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Russian Geology and Geophysics

2011 year, number 11

1.
MELTS AND FLUIDS IN NATURAL MINERAL AND ORE FORMATION: MODERN STUDIES OF FLUID AND MELT INCLUSIONS IN MINERALS

S.Z. Smirnova, b, V.V. Sharygina, Cs. Szaboc
aV.S. Sobolev Institute of Geology and Mineralogy, Siberian Branch of the Russian Academy of Sciences, pr. Akademika Koptyuga 3, Novosibirsk, 630090, Russia
bNovosibirsk State University, ul. Pirogova 2, Novosibirsk, 630090, Russia
3Lithosphere fluid Reseorch Lab, Department of Petrology and Ceochemistry, Eötvös University, Pãrmãny Péter sétány 1/C, H-1117 Budapest, Hungary
Pages: 1283-1285



2.
THE PHASE COMPOSITION OF CRYSTAL-FLUID NanoINCLUSIONS IN ALLUVIAL DIAMONDS IN THE NORTHEASTERN SIBERIAN PLATFORM

A.M. Logvinovaa, R. Wirthb, A.A. Tomilenkoa, V.P. Afanas'eva, and N.V. Soboleva
aV.S. Sobolev Institute of Geology and Mineralogy, Siberian Branch of the Russian Academy of Sciences, pr. Akademika Koptyuga 3, Novosibirsk, 630090, Russia
bGFZ, German Research Centre for Geosciences, Chemistry and Physics of Earth Materials, Telegrafenberg, C-120, D-14473 Potsdam, Germany
Keywords: Diamond, nanoinclusions, fluid, carbonates, spinel, clinohumites, subduction
Pages: 1286-1297

Abstract >>
The phase composition of crystal-fluid nanoinclusions in two types of placer diamonds of unknown genesis from the northeastern Siberian Platform (Ebelyakh diamondiferous region) has been first studied by transmission electron microscopy including electron diffraction, analytical electron microscopy (AEM), electron energy loss spectroscopy (EELS), and chromatography. The type I diamonds are transparent dodecahedroids, and the type II ones, widespread in this region, are dark rounded crystals assigned to variety V according to Orlov's mineralogical classification. Isotopic and IR-Fourie spectroscopic studies showed that the type II diamonds have a strongly light carbon isotope composition (δ13Cav = -22.4 ) and high concentrations of nitrogen admixture (1100-1800 ppm). Nitrogen is present mainly as an aggregate. It is shown that all inclusions no larger than 400 nm are polyphase particles consisting of solid (silicate, oxide, carbonate, salt) and fluid phases. The type I diamonds bear high-Mg carbonatite inclusions (up to 100 nm) consisting of magnesite, dolomite, Fe-spinel, and clinohumite. The fluid phase has high concentrations of K, Cl, and O. The inclusions are similar in composition to the near-solidus melts of saturated carbonatized peridotites; thus, they might have resulted either from the crystallization of the parental melt or from the quenching and crystallization of deep-seated carbonate-silicate melt. The type II diamonds bear low-Mg carbonatite polyphase nanoinclusions consisting of Ba-, Sr-, and Ca,Fe-carbonatites, K,Ba-phosphates, Ti,Si- and Ti,Al-phases, and abundant fluid segregations filled mainly with CO2, N, and hydrocarbons. These melts/solutions might have been supplied from subducted rocks of the oceanic and, partly, continental Earth's crust. The enrichment of these inclusions in incompatible elements might evidence the percolation of salt fluids enriched in Ba, Sr, P, Ti, K, and Cl through carbonatized eclogites.



3.
FIBROUS DIAMONDS FROM THE PLACERS OF THE NORTHEAST SIBERIAN CRATON: CARBONATE AND SILICATE CRYSTALLIZATION MEDIA

D.A. Zedgenizova, A.L. Ragozina, V.S. Shatskya,b, D. Araujoc, and W.L. Griffinc
aV.S. Sobolev Institute of Geology and Mineralogy, Siberian Branch of the Russian Academy of Sciences, pr. Akademika Koptyuga 3, Novosibirsk, 630090, Russia
bNovosibirsk State University, ul. Pirogova 2, Novosibirsk, 630090, Russia
cARC National Key Centre for GEMOC, Macquarie University, NSW 2113, Australia
Keywords: Diamond, microinclusions, fluid, melt, carbon isotope composition
Pages: 1298-1309

Abstract >>
The first data are presented on the composition of microinclusions in fibrous diamonds from the Ebelyakh placers, northeastern Siberian Platform. Their fluid / melt microinclusions are of silicate or carbonate composition. In general, the trace-element patterns for the microinclusions correspond to kimberlites and carbonatites. The major-element composition differs significantly; for example, the microinclusons are considerably enriched in K and Na. In two of the studied diamonds, the microinclusion composition differs considerably in the cores and rims. In one of them, the composition of the medium changes from chloride-carbonate to predominantly carbonate (sample HI-90); in the other one, from carbonate to silicate (sample HI-98). Similar carbon isotope characteristics of diamonds with microinclusions of two contrasting media suggest their crystallization from a mantle reservoir with the same carbon isotope characteristics. The geochemical features of the microinclusions in the placer diamonds revealed their relationship with protokimberlitic carbonate-silicate fluids. Such fluids might result from the metasomatic interaction of volatiles and/or the low-degree partial melting of peridotite and eclogite substrates.



