Ratios Of Fluid Inclusions Research Articles

Trace-element compositions and Br/Cl ratios of fluid inclusions in the Tsushima granite, Japan: Significance for formation of granite-derived fluids

Fluid inclusions in quartz samples from a miarolitic cavity, two quartz veins, and a hydrothermal ore vein in the Tsushima granite, Japan, were analyzed by particle-induced X-ray emission to examine the chemistry and process of formation of hydrothermal fluids in an island-arc granite. Most of the inclusions were polyphase or vapor, and there were smaller numbers of two-phase aqueous inclusions. The inclusions contained Cl, K, Ca, Ti, Mn, Fe, Cu, Zn, Ge, Br, Rb, Sr, Ba, and Pb. For each inclusion, there was a strong positive correlation between Cl content and contents of other elements identified. Concentration ranges for most elements (other than Rb and Ge) in polyphase inclusions from the miarolitic cavity were comparable to those from cavities in alkaline granites; those from the ore vein were comparable to large-scale continental hydrothermal ore deposits. The lower Rb and higher Ge contents in the polyphase inclusions of the Tsushima granite may be characteristic of hydrothermal fluids from calc-alkaline granites in an island-arc setting. Br/Cl ratios (by weight) for the vapor and two-phase inclusions were 0.0013–0.0030 and differed among the three geological settings. Br/Cl ratios of polyphase inclusions increased with increasing Cl content in single-crystal and polycrystalline quartz, and high values of more than 0.0100 were found. The high Br/Cl ratios and the differences among the geological settings sampled may be due to pressure dependences of partitioning of Cl and Br between fluid and magma during fluid segregation and between liquid and vapor during boiling. Using a simple model based on these dependences, we calculated Br/Cl ratios greater than 0.01 in brine generated at pressures <0.89kbar. Differences in Br/Cl ratios in polyphase and vapor inclusions from each geological setting were attributed to mixing between two end-member fluids: a high Br/Cl fluid generated at low pressure and a low Br/Cl fluid generated at high pressure. Br/Cl ratios of polyphase inclusions in quartz may be a key for understanding the conditions under which boiling fluids are generated in simple granite systems.

Fluid evolution and ore genesis of the giant Sanshandao gold deposit, Jiaodong gold province, China: Constrains from geology, fluid inclusions and H–O–S–He–Ar isotopic compositions

The Sanshandao gold deposit is located at the northwestern edge of the Jiaodong peninsula, North China Craton. It is mainly hosted in the Mesozoic granitoids. Gold mineralization occurs as disseminated- and stockwork-style ores, typically enveloped by broad alteration selvages. Mineralization and alterations are structurally controlled by the Sanshandao–Cangshang fault. Three paragenetic stages were identified with the early stage represented by quartz±pyrite, the middle stage by gold+quartz+pyrite or gold+quartz+base metal sulfides, and the late stage by quartz+carbonate±pyrite, respectively. Four types of fluid inclusions were distinguished, including (1) pure CO2 fluid inclusions (type I), (2) H2O–CO2–NaCl fluid inclusions (type II), (3) H2O–NaCl fluid inclusions (type III), and (4) daughter mineral-bearing or multiphase fluid inclusions (type IV). The early- and middle-stage quartz mainly contain primary type II fluid inclusions that completely homogenized at temperatures of 241–390°C with salinities of 2.96–18.39wt.% NaCl equivalent, and temperatures of 207–336°C with salinities of 2.06–17.57wt.% NaCl equivalent, respectively. A few primary type I fluid inclusions can be observed in the early-stage quartz, while the middle-stage quartz contains a few primary type I, type III and type IV fluid inclusions. In contrast, the late-stage quartz only contains type III fluid inclusions showing homogenization temperatures of 101–268°C, and salinities of 0.17–15.47wt.% NaCl equivalent. CH4, derived from extensive water–rock interaction between the ore-forming fluids and wall rocks in the main fault, is the key factor controlling the gold mineralization. CH4 changed the physico-chemical conditions of the ore fluids, and led to gold precipitation.Oxygen and hydrogen stable isotopic analyses for quartz from different ore-forming stages show that the ore-forming fluids are of magmatic origin, with gradual incorporation of meteoric water during/after mineralization. δ34S values of pyrite from different ore-forming stages vary between 1.9‰ and 11.9‰. 3He/4He ratios of fluid inclusions in the middle-stage pyrite mainly range from 0.14 to 2.94Ra, while it is from 675.10 to 5926.44 for 40Ar/36Ar. All these isotopic signatures suggest that the ore fluids could be derived from a combination of crustal and mantle components.

