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1.
System As–Na–S–Cl–H–O was studied. The research was carried out in three stages: (1) selection of the most likely complexes resulting from arsenic sulfide dissolution, (2) calculation of their thermodynamic constants, and (3) comparison of calculated data with thermodynamic database obtained in tests with the solution of inverse thermodynamic problems using the Selektor program complex. The system As–Na–S–Cl–H–O included more than 230 dependent components, which were divided into two groups, base and functional. The former group includes components of the solution (NaCl, NaOH, Na2S, NaHS, HCl, H2S, H2SO4, sulfates, H2SO3, sulfites, thiosulfates, Na+, Cl−,HS−, S2−), gas phase (43 components), and solid phase (orpiment, red arsenic, arsenolite, claudetite, arsenic, sulfur, sodium salts). Thermodynamic constants of the base components are contained in the Selektor database (they were borrowed from reference-books). The latter group includes 77 complexes labile in the solution but determining the solubility of arsenic and stability of its solid phases. Physicochemical modeling was performed in H2S (≥0.01 m, pH = 1–10), Na2S, and NaHS solutions at 25–250 °C and saturated-vapor pressure. It has been established that the dissolution of arsenic sulfide mineral phases in subneutral and alkaline solutions at low oxidation potential is favored by the formation of sulfoarsenides, which are more stable than arsenides and arsenates. Thermodynamic constants of functional complexes determining the orpiment solubility were calculated within the experimental error. It is shown that in hydrothermal iron-free systems with a low oxidation potential, the concentration of As in the solution decreases on cooling and with acidity increase.  相似文献   

2.
The concentration and transport of metals in hydrothermal solutions depend on how metals ions combine with ligands to form complexes, and experimental methods are necessary to identify the important complexes. UV-Vis-NIR spectrophotometry was used to study the formation of Cu(II)-chloride complexes in LiCl brines up to very high chlorinities (18 m LiCl), at temperatures between 25°C and 90°C. The number of Cu(II)-chloride complexes necessary to account for the variation in spectra with varying chloride molality at each temperature was estimated using principal component analysis. The molar absorptivity coefficients and concentrations of each complex were then determined using a “model-free” analysis, which does not require any assumption about the chemistry of the system, other than the number of absorbing species present. Subsequently, the results from the “model-free” analysis were integrated with independent experimental evidence to develop a thermodynamic speciation model, where the logarithms of the equilibrium constants for Cu(II)-chloride formation reactions were fitted to the data using a non-linear least-squares approach. Maps of the residual function were used to estimate uncertainties in the fitted equilibrium constants.The results of this study are similar to published properties of distorted octahedral [CuCl(OH2)5]+ and [CuCl2(OH2)4]0 at all temperatures, but diverge for [CuCl3(OH2)3]− and distorted tetrahedral [CuCl4]2−. Moreover, the data suggest the presence of [CuCl5]3−, probably with D3h point group, at very high salt concentration. This study demonstrates that it is possible to determine apparent thermodynamic equilibrium constants for the formation of complexes of trace amount of metals in highly concentrated brines, such as those associated with many ore deposits. The results are dependent on the choice of activity coefficients for charged and neutral aqueous complexes, but this influence is relatively small compared with the experimental uncertainty. This study shows that Cu2+ chloro-complexes, predominantly [CuCl2(OH2)4]0 and [CuCl4]2−, will play a dominant role in nature where free oxygen is available (near-surface), and where chloride activities are very high (evaporitic basins; hypersaline soils).  相似文献   

