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1.
We report the results of textural and mineralogical investigations of fragment #d(3–8)B of the Kaidun meteorite. The fragment is represented by six polished thin sections obtained by sequential sawing of a meteorite sample. Its main mineral is magnesian olivine; pyroxenes, augite and enstatite, are less abundant. The minor minerals are Fe-Ni sulfides, and the accessory minerals are chromian magnetite and apatite. The minerals show highly variable compositions. Several lithological types of material were distinguished on the basis of texture and composition. A characteristic feature is the presence of fractures, whose walls are enriched in olivine and, occasionally, sulfides. Some fractures contain relatively large euhedral crystals of zoned olivine. Olivines occurring on the walls of fractures and within fractures show a negative correlation between Mg# values and nickel content. The fragment has been subjected to multiple impact events. The material of the fragment bears evidence for intense multistage metasomatic alteration with the influx of olivine material and formation of pegmatoid-type segregations. This process has never previously been observed in meteorites, but is quite common in terrestrial massifs. The results of this study are in good agreement with our hypothesis that Phobos is the parent body of the Kaidun meteorite and indicate a possible Martian origin for Kaidun fragment #d(3–8)B. 相似文献
2.
Discussed in this paper are the processes of albitization and iron activation during the formation of iron deposits, the transport
and hydrolysis of iron, chemical reaction characteristic of wall-rock alteration responsible for the localization of iron
deposits, the dynamic factors affecting these reactions and systematic variations in pH of ore-forming solutions. A metasomatic
series of Na→ Ca→ Fe is noticed when diorite and dark minerals + anorthite + quartz react with 1–3m NaCl solutions at 400°–500°C.
Hydrolysis of FeCl2 has been experimentally studied as a function of temperature and pressure. It is suggested that the pH of ore-forming solutions
varies in the direction of alkalic→intermediate→acid→intermediate←kalic from early to late stages. 相似文献
3.
The effects of metamorphism on O and Fe isotope compositions in the Biwabik Iron Formation, northern Minnesota 总被引:3,自引:0,他引:3
Elizabeth Valaas Hyslop John W. Valley Clark M. Johnson Brian L. Beard 《Contributions to Mineralogy and Petrology》2008,155(3):313-328
The Biwabik Iron Formation of Minnesota (1.9 Ga) underwent contact metamorphism by intrusion of the Duluth Complex (1.1 Ga).
Apparent quartz–magnetite oxygen isotope temperatures decrease from ∼700°C at the contact to ∼375°C at 2.6 km distance (normal
to the contact in 3D). Metamorphic pigeonite at the contact, however, indicates that peak temperatures were greater than 825°C.
The apparent O isotope temperatures, therefore, reflect cooling, and not peak metamorphic conditions. Magnetite was reset
in δ18O as a function of grain size, indicating that isotopic exchange was controlled by diffusion of oxygen in magnetite for samples
from above the grunerite isograd. Apparent quartz–magnetite O isotope temperatures are similar to calculated closure temperatures
for oxygen diffusion in magnetite at a cooling rate of ∼5.6°C/kyr, which suggests that the Biwabik Iron Formation cooled from
∼825 to 400°C in ∼75 kyr at the contact with the Duluth Complex. Isotopic exchange during metamorphism also occurred for Fe,
where magnetite–Fe silicate fractionations decrease with increasing metamorphic grade. Correlations between quartz–magnetite
O isotope fractionations and magnetite–iron silicate Fe isotope fractionations suggest that both reflect cooling, where the
closure temperature for Fe was higher than for O. The net effect of metamorphism on δ18O–δ56Fe variations in magnetite is a strong increase in δ18OMt and a mild decrease in δ56Fe with increasing metamorphic grade, relative to the isotopic compositions that are expected at the low temperatures of initial
magnetite formation. If metamorphism of Iron Formations occurs in a closed system, bulk O and Fe isotope compositions may
be preserved, although re-equilibration among the minerals may occur for both O and Fe isotopes.
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. 相似文献
4.
