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1.
The Yonaguni Knoll IV hydrothermal vent field (24°51′N, 122°42′E) is located at water depths of 1370–1385 m near the western edge of the southern Okinawa Trough. During the YK03–05 and YK04–05 expeditions using the submersible Shinkai 6500, both hydrothermal precipitates (sulfide/sulfate/carbonate) and high temperature fluids (Tmax = 328°C) presently venting from chimney‐mound structures were extensively sampled. The collected venting fluids had a wide range of chemistry (Cl concentration 376–635 mmol kg?1), which is considered as evidence for sub‐seafloor phase separation. While the Cl‐enriched smoky black fluids were venting from two adjacent chimney‐mound structures in the hydrothermal center, the clear transparent fluids sometimes containing CO2 droplet were found in the peripheral area of the field. This distribution pattern could be explained by migration of the vapor‐rich hydrothermal fluid within a porous sediment layer after the sub‐seafloor phase separation. The collected hydrothermal precipitates demonstrated a diverse range of mineralization, which can be classified into five groups: (i) anhydrite‐rich chimneys, immature precipitates including sulfide disseminations in anhydrite; (ii) massive Zn‐Pb‐Cu sulfides, consisting of sphalerite, wurtzite, galena, chalcopyrite, pyrite, and marcasite; (iii) Ba‐As chimneys, composed of barite with sulfide disseminations, sometimes associated with realgar and orpiment overgrowth; (iv) Mn‐rich chimneys, consisting of carbonates (calcite and magnesite) and sulfides (sphalerite, galena, chalcopyrite, alabandite, and minor amount of tennantite and enargite); and (v) pavement, silicified sediment including abundant native sulfur or barite. Sulfide/sulfate mineralization (groups i–iii) was found in the chimney–mound structure associated with vapor‐loss (Cl‐enriched) fluid venting. In contrast, the sulfide/carbonate mineralization (group iv) was specifically found in the chimneys where vapor‐rich (Cl‐depleted) fluid venting is expected, and the pavement (group v) was associated with diffusive venting from the seafloor sediment. This correspondence strongly suggests that the subseafloor phase separation plays an important role in the diverse range of mineralization in the Yonaguni IV field. The observed sulfide mineral assemblage was consistent with the sulfur fugacity calculated from the FeS content in sphalerite/wurtzite and the fluid temperature for each site, which suggests that the shift of the sulfur fugacity due to participation of volatile species during phase separation is an important factor to induce diverse mineralization. In contrast, carbonate mineralization is attributed to the significant mixing of vapor‐rich hydrothermal fluid and seawater. A submarine hydrothermal system within a back‐arc basin in the continental margin may be considered as developed in a geologic setting favorable to a diverse range of mineralization, where relatively shallow water depth induces sub‐seafloor phase separation of hydrothermal fluid, and sediment accumulation could enhance migration of the vapor‐rich hydrothermal fluid.  相似文献   

2.
We present results of incubation studies conducted at low temperatures (∼4°C) in the vicinity of a seafloor hydrothermal vent system. We reacted Fe-, S-, Cu-, and Zn-bearing minerals including pyrite, marcasite, chalcopyrite, sphalerite, elemental sulfur, and a portion of a natural chimney sulfide structure for 2 months at the Main Endeavour Segment of the Juan de Fuca Ridge in the Pacific Ocean. Our study utilizes Fluorescent In Situ Hybridizations (FISH), Scanning and Transmission Electron Microscopy (SEM, TEM), and light microscopic analysis. The surfaces of these minerals are solely colonized by Bacteria and not by Archaea. Colonization densities vary over an order of magnitude with the following sequence: elemental sulfur > chimney sulfide > marcasite > pyrite > sphalerite > chalcopyrite, and correspond well with the abiotic oxidation kinetics of these materials, excepting elemental sulfur, which is both the least reactive to oxidizing species and the most heavily colonized. Colonization densities also correspond with apparent degree of reaction (dissolution pitting + accumulation of secondary alteration products). Heavy accumulations of secondary Fe oxides on Fe-bearing minerals, most notably on the chimney sulfide, form in situ as the result of mineral dissolution and the activity of neutrophilic Fe-oxidizing bacteria. Results suggest that mineral-oxidizing bacteria play a prominent role in weathering of seafloor sulfide deposits, and that microbial utilization of mineral substrates contributes to biomass production in seafloor hydrothermal environments.  相似文献   