3.
The Bairendaba vein-type Ag–Pb–Zn deposit, hosted in a Carboniferous quartz diorite, is one of the largest polymetallic deposits in the southern Great Xing'an Range. Reserves exceeding 8000 tonnes of Ag and 3 million tonnes of Pb?+?Zn with grades of 30 g/t and 4.5% have been estimated. We identify three distinct mineralization stages in this deposit: a barren pre-ore stage (stage 1), a main-ore stage with economic Ag–Pb–Zn mineralization (stage 2), and a post-ore stage with barren mineralization (stage 3). Stage 1 is characterized by abundant arsenopyrite?+?quartz and minor pyrite. Stage 2 is represented by abundant Fe–Zn–Pb–Ag sulphides and is further subdivided into three substages comprising the calcite–polymetallic sulphide stage (substage 1), the fluorite–polymetallic sulphide stage (substage 2), and the quartz–polymetallic sulphide stage (substage 3). Stage 3 involves an assemblage dominated by calcite with variable pyrite, galena, quartz, fluorite, illite, and chlorite. Fluid inclusion analysis and mineral thermometry indicate that the three stages of mineralization were formed at temperatures of 320–350°C, 200–340°C, and 180–240°C, respectively. Stage 1 early mineralization is characterized by low-salinity fluids (5.86–8.81 wt.% NaCl equiv.) with an isotopic signature of magmatic origin (δ18Ofluid = 10.45–10.65‰). The main ore minerals of stage 2 precipitated from aqueous–carbonic fluids (4.34–8.81 wt.% NaCl equiv.). The calculated and measured oxygen and hydrogen isotopic compositions of the ore-forming aqueous fluids (δ18Ofluid = 3.31–8.59‰, δDfluid?=??132.00‰ to??104.00‰) indicate that they were derived from a magmatic source and mixed with meteoric water. Measured and calculated sulphur isotope compositions of hydrothermal fluids (δ34S∑S?=??1.2–3.8‰) indicate that the ore sulphur was derived mainly from a magmatic source. The calculated carbon isotope compositions of hydrothermal fluids (δ13Cfluid?=??26.52‰ to??25.82‰) suggest a possible contribution of carbon sourced from the basement gneisses. The stage 3 late mineralization is dominated (1.40–8.81 wt.% NaCl equiv.) by aqueous fluids. The fluids show lower δ18Ofluid (?16.06‰ to??0.70‰) and higher δDfluid (?90.10‰ to??74.50‰) values, indicating a heated meteoric water signature. The calculated carbon isotope compositions (δ13Cfluid?=??12.82‰ to??6.62‰) of the hydrothermal fluids in stage 3 also suggest a possible contribution of gneiss-sourced carbon. The isotopic compositions and fluid chemistry indicate that the ore mineralization in the Bairendaba deposit was related to Early Cretaceous magmatism.  相似文献   

4.
Gold mineralization of the Seolhwa mine occurs in a single stage of massive quartz veins which filled the north‐east‐trending fault shear zones in the Jurassic granitoid of 161 Ma within the Gyeonggi Massif. The vein quartz contains three main types of fluid inclusions at 25°C: (i) aqueous type I inclusions (0–15 wt.% NaCl) containing small amounts of CO2; (ii) gas‐rich (more than 70 vol. %), vapor‐homogenizing, aqueous type II inclusions; and (iii) low‐salinity (less than 5 wt.% NaCl), liquid CO2‐bearing, type III inclusions. The H2O‐CO2‐CH4‐N2‐NaCl inclusions represent immiscible fluids trapped earlier along the solvus curve in the temperature range 250–430°C at pressures of ～1 kb. Detailed fluid inclusion chronologies suggest a progressive decrease in pressure during the mineralization. Aqueous inclusion fluids represent either later fluids evolved through extensive fluid unmixing from a homogeneous H2O‐CO2‐CH4‐N2‐NaCl fluid due to decreases in temperature and pressure, or the influence of deep circulated meteoric waters. Initial fluids were homogeneous H2O‐CO2‐CH4‐N2‐NaCl fluids as follows: 250° to 430°C, 16–62 mol% CO2, 5–14 mol% CH4, 0.06–0.31 mol% N2 and salinities of 0.4–4.9 wt.% NaCl. The T‐X data for the Seolhwa mine suggest that the hydrothermal system has been probably located nearer to the granitic melt, which facilitated the CH4 formation and resulted in a reduced fluid state indicated by the predominance of pyrrhotite. Measured and calculated isotopic compositions of the hydrothermal fluids [δ18O = 5.3–6.5‰; δD =?69 to ?84‰] provide evidence of the CH4‐H2O equilibria and further indicate that the auriferous fluids were magmatically derived. Both the dominance of δ34S values of sulfides close to the meteoric reference (?0.6–1.4‰; δ34SΣS values of 0.3–1.1‰) and the available δ13C data (?4‰) are consistent with their deep igneous source. The Seolhwa mine was probably formed by extensive fracturing and veining due to the thermal expansion of water derived from the Jurassic granitoid melt.  相似文献   