The Samgwang mine is located in the Cheongyang gold district (Cheonan Metallogenic Province) of the Republic of Korea. It
consists of eight massive, gold-bearing quartz veins that filled NE- and NW-striking fractures along fault zones in Precambrian
granitic gneiss of the Gyeonggi massif. Their mineralogy and paragenesis allow two separate vein-forming episodes to be recognized,
temporally separated by a major faulting event. The ore minerals occur in quartz and calcite of stage I, associated with fracturing
and healing of veins. Hydrothermal wall-rock alteration minerals of stage I include Fe-rich chlorite (Fe/(Fe+Mg) ratios 0.74-0.81),
muscovite, illite, K-feldspar, and minor arsenopyrite, pyrite, and carbonates. Sulfide minerals deposited along with electrum
during this stage include arsenopyrite, pyrite, pyrrhotite, sphalerite, marcasite, chalcopyrite, galena, argentite, pyrargyrite,
and argentian tetrahedrite. Only calcite was deposited during stage II. Fluid inclusions in quartz contain three main types
of C–O–H fluids: CO2-rich, CO2–H2O, and aqueous inclusions. Quartz veins related to early sulfides in stage I were deposited from H2O–NaCl–CO2 fluids (1,500–5,000 bar, average 3,200) with T
htotal values of 200°C to 383°C and salinities less than about 7 wt.% NaCl equiv. Late sulfide deposition was related to H2O–NaCl fluids (140–1,300 bar, average 700) with T
htotal values of 110°C to 385°C and salinities less than about 11 wt.% NaCl equiv. These fluids either evolved through immiscibility
of H2O–NaCl–CO2 fluids as a result of a decrease in fluid pressure, or through mixing with deeply circulated meteoric waters as a result
of uplift or unloading during mineralization, or both. Measured and calculated sulfur isotope compositions (δ34SH2S = 1.5 to 4.8‰) of hydrothermal fluids from the stage I quartz veins indicate that ore sulfur was derived mainly from a magmatic
source. The calculated and measured oxygen and hydrogen isotope compositions (δ18OH2O = −5.9‰ to 10.9‰, δD = −102‰ to −87‰) of the ore-forming fluids indicate that the fluids were derived from magmatic sources
and evolved by mixing with local meteoric water by limited water–rock exchange and by partly degassing in uplift zones during
mineralization. While most features of the Samgwang mine are consistent with classification as an orogenic gold deposit, isotopic
and fluid chemistry indicate that the veins were genetically related to intrusions emplaced during the Jurassic to Cretaceous
Daebo orogeny. 相似文献
5.
Dexter Perkins Elizabeth Y. Anthony 《Contributions to Mineralogy and Petrology》2011,162(6):1139-1157
In peridotites, olivine, clinopyroxene, and orthopyroxene are complex solid solutions with wide stability fields. Depending
mostly on bulk composition and pressure, these minerals may be accompanied by plagioclase (low pressure), spinel (moderate
pressure), or garnet (high pressure), resulting in 4-phase and rarer 5-phase assemblages. Although a particular mineral assemblage
is stable over a range of P–T, the compositions of the individual minerals vary with changing P–T conditions. Application
of standard geothermobarometers to olivine–clinopyroxene–orthopyroxene–spinel peridotites is problematic. An alternative approach
is to use a bulk rock composition to calculate equilibrium phase diagrams to determine the conditions under which a particular
assemblage is stable. This requires consideration of the 7-component system SiO2–Al2O3–Cr2O3–FeO–MgO–CaO–Na2O, internally consistent thermodynamic data for end members, and reliable mixing models for all mineral solutions. Experimental
studies in simpler systems, and solution models from the literature, permit derivation of multicomponent thermodynamic mixing
models for the key minerals. The models, when applied to xenoliths from Kilbourne Hole, constrain P and T of equilibration
and are less sensitive to mineral compositional variations, or uncertainty in activity models, than standard thermobarometry.
Our modeling provides the first tightly constrained pressure estimates for Kilbourne Hole, placing the xenoliths in the spinel
stability field at depths (30–45 km) that correspond to the uppermost mantle beneath the Rio Grande Rift. The fine-grained
equigranular lherzolite, porphyroclastic lherzolite, and some harzburgite-dunite specimens equilibrated at average conditions
of 11.5 Kbar-930°C, 12 Kbar-990°C, and 13 Kbar-1,080°C, respectively. The mantle beneath the Rio Grande Rift is layered; the
fine-grained equigranular lherzolite derives from relatively shallow depth (35 km average), and the porphyroclastic lherzolite
from slightly deeper levels. Lying 5–10 km beneath both lherzolites, the harzburgite-dunite represents a depth where melt
extraction has significantly altered mantle chemistry and where local thermodynamic equilibrium has not been maintained. 相似文献
6.
H. A. Gilg A. Lima R. Somma H. E. Belkin B. De Vivo R. A. Ayuso 《Mineralogy and Petrology》2001,73(1-3):145-176
Summary We present new mineral chemistry, fluid inclusion, stable carbon and oxygen, as well as Pb, Sr, and Nd isotope data of Ca-Mg-silicate-rich
ejecta (skarns) and associated cognate and xenolithic nodules from the Mt. Somma-Vesuvius volcanic complex, Italy. The typically
zoned skarn ejecta consist mainly of diopsidic and hedenbergitic, sometimes “fassaitic” clinopyroxene, Mg-rich and Ti-poor
phlogopite, F-bearing vesuvianite, wollastonite, gehlenite, meionite, forsterite, clinohumite, anorthite and Mg-poor calcite
with accessory apatite, spinell, magnetite, perovskite, baddeleyite, and various REE-, U-, Th-, Zr- and Ti-rich minerals.
