review of the theories related to the mechanochemistry and discusses commonly used models. The paper also analyzes various key factors and parameters controlling the mechanochemical activation process. The optimization and control of the several factors, as the filling ratio, the grinding media, the velocity, the time of grinding, etc., can promote developments and new research opportunities on different fields of application. Examples of applications, with a special focus on mechanochemically activated clay minerals and their use as cementitious binders, are listed as well.
42 citations
TL;DR: In this paper, the authors presented data of in-situ mineral major and trace element chemistry, whole-rock major, trace element and Sr-Nd isotope geochemistry, as well as zircon U-Pb dating and Lu-Hf isotope studies of andesite dykes from the Sulu orogenic belt of eastern China to evaluate their petrogenesis and thus to provide insights into crust-mantle interactions in a tectonic terrane that underwent continental subduction and was then overprinted by oceanic subduction.
Abstract: This study presents data of in-situ mineral major and trace element chemistry, whole-rock major and trace element and Sr–Nd isotope geochemistry, as well as zircon U–Pb dating and Lu–Hf isotope studies of andesite dykes from the Sulu orogenic belt of eastern China to evaluate their petrogenesis and thus to provide insights into crust–mantle interactions in a tectonic terrane that underwent continental subduction and was then overprinted by oceanic subduction. The andesites mainly comprise plagioclase, hornblende, clinopyroxene and magnetite as phenocrysts that are embedded in a groundmass of fine-grained quartz and K-feldspar, with minor amounts of biotite, magnetite, titanite, apatite and zircon. They possess intermediate concentrations of SiO2 (54.97–62.24 wt.%), Na2O + K2O (6.35–7.24 wt.%) and MgO (3.37–7.12 wt.%) with high Mg# values [Mg# = 100 × Mg/(Mg + Fe2+) molar] of 54–64, and are characterized by arc-like trace element patterns that are enriched in light rare earth elements (LREE) and large ion lithophile elements (LILE) but depleted in high field strength elements (HFSE). The hornblende and clinopyroxene phenocrysts exhibit enrichment in Th and U but an obvious depletion of HFSE. The andesites have high initial 87Sr/86Sr ratios of 0.7073–0.7086 and negative ɛNd(t) values of −15.7 to −14.4 for whole-rock, and newly crystallized magmatic zircons show negative ɛHf(t) values of −27.0 to −17.6. U–Pb dating on syn-magmatic zircons yields consistent ages of 124 ± 2 to 116 ± 1 Ma, indicating eruption of the andesitic lavas during the Early Cretaceous. Inherited zircons are present and yield Neoproterozoic, Paleoproterozoic and Archean U–Pb ages. Taking into account all these geochemical and geochronological data, and the compositional features of contemporaneously formed mafic–andesitic igneous rocks from the Sulu belt and the adjacent continental crust of the North China Craton, we propose that the andesites crystallized from primary andesitic magmas derived from partial melting of enriched metasomatites in the subcontinental lithospheric mantle. The enriched metasomatites are inferred to be formed by a two-step process: firstly by crust–mantle interactions during the Triassic collisional orogeny and secondly by a subsequent modification by fluids/melts that mainly derive from seafloor sediments during subduction of the paleo-Pacific plate in eastern Asia. Slab rollback of the subducted paleo-Pacific slab and concomitant asthenosphere upwelling are an appropriate geodynamic mechanism for the generation of extensive arc-like magmatism during the Early Cretaceous in the Sulu belt.
33 citations
TL;DR: The uniaxial compressive strength of granite decreased from 88.17MPa at 25°C to 18.61 MPa at 800°C as discussed by the authors, and the decrease was mainly contributed by the partial melt of rock, and magma intruding and solidifying.
Abstract: The microwave high-temperature irradiation was introduced to deal with the low efficiency of traditional microwave treatments for breaking granite. Structural evolution of granite between 300 °C and 800 °C was assessed through the morphology, mineral characteristics and mechanical performance. A spherical melt cavity with radial cracks formed near the biotite-rich area at 600 °C and the rock completely disintegrated at 800 °C. Intergranular crack was the main mode of micro-cracks. Besides, the micro crack propagation at 600 °C was affected by the distribution and shapes of mineral grains and original cracks. Furthermore, the intergranular crack in the biotite grain boundary induced many secondary smaller cracks. Feldspar and biotite melted at 800 °C. Thus, the melt probably initiated from the cracked-intensive feldspar near biotite-rich area. The uniaxial compressive strength of granite decreased from 88.17 MPa at 25 °C to 18.61 MPa at 800 °C. Between 300 and 600 °C, the decrease in the uniaxial compressive strength was associated with moisture releasing, quartz transition and thermal induced cracks, and 600–800 °C, the decrease was mainly contributed by the partial melt of rock, and magma intruding and solidifying.
31 citations
TL;DR: In this article, a comprehensive approach to combine chemical, mineralogical and textural information from energy dispersive x-ray fluorescence mapping (μ-EDXRF) or hyperspectral imaging (HSI) for petrographic analysis of plutonic rocks is described.
Abstract: Petrography and mineralogy are fundamental for understanding processes in various geoscientific fields. Plutonic rock nomenclature is based on mineralogical composition. Therefore, identifying and quantifying minerals is a key for plutonic rock classification. To accomplish this, novel advancements in instrumentations, such as energy dispersive x-ray fluorescence mapping (μ-EDXRF) or hyperspectral imaging (HSI) provide fast and non-destructively spatially resolved and large-scale chemical information. This work describes a comprehensive approach to combine chemical, mineralogical and textural information from μ-EDXRF, Laser Induced Breakdown Spectroscopy (LIBS) and HSI for petrographic analysis of plutonic rocks. Using supervised classification of spectral information, mineral distribution maps are obtained for image analysis including geometrical data of each grain, such as grain size, grain orientation and grain location for subsequent targeted analysis and the modal mineralogy for plutonic rock classification in a QAPF-diagram for 20 rock slabs. The combination of the three mapping techniques can provide valuable information within the limit of each technique such as of spatial resolution or element sensitivity, but with little time needed for sample preparation and measurement. In general, it is an objective, repeatable and quantifiable way for modal mineralogy and petrographic image analysis.
27 citations
TL;DR: Murashkoite, FeP, is a new mineral found in pyrometamorphic rocks of the Hatrurim Formation, South Levant as discussed by the authors, which is a typical accessory phase in the marbles and paralavas in the southern Negev Desert, Israel and on the Transjordan Plateau, Jordan.
