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1.
A. I. Grabezhev B. G. Pokrovskii F. P. Buslaev V. V. Zaikov G. N. Pshenichnyi 《Lithology and Mineral Resources》2000,35(1):70-75
Substantial differences in isotopic compositions of micas and pyrophyllites from metasomatites related to various stages of
the process that formed the giant Gai massive sulfide deposit have been established. The illite from the earliest and predominant
chlorite-illite-quartz metasomatite is characterized by the least δD values of −(50–85)‰ and δ18O=7–11‰. The pyrophyllite-quartz metasomatite as well as illite and pyrophyllite schists developed locally in the southern
part of the deposit that likely correspond to the site of discharge of late geothermal paleosystem, contain pyrophyllite and
illite with much higher values of δD=−(25–45)‰ and δ18O=4–9‰. Local zones of illite-paragonite schist complete the mineral formation and are characterized by the transitional δD values of −(30–55)‰ and elevated δ18O of 10–11‰. The most plausible model of isotopic evolution in the hydrothermal system, with an initial temperature of mica
formation at 250°C, assumes the mixing of transformed sea water with a magmatic (metamorphic) water at the initial stage when
the background metasomatites and massive sulfide orebodies of the northern lode have been formed. Subsequently, after the
burial of the northern lode beneath basaltic andesite flows, the repeated sea water invasions took place in the southern discharge
site of the system. As a result, the pyrophyllite-quartz metasomatite was formed; the pyrophyllite and illite schists originated
in tectonic compression zones. The interaction of this water with silicate rocks was completed by a formation of illite-paragonite
schist. In general, the substantial contribution of sea water to the formation of metasomatic halo of the deposit casts no
doubt. 相似文献
2.
The source of metasomatic fluids in iron-oxide–copper–gold districts is contentious with models for magmatic and other fluid sources having been proposed. For this study, δ
18O and δ
13C ratios were measured from carbonate mineral separates in the Proterozoic eastern Mt Isa Block of Northwest Queensland, Australia. Isotopic analyses are supported by petrography, mineral chemistry and cathodoluminescence imagery. Marine meta-carbonate rocks (ca. 20.5‰ δ
18O and 0.5‰ δ
13C calcite) and graphitic meta-sedimentary rocks (ca. 14‰ δ
18O and −18‰ δ
13C calcite) are the main supracrustal reservoirs of carbon and oxygen in the district. The isotopic ratios for calcite from the cores of Na–(Ca) alteration systems strongly cluster around 11‰ δ
18O and −7‰ δ
13C, with shifts towards higher δ
18O values and higher and lower δ
13C values, reflecting interaction with different hostrocks. Na–(Ca)-rich assemblages are out of isotopic equilibrium with their metamorphic hostrocks, and isotopic values are consistent with fluids derived from or equilibrated with igneous rocks. However, igneous rocks in the eastern Mt Isa Block contain negligible carbon and are incapable of buffering the δ
13C signatures of CO2-rich metasomatic fluids associated with Na–(Ca) alteration. In contrast, plutons in the eastern Mt Isa Block have been documented as having exsolved saline CO2-rich fluids and represent the most probable fluid source for Na–(Ca) alteration. Intrusion-proximal, skarn-like Cu–Au orebodies that lack significant K and Fe enrichment (e.g. Mt Elliott) display isotopic ratios that cluster around values of 11‰ δ
18O and −7‰ δ
13C (calcite), indicating an isotopically similar fluid source as for Na–(Ca) alteration and that significant fluid–wallrock interaction was not required in the genesis of these deposits. In contrast, K- and Fe-rich, intrusion-distal deposits (e.g. Ernest Henry) record significant shifts in δ
18O and δ
13C towards values characteristic of the broader hostrocks to the deposits, reflecting fluid–wallrock equilibration before mineralisation. Low temperature, low salinity, low δ
18O (<10‰ calcite) and CO2-poor fluids are documented in retrograde metasomatic assemblages, but these fluids are paragenetically late and have not contributed significantly to the mass budgets of Cu–Au mineralisation. 相似文献
3.
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
4.
