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1.
Abstract. Carboniferous-Permian limestones of the Akiyoshi Plateau, in the Inner Zone of southwestern Japan, are composed of essentially pure calcium carbonate containing only small amounts of other elements, and they are accompanied by marble and copper skarn deposits near the contact with late Cretaceous granitoids. The δ18O values of the Akiyoshi limestones range widely from 7.6 to 28.3% and are mostly lower than those of other areas of the same age (23–29%), whereas the differences among the δ13C values are small. The δ18O values are negatively correlated with Mn and Fe contents. Samples with high δ18O (>25%) and δ13C (>2%) values do not contain Fe, Zn, or Pb, but those with low δ18O values tend to be rich in these elements, indicating that these elements were introduced by interaction with H2O dominant fluids, possibly of magmatic origin. Potential scores for evaluating the degree of interaction with hydro thermal fluids were calculated for δ18O, δ13C, Fe, Mn, Zn, Pb, and Sr. Higher scores implying much hydrothermal interaction were evident in the Mt. Hananoyama area, where there are many skarn deposits, and along faults oriented mainly NNW-SSE. Therefore, these are promising areas for exploring for blind deposits. It is likely that the hydrothermal fluid traveled through the limestones along fractures at the time of the granitic intrusions. However, the potential scores here are much smaller than those in the Pb-Zn mineralized area of the Kamioka mine, so more detailed petrological and mineralogical investigations are necessary.  相似文献   

2.
Abstract: In order to know the cause of the high δ34S values of the Korean ore deposits (Ishihara et al., 2000), Geumseong molybdenum skarn deposit and related Jurassic granitoids and Cambro-Ordovician carbonates were selected for the δ34S analyses. Two sulfide samples occurring in hydrothermal veins in fresh granitoids quarry at Songhaksan yielded δ34S values of +6.9 and +8.8 permil. These are slightly higher than +5.3 permil δ34S of the averaged rock sulfides for the Jurassic Daebo granitoids. Pyrite and molybdenite from the Geumseong deposit vary from +8.6 to +11.5 permil (average + 10.7 permil). The intruded carbonates contain very low amount of SSS (structurally substituted sulfate) as 2.9 to 8.1 ppm with high δ34S values between +28.8 and + 40.0 permil, and sulfides sulfur of 52 to 779 ppm with variable δ34S values between +3.2 and +22.5 per–mil. It is concluded that sulfur of the host carbonates was extracted and migrated into the skarn deposit at the time of the granitoid intrusion and the related hydrothermal convection, on the basis of the location of the skarn deposit occurring between the carbonates and Jurassic granitoids, and of very low contents of SSS sulfur in the carbonates. A part of SSS possibly contaminated into the Jurassic granite.  相似文献   

3.
Abstract. Primary fluid inclusions in quartz and carbonates from the Kanggur gold deposit are dominated by aqueous inclusions, with subsidiary CO2-H2O inclusions that have a constant range in CO2 content (10–20 vol %). Microthermometric results indicate that total homogenization temperatures have a wide but similar range for both aqueous inclusions (120 to 310C) and CO2-H2O inclusions (140 to 340C). Estimates of fluid salinity for CO2-H2O inclusions are quite restricted (5.9∼10.3 equiv. wt% NaCl), whereas aqueous inclusions show much wider salinity ranging from 2.2 to 15.6 equivalent wt %NaCl.
The 6D values of fluid inclusions in carbonates vary from -45 to -61 %, in well accord with the published δD values of fluid inclusions in quartz (-46 to -66 %). Most of the δ18O and δD values of the ore-forming fluids can be achieved by exchanged meteoric water after isotopic equilibration with wall rock by fluid/rock interaction at a low water/rock ratio. However, the exchanged meteoric water alone cannot explain the full range of δ18O and δD values, magmatic and/or meta-morphic water should also be involved. The wide salinity in aqueous inclusions may also result from mixing of meteoric water and magmatic and/or metamorphic water.  相似文献   