Abstract: Murashkoite, FeP, is a new mineral found in pyrometamorphic rocks of the Hatrurim Formation, South Levant. It is a typical accessory phase in the marbles and paralavas in the southern Negev Desert, Israel and on the Transjordan Plateau, Jordan. Murashkoite occurs as grains and aggregates up to 2 mm closely associated with barringerite, (Fe,Ni)2P, and zuktamrurite, FeP2. The rock-forming minerals include pyroxenes of the diopside-hedenbergite series, anorthite with subordinate gehlenite, tridymite, cristobalite, pyrrhotite, fluorapatite, chromite, magnetite, hematite, merrillite and late hydrothermal carbonates, silicates and sulfates. Macroscopically, murashkoite is yellowish-grey in colour and has a metallic lustre. In reflected light, the mineral is white with a beige tint and it is non-pleochroic. The anisotropy is distinct, from yellow-grey to greyish-blue. Selected reflectance values [Rmax–Rmin, % (λ, nm)] are: 42.7–40.8 (400), 42.0–40.6 (500), 44.5–43.4 (600), 48.0–47.7 (700). It is brittle. VHN20 = 468 kg mm−2. The holotype material has the chemical composition (electron microprobe): Fe 63.82; Ni 0.88; P 35.56; total 100.26 wt.%. The empirical formula calculated on the basis of 2 apfu is (Fe0.99Ni0.01)1.00P1.00 corresponding to FeP. Murashkoite is orthorhombic, space group Pnma, unit cell parameters refined from the single-crystal data are: a 5.099(2), b 3.251(2), c 5.695(2) A, V 94.41(8) A3, Z = 4, Dx = 6.108(5) g cm−3. The crystal structure was solved and refined to R1 = 0.0305 on the basis of 131 unique reflections with I > 2σ(I). The strongest lines of the powder X-ray diffraction pattern [(d, A) (I, %) (hkl)]: 2.831(75)(002,011); 2.548(22)(200); 2.477(46)(102,111); 1.975(47)(112); 1.895(100)(202,211); 1.779(19)(103); 1.632(45)(013,301,020). The mineral is named in honour of Dr. Mikhail Nikolaevich Murashko (born 1952), for his contributions to the mineralogy of the Hatrurim Formation. Murashkoite is a natural counterpart of synthetic FeP, the compound widely used in heterogeneous catalysis and electrocatalysis.
25 citations
TL;DR: The Huize Zn-Pb-Ag deposit in SW China has an ore reserve in excess of 5 Mt. with an ore grade of ≥ 25% Zn+Pb and 46-100g/t Ag as mentioned in this paper.
Abstract: The Huize Zn–Pb–Ag deposit in SW China has an ore reserve in excess of 5 Mt. with an ore grade of ≥25 wt% Zn + Pb and 46–100 g/t Ag. This deposit is hosted in Carboniferous dolostone and limestone. Sulfide mineralization is dominated by sphalerite, galena, and pyrite. Four types of pyrite (Py1 to Py4) are temporally and spatially related to mineralization distinguished on the basis of textural features and mineral associations. Pyrite 1 to 3 corresponds to the pyrite-sphalerite sub-stage, whereas Py4 corresponds to sphalerite-galena-pyrite sub-stage. Pyrite 1 shows zoned texture composed of an inclusion-rich core and an inclusion-free rim, whereas Py2, Py3, and Py4 show replacement relic or overgrowth textures. The zoned texture in Py1 was formed by multiple stages of ore fluids, whereas replacement relic texture in Py2 to Py4 was formed by replacement of pyrite by late Pb-Zn-rich fluids. Trace element variation in pyrite results from a combination of mineral inclusions, co-precipitating minerals, and various fluid compositions. Sphalerite, pyrite, and galena have δ34S values of 10.4–23.5‰, suggesting that sulfur was probably derived from the thermochemical reduction of marine sulfates. The Huize pyrite has Co and Ni concentrations (0.02–9.5 ppm and 0.08–143 ppm, respectively) and Co/Ni ratios (~0.01–2.63) similar to pyrite from sedimentary exhalative deposits, submarine hydrothermal vents, and sedimentary pyrite, which may be due to pyrite precipitation from low-temperature (<~250 °C), basin brines or seawater. The Co/Ni ratios of the Huize pyrite are lower than those (~0.2–7.2) of pyrite from Mississippi Valley-type Zn-Pb deposits. The Huize pyrite has Co and Ni contents lower than those associated with volcanogenic massive sulfide, iron oxide copper gold, and porphyry Cu deposits, arguing against the involvement of a magmatic/volcanic component and a direct genetic link between Permian Emeishan basalts and Pb-Zn mineralization. Combining with fluid inclusion temperatures and silver grade, we define the Huize deposit as a transitional type between Mississippi Valley-type and high-temperature carbonate-replacement Zn-Pb deposits.
23 citations
TL;DR: In this article, the authors present petrologic, whole-rock geochemical and zircon U-Pb and Lu-Hf data from metamorphic intermediate mafic and ultramafic rocks in central Jilin Province, NE China, to constrain the Early Paleozoic tectonic evolution of the southeastern margin of the Xing’an-Mongolia Orogenic Belt.
Abstract: Magmatic and metasomatic rock suites can be commonly found in active convergent margins as the suprasubduction zone mantle wedge is usually impregnated by melts and fluids. Here we present petrologic, whole-rock geochemical and zircon U-Pb and Lu-Hf data from metamorphic intermediate-mafic and ultramafic rocks in central Jilin Province, NE China, to constrain the Early Paleozoic tectonic evolution of the southeastern margin of the Xing’an-Mongolia Orogenic Belt. Lithologically, the meta-igneous rocks are composed of plagioclase-actinolite, meta-allgovite, tremolitized pyroxenite, and serpentinized peridotite. Geochronological results indicate that the protoliths of the meta-igneous rocks formed during the Early–Middle Ordovician (474–466 Ma). Geochemical features suggest that the rocks are calc-alkaline and transitional-series rocks relatively enriched in large-ion lithophile and light rare earth elements and depleted in high field strength and heavy rare earth elements, implying that they formed in a supra-subduction zone environment. Additionally, the protoliths of the plagioclase-actinolites, which display an affinity for sanukites, resulted from an equilibrium reaction between mantle peridotite and slab melts derived from the partial melting of subducting sediments during early-stage subduction; the meta-allgovite rocks were likely derived from a juvenile depleted lithospheric mantle that was metasomatized by subduction-related fluids; the ultramafic rocks are magmatic cumulates formed in a suprasubduction zone mantle wedge. Furthermore, the meta-allgovite rocks display both arc-like and MORB-like geochemical characteristics, suggesting an intra-continental back-arc basin setting. These features, combined with the presence of the abundance of zircon xenocrysts with Neoproterozoic–Paleozoic ages, as well as the results of previous studies, reflect that a small-scale and limited back-arc basin, which was related to the northward subduction of the Paleo-Asian oceanic plate, probably existed close to the Songnen-Zhangguangcai Range Massif during the Early–Middle Ordovician.
17 citations
TL;DR: The Peregrina Tonalite (PTo) is an orphaned block associated with an enigmatic Carboniferous magmatic arc located along the north-western margin of Gondwana as discussed by the authors.
