Carbon Isotopic Compositions Of Calcite Research Articles

Sources of Hydrothermal Fluids Inferred from Oxygen and Carbon Isotope Composition of Calcite, Keweenaw Peninsula Native Copper District, Michigan, USA

The Mesoproterozoic North American Midcontinent Rift hosts the world’s largest accumulation of native copper in Michigan’s Keweenaw Peninsula. During a regional metamorphogenic-hydrothermal event, native copper was deposited along with spatially zoned main-stage minerals in a thermal high. This was followed by deposition of late-stage minerals including minor copper sulfide. Inferences from the oxygen and carbon isotopic composition of main-stage hydrothermal fluids, as calculated from 296 new and compiled isotopic measurements on calcite, are consistent with existing models that low-sulfur saline native copper ore-forming fluids were dominantly derived by burial metamorphic processes from the very low sulfur basalt-dominated rift fill at depth below the native copper deposits. Co-variation of oxygen and carbon isotopic compositions are consistent with mixing of metamorphic-derived fluids with two additional isotopically different fluids. One of these is proposed to be evolved seawater that provided an outside source of salinity. This fluid mixed at depth and participated in the formation of a well-mixed hybrid metamorphic-dominated ore-forming fluid. Secondary Ion Mass Spectrometry in-situ isotopic analyses of calcite demonstrate a high degree of variability within samples that is attributed to variable degrees of shallow mixing of the hybrid ore-forming fluid with sulfur-poor, reduced evolved meteoric water in the zone of precipitation. The oxygen and carbon isotopic compositions of 100 new and compiled measurements on late-stage calcite are mostly isotopically different than the main-stage hydrothermal fluids. The late-stage hydrothermal fluids are interpreted as various proportions of mixing of evolved meteoric water, main-stage hybrid ore-forming fluid, and shallow, evolved seawater in the relatively shallow zone of precipitation.

The temporal evolution of the carbon isotope composition of calcite in the presence of cyanobacteria

Quantifying the link between cyanobacterial activity and the carbon isotope signature of precipitated carbonate minerals is crucial for reconstructing the environmental conditions present at the time of carbonate mineral formation. In this study, calcite was precipitated in the presence and absence of Synechococcus sp. cyanobacteria in batch reactors. The temporal evolution of the carbon isotope composition of calcite (δ13CCalcite) and dissolved inorganic carbon (δ13CDIC) was monitored to evaluate the rate and degree to which the carbon isotope compositions in calcite are modified during and after its precipitation. The presence of cyanobacteria promoted calcium carbonate formation by increasing fluid pH and the CaCO3 saturation state. It also changed significantly the carbon isotope composition of dissolved inorganic carbon due to the preferential incorporation of 12C into the biomass. This generated an isotope disequilibrium between the calcite and the aqueous fluid phase over time after the calcite precipitated. The carbon isotope composition of the calcite evolved continuously towards mineral-fluid isotope equilibrium after its precipitation, at geometric surface area normalized rates ranging from 1.75 × 10−14 to 1.71 × 10−13 mol 13C/m2/s. These rates are sufficiently fast such that the δ13CDIC value of aqueous fluids in calcite-rich rocks would be buffered by the δ13CCalcite value of the co-existing calcite. Mass balance calculations suggest that the carbon isotope composition of calcite could change noticeably when the calcite is in isotope disequilibrium with its co-existing fluid, for example through the presence of a local 12C sink such as photosynthetic microorganisms or 12C source such as decomposition of organic material.

Geological, fluid inclusion, and O–C–S–Pb–He–Ar isotopic constraints on the genesis of the Honghuagou lode gold deposit, northern North China Craton