A high-resolution fluid inclusion δ18O record from a stalagmite in SW France: modern calibration and comparison with multiple proxies

The δ18O of speleothem fluid inclusions can provide information about local climate and the atmospheric circulation if the fate of oxygen isotopes from precipitation to the stalagmite is well understood. At Villars cave, SW France, the present-day relationship between the δ18O of precipitation and the δ18O of cave drip water has been determined by previous monitoring studies. In this article, we examine the link between drip water and fluid inclusions in speleothems from the same cave, and investigate whether the fossil water in the stalagmites provides a record of the isotopic composition of precipitation.Replicated fluid inclusion isotope measurements (δD and δ18O) from two modern calcite samples, which had precipitated under the monitored stalactites, are in agreement with the corresponding contemporaneous drip waters. The drip water, in turn, represents average pluri-annual precipitation. This gives strong evidence that the isotopic composition of the infiltrating water is preserved in the pores of speleothem calcite, thus providing a record of average precipitation δ18O at the site.Furthermore, we measured isotope ratios in fluid inclusions in the stalagmite vil-stm1, a 2300 year old sample with a high growth rate (up to 0.6 mm yr−1) and a high water content, which allows a high-resolution reconstruction of the drip water isotopic composition covering the last two millennia. The stalagmite is well dated by 13 U–Th ages and the counting of annual growth layers. The fluid inclusion δ18O varies by 2‰, with high δ18O values in Medieval times, and low values during the Little Ice Age, indicating a temperature influence on precipitation δ18O. However, temperature change alone cannot account for the full range of variability observed.Other proxies measured in the same stalagmite indicate that the cave environment has undergone substantial changes during this period: Stable isotopes and trace element concentrations in calcite show large variations, with amplitudes similar to those found in other Villars speleothems during large climatic shifts such as Dansgaard–Oeschger events or glacial–interglacial transitions. In the context of the last 2000 years, the proxy variability cannot be attributed to climate alone, but is likely influenced by anthropogenic deforestation and the associated changes in carbon dynamics and hydrology.These changes might also have an influence on the isotope ratios in drip water relative to precipitation, e.g. through an altered evaporation–transpiration ratio. Nevertheless, despite some common trends in all proxy records, the marked shifts in the other proxies are not seen in the fluid inclusion stable isotopes, which gives evidence that the relationship between precipitation and drip water δ18O in the past was similar to present-day conditions, and not much affected by the anthropogenic impact. A replication of the fluid inclusion isotope record using stalagmites from the same region will be necessary to determine whether local cave processes or large-scale temperature and atmospheric circulation dominate the fluid inclusion δ18O signal, and in how far the fluid inclusions can provide a direct record of precipitation δ18O.

