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1.
Ore lead and sulphur isotope pattern from the low-temperature veins of the Catalonian Coastal Ranges (NE Spain) 总被引:4,自引:0,他引:4
The lead isotopic composition of galenas from low-temperature veins of the Catalonian Coastal Ranges (NE Spain) displays
a small but distinct range of values: 18.318 ≤206Pb/204Pb ≤ 18.678; 15.678 ≤207Pb/204Pb ≤ 15.767 and 38.534 ≤ 208Pb/204Pb ≤ 39.189. The data define a linear trend in the 208Pb/204Pb versus 206Pb/204Pb diagram that can be interpreted in terms of mixing of lead from different reservoirs. The lead appears to be derived from
a solution that preferentially leached granites of Late-Hercynian age. Sulphur isotopic compositions of the galenas range
from −8.5 to + 7.3‰ but variations in a single deposit are small (1–2‰), pointing to different sources of sulphur. In a δ34S versus 206Pb/204Pb plot no clear correlation trends appear. Lead isotope data from deposits of similar characteristics situated within the
Hercynian orogenic belt as the Linares-La Carolina district (S Spain) and the Inglesiente-Sulcis area (Sardinia) show slight
differences indicating a source area of similar lead isotopic composition. In the CCR and Linares-La Carolina districts,
the main source of lead is related to the Hercynian granites of each area, although small contributions from metasediments
cannot be ruled out. The contribution of lead from metasedimentary rocks is particularly seen in the Sardinian (Hercynian
vein-type) ores.
Received: 8 August 1996 / Accepted: 5 December 1996 相似文献
2.
From basalt to dacite: origin and evolution of the calc-alkaline series of Salina, Aeolian Arc, Italy 总被引:1,自引:1,他引:0
The island of Salina comprises one of the most distinct calc-alkaline series of the Aeolian arc (Italy), in which calc-alkaline,
high-K calc-alkaline, shoshonitic and leucite-shoshonitic magma series are developed. Detailed petrological, geochemical and
isotopic (Sr, Nd, Pb, O) data are reported for a stratigraphically well-established sequence of lavas and pyroclastic rocks
from the Middle Pleistocene volcanic cycle (430–127 ka) of Salina, which is characterized by an early period of basaltic volcanism
(Corvo; Capo; Rivi; Fossa delle Felci, group 1) and a sequence of basaltic andesites, and andesites and dacites in the final
stages of activity (Fossa delle Felci, groups 2–8). Major and trace element compositional trends, rare earth element (REE)
abundances and mineralogy reveal the importance of crystal fractionation of plagioclase + clinopyroxene + olivine/ orthopyroxene ± titanomagnetite ± amphibole ± apatite
in generating the more evolved magma types from parental basaltic magmas, and plagioclase accumulation in producing the high
Al2O3 contents of some of the more evolved basalts. Sr isotope ratios range from 0.70410 to 0.70463 throughout the suite and show
a well-defined negative correlation with 143Nd/144Nd (0.51275–0.51279). Pb isotope compositions are distinctly radiogenic with relatively large variations in 206Pb/204Pb (19.30–19.66), fairly constant 207Pb/204Pb (15.68–15.76) and minor variations in 208Pb/204Pb ratios (39.15–39.51). Whole-rock δ18O values range from +6.4 to +8.5‰ and correlate positively with Sr isotope ratios. Overall, the isotopic variations are correlated
with the degree of differentiation of the rocks, indicating that only small degrees of crustal assimilation are overprinting
the dominant evolution by crystal–liquid fractionation (AFC-type processes). The radiogenic and oxygen isotope composition
of the Salina basalts suggests derivation from primary magmas from a depleted mantle source contaminated by slab-derived fluids
and subducted sediments with an isotopic signature of typical upper continental crust. These magmas then evolved further to
andesitic and dacitic compositions through the prevailing process of low-pressure fractional crystallization in a shallow
magma reservoir, accompanied by minor assimilation of crustal lithologies similar to those of the Calabrian lower crust.
Received: 29 November 1999 / Accepted: 16 April 2000 相似文献
3.
Distinguishing magmatic from subsolidus epidote: laser probe oxygen isotope compositions 总被引:1,自引:0,他引:1
Epidote occurs in four textural varieties in the Mount Lowe intrusion of southern California: euhedra, anhedra, intergrowths
and cross-cutting veins. Of these, conspicuous elongate euhedra, which range up to 3 cm in length, meet most of the established
textural criteria for magmatic epidote. Equant anhedral grains, which are ˜5 mm in diameter, are texturally ambiguous although
rare allanite cores are suggestive of a magmatic origin. Epidote intergrowths with hornblende and biotite also meet certain
textural criteria for crystallization from a magma, notably, euhedral faces against biotite. Finally, late-stage veins of
epidote cross-cut all phases in the rock and are likely subsolidus. Oxygen isotopic compositions of these four textural varieties
of epidote determined using the laser probe indicate that the use of textural criteria alone in establishing epidote parageneses
can be misleading. Intracrystalline δ18O variations in the euhedra document both magmatic and subsolidus compositions. Oxygen isotope compositions are bimodal averaging
5.36 ± 0.13‰ (n = 11) and 4.66 ± 0.23‰ (n = 21). These data combined with plagioclase and zircon δ18O values are interpreted to indicate that magmatic oxygen isotopic compositions have been preserved where epidote δ18O is greater than 5‰. Significant portions of each euhedral crystal have been affected by subsolidus exchange and are characterized
by epidote δ18O values less than 5‰. Intracrystalline δ18O values of epidote anhedra range from 4.50 to 6.08‰ and thus also document both magmatic and subsolidus compositions. Subsolidus
exchange is volumetrically less significant in the anhedra than in the euhedra. Values of δ18O for intergrowths and late-stage cross-cutting veins of epidote average 3.81 ± 0.22‰ and document clearly subsolidus growth.
