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1.
Most altered clay minerals in uranium ore deposits in granites in the selected provinces of South China haveδ 18O m values ranging from 6.22 to 7.24,δDm from −60 to −70,δ 18O from +3.05 to −3.07, and from −20.2 to −37.5‰. Relative enrichment of32S in the uranium ore deposits and greater variations in Pb isotopic composition of galenas from them show that uranium ores in the granites were formed in such a way that uranium in shallow-source granites had been mobilized by heated meteoric waters and then migrated to local favourable locations along great faults to form uranium ore deposits. Zhang Shaoli, Yang Wenjin, Tang Chunjing and Xu Wenxin did part of this work.  相似文献   

2.
The Hongshan copper deposit is a typical cryptoexplosive breccia-type deposit, which occurs in a metamorphic rock series of the Mesoproterozoic Taoxiyuan Formation. Orebodies are distributed inside and outside porphyry-cryptoexplosive breccia pipes. The isotope geochemistry of the deposit is consistent with the origin of porphyry breccia: the δ18OH2O values ranging from 1.2‰ to 6.1‰ and the δ34S values varying from 0 to 2.5‰. 206Pb/204Pb, 207Pb/204Pb and 208Pb/204Pb ratios of pyrite, which coexists with ore minerals, indicate it was derived from the orogenic belt. Thermodynamic analysis indicates that the main metals were deposited largely as a result of the decreasing of proton concentrations associated with H2S and CO2 exsolution during explosion and temperature dropping. Based on K-Ar dating of quartz coexisting with ore minerals, the age of mineralization was estimated to be 97.1–98.8 Ma, which suggests that mineralization occurred between the Early and Late Cretaceous. According to the relevant information obtained, a diagenetic and metallogenic pattern in the area has been presented in this paper.  相似文献   

3.
The Rushan gold deposit, explored in recent years in the Jiaodong area, Shandong Province, is a quartz vein-type gold deposit hosted in granite. The temperature of its major mineralization episode is between 220°C and 280°C. The salinity of the ore-forming fluid is 5 % to 9% NaCl equivalent, with H2O and CO2 as the dominant gas constituents. The fluid is rich in Na+, Ca2+ and Cl−, but relatively impoverished in K+ and F−, characterized by either Ca2+ > Na+ > K+ (in three samples) or Na+ > Ca2+ > K+ (in six samples). Hydrogen and oxygen isotopes in the ore-forming fluid are highly variable with δ18 ranging between − 7.70‰ and 5. 97‰ and between − 128‰ and − 71‰. The possibility of lamprophyre serving as the source of gold can be excluded in view of its low gold content on the order of 2.5 × 10−9. Rb-Sr isochron ages of the deposit and the host Kunyushan granite are ( 104.8 ± 1.5) Ma and 134.6 Ma respectively with the respective initial Sr ratios of 0. 71307 and 0.7096. It is considered that the emplacement of the lamprophyre under a tensile environment had provided sufficient heat energy to facilitate deep circulation of meteoric water by which ore metals were extracted from the Kunyushan granite through long-term water-rock reaction. This project was financially supported by the National Natural Science Foundation of China.  相似文献   

