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The ore at the Dwyer fluorite mine, near Wilberforce, Ontario, consists of calcite–fluorite dikes that show clear signs of flowage. Those dikes and the large-scale development of fenites at the expense of a granite–monzonite pluton can only be explained by the existence of a subjacent body of carbonatite. The dikes consist of ribbons of calcite and fluorite and contain subhedral crystals of fluorapatite aligned with the ribbons. The dikes also carry crystals of aegirine-augite, titanite, and bastnäsite-(Ce). Both the fluorapatite and aegirine-augite contain micrometric globules of boundary-layer melt that crystallized in situ to calcite, fluorite, quartz, bastnäsite-(Ce), hematite, and titanite. Fragments of the REE-enriched fenite show signs of incipient rheomorphism at a temperature estimated to be at least 725 °C. The large-scale alkali metasomatism occurred toward the end of the Grenville orogenic cycle, at a time of crustal relaxation, roughly 200 million years after emplacement of a granite–monzonite pluton. By analogy with occurrences elsewhere, it is likely that the carbonatitic melt separated immiscibly from a nepheline syenitic parental melt. Fluor-calciocarbonatitic magmatism likely is genetically linked to the U and Th mineralization in the area and contributed to the unusual geological complexity of the Bancroft–Haliburton region.

The origin of an array of marble samples found in both the Grenville Province and southwestern Sri Lanka remains uncertain, whether magmatic, sedimentary, or mixed, due to their proximity to both carbonatite bodies and carbonate-rich metasedimentary rocks. This study reports boron and trace element abundances, in addition to carbon, oxygen, boron, and strontium isotopic compositions, to determine the petrogenesis of these carbonate-rich samples. Boron abundances for all of the samples are relatively high and variable (1.48–71.1 ppm) compared to those for carbonatites worldwide (≤1 ppm), and mostly overlap those documented for sedimentary sources (up to 54 ppm). The rare earth element (REE) abundances (0.5–1068 ppm) for the marbles studied are similar to those for local sedimentary units and thus contain, in general, lower REE contents than both the average worldwide calciocarbonatite and respective neighboring carbonatite bodies. The δ13CV-PDB and δ18OV-SMOW compositions for all of the samples range between –2.9 to +3.2 ± 0.1‰ and +14.3 to +25.8 ± 0.2‰, respectively, and are considerably heavier than those reported for magmatic or metamorphosed carbonatites. The 87Sr/86Sr ratios reported here range from 0.70417 to 0.70672, which are more radiogenic than the average 87Sr/86Sr (~0.70345) reported for carbonatites included for comparison in this study. Importantly, the boron isotopic compositions (δ11B‰) for samples from the Grenville Province range from +7.5 to +15.7 ± 0.5‰, which are consistent with those reported for biogenic carbonate (+4.9 to +35.1‰). In contrast, δ11B values for the samples of marble from Sri Lanka vary from –9.8 to –14.3 ± 0.5‰ overlapping with those estimated for average bulk continental crust (–9.1 ± 2.4‰). Together, the boron compositions, chemical data, stable (C, O), and radiogenic Sr isotopic data overwhelmingly point to a sedimentary origin for the marble samples examined here. Specifically, the samples from the Grenville Province represent marble formed during high-temperature regional metamorphism of limestone units. The Sri Lankan samples were formed from carbonate-rich and 11B-poor fluids derived from a crustal source. The boron isotopic compositions for the samples studied here are also compared to those reported for mantle-derived carbonate (i.e., carbonatites) worldwide, along with their associated δ13CV-PDB and 87Sr/86Sr values. This comparison results in defining three isotopically distinct fields; mantle-derived carbonates, sedimentary carbonates derived from heterogeneous limestone protoliths, and carbonates derived from meteoric water interacting with crustal material. This work establishes the effective use of boron isotopic compositions in determining the origin of carbonate-rich rocks of contentious petrogenesis.

The maximum value of Mg# [= 100Mg/(Mg + Fe2+ + Mn)] in chromium-bearing spinel-group minerals (Chr) in the Ultrabasic Core Zone (UCZ) of the Lyavaraka orthopyroxenite – harzburgite – dunite complex of the Serpentinite Belt in the Kola Peninsula is 54.5–67.5. Such highly magnesian compositions of spinel are associated with notable enrichments of ferric iron (Fe3+# 58–63). There are two generations of accessory Chr in the UCZ unit. The first generation occurs as inclusions in olivine that is not unusually magnesian (Mg# 90.3), and the second is closely associated with serpentine. The compositional series of Chr at Lyavaraka attains more aluminous compositions than was observed in nearby intrusive bodies. The anomalously high level of Mg in Chr, also manifest in ilmenite, is mainly a result of the high intrinsic fugacity of oxygen attained locally in the melt. A progressive buildup in H2O and increase in fO2 likely resulted from efficient vesiculation and selective loss of H2 from the Al-undepleted komatiitic magma crystallizing in a shallow setting. The chromian spinel forming in such a modified magma is virtually unzoned in Mn, and a minor quantity of Mn is also present in olivine and orthopyroxene. In contrast, zinc is strongly partitioned in the core of Chr, as it is relatively incompatible in the coexisting olivine and orthopyroxene at that stage. Zinc efficiently partitioned into the H2O-enriched melt, which crystallized as the pegmatitic orthopyroxenite near the contacts at Lyavaraka. A high potential of oxidation appears to be characteristic of all orthopyroxenite – harzburgite – dunite suites of the Serpentinite Belt formed from a primitive melt of komatiitic composition.

