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1.
Summary ?Fluid inclusions from two Mesoproterozoic, metamorphosed layered intrusive complexes, Niquelandia and Barro Alto, Goiás State,
Brazil record multiple fluid influx events from the magmatic to granulitic and retrograde metamorphic stages.
1. The oldest inclusions contain high density CO2 ± N2 ± CH4 and are found as primaries in plagioclase and orthopyroxene in mafic granulite with homogenization temperatures between − 48
and − 28 °C. These inclusions may correspond to the early, magmatic stage. This type was found in samples from both the Niquelandia
and the Barro Alto complexes.
2. Intragranular, relatively high density CO2 + N2 inclusions (Th between − 33 and − 26 °C) together with decrepitated and reequilibrated N2 inclusions (Th between − 160 and − 151 °C) in the rock-forming minerals can be associated with the granulite facies metamorphism. Such inclusions
were found only in the Barro Alto complex.
3. Transgranular, high density, CO2–N2 inclusions (93% CO2 and 7% N2, according to Raman analysis, with Th between − 66.6 and − 50.4 °C) as well as the low density, secondary CO2 ± N2 ± CH4 inclusions (Th between − 13.0 and + 18.7 °C) and the H2O–NaCl–CaCl2 hypersaline inclusions (with halite dissolution temperature between 132 and 354 °C, and Th between 212 and 490 °C) are attributed to different fluid influx events during the retrograde metamorphism. This inclusion
type can be found both in the Niquelandia and in the Barro Alto complexes.
The fluid inclusion textures and compositions show several stages of fluid evolution. The fluid inclusion measurements and
the geothermobarometric data indicate an anticlockwise P-T path for both the Barro Alto and the Niquelandia complexes.
Received October 16, 2000; revised version accepted November 20, 2001 相似文献
2.
Gold ore-forming fluids of the Tanami region, Northern Australia 总被引:1,自引:0,他引:1
Fluid inclusion studies have been carried out on major gold deposits and prospects in the Tanami region to determine the compositions
of the associated fluids and the processes responsible for gold mineralization. Pre-ore, milky quartz veins contain only two-phase
aqueous inclusions with salinities ≤19 wt% NaCl eq. and homogenization temperatures that range from 110 to 410°C. In contrast,
the ore-bearing veins typically contain low to moderate salinity (<14 wt% NaCl eq.), H2O + CO2 ± CH4 ± N2-bearing fluids. The CO2-bearing inclusions coexist with two-phase aqueous inclusions that exhibit a wider range of salinities (≤21 wt% NaCl eq.).
Post-ore quartz and carbonate veins contain mainly two-phase aqueous inclusions, with a last generation of aqueous inclusions
being very CaCl2-rich. Salinities range from 7 to 33 wt% NaCl eq. and homogenization temperatures vary from 62 to 312°C. Gold deposits in
the Tanami region are hosted by carbonaceous or iron-rich sedimentary rocks and/or mafic rocks. They formed over a range of
depths at temperatures from 200 to 430°C. The Groundrush deposit formed at the greatest temperatures and depths (260–430°C
and ≤11 km), whereas deposits in the Tanami goldfield formed at the lowest temperatures (≥200°C) and at the shallowest depths
(1.5–5.6 km). There is also evidence in the Tanami goldfield for late-stage isothermal mixing with higher salinity (≤21 wt%
NaCl eq.) fluids at temperatures between 100 and 200°C. Other deposits (e.g., The Granites, Callie, and Coyote) formed at
intermediate depths and at temperatures ranging from 240 to 360°C. All ore fluids contained CO2 ± N2 ± CH4, with the more deeply formed deposits being enriched in CH4 and higher level deposits being enriched in CO2. Fluids from deposits hosted mainly by sedimentary rocks generally contained appreciable quantities of N2. The one exception is the Tanami goldfield, where the quartz veins were dominated by aqueous inclusions with rare CO2-bearing inclusions. Calculated δ
18O values for the ore fluids range from 3.8 to 8.5‰ and the corresponding δD values range from −89 to −37‰. Measured δ
13C values from CO2 extracted from fluid inclusions ranged from −5.1 to −8.4‰. These data indicate a magmatic or mixed magmatic/metamorphic source
for the ore fluids in the Tanami region. Interpretation of the fluid inclusion, alteration, and structural data suggests that
mineralization may have occurred via a number of processes. Gold occurs in veins associated with brittle fracturing and other
dilational structures, but in the larger deposits, there is also an association with iron-rich rocks or carbonaceous sediments,
suggesting that both structural and chemical controls are important. The major mineralization process appears to be boiling/effervescence
of a gas-rich fluid, which leads to partitioning of H2S into the vapor phase resulting in gold precipitation. However, some deposits also show evidence of desulfidation by fluid–rock
interaction and/or reduction of the ore-fluid by fluid mixing. These latter processes are generally more prevalent in the
higher crustal-level deposits. 相似文献
3.