4.
New mineralogical, thermobarometric, isotopic, and geochemical data provide evidence for long and complex formation history of the Sarylakh and Sentachan Au-Sb deposits conditioned by regional geodynamics and various types of ore mineralization, differing in age and source of ore matter combined in the same ore-localizing structural units. The deposits are situated in the Taryn metallogenic zone of the East Yakutian metallogenic belt in the central Verkhoyansk-Kolyma Fold Region. They are controlled by the regional Adycha-Taryn Fault Zone that separates the Kular-Nera Terrane and the western part of the Verkhoyansk Fold-Thrust Belt. The fault extends along the strike of the northwest-trending linear folds and is deep-rooted and repeatedly reactivated. The orebodies are mineralized crush zones accompanied by sulfidated (up to 100 m wide) quartz-sericite metasomatic rocks and replacing dickite-pyrophyllite alteration near stibnite veinlets. Two stages of low-sulfide gold-quartz and stibnite mineralization are distinguished. The formation conditions of the early milk white quartz in orebodies with stibnite mineralization at the Sarylakh and Sentachan deposits are similar: temperature interval 340–280°C, salt concentration in fluids 6.8–1.6 wt % NaCl equiv, fluid pressure 3430–1050 bar, and sodic bicarbonate fluid composition. The ranges of fluid salinity overlapped at both deposits. In the late regenerated quartz that attends stibnite mineralization, fluid inclusions contain an aqueous solution with salinity of 3.2 wt % NaCl equiv and are homogenized into liquid at 304–189°C. Syngenetic gas inclusions contain nitrogen 0.19 g/cm3 in density. The pressure of 300 bar is estimated at 189°C. The composition of the captured fluid is characterized as K-Ca bicarbonatesulfate. The sulfur isotopic composition has been analyzed in pyrite and arsenopyrite from ore and metasomatic zones, as well as in coarse-, medium-, and fine-grained stibnite varieties subjected to dynamometamorphism. The following δ34S values, ‰ have been established at the Sarylakh deposit: −2.0 to −0.9 in arsenopyrite, −5.5 to −1.1 in pyrite, and −5.5 to −3.6 in stibnite. At the Sentachan deposit: −0.8 to +1.0 in arsenopyrite, +0.5 to +2.6 in pyrite, and −3.9 to +0.6 in stibnite. Sulfides from the Sentachan deposit is somewhat enriched in 34S. The 18O of milk white quartz at the Sarylakh deposit varies from +14.8 to 17.0‰ and from +16.4 to + 19.3‰ at the Sentachan. The δ18O of regenerated quartz is +16.5‰ at the Sarylakh and +17.6 to +19.8‰ at the Sentachan. The δ18O of carbonates varies from +15.0 to 16.3% at the Sarylakh and from +16.7 to +18.2‰ at the Sentachan. The δ13C of carbonates ranges from −9.5 to −12.1‰ and −7.8 to −8.5‰, respectively. The calculated $ \delta ^{18} O_{H_2 O} $ \delta ^{18} O_{H_2 O} of the early fluid in equilibrium with quartz and dolomite at 300δC are +7.9 to +10.1‰ for the Sarylakh deposit and +9.5 to +12.4‰ for the Sentachan deposit (+4.9 and 6.0‰ at 200°C for the late fluid, respectively). Most estimates fall into the interval characteristic of magmatic water (°18O = +5.5 to +9.5‰).  相似文献   

5.
Five Cu–Au epidote skarns are associated with the Mt. Shea intrusive complex, located in the 2.7–2.6 Ga Eastern Goldfields Province of the Archean Yilgarn craton, in greenstones bounded by the Boulder Lefroy and Golden Mile strike-slip faults, which control the Golden Mile (1,435 t Au) at Kalgoorlie and smaller “orogenic” gold deposits at Kambalda. The Cu–Au deposits studied are oxidized endoskarns replacing faulted and fractured quartz monzodiorite–granodiorite. The orebodies are up to 140 m long and 40 m thick. Typical grades are 0.5% Cu and 0.3 g/t Au although parts are richer in gold (1.5–4.5 g/t). At the Hannan South mine, the skarns consist of epidote, calcite, chlorite, magnetite (5–15%), and minor quartz, muscovite, and microcline. Gangue and magnetite are in equilibrium contact with pyrite and chalcopyrite. The As–Co–Ni-bearing pyrite contains inclusions of hematite, gold, and electrum and is intergrown with cobaltite and Cu–Pb–Bi sulfides. At the Shea prospect, massive, net-textured, and breccia skarns are composed of multistage epidote, actinolite, albite, magnetite (5%), and minor biotite, calcite, and quartz. Gangue and magnetite are in equilibrium with Co–Ni pyrite and chalcopyrite. Mineral-pair thermometry, mass-balance calculations, and stable-isotope data (pyrite δ34SCDT = 2.5‰, calcite δ13CPDB = −5.3‰, and δ18OSMOW = 12.9‰) indicate that the Cu–Au skarns formed at 500 ± 50°C by intense Ca–Fe–CO2–S metasomatism from fluids marked by an igneous isotope signature. The Mt. Shea stock–dike–sill complex postdates the regional D1 folding and metamorphism and the main phase of D2 strike-slip faulting. The suite is calc-akaline and comprises hornblende–plagioclase monzodiorite, quartz monzodiorite, granodiorite, and quartz–plagioclase tonalite porphyry. The intrusions display a wide range in silica content (53–73 wt% SiO2), in ratio (0.37–0.89), and in ratio (0.02–0.31). Chromium (62–345 ppm), Ni (23–158), Sr (311–1361 ppm), and Ba (250–2,581 ppm) contents are high, Sr/Y ratios are high (24–278, mostly >50), and the rare earth element patterns are fractionated . These features and a negative niobium anomaly relative to the normal mid-ocean ridge basalt indicate that the suite formed by hornblende fractionation from a subduction-related monzodiorite magma sourced from metasomatized peridotite in the upper mantle. The magnesian composition of many intrusions was enhanced due to hornblende crystallization under oxidizing hydrous conditions and during the subsequent destruction of igneous magnetite by subsolidus actinolite–albite alteration. At the Shea prospect, main-stage Cu–Au epidote skarn is cut by biotite–albite–dolomite schist and by red biotite–albite replacement bands. Post-skarn alteration includes 20-m-thick zones of sericite–chlorite–ankerite schist confined to two D3 reverse faults. The schists are mineralized with magnetite + pyrite + chalcopyrite (up to 0.62% Cu, 1.6 g/t Au) and are linked to skarn formation by shared Ca–Fe–CO2 metasomatism. Red sericitic alteration, marked by magnetite + hematite + pyrite, occurs in fractured porphyry. The biotite/sericite alteration and oxidized ore assemblages at the Shea prospect are mineralogically identical to magnetite–hematite-bearing gold lodes at Kambalda and in the Golden Mile. Published fluid inclusion data suggest that a “high-pressure”, oxidized magmatic fluid (2–9 wt% NaCl equivalent, , 200–400 MPa) was responsible for gold mineralization in structural sites of the Boulder Lefroy and Golden Mile faults. The sericite–alkerite lodes in the Golden Mile share the assemblages pyrite + tennantite + chalcopyrite and bornite + pyrite, and accessory high-sulfidation enargite with late-stage sericitic alteration zones developed above porphyry copper deposits.  相似文献   