—The paper focuses on compositional variations of olivine and chromian spinel in the Monchepluton and Pados-Tundra layered intrusions, which host significant chromitite mineralization. Ore-bearing dunite (with up to 25–30 vol.% Mcr) in the Sopcheozerskoe chromite deposit from the Monchepluton complex, Kola Peninsula, Russia, bears an assemblage of phases with exceptionally high magnesium contents: Fo96 + augite (Mg# = 94) + magnesiochromite, Mcr (Mg# ≈ 65); Mg# = 100·Mg/(Mg + Fe2+ + Mn). However, olivine in the host dunite has normal maximum values of Mg# comparable to those in cumulus olivine from layered intrusions worldwide (Fo≤91–92). The Fo96 phase in the Sopcheozerskoe deposit shows the most primitive composition ever reported from any layered intrusion. Magnesiochromite occurs as unzoned homogeneous euhedral crystals unaffected by subsolidus exchange or metasomatic effects. Olivine in ore-bearing dunite (20–25 vol.% magnesian chromite) from the Pados-Tundra complex attains Fo93, with the Mg# value notably higher than the range (Fo85.5–90.6) in olivine from orthopyroxenite, harzburgite, and dunite within the intrusion. Olivine and chromian spinel in the two complexes behave coherently, with covarying patterns of Mg# and Ni contents in olivine at R = 0.75 (n = 160) and positive correlation between Mg# in coexisting chromian spinel and olivine grains at R = 0.8 (n = 150). This behavior indicates that the two phases attained equilibrium during crystallization. It appears unlikely that the extremely high Mg enrichment in olivine (Fo96), as well as in all associated phases of the Monchepluton complex, would result from a subsolidus reaction between olivine and chromian spinel or low-temperature alteration of olivine. We suggest a more realistic explanation that the olivine (+ high-Mg augite)–chromian spinel assemblage crystallized from komatiitic magma under the conditions of progressively increasing oxygen fugacity (fO2). The high Mg# in the Mcr-chromite-enriched system, above the maximum values common in cumulus olivine from layered intrusions (up to Fo96 against Fo≤91–92), may be caused by shortage of ferrous iron.

Author(s): Barkov, AY; Bindi, L; Tamura, N; Martin, RF; Ma, C; Winkler, B; Shvedov, GI; Morgenroth, W | Abstract: Fleetite, Cu2RhIrSb2, a new species of platinum-group mineral (PGM), was discovered intergrown with an Os–Ir–Ru alloy in the Miass Placer Zone (Au–PGE), southern Urals, Russia. A single grain 50 lm across was found. Osmium, ruthenium, and iridium are the main associated minerals; also present are Pt–Fe alloys, laurite, Sb-rich irarsite, Rh-rich tolovkite, kashinite, anduoite, ferronickelplatinum, heazlewoodite, PGE-bearing pentlandite and digenite, as well as micrometric inclusions of forsterite (Fo93.7), chromite–magnesiochromite, and Mg-rich edenite. In reflected light, fleetite is light gray; it is opaque, isotropic, non-pleochroic, and non-bireflectant. We report reflectance values measured in air. A mean of seven point-analyses (wavelength-dispersive spectrometry) gave Cu 13.93, Ni 8.60, Fe 0.10, Ir 28.07, Rh 7.91, Ru 1.96, Sb 39.28, total 99.85 wt.%, corresponding to (Cu1.41Ni0.58Fe0.01)R2.00(Rh0.49Ni0.36Ru0.12)R0.97Ir0.95Sb2.08 on the basis of six atoms per formula unit, taking into account the structural results. The calculated density is 10.83 g/cm3. Single-crystal X-ray studies show that fleetite is cubic, space group Fd3m (#227), a = 11.6682(8) A, V = 1588.59(19) A3, and Z = 16. A least-squares refinement of X-ray powder-diffraction data gave a = 11.6575(5) A and V = 1584.22(19) A3. The strongest five reflections in the powder pattern [d in A(I)(hkl)] are: 6.70(75)(111), 4.13(100)(220), 3.52(30)(311), 2.380(50)(422), 2.064(40)(440). Results of synchrotron micro-Laue diffraction experiments are consistent [a ¼ 11.66(2) A]. The crystal structure of fleetite was solved and refined to R ¼ 0.0340 based upon 153 reflections with Fo . 4r(Fo). It is isotypic with Pd11Bi2Se2 and best described as intermetallic, with all metal atoms in 12-fold coordination. Fleetite and other late exotic phases were formed by reaction of the associated alloy phases with a fluid phase enriched in Sb, As, and S in circulation in the cooling ophiolite source-rock. The mineral is named after Michael E. Fleet (1938–2017) in recognition of his significant contributions to the Earth Sciences.

The Lenadora quarry, located 25 km north of Matale, in central Sri Lanka, exploits dolomitic marble on an artisanal scale. It is located in the Highland Complex but very close to its thrust contact with the Wanni Complex. The rocks have undergone metamorphism to the granulite facies; by analogy with metasedimentary rocks in a similar position south of Kandy, conditions of metamorphism may even have surpassed 900°C and 0.9 GPa. How did dolomitic marble fare in such an ultrahigh-temperature environment? High-resolution large-area image mosaics of imaged polished thin sections were acquired by using both light microscopy and scanning electron microscopy. We focus on fifty areas of interest. As expected, diopside and forsterite porphyroblasts appeared during prograde metamorphism. However, we did not anticipate to see subhedral porphyroblasts of forsterite mimetically replaced by diopside + dolomite. The conversion could have involved a fluid phase or a carbonate melt that had become locally enriched in silica. The presence of a melt accounts for composite calcite + dolomite globules trapped in forsterite. There is no evidence of breakdown products of dolomite, like periclase or brucite. The evidence that a carbonate melt was present is circumstantial; carbonate systems are notorious for erasing telltale evidence of melting. Other minerals encountered in the dolomitic matrix are phlogopite, pargasite, rutile, hydroxylapatite, zirconolite, lakargiite, a magnesiobeltrandoite-like phase, pyrrhotite, and calcite as a minor phase, some of which is of a second generation. Unreplaced relics of forsterite were partially serpentinized at a retrograde stage.