The Honghuagou Au deposit is located in the Chifeng-Chaoyang region within the northern margin of the North China Craton. The auriferous quartz veins are mainly hosted in the mafic gneiss and migmatite of the Neoarchean Xiaotazigou Formation along NNW- and NE-striking faults, with pyrite as the predominant ore mineral. The gold mineralization process can be divided into two stages, involving stage I quartz-pyrite and stage II quartz-calcite-polymetallic sulfide. Three types of fluid inclusions (FIs) have been identified in the Honghuagou deposit, namely, carbonic inclusions, aqueous‑carbonic inclusions, and aqueous inclusions. Quartz of stage I contains all types of FIs, whereas only aqueous inclusions are evident in stage II veins. The FIs of stages I and II yield homogenization temperatures of 275–340 °C and 240–290 °C with salinities of 3.4–10.7 wt% and 1.4–9.7 wt% NaCl eqv., respectively. The ore-forming fluids are characterized by medium temperature and low salinity, belonging to the H2O–NaCl–CO2 system. The δ18OH2O values of the ore fluids are between 2.1‰ and 5.9‰, within the range of enriched mantle-derived fluids in the North China Craton. The carbon isotope compositions of calcite (δ13CPDB = −4.4‰ to −4‰) are also similar to mantle carbon. He-Ar isotope data (3He/4He = 0.38–0.44 Ra; 40Ar/36Ar = 330–477) of fluid inclusions in pyrite indicate a mixed crustal and mantle source for the ore-forming fluids. Whereas, S-Pb isotope compositions of sulfides reveal that ore metals are principally derived from crustal rocks. On the basis of available geological and geochemical evidence, we suggest that the Honghuagou deposit is an orogenic gold deposit.

Reading a 400,000-year record of earthquake frequency for an intraplate fault

Our understanding of the frequency of large earthquakes at timescales longer than instrumental and historical records is based mostly on paleoseismic studies of fast-moving plate-boundary faults. Similar study of intraplate faults has been limited until now, because intraplate earthquake recurrence intervals are generally long (10s to 100s of thousands of years) relative to conventional paleoseismic records determined by trenching. Long-term variations in the earthquake recurrence intervals of intraplate faults therefore are poorly understood. Longer paleoseismic records for intraplate faults are required both to better quantify their earthquake recurrence intervals and to test competing models of earthquake frequency (e.g., time-dependent, time-independent, and clustered). We present the results of U-Th dating of calcite veins in the Loma Blanca normal fault zone, Rio Grande rift, New Mexico, United States, that constrain earthquake recurrence intervals over much of the past ∼550 ka-the longest direct record of seismic frequency documented for any fault to date. The 13 distinct seismic events delineated by this effort demonstrate that for >400 ka, the Loma Blanca fault produced periodic large earthquakes, consistent with a time-dependent model of earthquake recurrence. However, this time-dependent series was interrupted by a cluster of earthquakes at ∼430 ka. The carbon isotope composition of calcite formed during this seismic cluster records rapid degassing of CO2, suggesting an interval of anomalous fluid source. In concert with U-Th dates recording decreased recurrence intervals, we infer seismicity during this interval records fault-valve behavior. These data provide insight into the long-term seismic behavior of the Loma Blanca fault and, by inference, other intraplate faults.

Early Cretaceous tungsten mineralization in Southeastern China: the Wuning example

ABSTRACTThe Wuning tungsten deposits in northwestern Jiangxi are located in the Middle-Lower Yangtze River metallogenic belt of SE China. This article decodes the large tungsten-mineralized ore field by analysing three typical deposits: Shimensi, Dahutang, and Shiwendong. The Shimensi deposit shows three mineralization styles, and the associated hydrothermal alteration mainly includes K-feldspathization, greisenization, chloritization, silicification, and carbonatization. The sulphur isotopic compositions of sulphides in the Dahutang deposit indicate that the sulphur source was homogeneous and closely related to magmatic sulphur. The lead isotopic compositions of sulphides suggest multiple sources that were also closely related to magmatism. The carbon isotopic compositions of calcite indicate that hydrothermal fluids were derived from the granitic magma. Hydrogen and oxygen isotopic compositions of quartz veins indicate that the ore-forming fluids had a magmatic-hydrothermal origin, but mixed with meteoric water. Fluid inclusions from the Shiweidong deposit are low density, indicating medium-high T and low-medium salinity, further suggesting that it was a shallow magmatic-hydrothermal deposit, and the metallogenic hydrotherm mingled with the surface water late in the evolution of the system. Mineralization was related to Early Cretaceous magmatism in eastern China. The subduction of the palaeo-Pacific plate and the subsequent lithospheric delamination reflected transition from a compressional to extensional tectonic regime. The upwelling of the hot asthenosphere triggered partial melting of the Neoproterozoic Shuangqiaoshan Group, with high W background concentrations. The ascent of the magma resulted in the exsolution of the ore-bearing magmatic hydrothermal fluid.