3.
A sulfide chimney ore sampled from the flank of the active Tiger vent area in the Yonaguni Knoll IV hydrothermal field, south Okinawa trough, consists of anhydrite, pyrite, sphalerite, galena, chalcopyrite and bismuthinite. Electron microprobe analysis indicates that the chalcopyrite contains up to 2.4 wt% Sn, whereas bismuthinite contains up to 1.7 wt% Pt, 0.8 wt% Cu and 0.5 wt% Fe. The Sn‐rich chalcopyrite and Pt–Cu–Fe‐bearing bismuthinite are the first reported occurrence of such minerals in an active submarine hydrothermal system. The results confirm that Sn enters the chalcopyrite as a solid solution towards stannite by the coupled substitution of Sn4+Fe2+ for Fe3+Fe3+, whereas Pt, Cu and Fe enter the bismuthinite structure as a solid solution during rapid nucleation. The fluid inclusions homogenization temperatures in anhydrite (220–310°C) and measured end‐member temperature of the vent fluids on‐site (325°C) indicate that Sn‐bearing chalcopyrite and Pt–Cu–Fe‐bearing bismuthinite express the original composition of the minerals that precipitated as metastable phases at a temperature above 300°C. The result observed in this study implies that sulfides in ancient volcanogenic massive sulfide deposits have similar trace element distribution during nucleation but it is remobilised during diagenesis, metamorphism or supergene enrichment processes.  相似文献   

4.
Petrographic, SEM, and EPMA analyses are used to study the micro-textures and mineralogical composition of samples collected by a TV-grab from the 26°S SMAR (southern Mid-Atlantic Ridge) hydrothermal field. The investigated samples include the outermost chimney walls and sulfide debris. Isocubanite-chalcopyrite intergrowths are the major Cu-Fe sulfide phase in the chimney wall samples. These intergrowths include normal chalcopyrite, anomalous chalcopyrite (Cu-poor, Zn- and Fe-rich), normal isocubanite with Cu/Fe < 0.50, and Cu-rich isocubanite with Cu/Fe > 0.50. Anomalous chalcopyrite and Cu-rich isocubanite represent the intermediate phases between stoichiometric chalcopyrite and isocubanite in the Cu-Fe-S system. Anomalous chalcopyrite occurs as cores or thin rims bordering isocubanite, which associated with sphalerite. While Cu-rich isocubanite commonly associates pyrite. Based on textural relationships and microanalytical data of both phases, we interpret the abundant anomalous chalcopyrite and Cu-rich isocubanite as metastable or as high-temperature (~300 °C) rapidly precipitated hydrothermal sulfides. This interpretation advocates the SMAR 26°S hydrothermal field as an immature and short-living system.  相似文献   

5.
Sulfide sulfur in mid-oceanic ridge hydrothermal vents is derived from leaching of basaltic-sulfide and seawater-derived sulfate that is reduced during high temperature water rock interaction. Conventional sulfur isotope studies, however, are inconclusive about the mass-balance between the two sources because 34S/32S ratios of vent fluid H2S and chimney sulfide minerals may reflect not only the mixing ratio but also isotope exchange between sulfate and sulfide. Here, we show that high-precision analysis of S-33 can provide a unique constraint because isotope mixing and isotope exchange result in different Δ33S (≡δ33S-0.515 δ34S) values of up to 0.04‰ even if δ34S values are identical. Detection of such small Δ33S differences is technically feasible by using the SF6 dual-inlet mass-spectrometry protocol that has been improved to achieve a precision as good as 0.006‰ (2σ).Sulfide minerals (marcasite, pyrite, chalcopyrite, and sphalerite) and vent H2S collected from four active seafloor hydrothermal vent sites, East Pacific Rise (EPR) 9-10°N, 13°N, and 21°S and Mid-Atlantic Ridge (MAR) 37°N yield Δ33S values ranging from −0.002 to 0.033 and δ34S from −0.5‰ to 5.3‰. The combined δ34S and Δ33S systematics reveal that 73 to 89% of vent sulfides are derived from leaching from basaltic sulfide and only 11 to 27% from seawater-derived sulfate. Pyrite from EPR 13°N and marcasite from MAR 37°N are in isotope disequilibrium not only in δ34S but also in Δ33S with respect to associated sphalerite and chalcopyrite, suggesting non-equilibrium sulfur isotope exchange between seawater sulfate and sulfide during pyrite precipitation. Seafloor hydrothermal vent sulfides are characterized by low Δ33S values compared with biogenic sulfides, suggesting little or no contribution of sulfide from microbial sulfate reduction into hydrothermal sulfides at sediment-free mid-oceanic ridge systems. We conclude that 33S is an effective new tracer for interplay among seawater, oceanic crust and microbes in subseafloor hydrothermal sulfur cycles.  相似文献   