Abstract: The Huizachal–Peregrina Anticlinorium basement of the Sierra Madre Oriental in north-eastern (NE) Mexico comprises a wide variety of Precambrian and Paleozoic units. A granitic unit, described in this work as the Peregrina Tonalite (PTo), intruded the Neoproterozoic Novillo Gneiss, which is the northernmost expression of the Oaxaquia microcontinent. In contrast, the PTo’s contact with the Carboniferous Granjeno Schist is tectonic along vertical faults with a strike-slip component. This Paleozoic lithodeme is part of the Granjeno–Acatlan Belt. The PTo has been described as an orphaned block associated with an enigmatic Carboniferous magmatic arc located along the north-western (NW) margin of Gondwana. In this study, new U–Pb LA–ICP–MS data from PTo zircons included a youngest Late Ordovician (Katian stage) population at 448.8 ± 2.9 Ma, interpreted as the crystallisation age, and an oldest Grenvillian population interpreted as the potential age of its protolith. Additionally, major and trace element concentrations and ratios indicate a link to a continental arc that developed along the NW margin of Gondwana. Given this proposed arc’s age and position, a comprehensive model for the development of the NE Mexican basement without the involvement of exotic or orphaned terranes is now proposed. The PTo outcropping near Ciudad Victoria, Tamaulipas, is interpreted to be part of a previously unreported magmatic arc in NE Mexico established during the Late Ordovician, herein described as the Peregrina–Mochonian Orogeny. It represents an extension of the South American Famatinian arc into Mexico.
16 citations
TL;DR: Fluorbarytolamprophyllite as discussed by the authors is an early generation of lamprophylla-group minerals (LGM) and forms brown prismatic crystals.
Abstract: Unusual agpaitic syenites containing up to 25 vol.% lamprophyllite-group minerals (lamprophyllite, fluorlamprophyllite, barytolamprophyllite, and the new mineral species fluorbarytolamprophyllite, IMA 2016–089) have been discovered in the Niva intrusion and Mokhnatye Roga alkaline dyke belonging to the Kola Alkaline Province, northwestern Russia. The other main components of the rocks are potassium feldspar, Ti-rich aegirine-augite, aenigmatite, alkaline amphiboles, astrophyllite, natrolite, and ferripyrophyllite. Three generations of lamprophyllite-group minerals can be distinguished based on their morphological features. The new mineral fluorbarytolamprophyllite is the F-dominant analogue of barytolamprophyllite and the Ba-dominant analogue of fluorlamprophyllite. It represents the early generation of lamprophyllite-group minerals (LGM) and forms brown prismatic crystals, their radial aggregates and marginal zones of fluorlamprophyllite crystals. The lustre of the new mineral is vitreous to pearly. Mohs hardness is 2.5. Dcalc is 3.662 g/cm3. The mineral is optically biaxial (+), α = 1.738(3), β = 1.745(4), γ = 1.777(4) (589 nm), 2 V (meas.) = 55(5)°, 2 V (calc.) = 51°. The chemical composition (electron microprobe, water determined by TGA, wt.%) is: Na2O 10.01, K2O 2.65, MgO 0.43, CaO 0.64, SrO 5.59, BaO 16.23, MnO 0.50, FeO 4.44, Al2O3 0.08, TiO2 27.31, ZrO2 0.22, Nb2O5 0.91, Ta2O5 0.15, SiO2 29.35, F 2.41, H2O 0.26, total 101.18. The empirical formula based on 18 anions is (Ba0.865Sr0.44K0.46Na0.26)Σ2.025(Na2.38Ca0.09Fe0.47Mn0.06)Σ3.00(Ti2.79Mg0.09Fe0.035Nb0.06Zr0.015Ta0.01)Σ3.00(Si3.99Al0.01)Σ4.00 O16[F1.04O0.72(OH)0.24]Σ2.00. The IR spectrum is given. The strongest lines of the powder X-ray diffraction pattern are [d, A (I,%) (hkl)]: 9.692 (40) (200), 3.726 (59) (−311), 3.414 (67) (311), 3.230 (96) (300), 3.013 (53) (−5–11), 2.780 (100) (221), 2.662 (52) (002). The crystal structure has been solved and refined to R1 = 5.07 based on 2897 independent reflections with I > 2σ(I). Fluorbarytolamprophyllite is monoclinic, space group C2/m. The unit-cell parameters refined from the powder data are: a = 19.520(5), b = 7.0995(17), c = 5.3896(20) A, β = 96.657(23)°; V = 741.86(24) A3, Z = 2. At Niva and Mokhnatye Roga, most of the LGM were formed during magmatic stage of syenite crystallization from alkaline melt enriched in Na, K, Ba, Fe, Ti and F. Compositional variation of the examined LGM and their textural relations show changes in the Sr/Ba ratio in the parental melt and increasing activity of F and Ba in derivatives fluids as the main factors driving this variation.
12 citations
TL;DR: In this article, the main and trace elements and isotopic data are presented for 14 coarse-grained eclogite xenoliths from the V. Grib kimberlite pipe in the central part of the Arkhangelsk Diamondiferous Province.
Abstract: In this paper, new main and trace elements and isotopic data are presented for 14 coarse-grained eclogite xenoliths from the V. Grib kimberlite pipe in the central part of the Arkhangelsk Diamondiferous Province. Based on reconstructed whole rock MgO content, this suite is divided into high-MgO and low-MgO varieties. Eclogitic groups have a similar range of variations in the trace element compositions of garnet, clinopyroxene and reconstructed whole rock. All eclogites show positive Eu anomalies in garnet and Sr anomalies in the whole rock. The negative correlation between the Mg#, Sr/Lu ratio and HREE in a whole rock points to upper and lower oceanic crustal rocks as a protolith for eclogites with high and low whole rock HREEs, respectively. Low-MgO eclogites with higher whole rock HREEs have the basaltic upper oceanic crustal protolith, whereas the protoliths of eclogites with lower whole rock HREEs could be of gabbroic composition from the lower oceanic crust. High-MgO eclogites could represent MgO-rich portions of oceanic crustal rocks: picritic/MgO basalt portions in the upper oceanic crust and troctolite portions in the lower oceanic crust. The Sr and Nd isotope compositions suggest a complex history of eclogites during their residence in the lithospheric mantle. Similarities in the Nd isotope compositions and two-point Sm-Nd isochron ages are evidence for re-equilibration of the Sm-Nd isotope system between the eclogite garnet and clinopyroxene via a pre-kimberlite thermal event at 396 ± 24 Ma. The subset of clinopyroxenes from four eclogites has a Sr isotope composition that plots on the isochron at an age of 2.84 Ga, which reflects the time of the subduction event and emplacement into the lithosphere and corresponds to the time of the Belomorian Eclogite Province of Baltic Shield formation.
TL;DR: In this paper, the major and trace element compositions for 31 basaltic lava and glass samples from the Mariana Trough back-arc spreading center were presented, and the studied lavas include phenocrysts of plagioclase, olivine and pyroxene.