Seepage carbonate mounds in Cenozoic sedimentary sequences from the Las Minas Basin, SE Spain

A number of carbonate mounds composed of indurate, strongly folded and/or brecciated calcite and dolomite beds occur interstratified in Cenozoic sedimentary sequences from the Las Minas Basin. Part of the fabric of the rock forming the carbonate mounds is composed of laminated to banded dolostone similar to the host rock but showing contrasted lithification. Moreover, the carbonate deposits of the mounds display aggrading neomorphism of dolomite, partial replacement of dolomite by calcite, calcite cementation, and extensive silicification, locally resulting in box-work fabric. Eight main lithofacies were distinguished in the carbonate mound deposits. In some lithofacies, chert is present as both microcrystalline to fibro-radial quartz and opal, the latter occurring mainly as cement whereas the former replace the carbonate and infill voids. Yet one of the carbonate mounds shows distinctive petrography and geochemical features thus suggesting a distinctive growth pattern. The carbon isotope compositions of calcite from the mound samples range from −11.56 to −5.15 δ‰ whilst dolomite is depleted in 13C, with values of −12.38 to 3.02 δ‰. Oxygen isotopic compositions vary from −9.42 to −4.64 δ‰ for calcite and between −6.68 and 8.19 δ‰ for dolomite. Carbonate in the mounds shows significant enrichment in Co, Cr, Ni and Pb content, especially in the strongly deformed (F-2-2 lithofacies) and brecciated carbonate (F-4). The carbonate deposits show depletion in REE and Y in contrast to that determined in lutite. The formation of the carbonate mounds was related to local artesian seepage thermal water flows of moderate to relative high temperatures. Pressure differences between the low permeability host rock and the circulating fluids accounted for dilational fracturing and brecciation of the host sediment packages, which combined with precipitation of new carbonate and silica mineral phases. Locally, some carbonate mounds developed where groundwater intersected the lake floor, this resulting in bedded carbonate deposits composed of organic constituents.

Calibration of stable isotope composition of Thoracosphaera heimii (dinoflagellate) calcite for reconstructing paleotemperatures in the intermediate photic zone

AbstractIn this study we investigate the temperature dependence of oxygen isotope ratios preserved in calcite formed by the dinoflagellate Thoracosphaera heimii, focusing primarily on the development of a geological proxy. Geochemical analysis of the calcite shells produced by this species represents a valuable proxy for reconstructing environmental conditions in the intermediate photic zone. Calibration is based on isotopic analysis from culture experiments performed in very dilute batch conditions, as well as from near‐monospecific T. heimii assemblages separated from core top sediments. Results are similar for both approaches and indicate that T. heimii shells have oxygen isotope compositions close to equilibrium values predicted for inorganic calcite precipitation. This calibration of the isotopic composition of dinoflagellate calcite indicates that monospecific assemblages of T. heimii can be used to unravel paleotemperatures in the intermediate photic zone by applying isotopic transfer functions for equilibrium calcite. In culture, however, a δ18O offset of −1‰ is observed at temperatures <17°C, which falls below the natural temperature range of this species. Culture analyses also reveal a relationship between temperature and carbon isotope composition of calcite. The mechanisms behind this relationship remain to be explored, but their identification may provide a better understanding of carbon isotope systematics from both biogeochemical and geological perspectives. Comparison of the oxygen isotope composition of T. heimii shells with that of shallower dwelling organisms, such as the coccolithophores, represents a valuable proxy for determining temperature gradients within the photic zone and may enable reconstruction of the evolution of the depth of the thermocline.

OXYGEN AND CARBON ISOTOPIC COMPOSITION OF GRENVILLE MARBLE, AND AN APPRAISAL OF EQUILIBRIUM IN THE DISTRIBUTION OF ISOTOPES BETWEEN CALCITE AND ASSOCIATED MINERALS, OTTER LAKE AREA, QUEBEC, CANADA