6.
Equilibrium path calculations have been used to model mixing between hot (350°C) hydrothermal solutions and ambient seawater, in an attempt to simulate mineral precipitation at seafloor vents. These calculations predict temperatures of precipitation, paragenetic sequence of minerals, and chemical composition of chimney deposits associated with vents on the seafloor at 21°N, EPR. Assuming sulfate-sulfide disequilibrium during mixing, the paragenetic sequence revealed is: chalcopyrite, anhydrite, pyrrhotite, pyrite, sphalerite, graphite, and barite. When sulfate-sulfide equilibria is permitted during mixing, however, reduction of small amounts of sulfate results in early precipitation of pyrite and a sequence of Cu-rich sulfide minerals (chalcopyrite-bornite-chalcocite-covellite). This sequence is analogous to that observed in thin chimney walls. The calculations indicate that sulfide mineral precipitation occurs in response to both cooling and change in composition of the hydrothermal solutions as a result of mixing. Varying the amount of mixing with respect to temperature, simulating conductive heating of seawater prior to mixing, results in only minor variations in the sequence and abundance of precipitated phases.Anhydrite precipitation during mixing occurs early, which is consistent with formation of an anhydrite leading edge of chimney structures. Similarly, extrapolation of warm spring data from Galapagos to zero SO4 concentration suggests anhydrite formation due to mixing with seawater beneath the seafloor, most likely below the level of reactive calcareous sediments. Subsequent interaction of the mixed hydrothermal solution with those sediments results in elevated and variable Ca concentrations estimated for end-member solutions from the Galapagos.Precipitation of Mg hydroxide sulfate hydrate in the walls of the vent chimneys at 21°N, EPR, occurs as a result of conductive heating of ambient seawater with only very minor amounts of mixing. In contrast, precipitation of amorphous silica in the vents must be due to conductive cooling of the hydrothermal solutions.Thus, incremental reaction calculations demonstrate that reactions occurring in and associated with venting ridge crest hydrothermal solutions can be effectively modeled using the thermodynamic data and reaction modeling codes available today. Departures from equilibrium required to accurately model the mixing process are easily accommodated and consistent with data from the vents and vent forming materials.  相似文献   