Four major types of fluid inclusions were observed in wollastonite, vesuvianite, gehlenite, clinopyroxene and calcite: a)
primary silicate melt inclusions (THOM = 1000–1050 °C), b) CO2 ± H2S-rich fluid inclusions (THOM = 20–31.3 °C into the vapor phase), c) multiphase aqueous brine inclusions (THOM = 720–820 °C) with mainly sylvite and halite daughter minerals, and d) complex chloride-carbonate-sulfate-fluoride-silicate-bearing
saline-melt inclusions (THOM = 870–890 °C). The last inclusion type shows evidence for immiscibility between several fluids (silicate melt – aqueous chloride-rich
liquid – carbonate/sulfate melt?) during heating and cooling below 870 °C. There is no evidence for fluid circulation below
700 °C and participation of externally derived meteoric fluids in skarn formation. Skarns have considerably variable 206Pb/204Pb (19.047–19.202), 207Pb/204Pb (15.655–15.670), and 208Pb/204Pb (38.915–39.069) and relatively low 143Nd/144Nd (0.51211–0.51244) ratios. The carbon and oxygen isotope compositions of skarn calcites (δ13CV-PDB = −5.4 to −1.1‰; δ18OV-SMOW = 11.7 to 16.4‰) indicate formation from a 18O- and 13C-enriched fluid. The isotope composition of skarns and the presence of silicate melt inclusion-bearing wollastonite nodules
suggests assimilation of carbonate wall rocks by the alkaline magma at moderate depths (< 5 km) and consequent exsolution
of CO2-rich vapor and complex saline melts from the contaminated magma that reacted with the carbonate rocks to form skarns.
Received March 1, 2000; revised version accepted November 2, 2000 相似文献
7.
M. A. Nazarov L. Ya. Aranovich S. I. Demidova T. Ntaflos F. Brandstätter 《Petrology》2011,19(1):13-25
Fragments of aluminous enstatite from lunar meteorites of highland origin were investigated. It was found that such fragments
usually occur in impact breccias of troctolitic composition. The aluminous enstatite contains up to 12 wt % Al2O3 and shows low CaO (<1 wt %) and almost constant high Mg/(Mg + Fe) ratio (89.5 ± 1.4 at %) identical to that of the Earth’s
mantle. With respect to these parameters, the aluminous enstatites are distinctly different from common orthopyroxene of lunar
rocks. The aluminous enstatite associates with spinel (pleonaste), olivine, anorthite (clinopyroxene was never found), and
accessory minerals: rutile, Ti-Zr oxides, troilite, and Fe-Ni metal. The same assemblage was described in rare fragments of
spinel cataclasites from the samples of the Apollo missions. Thermobarometry and the analysis of phase equilibria showed that
the rocks hosting aluminous enstatite are of deep origin and occurred at depths from 25 km to 130–200 km at T from 800 to 1300°C, i.e., at least in the lower crust and, possibly, in the upper mantle of the Moon. These rocks could form
individual plutons or dominate the composition of the lower crust. The most probable source of aluminous enstatite is troctolitic
magnesian rocks and, especially, spinel troctolites with low Ca/Al and Ca/Si ratios. The decompression of such rocks must
produce cordierite-bearing assemblages. The almost complete absence of such assemblages in the surficial rocks of lunar highlands
implies that vertical tectonic movements were practically absent in the lunar crust. The transport of deep-seated materials
to the lunar surface was probably related to impact events during the intense meteorite bombardments >3.9 Ga ago. 相似文献
8.
The oxygen isotopic distribution in an amoeboid olivine aggregate (AOA), TTA1-02, from the Allende CV3 chondrite has been determined by secondary ion mass spectrometry. The irregular shaped TTA1- 02 (5×3mm) consists mostly of olivine grains of ca. 5μm in diameter. Olivine grains of Mg-rich (Fo95) and Fe-rich (Fo60) composition are in direct contact with each other, with a sharp compositional boundary. Oxygen isotopic compositions of Fe-rich olivine grains are 16O-poor (Δ17O ≅ −5‰), whereas Mg-rich olivine is 16O-rich (Δ17O ≅ −25‰). Several Al-rich inclusions (<ca. 500 μm in diameter) are enclosed by olivine grains in the AOA. Oxygen isotopic compositions of spinel and fassaite in Al-rich inclusions are 16O-rich (Δ17O ≅ −20‰), whereas those of anorthite, nepheline and phyllosilicate are 16O-poor (Δ17O ≅ −5‰). We propose the following sequence of events during the formation of AOAs in the Allende meteorite: 1) Formation of Al-rich inclusions with 16O-rich oxygen isotopic composition; 2) Accretion of Mg-rich olivine grains with 16O-rich oxygen isotopic composition around Al-rich inclusions; 3) Accretion into parent body; and 4) Aqueous alteration in the parent body, which led to crystallization of 16O-poor minerals, Fe-rich olivine, anorthite, nepheline, and phyllosilicate. This is reflecting reactions among primary 16O-rich AOA minerals and aqueous fluid having 16O-poor oxygen isotopic composition. Fe-rich olivine grains precipitated from aqueous fluids, which partially dissolved pre-existing Mg-rich olivine grains. Sintering and Mg-Fe diffusion occurred during thermal metamorphism. Anorthite, nepheline and phyllosilicate in Al-rich inclusions replaced primary anorthite or melilite during the aqueous alteration stage. 相似文献
9.