Epithermal Gold Mineralization in the Trenggalek District, East Java, Indonesia

AbstractGold‐mineralized quartz veins at the Trenggalek district of the Southern Mountains Range in East Java, Indonesia, are hosted by Oligo‐Miocene volcaniclastic and volcanic rocks, and are distributed close to andesitic plugs in the northern prospects (Dalangturu, Suruh, Jati, Gregah, Jombok, Salak, and Kojan) and the southern prospects (Sentul and Buluroto). The plugs are subalkaline tholeiitic basaltic‐andesite to calc‐alkaline andesite in composition. 40Ar–39Ar dating of a quartz‐adularia vein at the Dalangturu prospect yielded an age of 16.29 ± 0.56 Ma (2σ), and a crystal tuff of a limestone‐pyroclastic rock sequence at the southwest of the Dalangturu prospect was determined as 15.6 ± 0.5 Ma (2σ). Statistic overlap of ages suggests that the gold mineralization in the northern prospects took place in a shallow marine to subaerial transitional environment. Hydrothermal alteration of the host rocks is characterized by the replacement of quartz, illite and adularia. Quartz veins in surface outcrops are up to 50 cm wide in the northern prospects and up to 3 m wide in the southern prospects, showing a banded or brecciated texture, and are composed of quartz, adularia, carbonates with pyrite, electrum, sphalerite, galena, and polybasite. Gold contents of quartz veins are positively correlated with Ag, Zn, Pb, and Cu contents in both the northern and southern prospects. The quartz veins at the Jati, Gregah, and Sentul prospects have relatively lower gold‐silver ratios (Ag/Au = 23.2) compared to those at the Kojan, Dalangturu, Salak, and Suruh prospects (Ag/Au = 66.8). The quartz veins at the Dalangturu prospect are relatively rich in base metal sulfides. Ag/(Au+Ag) ratios of electrum in the Dalangturu prospect range from 45.2 to 65.0 at%, and FeS contents of sphalerite range from 1.2 to 6.4 mol%. Fluid inclusion microthermometry indicates ore‐forming temperatures of 190–200°C and 220–230°C at the Sentul and Kojan prospects, respectively. Widely variable vapor/liquid ratio of fluid inclusions indicates that fluid boiling took place within the hydrothermal system at the Sentul prospect. Salinities of ore‐fluids range from 0 to 0.7 wt% (av. 0.4 wt% NaCl equiv.) and from 0.5 to 1.4 wt% (av. 0.9 wt%) for the Sentul and Kojan prospects, respectively. The boiling of hydrothermal fluid was one of the gold deposition mechanisms in the Sentul prospect.

C, N, He, and Ar isotope and element ratios in fluid inclusions from MORB chilled glasses: Stepwise crushing data

C, N, He, and Ar isotope and element ratios in fluid inclusions from MORB chilled glasses: Stepwise crushing data

Source characteristics and fluid evolution of the Beiyingxigou Pb–Zn–Ag deposit, central North China Craton: An integrated stable isotope investigation

The Beiyingxigou quartz vein and alteration type Pb–Zn–Ag deposit forms part of the metallogenic region southwest of the Mapeng batholith in the Central North China Craton. The quartz vein-type polymetallic deposit is associated with intermediate-felsic intrusives emplaced with Mesoarchean metamorphic basement. The mineralization is dominantly controlled by N–S and NW–SE trending faults. We identify four distinct stages of mineralization associated with the hydrothermal activity: pyrite phyllic stage, quartz–pyrite stage, quartz–polymetallic sulfide stage, and quartz–carbonate stage. Among these, the first two stages and the quartz–polymetallic sulfide stage represent the early and main metallogenic stages, respectively. Here we present results from integrated stable isotope studies (S, Pb, He–Ar and H–O) to deduce the possible sources of the mineralizing fluids and metals. The δ34S values recorded in the sulfide minerals of the early and main metallogenic stages show ranges of +0.4‰ to +2.2‰, and −11.4‰ to −6.8‰, respectively. The data illustrate two distinct pulses of hydrothermal fluids with δ34S mean values of 1.1‰ and −8.7‰. The S isotopes of pyrite and galena, sphalerite from the early and main metallogenic stages suggest a mixed source from the Mesozoic magmatism and the Precambrian basement. We infer that the slow cooling magma at the main metallogenic stage led to a larger interaction with the country rocks and resultant contamination, as compared to the early–middle metallogenic stage. The lead isotopic composition of pyrite, galena and sphalerite from the early to main stages shows restricted ranges with 206Pb/204Pb, 207Pb/204Pb and 208Pb/204Pb ratios of 15.720–16.275, 15.068–15.140 and 38.688–41.316, respectively. The data are all characterized by lower crustal nature, suggesting the contribution of Pb from both the Mesozoic intrusions and the basement rocks in the region. The 3He/4He and 40Ar/36Ar ratios of fluid inclusions from the Beiyinxigou Pb–Zn–Ag deposit show a range of 0.01–0.23 Ra and 270.2–298.1, respectively. The 4He and 40Ar concentrations vary from 26.6 to 340.6 (10−7cm3STP/g) and 165.6 to 357.9 (10−7cm3STP/g), respectively, suggesting dominantly crustal contribution. The δ18OQ values of quartz and the δ18Dw values show ranges of 10.9‰ to 13.6‰ and −85.2‰ to −57.8‰, respectively. The calculated δ18OW values of the mineralizing fluids show a range of 3.7‰ to 7.5‰. Our data suggest that the hydrothermal fluids were a mixture of both magmatic and meteoric water. The results presented in this study link the Beiyinxigou Pb–Zn–Ag deposit to metallogeny associated with Mesozoic magmatism in the North China Craton.