5.
Sodic–calcic alteration is common in mineralized hydrothermal systems, yet the relative importance of igneous vs. basinal fluid sources remains controversial. One of the most extensive volumes of sodic–calcic rocks occurs near Cloncurry, NW Queensland, and was formed by overlapping hydrothermal systems that were active synchronously with emplacement of mid‐crustal batholithic granitoids (c. 1.55–1.50 Ga). Altered rocks contain albite–oligoclase, actinolite, diopside, titanite and magnetite. Alteration was localized by: (A) composite veins and breccias containing crystallized magma intimately intergrown with hydrothermal precipitates; (B) intrusions that host setting A veins and breccias; and (C) extensive breccia and vein systems linked to regional fault systems. Isotope analyses of actinolites in settings A and B indicate calculated δ18OH2O (+8.2 to +10.6‰) and variably depleted δDH2O (?130 to ?54‰) compared with typical magmatic fluids, whereas those from setting C typically indicate calculated δ18OH2O (+8.0 to +12.8‰) and δDH2O (?29 to ?99‰). The lowest δDH2O values are interpreted as representing residual fluids after significant (> 90%) open‐system magmatic degassing. Overall the stable isotope, field, geochronological and geobarometric data suggest that these sodic–calcic alteration systems were formed by the episodic incursion of magmatic fluids that underwent minor isotopic modification as a result of varying degrees of interaction with country rocks.  相似文献   

6.
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7.
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8.
The spectra of chlorolead(II) complexes in the ultraviolet region have been measured in acid chloride solutions from 0.0012 to 3.223 m and at temperatures from 25 to 300°C. The thermodynamic cumulative and stepwise formation constants as well as the spectra of the individual chlorolead(II) species have been calculated from the spectrophotometric data. At 25°C, the five species PbCl2?nn (0 ≤ n ≤ 4) occur, however, at 300°C the predominant species were PbCl+, PbCl02 and PbCl?3. Pb2+ occurs as a minor species in dilute solutions where total chloride is <0.003 m at 300°C and the presence of PbCl2?4 in concentrated solutions was not detected above 150°C. With increasing temperature, chlorolead(II) complex stability is characterised by large endothermic enthalpies and large positive entropies of formation. Lead(II) chloride complexes are important in the transport and deposition of lead by hydrothermal ore solutions of moderate to high salinity.  相似文献   

9.
Aqueous Co(II) chloride complexes play a crucial role in cobalt transport and deposition in ore-forming hydrothermal systems, ore processing plants, and in the corrosion of special Co-bearing alloys. Reactive transport modelling of cobalt in hydrothermal fluids relies on the availability of thermodynamic properties for Co complexes over a wide range of temperature, pressure and salinity. Synchrotron X-ray absorption spectroscopy was used to determine the speciation of cobalt(II) in 0-6 m chloride solutions at temperatures between 35 and 440 °C at a constant pressure of 600 bar. Qualitative analysis of XANES spectra shows that octahedral species predominate in solution at 35 °C, while tetrahedral species become increasingly important with increasing temperature. Ab initio XANES calculations and EXAFS analyses suggest that in high temperature solutions the main species at high salinity (Cl:Co >> 2) is CoCl42−, while a lower order tetrahedral complex, most likely CoCl2(H2O)2(aq), predominates at low salinity (Cl:Co ratios ∼2). EXAFS analyses further revealed the bonding distances for the octahedral Co(H2O)62+ (octCo-O = 2.075(19) Å), tetrahedral CoCl42− (tetCo-Cl = 2.252(19) Å) and tetrahedral CoCl2(H2O)2(aq) (tetCo-O = 2.038(54) Å and tetCo-Cl = 2.210(56) Å). An analysis of the Co(II) speciation in sodium bromide solutions shows a similar trend, with tetrahedral bromide complexes becoming predominant at higher temperature/salinity than in the chloride system. EXAFS analysis confirms that the limiting complex at high bromide concentration at high temperature is CoBr42−. Finally, XANES spectra were used to derive the thermodynamic properties for the CoCl42− and CoCl2(H2O)2(aq) complexes, enabling thermodynamic modelling of cobalt transport in hydrothermal fluids. Solubility calculations show that tetrahedral CoCl42− is responsible for transport of cobalt in hydrothermal solutions with moderate chloride concentration (∼2 m NaCl) at temperatures of 250 °C and higher, and both cooling and dilution processes can cause deposition of cobalt from hydrothermal fluids.  相似文献   