The data confirm that in the Mount Lowe intrusion, large euhedra of epidote are magmatic in origin, consistent with textural
evidence. The data also indicate that equant anhedra of epidote are also magmatic in origin and thus the absence of good crystal
faces does not necessarily indicate subsolidus growth. The subsolidus origin of intergrowths of epidote with euhedral faces
against biotite indicates that well developed crystal faces do not require growth from a magma. Finally, the subsolidus origin
of the vein epidote is consistent with textural evidence. The increased resolution available with laser-based oxygen isotope
measurements offers an important test for documenting whether epidote is of magmatic or subsolidus origin. Given the barometric
significance of magmatic epidote, oxygen isotope compositions can be used to aid in the interpretation of epidote-bearing
plutons.
Received: 9 April 1996 / Accepted: 3 August 1996 相似文献
4.
The Marcona–Mina Justa deposit cluster, hosted by Lower Paleozoic metaclastic rocks and Middle Jurassic shallow marine andesites,
incorporates the most important known magnetite mineralization in the Andes at Marcona (1.9 Gt at 55.4% Fe and 0.12% Cu) and
one of the few major iron oxide–copper–gold (IOCG) deposits with economic Cu grades (346.6 Mt at 0.71% Cu, 3.8 g/t Ag and
0.03 g/t Au) at Mina Justa. The Middle Jurassic Marcona deposit is centred in Ica Department, Perú, and the Lower Cretaceous
Mina Justa Cu (Ag, Au) prospect is located 3–4 km to the northeast. New fluid inclusion studies, including laser ablation
time-of-flight inductively coupled plasma mass spectrometry (LA-TOF-ICPMS) analysis, integrated with sulphur, oxygen, hydrogen
and carbon isotope analyses of minerals with well-defined paragenetic relationships, clarify the nature and origin of the
hydrothermal fluid responsible for these contiguous but genetically contrasted deposits. At Marcona, early, sulphide-free
stage M-III magnetite–biotite–calcic amphibole assemblages are inferred to have crystallized from a 700–800°C Fe oxide melt
with a δ18O value from +5.2‰ to +7.7‰. Stage M-IV magnetite–phlogopite–calcic amphibole–sulphide assemblages were subsequently precipitated
from 430–600°C aqueous fluids with dominantly magmatic isotopic compositions (δ34S = +0.8‰ to +5.9‰; δ18O = +9.6‰ to +12.2‰; δD = −73‰ to −43‰; and δ13C = −3.3‰). Stages M-III and M-IV account for over 95% of the magnetite mineralization at Marcona. Subsequent non-economic,
lower temperature sulphide–calcite–amphibole assemblages (stage M-V) were deposited from fluids with similar δ34S (+1.8‰ to +5.0‰), δ18O (+10.1‰ to +12.5‰) and δ13C (−3.4‰), but higher δD values (average −8‰). Several groups of lower (<200°C, with a mode at 120°C) and higher temperature
(>200°C) fluids can be recognized in the main polymetallic (Cu, Zn, Pb) sulphide stage M-V and may record the involvement
of modified seawater. At Mina Justa, early magnetite–pyrite assemblages precipitated from a magmatic fluid (δ34S = +0.8‰ to +3.9‰; δ18O = +9.5‰ to +11.5‰) at 540–600°C, whereas ensuing chalcopyrite–bornite–digenite–chalcocite–hematite–calcite mineralization
was the product of non-magmatic, probably evaporite-sourced, brines with δ34S ≥ +29‰, δ18O = 0.1‰ and δ13C = −8.3‰. Two groups of fluids were involved in the Cu mineralization stage: (1) Ca-rich, low-temperature (approx. 140°C)
and high-salinity, plausibly a basinal brine and (2) Na (–K)-dominant with a low-temperature (approx. 140°C) and low-salinity
probably meteoric water. LA-TOF-ICPMS analyses show that fluids at the magnetite–pyrite stage were Cu-barren, but that those
associated with external fluids in later stages were enriched in Cu and Zn, suggesting such fluids could have been critical
for the economic Cu mineralization in Andean IOCG deposits. 相似文献
5.