Ångström exponents (

We describe an unusual example of rhythmically layered peraluminous granitic pegmatite locally developed in the intragranitic Potrerillos NYF pegmatites derived from the A-type host granites of the Las Chacras–Potrerillos batholith, Sierra de San Luis, Argentina. The strikingly rhythmic layers in the Zebra pegmatite consist of units of albite–K-feldspar–quartz–K-feldspar–albite, with accessory tourmaline and minor muscovite. The layers crystallized from a boron-bearing melt ponded and thermally insulated in the intermediate zone. A layer of low albite 1–2 cm thick was followed by coarser-grained K-feldspar, then well-ordered microcline, which gives way to quartz grains, also coarser-grained, in optical continuity. Zoned prismatic crystals of schorl nucleated in the feldspathic layer in random orientation. Muscovite is scarce. The rock has a granitic composition enriched in Rb, Cs, and B, and is depleted in the rare-earth elements compared to its precursor. We contend that the normative composition, 35.3% Or, 38.1% Ab, and 21.3% Q, was close to the eutectic in the granite system modified by dissolved H2O, F, and B, at a P(H2O) close to 3.5 kbar and a temperature in the range 575–600 °C. Repeated incursions from the field of Ab + Or to the field of quartz and back again as the melt was producing bubbles of H2O can account for the rhythmic crystallization and the local truncation or merging of the feldspathic layers. Occasional larger crystals of K-feldspar may have become detached from the wall or roof of the chamber.

For the first time, corona-type textures are described in ultrabasic rocks in three complexes of the Serpentinite Belt on the Kola Peninsula in the northeastern Fennoscandian Shield. Three variants of the corona texture formed at different stages during the crystallization of a komatiitic, Al-undepleted melt emplaced in a subvolcanic setting. The first type crystallized at an early stage (Mg# Ol = 87) in a fine-grained harzburgite of the Chapesvara-I sill, with the following order in the corona: Ol → Opx → Cpx → Pl → Amp (aluminous sodic-calcic). The second type displays the sequence Opx → Cpx → Amp → Pl → Qz, which is observed in the orthopyroxenite zone in the Lotmvara-I sill. The third type involves a symplectitic corona in a plagioclase-bearing orthopyroxenite in the Lyavaraka complex, in which the inferred order is: Cpx → Amp (aluminous hornblende) + symplectitic Qz, formed in direct contact with grains of Pl. The corona-type textures occur in fresh rocks and are not related to regional metamorphism. They likely formed as consequences of two important factors: (1) rapid cooling, leading to unsteady conditions of crystallization in a shallow setting; and (2) an intrinsic enrichment in H2O and other volatiles in the parental magma, giving rise to fluid-saturated environments at advanced stages of crystallization. This was followed by a deuteric deposition of Amp rims as a result of the accumulation of H2O and reaction of H2O-bearing fluid with early grains of pyroxene and late plagioclase. The likely existence of a close relationship is suggested by the drusites of the Belomorian complex, which are coeval. In addition, unusual occurrences of lamellar inclusions of phlogopite and Al2SiO5 are documented, hosted by interstitial grains of plagioclase in the orthopyroxenite zone of the Lotmvara-I sill. These are attributed to crystallization from late portions of remaining melt enriched in Al, K, Na, H2O, and Cl, which is indicated by the recorded occurrence of chlorapatite in this association. Thus, our findings indicate the presence and abundance of intrinsic volatiles, Cl, F, CO2, and especially magmatic H2O, which were important to lower the liquidus, decrease the density and viscosity of the highly magnesian melt of Al-undepleted komatiite, thus enabling its transport from the mantle to a shallow level in the crust.

Ferrotorryweiserite, Rh5Fe10S16, occurs as small grains (≤20 µm) among droplet-like inclusions (up to 50 μm in diameter) of platinum-group minerals (PGM), in association with oberthürite or Rh-bearing pentlandite, laurite, and a Pt-Pd-Fe alloy (likely isoferroplatinum and Fe-Pd-enriched platinum), hosted by placer grains of Os-Ir alloy (≤0.5 mm) in the River Ko deposit. The latter is a part of the Sisim placer zone, which is likely derived from ultramafic units of the Lysanskiy layered complex, southern Krasnoyarskiy kray, Russia. The mineral is opaque, gray to brownish gray in reflected light, very weakly bireflectant, not pleochroic to weakly pleochroic (grayish to light brown tints), and weakly anisotropic. The calculated density is 5.93 g·cm–3. Mean results (and ranges) of four WDS analyses are: Ir 18.68 (15.55–21.96), Rh 18.34 (16.32–20.32), Pt 0.64 (0.19–1.14), Ru 0.03 (0.00–0.13), Os 0.07 (0.02–0.17), Fe 14.14 (13.63–14.64), Ni 13.63 (12.58–14.66), Cu 4.97 (3.42–6.41), Co 0.09 (0.07–0.11), S 29.06 (28.48–29.44), and total 99.66 wt.%. They correspond to the following formula calculated for a total of 31 atoms per formula unit: (Rh3.16Ir1.72Pt0.06Ru0.01Os0.01)Σ4.95(Fe4.48Ni4.11Cu1.38Co0.03)Σ10.00S16.05. The results of synchrotron micro-Laue diffraction studies indicate that ferrotorryweiserite is trigonal; its probable space group is R3¯m (#166) based on its Ni-analog, torryweiserite. The unit-cell parameters refined from 177 reflections are a = 7.069 (2) Å, c = 34.286 (11) Å, V = 1484 (1) Å3, and Z = 3. The c:a ratio is 4.8502. The strongest eight peaks in the X-ray diffraction pattern derived from results of micro-Laue diffraction study [d in Å(hkil)(I)] are 2.7950 (202¯5) (100); 5.7143 (0006) (60); 1.7671 (224¯0) (44.4); 3.0486 (202¯1) (39.4); 5.7650 (101¯2) (38.6); 2.5956 (202¯7) (37.8); 3.0058 (112¯6) (36.5); and 1.5029 (42¯ 2¯12) (35.3). Ferrotorryweiserite and the associated PGM crystallized from microvolumes of residual melt at late stages of crystallization of grains of Os- and Ir-dominant alloys occurred in lode zones of chromitites of the Lysanskiy layered complex. In a particular case, the residual melt is disposed peripherally around a core containing a disequilibrium association of magnesian olivine (Fo72.9–75.6) and albite (Ab81.6–86.4), with the development of skeletal crystals of titaniferous augite: Wo40.8–43.2En26.5–29.3Fs20.3–22.6Aeg6.9–9.5 (2.82–3.12 wt.% TiO2). Ferrotorryweiserite represents the Fe-dominant analog of torryweiserite. We also report occurrences of ferrotorryweiserite in the Marathon deposit, Coldwell Complex, Ontario, Canada, and infer the existence of the torryweiserite–ferrotorryweiserite solid solution in other deposits and complexes.