Abstract: The Mariana Trough, a relatively simple intra-oceanic back-arc basin, is ideal for investigating magmatic processes and mantle-crust interaction in a subduction setting. We present new major- and trace element compositions for 31 basaltic lava and glass samples from the Mariana Trough back-arc spreading center. The studied lavas include phenocrysts of plagioclase, olivine and pyroxene. Major element compositions show that these lavas range from tholeiitic basalt to basaltic andesite, and belong to a sub-alkali tholeiitic series produced by fluid-influenced fractional crystallization of primary basaltic melts. Trace element compositions show that these lavas are transitional between typical normal mid-ocean ridge basalts (MORB) and island arc basalt (IAB), and are enriched in large ion lithophile elements (LILEs) and light rare earth elements (LREEs). Trace element ratios, e.g., Ba/Th, Pb/Ce, Th/Nd, La/Sm, Th/Nb, Ba/Nb and Th/Nb, indicate that the mantle from which these lavas were derived underwent modification resulting from the addition of multiple subduction components. Some typical trace element ratios (e.g., Ba/Nb- total subduction component, Ba/Th- shallow subduction, and Th/Nb-deep subduction component) from our new data and the literature suggest that a latitudinal variation exists in addition to subduction components, and indicates a more complex and heterogeneous distribution of subduction components in the Mariana back-arc region. We suggest that, (1) compared to back-arc locations at 18° N and 15.5° N, lavas from back-arc locations at 17° N indicate higher levels of modification by hydrous fluid released from the subducted slab, and (2) compared to back-arc locations at 17° N and 15.5° N, petrogenesis of lavas from back-arc locations at 18° N indicates a greater influence of sediment melt.
TL;DR: In this paper, the structural properties of maruyamaite (K-dominant tourmaline) X(K0.54Na0.28Ca0.17Fe0.39Ti0.31] from the ultrahigh-pressure metamorphic rocks of Kokchetav massif were studied using synchrotron-based single-crystal diffraction up to 20 GPa.
Abstract: The structural behaviour of maruyamaite (K-dominant tourmaline) X(K0.54Na0.28Ca0.19)Y(Mg1.3Al1.17Fe0.39Ti0.14)Z(Al5Mg)[Si5.95Al0.05O18](BO3)3V,W[O1.69(OH)2.31] from the ultrahigh-pressure metamorphic rocks of Kokchetav massif was studied using synchrotron based single-crystal diffraction up to 20 GPa. Within the whole pressure range the compression is regular and anisotropic, with the c direction being more compressible than the a direction. Fitting the V/P data with the 2nd and 3rd order Birch-Murnaghan equations of state gives: V0 = 1587.2(7) A3, K0 = 115.6(9) GPa at fixed K′ = 4, and V0 = 1588(1) A3, K0 = 112(3) GPa, K′ = 4.5(4). The bulk modulus values are slightly higher as compared to those found for dravite and cation-deficient synthetic K-dravite. The pressure evolution of the main structural parameters of K-tourmaline is similar to those of dravite. However, a minor change in the rigidity of local contacts of the X site with 6-membered ring, due to the presence of K, is apparently critical for stabilization of tourmaline structure within 15–20 GPa, which is evinced by the absence of the phase transition observed in dravite near 15.4 GPa. The stabilizing function of K becomes apparent at P > 15 GPa. The comparison of the HP structural behaviour of maruyamaite and dravite supports the recent suggestion that the large X site plays a secondary role in the elastic behaviour of tourmaline, compared to the octahedral framework. In addition, the present study reveals several new features of polyhedra distortions, which demonstrate their complex interaction on compression.
TL;DR: The N-S trending Central-Aldan magnesiocarbonatite province is located in the Aldan-Stanovoy shield (South Yakutia, Russia) as mentioned in this paper.
Abstract: The N-S trending Central-Aldan magnesiocarbonatite province is located in the Aldan-Stanovoy shield (South Yakutia, Russia). Several apatite-dolomitic carbonatite occurrences were studied: Seligdar, Muostalaah, Ust-Chulman and Birikeen. Mineralogical and petrographic investigations indicate intense hydrothermal-metasomatic alteration and metamorphism, which are reflected in the evolution of the mineral parageneses. The primary minerals are fluorapatite, magnetite, ilmenite, dolomite, K-feldspar, phlogopite and accessory zircon, titanite, baddeleyite and thorite. The hydrothermal-metasomatic minerals are quartz, calcite and siderite aggregates with haematite, monazite-(Ce), xenotime-(Y), rutile-(Nb), barite-(Sr), anhydrite, ancylite-(Ce) and rare sulphide mineral phases. Alkaline rocks associated with the Muostalaah complex, were also studied. The following U-Pb ages have been obtained (Ma): 1930 ± 7 for Muostalaah alkaline basic rocks, 1906 ± 6 for Muostalaah carbonatites, and 1880 ± 13 and 1878 ± 17 for Seligdar and Ust-Chulman carbonatites, respectively.
TL;DR: The multilayer coronae between olivine and plagioclase are a common replacement texture in mafic rocks by magmatic and metamorphic processes as discussed by the authors.
Abstract: Coronae between olivine and plagioclase are a common replacement texture in mafic rocks by magmatic and metamorphic processes. Mafic dykes from Palghat Cauvery Shear Zone (PCSZ) of the granulite terrane of southern India display such multilayer coronae between olivine (Ol) and plagioclase (Pl), composed of orthopyroxene-magnetite (OM) and amphibole (Prg). Deformation twins, kinking, bending and fractures in plagioclase laths suggest that the rock underwent post-emplacement deformation. However, amphibole in the plagioclase fractures and preservation of delicate coronae texture indicate that the replacement texture grew in a static condition. Field occurrence and textural relations suggest that the coronae developed in two stages: (1) Stage-I: Ol → OM, followed by (2) Stage-II: OM + Pl = Prg during rehydration of the granulite host rock. Balanced chemical reactions and formation of hydrous amphibole at the expense of anhydrous reactants during Stage-II demonstrates that replacement of earlier minerals occurred in a fluid-present open system. Results from the pseudosection and the μMgO–μCaO phase diagram, suggest fluid played a crucial role in the transition from Stage-I to Stage-II corona at a P-T condition of ~650 ± 50 °C and 5.5–6 kbar. The multilayer coronae is likely to have resulted from late Neoproterozoic thermal metamorphism of granulite terrane of southern India during Pan-African orogeny.
TL;DR: In this paper, an established crystallization sequence (spinel→clinopyroxene→plagioclase±Fe-Ti oxides) was found to be typical for the boninite series from the suprasubduction zones (SSZ) in the Late Jurassic to Early Cretaceous ophiolite melange from the Mt. Medvednica blocks of boninite rocks have been documented.