10.
The coupled solubility of Au(cr) and Pt(cr) has been measured in acidic chloride solutions at 350–450°С and 0.5 and 1 kb using the autoclave technique with determination of dissolved metal contents after quenching. The constants of the reaction combining the dominant species of Au and Pt in high-temperature hydrothermal fluids (K(Au–Pt)) have been determined: 2 Au(cr) + PtCl42- = Pt(cr) + 2AuCl2-; log K(Au–Pt) =–1.02 ± 0.25 (450°С, 1 kb), 0.09 ± 0.15 (450°С, 0.5 kb), and –1.31 ± 0.20 (350°С, 1 kb). It has been established that the factors affecting the Au/Pt concentration ratio in hydrothermal fluids and precipitated ores are temperature, pressure, redox potential, and sulfur fugacity. An increase in temperature results in an increase in the Au/Pt concentration ratio (up to ~550°С at P = 1 kb). A decrease in pressure and redox potential leads to enrichment of fluid in Au. An increase in sulfur fugacity in the stability field of Pt sulfides results in increase in the Au/Pt concentration ratio. Native platinum is replaced by sulfide mineral in low-temperature systems enriched in Pt (relative to Au).  相似文献   

11.
Abstract: The Daejang mine is located within the Cretaceous Gyeongsang basin. Mineral paragenesis can be divided into four stages (stages I, II, III and IV) by major tectonic fracturing. Stages I, III and IV are economically barren. Stage II, at which the precipitation of major ore minerals occurred, is further divided into three substages with paragenetic time based on minor fractures and discernible mineral assemblages: substage IIa, marked by deposition of quartz and Fe–sulfides; substage IIb, by introduction of base-metal sulfides within carbonates and some quartz; substage IIc, by quartz and carbonates with various sulfosalts. Fluid inclusion data indicate a complex geochemical evolution of hydrothermal fluids. Both CO2–rich and H2O–rich fluids were trapped in fluid inclusions at stage I and substage IIa. It is suggested that a compositionally heterogeneous fluid was formed by fluid boiling and CO2 immiscibility at temperatures of about 400° to 300°C. Composite lodes of base-metal sul–fides, carbonates and quartz at substage IIb were deposited in open spaces created by fracturing. The fracturing event prompted rapid decreases in pressure and temperature of residual fluids and resulted in retrograde fluid boiling at about 200 bars and 300°–250°C during substage IIb. The progressive loss of CO2 by CO2 effervescence and retrograde boiling from substage IIa and IIb fluids resulted in pH increase and related increase in carbonate activity, causing deposition of abundant carbonates. The change in pH also caused the decrease of stability of hydrogen sulfide with Cu, Zn and Pb chloride complexes (as main transporting agents at Daejang) and resulted in the pricipitation of base-metal minerals. Deposition of Ag– and Sb-bearing sul–fides and sulfosalts of substage IIc occurred at temperatures of about 250° to 150°C from a dominantly aqueous fluid with low salinity (down to 3. 0 equiv. wt % NaCl). At this substage, aqueous fluid formed by mixing with cooler and less saline meteoric groundwater. There is a systematic decrease in caculated δ18Owater values with the mineralization stage (and decreasing temperature) in the Daejang hydrothermal system, from values of about 11% for stage I, through about 4% for stages II and III, to about –3 per mil for stage IV. The result of stable isotope and fluid inclusion studies are interpreted to indicate progressive less evolved and/or unexchanged meteoric water influx of an early hydrothermal system formed by highly evolved meteoric waters.  相似文献   