Friedrich Lucassen Sven Lewerenz Gerhard Franz José Viramonte Klaus Mezger 《Contributions to Mineralogy and Petrology》1999,134(4):325-341
Crustal xenoliths from basanitic dikes and necks that intruded into continental sediments of the Cretaceous Salta Rift at
Quebrada de Las Conchas, Provincia Salta, Argentina were investigated to get information about the age and the chemical composition
of the lower crust. Most of the xenoliths have a granitoid composition with quartz-plagioclase-garnet-rutile ± K-feldspar
as major minerals. The exceedingly rare mafic xenoliths consist of plagioclase-clinopyroxene-garnet ± hornblende. All xenoliths
show a well equilibrated granoblastic fabric and the minerals are compositionally unzoned. Thermobarometric calculations indicate
equilibration of the mafic xenoliths in the granulite facies at temperatures of ca. 900 °C and pressures of ca. 10 kbar. The
Sm-Nd mineral isochron ages are 95.1 ± 10.4 Ma, 91.5 ± 13.0 Ma, 89.0 ± 4.2 Ma (granitoid xenoliths), and 110.7 ± 23.6 Ma (mafic
xenolith). These ages are in agreement with the age of basanitic volcanism (ca. 130–100 and 80–75 Ma) and are interpreted
as minimum ages of metamorphism. Lower crustal temperature at the time given by the isochrons was above the closure temperature
of the Sm-Nd system (>600–700 °C). The Sm-Nd and Rb-Sr isotopic signatures (147Sm/144Nd = 0.1225–0.1608; 143Nd/144Ndt
0 = 0.512000–0.512324; 87Rb/86Sr = 0.099–0.172; 87Sr/86Srt
0 = 0.708188–0.7143161) and common lead isotopic signatures (206Pb/204Pb = 18.43–18.48; 207Pb/204Pb = 15.62–15.70; 208Pb/204Pb = 38.22 –38.97) of the granitoid xenoliths are indistinguishable from the isotopic composition of the Early Paleozoic metamorphic
basement from NW Argentina, apart from the lower 208Pb/204Pb ratio of the basement. The Sm-Nd depleted mantle model ages of ca. 1.8 Ga from granitoid xenoliths and Early Paleozoic
basement point to a similar Proterozoic protolith. Time constraints, the well equilibrated granulite fabric, P-T conditions and lack of chemical zoning of minerals point to a high temperature in a crust of nearly normal thickness at ca.
90 Ma and to a prominent thermal anomaly in the lithosphere. The composition of the xenoliths is similar to the composition
of the Early Paleozoic basement in the Andes of NW Argentina and northern Chile. A thick mafic lower crust seems unlikely
considering low abundance of mafic xenoliths and the predominance of granitoid xenoliths.
Received: 21 July 1998 / Accepted: 27 October 1998 相似文献
6.
Craig R. McClung Jens Gutzmer Nicolas J. Beukes Klaus Mezger Harald Strauss Ellen Gertloff 《Mineralium Deposita》2007,42(5):537-549
Stratiform and stratabound barite ± magnetite beds are intimately associated with the polymetallic Broken Hill-type (BHT)
massive sulfide deposits of the Aggeneys-Gamsberg Pb–Zn–Cu ± Ag–Ba district in the Northern Cape Province, South Africa. Barite
samples were collected and studied from four localities in the district. Although metamorphic water–rock interaction processes
have partially altered the chemical and to a lesser degree the isotopic composition of barite, samples identified as being
the least altered display distinctly different isotopic compositions that are thought to reflect different modes of origin.
All barite samples are marked by low concentrations of SrO (0.5 ± 0.2 wt%), highly radiogenic 87Sr/86Sr ratios, elevated δ
34S and δ
18O values compared to contemporaneous Mesoproterozoic seawater. Radiogenic 87Sr/86Sr signatures (0.7164 ± 0.0028) point to an evolved continental crustal source for Sr and Ba, while elevated δ
34S values (27.3 ± 4.9‰) indicate that contemporaneous seawater sulfate, modified by bacterial sulfate reduction, was the single
most important sulfur reservoir for barite deposition. Most importantly, δ
18O values suggest a lower temperature of formation for the Gamsberg deposit compared with the occurrences in the Aggeneys area,
i.e. Swartberg-Tank Hill and Big Syncline. The obvious differences in temperature of formation are in good agreement with
the Cu-rich, Ba-poor nature of the sulfide mineralization of the Aggeneys deposits vs the Cu-poor, Ba-rich character of the
Gamsberg deposit. In conjunction with this, isotopic and petrographic arguments favor a sub-seafloor replacement model for
the stratabound barite occurrences of the Aggeneys deposits, while at Gamsberg, deposition at the sediment–water interface
as a true sedimentary exhalite appears more likely. 相似文献
7.
