Major Mineral Phases Research Articles

Characterisation of Typical Indian Iron Ore Slime through Quantitative Mineralogy to Evaluate Beneficiation Prospect

The current work was taken up to predict the yield of the concentrate with 2 mass% target alumina from the available iron ore slime material. It was found that the conventional method was not suitable for characterisation of the slime. As an alternative method, a third generation of automated mineral analysis machine named “QEMSCAN” is used to find out the liberation characteristics. However, data generated through this routine method was also inadequate for the assigned job. The routine method predicted a low yield for the concentrate. This was due to skewed distribution of mineral phases and wide variation in chemical composition of the major mineral phases. The database of this machine was then modified so that it recognises three broad subtypes of the major mineral phase. The new set of data was used to establish the yield–grade relation for the concentrate from the slime. This vital information on liberation characteristics depicted the beneficiation prospect of the slime.

Magnetic and flotation studies of banded hematite quartzite (BHQ) ore for the production of pellet grade concentrate

To identify and establish beneficiation techniques for banded hematite quartzite (BHQ) iron ore, a comprehensive research on BHQ ore treatment was carried out. The BHQ ore was assayed as 38.9wt% Fe, 42.5wt% SiO2, and 1.0wt% Al2O3. In this ore, hematite and quartz are present as the major mineral phases where goethite, martite, and magnetite are present in small amounts. The liberation of hematite particles can be enhanced to about 82% by reducing the particle size to below 63 μm. The rejection of silica particles can be obtained by magnetic and flotation separation techniques. Overall, the BHQ ore can be enriched to 65.3wt% Fe at 61.9% iron recovery. A flowsheet has been suggested for the commercial exploitation of the BHQ ore.

Slip Systems in MgSiO 3 Post-Perovskite: Implications for D ′′ Anisotropy

Understanding deformation of mineral phases in the lowermost mantle is important for interpreting seismic anisotropy in Earth's interior. Recently, there has been considerable controversy regarding deformation-induced slip in MgSiO(3) post-perovskite. Here, we observe that (001) lattice planes are oriented at high angles to the compression direction immediately after transformation and before deformation. Upon compression from 148 gigapascals (GPa) to 185 GPa, this preferred orientation more than doubles in strength, implying slip on (001) lattice planes. This contrasts with a previous experiment that recorded preferred orientation likely generated during the phase transformation rather than deformation. If we use our results to model deformation and anisotropy development in the D'' region of the lower mantle, shear-wave splitting (characterized by fast horizontally polarized shear waves) is consistent with seismic observations.

Chemical reactions during the preparation of P and NPK fertilizers from thermochemically treated sewage sludge ashes

In the present paper we show how P and NPK fertilizers can be prepared from thermochemically treated sewage sludge ashes (SSA) and which chemical reactions occur during these post-treatment steps. The SSA used for this investigation was treated thermochemically at a temperature of 1,000°C in a rotary kiln after the addition of calcium chloride hydrate or magnesium chloride hydrate to remove heavy metals and to increase the bioavailability of phosphorus (hereafter the products of thermochemical treatment are referred to as SSA-Ca and SSA-Mg). The major P-bearing mineral phase in SSA-Ca was chlorapatite (Ca5(PO4)3Cl), whereas in SSA-Mg the major P-bearing mineral phases were farringtonite (Mg3(PO4)2) and chlorapatite. Transformations of the mineral phases were observed when the P content of the products was adjusted by the addition of phosphoric acid (PA). The products of the reaction of SSA-Ca with PA were brushite (dicalcium phosphate dihydrate) and monocalcium phosphate monohydrate (MCPM). Further reaction products were found after the addition of PA to SSA-Mg: newberyite (MgHPO4·3H2O) and garyansellite ((Mg,Fe)3(PO4)2(OH)1.5·1.5H2O)). In addition, NPK fertilizers were prepared from SSA-Ca by mixing with molten NH4NO3 at approximately 180°C. No reaction occurred with the P-bearing mineral phase chlorapatite. When SSA-Ca was spiked with MCPM (to adjust the P content) before mixing it with molten NH4NO3, water-soluble NH4H2PO4 (monoammonium phosphate) was detected as a reaction product.