Fluid inclusion and stable isotope (O, H, C, and S) constraints on the genesis of the Serrinha gold deposit, Gurupi Belt, northern Brazil 总被引:1,自引:0,他引:1
Evandro L. Klein Chris Harris Christophe Renac André Giret Candido A. V. Moura Kazuo Fuzikawa 《Mineralium Deposita》2006,41(2):160-178
The Serrinha gold deposit of the Gurupi Belt, northern Brazil, belongs to the class of orogenic gold deposits. The deposit is hosted in highly strained graphitic schist belonging to a Paleoproterozoic (∼2,160 Ma) metavolcano-sedimentary sequence. The ore-zones are up to 11 m thick, parallel to the regional NW–SE schistosity, and characterized by quartz-carbonate-sulfide veinlets and minor disseminations. Textural and structural data indicate that mineralization was syn- to late-tectonic and postmetamorphic. Fluid inclusion studies identified early CO2 (CH4-N2) and CO2 (CH4-N2)-H2O-NaCl inclusions that show highly variable phase ratios, CO2 homogenization, and total homogenization temperatures both to liquid and vapor, interpreted as the product of fluid immiscibility under fluctuating pressure conditions, more or less associated with postentrapment modifications. The ore-bearing fluid typically has 18–33mol% of CO2, up to 4mol% of N2, and less than 2mol% of CH4 and displays moderate to high densities with salinity around 4.5wt% NaCl equiv. Mineralization occurred around 310 to 335°C and 1.3 to 3.0 kbar, based on fluid inclusion homogenization temperatures and oxygen isotope thermometry with estimated oxygen fugacity indicating relatively reduced conditions. Stable isotope data on quartz, carbonate, and fluid inclusions suggest that veins formed from fluids with δ18OH2O and δDH2O (310–335°C) values of +6.2 to +8.4‰ and −19 to −80‰, respectively, which might be metamorphic and/or magmatic and/or mantle-derived. The carbon isotope composition (δ13C) varies from −14.2 to −15.7‰ in carbonates; it is −17.6‰ in fluid inclusion CO2 and −23.6‰ in graphite from the host rock. The δ34S values of pyrite are −2.6 to −7.9‰. The strongly to moderately negative carbon isotope composition of the carbonates and inclusion fluid CO2 reflects variable contribution of organic carbon to an originally heavier fluid (magmatic, metamorphic, or mantle-derived) at the site of deposition and sulfur isotopes indicate some oxidation of the originally reduced fluid. The deposition of gold is interpreted to have occurred mainly in response to phase separation and fluid-rock interactions such as CO2 removal and desulfidation reactions that provoked variations in the fluid pH and redox conditions. 相似文献
4.
High CO2 content of fluid inclusions in gold mineralisations in the Ashanti Belt, Ghana: a new category of ore forming fluids? 总被引:4,自引:0,他引:4
Fluid inclusions were studied in samples from the Ashanti, Konongo-Southern Cross, Prestea, Abosso/Damang and Ayanfuri gold
deposits in the Ashanti Belt, Ghana. Primary fluid inclusions in quartz from mineralised veins of the Ashanti, Prestea, Konongo-Southern
Cross, and Abosso/Damang deposits contain almost exclusively volatile species. The primary setting of the gaseous (i.e. the
fluid components CO2, CH4 and N2) fluid inclusions in clusters and intragranular trails suggests that they represent the mineralising fluids. Microthermometric
and Raman spectroscopic analyses of the inclusions revealed a CO2 dominated fluid with variable contents of N2 and traces of CH4. Water content of most inclusions is below the detection limits of the respective methods used. Aqueous inclusions are rare
in all samples with the exception of those from the granite-hosted Ayanfuri mineralisation. Here inclusions associated with
the gold mineralisation contain a low salinity (<6 eq.wt.% NaCl) aqueous solution with variable quantities of CO2. Microthermometric investigations revealed densities of the gaseous inclusions of 0.65 to 1.06 g/cm3 at Ashanti, 0.85 to 0.98 g/cm3 at Prestea, up to 1.02 g/cm3 at Konongo-Southern Cross, and 0.8 to 1.0 g/cm3 at Abosso/Damang. The fluid inclusion data are used to outline the PT ranges of gold mineralisation of the respective gold deposits. The high density gaseous inclusions found in the auriferous
quartz at Ashanti and Prestea imply rather high pressure trapping conditions of up to 5.4 kbar. In contrast, mineralisation
at Ayanfuri and Abosso/Damang is inferred to have occurred at lower pressures of only up to 2.2 kbar. Mesothermal gold mineralisation
is generally regarded to have formed from fluids characterized by H2O > CO2 and low salinity ( ± 6 eq.wt.%NaCl). However, fluid inclusions in quartz from the gold mineralisations in the Ashanti belt
point to distinctly different fluid compositions. Specifically, the predominance of CO2 and CO2 >> H2O have to be emphasized. Fluid systems with this unique bulk composition were apparently active over more than 200␣km along
strike of the Ashanti belt. Fluids rich in CO2 may present a hitherto unrecognised new category of ore-forming fluids.