4.
THE PHASE STATE OF NAF-CONTAINING FLUID AT 700?C AND 1, 2, AND 3 kbar ( from the results of study of synthetic fluid inclusions in quartz )

Z.A. Kotel'nikovaa and A.R. Kotel'nikovb
aInstitute of Geology of Ore Deposits, Petrography, Mineralogy and Geochemistry, Russian Academy of Sciences, Staromonetnyi per. 35, Moscow, 119017, Russia
bInstitute of Experimental Mineralogy, Russian Academy of Sciences, Chernogolovka, Noginsk District, Moscow Region, 142432, Russia
Keywords: Synthetic fluid inclusions, liquid immiscibility, heterogenization, phase diagrams
Pages: 1310-1318

Abstract >>
Fluid inclusions containing NaF have been extracted by healing quartz cracks at 700?C and 1, 2, and 3 kbar. The aqueous NaF solutions belong to P-Q -type systems. They are characterized by the existence of two stable and one metastable immiscibility regions. Study of the inclusions showed that under these conditions, the fluid was in the heterogeneous state. The least dense phase detected in two-phase inclusions with the largest vapor bubble is an undersaturated aqueous solution. Its salt content points to a chemical interaction of NaF with quartz, which led to a change in the component composition of the system. As temperature grows, the highly viscous liquid of the inclusions is separated into layers, and a new phase appears either around the vapor bubble or near the inclusion walls. At 3 kbar, one more type of inclusions with a vitreous phase forms, which shows anomalous behavior on heating. The phase changes in these inclusions can be interpreted only tentatively. Based on the data obtained, we suggest the existence of quasi-polymer compounds containing sodium hydrosilicates, in which OH- groups are partly substituted by F-. The results obtained are applied to study of natural processes involving fluids belonging to the P-Q -type systems.



5.
GENESIS OF SCAPOLITE FROM GRANULITES ( lower-crustal xenoliths from the Pamir diatremes ): RESULTS OF STUDY OF MELT INCLUSIONS

I.A. Madyukova, V.P. Chupina,b, and D.V. Kuz'mina,c
aV.S. Sobolev Institute of Geology and Mineralogy, Siberian Branch of the Russian Academy of Sciences, pr. Akademika Koptyuga 3, Novosibirsk, 630090, Russia
bNovosibirsk State University, ul. Pirogova 2, Novosibirsk, 630090, Russia
cMax Planck Institut fur Chemie, 27 Joh.-Joachim-Becher-Weg, Mainz, 55128, Germany
Keywords: Scapolite, granulite xenolith, melt inclusions, incongruent melting, lower crust, Pamir
Pages: 1319-1333

Abstract >>
The results of mineralogical and thermobarogeochemical studies of lower-crustal xenolith of scapolite-bearing granulites from the fergusite-porphyry diatremes in Southeastern Pamir (Tajikistan) are presented. All minerals (including garnet, clinopyroxene, and scapolite) of these granulites contain primary melt inclusions, which were studied using thermometric and microprobe methods (EPMA, SIMS, Raman spectroscopy). We have established that their compositions correspond to acid (from rhyodacites to rhyolites), essentially potassic melts of normal and high alkalinity with H2O ≤ 4 wt.%, Cl ≤ 0.8 wt.%, and CO2 ~ 1 wt.%. The melts are depleted in HREE and have high Th/U ratios (7.7-9.4). Study of melt inclusions using mineralogical thermobarometers showed that the scapolite-bearing granulite crystallized at ~1000?C and ~15 kbar. This rock resulted, most likely, from the incongruent melting of carbonate-bearing biotite-quartz-plagioclase substrate in the lower crust, which was accompanied by the crystallization of garnet, clinopyroxene, sphene, plagioclase, and scapolite trapping microportions of acid melts as inclusions. The minerals crystallized not from melt but in its presence. High-Ca scapolite (Me67-69) crystallized instead of plagioclase when the melts reached high contents of CO2 (~1 wt.%) and Cl (≤0.8 wt.%) in the presence of CO2-rich fluid.



6.
RHÖNITE IN ALKALI BASALTS: SILICATE MELT INCLUSIONS IN OLIVINE PHENOCRYSTS

V.V. Sharygina, K. Kóthayb, Cs. Szabób, T.Ju. Timinaa, K. Törökb,c, Ye. Vapnikd, and D.V. Kuz'mina,e
aV.S. Sobolev Institute of Geology and Mineralogy, Siberian Branch of the Russian Academy of Sciences, pr. Akademika Koptyuga 3, Novosibirsk, 630090, Russia
bLithosphere Fluid Research Lab, Department of Petrology and Geochemistry, Eötvös University, Pázmány Péter sétány 1/C, H-1117 Budapest, Hungary
cResearch Group for Environmental Physics and Geophysics of the Hungarian Academy of Sciences, Department of Geophysics, Eötvös University, Pázmány Péter sétány 1/C, H-1117 Budapest, Hungary
dDepartment of Geological and Environmental Sciences, Ben-Gurion University of the Negev, P.O. Box 653, 84105 Beer-Sheva, Israel
eGeochemistry Division, Max Planck Institute fur Chemie, Joh.-Joachim-Becher-Weg 27, Mainz, 55128, Germany
Keywords: Rhönite, cinopyroxene, spinel, silicate melt inclusions, olivine phenocryst, alkali basalts
Pages: 1334-1352