6.
The role of municipal solid waste (MSW) landfill leachate on the genesis of minor amounts of pyrite associated with gypsum in an otherwise predominantly evaporitic sequence was studied in geological and geochemical terms. The potential association between landfill leachate and the conditions required for bacterial reduction of sulfate and fixation of H2S as pyrite were examined. The lithological column was generally found to contain little or no Fe. The δ34S values for sulfates were consistent with previously reported data; however, the measured δ18O values were slightly higher. Sulfides disseminated in the marl/lutite exhibited higher δ34S values (≈−8‰) than gypsum-coating pyrite crystals (δ34S < −30‰). Dissolution of gypsum to sulfate and the supply of metabolizable organic matter and Fe required for H2S fixation as sulfides may have originated from landfill leachate. Intermittent availability of leachate, a result of the precipitation regime, can facilitate sulfur disproportionation and lead to fractionations as high as   相似文献   

7.
Summary The eastern Pyrenees host a large number of talc-chlorite mineralizations of Albian age (112–97 Ma), the largest of which occur in the St. Barthelemy massif. There talc develops by hydrothermal replacement of dolostones, which were formed by alteration of calcite marbles. This alteration is progressive. Unaltered calcite marbles have oxygen isotope composition of about 25‰ (V-SMOW). The δ18O values decrease down to values of 12‰ towards the contact with dolostones. This 18O depletion is accompanied by Mg enrichment, LREE fractionation and systematic shifts in the Sr isotope compositions, which vary from 87Sr/86Sr = 0.7087–0.7092 in unaltered calcite marbles to slightly more radiogenic compositions with 87Sr/86Sr = 0.7094 near dolomitization fronts. Dolostones have δ18O values (about 9‰) lower than calcitic marbles, higher REE content and more radiogenic Sr isotope composition (87Sr/86Sr = 0.7109 to 0.7130). Hydrothermal calcites have δ18O values close to dolostones but substantially lower δ13C values, down to −6.5‰, which is indicative of the contribution of organic matter. The REE content of hydrothermal calcite is one order of magnitude higher than that of calcitic marbles. Its highly radiogenic Sr composition with 87Sr/86Sr = 0.7091 to 0.7132 suggests that these elements were derived from silicate rocks, which experienced intense chlorite alteration during mineralization. The chemical and isotopic compositions of the calcite marbles, the dolostones and the hydrothermal calcites are interpreted as products of successive stages of fluid-rock interaction with increasing fluid-rock ratios. The hydrothermal quartz, calcite, talc and chlorite are in global mutual isotopic equilibrium. This allows the calculation of the O isotope composition of the infiltrating water at 300 °C, which is in the δ18O = 2–4.5‰ range. Hydrogen isotope compositions of talc and chlorite indicate a δD = 0 to −20‰. This water probably derived from seawater, with minor contribution of evolved continental water.  相似文献   