Z. Johan 《Mineralogy and Petrology》2006,87(1-2):1-30
Summary The study of platinum-group minerals (PGM) concentrates from the Nizhni Tagil placers related to the Soloviev Mountain (Gora
Solovieva) Uralian-Alaskan-type intrusion revealed a predominance of (Pt, Fe) alloys over Ir-, and Os-bearing alloys. (Pt,
Fe) alloys (“isoferroplatinum-type”) are interstitial with respect to chromite and show important variations in their chemical
compositions, which are, however, falling within the experimentally determined stability field of isoferroplatinum. Tetraferroplatinum,
enriched in Cu and Ni and tulameenite represent low-temperature mineral phases replacing (Pt, Fe) alloys. Alloys belonging
to the Os–Ir–Ru ternary system have compositions corresponding to native osmium, iridium and ruthenium, respectively, and
to rutheniridosmine. Osmium exsolutions appear in Ir-, and (Pt, Fe) alloys, and iridium exsolutions in (Pt, Fe) alloys. Laurite
is a high-temperature phase included in native iridium and (Pt, Fe) alloys. Low-temperature PGM association comprises Ir-bearing
sulpharsenides, including a phase (Ir, Os, Fe, Pt, Ru, Ni)3(As, Sb)0.85S, and a palladium antimonide Pd20Sb7. These two phases were previously unknown in nature. Furthermore, native palladium occurs in the studied concentrates. This
low-temperature paragenesis indicates an interaction of Pt-, Os-, Ir- and Ru-bearing alloys with late fluids enriched in volatiles,
As and Sb. The chromite composition is characterized by the predominance of Cr3+ → Fe3+ substitution like in other Uralian-Alaskan-type intrusions; that indicates a fO2 variation during the chromite precipitation.
Monomineralic inclusions of euhedral clinopyroxene and chromite crystals in (Pt, Fe) alloys were observed. Furthermore, (Pt,
Fe) alloys contain polyphase silicate inclusions, which occupy the alloy negative crystals. Two types of silicate inclusions
were recognized: (1) Low-pressure inclusions composed of amphibole, biotite, Jd-poor clinopyroxene, magnetite, apatite and
glass; (2) High-pressure inclusions include: omphacitic clinopyroxene (up to 56 mol.% Jd), tremolite, muscovite, apatite,
titanite and glass. In this case, the clinopyroxene is strongly zoned, revealing a pressure drop from about 25 to 5 kbar.
The chemical composition of glass is corundum-normative and its H2O content varies from about 12 to 15 wt.%. The composition of magmatic melts, from which the silicate inclusions have originated
was estimated using EPMA and image analysis interpreted by stereology. Their compositions are close to those obtained experimentally
by hydrous partial melting of upper mantle rocks. The interpretation of analytical data shows that magmatic melts entrapped
by (Pt, Fe) alloys crystallized from about 1100 to 700 °C. The (Pt, Fe) alloys formed after the crystallization of chromite,
clinopyroxene and albite. Consequently, the precipitation temperature of (Pt, Fe) alloys is estimated at about 900 °C. The
significant pressure drop implies a decrease of volatile concentrations in the magmatic melt and the possible formation of
a fluid phase, which might have generated, the precipitation of chromite and PGM. 相似文献
10.
We studied the mobility of silver, heavy metals and europium in waste from the Las Herrerías mine in Almería (SE Spain). The
most abundant primary mineral phases in the mine wastes are hematite, hydrohematite, barite, quartz, muscovite, anorthite,
calcite and phillipsite. The minor phase consisted of primary minerals including ankerite, cinnabar, digenite, magnesite,
stannite, siderite and jamesonite, and secondary minerals such as glauberite, szomolnokite, thenardite and uklonscovite. The
soils show high concentrations of Ag (mean 21.6 mg kg–1), Ba (mean 2.5%), Fe (mean 114,000 mg kg–1), Sb (mean 342.5 mg kg–1), Pb (mean 1,229.8 mg kg–1), Zn (mean 493 mg kg–1), Mn (mean 4,321.1 mg kg–1), Cd (mean 1.2 mg kg–1) and Eu (mean 4.0 mg kg–1). The column experiments showed mobilization of Ag, Al, Ba, Cu, Cd, Eu, Fe, Mn, Ni, Sb, Pb and Zn, and the inverse modelling
showed that the dissolution of hematite, hausmannite, pyrolusite and anglesite can largely account for the mobilization of
Fe, Mn and Pb in the leaching experiment. The mobility of silver may be caused by the presence of kongsbergite and chlorargyrite
in the waste, while the mobility of Eu seems to be determined by Eu(OH)3, which controls the solubility of Eu in the pH–Eh conditions of the experiments. The mineralogy, pH, Eh and geochemical composition
of the mine wastes may explain the possible mobilization of heavy metals and metalloids. However, the absence of contaminants
in the groundwater may be caused by the carbonate-rich environment of “host-rocks” that limits their mobility. 相似文献
11.