Precipitation and Transformation of Secondary Fe Oxyhydroxides in a Histosol Impacted by Runoff from a Lead Smelter

AbstractSecondary Fe(III) oxyhydroxides play a key role in controlling the mobility and bioavailability of trace metals in acidic, sulfate-rich soils, such as mining and smelter sites. Schwertmannite, jarosite, goethite, and ferrihydrite are the most common mineral phases identified in such soils. A good understanding of the precipitation and transformation of these minerals in soils is very important for predicting the mobility and long-term stability of trace metals associated with them. In the present study, bulk powder X-ray diffraction (XRD), scanning electron microscopy (SEM), synchrotron based micro- X-ray diffraction (µ-XRD), and micro X-ray fluorescence (µ-SXRF) spectroscopy were used to investigate precipitates fromthe surface horizon of an organic soil (Histosol) at a site that once contained a lead smelter. Soil samples were collected from 0 to ≈10 cm depth during both wet and dry seasons. Goethite and akaganeite were identified as the major mineral phases in this soil. Schwertmannite and jarosite were also occasionally identified, particularly in the soil samples from dry periods. The peaks in the akaganeite XRD pattern were significantly broadened and the relative intensities of some major peaks were distinctly different compared with the diffraction pattern of synthetic akaganeite, possibly due to the effects of pH and the incorporation of sulfate. The SEM and µ-XRD data support the hypothesis that the goethite in the precipitates is not the product of direct precipitation froms olution but the transformation of previously precipitated schwertmannite or akaganeite.

Study of a Chilean petroleum coke fluidized bed combustion fly ash and its potential application in copper, lead and hexavalent chromium removal

This work deals with the characterization of a circulated fluidized bed combustion (CFCB) Chilean petroleum coke fly ash (FA) from a petroleum coke power plant, and its potential use in neutralization and heavy metals removal from acid wastewaters. FA presents a high Ca and SO 4 2 - content, being anhydrite the major crystalline mineral phase, with minor proportions of calcite, portlandite and lime. Regarding to environmental characterization of this fly ash, leaching tests allowed concluding that FA is a non-hazardous residue. Heavy metals removal tests indicate that FA is able to remove Cu 2+ and Pb 2+ mainly due to a precipitation process, while Cr(VI) is being removed probably due to a reduction process to Cr(III), at high liquid to solid ratios. Cu 2+, Pb 2+ and Cr(VI) kinetic experimental data present acceptable fit to a pseudo-second order kinetic model. According to these results, FA may be used to remove heavy metals and neutralize acid wastewaters, suggesting a possible replacement of pure and costly alkaline materials.

Phase formation and properties of the LTCC composite based on the eutectic system BaO–ZnO–SiO 2–B 2O 3

In this work, a low-temperature co-fired ceramic (LTCC) composite based on the eutectic system BaO–ZnO–SiO 2–B 2O 3 is fabricated. The phase formation in the LTCC composite is investigated by XRD, SEM and DSC technologies. Dielectric and thermal properties are discussed in terms of the phase composition. The results indicate that major mineral phases of the LTCC composite are barium silicate, willemite, SiO 2 crystal phases and additional quartz. Due to the peculiar physical characteristics of these mineral phases, the LTCC composite can express different dielectric and thermal properties along with the evolution of the major mineral phases.

The role of fluorine in the concentration and transport of lithophile trace elements in felsic magmas: Insights from the Gawler Range Volcanics, South Australia