12.
《Chemical Geology》1992,94(3):215-227
Tourmaline is a ubiquitous mineral in the Mid-Proterozoic, peraluminous, syn- to post-tectonic granites and aplites and the related hydrothermal rocks of the Karagwe-Ankolean belt in northwest Tanzania. Electron microprobe analysis indicates that tourmalines from all of the intrusive and hydrothermal lithologies: (1) belong to the schorl-dravite solid-solution series; and (2) plot within the field occupied by tourmaline from Li-poor granitoids on the Fe-Al-Mg classification diagram. Oxygen isotope compositions range from +12.2 to +11.6‰ (SMOW) for magmatic tourmalines and from +10.8 to +9.8‰ for those of hydrothermal origin. Hydrogen isotope compositions vary from −79 to − 65‰ (SMOW) for magmatic tourmalines and from −99 to −84‰ for hydrothermal tourmalines. Water contents measured by manometry are constant at 3.0–3.2 wt.%. Within the broad grouping there arc systematic variations in both chemical [particularly Fetot/(Fetot + Mg ratio)] and isotopic composition that relate to evolving magmatic and hydrothermal conditions. Igneous differentiation [increasing Fetot/(Fetot + Mg) in magmatic tourmaline] has produced trends with higher δ18O in quartz, lower δ18O in tourmaline, and larger ΔQTZ.−TOUR.-values, that reflect a combination of a reduction of crystallization temperature and an increase of Fetot/ (Fetot + Mg) in the residual melt. Subsequent cooling and interaction of an exsolved, B-rich magmatic fluid with the pelitic country rocks, resulted in the deposition of hydrothermal tourmaline with increasing Fetot/(Fetot + Mg) ratios, and progressively lower δ18O and δD -values.  相似文献   

13.
The Early Cretaceous Duolong gold‐rich porphyry copper deposit is a newly discovered deposit with proven 5.38 Mt Cu resources of 0.72% Cu and 41 t gold of 0.23 g t?1 in northern Tibet. Granodiorite porphyry and quartz diorite porphyrite are the main ore‐bearing porphyries. A wide range of hydrothermal alteration associated with these porphyries is divided into potassic, argillic and propylitic zones from the ore‐bearing porphyry center outward and upward. In the hydrothermal alteration zones, secondary albite (91.5–99.7% Ab) occurs along the rim of plagioclase phenocryst and fissures. Secondary K‐feldspar (75.1–96.9% Or) replaces plagioclase phenocryst and matrix or occurs in veinlets. Biotite occurs mainly as matrix and veinlet in addition to phenocryst in the potassic zone. The biotite are Mg‐rich and formed under a highly oxidized condition at temperatures ranging from 400°C to 430°C. All the biotites are absent in F, and have high Cl content (0.19–0.26%), with log (XCl/XOH) values of ?2.74 to ?2.88 and IV (Cl) values of ?3.48 to ?3.35, suggesting a significant role of chloride complexes (CuCl2‐ and AuCl2‐) in transporting and precipitating copper and gold. Chlorites are present in all alteration zones and correspond mainly to pycnochlorite. They have similar Fe/(Fe+Mg), Mn/(Mn+Mg) ratios, and a formation temperature range of 280–360°C. However, the formation temperature of chlorite in the quartz‐gypsum‐carbonate‐chlorite vein is between 190°C and 220°C, indicating that it may have resulted from a later stage of hydrothermal activity. Fe3+/Fe2+ ratios of chlorites have negative correlation with AlIV, suggesting oxygen fugacity of fluids increases with decreasing temperature. Apatite mineral inclusions in the biotite phenocrysts show high SO3 content (0.44–0.82%) and high Cl content (1–1.37%), indicating the host magma had a high oxidation state and was enriched in S and Cl. The highest Cl content of apatite in the propylitic zone may have resulted from pressure decrease, and the lowest Cl content of apatite in the argillic zone may have been caused by a low Cl content in the fluids. The low concentration of SO3 content in the hydrothermal apatite compared to the magmatic one may have resulted from the decrease of oxygen fugacity and S content in the hydrothermal fluid, which are caused by the abundant precipitation of magnetite.  相似文献   

14.
The solubility of hematite in chloride-bearing hydrothermal fluids was determined in the temperature range 400–600°C and at 1000 and 2000 bars using double-capsule, rapid-quench hydrothermal techniques and a modification of the Ag + AgCl buffer method (Frantz and Popp, 1979). The changes in the molalities of associated hydrogen chloride (mHCl0) as a function of the molality of total iron in the fluid at constant temperature and pressure were used to identify the predominant species of iron in the hydrothermal fluid. The molality of associated HCl varied from 0.01 to 0.15. Associated FeCl20 was found to be the most abundant species in equilibrium with hematite. Determination of Cl/Fe in the fluid in equilibrium with hematite yields values approximately equal to 2.0 suggesting that ferrous iron is the dominant oxidation state.The equilibrium constant for the reaction Fe2O3 + 4HCl0 + H2 = 2FeCl20 + 3H2O was calculated and used to estimate the difference in Gibbs free energy between FeCl20 and HCl0 in the temperature range 400–600°C at 1000 and 2000 bars pressure.  相似文献   