8.
The Xihuashan tungsten deposit, Jiangxi province, China, is a world-class vein-type ore deposit hosted in Cambrian strata and Mesozoic granitic intrusions. There are two major sets of subparallel ore-bearing quartz veins. The ore mineral assemblage includes wolframite and molybdenite, with minor amounts of arsenopyrite, chalcopyrite, and pyrite. There are only two-phase aqueous-rich inclusions in wolframite but at least three major types of inclusions in quartz: two- or three-phase CO2-rich inclusions, two-phase pure CO2 inclusions and two-phase aqueous inclusions, indicating boiling. Fluid inclusions in wolframite have relatively higher homogenization temperatures and salinities (239–380°C, 3.8–13.7 wt.% NaCl equiv) compared with those in quartz (177–329°C, 0.9–8.1 wt.% NaCl equiv). These distinct differences suggest that those conventional microthermometric data from quartz are not adequate to explain the ore formation process. Enthalpy–salinity plot shows a linear relationship, implying mixing of different sources of fluids. Although boiling occurred during vein-type mineralization, it seems negligible for wolframite deposition. Mixing is the dominant mechanism of wolframite precipitation in Xihuashan. δ34S values of the sulfides range from −1.6 to +0.1‰, indicative of a magmatic source of sulfur. δ18O values of wolframite are relatively homogeneous, ranging from +4.8‰ to +6.3‰. Oxygen isotope modeling of boiling and mixing processes also indicates that mixing of two different fluids was an important mechanism in the precipitation of wolframite.  相似文献   

9.
Interdiffusion of Fe and Mg in (Mg,Fe)O has been investigated experimentally under hydrous conditions. Single crystals of MgO in contact with (Mg0.73Fe0.27)O were annealed hydrothermally at 300 MPa between 1,000 and 1,250°C and using a Ni–NiO buffer. After electron microprobe analyses, the dependence of the interdiffusivity on Fe concentration was determined using a Boltzmann–Matano analysis. For a water fugacity of ∼300 MPa, the Fe–Mg interdiffusion coefficient in Fe x Mg1−x O with 0.01 ≤ x ≤ 0.25 can be described by with and C = −80 ± 10 kJ mol−1. For x = 0.1 and at 1,000°C, Fe–Mg interdiffusion is a factor of ∼4 faster under hydrous than under anhydrous conditions. This enhanced rate of interdiffusion is attributed to an increased concentration of metal vacancies resulting from the incorporation of hydrogen. Such water-induced enhancement of kinetics may have important implications for the rheological properties of the lower mantle.
Sylvie DemouchyEmail:
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10.
The Qixia gold deposit is one of the important quartz vein-type deposits hosted in metamorphic rocks in the east of Shandong, China. Compositionally the wolframite which is associated with gold mineralization in the deposit is rich in iron, but poor in manganese, showing that this mineral crystallized from hydrothermal solution at low temperature. The temperatures at the main metallogenic stage of the Qixia gold deposit are within the range of 160–270°C. The gaseous phases in fluid inclusions are dominated by H2O and CO2, while Na+, Ca2+ and Cl− are the major species in the fluid phase with K+ and F− present in relatively small amounts. The salinities of fluids are 4.2 wt% –8.0 wt% NaCl equiv. Meanwhile, the fluid is characterized by either Ca2+ < Na+ < K+ (in five samples) or Na+ < Ca2+ < K+ (in two samples), quite similar to the composition of ore-forming fluid derived from meteoric water. Primary data on the hydrogen and oxygen isotopic compositions of the ore-forming fluid fall within a wide range: = − 56‱ − 95‱. and = − 3. 6‱ − 4. 5‱ relative to SMOW. These isotopic values fully reflect the distribution features of meteoric water which has exchanged with the metamorphic rocks of the Jiaodong Group at different temperatures and W/ R ratios, and the metallogenic process is characterized by low W/R ratios. The Rb-Sr isochron age of the Qixia gold deposit is 125.8 ± 1.7 Ma, with (87Sr/86Sr)i being 0.7168, and the time interval between the gold deposit and its country rocks (granite or metamoprhic rocks) is very large. The formation of the Qiaxia gold deposit is directly related to the evolution of geological history in eastern Shandong, and a genetic model in which the deep convective circulating meteoric water reacts with the country rocks can be used to explain the metallogenic mechanism of the deposit. This project was financially supported by the National Natural Science Foundation of China (No. 49000020).  相似文献   