Rhyolites of the Mesoproterozoic Gawler Range Volcanics (GRV) of South Australia are characterised by high concentrations of some trace elements (REE, Y. HFSE, Rb and F, in particular). Whole rock geochemical data suggest that these elements were incompatible during magma crystallisation. Accessory minerals (fluorite, zircon, REE-F-carbonate, Ti oxide, apatite, and titanite) can account for most of the trace element content of the rocks. These minerals occur in vesicles, micromiaroles, lithophysal vugs and in interstices between major mineral phases (quartz and feldspar as both phenocrysts and groundmass). Such textural evidence indicates that accessory minerals crystallised late in the history of the magma and that they were deposited from a volatile-rich (fluid) phase. These features are explained by the following sequence of events: 1) F dissolved in the magma lowered the crystallisation temperature of accessory minerals, causing trace elements (REE, Y. and HFSE) to behave as incompatible elements. 2) Protracted crystallisation of major mineral phases (quartz, feldspar, and oxides) formed a volatile- and trace element-enriched residual liquid. 3) A volatile element (H2O, F, and CO2)-rich phase (late-stage magmatic fluid) evolved from the magma. High concentration of fluorine and other complexing agents in this phase allowed trace elements to be transported in solution. 4) Accessory minerals crystallised from such a phase in vesicles, micromiaroles and interstices between the major mineral phases

Primary sink and source of geogenic arsenic in sedimentary aquifers in the southern Choushui River alluvial fan, Taiwan

Abstract This work characterized the sink and source/mobility of As in the As-affected sedimentary aquifers of the southern Choushui River alluvial fan, central Taiwan. Major mineral phases and chemical components were determined by XRD and X-ray photoelectron spectroscopy (XPS). The partitioning of As and Fe among cores were determined by sequential extraction. Based on XPS results, the primary forms of Fe were hematite, goethite and magnetite. Sequential extraction data and the XRF analysis indicated that Fe oxyhydroxides and sulfides were likely to be the major sinks of As, particularly in the distal-fan. Furthermore, Fe oxyhydroxides retained higher As contents than As-bearing sulfides. The reductive dissolution of Fe oxyhydroxides, which accompanied high levels of HCO 3 - and NH 4 + concentrations, was likely the principal release mechanism of As into groundwater in this area. The dual roles of Fe oxyhydroxides which are governed by the local redox condition act as a sink and source in the aquifer. Ionic replacement by PO 4 3 - and HCO 3 - along with seasonal water table fluctuation, caused by monsoons and excessive pumping, contributed specific parts of As in the groundwater. The findings can be used to account for the inconsistency between Fe and As concentrations observed in groundwater.

Atmospherically Stable Nanoscale Zero-Valent Iron Particles Formed under Controlled Air Contact: Characteristics and Reactivity

Atmospherically stable NZVI (nanoscale zero-valent iron) particles were produced by modifying shell layers of Fe(H2) NZVI particles (RNIP-10DS) by using a controlled air contact method. Shell-modified NZVI particles were resistant to rapid aerial oxidation and were shown to have TCE degradation rate constants that were equivalent to 78% of those of pristine NZVI particles. Fe(H2) NZVI particles that were vigorously contacted with air (rapidly oxidized) showed a substantially compromised reactivity. Aging of shell-modified particles in water for one day resulted in a rate increase of 54%, implying that depassivation of the shell would play an important role in enhancing reactivity. Aging of shell-modified particles in air led to rate decreases by 14% and 46% in cases of one week and two months of aging, respectively. A series of instrumental analyses using transmission electron microscopy, X-ray diffractography, X-ray photoelectron spectroscopy, and X-ray absorption near-edge structure showed that the shells of modified NZVI particles primarily consisted of magnetite (Fe(3)O(4)). Analyses also implied that the new magnetite layer produced during shell modification was protective against shell passivation. Aging of shell-modified particles in water yielded another major mineral phase, goethite (alpha-FeOOH), whereas aging in air produced additional shell phases such as wustite (FeO), hematite (alpha-Fe(2)O(3)), and maghemite (gamma-Fe(2)O(3)).