He-Ar-H-O isotopic signatures in Au[sbnd]Ag bearing ore fluids of the Sunshin epithermal gold-silver ore deposits, South Korea

Helium (3He/4He), argon (40Ar/36Ar) and oxygen (18O/16O) isotopic ratios in fluid inclusions trapped in quartz and pyrite from the Sunshin epithermal gold-silver ore deposits in South Korea were analyzed to investigate the magmatic contribution to ore forming fluids. Mantle helium with high 3He/4He ratios (up to 3He/4He~9RA, where RA=1.4×10−6 for air) were identified from fluid inclusions in auriferous quartz veins, which are characterized as low sulfidation (adularia-sericite) type. The ratios provide direct evidence of links between low sulfidation ore fluids in epithermal gold deposits and magma from a mantle source. Interestingly, the oxygen and hydrogen isotopic compositions of the ore fluids (δ18O=−1.9 to −6.6‰, δD=−82 to −100‰), calculated from ore quartz, indicate that meteoric waters were predominant during precipitation of the AuAg ore. Microthermometric measurements for fluid inclusions indicate relatively low temperatures (≤300°C) for the formation of the low sulfidation epithermal ore deposits.

Helium isotopic ratios in fluid inclusions from fluorite-rich Mississippi Valley-Type district of Asturias, northern Spain

Helium isotopes have been measured in fluorite and sulphides from fluorite-rich Mississippi Valley-type (MVT) deposits from Asturias, Spain, in order to assess the involvement of mantle and crust-derived volatiles in the genesis of the deposits. The 3He/4He of the ore fluids are ≤0.1 Ra ruling out a contribution of mantle-derived magmatic helium in the inclusion fluids. Data support a crustal source for the volatiles and is consistent with the existing basinal model for the genesis of the Asturias MVT mineralization by mixing of sedimentary brines with infiltrating superficial fluids.

Origin of fluids in iron oxide–copper–gold deposits: constraints from δ 37Cl, 87Sr/86Sri and Cl/Br

The origin of the hypersaline fluids (magmatic or basinal brine?), associated with iron oxide (Cu–U–Au–REE) deposits, is controversial. We report the first chlorine and strontium isotope data combined with Cl/Br ratios of fluid inclusions from selected iron oxide–copper–gold (IOCG) deposits (Candelaria, Raúl–Condestable, Sossego), a deposit considered to represent a magmatic end member of the IOCG class of deposit (Gameleira), and a magnetite–apatite deposit (El Romeral) from South America. Our data indicate mixing of a high δ 37Cl magmatic fluid with near 0‰ δ 37Cl basinal brines in the Candelaria, Raúl–Condestable, and Sossego IOCG deposits and leaching of a few weight percent of evaporites by magmatic-hydrothermal (?) fluids at Gameleira and El Romeral. The Sr isotopic composition of the inclusion fluids of Candelaria, Raúl–Condestable, and El Romeral confirms the presence of a non-magmatic fluid component in these deposits. The heavy chlorine isotope signatures of fluids from the IOCG deposits (Candelaria, Raúl–Condestable, Sossego), reflecting the magmatic-hydrothermal component of these fluids, contrast with the near 0‰ δ 37Cl values of porphyry copper fluids known from the literature. The heavy chlorine isotope compositions of fluids of the investigated IOCG deposits may indicate a prevailing mantle Cl component in contrast to porphyry copper fluids, an argument also supported by Os isotopes, or could result from differential Cl isotope fractionation processes (e.g. phase separation) in fluids of IOCG and porphyry Cu deposits.

Helium Isotope Geochemistry of Ore‐forming Fluids from Furong Tin Orefield in Hunan Province, China

Abstract. The Furong tin orefield, located in southern Hunan, China, is a newly‐discovered super‐large tin orefield. In contrast to most other tin deposits associated with S‐type granites, the Furong tin deposit is closely associated with the Qitianling A‐type granite. The 3He/4He ratios of fluid inclusions in pyrite and arsenopyrite from this orefield range from 0.13 to 2.95 Ra. The influence of various post‐mineralization processes on the helium isotopic composition of ore‐forming fluid inclusions are estimated negligible. Thus, the analytical values of helium isotopic composition basically represent the original values of ore‐forming fluids at the time they were trapped.The 3He/4He ratios of ore‐forming fluids from the Furong orefield indicate the existence of mantle‐source components. It supports the idea that both the Furong tin orefield and Qitianling granite formed under the geodynamic background of mantle upwelling and crustal extension.

