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961.
Xiomara Cazañas Pura Alfonso Joan Carles Melgarejo Joaquín Antonio Proenza Anthony Edward Fallick 《Mineralium Deposita》2008,43(7):805-824
The El Cobre deposit is located in eastern Cuba within the volcanosedimentary sequence of the Sierra Maestra Paleogene arc.
The deposit is hosted by tholeiitic basalts, andesites and tuffs and comprises thick stratiform barite and anhydrite bodies,
three stratabound disseminated up to massive sulphide bodies produced by silicification and sulphidation of limestones or
sulphates, an anhydrite stockwork and a siliceous stockwork, grading downwards to quartz veins. Sulphides are mainly pyrite,
chalcopyrite and sphalerite; gold occurs in the stratabound ores. Fluid inclusions measured in sphalerite, quartz, anhydrite
and calcite show salinities between 2.3 and 5.7 wt% NaCl eq. and homogenisation temperatures between 177 and 300°C. Sulphides
from the stratabound mineralisation display δ
34S values of 0‰ to +6.0‰, whilst those from the feeder zone lie between −1.4‰ and +7.3‰. Sulphides show an intra-grain sulphur
isotope zonation of about 2‰; usually, δ
34S values increase towards the rims. Sulphate sulphur has δ
34S in the range of +17‰ to +21‰, except two samples with values of +5.9‰ and +7.7‰. Sulphur isotope data indicate that the
thermochemical reduction of sulphate from a hydrothermal fluid of seawater origin was the main source of sulphide sulphur
and that most of the sulphates precipitated by heating of seawater. The structure of the deposit, mineralogy, fluid inclusion
and isotope data suggest that the deposit formed from seawater-derived fluids with probably minor supply of magmatic fluids. 相似文献
962.
M. -S. Krienitz R. B. Trumbull A. Hellmann J. Kolb F. M. Meyer M. Wiedenbeck 《Mineralium Deposita》2008,43(4):421-434
We determined the boron isotope and chemical compositions of tourmaline from the Hira Buddini gold deposit within the Archean
Hutti-Maski greenstone belt in southern India to investigate the evolution of the hydrothermal system and to constrain its
fluid sources. Tourmaline is a minor but widespread constituent in the inner and distal alteration zones of metabasaltic and
metadacite host rocks associated with the hydrothermal gold mineralization. The Hira Buddini tourmaline belongs to the dravite–schorl
series with variations in Al, Fe/(Fe+Mg), Ca, Ti, and Cr contents that can be related to their host lithology. The total range
of δ11B values determined is extreme, from −13.3‰ to +9.0‰, but 95% of the values are between −4 and +9‰. The boron isotope compositions
of metabasalt-hosted tourmaline show a bimodal distribution with peak δ11B values at about −2‰ and +6‰. The wide range and bimodal distribution of boron isotope ratios in tourmaline require an origin
from at least two isotopically distinct fluid sources, which entered the hydrothermal system separately and were subsequently
mixed. The estimated δ11B values of the hydrothermal fluids, based on the peak tourmaline compositions and a mineralization temperature of 550°C,
are around +1 and +10‰. The isotopically lighter of the two fluids is consistent with boron released by metamorphic devolatilization
reactions from the greenstone lithologies, whereas the 11B-rich fluid is attributed to degassing of I-type granitic magmas that intruded the greenstone sequence, providing heat and
fluids to the hydrothermal system.
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. 相似文献
963.
Metamorphic fluid origins in the Osborne Fe oxide–Cu–Au deposit,Australia: evidence from noble gases and halogens 总被引:1,自引:1,他引:0
The Osborne iron oxide–copper–gold (IOCG) deposit is hosted by amphibolite facies metasedimentary rocks and associated with
pegmatite sheets formed by anatexis during peak metamorphism. Eleven samples of ore-related hydrothermal quartz and two pegmatitic
quartz–feldspar samples contain similarly complex fluid inclusion assemblages that include variably saline (<12–65 wt% salts)
aqueous and liquid carbon dioxide varieties that are typical of IOCG mineralisation. The diverse fluid inclusion types present
in each of these different samples have been investigated by neutron-activated noble gas analysis using a combination of semi-selective
thermal and mechanical decrepitation techniques. Ore-related quartz contains aqueous and carbonic fluid inclusions that have
similar 40Ar/36Ar values of between 300 and 2,200. The highest-salinity fluid inclusions (47–65 wt% salts) have calculated 36Ar concentrations of approximately 1–5 ppb, which are more variable than air-saturated water (ASW = 1.3–2.7 ppb). These fluid
inclusions have extremely variable Br/Cl values of between 3.8 × 10−3 and 0.3 × 10−3, and I/Cl values of between 27 × 10−6 and 2.4 × 10−6 (all ratios are molar). Fluid inclusions in the two pegmatite samples have similar 40Ar/36Ar values of ≤1,700 and an overlapping range of Br/Cl and I/Cl values. High-salinity fluid inclusions in the pegmatite samples
have 2.5–21 ppb 36Ar, that overlap the range determined for ore-related samples in only one case. The fluid inclusions in both sample groups
have 84Kr/36Ar and 129Xe/36Ar ratios that are mainly in the range of air and air-saturated water and are similar to mid-crustal rocks and fluids from
other settings. The uniformly low 40Ar/36Ar values (<2,200) and extremely variable Br/Cl and I/Cl values do not favour a singular or dominant fluid origin from basement-
or mantle-derived magmatic fluids related to A-type magmatism. Instead, the data are compatible with the involvement of metamorphic
fluids that have interacted with anatectic melts to variable extents. The ‘metamorphic’ fluids probably represent a mixture
of (1) inherited sedimentary pore fluids and (2) locally derived metamorphic volatilisation products. The lowest Br/Cl and
I/Cl values and the ultra-high salinities are most easily explained by the dissolution of evaporites. The data demonstrate
that externally derived magmatic fluids are not a ubiquitous component of IOCG ore-forming systems, but are compatible with
models in which IOCG mineralisation is localised at sites of mixing between fluids of different origin.