Old Sm–Nd ages for cumulate eucrites and redetermination of the solar system initial 146Sm/ 144Sm ratio

Short-lived 146Sm– 142Nd and long-lived 147Sm– 143Nd chronometers have been measured in three cumulate eucrites (Binda, Moore County and Moama). The two major mineral phases (plagioclase and pyroxene) present in these achondrites are characterized by a wide range of Sm/Nd ratios that allows well-resolved Sm–Nd isochrons. This group of meteorites thus is suitable to better constrain the initial 146Sm/ 144Sm ratio of the solar system. Binda and Moore County give concordant ages of 4544 ± 88 and 4542 ± 85 Ma, respectively, with initial 143Nd/ 144Nd ratios slightly higher, to within error, of chondritic. These ages are in agreement with most of the radiometric ages determined on basaltic eucrites. A best estimate for the solar system initial 146Sm/ 144Sm ratio is obtained using the five-point regression line determined for Binda. The 146Sm/ 144Sm ratio of 0.00728 ± 57 obtained for this sample translates to a 146Sm/ 144Sm ratio at 4568 Ga of 0.0085 considering the age of isotopic closure obtained from 147Sm– 143Nd systematics. When 146Sm– 142Nd data from the literature are examined in detail, four eucrites have concordant 147Sm– 143Nd and 146Sm– 142Nd systematics. Their weighted average 147Sm– 143Nd age is equal to 4546 ± 8 Ma. An initial 146Sm/ 144Sm ratio at 4568 Ma calculated from these samples is 0.0084 ± 0.0005. A similar ratio of 0.0085 ± 0.0007 is calculated if data from different groups of achondrites (angrite and mesosiderite) are included in the calculation. No difference in the 146Sm/ 144Sm ratios or initial 142Nd/ 144Nd ratios is observed among different groups of achondrites relative to ordinary chondrites. This work suggests that 146Sm was homogeneously distributed and that both Sm and Nd were isotopically uniform at the planetary scale in the solar system, at least in the region around where these planetary bodies formed.

Computer simulations of structures and properties of the biomaterial hydroxyapatite

Carbonated hydroxyapatite is the major mineral phase in natural bone and teeth and is therefore an attractive material for use in tissue replacement applications. However, its successful application as a biomaterial requires a detailed understanding of its bulk and surface structures, defect chemistry, growth and dissolution behaviour and interaction with complex biomolecules. Computer modelling can aid experiment by investigating at the atomic level highly complex structures, properties and processes, which are still difficult or impossible to access with experimental techniques. Here, we describe our use of a combination of complementary computational techniques to investigate a number of topical issues relevant to the use of hydroxyapatite in biomaterials applications, including the bulk and surface structures of the pure material; the structure and location of carbonate impurities in the lattice; the uptake of fluoride and its effect on hydroxyapatite dissolution; and crystal growth inhibition by citric acid.

Adsorption of Pb(II) Ions from Aqueous Solutions Using a Low Grade Iron Ore as an Effective Adsorbent

The use of banded hematite quartzite (BHQ), a low-grade iron ore, as an adsorbent for the removal of lead(II) ions from aqueous solutions was studied. X-Ray diffraction (XRD) studies of BHQ ore showed the presence of hematite and quartz as the major mineral phases, while FT-IR studies showed the presence of Si-OH and Fe-OH sites capable of exhibiting strong adsorption properties. SEM/EDS studies indicated that the particles of the materials were relatively fine and contained Fe, Si and O, together with trace amounts of Al. Batch adsorption studies demonstrated that BHQ exhibits a significant capacity towards the adsorption of Pb(II) ions from aqueous solution. The parameters of the adsorption process investigated in this study included the effect of agitation time, initial Pb(II) ion concentration, adsorbent dosage, pH and temperature. The adsorption of Pb(II) ions onto BHQ increased as the pH of the aqueous medium increased from 1.8 to 6.5. Maximum removal of Pb(II) ions (99.8%) from aqueous solutions with an initial Pb(II) ion content of 10 mg/ℓ occurred at pH 5.0. The sorptions data for Pb(II) ions were correlated using the Langmuir and Freundlich isotherms, thereby allowing an analysis of the equilibrium data obtained at room temperature. The Langmuir isotherm indicated monolayer formation on the adsorbent surface.