4.
Abstract. The Onsen site is an active submarine hydrothermal system hosted by the Desmos caldera in the Eastern Manus Basin, Papua New Guinea. The hydrothermal fluid is very acidic (pH=1.5) and abundant native sulfur is deposited around the vent. The δ34S values of native sulfur range from -6.5 to -9.3 %o. δ34S values of H2S and SO4 in the hydrothermal fluid are -4.3 to -9.9 %o and +18.6 to +20.0 %o, respectively. These δ34S values are significantly lower than those of the other hydrothermal systems so far reported. These low δ34S values and the acidic nature of the vent fluids suggest that volcanic SO2 gas plays an important role on the sulfur isotope systematic of the Onsen hydrothermal system. Relationship among the δ34S values of S-bearing species can be successively explained by the model based on the disproportionation reaction starting from the volcanic SO2 gas. The predicted δ34S values of SO2 agree with the measured whole rock δ34S values. δD and δ18O values of clay minerals separated from the altered rock samples also suggest the contribution of the magmatic fluid to the hydrothermal system. Present stable isotopic study strongly suggests that the Onsen hydrothermal site in the Desmos caldera is a magmatic submarine hydrothermal system.  相似文献   

5.
Oxygen isotope exchange and closure temperatures in cooling rocks   总被引：3，自引：0，他引：3  
Retrograde exchange of oxygen isotopes between minerals in igneous and metamorphic rocks by means of diffusion is explored using a finite difference computer model, which predicts both the zonation profile of δ18O within grains, and the bulk δ18O value of each mineral in the rock. Apparent oxygen isotope equilibrium temperatures that would be observed in these rocks are calculated from the δ18O values of each mineral pair within the rock. In systems which cool linearly from a sufficiently high temperature or at a low enough cooling rate, such that the final oxygen isotope values are not dependent upon the initial oxygen isotope values ('slow cooling'), the apparent oxygen isotope temperature derived for a rock composed of a single mineral pair can be shown to be simply related to the Dodson closure temperatures ( T c) for the two phases and the mode of the rock. Adding a third phase into a system which undergoes 'slow' cooling will cause the apparent temperature derived for the two minerals already present to differ from the simple relationship for a two-phase system. In some systems oxygen isotope reversals can be developed. If cooling is not 'slow', then the mineral δ18O values resulting from cooling will be partly dependent upon the initial temperature of the system concerned. The model successfully simulates the mineral δ18O values that are often observed in granitic rocks. Application of the model will help in assessing the validity of oxygen isotope thermometry in different geological settings, and allows quantitative prediction of the oxygen isotope fractionations that are developed in cooling closed systems.  相似文献   

6.
Abstract: Transportation of various kinds of elements occurred in wall rocks (Quaternary andesites) during the hydrothermal alteration accompanied by the Hishikari epithermal gold mineralization. For example, K2O and MgO contents of wall rocks decrease away from the gold-quartz veins, while (CaO+Na2O) content increases, and SiO2 content is variable near the veins. Hydrothermal alteration zoning and bulk compositional variations in wall rocks suggest that the mixing of hydrothermal solution and acidic groundwater took place an important role as the cause for the hydrothermal alteration and bulk compositional variations. The relationship between dissolved silica concentration and temperature of hydrothermal solution mixed with groundwater is obtained based on precipitation kinetics-fluid flow–mixing model, and the computed results are compared with the distribution of SiO2 minerals (quartz and cristobalite) in the hydrothermal alteration zones. This comparison suggests that the most reasonable flow rate of fluids migrating through hydrothermal alteration zones, and A/M (A: surface area of rocks interacting with fluid, M: mass of fluid) are estimated to be ca. 10-4.2 m/sec, and ca. 0.10 m2/kg, respectively. The mixing of two fluids (hydrothermal solution and acidic groundwater) can also explain δ18O zoning in the altered country rocks, hydrothermal alteration zoning from K-feldspar through K-mica to kaolinite from the center (veins) to margin, and deposition of gold.  相似文献   

7.
Large amounts of fluid, bound up in the hydrated upper layers of the ocean crust, are consumed at convergent margins and released in subduction zones through devolatilization. The liberated fluids may play an integral role in subduction zone processes, including the generation of arc-magmas. However, exhumed subduction zone rocks often record little evidence of large-scale fluid flow, especially at deeper levels within the subduction zone. Basaltic pillows from the high-pressure Corsican and Zermatt-Saas ophiolites show a range of δ18O values that overall reflect seafloor alteration prior to subduction. However, comparison between the δ18O values of the cores and rims of the pillows suggests that the δ18O values of the pillow rims at least have been modified during subduction and high-pressure metamorphism. Pillows that have not undergone high-pressure metamorphism generally have rims with higher δ18O values than their cores, whereas the converse is the case in pillows that have undergone high-pressure metamorphism. This reversal in the core to rim oxygen isotope relationship between unmetamorphosed and metamorphosed pillows is strong evidence for fluid–rock interaction occurring during subduction and high-pressure metamorphism. However, the preservation of different δ18O values in the cores and rims of individual pillows and within and between different pillows suggests that fluid flow within the subduction zone was strongly channelled. Resetting of the δ18O values in the pillow rims was probably due to fluid-hosted diffusion that occurred over relatively short time-scales (<1 Myr).  相似文献   