Ian Cartwright Ian S. Buick Roland Maas 《Contributions to Mineralogy and Petrology》1997,128(4):335-351
The Jervois region of the Arunta Inlier, central Australia, contains para- and orthogneisses that underwent low-pressure
amphibolite facies metamorphism (P = 200–300 MPa, T = 520–600 °C). Marble layers cut by metre-wide quartz + garnet ± epidote veins comprise calcite, quartz, epidote, clinopyroxene,
grandite garnet, and locally wollastonite. The marbles also contain locally discordant decimetre-thick garnet and epidote
skarn layers. The mineral assemblages imply that the rocks were infiltrated by water-rich fluids (XCO2 = 0.1–0.3) at ∼600 °C. The fluids were probably derived from the quartz-garnet vein systems that represent conduits for fluids
exsolved from crystallizing pegmatites emplaced close to the metamorphic peak. At one locality, the marble has calcite (Cc)
δ18O values of 9–18‰ and garnet (Gnt) δ18O values of 10–14‰. The δ18O(Gnt) values are only poorly correlated with δ18O(Cc), and the δ18O values of some garnet cores are higher than the rims. The isotopic disequilibrium indicates that garnet grew before the
δ18O values of the rock were reset. The marbles contain ≤15% garnet and, for water-rich fluids, garnet-forming reactions are
predicted to propagate faster than O-isotopes are reset. The Sm-Nd and Pb-Pb ages of garnets imply that fluid flow occurred
at 1750–1720 Ma. There are no significant age differences between garnet cores and rims, suggesting that fluid flow was relatively
rapid. Texturally late epidote has δ18O values of 1.5–6.2‰ implying δ18O(H2O) values of 2–7‰. Waters with such low-δ18O values are probably at least partly meteoric in origin, and the epidote may be recording the late influx of meteoric water
into a cooling hydrothermal system.
Received: 29 April 1996 / Accepted: 12 March 1997 相似文献
8.
Benita Putlitz Alan Matthews John W. Valley 《Contributions to Mineralogy and Petrology》2000,138(2):114-126
Oxygen and hydrogen stable isotope ratios of eclogite-facies metagabbros and metabasalts from the Cycladic archipelago (Greece)
document the scale and timing of fluid–rock interaction in subducted oceanic crust. Close similarities are found between the
isotopic compositions of the high-pressure rocks and their ocean-floor equivalents. High-pressure minerals in metagabbros
have low δ18O values: garnet 2.6 to 5.9‰, glaucophane 4.3 to 7.1‰; omphacite 3.5 to 6.2‰. Precursor actinolite that was formed during
the hydrothermal alteration of the oceanic crust by seawater analyses at 3.7 to 6.3‰. These compositions are in the range
of the δ18O values of unaltered igneous oceanic crust and high-temperature hydrothermally altered oceanic crust. In contrast, high-pressure
metabasalts are characterised by 18O-enriched isotopic compositions (garnet 9.2 to 11.5‰, glaucophane 10.6 to 12.5‰, omphacite 10.2 to 12.8‰), which are consistent
with the precursor basalts having undergone low-temperature alteration by seawater. D/H ratios of glaucophane and actinolite
are also consistent with alteration by seawater. Remarkably constant oxygen isotope fractionations, compatible with isotopic
equilibrium, are observed among high-pressure minerals, with Δglaucophane−garnet = 1.37 ± 0.24‰ and Δomphacite−garnet = 0.72 ± 0.24‰. For the estimated metamorphic temperature of 500 °C, these fractionations yield coefficients in the equation
Δ = A * 106/T
2 (in Kelvin) of Aglaucophane−garnet = 0.87 ± 0.15 and Aomphacite−garnet = 0.72 ± 0.24. A fractionation of Δglaucophane–actinolite = 0.94 ± 0.21‰ is measured in metagabbros, and indicates that isotopic equilibrium was established during the metamorphic
reaction in which glaucophane formed at the expense of actinolite. The preservation of the isotopic compositions of gabbroic
and basaltic oceanic crust and the equilibrium fractionations among minerals shows that high-pressure metamorphism occurred
at low water/rock ratios. The isotopic equilibrium is only observed at hand-specimen scale, at an outcrop scale isotopic compositional
differences occur among adjacent rocks. This heterogeneity reflects metre-scale compositional variations that developed during
hydrothermal alteration by seawater and were subsequently inherited by the high-pressure metamorphic rocks.
Received: 4 January 1999 / Accepted: 7 July 1999 相似文献
9.