11.
The objective of this study was to describe the proton promoted disproportion of synthetic manganite (γ-MnOOH) and to characterise the resulting phase transformations. The solution and remaining solid phase after disproportionation was analysed by techniques including atomic absorbance spectroscopy, X-ray diffraction (XRD), atomic force microscopy (AFM) and scanning electron microscopy (SEM). In suspensions with pH between 5 and 7, −log[H+] was monitored for 17 months and equilibrium constants were determined at 9, 12 and 17 months of reaction time for the following reaction (25 °C, 0.1 M (Na)NO3):
The formed MnO2 ages with time and the equilibrium constant for a metastable phase (ramsdellite or nsutite) as well as the most stable phase, pyrolusite (β-MnO2), was determined. Furthermore, combined pH and pe (Eh) measurements were performed to study the equilibrium;
Real-time AFM measurements of the dissolution showed shrinkage of the length of the manganite needles with time (2 hours). After 1 week SEM images showed that this decreased length also was followed by a reduced thickness of the manganite needles. From the SEM images the morphology of the formed Mn(IV) oxides was studied. At pH 2.6, pyrolusite (β-MnO2) and MnCl2 were found in the XRD patterns. Throughout the pH range there were indications of ramsdellite (MnO1.97) in the XRD patterns, which coincided with the existence of a fraction of needle shaped crystals with smaller dimensions (compared to manganite) in the SEM images. These observations together with the long term dissolution experiments suggest that the dissolution of manganite initially forms a ramsdellite or nsutite phase that over time rearranges to form pyrolusite.  相似文献   

12.
Isotopic compositions were determined for quartz, sericite and bulk rock samples surrounding the Uwamuki no. 4 Kuroko ore body, Kosaka, Japan. 18O values of quartz from Siliceous Ore (S.O.), main body of Black Ore B.O.) and the upper layer of B.O. are fairly uniform, +8.7 to +10.5. Formation temperatures calculated from fractionation of 18O between sericite and quartz from B.O. and upper S.O. are 250° to 300° C. The ore-forming fluids had 18O values of +1 and D values of –10, from isotope compositions of quartz and sericite.Tertiary volcanic rocks surrounding the ore deposits at Kosaka have uniform 18O values, +8.1±1.0 (n=50), although their bulk chemical compositions are widely varied because of different degrees of alteration. White Rhyolite, which is an intensely altered rhyolite occurring in close association with the Kuroko ore bodies, has also uniform 18O values, +7.9±0.9 (n=19). Temperatures of alteration are estimated to be around 300° C from the oxygen isotope fractionation between quartz and sericite. Paleozoic basement rocks phyllite and chert, have high 18O values, +18 and +19. The Sasahata formation of unknown age, which lies between Tertiary and Paleozoic formations, has highly variable 18O, +8 to +16 (n=4). High 18O values of the basement rocks and the sharp difference in 18O at their boundary suggest that the hydrothermal system causing Kuroko mineralization was mainly confined within permeable Tertiary rocks. D values of altered Tertiary volcanic rocks are highly variable ranging from –34 to –64% (n=12). The variation of D does not correlate with change of chemical composition, 18O values, nor distance from the ore deposits. The relatively high D values of the altered rocks indicate that the major constituent of the hydrothermal fluid was sea water. However, another fluid having lower D must have also participated. The fluid could be evolved sea water modified by interaction with rocks and the admixture of magmatic fluid. The variation in D may suggest that sea water mixed dispersively with the fluid.  相似文献   