8.
Many different types of water and processes have been proposed for the formation of dolomites. The three phases of hydrothermal dolomites in the Middle Atlas Causse were investigated to elucidate their formation processes. The first two of these are associated with sphalerite and galena in stratiform and open space-filling deposits. These formed early in the history of the deposition of the Pb–Zn mineralization and commonly reveal a paragenetic overlap. A later phase, post-dating Pb–Zn mineralization, is reflected in saddle dolomite.
All three phases show a decrease in δ18O and δ13C values passing from sterile (unmineralized) to mineralized rocks, and isotopic signatures are independent of the carrier facies. However, early-formed dolomites can be separated into two distinct groups on the basis of δ18O values. Type 1 dolomites host stratiform ore deposits, whereas type 2 dolomites host an open space-filling ore-body. Later saddle dolomites are more depleted in 18O than either of these.
The early hydrothermal and saddle dolomites precipitated from similar fluids during three distinct events, but formed by two mechanisms: replacement (hydrothermal dolomite) and cement precipitation (saddle dolomite). They show different isotopic signatures and apparently formed at different temperatures. Field data, petrographic and stable isotope results suggest a continuum of replacement, during the Carixian for the early hydrothermal dolomite 1, and during the Toarcian for early hydrothermal dolomite 2, followed by a cement precipitation phase for saddle dolomite.  相似文献   

9.
Abstract: A comprehensive stable isotope investigation was carried out to clarify the geneses of the ore deposits in the Langshan Pb-Zn mineral district. The lead isotope study shows that these deposits were probably formed from 2. 0 to 1. 5 Ga, and were deformed and metamorphosed 1. 45 Ga. Ore lead could be a mixture of mantle lead and crustal lead. The C and S isotope results indicate that these deposits were precipitated in closed or semi-closed rift basins, and the source of sulfur might be Proterozoic ocean sulfate. The H and O isotope results indicate that the δD and δ18O values of rocks were changed by water-rock interaction during metamorphism and hydrothermal alteration. The scale of δD and δ18O shift of rocks reflects the grade of metamorphism and alteration as well as the water-rock ratios. However, the water-rock ratios in the metamorphic processes of Langshan mineral district were relatively low, and the source of water during metamorphism is suggested to be ancient meteoric water. Based on isotopic results and the geological background, it is concluded that these deposits may belong to Proterozoic sedimentary exhalative (SEDEX) type.  相似文献   

10.
Abstract: Plio–Pleistocene hydrothermal activity resulted in high grade low sulfidation epithermal gold mineralization in the Seta area, the southern end of the Monbetsu-Kamishihoro Graben of northeastern Hokkaido, Japan. Hydrothermal activity and accompanying hydrothermal eruptions began at approximately 2 Ma along NNW-SSE trending faults, the Tohbu-ko fault I and II. This activity resulted in two main zones of gold mineralization, the west quartz-adularia veins(QAV) and east stock-work zone(STZ), formed between 1. 8 and 1. 2 Ma. A smectite-chlorite alteration zone is observed at deeper levels, while kaolinite and kaolinite-smectite zones occur at shallower levels with an acid-leached zone present near the surface. The kaoli-nite and kaolinite-smectite zones are also distributed along faults and the STZ, to depths of several hundred meters. δ34S values of pyrite and alunite from the kaolinite and silicified zones indicate alunite formed by the oxidation of sulfide, either H2S(vapor) or mineral.
Formation of the STZ and the southern part of the QAV took place during lacustrine sedimentation, while formation of the northern part of the QAV took place after eruption of andesitic lava; the latter being associated with widespread alteration formed under neutral-pH conditions. δ18O values of quartz veins and silicified rocks indicate that the paleo-hydrothermal waters have a large meteoric component, increasing with decreasing depth in the STZ. Acid hydrothermal waters, resulting from near surface oxidation of H2S were responsible for acid-leaching and kaolinization of surrounding rocks. Between 1. 4 and 0. 3 Ma, the acid hot waters drained back along the STZ to depths of at least 500m, as a result of a fall in the paleo-water table level.  相似文献   