P. M. E. Tollan I. Bindeman J. D. Blundy 《Contributions to Mineralogy and Petrology》2012,163(2):189-208
In order to shed light on upper crustal differentiation of mantle-derived basaltic magmas in a subduction zone setting, we
have determined the mineral chemistry and oxygen and hydrogen isotope composition of individual cumulus minerals in plutonic
blocks from St. Vincent, Lesser Antilles. Plutonic rock types display great variation in mineralogy, from olivine–gabbros
to troctolites and hornblendites, with a corresponding variety of cumulate textures. Mineral compositions differ from those
in erupted basaltic lavas from St. Vincent and in published high-pressure (4–10 kb) experimental run products of a St. Vincent
high-Mg basalt in having higher An plagioclase coexisting with lower Fo olivine. The oxygen isotope compositions (δ18O) of cumulus olivine (4.89–5.18‰), plagioclase (5.84–6.28‰), clinopyroxene (5.17–5.47‰) and hornblende (5.48–5.61‰) and hydrogen
isotope composition of hornblende (δD = −35.5 to −49.9‰) are all consistent with closed system magmatic differentiation of
a mantle-derived basaltic melt. We employed a number of modelling exercises to constrain the origin of the chemical and isotopic
compositions reported. δ18OOlivine is up to 0.2‰ higher than modelled values for closed system fractional crystallisation of a primary melt. We attribute this
to isotopic disequilibria between cumulus minerals crystallising at different temperatures, with equilibration retarded by
slow oxygen diffusion in olivine during prolonged crustal storage. We used melt inclusion and plagioclase compositions to
determine parental magmatic water contents (water saturated, 4.6 ± 0.5 wt% H2O) and crystallisation pressures (173 ± 50 MPa). Applying these values to previously reported basaltic and basaltic andesite
lava compositions, we can reproduce the cumulus plagioclase and olivine compositions and their associated trend. We conclude
that differentiation of primitive hydrous basalts on St. Vincent involves crystallisation of olivine and Cr-rich spinel at
depth within the crust, lowering MgO and Cr2O3 and raising Al2O3 and CaO of residual melt due to suppression of plagioclase. Low density, hydrous basaltic and basaltic andesite melts then
ascend rapidly through the crust, stalling at shallow depth upon water saturation where crystallisation of the chemically
distinct cumulus phases observed in this study can occur. Deposited crystals armour the shallow magma chamber where oxygen
isotope equilibration between minerals is slowly approached, before remobilisation and entrainment by later injections of
magma. 相似文献
12.
Jürgen Konzett Daniel J. Frost Alexander Proyer Peter Ulmer 《Contributions to Mineralogy and Petrology》2008,155(2):215-228
Experiments have been conducted in the P-T range 2.5–15 GPa and 850–1,500°C using bulk compositions in the systems SiO2–TiO2–Al2O3–Fe2O3–FeO–MnO–MgO–CaO–Na2O–K2O–P2O5 and SiO2–TiO2–Al2O3–MgO–CaO–Na2O to investigate the Ca-Eskola (CaEs Ca0.5□0.5AlSi2O6) content of clinopyroxene in eclogitic assemblages containing garnet + clinopyroxene + SiO2 ± TiO2 ± kyanite as a function of P, T, and bulk composition. The results show that CaEsss in clinopyroxene increases with increasing T and is strongly bulk composition dependent whereby high CaEs-contents are favoured by bulk compositions with high normative
anorthite and low diopside contents. In this study, a maximum of 18 mol% CaEsss was found at 6 GPa and 1,350°C in a kyanite-eclogite assemblage garnet + clinopyroxene + kyanite + rutile + coesite. By comparison,
no significant increase in CaEsss with increasing P could be observed. If the formation of oriented SiO2-rods frequently observed in eclogititc clinopyroxenes is due to the retrogressive breakdown of a CaEs-component then these
textures are a cooling rather than a decompression phenomenon and are most likely to be found in kyanite-bearing eclogites
cooled from temperatures ≥750°C. The presence of clinopyroxene with approx. 4 mol% CaEsss in an experiment conducted at 2.5 GPa/850°C confirms earlier suggestions based on field data that vacancy-rich clinopyroxenes
are not necessarily restricted to ultrahigh pressure metamorphic conditions.
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. 相似文献
13.
Highly purified picked minerals of cassiterite and associated new recorded minerals were chemically and mineralogically investigated.
Most of the investigated cassiterite exhibits homogeneous grains without obvious zoning. The analyzed cassiterites have more
than 98 wt.% SnO2, which reveal clearly their considerable purity. Minor gold with traces of ferrotapiolite, cinnabar, native lead, chromite,
and chevkinite are well detectable within the obtained cassiterite concentrate. The origin of the present cassiterite and
the associated minerals is also discussed. The variation in color and grain size of cassiterite may be attributed to the various
lithology and/or areas drained by the River Nile. The color of cassiterite is appeared to be intensified with increased Nb
and Fe contents. Three categories of cassiterites are identified, (a) Ta2O5-rich (0.46–2.65 wt.%); (b) TiO2-rich (0.42–1.41 wt.%), and (c) Ta2O5-Nb2O5-Fe2O3 rich one (Ta2O5:0.42–3.58 wt.%, Nb2O5: 0.7–1.98 wt.% and Fe2O3: 0.56–1.02 wt.%). Sn is usually substituted by Ta, Nb, and Fe. Minor gold with traces of new recorded ferrotapiolite, cinnabar,
native lead, chromite, and chevkinite are well detectable within the obtained cassiterite concentrate. Ferrotapiolite is composed
mainly of Ta, Fe, and Nb with minor Ti, Sn, and Mn, which similar to that derived from pegmatites and quartz veins. Chevkinite
is generally enriched in Ti, Fe, and LREEs and depleted in P, Th, and U which analogous to that crystallized from felsic igneous
rock suites. 相似文献
14.