Received: 30 May 1996 / Accepted: 8 October 1996 相似文献
5.
Synorogenic veins from the Proterozoic Eastern Mount Isa Fold Belt contain three different types of fluid inclusions: CO2-rich, aqueous two-phase and rare multiphase. Inclusions of CO2 without a visible H2O phase are particularly common. The close association of CO2-rich inclusions with aqueous two-phase, and possibly multiphase inclusions suggests that phase separation of low- to -moderate
salinity CO2-rich hydrothermal fluids led to the selective entrapment of the CO2. Microthermometric results indicate that CO2-rich inclusions homogenize between –15.5 and +29.9 °C which corresponds to densities of 0.99 to 0.60 g.cm−3. The homogenization temperatures of the associated aqueous two-phase inclusions are 127–397 °C, with salinities of 0.5 to
18.1 wt.% NaCl equivalent. The rarely observed multiphase inclusions homogenize between 250 and 350 °C, and have salinities
ranging from 34.6 to 41.5 wt.% NaCl equivalent. Evidence used to support the presence of fluid immiscibility in this study
is mainly derived from observations of coexisting H2O-rich and CO2-rich inclusions in groups and along the same trail. In addition, these two presumably unmixed fluids are also found on adjacent
fractures where monophase CO2-rich inclusions are closely related to H2O-rich inclusions. Similar CO2-rich inclusions are widespread in mineral deposits in this region, which are simply metal-enriched synorogenic veins. Therefore,
we argue that fluid immiscibility caused volatile species such as CO2 and H2S to be lost from liquid, thus triggering ore deposition by increasing the fluid pH and decreasing the availability of complexing
ligands.
Received: 28 April 1997 / Accepted: 4 January 1999 相似文献
6.
The Archean Shawmere anorthosite lies within the granulite facies portion of the Kapuskasing Structural Zone (KSZ), Ontario,
and is crosscut by numerous linear alteration veins containing calcite + quartz ± dolomite ± zoisite ± clinozoisite ± margarite ±paragonite ± chlorite.
These veins roughly parallel the trend of the Ivanhoe Lake Cataclastic Zone. Equilibria involving clinozoisite + margarite + quartz ± calcite
± plagioclase show that the vein minerals were stable at T < 600 °C, XCO2 < 0.4 at P ≈ 6 kbar. The stabilities of margarite and paragonite in equilibrium with quartz are also consistent with T < 600 °C and XCO2 < 0.4 at 6 kbar. Additional assemblages consisting of calcite + clinochlore + quartz + talc + margarite indicate T < 500 °C with XCO2 > 0.9. Thus, vein formation, while clearly retrograde, spanned a range of temperatures, and fluid compositions evolved from
H2O-rich to CO2-rich. The calcite in the retrograde veins has δ18O values that range from 8.4 to 11.2‰ (average = +9.7 ± 0.9‰) and δ13C values that range from −3.9 to −1.6‰ (average = −3.1 ± 0.6‰). These values indicate that the fluids from which calcite precipitated
underwent extensive exchange with the anorthosite and other crustal lithologies. The fluids may have been initially derived
either from devolatilization of metamorphic rocks or crystallization of igneous rocks in the adjacent Abitibi subprovince.
Vein quartz contains CO2-rich fluid inclusions (final melting T = −57.0 to −58.7 °C) that range in size from 5 to 17 μm. Measured homogenization temperatures (T h) range from −44.0 to 14.5 °C, however for most inclusions (46 of S1), T h = −44.0 to −21.1 °C (ρCO2 ≈ 1.13 to 1.05 g/cm3). At 400 to 600 °C, these densities correspond to pressures of 3.5 to 7 kbar, which is the best estimate of pressures of
vein formation. It has been argued that some high density CO2-rich fluid inclusions found in the KSZ were formed during peak metamorphism and thus document the presence of a CO2-rich fluid during peak granulite facies metamorphism (Rudnick et al. 1984). The association of high density CO2-rich fluid inclusions with clearly retrograde veins documents the formation of similar composition and density inclusions
after the peak of metamorphism. Thus, the coincidence of entrapment pressures calculated from fluid inclusion density measurements
with peak metamorphic pressures alone should not be considered strong evidence for peak metamorphic inclusion entrapment.
All fluid inclusion results are consistent with an initially semi-isobaric retrograde P–T path.
Received: 2 April 1996 / Accepted: 15 November 1996 相似文献
7.