The strata-bound Cu−Pb−Zn polymetallic sulfide deposits occur in metamorphic rocks of greenschist phase of the middle-upper
Proterozoic Langshan Group in central Inner Mongolia. δ34S values for sulfides range from −3.1‰ to +37.3‰, and an apparent difference is noticed between vein sulfides and those in
bedded rocks. For example, δ34S values for bedded pyrite range from +10.6‰ to +20.0‰, while those for vein pyrite vary from −3.1‰ to +14.1‰. δ34S of bedded pyrrhotite is in the range +7.9‰–+23.5‰ in comparison with +6.5‰–+17.1‰ for vein pyrrhotite. The wide scatter
of δ34S and the enrichment of heavier sulfur indicate that sulfur may have been derived from H2S as a result of bacterial reduction of sulfates in the sea water. Sulfur isotopic composition also differs from deposit to
deposit in this area because of the difference in environment in which they were formed. The mobilization of bedded sulfides
in response to regional metamorphism and magmatic intrusion led to the formation of vein sulfides.
δ18O and δ13C of ore-bearing rocks and wall rocks are within the range typical of ordinary marine facies, with the exception of lower
values for ore-bearing marble at Huogeqi probably due to diopsidization and tremalitization of carbonate rocks.
Pb isotopic composition is relatively stable and characterized by lower radio-genetic lead. The age of basement rocks was
calculated to be about 23.9 Ma and ore-forming age 7.8 Ma.207Pb/204Pb−206Pb/204Pb and208Pb/204Pb−206Pb/204Pb plots indicate that Pb may probably be derived from the lower crust or upper mantle.
It is believed that the deposits in this region are related to submarine volcanic exhalation superimposed by later regional
metamorphism and magmatic intrusion. 相似文献
5.
1 IntroductionThe compositional characteristics of natural gasesand their carbon isotopic composition are controlledmainly by the type of organic matter and the degree ofits thermal evolution in the source rocks (Song Yan,1995; Xu Yongchang et al., 1994; … 相似文献
6.
Groundwater is often the only water source in semi-arid regions of Turkey. Günyüzü Basin, located in the Sakarya River basin,
SW of Eskişehir, exhibits semi-arid conditions. The study area is composed of Paleozoic metamorphic rocks, Eocene granitic
rocks, Neogene sedimentary rocks, and Quaternary alluvium. In the basin, Paleozoic Marbles are the main reservoir rocks for
hot and cold water, bordered by impermeable diabases dykes at the sides and by impermeable granites and schists. Neogene-aged
limestones, conglomerates and alluvium represent the other significant aquifers. Water samples chosen to exemplify the aquifer
characteristics, were collected from springs and wells in both the dry and the wet seasons. The cation and anion permutation
of the samples show that carbonates are the dominant lithology in the formation of chemical composition. δ18O (−11.2 to −8.9‰) and δ2H (−79 to −60‰) isotopic values show that all waters (thermal and cold) are meteoric in origin. The hydrological, hydrochemical,
and isotopic properties of the waters reveal that there exist two main groups of groundwater systems; one of these is deep
circulating, while the other one is shallow. Tritium values, 0–4 TU (Tritium Unit) indicate the presence of old, static water
in these aquifer systems. 相似文献
7.
M. A. Semikhatov A. B. Kuznetsov A. V. Maslov I. M. Gorokhov G. V. Ovchinnikova 《Stratigraphy and Geological Correlation》2009,17(6):574-601
The main objective of this work is the generalization of lithostratigraphic, biostratigraphic and isotopic-geochronological
data characterizing carbonate rocks from type succession of the broadly acknowledged chronostratigraphic subdivision of the
Lower Riphean, such as the Burzyan Group of the Southern Urals and its analogs. Using an original approach to investigation
of the Rb-Sr and Pb-Pb isotopic systems in carbonates and strict criteria of their retentivity, we studied the least altered
(“best”) samples of the Burzyan carbonates, which retain the 87Sr/86Sr ratio of the sedimentation environment. As long ago as 1550 ± 30 and 1430 ± 30 Ma, that ratio corresponded to 0.70460–0.70480
and 0.70456–0.70481. The results confirm the influx of the mantle material predominantly into the World Ocean of the Early
Riphean. The influence of meteoric diagenesis was likely responsible for local declines of δ18O in the Burzyan carbonates down to the values of −2.5 to −1.5‰ V-PDB. In the “best” samples, this parameter ranges from −0.7
to 0‰, which is consistent with the assumption that δ18O values (0 ± 1‰) characterized the stasis of the carbonate carbon isotopic composition in oceanic water 2.06–1.25 Ga ago.
C-isotopic data on carbonate from the Paleoproterozoic-Lower Riphean boundary formations of the Urals, India, North America
and Siberia suggest that the mentioned stasis ended by the commencement of the Early Riphean ca. 1.6–1.5 Ga ago. In the least
altered carbonates of the Early Riphean, the δ18O variation range corresponds to 4.0–4.5‰. 相似文献
8.