15.
Considerable fractions of the Hg content of lake and river systems in Scandinavia are discharged from the soil of the catchments. An important soil type in Scandinavia is the iron–humus podzol. The sorption characteristics of this soil type for inorganic Hg(II) and monomethyl mercury were investigated by batch experiments. The solubility of Hg2+ and CH3Hg+ in the soil horizons containing organic matter increases with increasing pH of the soil solution by favoring the formation of solute organic matter–mercury complexes. While the solubility of Hg2+ is strongly dependent on complexation to dissolved organic matter, the solubility of CH3Hg+ is more dependent on ion exchange. The concentration of solute inorganic Hg(II) increased with increasing temperature probably because of an increase in the concentration of dissolved organic carbon. There was no effect of temperature on the concentration of solute CH3Hg+. At pH values where inorganic mercury–hydroxo complexes are formed, inorganic Hg(II) is efficiently sorbed to the metal oxides of the mineral soil. The soil–water distributions of inorganic Hg(II) in the different soil horizons were described by Freundlich isotherms or linear isotherms for common and contaminated mercury contents in the soils.  相似文献   

16.
The phase state of fluid in the system H3BO3–NaF–SiO2–H2O was studied at 350–800 °C and 1–2 kbar by the method of synthetic fluid inclusions. The increase in the solubility of quartz and the high reciprocal solubility of H3BO3 and NaF in water fluid at high temperatures are due to the formation of complexes containing B, F, Si, and Na. At 800 °C and 2 kbar, both liquid and gas immiscible phases (viscous silicate-water-salt liquid and three water fluids with different contents of B and F) are dispersed within each other. The Raman spectra of aqueous solutions and viscous liquid show not only a peak of [B(OH)3]0 but also peaks of complexes [B(OH)4]–, polyborates [B4O5(OH)4]2–, [B3O3(OH)4]–, and [B5O6(OH)4]–, and/or fluoroborates [B3F6O3]3–, [BF2(OH)2]–, [BF3(OH)]–, and [BF4]–. The high viscosity of nonfreezing fluid is due to the polymerization of complexes of polyborates and fluorine-substituted polyborates containing Si and Na. Solutions in fluid inclusions belong to P–Q type complicated by a metastable or stable immiscibility region. Metastable fluid equilibria transform into stable ones owing to the formation of new complexes at 800 ºC and 2 kbar as a result of the interaction of quartz with B-F-containing fluid. At high concentrations of F and B in natural fluids, complexes containing B, F, Si, and alkaline metals and silicate-water-salt dispersed phases might be produced and concentrate many elements, including ore-forming ones. Their transformation into vitreous masses or viscous liquids (gels, jellies) during cooling and the subsequent crystallization of these products at low temperatures (300–400 °C) should lead to the release of fluid enriched in the above elements.  相似文献   

17.
The results of thermobaric geochemical study of ores of the Dvoinoye epithermal Au–Ag deposit are considered. Study of the fluid inclusions has shown that the ores were formed from low-salinity hydrothermal solutions with Na, Ka, and Mg chlorides and CO2, HS–, CH4 trace fluxes at the time when the temperature dropped from 370 to 130°C. The results are compared with data obtained from the closely located Kupol and Sentyabr’skoye deposits.  相似文献   