The Bulong Gold Deposit—a Quartz‐Barite Vein Type Gold Deposit in Xinjiang: Geological Characteristics and S, He and Ar Isotopic Compositions

Abstract The Bulong gold deposit, located in the southwest Tianshan in China, occurs in the Upper Devonian finegrained clastic rocks. The gold orebodies are controlled by an gently inclined interlayer fractured zone. They are hosted only in quartz‐barite veins though there are barite veins and quartz veins in the ore district. The δ34S values of pyrite in the ores range from 14.6‰ to 19.2‰ and those of barite from 35.0‰ to 39.6‰, indicating that the sulfur was derived from the strata. 3He/4 He ratios of fluid inclusions in pyrite are 0.24–0.82 R/Ra, approximating to that of the crust. The 40Ar/36Ar ratios range from 338 to 471, slightly higher than that of the atmosphere. 40Ar /4He ratios of ore fluids range from 0.015 to 0.412 with a mean of 0.153. Helium and argon isotope compositions of fluid inclusions show that the ore fluids of the Bulong gold deposit were mainly derived from the crust.

Palaeo-climate reconstruction from stable isotope variations in speleothems: a review

Speleothems are now regarded as valuable archives of climatic conditions on the continents, offering a number of advantages relative to other continental climate proxy recorders such as lake sediments and peat cores. They are ideal materials for precise U-series dating, yielding ages in calendar years, thereby circumventing the radiocarbon calibration problems associated with most other continental records. Stable isotope studies in speleothems have shifted away from attempting to provide palaeo-temperature reconstructions to the attainable goal of providing precise estimates for the timing and duration of major O isotope-defined climatic events characterised by high signal to noise ratios (e.g. glacial/interglacial transitions, Dansgaard–Oeschger oscillations, the ‘8200-year’ event). Unlike the marine records, speleothem data sets are not ‘tuned’, and their independent chronology offers opportunities to critically assess leads and lags in the climate system, that in turn can provide important insights into forcing and feedback mechanisms. Improved procedures for the extraction and measurement of stable isotope ratios in fluid inclusions trapped in speleothems are likely to provide, in the near future, a much enhanced basis for the quantitative interpretation of O isotope ratios in speleothem calcite. The latter developments open up once again the tantalising prospect of palaeo-temperature estimates, but more importantly perhaps, provide a direct test for a new generation of general circulation models whose hydrological cycles will incorporate the ‘water isotopes’. The literature is reviewed briefly to provide for the reader a sense of the current state-of-the-art, and to provide some pointers for future research directions.

LIMIST ON THE METAL CONTENT OF FLUID INCLUSIONS IN GANGUEMINERALS FROM THE VIBURNUM TREND, SOUTHEAST MISSOURI, DETERMINED BY LASERABLATION ICP-MS