Abstract: In the Late Jurassic to Early Cretaceous ophiolite melange from the Mt. Medvednica (Vardar Ocean) blocks of boninite rocks have been documented. They emerge as massive lavas made of augite, spinel, albite and secondary hydrous silicates (e.g., chlorite, epidote, prehnite, and pumpellyite). An established crystallization sequence (spinel→clinopyroxene→plagioclase±Fe-Ti oxides) was found to be typical for the boninite series from the suprasubduction zones (SSZ). Augite crystallization temperatures and low pressures of ~1048 to 1260 °C and ~0.24 to 0.77 GPa, respectively, delineated the SSZ mantle wedge as a plausible source of boninite parental lavas. Their whole-rock geochemistry is characterised by low Ti, P2O5, Zr, Y, high-silica, and high Mg# and Cr# values. Low and U-shaped REE profiles are consistent with the negative Nb-Ta, P and Ti anomalies indicative for SSZ. Thorium and LILE enrichment, and very low initial Nd-isotopic values (eNd(T = 150 Ma) + 0.49 to +1.27) act as vestiges of mantle-wedge metasomatism. The mantle source was likely depleted by the MORB and IAT melt extraction and was contemporaneously affected by subduction fluids, prior to the large-scale adiabatic melting of the mantle hanging wall. This eventually gave rise to boninite lavas and an ultra-refractory harzburgite residiuum. The genesis of boninites is related to the Tithonian mature forearc setting that evolved from an intra-oceanic, Callovian to Oxfordian, island-arc environment. The Mt. Medvednica boninite rocks stand for the youngest SSZ-related Jurassic oceanic crust from the NW segment of the Dinaric-Vardar Tethys that are nowadays obducted onto the passive margins of Adria. Taking into account the existence of similar rocks in the ophiolite zones of Serbia, Albania and Greece, the boninites of Mt. Medvednica strongly favours the single Tethyan oceanic basin that existed in this part of Europe during the Late Jurassic.
TL;DR: In this article, highly siderophile element (HSE; Au, Pt, Pd, Ir, Os, Rh and Ru) concentrations in relatively unweathered and unaltered marine shales from the Barberton, Witwatersrand and Transvaal supergroups in the Kaapvaal Craton revealed systematic differences, interpreted to reflect secular changes in the HSE content of Mesoarchaean to Palaeoproterozoic seawater.
Abstract: Determination of highly siderophile element (HSE; Au, Pt, Pd, Ir, Os, Rh and Ru) concentrations in relatively unweathered and unaltered marine shales from the Barberton, Witwatersrand and Transvaal supergroups in the Kaapvaal Craton revealed systematic differences, interpreted to reflect secular changes in the HSE content of Mesoarchaean to Palaeoproterozoic seawater. Most of the studied marine shales have HSE concentrations in the range given for average Archaean crustal rocks (0.5–5 ppb), with the exception of the shales in the Witwatersrand Supergroup. These shales contain up to three times more HSE, independent of source rock lithology in the granitoid-greenstone-dominated hinterland. Although sedimentary pyrite incorporated gold from synsedimentary to early diagenetic waters, its modal proportion (<3 vol.%) is too small to account for the total amount of Au and PGE in the studied marine shales. Instead, our results suggest that in addition to contributions from pyrite, some colloidal gold was attached to clay-sized sediments during source area weathering. Probably, colloidal gold and some of the platinum group elements were mechanically aggregated during sediment suspension and deposited synchronously with the host marine sediments.
TL;DR: Clinopyroxene megacrysts from a scoria cone on Marion Island, Antarctic Ocean are zoned, with compositionally distinct low (Al + Ti) and high (Al ǫ+ǫ) patches arranged haphazardly throughout crystals.
Abstract: Clinopyroxene megacrysts (up to 5 cm) from a scoria cone on Marion Island, Antarctic Ocean are zoned, with compositionally distinct low (Al + Ti) and high (Al + Ti) patches arranged haphazardly throughout crystals. Inclusions of olivine, pyrrhotite, oxides, sulphides, and rounded inclusions with euhedral micro-crystals interpreted as former melt inclusions are observed. Olivine inclusions have variable compositions, ranging from primary Ti-poor crystals to Ti-rich crystals hosting secondary haematite crystals formed by hydrogenation. The crystals contain voids that are concentrated in the middle of each crystal indicating that the initial crystal growth was skeletal. Subsequent crystallisation filled in the skeletal framework creating the patchy zoning in the crystals. The Marion Island megacrysts are not homogenous, but the combination of crustal clinopyroxene compositions, primary and hydrogenated olivine, and the mode of eruption in scoria eruptions indicates that these crystals most likely formed in a shallow magma chamber. Primary olivines crystallised from a mafic magma and secondary altered olivines were incorporated into a rapidly growing megacryst in a super-saturated, fluid-rich environment, prior to being ejected onto surface in a scoria eruption.
TL;DR: The Spiaggia Lunga basalts are the most primitive magmas that erupted at Vulcano after 28 ka and overlap geochemically with a monzogabbroic intrusion of similar age as mentioned in this paper.
Abstract: Vulcano is part of the Aeolian volcanic arc in the southern Tyrrhenian Sea. Its products were emplaced through multiple episodes of edifice building and collapse since about 120 ka B.P. to present. A major discontinuity in the activity occurred after about 28 ka, while the focus of volcanism moved from SE to NW. The older products are basalts to shoshonites, and have lower K2O than the younger ones, shoshonites to rhyolites. Between these two groups, Lentia latites-rhyolites, Spiaggia Lunga basalts, and Quadrara shoshonite-trachytes, erupted along the western side of Vulcano Island. The Spiaggia Lunga basalts (i) are the most primitive magmas erupted at Vulcano after 28 ka (ii) mark the change between older and younger phases, and (iii) overlap geochemically with a monzogabbroic intrusion of similar age. This work focuses on the Spiaggia Lunga products, discussed within a large dataset of geochemical and radiogenic isotope analyses on the entire Vulcano sequence. Older products have more primitive geochemical and isotope characteristics, and lower incompatible element contents, than younger ones. The Spiaggia Lunga basalts exhibit intermediate geochemical characteristics between the older and the younger groups, and can likely be regarded as a third magmatic phase, which represents a distinct mantle reservoir active during the magmatic history of Vulcano. Significant variations of Sr, Nd, and Pb isotope ratios, and isotopic disequilibrium between phenocrysts and groundmass, are present among the Vulcano products. This variability suggests crustal assimilation in shallow-level magma chambers, which also accounts for the formation of evolved products by combined assimilation and fractional crystallization, particularly in the younger series. Considering only the mafic products, incompatible element patterns with high LILE/HFSE and enriched signatures of Sr, Nd, and Pb isotope ratios, indicate enriched mantle sources. Besides, chemical and isotope variability among older, younger, and Spiaggia Lunga mafic rocks, suggests an origin from geochemically diverse primary melts, derived from distinct mantle reservoirs. Their parent magmas, based on geochemical and isotope patterns, were from both MORB- and OIB-type mantle sources, subject to variable degrees of metasomatism by subducted sediments.