We describe a potentially new species of a platinum cupride–stannide mineral (PCSM) of composition Pt(Cu0.67Sn0.33). It occurs in a placer deposit in the River Bolshoy Khailyk, southern Krasnoyarskiy kray, Russia. A synthetic equivalent of PCSM was obtained and characterized. The PCSM occurs as anhedral or subhedral grains up to 15 μm × 30 μm in association with various platinum-group minerals, Rh–Co-rich pentlandite and magnetite, all hosted by a placer grain of Cu–Au–Pt alloy. Synchrotron micro-Laue diffraction studies indicate that the PCSM mineral is tetragonal and belongs to the inferred space-group P4/mmm (#123). Its unit-cell parameters are a = 2.838 (3) Å, c = 3.650 (4) Å, and V = 29.40 (10) Å3, and Z = 1. The c:a ratio calculated from the unit-cell parameters is 1.286. These characteristics are in good agreement with those obtained for specimens of synthetic Pt(Cu0.67Sn0.33). A review on related minerals and unnamed phases is provided to outline compositional variations and extents of solid solutions in the relevant systems PtNi–PtFe–PtCu, PdCu–PdHg–PdAu, PdHg–PtHg, and AuCu–PtCu. The PCSM-bearing mineralization appears to be related genetically with an ophiolitic source-rock of the Aktovrakskiy complex of the western Sayans. The unnamed phase likely crystallized from microvolumes of a highly fractionated melt rich in Cu and Sn.

We have investigated a locality very well known to mineral collectors, the Yates U-Th prospect near Otter Lake, Québec. There, dikes of orange to pink calcite enclose euhedral prisms of fluorapatite, locally aligned. Early investigators pointed out the importance of micro-inclusions in the prisms. We describe and image the micro-inclusions in two polished sections of fluorapatite prisms, one of them with a millimetric globule of orange calcite similar to that in the matrix. We interpret the globule to have been an inclusion of melt trapped during growth. Micro-globules disseminated in the fluorapatite are interpreted to have crystallized in situ from aliquots of the boundary-layer melt enriched in constituents rejected by the fluorapatite; the micro-globules contain a complex jigsawed assemblage of carbonate, silicate, and sulfate minerals. Early minerals to crystallize are commonly partly dissolved and partly replaced by lower-temperature phases. Such jigsawed assemblages seem to be absent in the carbonate matrix sampled away from the fluorapatite prisms. The pressure and temperature attained at the Rigolet stage of the Grenville collisional orogeny were conducive to the anatexis of marble in the presence of H2O. The carbonate melt is considered to have become silicocarbonatitic by assimilation of the enclosing gneisses, which were also close to their melting point. Degassing was important, and the melt froze quickly. The evidence points to a magmatic origin for the carbonate dikes and the associated clinopyroxenite, rather than a skarn-related association.

We describe the new species ognitite, NiBiTe, and a Co-rich variety of maucherite, hitherto unreported; both were discovered in the Ognit ultramafic complex of Neoproterozoic age in Eastern Sayans, Russia. The mean composition of ognitite (n = 7) is: Ni 17.05, Fe 0.07, Cu 0.14, Pd 0.14, Te 32.53, Bi 49.64, total 99.57 wt.%, corresponding to: (Ni1.11Cu0.008Fe0.005Pd0.005)Σ1.13Bi0.90Te0.97 (Σ atoms = 3 apfu). Ognitite is trigonal, space group P3m1 [R1 = 0.0276 for 81 reflections with Fo > 4σ(Fo)]. The unit-cell parameters derived from the single-crystal X-ray diffraction data are: a = 3.928(1) Å, c = 5.385(1) Å and V = 71.95(4) Å3, with Z = 1. The c:a ratio is 1.37. The powder X-ray diffraction data obtained on the same fragment used for the single-crystal study are: a = 3.9332(4) Å, c = 5.3920(6) Å and V = 72.24(1) Å3. Ognitite exhibits the brucite-type structure with edge-sharing NiTe3Bi3 octahedra forming sheets parallel to (0001). It is related to melonite, but is distinct compositionally by the extreme Bi-enrichment (melonite and its synthetic analogue contain At more than 9 wt.% Co, or ~2 apfu Co, the core of Co-rich maucherite [(Ni,Co)11As8] in a zoned crystal, which is surrounded by Co-depleted orcelite, far surpasses the norm (≤1 and up to 3.9 wt.% Co). The unit-cell parameters of the Co-rich maucherite are: a = 6.85(2) and c = 21.83(5) Å, which are based on results of synchrotron micro-Laue diffraction.The host rock consists of serpentine, clinochlore (Mg# 95–97) and skeletal chromite. We favour the metastable crystallisation of fluid-saturated globules of a sulfide–arsenide melt to explain the anomalous compositions of ore minerals at Ognit. These anomalies seem consistent with rapid cooling in a fluid-enriched system, possibly related to late-stage degassing of the magma, as reflected in a prominent metasomatic aureole at the contact with the enclosing gneissic rocks.