Influence of (Calcium−)Uranyl−Carbonate Complexation on U(VI) Sorption on Ca- and Na-Bentonites

The influence of uranyl-carbonate and calcium-uranyl-carbonate complexations on the kinetics of U(VI) (approximately 3.4 x 10(-3) mol L(-1)) sorption from NaNO3 and Ca(NO3)2 solutions on Na- and Ca-bentonites at circumneutral ambient conditions was investigated. Complexation of U(VI) in Ca2UO2(CO3)3(aq) aqueous species, dominating the U(VI) speciation in Ca(NO3)2 solution, reduces its adsorption on bentonite by a factor of 2-3 in comparison with that in (UO2)2CO3(OH)3- species, dominating in NaNO3 solution, within the studied period of time (21 days). As a result of the dissolution of accessory calcite, Ca2UO2(CO3)3(aq) can be formed in the initially Ca-free solution in contact with either Na- or Ca-bentonite. U(VI) adsorption on Na-bentonite is a factor of approximately 2 higher than that on Ca-bentonite for solutions with the Ca2UO2(CO3)3(aq) complex dominating aqueous U(VI) speciation. This favors use of Na-bentonite over that of Ca-bentonite in final disposal of radioactive waste. Furthermore, the observed strong correlation between U(VI) adsorption and Mg release as a result of montmorillonite dissolution indicates in agreement with previous findings that under the applied conditions U(VI) is adsorbed on the edge surface of montmorillonite, which is a major mineral phase of the studied clays.

Calcite precipitation dominates the electrical signatures of zero valent iron columns under simulated field conditions

Calcium carbonate is a secondary mineral precipitate influencing zero valent iron (ZVI) barrier reactivity and hydraulic performance. We conducted column experiments to investigate electrical signatures resulting from concurrent CaCO 3 and iron oxides precipitation under simulated field geochemical conditions. We identified CaCO 3 as a major mineral phase throughout the columns, with magnetite present primarily close to the influent based on XRD analysis. Electrical measurements revealed decreases in conductivity and polarization of both columns, suggesting that electrically insulating CaCO 3 dominates the electrical response despite the presence of electrically conductive iron oxides. SEM/EDX imaging suggests that the electrical signal reflects the geometrical arrangement of the mineral phases. CaCO 3 forms insulating films on ZVI/magnetite surfaces, restricting charge transfer between the pore electrolyte and ZVI particles, as well as across interconnected ZVI particles. As surface reactivity also depends on the ability of the surface to engage in redox reactions via charge transfer, electrical measurements may provide a minimally invasive technology for monitoring reactivity loss due to CaCO 3 precipitation. Comparison between laboratory and field data shows consistent changes in electrical signatures due to iron corrosion and secondary mineral precipitation.

Composition of ferromanganese nodules from Riga Bay (Baltic Sea)

An average sample of ferromanganese nodules from Riga Bay was investigated by analytical electron microscopy coupled with atomic absorption, neutron activation, and ICP-MS methods. It is established that the nodules consist of colloform and poorly crystallized Fe and Mn hydroxides with an admixture of dispersed inclusions of better crystallized particles allowing revealing their mineralogical nature by the microdiffraction method. The major mineral phases are ferroxigite and Fe-vernadite with subordinate magnetite, asbolane, and todorokite. The chemical composition of the nodules is dominated by iron followed by cobalt and lead, while nickel, molybdenum, and tungsten associate with the manganese phase. The concentration of several minor elements in the Riga Bay nodules is slightly lower as compared with their average values for the entire Baltic Sea; some elements such as silver, bismuth, cadmium, niobium, tin, and thallium were never analyzed before.

Leaching characteristics of selected South African fly ashes: Effect of pH on the release of major and trace species