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorised users. 相似文献
964.
Coastal sea-surface temperature (SST) and sea-surface salinity (SSS), including seasonality, in northwest (NW) Europe during the early phase of the Eemian interglacial ca. 125 ka ago were reconstructed from Littorina littorea (common periwinkle) gastropods. The results were based on intra-annual δ18O analyses in recent and fossil shells, mainly originating from the sea of Kattegat (Sweden) and the English Channel (United Kingdom), and confined to intertidal settings. The Eemian L. littorea shells indicated annual SSTs in the range 8–18°C for the English Channel and 8–26°C for Kattegat. All specimens from the Eemian sites experienced summer SSTs of ca. 1–3°C above recent conditions. The estimated winter SST in the English Channel during the Eemian was comparable to modern measurements of ca. 8°C. However, the Kattegat region displayed Eemian winter SST approximately 8°C warmer than today, and similar to conditions in the western English Channel. The recent-fossil isotope analogue approach indicated high SSS above 35 practical salinity units (psu) for a channel south of England in full contact with the North Atlantic Ocean during the last interglacial. In addition, the Kattegat shells indicated a SSS of ca. 29 psu, which points out a North Sea affinity for this region during the Eemian. 相似文献
965.
Based on the analysis of siderite distribution,occurrence,chemical compositionk,structureal characteristics,carbon-oxygen isotopic characteristics and relationship between siderite and hematite,this paper presents a systematic study of siderite in the region studied.suggesting that the siderite in the Xuanlong area genetically resulted from organically reduced primary hematite during the diagenesis.The ferric and ferrous relations directly depend on organic contents.In the presence of organic matter ferrous iron can be converted to ferric iron through or ganic reduction.The above conclusion has also been proved by organic geochemistry.data. 相似文献
966.
汉诺坝玄武岩中辉石岩类包体Nd、Sr、Pb同位素及其成因信息 总被引:13,自引:1,他引:13
对汉诺坝地区的12个辉石岩和1个麻粒岩包体进行了Nd、Sr、Pb同位素测定,发现辉石岩组成有很大变化,143Nd/144Nd比值为0.51160—0.51314,87Sr/86Sr比值为0.7029—0.7086,206Pb/204Pb比值为15.942—18.683,207Pb/204Pb比值为15.264—15.569,208Pb/204Pb比值为36.213—38.744,显示了其复杂成因q推测具有高Sr、低Nd和低Pb同位素组成的辉石岩是地幔早期富集的产物,与麻粒岩、辉长岩包体有类似成因;具有弱至中等亏损的Nd、Sr同位素和高放射成因Pb的辉石岩是亏损地幔近期富集或交代的产物 相似文献
967.
968.
Z. Kattan 《Journal of Arid Environments》1997,35(4):601-615
Waters from a network of rainfall collection covering nine meteorological stations distributed mainly in the western part of Syria have been assayed using chemical and environmental isotope techniques for a period of 5 months from Dec 1989 to Apr 1990. The chemistry of rain waters falling over the mountainous stations shows a low solute concentration (20–105 mg−1/L) compared with those falling over the coastal and anterior stations (50–210 mg−1/L). The rain waters are generally characterized by a high deuterium excess (d = 19 ‰) compared with that of typical global meteoric waters (d = 10 ‰). The estimated deuterium excess is lower than that for the eastern Mediterranean meteoric waters (d = 22 ‰). The altitude effect is shown up by a depletion of heavy stable isotopes of about −0·23 ‰ and −1·65 ‰ per 100 m elevation of δ18O and δD, respectively. The spatial distribution pattern of tritium contents shows a gradual build up with increasing distance from the Syrian coast. The weighted mean tritium content in rain waters falling over the country is estimated to amount to 9·5 tritium units (TU) during the period of observation. 相似文献
969.
根据国内外许多钾盐矿床大量样品测定的结果:通常石盐(岩)的37Cl/35Cl比值和δ37Cl(%)值高于钾石盐(岩);钾石盐高于光卤石(岩)。例如:西班牙Catalonia盆地钾盐矿床,其石盐岩为0.31958—0.31941和+1.002─+0.470‰,钾石盐岩为0.31913和─0.407‰,光卤石岩为0.31887和─1.221‰,等等。这说明了这些蒸发岩是在水体浓缩的不同阶段形成的,是氯同位素分馏作用长期不断进行的结果。其氯同位素组成与Br、K和Mg含量有着密切关系。困而在我国找钾过程中,可将氯同位素组成及Br、K、Mg含量结合起来作为找钾标志考虑。 相似文献
970.
Cr(III) sorbed at the solid/water interface of latex and hectorite was studied by ESR spectroscopy in the presence of different inorganic ligands. The ESR spectra of the surface obtained in the presence of selenite, phosphate and fluoride can be explained in terms of ternary surface complex formation. This is contrasted by the behaviour of sulfate and selenate ions which were found to have no effect on the ligand field of Cr(III), either in the adsorbed state or in solution. 相似文献