The effect of CaO and MgO, with or without TiO2 and P2O5, on the two-melt field in the simplified system Fe2SiO4–KAlSi3O8–SiO2 has been experimentally determined at 1,050°–1,240°C, 400 MPa. Despite the suppressing effect of MgO, CaO, and pressure on silicate melt immiscibility, our experiments show that this process is still viable at mid-crustal pressures when small amounts (0.6–2.0 wt%) of P2O5 and TiO2 are present. Our data stress that the major element partition coefficients between the two melts are highly correlated with the degree of polymerisation (nbo/t) of the SiO2-rich melt, whatever temperature, pressure, or exact composition. Experimental immiscible melt compositions in natural systems at 0.1 MPa from the literature (lunar and tholeiitic basalts) plot on similar but distinct curves compared to the simplified system. These relations between melt polymerisation and partition coefficients, which hold for a large range of compositions and fO2, are extended to various volcanic and plutonic rocks. This analysis strengthens the proposal that silicate melt immiscibility can be important in volcanic rocks of various compositions (from tholeiitic basalts to lamprophyres). However, the majority of proposed immiscible compositions in plutonic rocks are at least not coexisting melts, but may have suffered accumulation of early crystallized minerals. 相似文献
15.
T. Gasparik 《Physics and Chemistry of Minerals》2002,29(3):170-180
Multianvil experiments were carried out at 10–15 GPa and 1600–1700 °C to match the compositions of majoritic garnet inclusions
from diamonds, and to determine the compositions of other phases potentially coexisting with these inclusions in the source.
Most experiments produced coexisting majoritic garnet, diopsidic clinopyroxene, one or more (Mg,Fe)2SiO4 polymorphs, and quenched carbonatic melt. The experimental garnets had relatively high Ca and Fe contents similar to the
observed Ca and Fe contents of the inclusions. The resulting Si contents confirmed that the depth of origin of the inclusion
with the highest Si content did not exceed 410 km, thus none of the majoritic garnet inclusions found so far originated in
the transition zone (410–660 km). The evidence from inclusions and experiments is consistent with the presence of an eclogite
layer occurring globally between 200 and 410 km. Compositional variations observed among more than 100 majoritic garnet inclusions
with their Si content, which is a measure of pressure and depth, are consistent with the origin of the eclogite layer by crystal
fractionation in a magma ocean. The compositions of olivine coexisting with majoritic garnet in the experimental products
had the average Fe/(Fe + Mg) ratios between 0.16 and 0.28. Inclusions with such high Fe contents have not been found; the
Fe/(Fe + Mg) ratio of the olivine inclusions in diamonds usually varies between 0.05 and 0.09. Hence, the mantle between 200
and 410 km may not contain olivine. In the absence of olivine, the discontinuity at 410 km is most likely a chemical boundary
between the 200-km-thick eclogite layer and a more mafic transition zone.
Received: 15 March 2001 / Accepted: 14 September 2001 相似文献
16.
Two examined fragments of the Kaidun meteorite principally differ in the concentrations of isotopes of noble gases and are very heterogeneous in terms of the isotopic composition of the gases. Because these fragments belong to two basically different types of meteoritic material (EL and CR chondrites), these characteristics of noble gases could be caused by differences in the cosmochemical histories of the fragments before their incorporation into the parent asteroid. As follows from the escape kinetics of all gases, atoms of trapped and cosmogenic noble gases are contained mostly in the structures of two carrier minerals in the samples. The concentrations and proportions of the concentrations of various primary noble gases in the examined fragments of Kaidun are obviously unusual compared to data on most currently known EL and CR meteorites. In contrast to EL and CR meteorites, which contain the primary component of mostly solar provenance, the elemental ratios and isotopic composition of Ne and He in the fragments of Kaidun correspond to those typical of the primary components of A and Q planetary gases. This testifies to the unique conditions under which the bulk of the noble gases were trapped from the early protoplanetary nebula. The apparent cosmic-ray age of both of the Kaidun fragments calculated based on cosmogenic isotopes from 3He to 126Xe varies from 0.027 to 246 Ma as a result of the escape of much cosmogenic isotopes at relatively low temperatures. The extrapolated cosmic-ray age of the Kaidun meteorite, calculated from the concentrations of cosmogenic isotopes of noble gases, is as old as a few billion years, which suggests that the material of the Kaidun meteorite could be irradiated for billions of years when residing in an unusual parent body. 相似文献
17.