Mark E. Brandriss Richard J. Nevle Dennis K. Bird James R. O’Neil 《Contributions to Mineralogy and Petrology》1995,121(1):74-86
Hydrogen and oxygen isotope analyses have been made of hydrous minerals in gabbros and basaltic xenoliths from the Eocene
Kap Edvard Holm intrusive complex of East Greenland. The analyzed samples are of three types: (1) primary igneous hornblendes
and phlogopites that crystallized from partial melts of hydrothermally altered basaltic xenoliths, (2) primary igneous hornblendes
that formed during late–magmatic recrystallization of layered gabbroic cumulates, and (3) secondary actinolite, epidote and
chlorite that formed during subsolidus alteration of both xenoliths and gabbros. Secondary actinolite has a δ18O value of −5.8‰ and a δD value of −158‰. These low values reflect subsolidus alteration by low–δ18O, low–δD hydrothermal fluids of meteoric origin. The δD value is lower than the −146 to −112‰ values previously reported
for amphiboles from other early Tertiary meteoric–hydrothermal systems in East Greenland and Scotland, indicating that the
meteoric waters at Kap Edvard Holm were isotopically lighter than typical early Tertiary meteoric waters in the North Atlantic
region. This probably reflects local climatic variations caused by formation of a major topographic dome at about the time
of plutonism and hydrothermal activity. The calculated isotopic composition of the meteoric water is δD=−110 ± 10‰, δ18O ≈−15‰. Igneous hornblendes and phlogopites from pegmatitic pods in hornfelsed basaltic xenoliths have δ18O values between −6.0 and −3.8‰ and δD values between −155 and −140‰. These are both much lower than typical values of fresh
basalts. The oxygen isotope fractionations between pegmatitic hornblendes and surrounding hornfelsic minerals are close to
equilibrium fractionations for magmatic temperatures, indicating that the pegmatites crystallized from low–δ18O partial melts of xenoliths that had been hydrothermally altered and depleted in 18O prior to stoping. The pegmatitic minerals may have crystallized with low primary δD values inherited from the altered country
rocks, but these values were probably overprinted extensively by subsolidus isotopic exchange with low–δD meteoric–hydrothermal
fluids. This exchange was facilitated by rapid self–diffusion of hydrogen through the crystal structures. Primary igneous
hornblendes from the plutonic rocks have δ18O values between +2.0 and +3.2‰ and δD values between −166 and −146‰. The 18O fractionations between hornblendes and coexisting augites are close to equilibrium fractionations for magmatic temperatures,
indicating that the hornblendes crystallized directly from the magma and subsequently underwent little or no oxygen exchange.
The hornblendes may have crystallized with low primary δD values, due to contamination of the magma with altered xenolithic
material, but the final δD values were probably controlled largely by subsolidus isotopic exchange. This inference is based
partly on the observation that coexisting plagioclase has been extensively depleted in 18O via a mineral–fluid exchange reaction that is much slower than the hydrogen exchange reaction in hornblende. It is concluded
that all hydrous minerals in the study area, whether igneous or secondary, have δD values that reflect extensive subsolidus
isotopic equilibration with meteoric–hydrothermal fluids.
Received: 22 March 1994 / Accepted: 26 January 1995 相似文献
9.
Early carbonate cements in the Yanchang Formation sandstones are composed mainly of calcite with relatively heavier carbon isotope (their δ^18O values range from -0.3‰- -0.1‰) and lighter oxygen isotope (their δ^18O values range from -22.1‰- -19.5‰). Generally, they are closely related to the direct precipitation of oversaturated calcium carbonate from alkaline lake water. This kind of cementation plays an important role in enhancing the anti-compaction ability of sandstones, preserving intragranular volume and providing the mass basis for later disso- lution caused by acidic fluid flow to produce secondary porosity. Ferriferous calcites are characterized by relatively light carbon isotope with δ^13C values ranging from -8.02‰ to -3.23‰, and lighter oxygen isotope with δ^18O values ranging from -22.9‰ to -19.7‰, which is obviously related to the decarboxylation of organic matter during the late period of early diagenesis to the early period of late diagenesis. As the mid-late diagenetic products, ferriferous cal- cites in the study area are considered as the characteristic authigenic minerals for indicating large-scaled hydrocarbon influx and migration within the clastic reservoir. The late ankerite is relatively heavy in carbon isotope with δ^13C values ranging from -1.92‰ to -0.84‰, and shows a wide range of variations in oxygen isotopic composition, with δ^18O values ranging from -20.5‰ to -12.6‰. They are believed to have nothing to do with decarboxylation, but the previously formed marine carbonate rock fragments may serve as the chief carbon source for their precipitation, and the alkaline diagenetic environment at the mid-late stage would promote this process. 相似文献
10.