13.
The solubility of pentatungstate of sodium (PTS) Na2W5O16 · H2O and sodium tungsten bronzes (STB) Na0.16WO3 in acid chloride solutions containing 0.026, 0.26, and 3.02m NaCl have been studied at 500°C, 1000 bar, given fO2 (Co-CoO, Ni-NiO, PTS-STB buffers), and constant NaCl/HCl ratio (Ta2O5-Na2Ta4O11 buffer). Depending on experimental conditions, the tungsten content in the solutions after experiments varied from 10−3 to 2 × 10−2 mol/kg H2O. Obtained data were used to calculate the formation constants of predominant tungsten complexes (VI, V): H3W3VIO123−, W3VO93−, [WVW4VIO16]3−, for reactions
$ \begin{gathered} 3H_2 WO_4^0 \leftrightarrow H_3 W_3 O_{12}^{3 - } + 3H^ + \log K_p = - 7.5 \pm 0.1, \hfill \\ 3H_2 WO_4^0 \leftrightarrow W_3 O_9^{3 - } + 1.5H_2 O + 3H^ + + 0.75O_2 \log K_p = - 25.7 \pm 0.2, \hfill \\ 5H_2 WO_4^0 \leftrightarrow \left[ {W^V W_4^{VI} O_{16} } \right]^{3 - } + 3H^ + + 3.5H_2 O + 0.25O_2 \log K_p = - 4.6 \pm 0.1 \hfill \\ \end{gathered} $ \begin{gathered} 3H_2 WO_4^0 \leftrightarrow H_3 W_3 O_{12}^{3 - } + 3H^ + \log K_p = - 7.5 \pm 0.1, \hfill \\ 3H_2 WO_4^0 \leftrightarrow W_3 O_9^{3 - } + 1.5H_2 O + 3H^ + + 0.75O_2 \log K_p = - 25.7 \pm 0.2, \hfill \\ 5H_2 WO_4^0 \leftrightarrow \left[ {W^V W_4^{VI} O_{16} } \right]^{3 - } + 3H^ + + 3.5H_2 O + 0.25O_2 \log K_p = - 4.6 \pm 0.1 \hfill \\ \end{gathered}   相似文献   

14.
The low-temperature heat capacity of -Mg2PO4OH was measured between 10 and 400 K by adiabatic calorimetry. No phase transition was observed over this temperature range. A relative enthalpy increment of 22,119 J mol–1 and an absolute entropy value of 127.13±0.25 J mol–1 K–1 at 298.15 K are derived from the results. The low-temperature heat-capacity data are compared with the DSC data obtained from 143 K to 775 K and show marginal differences in the common temperature range. The latter data are fitted by the polynomial
which allows extrapolation to high temperatures.Software information: WINDOWS operating system, WORD word processing, SigmaPlot diagrams exported in tiff format.  相似文献   