7.
Modern massive sulfide deposits are known to occur in diverse tectonic settings and it is generally expected that hydrothermal deposits of similar geological settings shall have more or less similar mineralogical and geochemical signatures. However, the Mount Jourdanne sulfide deposits along the super-slow spreading Southwest Indian Ridge deviate from this common concept. These sulfide precipitates are Zn-rich (up to 35 wt.%) and are characterized by high concentrations of Pb (≤ 3.5 wt.%), As (≤ 1.1 wt.%), Ag (≤ 0.12 wt.%), Au (≤ 11 ppm), Sb (≤ 967 ppm), and Cd (≤ 0.2 wt.%) which are unusual for a modern sediment-free mid-oceanic ridge system. Therefore, we have reinvestigated the sulfide samples collected during the INDOYO cruise in 1998, in order to explain their unusual mineralogy and geochemical composition. The sulfide samples are polymetallic and are classified as: a) chimneys, b) mounds, and c) hydrothermal breccias. The chimneys are small tube-like symmetrical bodies (30–40 cm high; ~ 10 cm diameter) and consist mainly of sphalerite and less chalcopyrite, set in a matrix of late amorphous silica. The inner wall shows a late-stage colloform sphalerite containing co-precipitates of galena and/or Pb–As sulfosalts. In contrast, the mound samples are dominated either by Fe-sulfides (pyrite) or by a mixture of pyrite and chalcopyrite with less sphalerite, pyrrhotite, amorphous silica and barite. Both, the chimney and mound samples, are characterized by layering and mineral zonation. The hydrothermal breccias are highly altered and mineralogically heterogeneous. They consist of silicified basaltic material that are impregnated with sulfides and contain cm-sized chimney fragments within a matrix of low-temperature minerals such as sphalerite and pyrite. The latter fragments mainly consist of chalcopyrite with isocubanite lamellae. In addition, these breccias contain late-stage realgar, boulangerite, galena, Pb–As sulfosalts and barite that are mostly confined to vugs or fractures. At least five mineralogical associations are distinguished that indicate different thermal episodes ranging from black smoker mineralization conditions to cessation of the hydrothermal activity. Based on the mineralogical associations and established literature in this regard, it is inferred that the mineralization at Mt. Jourdanne occurred mainly in three temperature domains. Above 300 °C, the chalcopyrite (with isocubanite)–pyrrhotite association formed whereas the sphalerite dominated assemblage with much less chalcopyrite and pyrite formed around and below 300 °C. The late-stage mineralization (below 200 °C) contains colloform sphalerite, galena, Pb–As sulfosalts, realgar and barite. The unusual mineralogy and trace element chemistry for this modern VHMS deposit could be explained assuming hydrothermal leaching of some felsic differentiates underneath the basaltic cover and subsequent zone refining processes.  相似文献   

8.
南大西洋中脊的26°S热液区广泛发育多金属硫化物、底泥、枕状熔岩、非活动性烟囱体和活动性烟囱体。为了有效探索硫、铜等成矿物质的来源以及成矿作用过程,分别以玄武岩、烟囱体残片及块状多金属硫化物为研究对象,开展了熔融包裹体、硫同位素和铜同位素研究。结果显示：区内玄武岩新鲜未蚀变且斑晶中产出大量熔融包裹体;熔融包裹体气泡壁附着黄铜矿、黄铁矿及磁铁矿等子矿物,说明在岩浆作用过程中可从熔浆中分离出成矿所需的金属元素和硫,这些成矿元素随着岩浆去气作用进入挥发分中,并随着脱气作用迁移出来。通过对烟囱体残片及块状多金属硫化物中黄铁矿的硫同位素组成进行比对分析,发现26°S热液区内硫化物的硫同位素与大西洋各热液区硫化物的硫同位素变化范围相一致,但δ34SV-CDT值略低（3.0‰~3.9‰）。低的δ34SV-CDT值指示硫以岩浆硫源为主,海水硫酸盐还原硫占比低。黄铜矿呈现略微富铜重同位素特征且分馏程度较低,其δ65Cu值（0.171‰~0.477‰）趋近于大洋中脊玄武岩的铜同位素值（0）。综合硫同位素及铜同位素特征,表明热液流体经历了岩浆和海水的混合过程,成矿物质主要来自于岩浆热液,成矿作用过程中可能有少量海水混入。  相似文献   