Evolution of metamorphic volatiles during exhumation of microdiamond-bearing granulites in the Western Gneiss Region, Norway 总被引:1,自引:0,他引:1
Rune B. Larsen Elizabeth A. Eide Ernst A. J. Burke 《Contributions to Mineralogy and Petrology》1998,133(1-2):106-121
Fluid inclusions in garnet, kyanite and quartz from microdiamond-bearing granulites in the Western Gneiss Region, Norway,
document a conspicuous fluid evolution as the rocks were exhumed following Caledonian high- and ultrahigh-pressure (HP–UHP) metamorphism. The most important of the various fluid mixtures and daughter minerals in these rocks are: (N2 + CO2 + magnesian calcite), (N2 + CO2 + CH4 + graphite + magnesian calcite), (N2 + CH4), (N2 + CH4 + H2O), (CO2) and (H2O + NaCl + CaCl2 + nahcolite). Rutile also occurs in the N2 + CO2 inclusions as a product of titanium diffusion from the garnet host into the fluid inclusions. Volatiles composed of N2 + CO2 + magnesian calcite characterise the ambient metamorphic environment between HP–UHP (peak) and early retrograde metamorphism. During progressive decompression, the mole fraction of N2 increased in the fluid mixtures; as amphibolite-facies conditions were reached, CH4 and later, H2O, appeared in the fluids, concomitant with the disappearance of CO2 and magnesian calcite. Graphite is ubiquitous in the host lithologies and fluid inclusions. Thermodynamic modelling of the
metamorphic volatiles in a graphite-buffered C-O-H system demonstrates that the observed metamorphic volatile evolution was
attainable only if the f
O2 increased from c. −3.5 (±0.3) to −0.8 (±0.3) log units relative to the FMQ oxygen buffer. External introduction of oxidising
aqueous solutions along a system of interconnected ductile shear zones adequately explains the dramatic increase in the f
O2. The oxidising fluids introduced during exhumation were likely derived from dehydration of oceanic crust and continental
sediments previously subducted during an extended period of continental collision in conjunction with the Caledonian orogeny.
Received: 15 December 1997 / Accepted: 25 May 1998 相似文献
8.
J. P. Richards C. J. Bray D. M. DeR. Channer E. T. C. Spooner 《Mineralium Deposita》1997,32(2):119-132
The Porgera gold deposit in Papua New Guinea is a world-class example of an alkalic-type epithermal gold system (stage II),
which overprints a precursor stage of magmatic-hydrothermal gold mineralization (stage I). Gas and ion chromatographic analyses
of fluid inclusions contained in vein minerals from both mineralization stages have been carried out in order to constrain
the compositions of the fluids involved in, and the processes attending, ore deposition. These data indicate the presence
of three end-member liquids, the most dilute of which was present throughout the mineralization history and is interpreted
to represent evolved groundwater of meteoric origin. Its composition is estimated to have been approximately 500 mM Na+, 10 mM K+, 5 mM Li+, 250 mM Cl−, 0.15 mM Br−, and 0.01 mM I−, plus significant concentrations of dissolved gases. More saline liquids were also present during the two main stages of
ore formation, and although their compositions differ, both are interpreted to have been derived at least in part from magmatic
fluids, and to have been the media by which gold was introduced into the system. Stage I minerals contain fluid inclusions
which decrease in salinity towards this dilute end-member composition through the vein paragenesis, reflecting progressive
dilution at depth of the magmatic fluid source by groundwaters. Ore deposition is thought to have been caused largely by simple
cooling and/or wallrock reactions, although limited in situ fluid mixing may also have occurred. The most saline fluids, present
in early quartz and pyrite, contain at least 810 mM Na+, 530 mM Ca2+, 130 mM K+, 12 mM Li+, 87 mM SO4
2−, 960 mM Cl−, 1.1 mM Br−, and 0.05 mM I−, plus significant but variable concentrations of dissolved gases. Fluid inclusions from stage II hydraulic breccia veins
reveal the presence of two distinct liquids with contrasting salinities, which were present at different times during vein
formation. A higher salinity liquid appears to have predominated during mineralization, whereas lower salinity groundwaters
filled the structures during intervening periods. The ore-forming fluid may have been forcibly injected into the veins from
depth during fracturing and depressurization events, displacing the resident groundwaters in the process. The original composition
of this fluid is estimated to have been at least 1770 mM Na+, 59 mM K+, 180 mM Li+, 210 mM SO4
2−, 680 mM Cl−, 1.4 mM Br−, and 0.09 mM I−, plus 1.5 mol% CO2, 0.19 mol% CH4, and 0.04 mol% N2. Gas chromatographic analyses of fluid inclusions from stage II samples show a decrease in total gas content between early
unmineralized veins and post-mineralization vuggy quartz (suitable samples could not be obtained from the ore stage itself).
Post-mineralization samples plot along an experimental gas-saturation curve in the CO2-CH4-H2O-NaCl system, obtained at conditions similar to those attending stage II ore deposition at Porgera (200–300 bar, ˜165 °C).
These results are interpreted to indicate a period of depressurization-induced phase separation during hydraulic fracturing,
which resulted in rich ore deposition. Volatile gases such as CH4 and N2, in addition to CO2 in solution, are shown to have a significant negative effect on total gas solubility. This effect may be of critical importance
in lowering the temperature and increasing the depth (pressure) at which phase separation can occur in epithermal systems.
Received: 28 November 1995 / Accepted: 17 July 1996 相似文献
9.