15.
In northern Chile, between 27 and 33°S, there are numerous deposits where residual petroleum is associated with Cu-(Ag) mineralisation (the most famous being El Soldado). All of these deposits are hosted by Lower Cretaceous volcanic or volcanoclastic facies along the axis of a former backarc basin. This close relationship suggests that the generation, migration and emplacement of hydrocarbons in the Cretaceous volcanic units is a regional process, associated with the evolution of the Cretaceous backarc basin and points to the importance of pyrobitumen as an exploration tool for similar Cu–(Ag) deposits. The present work analyses four small strata-bound copper deposits located along a north–south belt approximately 10 km east of Copiapó in northern Chile. These deposits are typically hosted by pyrobitumen-rich andesitic volcanic to volcanoclastic rocks intercalated with the marine carbonate Pabellón Formation, the youngest formation within the Chañarcillo Group. The strong genetic and spatial relationships between the pyrobitumen-rich lavas and the mineral deposits allow us to define this volcanic belt as the Ocoita-Pabellón Metallotect. Two hydrothermal events can be distinguished based on the mineralogical, textural, fluid inclusion and isotope data of ore and gangue and on the optical properties of residual petroleum. During the early event, petroleum was mobilised from the source rocks into the primary and secondary porosity of the lavas by Fe-rich hydrothermal fluids, which precipitated pyrite as an early sulphide phase. The second event is characterised by Cu-rich hydrothermal fluids, which induced three successive sub-stages of Cu-sulphide precipitation. The hydrothermal fluids chemically and thermally altered the first-stage bitumen, transforming it into pyrobitumen. The present work documents similarities between the Ocoita-Pabellón Metallotect and the El Soldado ore deposit and emphasises important differences. In the El Soldado host rocks, a petroleum reservoir existed prior to the arrival of the mineralising hydrothermal fluids, the framboidal pyrite was formed by assistance of bacteria, the S of the Cu sulphides was inherited from the pyrite, and the fluid source was basin connate-metamorphic brine. In the Ocoita-Pabellón Metallotect, the hydrocarbons were mobilised into the host rocks by hydrothermal fluids; the pyrite is epigenetic, the δ34S values of pyrite and copper sulphides are very different, with distinctive light δ34S signature of Cu sulphides (δ34S between −44.7 and −17.9‰), and the calculated δ18O of hydrothermal fluids indicates the participation of meteoric water in the late phases of the hydrothermal system.
Juan HermosillaEmail:
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16.
Hydrothermally-altered mesozonal synmetamorphic granitic rocks from Maine have whole-rock 18O (SMOW) values 10.7 to 13.8. Constituent quartz, feldspar, and muscovite have 18O in the range 12.4 to 15.2, 10.0 to 13.2, and 11.1 to 12.0, respectively. Mean values of Q–F ( 18Oquartz– 18Ofeldspar)=2.4 and Q–M ( 18Oquartz– 18Omuscovite)=3.3 are remarkably uniform (standard deviations of both are 0.2). Measured Q–F and Q–M values demonstrate that the isotopic compositions of the minerals are altered from primary magmatic 18O values but that the minerals closely approached oxygen isotope exchange equilibrium at subsolidus temperatures. Analyzed muscovites have D (SMOW) values in the range –65 to –82.Feldspars in the granitic rocks are mineralogically altered to either (a) muscovite+calcite, (b) muscovite+calcite+epidote, (c) muscovite+epidote, or (d) muscovite only. A consistent relation exists between the assemblage of secondary minerals and the oxygen isotope composition of whole rocks, quartz, and feldspar. Rocks with assemblage (a) have whole-rock 18O>12.1 and contain quartz and feldspar with 18O>13.8 and >11.4, respectively. Rocks with assemblages (b), (c), and (d) have whole-rock 18O<11.4 and contain quartz and feldspar with 18O< 13.1 and <11.0, respectively. The correlation suggests that the mineralogical alteration of the rocks was closely coupled to their isotopic alteration.Three mineral thermometers in altered granite suggest that the hydrothermal event occurred in the temperature range 400°–150° C, 100°–150° C below the peak metamorphic temperature inferred for country rocks immediately adjacent to the plutons. Calculations of mineral-fluid equilibria indicate that samples with assemblage (a) coexisted during the event with CO2-H2O fluids of and 18O=10.8 to 12.2 while samples with assemblages (b), (c), or (d) coexisted with fluids of and 18O=9.4 to 10.1. Compositional variations of the hydrothermal fluids were highly correlated: fluids enriched in CO2 were also enriched in 18O. Because CO2 was added to the granites during hydrothermal alteration and because fluids enriched in CO2 were enriched in 18O, some or all of the variation in 18O of altered granites may have been caused by addition of 18O to the rocks during the hydrothermal event. The source of both the CO2 and 18O could have been high-18O metasedimentary country rocks. The inferred change in isotopic composition of the granites is consistent with depletion of the metacarbonate rocks in 18O close to the plutons and with large volumes of fluid that were inferred from petrologic data to have infiltrated the metacarbonate rocks during metamorphism.A close approach of minerals to oxygen isotope exchange equilibrium in altered mesozonal rocks from Maine is in marked contrast to hydrothermally-altered epizonal granites whose mineral commonly show large departures from oxygen isotope exchange equilibrium. The difference in oxygen isotope systematics between altered epizonal granites and altered mesozonal granites closely parallels a differences between their mineralogical systematics. Both differences demonstrate the important control that depth exerts on the products of hydrothermal alteration. Deeper hydrothermal events occur at higher temperature and are longer-lived. Minerals and fluid have sufficient time to closely approach both isotope exchange and heterogeneous chemical equilibrium. Shallower hydrothermal events occur at lower temperatures and are shorter-lived. Generally there is insufficient time for fluid to closely approach equilibrium with all minerals.  相似文献   