Chromitite zones associated with ultramafic units of the Lysanskiy layered complex of dunite–peridotite–gabbro composition could well represent the primary source for the placers bearing platinum-group minerals (PGM) of the entire drainage of the River Sisim and its tributaries, the rivers Ko and Seyba, eastern Sayans. Alluvial gold present in the placers of River Seyba, as elsewhere in the Sisim Placer Zone, reflects mineralisation during a recent period of tectonic activity. We focus on the PGM in the Seyba suite, and in particular on the attributes of pentlandite enriched in platinum-group-elements (PGE) and the compositionally similar and recently defined ferhodsite, which were trapped in host grains of Os–Ir–Ru alloy. Both minerals formed from small volumes of fractionated Fe–Ni–Cu melt considerably enriched in the PGE. In the Seyba suite, as in several others, the amounts of PGE in ferhodsite exceeds that in pentlandite, which results in a greater proportion of vacancies than in pentlandite.

The purpose of this study was to characterize emergency pediatric burn care triage at a tertiary children's hospital to identify targets for quality improvement.A retrospective review of patients18 years with primary burn injuries who presented to a children's emergency department in 2016 was conducted. Demographic and injury characteristics were recorded. Low acuity was defined by size (5% total body surface area burn), depth (not third degree), and no need for conscious sedation for debridement. Multiple logistic regression was used for analysis.A total of 309 pediatric burn patients were triaged in the emergency department. Patients were typically young (median 3.3 years), male (59%), Hispanic (47%), publically insured (77%), and transferred in (65%). Scalding was the most common mechanism (59%). Though most burns were small (median 2% total body surface area), not deep (third degree: 91%), and debrided without sedation (70%), most patients were admitted (80%). On regression, larger total body surface area, child protective services involvement, and in-transfer, but not mechanism, location of injury, or time of day, were associated with observation admission (24 hours) versus emergency department discharge.Though burns were low acuity, most children were admitted. Social factors may play an important role in triage decisions but there may be an opportunity for improved resource utilization.

Tamuraite, ideally Ir5Fe10S16, occurs as discrete phases (≤20 μm) in composite inclusions hosted by grains of osmium (≤0.5 mm across) rich in Ir, in association with other platinum-group minerals in the River Ko deposit of the Sisim Placer Zone, southern Krasnoyarskiy Kray, Russia. In droplet-like inclusions, tamuraite is typically intergrown with Rh-rich pentlandite and Ir-bearing members of the laurite–erlichmanite series (up to ~20 mol.% “IrS2”). Tamuraite is gray to brownish gray in reflected light. It is opaque, with a metallic luster. Its bireflectance is very weak to absent. It is nonpleochroic to slightly pleochroic (grayish to light brown tints). It appears to be very weakly anisotropic. The calculated density is 6.30 g·cm−3. The results of six WDS analyses are Ir 29.30 (27.75–30.68), Rh 9.57 (8.46–10.71), Pt 1.85 (1.43–2.10), Ru 0.05 (0.02–0.07), Os 0.06 (0.03–0.13), Fe 13.09 (12.38–13.74), Ni 12.18 (11.78–13.12), Cu 6.30 (6.06–6.56), Co 0.06 (0.04–0.07), S 27.23 (26.14–27.89), for a total of 99.69 wt %. This composition corresponds to (Ir2.87Rh1.75Pt0.18Ru0.01Os0.01)Σ4.82(Fe4.41Ni3.90Cu1.87Co0.02)Σ10.20S15.98, calculated based on a total of 31 atoms per formula unit. The general formula is (Ir,Rh)5(Fe,Ni,Cu)10S16. Results of synchrotron micro-Laue diffraction studies indicate that tamuraite is trigonal. Its probable space group is R–3m (#166), and the unit-cell parameters are a = 7.073(1) Å, c = 34.277(8) Å, V = 1485(1) Å3, and Z = 3. The c:a ratio is 4.8462. The strongest eight peaks in the X-ray diffraction pattern [d in Å(hkl)(I)] are: 3.0106(26)(100), 1.7699(40)(71), 1.7583(2016)(65), 2.7994(205)(56), 2.9963(1010)(50), 5.7740(10)(45), 3.0534(20)(43) and 2.4948(208)(38). The crystal structure is derivative of pentlandite and related to that of oberthürite and torryweiserite. Tamuraite crystallized from a residual melt enriched in S, Fe, Ni, Cu, and Rh, these elements were incompatible in the Os–Ir alloy that nucleated in lode zones of chromitites in the Lysanskiy layered complex, Eastern Sayans, Russia. The name honors Nobumichi Tamura, senior scientist at the Advanced Light Source of the Lawrence Berkeley National Laboratory, Berkeley, California.

The lopolithic Pados-Tundra layered complex, the largest member of the Serpentinite belt&ndash, Tulppio belt (SB&ndash, TB) megastructure in the Fennoscandian Shield, is characterized by (1) highly magnesian compositions of comagmatic dunite&ndash, harzburgite&ndash, orthopyroxenite, with primitive levels of high-field-strength elements, (2) maximum values of Mg# in olivine (Ol, 93.3) and chromian spinel (Chr, 57.0) in the Dunite block (DB), which exceed those in Ol (91.7) and Chr (42.5) in the sills at Chapesvara, and (3) the presence of major contact-style chromite&ndash, IPGE-enriched zones hosted by the DB. A single batch of primitive, Al-undepleted komatiitic magma crystallized normally as dunite close to the outer contact, then toward the center. A similar magma gave rise to Chapesvara and other suites of the SB&ndash, TB megastructure. Crystallization proceeded from the early Ol + Chr cumulates to the later Ol&ndash, Opx and Opx cumulates with accessory Chr in the Orthopyroxenite zone. The accumulation of Chr resulted from efficient cooling along boundaries of the Dunite block. The inferred front of crystallization advanced along a path traced by vectors of Ol and Chr compositions. Grains and aggregates of Chr were mainly deposited early after the massive crystallization of olivine. Chromium, Al, Zn and H2O, all incompatible in Ol, accumulated to produce podiform segregations or veins of chromitites. This occurred episodically along the moving front of crystallization. Crystallization occurred rapidly owing to heat loss at the contact and to a shallow level of emplacement. The Chr layers are not continuous but rather heterogeneously distributed pods or veins of Chr&ndash, Ol&ndash, clinochlore segregations. Isolated portions of melt enriched in H2O and ore constituents accumulated during crystallization of Ol. Levels of fO2 in the melt and, consequently, the content of ferric iron in Chr, increased progressively, as in other intrusions of the SB&ndash, TB megastructure. The komatiitic magma vesiculated intensely, which led to a progressive loss of H2 and buildup in fO2. In turn, this led to the appearance of anomalous Chr&ndash, Ilm parageneses. Diffuse rims of Chr grains, abundant in the DB, contain elevated levels of Fe3+ and enrichments in Ni and Mn. In contrast, Zn is preferentially partitioned into the core, leading to a decoupling of Zn from Mn, also known at Chapesvara. The sulfide species display a pronounced Ni-(Co) enrichment in assemblages of cobaltiferous pentlandite, millerite (and heazlewoodite at Khanlauta), deposited at &le, 630 &deg, C. The oxidizing conditions have promoted the formation of sulfoselenide phases of Ru in the chromitites. The attainment of high degrees of oxidation during crystallization of a primitive parental komatiitic magma accounts for the key characteristics of Pados-Tundra and related suites of the SB&ndash, TB megastructure.