Fluid inclusions have been studied in three pegmatite fields in Galicia, NW Iberian Peninsula. Based on microthermometry
and Raman spectroscopy, eight fluid systems have been recognized. The first fluid may be considered to be a pegmatitic fluid
which is represented by daughter mineral (silicates)-rich aqueous inclusions. These inclusions are primary and formed above
500 °C (dissolution of daughter minerals). During pegmatite crystallization, this fluid evolved to a low-density, volatile-rich
aqueous fluid with low salinity (93% H2O; 5% CO2; 0.5% CH4; 0.2% N2; 1.3% NaCl) at minimum P–T conditions around 3 ± 0.5 kbar and 420 °C. This fluid is related to rare-metal mineralization. The volatile enrichment may
be due to mixing of magmatic fluids and fluids equilibrated with the host rock. A drop in pressure from 3 ± 0.5 to 1 kbar
at a temperature above 420 °C, which may be due to the transition from predominantly lithostatic to hydrostatic pressure,
is recorded by two-phase, water-rich inclusions with a low-density vapour phase (CO2, CH4 and N2). Another inclusion type is represented by two-phase, vapour-rich inclusions with a low-density vapour phase (CO2, CH4 and N2), indicating a last stage of decreasing temperature (360 °C) and pressure (around 0.5 kbar), probably due to progressive
exhumation. Finally, volatile (CO2)-rich aqueous inclusions, aqueous inclusions (H2O-NaCl) and mixed-salt aqueous inclusions with low Th, are secondary in charac- ter and represent independent episodes of hydrothermal fluid circulation below 310 °C and 0.5 kbar.
Received: 14 October 1999 / Accepted: 5 October 1999 相似文献
10.
Fluid Inclusions in the Gold—Bearing Quartz Veins at Um Rus Area,Eastern Desert,Egypt 总被引:2,自引:0,他引:2
MOHAMEDELTOKHI ABDALLAELMUSLEM 《中国地球化学学报》2002,21(2):131-139
Fluid inclusions in the gold-bearing quartz veins at the Um Rus area are of three types: H2O, H2O−CO2 and CO2 inclusions. H2O inclusions are the most abundant, they include two phases which exhibit low and high homogenization temperatures ranging
from 150 to 200°C and 175 to 250°C, respectively. The salinity of aqueous inclusions, based on ice melting, varies between
6.1 and 8 equiv. wt% NaCl. On the other hand, H2O−CO2 fluid inclusions include three phases. Their total homogenization temperatures range from 270 to 325°C, and their salinity,
based on clathrate melting, ranges between 0.8 and 3.8 equiv. wt% NaCl. CO2 fluid inclusions homogenize to a liquid phase and exhibit a low density range from 0.52 to 0.66 g/cm3. The partial mixing of H2O−CO2 and salt H2O−NaCl fluid inclusions is the main source of fluids from which the other types of inclusions were derived. The gold-bearing
quartz veins are believed to be of medium temperature hydrothermal convective origin. 相似文献
11.
The nature, origin and physicochemical controls of hydrothermal Mo-Bi mineralization in the Cadillac deposit, Quebec, Canada 总被引:2,自引:0,他引:2
Mo-Bi mineralization occurs in subvertical and subhorizontal quartz-muscovite-± K-feldspar veins surrounded by early albitic
and later K-feldspathic alteration halos in monzogranite of the Archean Preissac pluton, Abitibi region, Québec, Canada. Molybdenite
is intergrown with muscovite in the veins or associated with K-feldspar in the alteration halos. Mineralized veins contain
five main types of fluid inclusions: aqueous liquid and liquid-vapor inclusions, aqueous carbonic liquid-liquid-vapor inclusions,
carbonic liquid and vapor inclusions, halite-bearing aqueous liquid and liquid-vapor inclusions, trapped mineral-bearing aqueous
liquid and liquid-vapor inclusions. The carbonic solid in frozen carbonic and aqueous-carbonic inclusions melts in most cases
at −56.7 ± 0.1 °C indicating that the carbonic fluid consists largely of CO2. All aqueous inclusion types and the aqueous phase in carbonic inclusions have low initial melting temperatures (≥70 °C),
requiring the presence of salts other than NaCl. Leachate analyses show that the bulk fluid contains variable proportions
of Na, K, Ca, Cl, and traces of Mg and Li. The following solids were identified in the fluid inclusions by SEM-EDS analysis:
halite, calcite, muscovite, millerite (NiS), barite and antarcticite (CaCl2 · 6H2O). All are interpreted to be trapped phases except halite which is a daughter mineral, and antarcticite which formed during
sample preparation (freezing). Aqueous inclusions homogenize to liquid at temperatures between 75 °C and 400 °C; the mode
is 375 °C. Aqueous-carbonic inclusions homogenize to liquid or vapor between 210 °C and 400 °C. Halite-bearing aqueous inclusions
homogenize by halite dissolution at approximately 170 °C. Aqueous inclusions containing trapped solids exhibit liquid-vapor
homogenization at temperatures similar to those of halite-bearing aqueous inclusions. Temperatures of vein formation, based
on oxygen isotopic fractionation between quartz and muscovite, range from 342 °C to 584 °C. The corresponding oxygen isotope
composition of the aqueous fluid in equilibrium with these minerals ranges from 1.2 to 5.5 per mil with a mean of 3.9 per
mil, suggesting that the liquid had a significant meteoric component. Isochores for aqueous fluid inclusions intersect the
modal isotopic isotherm of 425 °C at pressures between 590 and 1900 bar. A model is proposed in which molybdenite was deposited
owing to decreasing temperature and/or pressure from CO2-bearing, moderate to high salinity fluids of mixed magmatic-meteoric origin that were in equilibrium with K-feldspar and
muscovite. These fluids resulted from the degassing of a monzogranitic magma and evolved through interaction with volcanic
(komatiitic) and sedimentary country rocks.