TL;DR: In this paper, the authors examined the microinclusions of five typical coated diamonds (from Udachnaya, Yubileynaya, and Aikhal kimberlite pipes) with untypically low microinclusion abundances and four monocrystalline diamonds that exhibit thin intermediate micro-inclusion-bearing zones.
Abstract: Five typical coated diamonds (from Udachnaya, Yubileynaya, and Aikhal kimberlite pipes) with untypically low microinclusion abundances and four monocrystalline diamonds (Udachnaya, Mir, Nyurbinskaya pipes) that exhibit thin intermediate microinclusion-bearing zones were examined in details for growth structures, characteristic infrared absorption and photoluminescence, and composition of microinclusions. The internal structures of diamonds of both types imply that fluid inclusions entrapment in diamonds does not necessarily relate to the terminal stage of rapid fibrous growth. Instead, nitrogen aggregation state in some diamonds showed that both fibrous coats and inclusion-bearing layers might experience an annealing during mantle residence long enough to pre-date the ultimate kimberlite eruption, whereas the diamonds with internal inclusion-bearing zones also experienced later protracted history of monocrystalline growth. The presence of chloride-carbonate-silicate fluids/melts in monocrystalline diamonds indicate their generation from media generally similar to that observed in some fibrous diamonds. However, the composition of these metasomatizing fluids is different for the mantle beneath Udachnaya (mostly carbonatitic) and other pipes (Aikhal, Yubileynaya, Mir; variable abundance of silicic high-density fluids). The abundance of silica-rich fluids record either a heterogeneous distribution of eclogites in the subcontinental lithospheric mantle, or the operation of silica-rich slab-derived fluids. The inclusion abundance as well as the type of growth (fibrous or monocrystalline) is considered to be controlled by the volume of fluid fluxes; in this case, fluid consumption leads to decreasing growth rates, diminishing inclusion entrainment and stability of layered octahedrons. The detected minor compositional variations of high-density fluids in these diamonds may be due to local scale thermal perturbation in the host source and/or limited chemical heterogeneity of the parental fluid. The high amount of chlorides in high-density fluids from monocrystalline diamonds provide a new evidence for compositions of fluids/melts acting as primary metasomatic agent in the deep mantle of Siberian craton.
TL;DR: In this article, a new surfactant butane-3-heptyloxy-1,2-diamine [CH3(CH2)6OCH(CH3)CH(NH2)CH2NH2; BHLD] was synthesized.
Abstract: A new surfactant butane-3-heptyloxy-1,2-diamine [CH3(CH2)6OCH(CH3)CH(NH2)CH2NH2; BHLD] was synthesized. It has been innovatively used as a collector in the flotation of quartz. In this present study, the flotation behaviors of quartz with BHLD were investigated by micro-flotation of quartz. It was found that the recovery of the quartz reaches 98.9%. Furthermore, the hydrogen bond lengths were measured, calculated and simulated in a molecular dynamics (MD) model, and the interaction energy between the four species of BHLD and the quartz surface were determined under vacuum and aqueous conditions. Based on the results of the zeta potential measurements, the FT-IR measurements and the MD simulation in this paper, it is revealed that the BHLD collector adsorbs onto the quartz surface through electrostatic adsorption and hydrogen bond adsorption. Furthermore, micro-flotations were studied by the radial distribution function (RDF) and the relative concentrations. The results show that the hydrogen bond adsorption between the O atom on the quartz surface and the H atom in BHLD are the main interactive forces causing BHLD to adsorb onto the quartz surface. The BHLD cations adsorb significantly more strongly than the BHLD molecules, which agrees well with the results of the micro-flotation tests.
TL;DR: In this paper, the first detailed structural investigation on natural bredigite has been performed and the problem of incorporating Ba incorporation into the bredigites structure is discussed, and the results of finding new Ba-bearing minerals in nature are provided for the first time.
Abstract: Bredigite, Сa7Mg(SiO4)4, is an indicator mineral of metasomatic rocks of the sanidinite facies formed at high temperatures (>800 °C) and low pressures ( 2σ(I) and 149 parameters. To the best of our knowledge this is the first detailed structural investigation on natural bredigite. In contrast to previous studies on samples retrieved from metallurgical slags there was no need to describe the structure in the acentric space group Pnn2. Furthermore, the problem of Ba incorporation into the bredigite structure is discussed. Data on the composition of Ba-bearing bredigites from pyrometamorphic rocks of the Hatrurim Complex from Jordan with simplified formula Ba0.7Ca13.3Mg2(SiO4)8 (based on 32 oxygen atoms) are provided for the first time, pointing out perspectives of finding new Ba-bearing minerals isostructural with bredigite in nature.
TL;DR: This paper investigated the paragenesis and ore mineral composition of heavy rare earth element (HREE) deposits/prospects of the Tanami and Hall Creek regions of Western Australia.
Abstract: This study investigates the paragenesis and ore mineral composition of xenotime [(Y,HREE)PO4] and florencite [LREEAl3(PO4)2(OH)6] from heavy rare earth element (HREE) deposits/prospects of the Tanami and Hall Creek regions of Western Australia. Two stages of xenotime-(Y) formation are recognized: (1) early xenotime-(Y) in breccias (breccia-hosted) and in quartz-xenotime-(Y) veins (vein-type); and (2) late xenotime-(Y) that occurs largely as dipyramidal-shaped overgrowths on the pre-existing early xenotime-(Y). Similarly, florencite-(Ce) formed in two stages including: (1) early florencite-(Ce) that coexists with and is enclosed by early xenotime-(Y) within mineralized veins; and (2) late florencite-(Ce) that replaces early xenotime-(Y), or appears as narrow rims on early florencite-(Ce). All xenotime-(Y) types from a number of examined HREE deposits/prospects are characterized by elevated U contents and marked negative Eu anomalies that we interpret to be inherited from the metasedimentary rocks from which REE and P required for the phosphate ore mineralization, were sourced. Compared to the early xenotime-(Y), the late xenotime-(Y) is richer in HREE and depleted in P, owing to the formation of the coexisting late florencite-(Ce). Moreover, early florencite-(Ce) has a near end-member florencite (s.s.) composition similar to those associated with unconformity-related U deposits, whereas late florencite-(Ce) sits on the florencite-svanbergite compositional spectrum. The high U content of xenotime-(Y) and composition of early florencite-(Ce) potentially support a genetic association between the HREE mineralization and the coeval unconformity-related U deposits of northern Australia. Nevertheless, we also urge for caution in using xenotime-(Y) composition in isolation as an indicator of geological setting.
TL;DR: Zhang et al. as discussed by the authors presented new zircon cathodoluminescence images, U-Pb dates, trace element and Lu-Hf isotope data for three late Neoarchean tonalitic-trondhjemitic-granodioritic (TTG) gneisses and one Paleoproterozoic mafic dyke from Tonghua region, southern Jilin Province.