Michel A. F. Rakotondrazafy B. Moine M. Cuney 《Contributions to Mineralogy and Petrology》1996,123(2):190-201
In Madagascar, hibonite occurs as a rather frequent mineral within thorianite-bearing skarns which are widespread in the
Pan African granulitic formations constituting the S-E part of the Island (Tranomaro area). In these skarns, leucocratic segregations
made up of CO3-scapolite to meionite (Anequivalent=89–95% which implies T≥850° C), spinel and corundum were formed at stage 1 of metasomatism in a titanite-bearing matrix consisting of scapolite
(Aneq=77–88) and aluminous diopside. During stage 2 of metasomatism, scapolite from the lenses were altered to anorthite+calcite
while the less calcic scapolite remained stable which indicates T≈800° C. Hibonite crystallized at the expense of corundum and spinel. Expressed as mol% of the CaAl12O19/Ca(Al10TiR2+)O19/REE(Al11R2+)O19 [+Th (Al10R2+
2)O19] end-members (R
2+=Mg, Fe2+, Zn2+; Al=Al, Fe3+; Ti=Ti, Si), its composition varies from 26/72/2 to 50/23/27. The ideal activity of the CaAl12O19 component is about 0.25. Fluid inclusions in corundum, hibonite and anorthite are composed of nearly pure CO2. In corundum, the isochores for primary inclusions are in agreement with the P-T estimates for regional metamorphism and stage 1 metasomatism (T≈850° C, P≈5 kbar). Inclusions with the highest density in hibonite and anorthite constrain P to about 3–3.5 kbar for T=800° C. Thermodynamic calculations indicate that, in addition to a low activity of CaAl12O19, stability of hibonite in equilibrium with anorthite and calcite implies an extremely low activity of silica (below the zircon-baddeleyite
buffer). By contrast the activity of CO2 may be high, in agreement with the observed fluid compositions. These results are corroborated by a short comparison with
the other granulite occurrences of hibonite in Tanzania and South India.
Received: 18 August 1994 / Accepted: 12 October 1995 相似文献
18.
Using various methods of melt inclusion investigation, including electron and ion microprobe techniques, we estimated the
composition, evolution, and formation conditions of melts producing the trachydacites and pantellerites of the Late Paleozoic
bimodal volcanic association of Dzarta-Khuduk, Central Mongolia. Primary crystalline and melt inclusions were detected in
anorthoclase from trachydacites and quartz from pantellerites and pantelleritic tuffs. Among the crystalline inclusions, we
identified hedenbergite, fluorapatite, and pyrrhotite in the trachydacites and F-arfvedsonite, fluorite, ilmenite, and the
rare REE diorthosilicate chevkinite in the pantellerites. Melt inclusions in anorthoclase from the trachydacites are composed
of glass, a gas phase, and daughter minerals (F-arfvedsonite, fluorite, villiaumite, and anorthoclase rim on the inclusion
wall). Melt inclusions in quartz from the pantellerites are composed of glass, a gas phase, and a fine-grained salt aggregate
consisting of Li, Na, and Ca fluorides (griceite, villiaumite, and fluorite). Melt inclusions in quartz crystalloclasts from
the pantelleritic tuffs are composed of homogeneous silicate glasses. The phenocrysts of the trachydacites and pantellerites
crystallized at temperatures of 1060–1000°C. During thermometric experiments with quartz-hosted melt inclusions from the pantellerites,
the formation of immiscible silicate and salt (fluoride) melts was observed at a temperature of 800°C. Homogeneous melt inclusions
in anorthoclase from the trachydacites have both trachydacite and rhyolite compositions (wt %): 68–70 SiO2, 12–13 Al2O3, 0.34–0.74 TiO2, 5–7 FeO, 0.4–0.9 CaO, and 9–12 Na2O + K2O. The agpaitic index ranges from 0.92 to 1.24. The glasses of homogenized melt inclusions in quartz from the pantellerites
and pantelleritic tuffs have rhyolitic compositions. Compared with the homogeneous glasses trapped in anorthoclase of the
trachydacites, quartz-hosted inclusions from the pantellerites show higher SiO2 (72–78 wt %) and lower Al2O3 contents (7.8–10.0 wt %). They also contain 0.14–0.26 wt % TiO2, 2.5–4.9 wt % FeO, 9–11 wt % Na2O + K2O, and 0.9–0.15 wt % CaO and show an agpaitic index of 1.2–2.05. Homogeneous melt inclusions in quartz from the pantelleritic
tuffs contain 69–72 wt % SiO2. The contents of other major components, including TiO2, Al2O3, FeO, and CaO, are close to those in the homogeneous glasses of quartzhosted melt inclusions in the pantellerites. The contents
of Na2O + K2O are 4–10 wt %, and the agpaitic index is 1.0–1.6. The glasses of melt inclusions from each rock group show distinctive volatile
compositions. The H2O content is up to 0.08 wt % in anorthoclase of the trachydacites, 0.4–1.4 wt % in quartz of the pantellerites, and up to
5 wt % in quartz of the pantelleritic tuffs. The content of F in the glasses of melt inclusions in the phenocrysts of the
trachydacites is no higher than 0.67 wt %, and up to 1.4–2.8 wt % in quartz from the pantellerites. The Cl content is up to
0.2 wt % in the glasses of melt inclusions in the minerals of the trachydacites and up to 0.5 wt % in the glasses of quartz-hosted
melt inclusions from the pantellerites. The investigation of trace elements in the homogenized glasses of melt inclusions
in minerals showed that the trachydacites and pantellerites were formed from strongly evolved rare-metal alkaline silicate
melts with high contents of Li, Zr, Rb, Y, Hf, Th, U, and REE. The analysis of the composition of homogeneous melt inclusions
in the minerals of the above rocks allowed us to distinguish magmatic processes resulting in the enrichment of these rocks
in trace and rare earth elements. The most important processes are the crystallization differentiation and immiscible separation
of silicate and fluoride salt melts. It was also shown that all the melts studied evolved in spatially separated magma chambers.