Several F, Pb, Zn and Ba deposits are located in the province of Zaghouan in north-eastern Tunisia. They are hosted in Lower
Liassic or Upper Jurassic reef limestones, and the overlying condensed Carixian phosphatic limestones and Campanian marls,
respectively. The mineralization occurs in three types of orebodies: stratiform replacement heaps and lenses (Jebel Stah and
Hammam Zriba), breccia fillings and dissolution void fillings (Sidi Taya) and lodes (Jebel Oust). More than one generation
of fluorite is observed in the stratiform deposits. Microthermometric analyses of the inclusion fluids observed in fluorite
and quartz show that the economic concentrations of fluorite have deposited from moderate to highly saline (12–22.5 wt% NaCl
equivalents) hydrothermal (110–160 °C) mineralizing fluids at the center (Jebel Stah, Sidi Taya) and to the east of the province
(Hammam Zriba). Late remobilizations, observed in the stratiform deposits, are related to the circulation of a warmer (up
to 185 °C) but less saline (10 wt% NaCl equivalents) fluid (Jebel Stah) and more saline (12–22 wt% NaCl equivalents) fluid
(Hammam Zriba). The highest temperature (up to 250 °C) and salinity (32–34 wt% NaCl equivalents) are observed to the west
of the province of Zaghouan (Jebel Oust). Less saline (3–6 wt% NaCl equivalents) and moderately hot to hot fluids (up to 220 ± 20 °C)
and rich in gaseous CO2 invade most of the ore deposits in later stages and give rise to the massive quartz within fractures at Jebel Stah. Chemical
analyses of the fluids extracted from the inclusions occuring in fluorite show compositions dominated by the presence of Na+, Ca2+ and Cl− ionic species and allow the mean temperature of the fluids in the source reservoir to be estimated as 275 ± 25 °C. The circulation
of the ore-forming fluids is triggered by a regional tectonic extensional phase which occurs within the post-Jurassic to ante-Miocene
time interval. The deposition of the economic concentrations of fluorite resulted from the decrease in pressure and temperature
of the hydrothermal brines (Jebel Oust), along with the increase in the dissolved calcium activity (Jebel Stah and Sidi Taya),
or a decrease in salinity due to the mixing with a hot, less saline and Na-poor, Ca-rich fluid (Hammam Zriba). The mineralogical
associations (CaF2, PbS, ZnS, BaSO4) hosted within carbonate rocks, the temperatures and the salinities of the fluids that gave rise to the more important ore
deposits (110–160 °C and 12–22.5 wt% NaCl equivalents), their composition (Na, Ca, Cl) and the molar ratios between the major
ionic species, as well as the presence of liquid hydrocarbons in the mineralizing fluids, show that the ore deposits of the
province of Zaghouan belong to the carbonate-hosted F, Pb, Zn, Ba Mississippi Valley-type deposits.
Received: 23 June 1995 / Accepted: 18 November 1996 相似文献
10.
Alluvial and colluvial gem sapphires are common in the basaltic fields of the French Massif Central (FMC) but sapphire-bearing
xenoliths are very rare, found only in the Menet trachytic cone in Cantal. The O-isotope composition of the sapphires ranges
between 4.4 and 13.9‰. Two distinct groups have been defined: the first with a restricted isotopic range between 4.4 and 6.8‰
(n = 22; mean δ18O = 5.6 ± 0.7‰), falls within the worldwide range defined for blue-green-yellow sapphires related to basaltic gem fields (3.0 < δ18O < 8.2‰, n = 150), and overlaps the ranges defined for magmatic sapphires in syenite (4.4 < δ18O < 8.3‰, n = 29). A second group, with an isotopic range between 7.6 and 13.9‰ (n = 9), suggests a metamorphic sapphire source such as biotite schist in gneisses or skarns. The δ18O values of 4.4–4.5‰ for the blue sapphire-bearing anorthoclasite xenolith from Menet is lower than the δ18O values obtained for anorthoclase (7.7–7.9‰), but suggest that these sapphires were derived from an igneous reservoir in
the subcontinental spinel lherzolitic mantle of the FMC. The presence of inclusions of columbite-group minerals, pyrochlore,
Nb-bearing rutile, and thorite in these sapphires provides an additional argument for a magmatic origin. In the FMC lithospheric
mantle, felsic melts crystallized to form anorthoclasites, the most evolved peraluminous variant of the alkaline basaltic
melt. The O-isotopic compositions of the first group suggests that these sapphires crystallized from felsic magmas under upper
mantle conditions. The second group of isotopic values, typified for example by the Le Bras sapphire with a δ18O of 13.9‰, indicates that metamorphic sapphires from granulites were transported to the surface by basaltic magma. 相似文献
11.