Abstract >>
Silicate melt inclusions containing rhonite Ca2 (Mg,Fe2+)4Fe3+Ti[Al3Si3O20] were studied in olivine phenocrysts from alkali basalts of six different volcanic regions: Udokan Plateau, North Minusa Depression, Tsagan-Khurtei Ridge (Russia), Bakony-Balaton Highland, Nógrád-Gömör Region (Hungary), and Makhtesh Ramon (Israel). Rhonite-bearing silicate melt inclusions are relatively common phenomena in alkali basalts and usually coexist with inclusions lacking rhönite. Inclusions with rhönite generally occur in the core of the olivine phenocrysts. According to heating experiments and CO2 microthermometry, all the rhönite-bearing inclusions in core of the olivine phenocrysts were trapped as silicate melt at T > 1300?C and P > 3-5 kbar. Rhönite crystallized in a narrow temperature range (1180-1260?) and P < 0.5 kbar. The petrography and thermometry of rhönite-bearing silicate melt inclusions show a general crystallization sequence: Al-spinel → rhönite → clinopyroxene → apatite → ± amphibole, Fe-Ti oxide (ilmenite or Ti-magnetite) → glass.
The majority of rhonites from melt inclusions have Mg/(Mg + Fe2+)>0.5 and belong to Mg-rich species Ca2Mg4Fe3+Ti[Al3Si3O20]. There are no significant differences in chemistry among rhönites from olivine-hosted silicate melt inclusions from phenocryst, from groundmass of alkali basalts, and from alteration products of kaersutitic amphibole mega/xenocrysts and of kaersutite in deep-seated xenoliths in alkali basalts. The rare occurrence of rhönite as essential constituents in rocks may be explained from its microstructural peculiarities. This mineral is an intermediate member of the polysomatic spinel-pyroxene series. Possibly, the structural feature of rhönite does explain why it is an unstable mineral under changing crystallization conditions. In general, the presence and chemistry of rhonite can be used for the rough estimation of temperature, pressure, and oxygen fugacity during the crystallization of alkali basalts.



7.
H2O AND CO2 IN PARENTAL MAGMAS OF VOLCANO KLIUCHEVSKOI ( inferred from study of melt and fluid inclusions in olivine )

N.L. Mironova and M.V. Portnyagina,b
aV.I. Vernadsky Institute of Geochemistry and Analytical Chemistry (GEOKHI), Russian Academy of Sciences, ul. Kosygina 19, Moscow, 119991, Russia
bLeibniz Institute of Marine Research, IFM-GEOMAR, Wischhofstrasse 1-3, 24148 Kiel, Germany
Keywords: Melt and fluid inclusions in olivine, parental magmas, H2O, CO2, Volcano Kliuchevskoi, Kamchatka
Pages: 1353-1367



8.
RHYOLITIC MELTS IN EASTERN TRANSBAIKALIA AND THE NORTH CAUCASUS: CHEMICAL COMPOSITION, VOLATILES, AND ADMIXTURE ELEMENTS ( from data of study of melt inclusions in minerals )

V.B. Naumov
V.I. Vernadsky Institute of Geochemistry and Analytical Chemistry, ul. Kosygina 19, Moscow, 119991, Russia
Keywords: Melt inclusions, volatiles, admixture elements, eastern Transbaikalia, North Caucasus
Pages: 1368-1377

Abstract >>
We studied melt inclusions in quartz phenocrysts from Late Jurassic rhyolites in eastern Transbaikalia (Strel'tsov caldera) and in quartz, apatite, and plagioclase phenocrysts from rhyolites in the North Caucasus (Northern Ossetia and Tyrnyauz region). More than 15 uranium deposits and ore occurrences are known in the Strel'tsov caldera, as well as Pb-Zn deposits in Northern Ossetia and the largest Mo-W deposit in the Tyrnyauz region. For the studies we used the inclusion homogenization methods and performed electron and ion microprobe analyses of glasses from more than 30 inclusions. The temperatures of the total homogenization of melt inclusions are shown to depend directly on the initial melting points of their glasses, which might be due to the different contents of volatiles (first of all, water). The experiments on determining the time required for the homogenization and heterogenization of melt inclusions showed that the melts in the inclusions are of different viscosity and homogenize at different temperatures. The rhyolitic melts from eastern Transbaikalia and the Northern Caucasus have similar contents of rock-forming elements (average, wt.%): 75.0 and 74.6 SiO2, 0.08 and 0.05 TiO2, 11.0 and 12.3 Al2O3, 0.74 and 0.40 FeO, 0.04 and 0.05 MgO, 0.29 and 0.64 CaO, 4.09 and 3.79 Na2O, and 4.30 and 4.24 K2O, respectively. But these melts differ significantly in the contents of Cl (on average, 0.20 and 0.08 wt.%, respectively), F (1.07 and 0.09 wt.%), and some admixture elements. The melts from the first region are much richer in Zr, Nb, La, Ce, Th, and U but poorer in Sr, Ba, and Eu than the melts from the second region, which evidences their deeper differentiation. The revealed high contents of Th and U in the melts from the Strel'tsov caldera agree with the literature data of the French geologists on the same caldera.