This caused the differences in the character of melt evolution between the trachydacites and pantellerites. During the final
stages of differentiation, when the magmatic system was saturated with respect to ore elements, Na-Ca fluoride melts were
separated and extracted considerable amounts of Li. 相似文献
19.
Effect of acid mine drainage on a karst basin: a case study on the high-As coal mining area in Guizhou province,China 总被引:2,自引:2,他引:0
Xiuzhen Tao Pan Wu Changyuan Tang Hong Liu Jing Sun 《Environmental Earth Sciences》2012,65(3):631-638
Acid mine drainage (AMD) is a common pollution in mining areas due to the oxidation of pyrite and associated sulfide minerals
at mines, tailings and mine dumps. Elevated metals (Fe, Mn, Al) and metalloids (As, Hg) in AMD would deteriorate the local aquatic
environment and influence the water supply. A carbonate basin with deposits of high-arsenic coal in Xingren County, southwestern
China, was chosen to study the behavior of As and other chemical constituents along a river receiving AMD. Heavy metals (Fe,
Mn) and major ions such as (Ca2+, Mg2+, Cl−, SO4
2−) in surface water, and As in sediment and surface water were analyzed. It was found that high concentrations of SO4
2− (1,324–7,560 mg/L) and Fe (369–1,472 mg/L) in surface water were mainly controlled by the interactions between water and
rocks such as the oxidation of pyrite in the local coal seams, precipitation and adsorption of iron minerals. Although ubiquitous
carbonate minerals in the bedrock and the riverbeds, low pH (<3) water was maintained until 2 km downstream from the AMD source
due to the Fe(hydro)oxide minerals coating on the surface of carbonate minerals to restrain the neutralization of acidic water.
Moreover, the formation of Fe(hydro)oxide precipitations absorbed As was dominated the attenuation of As from water to sediment.
Whereas, the dilution also played an important role in decrease of As in river water. 相似文献
20.
Situated in the Henan-Shaanxi fault-uplift area on the southern margin of the Sino-Korean Paraplatform, the Jinduicheng porphyry
molybdenum deposit is the most important molybdenum producer in China. During Yenshanian the Jinduicheng granite porphyry
was emplaced in metaspilite of the Proterozoic Xionger Group, controlled by a NW-trending fault. Mineral compositions are
mainly quartz (25–40%), microcline and microcline-perthite (27–40%) and plagioclase (An 8–14, 14–32%), associated with minor
biotite and muscovite, and phenocrysts are made up of K-feldspar, quartz and plagioclase. Accessory minerals include magmatite,
apatite and zircon. The porphyry contains SiO2 73.83% and K2O + Na2O 8.06% (with K2O/Na2O ratio being 1.82), beloning to the calc-alkaline series.
Mineralization occurs in the porphyry body and biotitized and hornfelsized spilite within the exocontact zone. The maximum
depth of mineralization reaches 1000 meters below the surface. According to mineral assemblage, ore veins are classified into
five types: (1) pyrite-quartz; (2) pyrite-K-feldspar-quartz; (3) pyrite-molybdenite-quartz; (4) pyrite-molybdenite-K-feldspar-quartz;
and (5) muscovitefluorite-pyrite-molybdenite-quartz.
As the most important economic molybdenum mineral, molybdenite occurs in various forms. Wall-rock alterations show a gross
zonation of K-feldspathization-greisenization → silicification → propylitization from the porphyry outwards, of which silicification
is most intense and has close genetic relationship with Mo mineralization.
Fluid inclusion studies yield homogeneous temperatures ranging from 250 to 240°C, with the main stage between 400 and 300°C.
Gas inclusions frequently coexist with multiphase inclusions containing such daughter minerals as halite, sylvite, molybdenite
and K-feldspar. Under moderate-high temperatures, lowerfo2, highfs2 and weak acidity conditions, boiling of ore-forming fluids is a prerequisite for the precipitation of molybdenite.
Sulfur, oxygen and carbon isotopic compositions suggest that at the high temperature stage (450°C) magmatic water is dominant
and at the main ore-forming stage a mixture of magmatic water and meteoric water is expected. At the late stage, the mixture
is predominated by meteoric water. Sulfur and molybdenum are mostly of magmatic origin. 相似文献