Marble occurs abundantly in a portion of the Grenville Province of the Canadian Shield extending from the Adirondack Mountains, through Ontario, and into the Laurentian Highlands of Quebec, a distance of 300 km. In the Otter Lake area of western Quebec, major marble units, which are obviously metamorphosed limestone, consist of combinations of calcite, dolomite, olivine, humite-group minerals, Ca pyroxene, Ca amphibole, biotite, graphite, and retrograde serpentine and brucite, whereas minor marble units, which are evidently metasomatic rocks, consist of combinations of (pink) calcite, Ca pyroxene, Ca amphibole, biotite, garnet, K-feldspar, scapolite, and titanite. The oxygen and carbon isotopic composition of calcite in the major marble units (δ18OVSMOW in the range 28 to 17‰; δ13CPDB–1 in the range +6 to −2‰) is the same as in the Adirondacks and in unmetamorphosed Proterozoic limestone; only slight shifts (~1‰) can be attributed directly to metamorphic reactions. In bodies of minor marble, mean concentrations of 18O and 13C are slightly lower (+14.5 and +0.23‰, respectively). Mean fractionation-factors (α, expressed as 1000 ln α, are as follows: 18O, calcite/dolomite, +0.295 ( n = 11); 13C, calcite/dolomite, −0.346 ( n = 12); 18O, calcite/biotite, +3.49 ( n = 5); 13C, calcite/graphite, +3.74 ( n = 5). Additional (exploratory) results ( n = 1) on the distribution of 18O are as follows: calcite/olivine, +3.5; calcite/clinohumite, +5.1; calcite/garnet, +2.4; calcite/titanite, +3.1; calcite/Ca pyroxene, +2.0; calcite/Ca amphibole, +2.4, calcite/K-feldspar +1.8; calcite/scapolite, +2.0; calcite/serpentine, +13.9; calcite/brucite, +19.7; a trend of increasing α is related to increasing OH/(O + OH) in the non-carbonates and the preference of OH for 16O. For the first group of mineral pairs ( n ≥ a small variation in α across the study area (relative standard deviation ~0.05%) is viewed as an expression of a close approach to isotopic exchange equilibrium, and for certain pairs from the second group ( n = 1), a temperature estimate close to 700° (the biotite–garnet temperature of associated gneisses) is also viewed as evidence for equilibrium. Attainment of isotopic exchange equilibrium was facilitated by dynamic recrystallization, which occurred during the peak of metamorphism.

Episodic Hydrocarbon Migration during Deposition of the Frio Clastic Wedge, Gulf of Mexico: Its Expression and Causes: ABSTRACT

A petrographic and geochemical studies of the Oligocene Frio Formation show that the carbon isotopic composition of calcite varies systematically with stratigraphy, due to varying hydrocarbon migration to the sea bed during Frio deposition. In the St. Charles Ranch fields, Aransas County, Texas, compositions in the Lower Frio are relatively heavy ([delta][sup 13]C = [approximately]-2[per thousand]), decreasing stratigraphically upward to -5.5[per thousand] in the Middle Frio, then increasing to -2[per thousand] in the Upper Frio. The average calcite composition is identical in sandstones and mudstones at specific stratigraphic levels. This pattern contrasts with [delta][sup 18]O, in which sandstone and mudstone calcite has different compositions and no stratigraphic control is evident. Two limestone beds have very light [delta][sup 13]C compositions ([approximately] -20[per thousand]); they are analogous to modern carbonate buildups in the Gulf of Mexico forming around methane vents. The carbon isotopic composition of calcite reflects the flux of hydrocarbons to the sea bed: low [delta][sup 13]C values indicate greater incorporation of hydrocarbon into calcite and therefore a large hydrocarbon flux, and vice versa. The data suggest that a pulse of hydrocarbon migration occurred during Frio deposition, peaking during Middle Frio deposition. Two mechanisms for this migration pulse are considered: first,more » deposition of the Frio resulted in sudden hydrocarbon maturation and generation in underlying source rocks; and second, growth faulting, associated with deposition of the Frio wedge, opened migration pathways. As sedimentation rates slowed during deposition of the Upper Frio, movement on growth faults decreased and migration pathways closed. These mechanisms are tested with numerical models.« less

Fluid evolution and geobarometry on the Ohtani and Kaneuchi tungsten-quartz vein deposits, Japan: oxygen and carbon isotopic evidence