11.
Calcsilicate xenoliths occur in large numbers in some lavas and pyroclastic flows of Lascar Volcano. Their whole-rock major element and REE compositions indicate that the protolith was the Upper Cretaceous Yacoraite Formation, which crops out extensively in NW Argentina. The whole-rock major element compositions of the xenoliths fall into specific groups suggesting a strong geochemical zonation in the skarn zone. Three geochemical zones have been identified; (1) an outer metamorphic zone rich in wollastonite; (2) a middle zone rich in pyroxene and garnet; (3) an inner zone rich in pyroxene and magnetite. The two innermost zones have developed from the wollastonite zone by infiltration of metasomatic fluids rich in Fe, Mn, Mg, Ti and Al. Whole-rock REE patterns have not changed significantly during prograde metamorphism and metasomatism, indicating REE immobility in the altering fluids. Retrograde alteration by acid-sulphate fluids produced anhydrite skarns and secondary calcite and wilkeite veins in the wollastonite zone. The carbon and oxygen isotopic compositions of this calcite indicate that it formed by Rayleigh crystallization from a low-temperature (<200 °C) fluid containing dissolved H2CO3. The calculated δ18O of the water in this fluid suggests a magmatic origin whereas the calculated δ13C of the dissolved carbonate is consistent with derivation from rocks of the Yacoraite Formation at 350 °C. It is suggested that the magmatic acid-sulphate fluid was responsible for leaching carbonate from the surrounding carbonate rocks and redepositing it in the skarn zone. REEs were mobilized during the retrograde acid-sulphate and acid-carbonate alteration. A negative Ce anomaly associated with this carbonate and sulphate indicates high oxygen fugacities in the mineralizing fluids.  相似文献   

12.
Nine stratigraphic sections, each ≈5 m thick, were sampled from the Alamogordo Member limestones of the Lake Valley Formation, Sacramento Mountains, New Mexico, USA. Four stratigraphic sections consist entirely of lime mudstone and wackestone, whereas the other five sections have a prominent layer of crinoidal packstone about 1 m thick at their base. Stable isotopic analyses reveal that the lime muds in the sections with basal packstone layers show a downward decrease in δ18O and constant δ13C values, whereas those in the sections solely composed of lime mudstone and wackestone have, in general, relatively uniform δ18O and δ13C values. The diagenesis of the Alamogordo Member limestones was previously believed to have been governed by the downward percolation of meteoric water from a regional pre-Pennsylvanian exposure surface ≈100 m above this unit. However, the uniform δ13C and downward decrease in δ18O values in the lime muds in the sections with basal packstones indicate that the meteoric water ascended within the Alamogordo Member, rather than descended from the overlying exposure surface. This indicates that the basal packstones were probably a conduit for meteoric water. This is further supported indirectly by the relatively uniform δ18O and δ13C values of the lime mud in the sections without basal packstones. The implications are that the oxygen isotopic gradients may be used to identify palaeoaquifers, flow directions within these aquifers and that meteoric diagenesis below an exposure surface could be governed by flow through a palaeoaquifer.  相似文献   

13.
Abstract. Fluid inclusion and oxygen isotope studies are performed to obtain temperatures and oxygen isotopic compositions of hydrothermal fluids for the vein-type tungsten-copper deposit at Takatori in Ibaraki Prefecture, Japan. Temperatures of the hydrothermal fluids are calculated from fluid inclusion data. The calculation incorporates the effects of the salinity, gas concentration, and fluid pressure. The fluid temperatures range from 370 to 460C. For these calculations, this study obtains a density equation for H2O-NaCl-CO2 solution at the vapor-liquid two-phase boundary. Then the present study combines the obtained equation with the equation of state by Bowers and Helgeson (1983).
The fluid temperatures determined in this study are applied to the calculation of oxygen isotopic compositions of the hydrothermal fluids. The calculation of the oxygen isotopic compositions is based on the oxygen isotope analyses of vein quartz. The oxygen isotopic compositions of vein quartz range from +13.5 to +14.4 % relative to SMOW. Then, the oxygen isotopic compositions of the hydrothermal fluids in equilibrium with the vein quartz are calculated to be from +9.7 to +10.5 %. These δ18Ofluid values agree with those of magmatic fluids derived from the ilmenite-series granitic rock, which is related to the mineralization. Keywords: Takatori tungsten-copper deposit, fluid inclusion, oxygen isotope, vein quartz, H2O-NaCl-CO2 solution, density  相似文献   