9.
ONGONITE-ELVAN MAGMAS OF THE KALGUTY ORE-MAGMATIC SYSTEM ( Gorny Altai ): COMPOSITION, FLUID REGIME, AND GENESIS

E.N. Sokolovaa,b, S.Z. Smirnova,b, E.I. Astrelinab, I.Yu. Annikovaa, A.G. Vladimirova,b,c, and P.D. Kotlerb
aV.S. Sobolev Institute of Geology and Mineralogy, Siberian Branch of the Russian Academy of Sciences, pr. Akademika Koptyuga 3, Novosibirsk, 630090, Russia
bNovosibirsk State University, ul. Pirogova 2, Novosibirsk, 630090, Russia
cTomsk State University, pr. Lenina 36, Tomsk, 634050, Russia
Keywords: Ongonites, elvans, rare-metal granites, melt inclusions, fluid inclusions, Kalguty deposit
Pages: 1378-1400

Abstract >>
The Kalguty ore-magmatic system (OMS) is a complex combination of a granite pluton, a hydrothermal Mo-W deposit, pegmatites, greisens, and a belt of rare-metal (RM) and ultrarare-metal (URM) elvan and ongonite dikes.
Studies of melt inclusions (MI) in quartz phenocrysts in the dike rocks have demonstrated that quenched glass has major-element contents close to those of the dike rocks but lower rare-element (Li, Rb, Be, Cs) and P contents. This suggests that the MI represent magma at the stage preceding the dike emplacement. The MI in quartz from the URM rocks are poorer in Si, Fe, Mg, and REE than those in quartz from the RM rocks but richer in Cs, Rb, Nb, and Ta, like the URM rocks themselves. This indicates that the melts had segregated into RM and URM ones before the studied quartz phenocrysts began to crystallize. The composition of MI glass corresponds to "the albite trend" of differentiation, suggesting that the initial melt compositions were ongonitic, while their K enrichment and formation of elvan magma followed the crystallization of the quartz phenocrysts.
According to our estimates, the melt contained 6-7 wt.% H2O. The quartz phenocrysts crystallized in a heterogeneous medium consisting of a silicate melt and an aqueous fluid. The latter was a high-density supercritical fluid with 3-12 wt.% NaCl equiv. Variations in the gas and salt compositions of the fluid inclusions (FI) are attributed to the interaction between fluids of magmatic and hydrothermal systems. This possibility is confirmed by ample evidence for their coeval formation.
Quartz crystallization from the RM melts took place at 630-650 C, whereas quartz from the URM melts formed at 20-30 C lower temperatures. Quartz phenocrysts crystallized at 4.5-5.5 kbar. Additional estimates with regard to the mineral composition and quartz compressibility yielded values of 3-6.5 kbar.
A petrogenetic model of some crystallization stages of the dike rocks within the Kalguty OMS was constructed on the basis of the results obtained in this study. The melts which formed the dikes of the East Kalguty belt are derivates of the same magma which formed the major-stage granite pluton. Quartz is present as intratelluric phenocrysts, which crystallized at considerably greater depths than those of the dike emplacement. Differentiation of the parental magma was accompanied by rare element and P accumulation. The compositions of the FI and MI confirm that the magma and hydrothermal system of the Kalguty OMS exchanged their substances. It is associated with the increasing K content of the melts and the subsequent elvan crystallization as well as considerable variations in the salt and gas compositions of the magmatic fluid inclusions



10.
Rb-Sr ISOTOPIC SYSTEM AND Rb AND Sr PARTITIONING IN THE ROCKS OF THE ARY-BULAK ONGONITE MASSIF, FORMED WITH THE PARTICIPATION OF FLUORIDE-SILICATE MAGMATIC IMMISCIBILITY

I.S. Peretyazhko, E.A. Savina, S.I. Dril', and N.S. Gerasimov
A.P. Vinogradov Institute of Geochemistry, Siberian Branch of the Russian Academy of Sciences, ul. Favorskogo 1a, Irkutsk, 664033, Russia
Keywords: Rb, Sr, Rb-Sr isotope system, porphyritic ongonite, aphyric rock, melt inclusions, immiscible fluoride and silicate melts
Pages: 1401-1411