The Ohtani and Kaneuchi deposits are tungsten-bearing quartz veins of hypothermal type which are hosted by Cretaceous granodiorite and sedimentary rocks respectively. Oxygen and carbon isotopic compositions were measured on minerals associated with the deposits to determine whether the ore-forming fluids were derived from related igneous bodies. The oxygen isotopic equilibrium temperatures of quartz-muscovite pairs within veins from the Ohtani and Kaneuchi deposits range from 530° to 190°C and from 400° to 300°C, respectively. The equilibrium temperatures of the granodiorite (600°C), greisen (590° to 530°C) and veins in the Ohtani deposit decrease in this order. The calculated oxygen isotopic composition of the Ohtani ore-forming fluid is around 12 ‰ (SMOW) above 500°C and lowers successively toward 3 ‰ as temperature decreases. The fluid at the earliest stage of mineralization could be in equilibrium with the granodiorite at about 600°C. These lines of evidence suggest that the granodiorite magma played a crucial role in the mineralization. The evolution trend of the Ohtani ore-forming fluid can be explained by a combined process of cooling due to heat conduction, adiabatic expansion and mixing of magmatic water with ground water. Calcites from the deposits have carbon isotopic ratios ranging from -11 to + 2‰ with the oxygen isotopic ratios in a narrow range. Since the CO2/CH4 fugacity ratio of the fluid is estimated to have been near unity, a slight fluctuation in fO2 caused the large variation in the carbon isotopic composition of calcite. The formation pressures for the Ohtani and Kaneuchi deposits are calculated to be 1.5 kb and 1.4 kb, respectively, on the basis of the difference between the pressure-dependent homogenization temperatures of fluid inclusions and the pressure-independent isotopic equilibrium temperatures. These values are reasonable for the depths in which hypothermal ore deposits have formed.

Source of Anomalous Magnetization in Area of Hydrocarbon Potential: Petrologic Evidence from Jurassic Preuss Sandstone, Wyoming-Idaho Thrust Belt

The Jurassic Preuss Sandstone, which crops out in the central part of the Wyoming-Idaho thrust belt on trend with a hydrocarbon-producing region to the south, has been previously identified as the source of anomalous magnetization in the area. Elsewhere, anomalous magnetization in sedimentary rocks near hydrocarbon accumulations has been attributed to hydrocarbon-engendered magnetic minerals, but magnetization of the Preuss is controlled by detrital magnetite. Evidence of a detrital origin for magnetite includes (1) concentration of magnetite grains along laminations containing other heavy minerals, (2) the presence of exsolved ilmenite, hematite, and spinel in the magnetite grains, and (3) titanium contents typical of igneous-derived magnetite. That detrital magnetite is responsible for the anomalous magnetization in the Preuss is further indicated by the systematic eastward decrease in magnetite abundance corresponding to a similar eastward decrease in magnetic susceptibility and remanent magnetization of the unit. Petrologic and vitrinite reflectance studies indicate a complex low-temperature (<150°C or 302°F) diagenetic history for the Preuss. Nevertheless, preservation of detrital magnetite, the presence of diagenetically early ferric oxide minerals, and the absence of sulfide minerals all indicate that the Preuss has not experienced sulfidic-reducing conditions common in areas of hydrocarbon seepage. The marine carbon isotopic composition of calcite that cements most Preuss sandstones (^dgr13C values ranging from -2.47 to 1.48^pmil is evidence that carbonate diagenesis also was not influenced by hydrocarbons. The results of this multidisciplinary study of the Preuss underscore the importance of similar studies when evaluating the sources of aeromagnetic anomalies in areas of hydrocarbon potential.

Post-Hydrocarbon Migration Deep Burial Diagenesis of Smackover Formation, Black Creek Field, Wiggins Arch, Mississippi Salt Basin: ABSTRACT

The Smackover Formation is buried to over 6 km in Black Creek field and exhibits diagenetic phases unique to deep burial. These include replacement of sulfates by calcite, pore-fill calcite cement, silicification, and elemental sulfur as cement. The above diagenetic products are the result of thermal reduction of sulfates and thermal degradation of hydrocarbons and have formed at temperatures greater than 140/degrees/C. Calcite replaces anhydrite in two textural forms, one of which is pseudomorphic. Pore-fill calcite cement contains inclusions of pyrobitumen and heals cracks formed in the pyrobitumen due to high thermal maturity. This indicates that calcite cement postdates bitumen formation. Silicification is a major deep burial event. Micron to millimetersize crystals of quartz replace the host carbonate rock as well as other deep burial diagenetic phases. Elemental sulfur occurs as inclusions in incompletely destroyed sulfates and as pore-fill cement. In both cases it exhibits extensive bubble-shaped cavities similar to pumiceous texture found in volcanic rocks. This indicates that elemental sulfur was possibly crystallized rapidly from a liquid sulfur while the cores were being taken. Similar diagenetic products are formed by low-temperature (< 80/degrees/C) bacterial reduction of sulfates and bacterial degradation of hydrocarbons. However, carbon isotopic composition of calcite, sulfurmore » isotopic composition of elemental sulfur, and textural characteristics of elemental sulfur produced by the two diagenetic processes are significantly different.« less