Fly ash samples from two South African coal-fired power stations were subjected to different leaching tests under alkaline and acidic conditions in an attempt to assess the effect of pH on the leachability of species from the fly ashes and also assess the potential impact of the fly ashes disposal on groundwater and the receiving environment. To achieve this, German Standard leaching (DIN-S4) and Acid Neutralization Capacity (ANC) tests were employed. Mineralogical characterization of the fresh fly ashes revealed mullite and quartz as the major mineral phases with minor peaks of CaO and calcite. Chemical characterization by X-ray fluorescence (XRF) spectrometry revealed that the two fly ashes are similar, and consist of SiO2, Al2O3, Fe2O3 and CaO as the main components with Cr, Co, Ni, Cu, Zn, V and Pb as minor components. Ca, Mg, Na, K and SO4 were significantly leached into solution under the two leaching conditions with the total amounts in ANC leachates higher than that of DIN-S4. This indicates that a large fraction of the soluble salts in unweathered fly ash are easily leached. These species represents the fraction that can be flushed off initially from the surface of ash particles on contacting the ash with water. Al and Si were only observed in the leachates of the ANC test. Results obtained from the total acid-digestion and DIN-S4 leaching test indicated some toxic elements in the fly ashes are not easily solubilized. The amounts of toxic trace elements such as As, Se, Cd, Cr and Pb leached out of the fly ashes when in contact with de-mineralized water (DIN-S4 test) were low and below the Target Water Quality Range (TWQR) of South Africa. This is explained by their low concentrations in the fly ashes and their solubility dependence on the pH of the leaching solution. However the amounts of some minor elements such as B, Mn, Fe, As and Se leached out at lower pH ranging between 10 to 4 (ANC test) were slightly higher than the TWQR, an indication that the pH of the leaching solution plays a significant role on the leaching of species in fly ash. The high concentrations of the toxic elements released from the fly ashes at lower pH gives an indication that the disposal of the fly ash could have adverse effects on the receiving environment if the pH of the solution contacting the ashes is not properly monitored. The study indicated that on contact with water in a disposal scenario fly ash will release high amounts of soluble species.

Sm–Nd isotope systematics of high-REE accessory minerals and major phases: ID-TIMS, LA-ICP-MS and EPMA data constrain multiple Permian–Triassic pegmatite emplacement in the Koralpe, Eastern Alps

Detailed Sm–Nd mineral ID-TIMS, EMPA and LA-ICP-MS analysis of meta-pegmatite minerals from the Koralpe–Stubalpe area, Austria, involving single crystal separation, step-wise dissolution and acid leaching techniques, yielded (i) information about the partitioning of REE between accessory and major mineral phases in meta-pegmatites, and (ii) age constraints on the long-lasting “Permian–Triassic event” in the Austroalpine basement units of the Eastern Alps. Internal Sm–Nd mineral isochrons performed on porphyroclast domains from the three localities Rostockbach, Kuppergrund and Wildbachgraben, including garnet, xenotime, apatite, monazite and feldspar indicate multiple emplacement of pegmatoid melts between 273 ± 2 and 258 ± 3 Ma. Other localities yielded younger ages, indicating that magmatic garnet crystallisation persisted from 251 ± 7 to c. 230 Ma. Ages calculated between high-REE accessories (monazite, apatite, xenotime) and the low-REE major phases feldspar and garnet are largely consistent. Zircon, however, plots clearly off the internal regression line. H 2SO 4 leaching experiments on meta-pegmatite garnet rich in micron-sized xenotime and apatite inclusions, locally affected by dynamic recrystallisation, yielded information about the behaviour of the Sm–Nd system during strong tectono-metamorphic overprinting. The data suggest multiple injections of pegmatite melts, at distinctly different times, during protracted crustal thinning and heating in the Permian–Triassic. Ky-paramorphs after andalusite, and micro-inclusions of kyanite, staurolite and sillimanite in magmatic garnet indicate crystallisation of the garnet at moderately high, but variable pressure conditions. During subsequent eclogite-facies overprinting (peak PT c. 700 °C/2.2 GPa) and intense deformation in Cretaceous time, the magmatic chemical and isotopic signatures of porphyroclasts were largely preserved, except for localized within-grain micro-shear zones and outermost rim domains, whereas part of the feldspar-rich matrix recrystallised during pervasive mylonitisation along the eclogite- to amphibolite-facies-grade exhumation path.