Abstract >>
The rocks of the Ary-Bulak ongonite massif (eastern Transbaikalia) have widely varying Rb (1499-4274 ppm) and Sr (10-2654 ppm) contents. In passing from porphyritic ongonites to aphyric rocks at the endocontact, the Rb content increases two to three times, and the Sr content, by two to three orders of magnitude. Feldspars and Fe-rich micas are the major Rb carriers and concentrators. The aphyric rocks accumulate Rb, because the weight percentage of sanidine in their total mineral balance increases relative to that in the porphyritic ongonites. In the latter, Sr is relatively uniformly distributed over the phenocrysts and groundmass. Prosopite and products of the quenching (glasses) and partial crystallization of a calcium fluoride melt accumulate a considerable amount of Sr. The presence of these phases in the porphyritic and aphyric rocks abnormally increases their Sr content. The Rb content of silicate glass in melt inclusions (MI) varies much more widely (634 ppm-3.17 wt.%) than that of the massif rocks (1435-4309 ppm), especially in terms of the maximum value. Most of silicate glass in the MI is much poorer in Sr (<1-2 ppm) than the rocks. The highest Sr content (376-422 ppm) was detected in silicate glass from an MI with segregations of immiscible fluoride glass.
Rubidium-strontium isotope dating confirmed the Early Cretaceous (141.6 ± 0.5 Ma) age of all the massif rocks, with (87Sr/86Sr)0 = 0.70817 ± 0.00025, i.e., intermediate between mantle and typical crustal values. A near-linear dependence has been detected between 1/Sr and 87Sr/86Sr, which is usually interpreted as a false isochron and explained by models involving mixed components with different 87Sr/86Sr. According to calculations of the weight percentage of Sr isotopes in the massif rocks, this linear dependence is explained by Sr and Rb partitioning in ongonitic magma, which has the same initial Sr isotope ratio.
Only fluoride-silicate liquid immiscibility determined the Rb and Sr partitioning in the ongonitic magma and, correspondingly, the subsequent evolution of the Rb-Sr isotopic system in the Ary-Bulak massif rocks. This immiscibility (liquation) in the ongonitic magma might have created very special rocks abnormally enriched in Ca, F, and Sr, even if the initial homogeneous silicate melt was relatively poor in these elements. The relatively low initial isotope ratio (87Sr/86Sr)0 ≈ 0.708 in the massif rocks does not contradict the hypothesis of the intense heating of a F-enriched crustal substrate and the formation of a rare-metal granitoid melt chamber (from which the residual ongonitic melt was produced) under the thermal effect of deep-seated basaltoid magma.



11.
THE PHYSICOCHEMICAL CONDITIONS OF HYDROTHERMAL ORE-FORMING SYSTEMS OF "BLACK SMOKERS" ASSOCIATED WITH MANTLE ULTRABASITES IN THE CENTRAL ATLANTIC REGION

N.S. Bortnikova, V.A. Simonovb, E.E. Amplievaa, O.O. Stavrovaa, and Y. Fouquetc
aInstitute of Geology of Ore Deposits, Petrography, Mineralogy and Geochemistry, Russian Academy of Sciences, Staromonetnyi per. 35, Moscow, 119017, Russia
bV.S. Sobolev Institute of Geology and Mineralogy, Siberian Branch of the Russian Academy of Sciences, pr. Akademika Koptyuga 3, Novosibirsk, 630090, Russia
cIFREMER, GM, BP70, Plouzane, 29280 France
Keywords: Physicochemical conditions, "black smokers", hydrothermal fields, fluid inclusions, Mid-Atlantic Ridge
Pages: 1412-1420

Abstract >>
Study of fluid inclusions in minerals from sulfide ores sampled in the Ashadze and Logatchev hydrothermal fields during the Serpentine cruise of the R/V Pourquoi Pas? in 2007 gave an insight into the physicochemical conditions of ore-forming systems of "black smokers" associated with mantle ultrabasites in the Central Atlantic region. It was established that the studied hydrothermal systems differ in mineral formation temperatures, fluid salinity, and hydrothermal processes running within basaltic complexes in both low-spreading (Mid-Atlantic Ridge) and high-spreading (East Pacific Rise) mid-ocean ridges. It was shown for the Ashadze and Logatchev hydrothermal fields that the temperatures and salinity of inclusion solutions in the minerals vary over a wider range of values than those of fluids flowing out from the ridge vents onto the ocean floor. Study of fluid inclusions showed that the Ashadze and Logatchev sulfide buildings resulted from the action of both high-temperature (up to 355?C) and low-temperature (no lower than 170?C) solutions. The salinity of fluid in the inclusions (mainly 8 wt.%) is more than twice as high as the salinity of seawater. The data obtained substantiate the phase separation of fluid in the deepest-water submarine hydrothermal Ashadze system and give an idea of the chemical composition and temperature of fluids forming sulfide deposits in the Ashadze and Logatchev hydrothermal fields in the Central Atlantic region.



12.
A FLUID INCLUSION STUDY OF URANIUM AND COPPER MINERAL SYSTEMS IN THE MURPHY INLIER ( Northern Australia )

T.P. Mernagha and A.S. Wygralakb
aGeoscience Australia, GPO Box 378, Canberra, ACT 2601, Australia
bNorthern Territory Geological Survey, GPO Box 2901, Darwin, NT 0801, Australia
Keywords: Fluid inclusions, uranium and copper deposits, northern Australia
Pages: 1421-1435