Oxygen and carbon isotope evidence for seawater-hydrothermal alteration of the Macquarie Island ophiolite

Rocks of the Miocene Macquarie Island ophiolite, south of New Zealand, have oxygen and carbon isotopic compositions comparable to those of seafloor rocks. Basalt glass and weathered basalts have δ 18O values at 5.8–6.0‰ and 7.9–9.5‰, respectively, similar to drilled seafloor rocks including samples from the Leg 29 DSDP holes near Macquarie Island. Compared to the basalt glass, the greenschist to amphibolite facies metaintrusives are depleted in 18O (δ 18O=3.2–5.9‰) similar to dredged seafloor samples, whereas the metabasalts are enriched (δ 18O=7.1–9.7‰). Although the gabbros are only slightly altered in thin-section they have exchanged oxygen with a hydrothermal fluid to a depth of at least 4.5 km. There is an approximate balance between 18O depletion and enrichment in the exposed ophiolite section. The carbon isotopic composition of calcite in the weathered basalts (δ 13C=1.0–2.0‰) is similar to those of drilled basalts, but the metamorphosed rocks have low δ 13C values (−14.6 to 0.9‰). These data are compatible with two seawater circulation regimes. In the upper regime, basalts were weathered by cold seawater in a circulation system with high water/rock ratios (≫1.0). Based on calcite compositions weathering temperatures were less than 20°C and the carbon was derived from a predominantly inorganic marine source. As previously suggested for the Samail ophiolite, it is postulated that the lower hydrothermal regime consisted of two coupled parts. At the deeper levels, seawater circulating at low water/rock ratios (0.2–0.3) and high temperatures (300–600°C) gave rise to 18O-depleted gabbro and sheeted dikes via open system exchange reactions. During reaction the seawater underwent a shift in oxygen isotopic composition (δ 18O=1.0–5.0‰) and subsequently caused 18O enrichment of the overlying metabasalts. In the shallower part of the hydrothermal regime the metabasalts were altered at relatively high water/rock ratios (1.0–10.0) and temperatures in the range 200–300°C. The relatively low water/rock ratios in the hydrothermal regime are supported by the low δ 13C values of calcite, interpreted as evidence of juvenile carbon in contrast to the inorganic marine carbon found in the weathered basalts.

Carbon isotopic study on graphite and carbonate in the Kamioka mining district, Gifu Prefecture, central Japan, in relation to the role of graphite in the pyrometasomatic ore deposition

Pyrometasomatic lead-zinc ore deposits of the Kamioka mine occur in the Hida metamorphic complex of central Japan. The pyrometasomatic ore deposition was followed by small scale hydrothermal ore deposition. Flaky graphite characteristically occurs in skarn, ores and in the surrounding crystalline limestone. δ13C values of graphite in the skarn and the ores are close to those of graphites in the crystalline limestone. Graphite in the skarn and ores is considered to be remains of graphite in the crystalline limestone which was replaced by the skarn and the ores. At the pyrometasomatic stage, the oxygen fugacity of fluid would control the carbon isotopic composition of calcite precipitated. On the assumption that graphite played a role of oxygen buffer, the oxygen fugacity of the fluid was estimated to be from 10−31,4 to 10−301 bars at 350 °C and total pressure of 1,000 bars. The predominant carbon species in the fluid would be carbon dioxide. The δ13C value of total carbon in fluid was estimated to be −3.6±1.7‰ (PDB) for the Tochibora and Maruyama deposits of the Kamioka mine, and the oxygen fugacity in the fluid was probably constant during the pyrometasomatic stage. It is likely that an important source of carbon was the carbon remained after the decarbonation of crystalline limestone. Oxygen isotopic studies on calcite of pyrometasomatic and hydrothermal stages revealed that meteoric water was an important source for most of the oxygen in fluid of both stages.