The hydrothermal fluids that deposited the ores of the Viburnum Trend of the Southeast Missouri district have long been recognized to be sedimentary basinal brines. The major element composition of these brines has been well characterized; however, there have been no attempts to measure their metal content, which is only loosely constrained by theoretical solubility relations. The present study is an effort to assess the metal content of these mineralizing brines by analyzing fluid inclusions from gangue minerals in the Viburnum Trend using laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) and microthermometry. By focusing on gangue minerals instead of metal sulfide minerals, interferences from the mineral matrix are avoided. A high priority was to determine whether brines of anomalously high metal content were circulating through southeast Missouri during the time of Mississippi Valley-type mineralization. Fluid inclusions in dolomite, quartz, and calcite gangue from throughout the Viburnum Trend and representative of the entire paragenesis were analyzed. None of the inclusions contained measurable quantities of Pb, Zn, or Cu and only a few contained measurable quantities of Ba, which ranged from about 100 to 500 ppm. Where detection limits were not exceeded, they indicated maximum possible concentrations of the element in the fluid inclusion. Maximum possible concentrations varied from inclusion to inclusion and were controlled by the mass of analyte within the fluid volume—the larger or more saline the inclusion, the lower the detection limit. These results showed that the fluid that deposited quartz, calcite, and most of the dolomite gangue in the Viburnum Trend is unlikely to have had order-of-magnitude concentrations of Pb and Zn higher than 102 ppm or order-of-magnitude concentrations of Cu higher than 101 ppm. Concentrations of Pb and Zn during deposition of stage 3 dolomite could not have been higher than 103 ppm, and concentrations of Cu could not have been higher than 102 ppm. These upper limits on possible metal concentrations, with the principal exception of those in stage 3 dolomite fluid inclusions, are of magnitude similar to the highest measured concentrations of Pb, Zn, Cu, and Ba found in typical sedimentary brines. Thus, the brines responsible for depositing gangue minerals in the Viburnum Trend are unlikely to have had higher ore metal concentrations than typical basinal brines. The lack of temporal overlap between gangue and metal sulfide deposition, and the higher K/Na and lower Ca/Mg ratios in fluid inclusions in the gangue minerals compared with fluid inclusions in the metal sulfides, leaves open the possibility that the metal content of the fluid that deposited the sulfides was different from that responsible for depositing gangue. However, the data show that fluid entering the Southeast Missouri district was not pervasively metal rich throughout time, and that if metal-enriched fluid ever entered the district it did so at discrete intervals.

Fluid inclusion noble gas and halogen evidence on the origin of Cu-Porphyry mineralising fluids

The naturally occurring noble gas isotopes (40Ar, 36Ar, 84Kr and 129Xe) and halogens (Cl, Br, I) have been determined simultaneously in irradiated quartz vein samples by noble gas mass spectrometry. Quartz vein samples were collected from the potassic and propylitic alteration zones of six porphyry copper deposits (PCD): Bingham Canyon, Utah; and Silverbell, Ray, Mission, Pinto Valley and Globe-Miami in Arizona. In addition, analyses of 3He/4He have been obtained from sulphide minerals hosted by the quartz veins at Silverbell, Ray, Pinto Valley and Globe-Miami.The majority of PCD fluids studied have Br/Cl and I/Cl ratios that overlap those of fluids included in mantle diamond, suggesting that the salinity had a juvenile origin. The high I/Cl (121 × 10−6 mole, M) in samples from the propylitic zone of Silverbell is attributed to the presence of sedimentary formation water.3He/4He ratios have R/Ra values in the range 0.3 to 1.72, and provide evidence for the involvement of a crustal component in addition to mantle volatiles. 40Ar/36Ar ratios vary from meteoric values of ∼317 in the propylitic zone of Bingham Canyon, and 323 in the skarn alteration of Mission up to 3225 in the potassic zone of Pinto Valley. Fluids in both the potassic and propylitic alteration zones of every deposit are a mixture of a low salinity end-member comprising meteoric water and air, and a high salinity end-member consisting of a mixed mantle and crustal fluid.The 40Ar/Cl ratio of fluid inclusions at Pinto Valley (∼10−4 M) is similar to values obtained previously for mantle fluids. The 40Ar/Cl value is two orders of magnitude lower at Bingham Canyon, where a depleted 36Ar concentration (0.2 × 10−6 cm3/g) below that of air saturated water (ASW), and a range of highly fractionated noble gas compositions (F84Kr = 13 and F129Xe = 160) indicate that boiling and pulsed fluid flow have occurred.

Volatile element isotopic systematics of the Rodrigues Triple Junction Indian Ocean MORB: implications for mantle heterogeneity