A. I. Grabezhev 《Geology of Ore Deposits》2010,52(2):138-153
The Early Devonian Gumeshevo deposit is one of the largest ore objects pertaining to the dioritic model of the porphyry copper
system paragenetically related to the low-K quartz diorite island-arc complex. The (87Sr/86Sr)t and (ɛNd)t of quartz diorite calculated for t = 390 Ma are 0.7038–0.7045 and 5.0–5.1, respectively, testifying to a large contribution of the mantle component to the composition
of this rock. The contents of typomorphic trace elements (ppm) are as follows: 30–48 REE sum, 5–10 Rb, 9–15 Y, and 1–2 Nb.
The REE pattern is devoid of Eu anomaly. Endoskarn of low-temperature and highly oxidized amphibole-epidote-garnet facies
is surrounded by the outer epidosite zone. Widespread retrograde metasomatism is expressed in replacement of exoskarn and
marble with silicate (chlorite, talc, tremolite)-magnetite-quartz-carbonate mineral assemblage. The 87Sr/86Sr ratios of epidote in endoskarn and carbonate in retrograde metasomatic rocks (0.7054–0.7058 and 0.7053–0.7065, respectively)
are intermediate between the Sr isotope ratios of quartz dioritic rocks and marble (87Sr/86Sr = 0.70784 ± 2). Isotopic parameters of the fluid equilibrated with silicates of skarn and retrograde metasomatic rocks
replacing exoskarn at 400°C are δ18O = +7.4 to +8.5‰ and δD = −49 to −61‰ (relative to SMOW). The δ13C and δ18O of carbonates in retrograde metasomatic rocks after marble are −5.3 to +0.6 (relative to PDB) and +13.0 to +20.2% (relative
to SMOW), respectively. Sulfidation completes metasomatism, nonuniformly superimposed on all metasomatic rocks and marbles
with formation of orebodies, including massive sulfide ore. The δ34S of sulfides is 0 to 2‰ (relative to CDT);87Sr/86Sr of calcite from the late calcite-pyrite assemblage replacing marble is 0.704134 ± 6. The δ13C and 87Sr/86Sr of postore veined carbonates correlate positively (r = 0.98; n = 6). The regression line extends to the marble field. Its opposite end corresponds to magmatic (in terms of Bowman, 1998b)
calcite with minimal δ13C, δ18O, and 87Sr/86Sr values (−6.9 ‰, +6.7‰, and 0.70378 ± 4, respectively). The aforementioned isotopic data show that magmatic fluid was supplied
during all stages of mineral formation and interacted with marble and other rocks, changing its Sr, C, and O isotopic compositions.
This confirms the earlier established redistribution of major elements and REE in the process of metasomatism. A contribution
of meteoric and metamorphic water is often established in quartz from postore veins. 相似文献
11.
Natural gases of shallow reservoirs with the carbon isotopic compositions of methane ranging from -50‰ to -60‰ (PDB) were considered as mixed gases of biogenic and thermogenic origins previously and some of them were considered as low-mature (or low temperature thermogenic) gases lately. In this paper natural gases with the carbon isotopic compositions of methane in the above range were identified using the molecular and stable carbon isotopic compositions of methane, ethane and propane. The mixed gases of biogenic and mature thermogenic origins display the characteristics of δ 13 C1 ranging from -50‰to -60‰,δ13C2 > -35‰,Δvalues (δ13C3 -δ13C2) < 5‰ and C1/∑C2 ratios < 40. Immature to low-mature gases display the characteristics of δ 13 C1 ranging from - 50‰ to - 60‰, δ13 C2 <- 40‰,Δ values (δ13C3 -δ13C2) >7‰, and C1/∑C 2 ratios >60. 相似文献
12.