We describe occurrences of platinum-group minerals (PGM) and an uncommon mineral enriched in Cl, and provide a brief review of Cl-bearing minerals associated with basic–ultrabasic complexes. An unusual phosphohedyphane-like phase (~30 µm), close to CaPb4(PO4)3Cl, occurs in one of the PGM-bearing veins of massive sulfides in the Monchepluton layered complex, Kola Peninsula, Russia. These veins consist of varying amounts of pyrrhotite, pentlandite, chalcopyrite, pyrite and accessory grains of galena; they are fairly abundant in the heavy-mineral concentrate, as are small (

This two-part study explores hyperspectral (300–700 nm) aerosol optical measurements obtained from in situ sampling methods employed during the May–June 2016 Korea United States – Ocean Color (KORUS-OC) cruise conducted in concert with the broader air quality campaign (KORUS-AQ). Part 1 focused on the hyperspectral measurement of extinction coefficients (σext) using the recently developed in situ Spectral Aerosol Extinction (SpEx) instrument and showed that 2nd order polynomials provided a better fit to the measured spectra than power law fits. Two dimensional mapping of the 2nd order polynomial coefficients (a1,a2) was used to explore the information content of the spectra. Part 2 expands on that work by applying a similar analytical approach to filter-based measurements of aerosol hyperspectral total absorption (σabs) and soluble absorption from filters extracted either with deionized water (σDI-abs) or methanol (σMeOH-abs). As was found for σext, 2nd order polynomials provided a better fit to all three absorption spectra sets. Averaging the measured σext from Part 1 over the filter sampling intervals in this work, hyperspectral single scattering albedo (ω) was calculated. Water-soluble aerosol composition from the DI extracts was used to examine relationships with the various measured optical properties. In particular, both σDI-abs(365 nm) and σMeOH-abs(365 nm) were found to be best correlated with oxalate (C2O42−), but elevated soluble absorption was found from two chemically and optically distinct populations of aerosols. The more photochemically aged aerosols of those two groups exhibited partial spectra (i.e., the longer wavelengths of the spectral range were below detection) while the less-aged aerosol of the other group exhibited complete spectra across the wavelength range. The chromophores of these groups may have derived from different sources and/or atmospheric processes, such that photochemical age may have been only one factor contributing to the differences in the observed spectra. The differences in the spectral properties of these groups was evident in (a1,a2) maps. The results of the two-dimensional mapping shown in Parts 1 and 2 suggest that this spectral characterization may offer new methods to relate in situ aerosol optical properties to their chemical and microphysical characteristics. However, 2nd order polynomials did not fully capture the evident features in the σabs and ω spectra, suggesting additional spectral analyses such as peak fitting will yield additional information. It is anticipated that future studies examining in situ aerosol hyperspectral properties will not only improve our ability to use optical data to characterize aerosol physicochemical properties, but that such in situ tools will be needed to validate hyperspectral remote sensors planned for space-based observing platforms.

In situ observations of spectrally-resolved aerosol extinction coefficients (300–700 nm at ~ 0.8 nm resolution) from the May–June 2016 Korea U.S. – Ocean Color (KORUS-OC) oceanographic field campaign are reported. Measurements were made with the custom-built Spectral Aerosol Extinction (SpEx) instrument that previously has been characterized only using laboratory-generated aerosols of known size and composition. Here, the performance of SpEx under realistic operating conditions in the field was assessed by comparison to extinction coefficients derived from commercial instruments that measured scattering and filter-based absorption coefficients at three discrete visible wavelengths. Good agreement was found between these two sets of extinction coefficients with slopes near unity for all 3 wavelengths within the SpEx measurement error (±5 Mm−1). The meteorological conditions encountered during the cruise fostered diverse ambient aerosol populations with varying sizes and composition at concentrations spanning two orders of magnitude. The sampling inlet had a 50 % size cut of 1.3 µm diameter particles such that the in situ aerosol sampling suite deployed aboard ship measured fine mode aerosols only. The extensive hyperspectral extinction data set acquired revealed that nearly all measured spectra exhibited curvature in logarithmic space, such that Ångström exponent (α) power law fits led to large errors compared to measured values, especially in the ultraviolet (UV) wavelength range. This problem was particularly acute for α values calculated over only visible wavelengths, then extrapolated to the UV, highlighting the need for measurements in this wavelength range. Second-order polynomial fits to the logarithmically-transformed data provided a much better fit to the measured spectra than the linear fits of power laws. Building on previous studies that used total column AOD observations to examine the information content of spectral curvature, the relationship between α and the second order polynomial fit coefficients (a1 and a2) was shown to depend on the characteristic wavelength (λch) of any given spectral measurement, such that differing curvature among aerosol size distributions with the same α will map to a line in (a1,a2) space with a slope related to λch. Thus, spectral curvature represented by (a1,a2) may provide more detailed aerosol size distribution information than α alone.