14.
Topaz granite is alkali-feldspar granite that contains essential albite, quartz, K-feldspar, lithium-mica, and topaz. As a group topaz granites are characterized by their extreme enrichment in F (up to 3 wt%) and a wide variety of lithophile elements. They can be subdivided into a 'low-P2O5 subtype' (P2O5 < 0.1 wt%, Al2O3 < 14.5 wt%, SiO2 > 73 wt%) and a 'high-P2O5 subtype' (P2O5 > 0.4 wt%, Al2O3 > 14.5 wt%, SiO2 < 73 wt%), the δ18O values of which indicate a dichotomy of source rock: the low-P2O5 subtype (δ18O < 10‰) having a meta-igneous protolith and the high-P2O5 subtype (δ18O > 10 ‰) a source with a significant component of pelitic material. The unusually high F contents enhance the efficacy of melt segregation and crystal-melt fractionation and so facilitate extreme differentiation in topaz granite magmas. Very low melt volumes restrict the bulk composition of the partial melts regardless of the nature of the source; and extreme fractionation forces them along a path of magmatic convergence, to produce a group of granitic rocks with near-minimum compositions so enriched in a variety of lithophile elements (Li, Nb, Ta, Sn) that economic mineralization often results.  相似文献   

15.
Abstract: Interstitial water expelled from gas hydrate-bearing and -free sediments in the Nankai Trough are analyzed in terms of Cl-, SO42-, δ18O and δD. The baselines for the Cl- concentration and δ18O value are close to seawater values (530 mM and 0%), indicating that the interstitial water is of seawater origin. The δD values decrease with depth, implying isotopic exchange of hydrogen between upwelling biogenic methane depleted in D and interstitial water. The Cl- concentrations in gas hydrate-bearing sediments are anomalously low, while the δ18O and δD values are both high, suggesting that the water forming these gas hydrates was poor in Cl- and enriched in 18O and D during gas hydrate formation. Calculation of the gas hydrate saturations using Cl "and δ18O anomalies gives results of up to 80 % in sand, and shows that the δ18O baseline is not consistent with the Cl" baseline. The δ18O baseline increases by +1% in gas hydrate-free clay and silt. This is considered to be caused by clustering of water molecules after gas hydrate dissociation in response to the upward migration of the base of gas hydrate stability, as indicated by the presence of a double bottom-simulating reflector at this site. The water clusters enriched in 18O are responsible for the increase in the δ18O baseline with normal Cl". The abrupt shallowing of the base of gas hydrate stability may induce the dissociation of gas hydrates and the accumulation of gases in the new stability zone, representing a geological process that increases gas hydrate saturation.  相似文献   

16.
Abstract. The supergiant Xikuangshan Sb deposit is located in the Middle to Upper Devonian limestone of central Hunan, China. Primary ores are composed of early-stage stibnite and calcite with rare pyrite, early main-stage stibnite and quartz, and late main-stage stibnite and calcite. New sulfur isotope data reveal the clustering of δ34S values (+5 ∼ +8 %) for both early and late main-stage stibnite; a single early-stage stibnite exhibits δ34S value (+7.5 %) identical to its main ore-stage counterparts and the coexisting calcite has almost unmodified carbon isotope composition (-4.4 %). The data suggest a probable common source of sulfur for stibnite that was deposited at different paragenetic stages. A much wider variation in δ34S values for early main-stage stibnite (+3.5 to +16.3 %, av. +7.5 %) compared to that for late main-stage stibnite (+5.3 to +8.1 %, av. +6.2 %) can be interpreted to be due to local interaction of earlier ore fluid with Devonian host rocks. The previous studies show that the Precambrian basement contains elevated Sb concentrations, and two distinctive sulfur reservoirs with δ34Spyrite values at ca. +11 ∼ +24 % and -7.0 ∼-11 %. The homogenizing effect for sulfur hydrothermally leached from the two reservoirs might have provided ore constituents for the Xikuangshan fluids.  相似文献   