Received: 6 February 1997 / Accepted: 28 January 1998 相似文献
12.
B. Cesare 《Contributions to Mineralogy and Petrology》1995,122(1-2):25-33
Equilibrium C–O–H fluid speciation calculations predict that graphite will precipitate from initially graphite saturated
fluid inclusions during cooling and exhumation of metamorphic rocks. In the case that no mass is gained or lost by the inclusions,
the original X
O ratio [O/(O+H)] of the fluid phase must be maintained. Given this closed system constraint, the down-temperature progress
of graphite precipitation can easily be monitored as a function of the varible X
O, and produces some effects that are of significance to fluid inclusion studies: 1. Variation of the H2O : CO2 : CH4 relationship in the graphite-saturated COH fluid, namely increase of X
H2
O and decrease of the carbonic fraction; 2. Decrease of fluid density due to precipitation of graphite, which is denser than
the residual fluid; 3. Alteration of the CO2 : CH4 ratio of the fluid, depending on the initial O : H ratio of the fluid: for X
O>1/3, fluids increase their CO2 : CH4 ratio with decreasing temperature, and vice-versa. This implies that the CO2 : CH4 ratio measured at room T will not represent the trapping value, which is in any case closer to unity. As a consequence of density reduction, isochores
extrapolated from densities observed at room temperature do not pass through the pressure-temperature conditions at which
the inclusion was trapped, with pressure underestimates of up to 2 kbar. Actual P-T trapping conditions are located along the equilibrium “bulk isochore” (curve of constant-X
O, constant-volume) of the fluid. Alteration of the CO2 : CH4 ratio is a mechanism by which a CO2-rich or CH4-rich carbonic phase can be formed from aqueous fluids that are slightly off the neutral X
O=1/3 value. Subsequent segregation of this phase from the aqueous counterpart may account for the formation of pure CO2 and CH4 fluids in the upper crust.
Received: 15 March 1995 / Accepted: 1 June 1995 相似文献
13.
The recently discovered Hanshan gold deposit in northern Gansu Province, northwestern China, is hosted by a WNW-striking
shear zone in Ordovician andesite and basalt. Mineralization consists of surface to near-surface oxidized ore (the yellow
sandy gossan type) and three types of primary ore, i.e. early-stage quartz-sericite-pyrite ores in stockworks, early-stage
disseminated ore, and the most important late-stage quartz ± calcite-sulfide veins. The ore system is characterized by variable
degrees of potassic and silicic alteration. Late-stage gold-related fluid inclusions have homogenization temperatures between
170 to 310 °C, with a peak around 260 °C and low salinities. The ore fluids had high contents of CO2, CH4, and N2. Sulfur isotope measurements of −1.9 to +1.7 per mil for hydrothermal pyrites could be consistent with a hydrothermal fluid
source from the mantle, but the oxygen and carbon isotope data from calcite and quartz suggest mixing between mantle and crustal
fluid sources. K-Ar ages for hydrothermal sericite from ore zones are 213.9 ± 3.1 and 224.4 ± 3.2 Ma. Due to the arid Cenozoic
climate, a yellow gold-bearing gossan developed, which consists of jarosite, gypsum, and relict quartz. It could be a widespread
and useful prospecting guide for gold in northwestern China.
Received: 1 February 1999 / Accepted: 1 August 1999 相似文献
14.