No abstract available

Megacryst-bearing alkaline basic rocks of Cenozoic age occur in scattered centers in western Europe, from the Rhine graben to southern Spain. We focus on two volcanic fields, La Garrotxa in northeastern Spain, and in particular the Pomareda and Roca Negra monogenetic cones in the Olot suite, and the Chuquet Genestoux occurrence, Puy-de-Dome, France. The explosive emplacement of the basanitic magma favored the entrainment of xenoliths of clearly crustal and mantle origin in both suites. We seek to characterize the megacrysts of scapolite and andesine. The sulfate-bearing scapolite crystallized in space group I 4/ m rather than the expected P 4 2 / n , likely because of disorder in the sulfate groups. The megacrysts in both suites are part of an igneous mantle-derived assemblage, to judge from δ 18 O values, supported by δ 13 C and δ 34 S values of the sulfate-bearing scapolite. We document signs of flash melting in both scapolite and plagioclase megacrysts from Pomareda. A white rim of up to 2 mm on the scapolite megacrysts consists of skeletal individuals of calcic plagioclase; these crystals contain wollastonite, silvialite, diopside, and myriads of vacuoles. The andesine megacryst also underwent melting at its margin, to a sieve-textured assemblage of neoformed labradorite, glass, and free silica. The flash melting of individual megacrysts encapsulated in basanitic melt, documented here for the first time, has produced metastable products. Progress of the melting reactions was arrested by a thermal quench upon eruption.

To “ensure depth and liquidity,” the European Central Bank intervened in sovereign debt markets through its Securities Markets Programme (SMP), providing a unique opportunity to estimate the effects of large-scale asset purchases on sovereign bond liquidity premia. From reduced-form estimates, we find robust, economically significant impact and lasting reductions in sovereign bonds’ liquidity premia in response to official purchases. We develop a search-based asset-pricing model to understand our empirical results. The theory implies that bond liquidity premia fall in response to both official purchases and rising sovereign default probabilities, as seen in the data.

There is a close spatial relation between high-grade gold mineralization in the Witwatersrand basin and carbonaceous nodules, veins and seams. Hydrocarbons thus may well have been essential in ore genesis. We have sampled four major gold-, uranium- and hydrocarbon-bearing ore horizons, namely the Carbon Leader, Vaal, B and Black reefs, to determine the role of hydrocarbons in the accumulation and hydrothermal fixation of gold. Our multipronged approach included high-resolution scanning and transmission electron microscopy (SEM, TEM), nanotomography with video clips, and geochemical modeling. Post-depositional hydrothermal activity at the peak of regional metamorphism produced an assemblage of quartz, phyllosilicates, brannerite, crandallite, florencite, monazite and gold in all four reefs. The gold, hydrocarbons and associated mineral assemblages are closely related on the micro to nano scale. Gold deposition occurred in interstices, as fracture fillings in detrital minerals, and on the surface of migrated solid hydrocarbon residues. The spherical to elliptical inclusions in the gold consist of an outer pyrobitumen phase and a central void space, partially associated with nanometric gold, uraninite, coffinite and silica. The hydrocarbon-bearing inclusion likely formed by the entrapment of a fossil liquid oil precursor during gold precipitation. The oil was subsequently thermally altered and converted into the final pyrobitumen and gaseous residues. Geochemical calculations to simulate the interaction of an invading hot hydrothermal fluid with the hydrocarbons in the reefs reveal that a very small amount of hydrocarbons will drastically decrease the aqueous solubility of gold and hence cause its instant precipitation. We extend our genetic model for the epigenetic formation of gold in the Witwatersrand. Regional metamorphism promoted the extensive and likely basin-wide circulation of hydrothermal fluids; these were capable of mobilizing substantial amounts of gold. The liquid, gaseous and solid hydrocarbons in the reefs acted as efficient chemical traps for the concentration of gold. Being strong chemical reductants, they caused the rapid precipitation and accumulation of gold on the surface of the fossil oil droplets and already solidified hydrocarbons. The release of the gases from accessible hydrocarbons into the sediments away from their source buffered the redox state of the hydrothermal solutions even at a considerable distance from the pyrobitumen seams and veins, likely resulting in the deposition of gold in the absence of visible hydrocarbons. Although our findings do not explain the ultimate origin and exceptional endowment of gold in the Witwatersrand, we do provide intriguing evidence for the large-scale hydrothermal mobilization, accumulation and fixation of gold mediated by hydrocarbons during post-depositional metamorphism.

Highly atypical mineralization involving Pd-Pt, Au-Ag, REE, Y, Zr, U, Th, and Cl-F-enriched minerals is found in zones with base metal sulfides (BMS, ~5 vol.% to 20 vol.%) in the eastern portion of the Oktyabrsky deposit in the Norilsk complex (Russia). The overall variations in Mg# index, 100 Mg/(Mg + Fe2+ + Mn), in host-rock minerals are 79.8 → 74.1 in olivine, 77.7 → 65.3 in orthopyroxene, 79.9 → 9.2 in clinopyroxene, and An79.0&nbsp, → An3.7. The span of clinopyroxene and plagioclase compositions reflects their protracted crystallization from early magmatic to late interstitial associations. The magnesian chromite (Mg# 43.9) trends towards Cr-bearing magnetite with progressive buildups in oxygen fugacity, ilmenite varies from early Mg-rich to late Mn-rich variants. The main BMS are chalcopyrite, pyrrhotite, troilite, and Co-bearing pentlandite, with less abundant cubanite (or isocubanite), rare bornite, Co-bearing pyrite, Cd-bearing sphalerite (or wurtzite), altaite, members of the galena-clausthalite series and nickeline. A full series of Au-Ag alloy compositions is found with minor hessite, acanthite and argentopentlandite. The uncommon assemblage includes monazite-(Ce), thorite-coffinite, thorianite, uraninite, zirconolite, baddeleyite, zircon, bastnäsite-(La), and an unnamed metamict Y-dominant zirconolite-related mineral. About 20 species of PGM (platinum group minerals) were analyzed, including Pd-Pt tellurides, bismuthotellurides, bismuthides and stannides, Pd antimonides and plumbides, a Pd-Ag telluride, a Pt arsenide, a Pd-Ni arsenide, and unnamed Pd stannide-arsenide, Pd germanide-arsenide and Pt-Cu arseno-oxysulfide. The atypical assemblages are associated with Cl-rich annite with up to 7.54 wt.% Cl, Cl-rich hastingsite with up 4.06 wt.% Cl, ferro-hornblende (2.53 wt.% Cl), chlorapatite (&gt, 6 wt.% Cl) and extensive solid solutions of chlorapatite, fluorapatite and hydroxylapatite, Cl-bearing members of the chlorite group (chamosite, up to 0.96 wt.% Cl), and a Cl-bearing serpentine (up to 0.79 wt.% Cl). A decoupling of Cl and F in the geochemically evolved system is evident. The complex assemblages formed late from Cl-enriched fluids under subsolidus conditions of crystallization following extensive magmatic differentiation in the ore-bearing sequences.