Oxygen isotopic composition was studied in the altered host rocks of the Dal’negorsk borosilicate deposit in order to establish
a boron source and the origin of ore-forming fluids responsible for deposition of economic borosilicate ore. The relationships
between oxygen isotopic composition and geochemistry of the altered igneous rocks occupying various structural and temporal
positions in the ore zone were studied, including premineral high-potassium minor intrusions located in the zones of datolite
mineralization; alkali basalt, gabbro, and breccia from the sedimentary framework of the deposit; and postmineral basaltic
andesite, basalt, and dolerite dikes. It was suggested that interaction of aqueous fluid with host rocks brought about not
only variation in oxygen isotopic composition but also shifts in geochemistry of these rocks, especially as concerns the chemical
elements contained in ore-forming fluid. The disturbance of oxygen isotopic system is typical of all studied rocks: δ18O values sharply decrease indicating interaction with aqueous fluid at elevated temperatures. The lowest δ18O (from −2.9 to +0.1‰) is characteristic of the premineral high-potassium and ultrapotassium minor intrusions from skarn-datolite
zone. Igneous rocks from the sedimentary framework of the deposit have δ18O of +2 to −0.9‰ The δ18O of postmineral basaltic andesite, basalt, and dolerite dikes varies from 0 to +7‰ with increasing distance from the ore
zone. The oxygen isotopic composition of aqueous fluid evidences its exogenic origin. The geochemical and isotopic characteristics
of ore-forming fluid show that it could have been deep-seated subsurface water similar to the contemporary water of the Alpine
fold zone, which contain up to 700–1000 mg/l B and is distinguished by high K, Li, Rb, Cs contents and high K/Na ratio. Similar
geochemistry is characteristic of the fluid inclusions in quartz from ore zones. It cannot be ruled out that continental evaporites
were a source of boron as well. The relationships between δ18O, K-Ar age, and geochemical parameters of premineral and postmineral altered intrusive bodies allow us to suggest that the
subsurface B-bearing water discharged through narrow channels controlled by premineral basaltic bodies. The discharge was
probably initiated by emplacement of basalt and dolerite dikes. 相似文献
13.
The strongly deformed Middle Devonian-Lower Carboniferous metasedimentary-volcanic successions of the Trevone Basin (SW England)
contain stratiform and Pb-Sb vein deposits that reveal a wide variation in δ34S and δ13C, reflecting mineral deposition during diagenesis, regional metamorphism and basin inversion. Pre-Variscan metasedimentary
sulphide (δ34S=−33.7 to −26.7‰) and metabasite sulphide (δ34S=+4.0 to +10.8‰) suggest two accessible source reservoirs for sulphur which were available for Sb-As-(Au) and Pb-Zn-(Ag)
mineralisation (δ34S=−3.3 to −15.0‰) during late Variscan semiductile-brittle shear. On the basis of pressure-corrected fluid inclusion temperatures,
the calculated composition of fluid sulphur reveals an enrichment in δ34SH2S in the individual vein parageneses and depletion of the fluid sulphur reservoir during evolution of the vein systems. Carbonates
in the same veins are partly contemporaneous with Pb-Sb mineralisation and late tensional deformation; their isotopic composition
(δ13C=−3.2 and −13.4‰) appears strongly influenced by the host formation. Fluid inclusions in post-tensional quartz show a marked
reduction in CO2, suggesting that episodes of CO2 degassing in response to punctuated reductions in pressure during uplift and brittle deformation was an important mechanism
for vein carbonation. An origin for the Pb-Sb mineralisation involving local remobilisation of sulphur from the mixed metasedimentary-volcanic
succession is probably inseparable from processes connected with Variscan metamorphism and deformation. Although the N Cornish
Variscan deformation is part of a spatially large-scale event, the isotopic evidence suggests compartmentalisation of sulphur
and carbon isotope features and short distances between sources and sinks.
Received: 15 August 1998 / Accepted: 8 October 1999 相似文献
14.