Ore-forming fluids associated with granite-hosted gold mineralization at the Sanshandao deposit, Jiaodong gold province, China 总被引:45,自引:0,他引:45
The Sanshandao gold deposit, with total resources of more than 60 t of gold, is located in the Jiaodong gold province, the most important gold province of China. The deposit is a typical highly fractured and altered, disseminated gold system, with high-grade, quartz-sulphide vein/veinlet stockworks that cut Mesozoic granodiorite. There are four stages of veins that developed in the following sequence: (1) quartz-K-feldspar-sericite; (2) quartz-pyrite±arsenopyrite; (3) quartz-base metal sulfide; and (4) quartz-carbonate. Fluid inclusions in quartz and calcite in vein/veinlet stockworks contain C-O-H fluids of three main types. The first type consists of dilute CO2–H2O fluids coeval with the early vein stage. Molar volumes of these CO2–H2O fluid inclusions, ranging from 50–60 cm3/mol, yield estimated minimum trapping pressures of 3 kbar. Homogenization temperatures, obtained mainly from CO2–H2O inclusions with lower CO2 concentration, range from 267–375 °C. The second inclusion type, with a CO2–H2O±CH4 composition, was trapped during the main mineralizing stages. These fluids may reflect the CO2–H2O fluids that were modified by fluid/rock reactions with altered wallrocks. Isochores for CO2-H2O±CH4 inclusions, with homogenization temperatures ranging from 204–325 °C and molar volumes from 55 to 70 cm3/mol, provide an estimated minimum trapping pressure of 1.2 kbar. The third inclusion type, aqueous inclusions, trapped in cross-cutting microfractures in quartz and randomly in calcite, are post-mineralization, and have homogenization temperatures between 143–228 °C and salinities from 0.71–7.86 wt% NaCl equiv. Stable isotope data show that the metamorphic fluid contribution is minimal and that ore fluids are of magmatic origin, most likely sourced from 120–126 Ma mafic to intermediate dikes. This is consistent with the carbonic nature of the fluid, and the cross-cutting nature of those deposits relative to the host Mesozoic granitoid.Editorial handling: R.J. Goldfarb 相似文献
15.
Well-formed, texturally-early fluid inclusions in garnets from the Archean Pikwitonei granulite domain, Manitoba, Canada,
have been analyzed using microthermometric methods. The mean CO2 homogenization temperature (to liquid) for inclusions in 12 of 13 samples from the Cauchon Lake-Nelson River area is +15.2°
C (n=125, 2σ=8.2° C), corresponding to a CO2 density of 0.82 g/cm3. Inclusions in the remaining sample have somewhat lower CO2 homogenization temperatures (mean=+5.4° C, n=24). The studied inclusions contain an estimated 10 to 20 vol. percent H2O, with minor amounts of other fluid species such as CH4, N2, and/or H2S. The fluid inclusions were probably trapped during early garnet growth at relatively low pressures (≤5 kbar if at 750° C),
and appear to have undergone only limited or possibly no subsequent re-equilibration. This interpretation is consistent with
the “anti-clock-wise” P-T-t path (heating before loading) determined for the Pikwitonei region by other workers. For such a prograde path, inclusions
entrapped early, at high temperatures but at relatively low pressures, would experience internal underpressures during most
of the subsequent prograde and retrograde phases of metamorphism. The texturally-early fluid inclusions in garnets from the
Pikwitonei region therefore cannot be used to provide direct information about the highest metamorphic temperature and pressure conditions (750° C and 7 kbar). However, the results obtained in this study suggest that texturally-early fluid
inclusions in garnets may, in some cases, retain evidence of the prograde metamorphic path. 相似文献
16.
Evandro Luiz Klein Reginaldo Alves dos Santos Kazuo Fuzikawa Rômulo Simões Angélica 《Mineralium Deposita》2001,36(2):149-164
Fluid inclusion and structural studies were carried out at the Guarim gold deposit in the Palaeoproterozoic Tapajós province
of the Amazonian craton. Guarim is a fault-hosted gold deposit cutting basement granitoids. It consists of a quartz vein,
which is massive in its inner portions, grading laterally either to a massive or to cavity-bearing quartz vein associated
with hydrothermal breccias. The wallrock alteration comprises chlorite, carbonate, white mica and sulphide minerals, with
free gold occurring within quartz grains and spatially associated with sulphide mineral grains. Petrographic, microthermometric
and Laser Raman investigations recognised CO2-rich, mixed H2O–CO2, and H2O fluid inclusions. The coexisting CO2 and H2O–CO2 inclusions were interpreted as primary immiscible fluids that formed the gold-bearing vein. The H2O inclusions were considered a product of later infiltration of fluids unrelated to the mineralising episode. The mineralising
fluid has CO2 ranging typically from 5–10 mol%, contains traces of N2, has salinities of ∼5 wt% NaCl equiv., and densities varying between 0.85 and 0.95 g/cm3. The P–T estimations bracket gold deposition between 270–320 °C and 0.86–2.9 kb; ƒO2–ƒS2–pH estimates suggest a reduced, near-neutral character for the fluid. Variations in the physico-chemical properties, as demonstrated
by the fluid inclusion study, resulted from a combination of fluid immiscibility and pressure fluctuation. This interpretation,
combined with textural and structural evidence, suggests the emplacement of the mineralised vein in an active fault and at
a rather shallow level (4–7 km). The geological and structural setting, deposit-scale textures and structures, wallrock alteration
and physico-chemical fluid properties are compatible with those of epizonal to mesozonal orogenic lode gold deposits.
Received: 3 March 2000 / Accepted: 21 October 2000 相似文献
17.