Mid-ocean ridge basalts (MORBs) from the Indian Ocean have been well-known to differ in Sr–Nd–Pb isotopic composition from those of the North Atlantic and the East Pacific. To understand if such heterogeneity exists also in volatile elements, we have measured elemental and isotopic composition of carbon, nitrogen, helium, and argon in trapped-gas-vesicles of the Rodrigues Triple Junction (RTJ) Indian Ocean MORBs (IOMs). The observed C–N–He–Ar isotopic ratios of the IOMs generally agree with average values of North Atlantic MORBs (NAMs) and East Pacific MORBs (EPMs). In contrast, the N 2/ 40Ar, C/N, and CO 2/ 3He ratios in fluid inclusions of the IOMs are quite unusual: current estimates of the N 2/ 40Ar, C/N, and CO 2/ 3He trapped in vesicles from the NAMs and EPMs are 91±20, 215∼4600, and (1.5±0.5)×10 9, respectively, whereas those of the IOMs are 120±36, 26∼190, and (0.3±0.1)×10 9, respectively. The 40Ar/ 36Ar and the 4He/ 40Ar * ratios indicate that the unusual N 2/ 40Ar, C/N, and CO 2/ 3He ratios of IOMs in this study have not been produced by atmospheric contamination or progressive fractional degassing, respectively, but more likely by mantle heterogeneity. The IOMs analyzed in this study seem to be depleted in the recycled carbon than the previous reported NAMs and EPMs. Assuming that values of IOMs in this study as those of the primitive (juvenile) mantle carbon, it is derived that most (65∼95%) carbon in the previously reported NAMs and EPMs is the recycled carbon (carbonate and organic matter) in origin, from a simple mass balance calculation. This may be one clue of the carbon recycling in the mantle.

Fluid composition and thermal regime during Zn-Pb mineralization in the lower Windsor Group, Nova Scotia, Canada

The Zn-Pb-Ba-Cu-Ag-F deposits hosted by Lower Windsor Group (early Carboniferous) carbonates in Nova Scotia are located along the southern margin of the Maritimes basin. Various geochemical studies indicate that the deposits were formed by fluids expelled from the basin, but it remains unclear whether the ore-forming fluids for different deposits were derived from a common source region in the central part of the basin, as proposed previously, or from separate source regions. It is also unknown how the ore fluids were conveyed from the source regions to the sites of mineralization and whether or not the mineralizing systems of different deposits were hydrologically related. This paper addresses these problems through a compilation of regional fluid composition and temperature data and thermal comparisons between the ore-forming fluids and their host rocks. The compositions and temperatures of the fluids were evaluated from fluid inclusion data, whereas host-rock temperatures were estimated from vitrinite reflectance measurements.The ore-forming fluids are characterized by: (1) variable, but generally high salinities (mainly between 15 and 30 wt % NaCl equiv), (2) variable, but generally detectable amounts of bivalent cations (mainly Ca (super 2+) ), (3) significant concentrations of hydrocarbon species, and (4) high temperatures (mainly between 150 degrees and 250 degrees C). NaCl/(NaCl + CaCl 2 ) wt ratios in fluid inclusions show a broad district-scale variation: mainly 0.4 for the Gays River and Walton deposits in mainland Nova Scotia. CH 4 /higher hydrocarbons ratios of the gas components are greater for the Gays River deposit (3.8-9.7) than the Jubilee deposit (0.7-1.3). Fluid inclusion homogenization temperatures do not show a negative correlation with the distance between the deposits and the central part of the Maritimes basin, as might be expected if the fluids for different deposits were derived from the same source region.The background temperatures prior to mineralization were estimated from mean vitrinite reflectance (R o ) in host rocks which were relatively far from the deposit, and were probably least affected by the mineralizing events, and from homogenization temperatures of fluid inclusions in preore minerals. These temperatures are in the range of 70 degrees to 155 degrees C, which are significantly lower than those of the ore-forming fluids. The paleogeothermal gradients estimated from the background temperatures and burial depths are ca. 65 degrees C/km. Vitrinite reflectance values in host rocks adjacent to the deposits indicate that these rocks were heated by the mineralizing fluids to variable degrees, but thermal equilibrium between the fluids and rocks was not attained in most eases. This thermal relationship suggests focused and short-lived, rather than pervasive and long-lived, fluid flow.The regional variation of fluid composition and thermal patterns supports a model in which the ore-forming fluids of individual deposits were derived from separate sources; fluid flow was focused along confined conduits and individual mineralizing systems were unconnected hydrologically. Under paleogeothermal gradients of ca. 65 degrees C/km, fluids with temperatures of ca. 250 degrees C could have been generated in sub-basins proximal to the deposits. Sudden release of overpressured fluids from the basal part of the proximal sub-basins, characterized by high flow rate and short duration, is proposed as the mechanism of ore-forming fluid flow.