17.
The Archean mafic–ultramafic complex of Lac des Iles, Ontario, Canada, hosts economic platinum group elements (PGE)-Au-Cu-Ni mineralization in the Roby Zone. All lithologies in the North Roby Zone have been affected by hydrothermal alteration. The alteration products include talc (the most dominant mineral), anthophyllite, serpentine, actinolite, tremolite, chlorite, hornblende, zoisite, clinozoisite, epidote and sericite. In the altered rocks, light rare earth elements (La, Ce, Nd, Sm), Pb, Rb, Ba, Cs, S and possibly Y have been added by hydrothermal solution whereas Eu and heavy rare earth elements (Yb, Gd, Dy, Er) remained immobile. There are five types of fluid inclusions in the pegmatitic plagioclase with homogenization temperature and salinity ranging from 240°C to 445°C and 15.37 to 48.52 wt% equivalent NaCl, respectively. The δ18O and δD of talc range form 6.2‰ to 6.9‰ and −28‰ to −48‰, respectively. δ18O and δD water in equilibrium with talc during the hydrothermal alteration suggest a modified source for the hydrothermal solution. Microthermometry and stable isotope studies suggest that high temperature–high salinity fluid was diluted by, and mixed with, low temperature–low salinity meteoric solution. This mechanism precipitated the hydrothermal assemblage and redistributed trace elements during and after pegmatite formation in the North Ruby Zone.  相似文献   

18.
The carbon (δ13 C) and oxygen (δ18O) isotopic composistion in mollusc shells in mainly determined by the isotopic composition of water and dissolved bicarbonate. The δ18O values of water show a good correlation with the salinity of the Baltic. This correlation served as a basis for reconstructing palaeosalinity and for stratifying the marine sediments according to the δ18O values of the carbonate skeletons of subfossil shells. The δ13C values in shells are mainly determined by the isotopic composition of land-originating bicarbonate, especially in the carbonate skeleton of Lymnaea balthica , which inhabits the immediate coastal zone. According to the δ18O data, salinity in the investigated area (the coastal area of W and NW Estonia) was highest (about 9–11%) during the Littorina stage. The Limnae a stage had, in general, a salinity similar to the contemporary one, but during some phases possibly exceeding it by 2–3%.  相似文献   

19.
Abstract: Carbonate rocks of Cambrian (18 samples) and lower-middle Ordovician (11 samples) ages from South Korea were analyzed for sulfur contents of structurally substituted sulfate (SSS) and sulfides and their δ34S values. The δ34S values of SSS ranging from +25.9 to +45.2 permil, are averaged as +33.6 and +33.5 permil for the Cambrian and Ordovician rocks, respectively, which indicate high δ34S values of the Cambro-Ordovician seawater. The SSS contents in the carbonate rocks are low being 2.9 to 17.3 ppm S (averaged as 7.0 ppm S). Sulfide sulfur, on the contrary, is much abundant containing 3 to 1,880 ppm S and the δ34S values range widely between –17.6 and +31.1 permil. Sulfide sulfur of the studied rocks excluding impure carbonates has an average content of 187 ppm S and δ34S value of +12.8 permil (n=24). The estimated δ34S (sulfate–sulfide) values, which range from 13.8 to 25.4 permil in general with a few exceptions from 36.5 up to 52.3 permil for some impure carbonates, may provide evidence for the persistent oceanic anoxia with its temporary recovery during the Cambro-Ordovician time.
The SSS and sulfide sulfurs have often higher δ34S values than the Mesozoic-Cenozoic ore sulfur (Ishihara et al., 2000). Since carbonate rocks are very reactive with circulating hydrothermal ore solution, high δ34S values of the Korean ore deposits might be caused to some extent by 34S enrichment from the host carbonates, resulting in the low SSS contents observed.  相似文献   

20.
Abstract: The physical and chemical mechanism of gold precipitation in the typical low-sulfidation epithermal gold deposit at the Hishikari mine was quantified by submillimeter scale oxygen isotope analyses of vein quartz. In situ CO2 laser-ablated fluorination was used to measure temporal δ18O excursions. The calculated oxygen isotopic compositions of the ore-forming fluid indicate a dynamic process of epithermal vein formation. Intermittent opening of the vein allowed introduction of metal-bearing deep fluid to the epithermal system, and associated boiling and subsequent mixing with meteoric water caused precipitation of precious metals.  相似文献   

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