Two kinds of mylonite series rocks, felsic and mafic, have been recognized in the NW-striking shear zone of the Jiapigou gold
belt. During ductile deformation, a large amount of fluid interacted intensively with the mylonite series rocks: plagioclases
were sericitized and theAn values declined rapidly, finally all of them were transformed to albites; dark minerals were gradually replaced by chlorites
(mostly ripidolite). Meanwhile, large-scale and extensive carbonation also took place, and the carbonatization minerals varied
from calcite to dolomite and ankerite with the development of deformation. The δ13C values of the carbonates are −3.0‰ – −5.6‰ suggesting a deep source of carbon. The ductile deformation is nearly an iso-volume
one (f
v≈1). With the enhancement of shear deformation, SiO2 in the two mylonite series rocks was depleted, while volatile components suchs as CO2 and H2O, and some ore-forming elements such as Au and S were obviously enriched. But it is noted that the enrichment of Au in both
the mylonite series rocks did not reach the paygrade of gold. The released SiO2 from water-rock interactions occurred in the form of colloids and absorbed gold in the fluid. When brittle structures were
formed locally in the ductile shear zone, the ore-forming fluids migrated to the structures along microfractures, and preciptated
auriferous quartz because of reduction of pressure and temperature. Fluid inclusion study shows that the temperature and pressure
of the ore-forming fluids are 245–292°C and 95.4–131.7 MPa respectively; the salinity is 12.88–16.33wt% NaCl; the fluid-phase
is rich in Ca2+, K+, Na+, Mg2+, F− and Cl−, while the gaseous phases are rich in CO2 and CH4. The δD and δ18O, values of the ore-forming fluid are −84.48‰ – −91.73‰ and −0.247‰ – +2.715‰ respectively, suggesting that the fluid is
composed predominantly of meteoric water.
This project is financially supported by the National Natural Science Foundation of China (No. 9488010). 相似文献
15.
J. Parr 《Mineralium Deposita》1992,27(3):200-205
Sulphur isotopic compositions of 29 sulphide samples from the Broken Hill-type Pinnacles Deposit, NSW, are found to cluster
at 0%. (mean −0.8‰). The restricted range of the (δ34S) values between −3.5 and + 3.7‰ with a mean of −0.8‰, is interpreted as reflecting partial oxidation of a dominantly magmatic
sulphur source. δ34S data for galena samples fall into two groups: (1) isotopically heavier galenas (range −0.7 to 0.0‰; mean −0.4‰) which come
mainly from the footwall Zn lode and (2) isotopically lighter galenas (range −3.5 to −0.8‰; mean −2.2‰) which are from the
main Pb lode. Sphalerite, pyrrhotite and chalcopyrite have slightly heavier isotopic compositions (range −1.6 to +3.7‰ mean
+0.3‰) but exhibit the same stratigraphic differentiation. These data are interpreted as representing fluctuating conditions
at the site of ore deposition, in which upwelling hydrothermal fluids were subject to increasing fO2 and decreasing temperature with time. 相似文献
16.
Robert B. Trumbull Marc-Sebastian Krienitz Günter Grundmann Michael Wiedenbeck 《Contributions to Mineralogy and Petrology》2009,157(3):411-427
Tourmalines from the Habachtal emerald deposit in the Eastern Alps formed together with emerald in a ductile shear zone during
blackwall metasomatism between pelitic country rocks and a serpentinite body. Electron microprobe and secondary ion mass spectrometric
(SIMS) analyses provide a record of chemical and B-isotope variations in tourmalines which represent an idealized profile
from metapelites into the blackwall sequence of biotite and chlorite schists. Tourmaline is intermediate schorl-dravite in
the country rock and become increasingly dravitic in the blackwall zones, while F and Cr contents increase and Al drops. Metasomatic
tourmaline from blackwall zones is typically zoned optically and chemically, with rim compositions rich in Mg, Ti, Ca and
F compared with the cores. The total range in δ11B values is −13.8 to −5.1‰ and the within-sample variations are typically 3–5‰. Both of these ranges are beyond the reach
of closed-system fractionation at the estimated 500–550°C conditions of formation, and at least two boron components with
contrasting isotopic composition are indicated. A key observation from tourmaline core analyses is a systematic shift in δ11B from the country rock (−14 to −10‰) to the inner blackwall zones (−9 to −5‰). We suggest that two separate fluids were channeled
and partially mixed in the Habachtal shear zone during blackwall alteration and tourmaline-emerald mineralization. A regional
metamorphic fluid carried isotopically light boron as observed in the metapelite country rocks. The other fluid is derived
from the serpentinite association and has isotopically heavier boron typical for MORB or altered oceanic crust.
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. 相似文献
17.