Abstract >>
The Palaeoproterozoic Murphy Inlier is situated at the southern end of the McArthur Basin in northern Australia. The inlier contains over 50 uranium, copper, tin, and base metal occurrences. Fluid inclusion studies were carried out on samples of quartz veining from the uranium and copper deposits as well as from the basement rocks to determine the composition of the fluids and to investigate how uranium and copper were transported in these fluids. Four types of fluid inclusions were observed in this study: Type A - vapor-rich inclusions with ≥ 30 vol.% vapor, Type B - two-phase aqueous inclusions with ≤ 20 vol.% vapor, Type C - multiphase inclusions with one or more solid phases, and Type D - liquid-only inclusions.
At least three different fluids were identified in the Murphy Inlier. There is a CaCl2 ± LiCl-rich brine, a NaCl-rich brine, and a low-salinity fluid. The fluids can also be grouped into a high-temperature (typically homogenizing above 210 C) population and a low-temperature (typically homogenizing below 240 C) population. Depending on location, the high-temperature fluid may be enriched in CO2, N2, or CH4. In the uranium deposits, gas-rich inclusions are dominated by CO2 indicating that these fluids are relatively oxidized, while in the copper deposits both CO2 and CH4 are present, indicating that these fluids are more reduced. The low-temperature population of Type B inclusions has a mode of homogenization at 190 C in the uranium deposits and a mode at 120 C in the copper deposits. Similarly, Type C inclusions have a mode of homogenization at 235 C in the uranium deposits and 170 C in the copper deposits.
Variations in the composition of the inclusions suggest that at least two stages of fluid mixing occurred. Firstly, there was mixing between a CaCl2 ± LiCl-rich brine and a NaCl-rich brine to produce a fluid of intermediate composition. This fluid then mixed with a low-salinity fluid. Geochemical modeling has shown that both uranium and copper can be transported in the same fluid at high ? O 2 and moderate to high-chloride concentrations. In the proposed model for mineralization, uranium and copper were leached from the volcanics or sediments in the McArthur Basin and were simultaneously transported in the oxidized, Na-Ca-Li-bearing saline fluids which had undergone mixing within the basin. Uranium precipitated when this fluid was reduced, either by reaction with Fe-rich mafic volcanics, carbonaceous rocks, or by mixing with a CH4-bearing low-salinity fluid derived from the basement. Copper remained in the fluid until further changes in salinity, ? O 2, or pH occurred, most probably as a result of mixing with lower-salinity meteoric fluids. The fluid may have continued to cool to near-surface temperatures, as evidenced by the trapping of liquid-only fluid inclusions in some veins.



13.
HETEROGENEITY IN FLUID CHARACTERISTICS IN THE RAMAGIRI-PENAKACHERLA SECTOR OF THE EASTERN DHARWAR CRATON: IMPLICATIONS TO GOLD METALLOGENY

S. Bhattacharya and M.K. Panigrahi
Department of Geology and Geophysics, Indian Institute of Technology, Kharagpur, 721302, India
Keywords: Aqueous-carbonic fluid, thermobarometry, Raman spectroscopy, methane, graphite, granite
Pages: 1436-1447

Abstract >>
The auriferous Penakacherla-Ramagiri schist belt is a part of the granite-greenstone terrain of the Eastern Dharwar Craton. It is surrounded by gneissose basement and has a close spatial association with the younger granitoid units. Fluid inclusion assemblages studied from quartz veins in schists, quartz veins in granites and matrix quartz in granite indicate heterogeneity in fluid characteristics with methane-poor aqueous-carbonic, methane-rich carbonic, low-salinity aqueous, and high-salinity aqueous fluids. Coexisting aqueous and carbonic inclusions do not seem to be the product of phase separation of a parent aqueous-carbonic fluid on all instances. This is corroborated by the fact that the pure carbonic fluid is richer in methane than the carbonic component of the aqueous-carbonic inclusions. This warrants a separate source of carbonic fluid during deposition of the gold-quartz ± sulfide veins. A high-salinity component in the fluid in the schist belt is unlikely to be contributed by metamorphism of the host volcanic units; it is rather comparable to the high-salinity fluid present in the closely associated granites. Thus, it may be surmised that the heterogeneous-fluid characteristics in the auriferous Penakacherla-Ramagiri schist belt raises the possibility of fluid derivation from diverse sources, including the granitoids, rather than from a single metamorphogenic source.



14.
THE FORMATION CONDITIONS AND COMPOSITION OF ORE-FORMING FLUIDS IN THE PROMEZHUTOCHNOE GOLD-SILVER DEPOSIT ( central Chukchi Peninsula, Russia )

A.V. Volkov and V.Yu. Prokof'ev
Institute of Geology of Ore Deposits, Petrography, Mineralogy, and Geochemistry, Russian Academy of Sciences, Staromonetnyi per. 35, Moscow, 109017 Russia
Keywords: Ore-forming fluid, conditions, gold, silver, model, deposit
Pages: 1448-1460

Abstract >>
The Promezhutochnoe and Sil'noe epithermal gold-silver deposits and orebodies of eastern areas of the Sopka Rudnaya deposit have been discovered in the Maiskoe ore cluster, central Chukchi Peninsula, in terrigenous flysch strata of the basements of the Okhotsk-Chukchi volcanic belt. Fluid inclusions in quartz from gold ore veins of Promezhutochnoe have been studied. Similar deposits and occurrences have been found in the terrigenous-sedimentary framing of some intrusion domes in tectonomagmatic zones in the Upper Yana-Kolyma fold belt. Terrigenous strata of similar compositions host the Vysokovol'tnoe and Kosmanychi gold and silver deposits in central Kyzyl Kum and the Balei and Taseevka deposits in Transbaikalia. The richest Hishikari deposit (250 tons of gold, the mean content 60 g/t) in Japan also occurs in terrigenous strata of the basement beneath a volcanic rock cover. However, deposits other than Hishikari, Balei, or Taseevka are small. The causes of this fact are discussed in the context of the geologic structure, chemical composition, and ore formation conditions in the Promezhutochnoe deposit. The main physicochemical parameters of the formation of the ores in this deposit are: temperature 247-194 C, pressure 270-30 bars, and salt concentration 4.3-2.9 wt.% NaCl equiv. The composition of the ore-forming fluids has been studied by gas chromatography, ion exchange chromatography, and inductively coupled plasma mass spectrometry.