Helium and argon isotopic geochemistry of Jinding superlarge Pb-Zn deposit

The study results of He and Ar isotopes from fluid inclusions in pyrites formed during mineralization stage of Jinding superlarge Pb-Zn deposit in west Yunnan, China are reported. The data show that the40Ar/36Ar and3He/4He ratios of fluid inclusions are respectively in the range of 301. 7–385. 7 and 0. 03–0.06Ra, suggesting the oreforming fluid is a kind of air saturated meteoric groundwater. On the basis of research on coupled relationships among He, Ar, S and Pb isotopes, the evolution history of ore-forming fluid of the deposit can be summarized as (i) air saturated meteogenic groundwater infiltrated down and was heated→ (ii) leached S, C and radiogenic He, Ar from the basinal strata → (iii) leached Pb and Zn from mantle-derived igneous rocks located in the bottom of the basin→ (iv) ore-forming fluid ascended and formed the deposit. Due to this process, the isotope signatures of crustal radiogenic He, atmospheric Ar (with partial radiogenic40Ar), crustal S and mantle-derived Pb remained in the ore-forming fluid.

The influence of oxygen fugacity on tungsten and molybdenum partitioning between silicate melts and ilmenite

The partitioning of molybdenum and tungsten between ilmenite (ilm) and silicic melts has been determined at 800 degrees C, 1 kbar of pressure, and at two oxygen fugacities. At the oxygen fugacity of the graphite-methane(-water) buffer, D (super ilm/melt) Mo = 0.42, and D (super ilm/melt) W = 0.39. Near the nickel-nickel oxide buffer, D (super ilm/melt) Mo = 0.22 and D (super ilm/melt) W = 0.5. The variations in the partition coefficients with f (sub o 2 ) are significant at the 0.06 and 0.33 levels for molybdenum and tungsten, respectively. The observed variation with oxygen fugacity is tentatively extrapolated to more complex systems and implies that the oxygen fugacity which prevails during magmatic crystallization may play a role in determining the Mo/W ratio in porphyry, skarn, or other hydrothermal mineral deposits. Examination of the literature on molybdenum- and tungsten-bearing mineral deposits indicates that systems with high W/Mo ratios are rather reduced and exhibit high CH 4 /CO 2 ratios in fluid inclusions, low Fe (super +3) /Fe (super +2) ratios in iron-bearing minerals, and low oxygen fugacities in associated igneous rocks. On the other hand, deposits with high Mo/W ratios are associated with rather oxidized magmatic systems. We suggest that f (sub o 2 ) -dependent sequestration of molybdenum and tungsten in ferromagnesian phases during plutonic consolidation exerts a control on the relative efficiencies of removal of these metals from magmas into ore-forming fluids.

High integrated fluid/rock ratios during metamorphism at Naxos: evidence from carbon isotopes of calcite in schists and fluid inclusions

Calcite in schists of the metamorphic complex at Naxos is depleted both in 13C and in 18O with respect to massive marbles. This effect is attributed to isotope exchange with circulating CO2-rich fluids, which had an \(X_{{\text{CO}}_{\text{2}} } \)>0.5 according to fluid inclusions. The carbon isotopic composition of the calcites is close to equilibrium with fluid inclusion CO2 at metamorphic temperatures. Mass balance calculations assuming initial δ13C values of 0 for calcite and −5 for the fluid, give integrated fluid/rock volume ratios between 0.1 and 2.0. Such high fluid/rock ratios are supported by observations on the distribution of CO2/H2O ratios of fluid inclusions, carbon isotopic compositions of fluid inclusion CO2 and oxygen isotope systematics of silicates.

Late Pleistocene palaeotemperature record from a Tasmanian speleothem

Multiple 230Th/234U age determinations on a uniform diameter calcite stalagmite from a Tasmanian cave show that it was deposited between 109 000 and 76 000 years BP at a constant rate of 4.3 cm per 100 years. Except for the first 9000 years, deposition occurred under conditions of oxygen isotope equilibrium enabling it to be used for palaeotemperature studies. Measurements of 18O/16O ratios of calcite and d/h ratios of fluid inclusions indicate that mean annual temperatures at the site were nearly always lower than at present from 100 000 to 76 000 BP. A positive relationship is found between mean annual temperature and the 18O/16O content of calcite. This is uncommon and represents the first such relationship recorded from the Southern Hemisphere. The stalagmite shows evidence of having grown during two distinct temperature phases. From 100 000 to 97 000 years BP mean annual temperatures were between 4°C and 6°C compared with a present day value of 9.5°C. At about 97 000 years BP there was a rapid transi...