Bulk δ
34Srock values, sulfur contents, and magnetic susceptibility were determined for 12 gold-related granitoid intrusions in southwestern
New Brunswick, the Canadian Appalachians. The sulfur isotope compositions of sulfide minerals in some of the granitoid samples
were also analyzed. This new dataset was used to characterize two distinctive groups of granitoids: (1) a Late Devonian granitic
series (GS) and (2) a Late Silurian to Early Devonian granodioritic to monzogranitic series (GMS). The GS rocks have a large
range in δ
34S values of −7.1‰ to +13‰ with an average of 2.2 ± 5.0‰ (1σ), low bulk-S contents (33 to 7,710 ppm) and low magnetic susceptibility
values (<10−4 SI), consistent with reduced ilmenite-series granites. The GMS rocks have a relatively narrower variation in δ
34S values of −4.4‰ to +7.3‰ with an average 1.2 ± 2.9‰ but with larger ranges in bulk-S contents (45 to 11,100 ppm) and high
magnetic susceptibility values (>10−3 SI), indicative of oxidized magnetite-series granites. The exceptions for the GMS rocks are the Lake George granodiorite
and Tower Hill granite that display reduced characteristics, which may have resulted from interaction of the magmas forming
these intrusions with graphite- or organic carbon-bearing sedimentary rocks. The bulk δ
34S values and S contents of the GMS rocks are interpreted in terms of selective assimilation–fractional crystallization (SAFC)
processes. Degassing processes may account for the δ
34S values and S contents of some GS rocks. The characteristics of our sulfur isotope and abundance data suggest that mineralizing
components S and Au in intrusion-related gold systems are dominantly derived from magmatic sources, although minor contaminants
derived from country rocks are evident. In addition, the molar sulfate to sulfide ratio in a granitic rock sample can be calculated
from the δ
34Srock value of the whole-rock sample and the δ
34Ssulfide (or δ
34Ssulfate) value of sulfide and/or sulfate mineral in the sample on the basis of S-isotope fractionation and mass balance under the
condition of magmatic equilibrium. This may be used to predict the speciation of sulfur in granitic rocks, which can be a
potential exploration tool for intrusion-related gold systems. 相似文献
18.
I. J. Richards Theodore C. Labotka Robert T. Gregory 《Contributions to Mineralogy and Petrology》1996,123(2):202-221
Late Proterozoic to Cambrian carbonate rocks from Lone Mountain, west central Nevada, record multiple post-depositional events
including: (1) diagenesis, (2) Mesozoic regional metamorphism, (3) Late Cretaceous contact metamorphism, related to the emplacement
of the Lone Mountain granitic pluton and (4) Tertiary hydrothermal alteration associated with extension, uplift and intrusion
of silicic porphyry and lamprophyre dikes. Essentially pure calcite and dolomite marbles have stable isotopic compositions
that can be divided into two groups, one with positive δ13C values from+3.1 to +1.4 ‰ (PDB) and high δ18O values from +21.5 to +15.8 ‰ (SMOW), and the other with negative δ13C values from –3.3 to –3.6‰ and low δ18O values from +16.9 to +11.1‰. Marbles also contain minor amounts of quartz, muscovite and phlogopite. Brown and blue luminescent,
clear, smooth textured quartz grains from orange luminescent calcite marbles have high δ18O values from +23.9 to +18.1‰, while brown luminescent, opaque, rough textured quartz grains from red luminescent dolomite
marbles typically have low δ18O values from +2.0 to +9.3‰. The δ18O values of muscovite and phlogopite from marbles are typical of micas in metamorphic rocks, with values between +10.4 and
+14.4‰, whereas mica δD values are very depleted, varying from −102 to −156‰. No significant lowering of the δ18O values of Lone Mountain carbonates is inferred to have occurred during metamorphism as a result of devolatilization reactions
because of the essentially pure nature of the marbles. Bright luminescence along the edges of fractures, quartz cements and
quartz overgrowths in dolomite marbles, low δD values of micas, negative δ13C values and low δ18O values of calcite and dolomite, and depleted δ18O values of quartz from dolomite marbles all indicate that meteoric fluids interacted with Lone Mountain marbles during the
Tertiary. Partial oxygen isotopic exchange between calcite and low 18O meteoric fluids lowered the δ18O values of calcite, resulting in uniform quartz-calcite fractionations that define an apparent pseudoisotherm. These quartz-calcite
fractionations significantly underestimate both the temperature of metamorphism and the temperature of post-metamorphic alteration.
Partial oxygen isotopic exchange between quartz and meteoric fluids also resulted in 18O depletion of quartz from dolomite marbles. This partial exchange was facilitated by an increase in the surface area of the
quartz as a result of its dissolution by meteoric fluids. The negative δ13C values in carbonates result from the oxidation of organic material by meteoric fluids following metamorphism. Stable isotopic
data from Lone Mountain marbles are consistent with the extensive circulation of meteoric hydrothermal fluids throughout western
Nevada in Tertiary time.