15.
THE GERFED GOLD DEPOSIT: FLUIDS AND PT -CONDITIONS FOR QUARTZ VEIN FORMATION ( Yenisei Ridge, Russia )

N.A. Gibshera, A.A. Tomilenkoa, A.M. Sazonovb, M.A. Ryabukhaa, and A.L. Timkinaa
aV.S. Sobolev Institute of Geology and Mineralogy, Siberian Branch of the Russian Academy of Sciences, pr. Akademika Koptyuga 3, Novosibirsk, 630090, Russia
bInstitute of Mining, Geology, and Geotechnology, Siberian Federal University, pr. Svobodnyi 79, Krasnoyarsk, 660041, Russia
Keywords: Fluid inclusions, quartz, gold, rare-earth elements
Pages: 1461-1473

Abstract >>
At the Gerfed gold deposit, fluid inclusions were studied by thermobarometry, gas chromatography, Raman spectroscopy, and ICP MS in quartz samples of three types: quartzites, feathering Au-poor (<1-2 ppm) feathering veins, and Au-rich (>2.8-10 ppm) feathering veins. It has been found that these three types were produced from fluids differing in composition and thermobarogeochemical parameters. The quartzites formed from low-salt (<7.0 wt.% NaCl equiv.) homogeneous fluids of essentially aqueous-chloride composition at 120-230 C and 0.1-0.5 kbar. The gas phase in these fluids comprises H2O, CO2, CH4, and N2, with CO2/(CO2 + H2O) = 0.04-0.15 and CO2/CH4 = 2.2-3.8. The Au-poor feathering veins formed from homogeneous and heterogeneous fluids at 150-300 C and 0.5-2.0 kbar. The fluid salinity increased to 10 wt.% NaCl equiv. The gas phase in them comprises H2O, CO2, N2, and CH4. Here, CO2/(CO2 + H2O) = 0.09-0.17 and CO2/CH4 = 2.2-2.3. The Au-rich feathering veins formed from heterogeneous and more saline (6.0-23.3 wt.% NaCl equiv.) CO2-H2O fluids at higher temperatures (150-400 C) and pressures (1.1-2.5 kbar). In this fluid CO2/(CO2 + H2O) = 0.18-0.27 and CO2/CH4 = 4.1-20.8. All three quartz types show negative Eu anomalies and a distinct predominance of LREE over HREE. Differently directed trends of REE and Eu/Sm in the quartzites and feathering veins suggest that the fluids were produced from different sources. The fluids of the gold-bearing quartz veins are enriched in K, Li, and Rb, and those of the Au-poor feathering veins, in Sr and Na. The quartzites have low Rb and Sr and similar Na and K contents. Areas with a high and bonanza gold content in feathering-vein stockworks formed when high-temperature saline H2O-CO2 fluids were superposed on Au-poor quartzites and feathering veins.



16.
FLUID INCLUSION AND STABLE C-O ISOTOPE CONSTRAINTS ON THE ORIGIN OF METASOMATIC MAGNESITE DEPOSITS OF THE WESTERN CARPATHIANS, SLOVAKIA

V. Huraia, M. Huraiováb, P. Koderac, W. Prochaskad, A. Vozárováb, and I. Dianiskae
aGeological Institute, Slovak Academy of Sciences, Dúbravská cesta 9, P.O. Box 109, 840 05 Bratislava, Slovakia
bDepartment of Mineralogy and Petrology, Comenius University, 842 15 Bratislava, Slovakia
cDepartment of Economic Geology, Comenius University, 842 15 Bratislava, Slovakia
dInstitut für Geowissenschaften, Montanuniversität Leoben, 8700 Leoben, Austria
eMierová 16, 048 01 Roznsava, Slovakia
Keywords: Fluid inclusions, magnesite deposits, Slovakia
Pages: 1474-1490