“Extreme boiling” model for variable salinity of the Hokko low-sulfidation epithermal Au prospect, southwestern Hokkaido, Japan 总被引:1,自引:0,他引:1
The Hokko prospect is located in the Minamikayabe area southwestern Hokkaido, Japan, where gold-bearing quartz veins of Pliocene
age are exposed at the surface. The alteration mineral assemblage is typical of low-sulfidation epithermal systems, with the
quartz veins associated with adularia alteration overprinted on Late Miocene propylitic alteration. Fluid inclusion studies
of the vein quartz reveal mean homogenization temperatures of approximately 220 °C, and the co-existence of low-salinity (<2
wt.% NaCl equivalent) and moderate salinity (2 to 12 wt.% NaCl equivalent) fluid inclusions within the same veins. The moderate
salinity fluid inclusions (2–12 wt.% NaCl equivalent) typically have relatively low homogenization temperatures between 150°
to 200 °C. The results obtained from stable isotope analysis of δ18O in quartz vein material showed a gradual decrease in δ18O signatures with increasing depth. The majority of the samples have calculated fluid source signatures (δ18OH2O) between −8.0 and −10.0‰, but there is a significant change in the composition above 185 m drill depth. The shallower samples
in particular show a wide range of oxygen isotope signatures that are associated with the moderate salinity fluid inclusions.
We interpret that low-salinity inclusions within the Hokko system represent the composition of the liquid phase of the fluid,
before boiling, and that the moderate-salinity inclusions are representative of the residual liquid phase, after extensive
non-adiabatic boiling and vapor loss in an open system. This mechanism resulted in the entrapment of fluids with variable
salinities at the same time, and in close proximity to each other. This is also reflected in the δ18OH2O values which become more variable and heavier where the moderate-salinity inclusions occur. Deposition of ore minerals within
the Hokko vein system also occurred at this time as a result of boiling and gas loss.
Received: 30 May 1997 / Accepted: 6 January 1998 相似文献
18.
The Jinman Cu deposit is hosted in sandstones and slates of the Jurassic Huakaizuo Formation in the Mesozoic to Cenozoic Lanping
basin in western Yunnan, China. Despite the fact that Cu mineralization occurs mainly in quartz–carbonate veins controlled
by faults and fractures, the Jinman deposit was classified as a sediment-hosted stratiform Cu deposit, mainly because it is
hosted in a sedimentary basin characterized by abundant red beds with many stratiform Cu deposits. A detailed petrographic
and microthermometric study of fluid inclusions from the Jinman deposit reveals the presence of abundant CO2-rich fluid inclusions, together with aqueous inclusions. The CO2-rich inclusions have CO2 melting temperatures mainly from −58.0°C to −56.6°C, homogenization temperatures of the carbonic phase (mostly into the liquid
phase) mainly between 22°C and 30°C, clathrate melting temperatures from 1.8°C to 9.2°C, with corresponding salinities from
1.6 to 13.4 wt.% NaCl equivalent, and total homogenization temperatures from 226°C to 330°C. The aqueous inclusions have first
melting temperatures from −60°C to −52°C, ice melting temperatures from −41.4°C to −2.3°C, with salinities from 3.9 to 29.0 wt.%
NaCl equivalent, and total homogenization temperatures mainly from 140°C to 250°C. These fluid inclusion characteristics are
comparable to those of orogenic or magmatic mineralization systems and are uncharacteristic of basinal mineralization systems,
suggesting that it is inappropriate to classify the Jinman deposit as a sediment-hosted stratiform Cu deposit. The results
of this study, together with geochemical data reported previously, suggest that the Jinman deposit formed in a hydrothermal
system that involved both extra-basinal, deeply sourced CO2-rich fluid and basinal, aqueous fluid. 相似文献
19.
Ni Shijun Luo Yutian Liu Lihua Wang Xuben Li Sue Luo Yangdi Han Dingrong 《中国地球化学学报》1994,13(3):193-201
This study focuses on the thermodynamics of diagenetic fluid from the Eogene Xingouzui Formation which represents the most
important reservoir in Field Oil T in the Jianghan Basin. The measured homogenization temperatures (110–139 °C) of fluid inclusions
in diagenetic minerals fell within the range of 67 –155 °C at the middle diagenetic stage. The pressure of diagenetic fluid
is estimated at 10.2 –56 MPa. The activity of ions in the fluid shows a tendency of Ca2+ > Mg2+ > Na+ > K+ > Fe3+ > Fe2+ for cations, and HCO
3
−
> SO
4
2−
> F− > Cl− > CO
3
2−
for anions. For the gaseous facies, there is a tendency of CO2> CO> H2S> CH4> H2. According to the thermodynamic calculations, the pH and Eh of the fluid are 5.86–6.47 and −0.73–−0.64V, respectively. As
a result of the interaction between such a diagenetic fluid and minerals in the sediments, feldspars were dissolved or alterated
by other minerals. The clay mineral kaolinite was instable and hence was replaced by illite and chloritoid.
This project was jointly funded by the National Natural Science Foundation of China (49133080) and the Open Laboratory of
Ore Deposit Geochemistry, Institute of Geochemistry, Chinese Academy of Sciences. 相似文献
20.
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