Received: 1 February 1994/Accepted: 12 September 1995 相似文献
19.
To characterize the isotopic composition of organisms at the base of the food web and the controls on their variability, the concentration and δ13C isotopic composition of dissolved inorganic carbon (DIC) and plankton δ13C, δ15N, and δ34S were measured. The measurements were made during periods of high and low river flow in Apalachicola Bay, Florida, United States, over 3 yr. DIC concentration and δ13C values were related to salinity, indicating that conservative mixing of riverine and marine waters was responsible for the overall distributions. The usefulness of DIC δ13C data for characterizing the trophic processes within the estuary was dependent upon the residence time of water within the season. Plankton δ13C values varied from −22‰ to −30‰ and were directly related to estuarine DIC δ13C, offset by a factor of roughly −20‰. This offset factor varied with salinity. Values of δ34S in estuarine plankton (station means ranged from 11.4‰ to 13.1‰) were depleted relative to marine plankton (17.7±0.4‰) possibly due to the admixture of34S-depleted sedimentary sulfide with estuarine samples. Values of δ34S in plankton were not related to δ13C values of plankton and were only weakly correlated to the salinity of the water from which the plankton were collected, indicating that marine sulfate was the primary source of planktonic sulfur. Values of δ15N in plankton varied from 5.5‰ to 10.7‰ and appeared related to dominance of the sample by phytoplankton or zooplankton. Estuarine plankton was15N enriched relative to offshore plankton and estuarine sediment. 相似文献
20.
Oxygen isotope systematics of gem corundum deposits in Madagascar: relevance for their geological origin 总被引:1,自引:1,他引:1
Gaston Giuliani Anthony Fallick Michel Rakotondrazafy Daniel Ohnenstetter Alfred Andriamamonjy Théogène Ralantoarison Saholy Rakotosamizanany Marie Razanatseheno Yohann Offant Virginie Garnier Christian Dunaigre Dietmar Schwarz Alain Mercier Voahangy Ratrimo Bruno Ralison 《Mineralium Deposita》2007,42(3):251-270
The oxygen isotopic composition of gem corundum was measured from 22 deposits and occurrences in Madagascar to provide a gemstone
geological identification and characterization. Primary corundum deposits in Madagascar are hosted in magmatic (syenite and
alkali basalt) and metamorphic rocks (gneiss, cordieritite, mafic and ultramafic rocks, marble, and calc-silicate rocks).
In both domains the circulation of fluids, especially along shear zones for metamorphic deposits, provoked in situ transformation
of the corundum host rocks with the formation of metasomatites such as phlogopite, sakenite, and corundumite. Secondary deposits
(placers) are the most important economically and are contained in detrital basins and karsts. The oxygen isotopic ratios
(18O/16O) of ruby and sapphire from primary deposits are a good indicator of their geological origin and reveal a wide range of δ18O (Vienna Standard Mean Ocean Water) between 1.3 and 15.6‰. Metamorphic rubies are defined by two groups of δ18O values in the range of 1.7 to 2.9‰ (cordieritite) and 3.8 to 6.1‰ (amphibolite). “Magmatic” rubies from pyroxenitic xenoliths
contained in the alkali basalt of Soamiakatra have δ18O values ranging between 1.3 and 4.7‰. Sapphires are classified into two main groups with δ18O in the range of 4.7 to 9.0‰ (pyroxenite and feldspathic gneiss) and 10.7 to 15.6‰ (skarn in marble from Andranondambo).
The δ18O values for gem corundum from secondary deposits have a wide spread between −0.3 and 16.5‰. The ruby and sapphire found in
placers linked to alkali basalt environments in the northern and central regions of Madagascar have consistent δ18O values between 3.5 and 6.9‰. Ruby from the placers of Vatomandry and Andilamena has δ18O values of 5.9‰, and between 0.5 and 4.0‰, respectively. The placers of the Ilakaka area are characterized by a huge variety
of colored sapphires and rubies, with δ18O values between −0.3 and 16.5‰, and their origin is debated. A comparison with oxygen isotope data obtained on gem corundum
from Eastern Africa, India, and Sri Lanka is presented. Giant placer deposits from Sri Lanka, Madagascar, and Tanzania have
a large variety of colored sapphires and rubies with a large variation in δ18O due to mingling of corundum of different origin: mafic and ultramafic rocks for ruby, desilicated pegmatites for blue sapphire,
syenite for yellow, green, and blue sapphire, and skarn in marbles for blue sapphire. 相似文献