Abstract >>
Primary fluid inclusions in metasomatic magnesite deposits hosted in Palaeozoic basement of the Western Carpathians are filled with lowly to moderately saline aqueous solutions, with locally increased CO2 concentrations (up to 34 mol.%). Brine inclusions with up to 42 wt.% dissolved salts are less frequent. The K/Na ratios in the fluid inclusion leachates indicate formation temperatures between 180-310 C in the Gemeric unit and 230-300 C in the Veporic tectonic unit.
Carbon isotopes in metasomatic magnesite and dolomite show a larger spread than oxygen ones. In some deposits, the 18 O values are almost fixed in various generations of the metasomatic Mg-carbonates, while 13 C values vary within several . The C- and O-isotope covariation reflects low concentrations of CO2 (less than several mol. %) in the aqueous fluid precipitating the Mg-carbonates in an open hydrothermal system and high fluid/rock ratios ( w/r > 5). Calculated 18 Ofluid values between 2 and 10 (V-SMOW) indicate isotopic exchange of the carbonate-precipitating fluid with crustal silicate rocks and/or marine carbonates at increased temperatures. Calculated 13 Ofluid values between -5 and 3 are thought to reflect dissolution of the metasomatised carbonate as well as the escape of lighter carbon isotope during the CO2 degassing.
Magnesium-carbonate-precipitating fluids typically contain increased Br concentrations resembling the halite-fractionated residual brines originated by seawater evaporation. However, the extent of the Br enrichment substantially exceeds the buffering capacity of the seawater evaporation and is even greater than that in the spatially associated siderite vein- and replacement-type deposits. Apart fr om the seawater evaporation, superimposed leaching of the organic matter from marine sediments probably played an important role. This mechanism has, however, little effect in open hydrothermal systems. Hence, the mechanism of the additional Br enrichment of the magnesite-forming fluids remains unknown.
The observed stable isotope record is a result of Alpine hydrothermal processes, as evidenced by coarse-grained dolomite with Alpine-type mineral assemblage (rutile, apatite, zircon, muscovite-phengite) identified also in the spatially associated siderite vein- and replacement-type deposits. Another evidence for the Alpine origin is frequently observed primary CO2-rich aqueous inclusions, up to 50 m in diameter, which could not survive the Early Cretaceous Alpine metamorphic overprint, as well as different covariation of stable isotopes in siderite deposits, wh ere larger oxygen isotope fluctuations are accompanied by less extensive carbon isotope fractionation. This indicates different precipitation mechanisms, i.e., CO2-devolatilization in an open system during Mg-metasomatism and devolatilization-absent precipitation of the siderite in a closed system triggered by rising temperature. The associated magnesite and siderite deposits may be consanguineous with respect to the presence of the evaporated seawater component in the ore-forming fluid, but they cannot be coeval because of the different compositions of primary fluid inclusions, hydrologic regimes (open versus closed hydrothermal system), and precipitation mechanisms. The fluid inclusion and stable isotope evidence does not definitely discard genetic models, linking the Mg-metasomatism with infiltration of bitter brines along faults during the Permo-Triassic rifting, but this process must have been entirely obliterated by the Late Alpine (Cretaceous) hydrothermal activity along shear zones formed during Middle-Late Cretaceous transtension-extension of the orogenic wedge. The Permo-Triassic rift-related origin of the magnesite must cope with the problem of complete loss of pristine isotopic signature of the metasomatic Mg-carbonates during the superimposed Alpine hydrothermal activity, contrasting with none or negligible Alpine metamorphic/hydrothermal overprint of the spatially associated Fe-carbonate vein- and replacement-type deposits.



17.
MIGRATION OF IMMISCIBLE HYDROCARBONS RECORDED IN CALCITE-HOSTED FLUID INCLUSIONS, ORDOS BASIN: A CASE STUDY FROM NORTHERN CHINA

Li Rongxia,b, Guzmics Tiborc, Liu Xioajiea,b, and Xie Guanchenga,b
aSchool of Earth Science and Resource, Chang'an University, Xian, 710054, China
bKey Laboratory of West Mineral Resource and Geology Engineering, Education Ministry of China, Chang'an University, Xian, 710054, China
cLithosphere Fluid Research Lab, Institute of Geography & Earth Sciences, Eötvös University Budapest (ELTE), Budapest, Hungary
Keywords: Hydrocarbon inclusion, boiling, oil migration, calcite veinlet, Ordos Basin
Pages: 1491-1503

Abstract >>
In this study one- (hydrocarbon liquid), two- (hydrocarbon liquid and vapor), and three- (hydrocarbon liquid and vapor, and aqueous liquid) phase fluid inclusions have been investigated in calcites occurring in veinlets in fine grained sandstones of Chang 7 source rock and Chang 8 reservoir rock. These rocks are parts of the Upper Triassic Yangchang Formation in the Ordos Basin, Northern China. The hydrocarbon inclusions studied show a high variance in vapor/liquid volume ratio at ambient temperature, suggesting a heterogeneous entrapment of vapor and liquid phases that existed before or during the formation of the calcite. This is supported by homogenization happened into both liquid and vapor phases. Homogenization temperatures range between 70 and 120?C. We assume that this wide range is the result of the heterogeneous entrapment of immiscible liquid and vapor phases rather than the high-temperature (e.g., 120 C) formation of the hydrocarbon inclusions. Therefore, the lower range of homogenization temperatures (around 80 C) seems to be probable for the formation of the hydrocarbon inclusions studied. Fluorescent microscopic results on the hydrocarbon inclusions show a bright yellow color for the oil. Fluorescence spectrum indices show that oil in the inclusions is quite mature, similarly to the oil extract from Chang 7 source rock.  The differences in fluorescent spectra among the hydrocarbon inclusions suggest their chemical modification during evolution, which might be determined by continuous separation of vapor phase (gas condensate) from the system. On the basis of organic geochemistry of the studied samples (e.g., akin distribution of normal alkanes and similar isoprenoid ratios), it can be concluded that the oil in the inclusions and the crude oil from the Chang 8 reservoir rock are actually derived from the Chang 7 source rock.  During the tectonic evolution, the hydrocarbon might undergo phase separation (boiling) yielding two phases (liquid and vapor) owing to the intense uplifting of the Ordos Basin after the Late Cretaceous. The boiling in the accumulated hydrocarbon could have resulted in overpressure in the source rock. This phenomenon might favor the formation of fractures and migration of hydrocarbons from their source toward sandstone reservoirs. Our study demonstrates the significance of detailed analytical investigation of hydrocarbon inclusions in correlation with their potential source rock.