Summary The Dachang Sn-polymetallic ore district is one of the largest tin producing districts in China. Its origin has long been
in dispute between magmatic-hydrothermal replacement and submarine exhalative-hydrothermal origin. The Dachang ore district
comprises several types of ore deposits, including the Lamo magmatogenic skarn deposit near a granite intrusion, the Changpo-Tongkeng
bedded and vein-type sulfide deposit, and the Gaofeng massive sulfide deposit. Sulfide minerals from the Lamo skarn ores show
δ34S values in the range between −3 and +4‰ with a mean close to zero, suggesting a major magmatic sulfur source that likely
was the intrusive Longxianggai granite. Sulfide minerals from the Gaofeng massive ores show higher δ34S values between +5 and +12‰, whereas sulfide minerals from the Changpo-Tongkeng bedded ores display lighter δ34S values between −7 and −0.2‰. The difference in the sulfur isotope ranges in the two deposits can be interpreted by different
degrees of inorganic thermochemcial reduction of marine sulfate using a one-step batch separation fractionation model. Sulfur
isotopic compositions from the vein-type ores at Changpo-Tongkeng vary widely from −8 to +4‰, but most of the data cluster
around −2.9‰, which is close to that of bedded ores (−3.6‰). The sulfur in vein-type ores might be derived from bedded ores
or it represents a mixture of magmatic- and sedimentary-derived sulfur. Pb isotopic compositions of sulfide minerals in the
Dachang ore district reveal a difference between massive and bedded ores, with the massive ores displaying more radiogenic
Pb isotope ratios. Correlations of 206Pb/204Pb and 207Pb/204Pb or 208Pb/204Pb for the massive and bedded ores are interpreted as two-component mixing of Pb leached from sedimentary host rocks and from
deep-seated Precambrian basement rocks composed of metamorphosed volcano-sedimentary rocks. Pb isotopic compositions of sulfide
minerals from vein-type ores overlap with those of bedded sulfides. Similar to the sulfur, the lead in vein-type ores might
be derived from bedded ores. Skarn ores at Lamo show very limited variations in Pb isotopic compositions, which may reflect
a major magmatic-hydrothermal lead source. Helium isotope data of fluid inclusions trapped in sulfides indicate that He in
the massive and bedded ores has a different origin than He in fluorite of granite-related veins. The 3He/4He ratios of 1.2–2.9 Ra of fluid inclusions from sulfides at Gaofeng and Changpo-Tongkeng imply a contribution of mantle-derived
fluids. Overall our data support a submarine exhalative-hydrothermal origin for the massive and bedded ore types at Dachang.
Supplementary material to this paper is available in electronic form at
Appendix available as electronic supplementary material 相似文献
12.
Oxygen and hydrogen isotope geochemistry of gneisses associated with ultrahigh pressure eclogites at Shuanghe in the Dabie Mountains 总被引:18,自引:0,他引:18
Bin Fu Yong-Fei Zheng Zhengrong Wang Yilin Xiao Bing Gong Shuguang Li 《Contributions to Mineralogy and Petrology》1999,134(1):52-66
The oxygen and hydrogen isotope compositions of minerals and whole rock were determined for two types of gneiss (biotite
gneiss and granitic gneiss) associated with ultrahigh pressure (UHP) eclogites in the Shuanghe district of the eastern Dabie
Mountains. There are significant differences in δ18O between the two gneisses: the UHP biotite gneiss varying from −4.3‰ to 10.6‰ similar to the associated eclogites, whereas
the non-UHP granitic gneiss ranges only from −3.8‰ to 1.2‰. The δD values are similar in the two gneisses with −37 to −64‰
for epidote/zoisite, −92 to −83‰ for amphibole, and −63 to −109‰ for biotite/phengite. Hydrogen isotope disequilibrium among
the coexisting hydroxyl-bearing minerals is ascribed to retrograde exchange subsequent to amphibolite-facies metamorphism.
Oxygen isotopic equilibrium has been preserved among various minerals in both gneisses regardless of the large variation in
rock δ18O. Oxygen isotopic geothermometers yield different but regular temperatures corresponding to the closure temperatures of oxygen
diffusion in the minerals. The metamorphic temperatures of both eclogite facies and amphibolite facies have been recovered
in mineral pairs from the biotite gneiss. The isotopic temperatures for the granitic gneiss are mostly in accordance with
amphibolite-facies metamorphism. However, high temperatures of 550 to 650 °C are obtained from those minerals resistant to
retrograde oxygen isotope exchange, implying that the granitic gneiss may have experienced higher temperature metamorphism
than expected from petrologic thermometers. The 18O-depletion of both gneisses is interpreted to result from meteoric-hydrothermal exchange before/during plate subduction.
Therefore, the measured δ18O values of the gneisses reflect the oxygen isotope compositions of their protoliths prior to the UHP metamorphism. It is
inferred that the UHP unit is in foreign contact with the non-UHP unit like a tectonic melange, but both of them experienced the two common stages of geodynamic evolution:
(1) 18O-depletion prior to the UHP metamorphism, (2) uplifting since the amphibolite-facies metamorphism.
Received: 5 May 1998 / Accepted: 27 August 1998 相似文献
13.