Chromite orebodies within the harzburgitic upper mantle have been investigated in several ophiolitic complexes, with a focus here on New Caledonia. The relationship between harzburgite and a dunite envelope around pods of chromitite points to a passive metasomatic transformation. The replacement of orthopyroxene by olivine leads to the necessary mobilization of Cr 3+ , not accepted by the neoformed olivine. A symplectitic intergrowth of enstatite + chromite at the interface between harzburgite and dunite may result from a silica-enriched fluid phase. Chromite in the orebodies contains micro-inclusions of olivine, clinopyroxene, orthopyroxene (rare), pargasite, aspidolite and nepheline. The olivine is hypermagnesian (up to 97 mol% Fo) and Ni-rich (0.25–1.05 wt%) and crystallized from a reducing fluid phase, not a magma. The pyroxenes and pargasite also are highly magnesian. The presence of Na in the environment accounts for pargasite, aspidolite and anomalously sodic nepheline. A Ni–Cu alloy is present. Chromite in the orebodies contains fluid inclusions, whereas chromite disseminated in harzburgite does not. The mixed fluid contains H 2 O (5 wt% equivalent of NaCl), with CO 2 and CH 4 in a 10 to 1 molar ratio. Values of δ 13 C VPDB (−22.1‰ for CO 2 and −28.1‰ for CH 4 , respectively) are typical of shallow marine hydrothermal systems. Experiments reveal that the precipitation of chromite from a fluid phase requires a reducing fluid and a temperature of ≤1050 °C. The appearance of olivine in the envelope results from the incongruent dissolution of enstatite in the fluid. The reaction is proven experimentally to be very efficient at a modest temperature (750 °C) and a low confining pressure (1.5 kbar). It leads to a shrinkage of the solid fraction, making the reaction self-propagating. Large volumes of harzburgite can be efficiently processed in an open, fluid-dominant reducing system. Relevant experiments show that the dissolution will increase in efficiency at higher temperatures and pressures. We do not negate the widely accepted explanation of chromitite formation by localized melt–harzburgite or melt–lherzolite interaction, but do point out that on the grounds of efficiency, such a process should be of secondary importance.

New Pd-Tl-(Bi,As)-rich compounds are described from the Anomal'nyi Cu-PGE deposit, Kondyor alkaline ultramafic complex, northeastern Russia. They occur in vein-type settings associated with bodies of 'kosvite' (magnetite-rich clinopyroxenite) in the dunite-(peridotite) core, in pegmatiticand micaceous rocks. The ore zones are substantially enriched in phlogopite; they consist of diopside, disseminated titaniferous magnetite and fluorapatite (Sr-bearing). The observed assemblages of ore minerals include sulfides of the chalcopyrite-bornite-(secondary chalcocite) associationand various species of platinum-group minerals (PGM) [isomertieite or arsenopalladinite rich in Sb, mertieite-II, mertieite-I, sobolevskite, kotulskite, merenskyite, zvyagintsevite, palarstanide, paolovite, sperrylite, maslovite or moncheite, hollingworthite and unnamed species of PGM] anda Ag-Au alloy. The oxides [Pd4(Bi,Te,Tl)O6 and Pd4(Tl,Bi,Te)O6] probably formed in situ by oxidation reactions at the expense of the associated PGM intergrowths. These involve palladium bismuthide-thallide phases, Pd5(Tl,As,Bi)and Pd5(As,Tl,Bi), which are documented here for the first time. A fairly evolved environment, enriched in Cu, Pd, Te, Bi, Pb and volatile components, is indicated for the vein-type deposit at Anomal'nyi.

We describe occurrences of palladoan melonite in intimate intergrowths with cobaltite-gersdorffite from the Neoproterozoic dunite-wehrlite-gabbro complexes of Kingash and Kuskanak, Eastern Sayans, Russia. The observed compositional trends of melonite are consistent with the overallvariations examined on the basis of numerous literature sources. The levels of Bi in NiTe2are normally limited to ≤0.25 Bi atoms per formula unit (apfu), under natural conditions. Greater levels (≤0.5 Bi apfu) are associated with the (Pd + Pt) enrichment in the palladoanvarieties. The telluride–sulfarsenide intergrowths probably formed at Kingash and Kuskanak late in the crystallization history of the ore zones, from microdroplets of residual melt rich in semimetals (Te, Bi, As) and noble metals (Pd and Ag), below the solidus of the enclosing gabbroicrocks and within a narrow range of temperatures (500–550°C). On the basis of our observations made on specimens of melonite and synthetic Ni(Te,Bi)2–x(x = 0.6), we infer that the limit of incorporation of Bi into a melonitetype phase is ≤0.5 Bi apfu.