Oxygen isotopic constraints on the origin of magnesian chondrules and on the gaseous reservoirs in the early Solar System

We report in situ ion microprobe analyses of the oxygen isotopic composition of the major silicate phases (olivine, low-Ca pyroxene, silica, and mesostasis) of 37 magnesian porphyritic (type I) chondrules from CV (Vigarano USNM 477-2, Vigarano UH5, Mokoia, and Efremovka) and CR (EET 92042, EET 92147, EET 87770, El Djouf 001, MAC 87320, and GRA 95229) carbonaceous chondrites. In spite of significant variations of the modal proportions of major mineral phases in CR and CV chondrules, the same isotopic characteristics are observed: (i) olivines are isotopically homogeneous at the ‰ level within a chondrule although they may vary significantly from one chondrule to another, (ii) low-Ca pyroxenes are also isotopically homogeneous but systematically 16O-depleted relative to olivines of the same chondrule, and (iii) all chondrule minerals analyzed show 16O-enrichments relative to the terrestrial mass fractionation line, enrichments that decrease from olivine (±spinel) to low-Ca pyroxene and to silica and mesostasis. The observation that, in most of the type I chondrules studied, the coexisting olivine and pyroxene crystals and glassy mesostasis have different oxygen isotopic compositions implies that the olivine and pyroxene grains are not co-magmatic and that the glassy mesostasis is not the parent liquid of the olivine. The δ 18O and δ 17O values of pyroxene and olivine appear to be strongly correlated for all the studied CR and CV chondrules according to: δ 18 O (pyroxene) = 0.72 - 0.16 + 0.13 × δ 18 O (olivine) + 1.21 - 0.54 + 0.79 δ 17 O (pyroxene) = 0.81 - 0.15 + 0.13 × δ 17 O (olivine) + 0.60 - 1.00 + 0.95 These correlations are consistent with mass balance of oxygen isotopes calculated in the case of chondrule formation according to the following gas–melt–mineral reactions: Mg 2 SiO 4(olivine) + SiO 2(melt) = Mg 2 Si 2 O 6(pyroxene) SiO 2(melt) = SiO (gas) + 1 / 2 × O 2(gas) These equations imply that 2/3 of the oxygen incorporated by low-Ca pyroxene during its crystallization in the melt is derived from the dissolution of precursor olivine and 1/3 from the addition of chemical components such as SiO from the nebular gas. The composition of the nebular gaseous reservoir in which type I CR and CV chondrules formed is determined from the present data set to be δ 18O (gas) ∼ 3.6 ± 1‰ and δ 17O (gas) ∼ 1.8 ± 1‰. This isotopic composition is in excellent agreement with that of the gaseous reservoir previously inferred from the oxygen isotope systematics of bulk chondrules from various chondrite groups (i.e., CV, CR, unequilibrated ordinary, and EH). Thus, the oxygen isotopic systematic strongly supports the idea that most of the olivines in type I chondrules are relict grains and that gas–melt interaction played a major role in the formation of type I chondrules.

Genesis and evolution of Eppawala carbonatites, Sri Lanka

Massive apatite-bearing carbonatites intruded into a Precambrian metamorphic terrain around Eppawala, North-central Sri Lanka, have been investigated using petrographic and geochemical methods. The geochemical study includes mineral compositions, whole rock elemental abundances, and Sr–Nd and C–O isotopes. The carbonatites are generally coarse grained, and are mineralogically and texturally layered. Calcite, dolomite, olivine, and apatite are the major mineral phases, whereas spinel, ilmenite, magnetite, amphiboles, and micas occur as minor phases. Major element compositions show variation from calciocarbonatite to magnesiocarbonatite. The calciocarbonatites are enriched in ΣREE relative to the magnesiocarbonatites, but all samples show broadly comparable REE patterns. Extreme depletion of Ni, Ti, Cs, Rb, Nb, Ta, Zr, and Hf are characteristic of the Eppawala carbonatites. Stable C–O isotope ratios vary from −1.9 to −3.5 δ 13C (PDB) and from 7.7 to 16.2 δ 18O (SMOW). Sr and Nd isotope data ( 87Sr/ 86Sr 0.7049–0.7052 and 143Nd/ 144Nd 0.5019–0.5020) are compatible with an enriched mantle source lying between EM-I and EM-II mantle components. The mineral chemistry and overall geochemical signatures are consistent with an igneous origin, in which primary carbonatite magma was derived from a low degree partial melting of carbonated eclogites.