T. Steuber 《International Journal of Earth Sciences》1999,88(3):551-570
Isotopic (δ13C, δ18O) and elemental (Mg, Sr, Mn, Fe) compositions were analysed in sclerochronological profiles of several shells of late Cretaceous
rudist bivalves from Greece, Turkey, Somalia and the Arabian Peninsula. The preservation of original compositions of low-Mg
calcite of outer shell layers is indicated by constant and high Sr, generally low Fe and Mn, and the preservation of fibrous-prismatic
ultrastructures. Cyclic variations in δ18O and Mg are interpreted to reflect seasonal temperature/salinity cycles and, thus, annual growth increments. In shells of
Torreites, amplitudes of correlated δ13C and δ18O cycles cannot be related to reasonable palaeotemperatures or salinity. This isotopic pattern reflects vital fractionations
of an extent which is unknown from modern bivalves. In contrast, almost identical ranges and amplitudes of δ18O cycles are observed in 13 shells of five species from Santonian-Campanian localities in central Greece and northern Turkey,
suggesting that seasonal variations in environmental conditions were recorded without significant vital fractionations. The
effect of seasonal salinity changes on δ18O of the shells is evaluated, and mean palaeotemperatures are constrained within the range of 30–32.5 °C. The annual range
of temperature was estimated to be 7 °C, assuming a constant salinity. This agrees with other isotopic proxies of Late Cretaceous
palaeotemperatures, and with global circulation models which predict higher low-latitude sea-surface temperatures than the
present ones.
Received: 12 February 1998 / Accepted: 24 May 1999 相似文献
14.
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
15.
Mid-Proterozoic anorthosite-suite magmatism is a major volumetric component of the southern Grenville Province, and provides
an important probe of the compositions and types of lower crustal rocks. The ∼1.15 Ga Morin Complex (Quebec) consists of two
anorthosite plutons with distinct compositions. Plagioclase from the western lobe of the anorthosite has δ18O values that average 9.6 ± 0.7‰, which is ∼3‰ higher than the values found in “normal” anorthosites and in mantle-derived
mafic igneous rocks worldwide. Plagioclase from the eastern lobe of the massif (deformed by the Morin Shear Zone) has δ18O values that average 8.7 ± 0.6‰, also high compared to mantle-derived rocks. Numerous lines of evidence, including homogeneity
of δ18O values within individual plutons, O–Sr–Nd mixing relations, and preservation of igneous δ18O in adjacent mangerite units argue against anorthosite interaction with high δ18O fluids as the cause of the high δ18O values seen in both anorthosite lobes. High δ18O values are best explained as primary magmatic compositions resulting from melting and assimilation of crustal materials
by the anorthosite's parent magma. The Morin and Marcy massifs are located in the Allochthonous Monocyclic Belt of the Grenville
Province, and have the highest known δ18O values for anorthosites in the Grenville. Although the Monocyclic Belt is juvenile in terms of radiogenic isotope systematics,
the new oxygen isotope data indicate the presence high δ18O supracrustal materials at the base of the crust, probably buried during the ∼1.2 Ga Elzevirian orogeny in the Monocyclic
Belt prior to anorthosite magmatism. This process is not recognized in other parts of the Grenville Province and points to
differences in the pre-1.2-Ga continental margins.
Received: 29 September 1999 / Accepted: 7 March 2000 相似文献
16.
Magnesite, siderite and dolomite are characteristic alteration minerals occurring in Miocene hanging wall rocks of dacitic
composition which host the Kuroko orebodies. These carbonates generally occur in a more stratigraphically upper horizon than
chlorite alteration zone surrounding the orebodies. The Mg/(Mg+Fe) ratios of the carbonates decrease from the central alteration
zone to marginal zone. The Mg/(Mg+Fe) ratios of carbonates and chlorite positively correlate. The δ18O and δ13C values of magnesite, siderite and dolomite positively correlate with each other and lie between the igneous and marine carbonate
values. The petrographic, isotopic and fluid inclusion characteristics and thermochemical modelling calculations indicate
that magnesite and dolomite formed in the central zone close to the orebodies due to the interaction of hydrothermal solutions
with the biogenic marine carbonates. Calcite formed further from the orebodies from hydrothermal fluids which did not contain
a biogenic marine carbon component. The compositional and textural relationships indicate that superimposed alterations (chlorite
alteration and carbonate alteration) occurred in hanging wall rocks. The mode of occurrences and the Mg/(Mg+Fe) ratios of
magnesite and dolomite occurring in hanging wallrocks are useful in the exploration for concealed volcanogenic massive sulfide-sulfate
deposits.
Received: 9 September 1997 / Accepted: 23 September 1997 相似文献
17.
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
18.