18.
The Na Son deposit is a small‐scale Pb–ZnPb–Zn–Ag deposit in northeast Vietnam and consists of biotite–chlorite schist, reddish altered rocks, quartz veins and syenite. The biotite–chlorite schist is intruded by syenite. Reddish altered rocks occur as an alteration halo between the biotite–allanite‐bearing quartz veins and the biotite–chlorite schist. Allanite occurs in the biotite–allanite‐bearing quartz veins and in the proximal reddish altered rocks. Rare earth element (REE) fluorocarbonate minerals occur along fractures or at rim of allanite crystals. The later horizontal aggregates of sulfide veins and veinlets cut the earlier reddish altered rocks. The earlier Pb–Zn veins consist of a large amount of galena and lesser amounts of sphalerite, pyrite and molybdenite. The later Cu veins cutting the Pb–Zn veins include chalcopyrite and lesser amounts of tetrahedrite and pyrite. The occurrences of two‐phase H2O–CO2 fluid inclusions in quartz from biotite–allanite‐bearing quartz veins and REE‐bearing fluorocarbonate minerals in allanite suggest the presence of CO2 and F in the hydrothermal fluid. The oxygen isotopic ratios of the reddish altered rocks, biotite–chlorite schist, and syenite range from +13.9 to +14.9 ‰, +11.5 to +13.3 ‰, and +10.1 to +11.6 ‰, respectively. Assuming an isotopic equilibrium between quartz (+14.6 to +15.8 ‰) and biotite (+8.6 ‰) in the biotite–allanite‐bearing quartz vein, formation temperature was estimated to be 400°C. At 400°C, δ18O values of the hydrothermal fluid in equilibrium with quartz and biotite range from +10.5 to +11.7 ‰. These δ18O values are consistent with fluid that is derived from metamorphism. Assuming an isotopic equilibrium between galena (+1.5 to +1.7 ‰) and chalcopyrite (+3.4 ‰), the formation temperature was estimated to be approximately 300°C. The formation temperature of the Na Son deposit decreased with the progress of mineralization. Based on the geological data, occurrence of REE‐bearing minerals and oxygen isotopic ratios, the REE mineralization is thought to result from interaction between biotite–chlorite schist and REE‐, CO2‐ and F‐bearing metamorphic fluid at 400°C under a rock‐dominant condition.  相似文献   

19.
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20.
Physicochemical factors of formation of Au-As,Au-Sb,and Ag-Sb deposits   总被引：1，自引：0，他引：1  
The physicochemical formation conditions of Au-As, Au-Sb, and Ag-Sb ores characterized by similar paragenetic mineral assemblages and sets of major ore elements but differing in their proportions have been studied. The composition of the solutions filling fluid inclusions in minerals of Au-Sb deposits, combined with mineralogical and geochemical data, indicates that these deposits were formed from a near-neutral to alkalescent chloride-sulfide (<5 wt % NaCl) solution. Au-As and Au-Sb deposits were formed from fluids of the same type, consisting of a predominately CO2-CH4 gas phase with N2 and a low-saline chloride-sulfide solution, where Au and Ag were predominantly transported as dihydrosulfide species and Sb as sulfide and hydroxy complexes. Superimposed minerals of the sulfide-sulfosalt stage that precipitated from chloride-rich solutions (up to 30 wt % NaCl equiv), which contained Ca and Fe chlorides in addition to NaCl, are identified at some Au-Sb deposits. These solutions are similar in composition to the ore-forming fluids of Ag-Sb deposits. Chloride complexes are dominant Au and Ag species in acid chloride-rich solutions of Ag-Sb deposits (up to 38 wt % NaCl equiv), while chloride and hydroxy complexes are characteristic of Sb. These solutions are distinguished by high concentrations of Ag, Sb, Cu, Fe, Mn, Bi, Pb, and Zn. The mineralogical and geochemical specialization of Ag-Sb ore is caused by chemical features of highly concentrated chloride solutions enriched in Ag, Sb, and Cu and by a relatively low Au content within the pH interval 3.5–4.0 (10?6 m). The factors controlling formation of Au-As deposits are a high capacity of a low-chloride sulfide solution with respect to metals and a high Au concentration therein (two orders higher than that of solutions of Ag-Sb deposits). The enrichment of the pyrite-arsenopyrite paragenetic assemblage in gold is a result of juxtaposed stability fields of native gold, arsenopyrite, and pyrite and their mass deposition with a decrease in temperature from 400 to 300°C. The main cause of the specific mineralogy and geochemistry of Au-Sb deposits is a high metal capacity of a near-neutral low-chloride sulfide fluid with respect to Sb, Au, and Ag, but a low Ag content. The mineralogical and fluid inclusion data combined with computer thermodynamic simulation allowed us to establish the factors of ore formation at P-T-X parameters close to natural conditions and made it possible to characterize the joint deposition of gold and silver in quantitative terms.  相似文献   

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