17.
Measurable molybdenum isotope fractionation in molybdenites from different ore deposits through time provides insights into ore genesis and a new technique to identify open-system behavior of Re–Os in molybdenites. Molybdenite samples from six porphyry copper deposits, one epithermal polymetallic vein deposit, four skarns, and three Fe-oxide Cu–Au deposits were analyzed. The δ97Mo‰ (where ) for all samples varied from 1.34 ± 0.09‰ to −0.26 ± 0.04‰. This is the largest molybdenum isotopic variation in molybdenite from high-temperature ore deposits recorded to date. δ97Mo‰ of molybdenite varies as a function of the deposit type and the rhenium and osmium concentrations of the samples. Isotope values for Mo also vary within the individual deposits. In general, molybdenites from porphyry copper deposits have the lightest values averaging 0.07 ± 0.23‰ (1σ). Molybdenites from the other deposit types average 0.49 ± 0.26‰ (1σ). The variations could be related to the fractionation of Mo into different mineral phases during the ore-forming processes. A comparison of the Mo isotope ratios and the Re–Os ages obtained from the same aliquot may possess a geochronological evaluation tool. Samples that yielded robust ages have different Mo isotopic compositions in comparison to samples that yielded geologically unreasonable ages. Another observed relationship between the Re–Os and Mo isotope data reveals a weak correspondence between Re concentration and Mo isotope composition. Molybdenites with higher concentrations of Re correspond to lighter Mo isotope values.  相似文献   

18.
The thermodynamic stability constants for the hydrolysis and formation of mercury (Hg2+) chloride complexes
have been used to calculate the activity coefficients for Hg(OH) n (2–n)+ and HgCl n (2–n)+ complexes using the Pitzer specific interaction model. These values have been used to determine the Pitzer parameters for the hydroxide and chloro complexes and C ML). The values of and have been determined for the neutral complexes (Hg(OH)2 and HgCl2). The resultant parameters yield calculated values for the measured values of log to  ±0.01 from I  =  0.1 to 3 m at 25°C. Since the activity coefficients of and are in reasonable agreement with the values for Pb(II), we have estimated the effect of temperature on the chloride constants for Hg(II) from 0 to 300°C and I = 0–6 m using the Pitzer parameters for complexes. The resulting parameters can be used to examine the speciation of Hg(II) with Cl− in natural waters over a wide range of conditions.  相似文献   

19.
The density ρ of Caspian Sea waters was measured as a function of temperature (273.15–343.15) K at conductivity salinities of 7.8 and 11.3 using the Anton-Paar Densitometer. Measurements were also made on one of the samples (S = 11.38) diluted with water as a function of temperature (T = 273.15–338.15 K) and salinity (2.5–11.3). These latter results have been used to develop an equation of state for the Caspian Sea (σ = ±0.007 kg m−3)
where ρ0 is the density of water and the parameters A, B and C are given by
Measurements of the density of artificial Caspian Sea water at 298.15 K agree to ± 0.012 kg m−3 with the real samples. These results indicate that the composition of Caspian Sea waters must be close to earlier measurements of the major components. Model calculations based on this composition yield densities that agree with the measured values to ± 0.012 kg m−3. The new density measurements are higher than earlier measurements. This may be related to a higher concentration of dissolved organic carbon found in the present samples (500 μM) which is much higher than the values in ocean waters (~65 μM).  相似文献   

20.
In the surroundings of the Gaoqing-Pingnan fault zone are developed quite a number of gas reservoirs. Based on gas compositions, they can be divided into two groups, i.e., CO2 and CH4. Their composition and isotope geochemistry were dealt with in this study. The CO2 contents range from 60.72%–99.99%, the δ13CCO2 values from -3.41‰– -9.8‰, and the 3He/4He ratios from 4.35×10-6–6.35×10-6 (i.e. R/Ra=4.45–4.35). Based on the data on composition and isotope geochemistry, deep geological background, deep faults and volcanic rocks, it is shown that CO2 ,distributed in the Gaoqing area, mostly originated from mantle-source inorganic matter which is associated with magmatic rocks. The favorable tectonic environment for the formation of CO2 reservoirs is the rift, which is related to great fault-magmatic activity, the formation of CO2 gas pools and their space-time correlation to the most recent magmatic activities. Hydrocarbon gas pools occur in the Huagou area. The CH4 contents are within the range of 88.83%–99.12%, and the δ13CCH4 values, -44.7‰– -54.39‰. This indicates that the hydrocarbon gas resulted from the decomposition of oil-type gas at high temperatures. Volcanic rocks in the CO2 gas pool-and CH4 gas pool-distributed areas show significant differences in Fe2O3 and FeO contents. This has proven that the hydrocarbon gas may have resulted from various chemical reactions. Magmatic activities are the primary reason for the distribution of CO2 and CH4 gas pools in the Gaoqing-Pingnan fault zone.  相似文献   

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