R. Altherr U. Henes-Klaiber E. Hegner M. Satir C. Langer 《International Journal of Earth Sciences》1999,88(3):422-443
Latest Devonian to early Carboniferous plutonic rocks from the Odenwald accretionary complex reflect the transition from
a subduction to a collisional setting. For ∼362 Ma old gabbroic rocks from the northern tectonometamorphic unit I, initial
isotopic compositions (εNd=+3.4 to +3.8;87Sr/86Sr =0.7035–0.7053;δ18O=6.8–8.0‰) and chemical signatures (e.g., low Nb/Th, Nb/U, Ce/Pb, Th/U, Rb/Cs) indicate a subduction-related origin by partial
melting of a shallow depleted mantle source metasomatized by water-rich, large ion lithophile element-loaded fluids. In the
central (unit II) and southern (unit III) Odenwald, syncollisional mafic to felsic granitoids were emplaced in a transtensional
setting at approximately 340–335 Ma B.P. Unit II comprises a mafic and a felsic suite that are genetically unrelated. Both
suites are intermediate between the medium-K and high-K series and have similar initial Nd and Sr signatures (εNd=0.0 to –2.5;87Sr/86Sr=0.7044–0.7056) but different oxygen isotopic compositions (δ18O=7.3–8.7‰ in mafic vs 9.3–9.5‰ in felsic rocks). These characteristics, in conjunction with the chemical signatures, suggest
an enriched mantle source for the mafic magmas and a shallow metaluminous crustal source for the felsic magmas. Younger intrusives
of unit II have higher Sr/Y, Zr/Y, and Tb/Yb ratios suggesting magma segregation at greater depths. Mafic high-K to shoshonitic
intrusives of the southern unit III have initial isotopic compositions (εNd=–1.1 to –1.8;87Sr/86Sr =0.7054–0.7062;δ18O=7.2–7.6‰) and chemical characteristics (e.g., high Sr/Y, Zr/Y, Tb/Yb) that are strongly indicative of a deep-seated enriched
mantle source. Spatially associated felsic high-K to shoshonitic rocks of unit III may be derived by dehydration melting of
garnet-rich metaluminous crustal source rocks or may represent hybrid magmas.
Received: 7 December 1998 / Accepted: 27 April 1999 相似文献
19.
V. Yu. Prokof’ev N. S. Bortnikov V. A. Kovalenker S. F. Vinokurov L. D. Zorina A. D. Chernova S. G. Kryazhev A. N. Krasnov S. A. Gorbacheva 《Geology of Ore Deposits》2010,52(2):81-113
The chemistry, REE patterns, and carbon and oxygen isotopic compositions of carbonates from ore veins of the Darasun deposit
are discussed. In addition to the earlier described siderite, calcite, and carbonates of the dolomite-ankerite series, kutnahorite
is identified. The total REE content in Fe-Mg carbonates of the dolomite-ankerite series (2.8–73 ppm) is much lower than in
later calcite (18–390 ppm). δ13C of Fe-Mg carbonates and calcite varies from +1.1 to −6.7‰ and from −0.9 to −4.9‰, respectively. δ18O of Fe-Mg carbonates and calcite varies from +17.6 to 3.6‰ and from +15.7 to −0.5‰, respectively. The REE sum and carbon
and oxygen isotopic compositions reveal zonal distribution relative to the central granodiorite porphyry stock. The correlation
between the carbon and oxygen isotopic compositions and REE sum reflects variations in the physicochemical formation conditions
and composition of ore-forming fluid. The isotopic composition of fluid is calculated, and possible sources of its components
are considered. Earlier established evidence for a magmatic source of ore-forming fluid and participation of meteoric water
in ore formation is confirmed. Geochemical evidence for interaction of ore-forming fluid with host rocks is furnished. The
relationships between the REE sum, on the one hand, and carbon and oxygen isotopic compositions of hydrothermal ore-forming
fluid, on the other, are established. 相似文献
20.
Carbon and oxygen isotopic analyses of silicate and carbonate minerals indicate that isotopic compositions in metasediments
of the Wallace Formation (Belt Supergroup) exposed northwest of the Idaho batholith have been affected by both prograde and
retrograde fluid-rock interaction. Silicates retain isotopic fractionations that reflect equilibration at peak metamorphic
temperatures. In contrast, calcite oxygen isotopic compositions range from δ18O(Calcite)=+2.3 to +18.6‰ SMOW (standard mean oceanic water) and indicate that some calcites have exchanged with low-δ18O meteorichydrothermal fluids. Values of Δ18O (Quartz-Calcite) as large as +15.5 clearly indicate that the isotopic depletion of these calcites postdates the peak of
regional metamorphism. Carbon isotopic compositions of 18O-depleted calcites are not significantly shifted relative to δ13C values in undepleted calcites, suggesting that the retrograde fluid was carbon-poor. Petrographically, retrograde fluid-rock
interaction is associated with the occurrence of fine-grained, highly-luminescent calcite overgrowths on less-luminescent,
metamorphic calcites, slight to moderate argillic alteration, and pseudomorphing of scapolite porphyroblasts by fine-grained
albite. Retrograde isotopic depletions may be related to shallow meteoric-hydrothermal fluid flow developed around the Idaho
batholith after intrusion and rapid uplift of the terrane. Peak metamorphic isotopic compositions in the Wallace Formation
reflect mineralogically heterogeneous protolith compositions and isotopic fractionation due to devolatilization and/or infiltration.
Variability in oxygen isotopic compositions on the order of 4–6‰ within the same rock type can be attributed to the combined
effects of inherited isotopic compositions and isotopic shifts resulting from prograde devolatilization. Isotopic and compositional
heterogeneity on the scale of mm to m precludes generalization of isotopic gradients on a regional scale. The isotopic data
presented here, and metamorphic fluid compositions determined in previous studies, are best reconciled with heterogeneous
bulk compositions, dominantly channelized prograde and retrograde fluid flow, and locally low fluid-rock ratios. 相似文献