Abstract: The early Precambrian basement of the North China Craton, China, records a complex history during the Neoarchean and Paleoproterozoic. Southern Jilin Province is one of the best regions to evaluate the early Precambrian crustal growth of the Eastern Block of the North China Craton. We herein present new zircon cathodoluminescence images, U–Pb dates, trace element and Lu–Hf isotope data for three late Neoarchean tonalitic–trondhjemitic–granodioritic (TTG) gneisses and one Paleoproterozoic mafic dyke from Tonghua region, southern Jilin Province. These results lent convincing support to the occurrence of multiple tectono-thermal events in southern Jilin Province during the Archean and Paleoproterozoic, and shed light on the formation and evolution of continental crust in the northeastern Eastern Block. Zircon LA–ICP–MS U–Pb isotopic analyses indicated three episodes of magmatism. Inherited (or captured) zircons with ages of ca. 2.6 Ga provided strong evidence for a pre-2.5 Ga magmatic event in this region. The second magmatic episode occurred at 2556–2522 Ma, as evidenced by extensive exposures of TTG gneisses. The third episode occurred at ca. 2200 Ma and is recorded by several mafic dykes that intruded the Archean TTG gneisses. Metamorphic zircons yielded consistent ages of 2493–2465 Ma, indicating a regional metamorphic event immediately after the late Neoarchean magmatism in southern Jilin Province. Zircon Hf isotope data of the TTG gneisses indicated that the main phase of crustal growth occurred in the late Neoarchean, with a minor input of Mesoarchean continental crustal materials. The combined geochronological, geochemical, and geological data suggested that the three episodes of crustal growth in the northeastern Eastern Block occurred at 2.8–2.7, 2.6–2.5, and 2.2 Ga.
TL;DR: In this article, mineralogical characterization of opaque assemblages from I- and S-type granites from the Aracuai orogen, southeastern Brazil that belong respectively, to the pre- and syn-collisional stages of the orogeny is presented.
Abstract: This study presents mineralogical characterization of opaque assemblages from I- and S-type granites from the Aracuai orogen, southeastern Brazil that belong respectively, to the pre- and syn-collisional stages of the orogeny. Although these granites are geochemically well-characterized, with a robust geochemical, isotopic and geochronological database, their opaque minerals have not yet been investigated, and they provide important information about the oxygen fugacity and temperature conditions of their magmas. I-type granites (G1 Supersuite) consist of biotite hornblende granites and their opaque assemblage is ilmenite + pyrite + pyrrhotite ± magnetite ± Fe-Ti oxides ± chalcopyrite. S-type rocks (G2 Supersuite) are biotite muscovite sillimanite granites with ilmenite + graphite + pyrrhotite + pyrite as opaques. Our results combined with literature data show that ranges for oxygen fugacity (fO2) are: I-type granitoids containing magnetite and free of pyrite and phyrrhotite likely crystallized under fO2 between 10−15 bars and 10–8.5 bars, whereas magnetite free rocks containing pyrite and pyrrhotite should have crystallized with fO2 higher than 10−18 bars and lower than 10−15 bars. Regarding S-type granites, they must have crystallized under fO2 lower than 10−18 bars.
TL;DR: In this paper, the authors present new precise laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) U-Pb zircon age data, geochemical data and Hf isotopic data on the porphyritic granodiorite at Dengjitun and use these data to improve their understanding of the Jurassic tectonic evolution of this region.
Abstract: The Dengjitun Cu deposit, located in the central Xing’an Block, represents a key target for medium- to large-sized porphyry Cu deposit exploration. The mineralization in this area is closely associated with silicification and propylitic alteration and occurs in a distinctive sequence of quartz-bearing veinlets as well as in a disseminated form within an altered porphyritic granodiorite. In this paper, we present new precise laser ablation inductively coupled plasma mass spectrometry (LA–ICP–MS) U–Pb zircon age data, geochemical data and Hf isotopic data on the porphyritic granodiorite at Dengjitun and use these data to improve our understanding of the Jurassic tectonic evolution of this region. Zircon U–Pb dating of two samples from the porphyritic granodiorite yield Early Jurassic ages of 174.2 ± 1.1 Ma and 173.9 ± 1.1 Ma, which are concordant within error. The Dengjitun porphyritic granodiorite is a high-K calc-alkaline and slightly peraluminous I-type granite. It is enriched in light rare earth elements (LREEs) and large ion lithophile elements (LILEs; e.g., K, Rb, and Ba), depleted in heavy rare earth elements (HREEs; LREE/HREE = 6.43–13.34) and high field strength elements (HFSE; e.g., Nb, Ti, P), and has weak positive Ce anomalies (δCe = 1.15–1.25) and negligible Eu anomalies (δEu = 0.85–0.99). The zircons from the porphyritic granodiorite have positive eHf(t) values (+ 8.7 to +11.7) and elevated 176Hf/177Hf ratios (0.282912–0.283000) that yield young TDM2 ages (428–602 Ma). Collectively, these data indicate that the porphyritic granodiorite formed from primitive magma that was generated by the partial melting of juvenile thickened mafic lower crust, which in turn was originally derived from depleted mantle during the Neoproterozoic. The thickened lower crustal material was metamorphosed under amphibolite- to eclogite-facies conditions at depths of >45 km during the subduction of the Mongol–Okhotsk Ocean, with the resulting magmas assimilating some mantle-derived material prior to emplacement. Combining these data with the tectonic history of this area, we suggest that the Dengjitun porphyritic granodiorite formed in a post-collisional extensional tectonic setting after the Early Jurassic final closure of the Mongol–Okhotsk Ocean.
TL;DR: In this paper, the results of the new Electron Microprobe Analysis of apatite, hornblende and biotite crystals of the Hornblende-biotite variety of the Strzegom-Sobotka granite indicate that these rocks experienced several phases during their evolution.
Abstract: The results of the new Electron Microprobe Analysis of apatite, hornblende and biotite crystals of the hornblende-biotite variety of the Strzegom-Sobotka granite indicate that these rocks experienced several phases during their evolution. During the first phase, the melting of the continental crust was caused by heating from basaltic magma. Nevertheless, the system was closed, and there is no evidence of the influence of any mafic component. The volatile compositions of apatite crystals recorded the signature of this phase. Afterwards, small quantities of mafic material were delivered into the crystallizing melt by ascending basaltic magma. The volatile composition of hornblende, together with dramatic changes in the F/Cl ratios between apatite and hornblende, indicates that the injection of mafic material occurred between the crystallization of both minerals. During the crystallization of hornblende, the system was closed. During the last episode, the volatile composition recorded by biotite indicates that the system opened again. This is represented by the decrease of Cl in the melt. Moreover, the estimated F concentrations in the melt range from ~2000 to ~3000 ppm and do not change significantly within the crystallization interval, whereas the Cl concentrations decreased from 1470-900 ppm at 829-768 °C to as low as 100 ppm at 710-650 °C, most likely due to the continuous exsolution of aqueous fluid from silicate melt or the crystallization of Cl-bearing minerals.
TL;DR: In this paper, a simple binary Hf-O isotope mixing model was used to show that the assimilation of 10−15% sediments by MORB could have generated the Bilihe granodioritic porphyry, and that the extraction of less than 5% of sediments from MORB generated the Hadamiao quartz diorite.
Abstract: The Xing-Meng Orogenic Belt (XMOB) hosts significant Au-dominant polymetallic mineral deposits. Although these deposits mostly formed in the Mesozoic, Permian Au deposits are also present but less well studied. In the Bilihe and Hadamiao gold mining areas, granitic intrusions that are associated with gold mineralization were dated by LA–ICP–MS at 272.7–259.7 Ma. These intrusions consist of granodioritic porphyry and quartz diorite that both represent calc-alkaline metaluminous I-type granites. These granitoids exhibit enrichment in LREEs and LILEs, depletion in HREEs and HFSEs, and low Sr/Y ratios, suggesting that these rocks have an island-arc affinity. The eHf(t) values of the Bilihe granodioritic porphyry and Hadamiao quartz diorite range from −0.3 to +8.9, with TDM2 values ranging from 0.7 to 1.3 Ga, and from +2.5 to +13.5, with TDM2 values ranging from 0.4 to 1.1 Ga, respectively. The zircon δ18O values of the granitic porphyry and quartz diorite range from 6.9 to 7.6‰ and from 5.0 to 6.4‰, respectively. A simple binary Hf–O isotope mixing model shows that the assimilation of 10–15% sediments by MORB could have generated the Bilihe granodioritic porphyry, and that the assimilation of less than 5% sediments by MORB could have generated the Hadamiao quartz diorite. Combined with previous studies of the Late Carboniferous to Permian igneous rocks in the southern region of the XMOB, these new data suggest that the Bilihe and Hadamiao ore-related intrusive rocks formed in a continental-arc setting associated with the subduction of the Paleo-Asian oceanic slab. This setting indicates the potential existence of subduction-related gold deposits that are related to contemporaneous igneous activity.
TL;DR: An assemblage of tantalite-(Mn), tantalian rutile, tapiolite-(Fe), titanowodginite, ferrotitanowodgenite, and hydroxycalciomicrolite occurs in the Nancy granitic pegmatite, San Luis range, Argentina as discussed by the authors.
Abstract: An assemblage of tantalite-(Mn), tantalian rutile, tapiolite-(Fe), titanowodginite, ferrotitanowodginite, and hydroxycalciomicrolite occurs in the Nancy granitic pegmatite, San Luis range, Argentina. The Nancy beryl-type, beryl–columbite–phosphate subtype of LCT (Li-Cs-Ta) rare-element pegmatite was emplaced in the Paleozoic Conlara pegmatitic field. The assemblage occurs at the core margin of the pegmatite, forming an irregularly shaped, 18 by 6 cm nodule. The chemical composition of tantalite-(Mn) shows median Ta# [= (Ta/(Ta + Nb) apfu (atoms per formula unit)] and Mn# [= (Mn/(Mn + FeT) apfu] values of 0.57 and 0.64, respectively; Ti, U and Zr show maximum and [median] contents of: 3.37 [1.25] wt.% TiO2, 0.58 [0.24] wt.% UO2, and 0.72 [0.50] wt.% ZrO2. The unit-cell parameters indicate a moderately ordered structure. Tantalian rutile occurs as anhedral grains replacing tantalite-(Mn), associated with hydroxycalciomicrolite. Its chemical composition shows moderate to high Ti contents, with a maximum and [median] of 64.77 [38.67] wt.% TiO2. The proportion of Ta is very high, with 49.67 [39.59] wt.% Ta2O5. Tapiolite-(Fe), with 82.49 [81.86] wt.% Ta2O5, 2.51 [2.33] wt.% Nb2O5, 0.94 [0.79] wt.% TiO2, and 13.31 [13.18] wt.% FeO, has uniform Ta# and Mn# values, 0.95 and 0.09, respectively. Titanowodginite shows Ta# values ranging from 0.82 to 0.88, whereas in ferrotitanowodginite it ranges from 0.88 to 0.94. The Mn# value is similar in titanowodginite (0.51–0.64), and decreases in the ferrotitanowodginite (0.04 to 0.41). These minerals form a replacement sequence of tantalite-(Mn). Hydroxycalciomicrolite occurs in two generations: I and II. The dominant A cation is Ca, with a median value of 14.39 wt.% CaO. The MnO content, with a median of 1.16 wt.% MnO, is relatively constant. The amount of UO2 is usually below 3 wt.%, but locally attains 6.9 wt.%, and exceptionally 43.6 wt.%, in irregular rims that show a low analytical total, giving compositions that depart from the expected stoichiometry; it is clearly a subsolidus phase. In the more plausible explanation for the evolution of this assemblage, the magmatic crystallization of tantalite-(Mn) was followed during the early subsolidus stage by its partial replacement by tantalian rutile + tapiolite-(Fe) + titanowodginite + ferrotitanowodginte, associated with hydroxycalciomicrolite I, and later, by hydroxycalciomicrolite II produced by the influx of a late Fe–Ti–Ca-bearing fluid phase likely entering the pegmatite from the wall rocks.
TL;DR: In the southeast of Hamedan, in the Sanandaj-Sirjan Zone of Iran, metamorphic rocks display different assemblages formed during dynamothermal and contact-metamorphic events.
Abstract: In the southeast of Hamedan, in the Sanandaj-Sirjan Zone of Iran, metamorphic rocks display different metamorphic assemblages formed during dynamothermal and contact metamorphic events. The isograds in metapelitic rocks vary across the region: in the south, the sequence is chlorite – biotite – garnet – staurolite, but in the east and southeast it is chlorite – garnet – biotite – andalusite – sillimanite. Based on microstructure, peak metamorphic conditions were the same for both Al2SiO5(ALS) bearing and Al2SiO5 free assemblages: 628 °C and 4.4 kbar for the sillimanite zone and 577 °C and 4.2 kbar for the staurolite zone. Pseudosections were constructed for two representative bulk rock compositions, in the Kamari area for ALS bearing rocks and in the Aliabad-Damagh area for ALS free rocks. Comparing pseudosections with the estimated P and T shows that the appearance of ALS polymorphs was controlled by the chemical composition of the parent rocks rather than variations in P and T. The P-T paths of both ALS-bearing and ALS-free sequences are similar and both follow an anticlockwise trend but the geothermal gradient is slightly higher for ALS-bearing schists. It is concluded that different zones in the area developed at the same time, during the same deformation phases, but under different geothermal gradients. Metamorphism of the Hamedan area occurred during the convergent orogeny and subduction of the Neo-Tethys in the Jurassic and was coeval with the main magmatic phases.