9.
Here, we report the first documented occurrences of “invisible” gold and silver in seafloor sulfide deposits from an active hydrothermal system on the Central Indian Ridge. A detailed mineralogical and geochemical study of polymetallic sulfides from the Edmond vent field was conducted in order to identify controls on the distribution of precious metals. Bulk samples (N = 18) contain up to 18.7 ppm Au and 1450 ppm Ag, with average concentrations of 2.3 ppm Au and 218.9 ppm Ag. Among them, several Zn-rich chimney fragments and anhydrite-dominated ore samples have higher contents of precious metals than Fe-Cu-rich massive sulfides and silica-rich hydrothermal precipitates. Native gold grains are mainly associated with sphalerite, anhydrite, barite and Fe-oxyhydroxides. Abundant submicroscopic Au-Ag alloys tend to occur along grain boundaries between Cu-Fe sulfides and tennantite, or close to the rims of Fe-poor sphalerite. In contrast to primary electrum with high Ag/Au ratios, the absence of detectable silver in high-purity gold indicates that secondary Au enrichment has probably occurred after a direct co-precipitation with Zn-rich mineral assemblages upon cooling and mixing of vent fluids with cold seawater. A suite of late-stage Ag-rich phases, including argentotennantite, pearceite and acanthite, occur as crack-filling veinlets and patches in low-temperature fahlores, or as tiny inclusions enclosed by pyrite, chalcopyrite and colloform sphalerite. By using HRTEM combined with HAADF-STEM imaging, we have found out that silver is also present in significant quantities as discrete colloidal nanoparticles in tennantite. Minor native copper is closely associated with altered chalcopyrite, sphalerite and covellite, exhibiting signs of dissolution, recrystallization and reprecipitation. Extensive hydrothermal reworking resulted from a long history of high-temperature venting in this field, together with post-depositional supergene replacement processes (involving oxidation, leaching or coupled dissolution-reprecipitation mechanisms facilitated by a permeable porosity generated in primary Cu-Fe sulfides) are considered to be important for the remobilization and local reconcentration of early-formed precious metals, and may have been responsible for the formation of relatively coarse-grained native gold or silver within recrystallized massive sulfides and chimney debris.  相似文献   

10.
Polymetallic sulfide-sulfate mineralization enriched in Pb-Ag-As-Sb-Hg occurs in the Bransfield Strait, a late Tertiary-Quaternary marginal basin close to the Antarctic Peninsula. The mineralization is associated with bimodal volcanism and pelagic and volcaniclastic sediment in rifted continental crust. Hydrothermal precipitates have been recovered from two shallow (1,050–1,000 m water depth) submarine volcanoes (Hook Ridge and Three Sisters) in the Central Bransfield Strait. Mineralization at Hook Ridge consists of polymetallic sulfides, massive barite, and pyrite and marcasite crusts in semilithified pelagic and volcaniclastic sediment. Native sulfur commonly infills void space and cements the volcaniclastic sediment. The polymetallic sulfides are dominated by sphalerite with minor galena, enargite, tetrahedrite-tennantite, pyrite, chalcopyrite, and traces of orpiment cemented by barite and opal-A. The presence of enargite at Hook Ridge, the abundance of native sulfur, and the low Fe content of sphalerite indicate a high sulfur activity of the hydrothermal fluids responsible for mineralization. The sulfur isotopic composition of Hook Ridge precipitates documents the complexity of the sulfur sources in this hydrothermal system with variable influence of biological activity and possibly magmatic contributions. Homogenization temperatures and salinities of fluid inclusions in barite and opal-A suggest that boiling may have affected the hydrothermal fluids during their ascent. The discovery of massive barite-silica precipitates at another shallow marine volcano (Three Sisters volcano) attests to the potential for hydrothermal mineralization at other volcanic edifices in the area. The characteristics of the mineralization in the Bransfield Strait with rifting of continental crust, the presence of bimodal volcanism, including highly evolved felsic volcanic rocks, the association with sediments, and the Pb-Ag-As-Sb-Hg enrichment are similar to the setting of massive sulfide deposits in the Okinawa Trough, and distinct from those of sediment-dominated hydrothermal systems such as Escanaba Trough, Middle Valley, and Guaymas Basin. The geological setting of the Bransfield Strait is also broadly similar to that of some of the largest volcanogenic massive sulfide deposits in the ancient record, such as the Iberian Pyrite Belt.Editorial handling: B. Lehmann  相似文献   

11.
The Sargaz Cu–Zn massive sulfide deposit is situated in the southeastern part of Kerman Province, in the southern Sanandaj–Sirjan Zone of Iran. The stratigraphic footwall of the Sargaz deposit is Upper Triassic to Lower Jurassic (?) pillowed basalt, whereas the stratigraphic hanging wall is andesite. Mafic volcanic rocks are overlain by andesitic volcaniclastics and volcanic breccias and locally by heterogeneous debris flows. Rhyodacitic flows and volcaniclastics overlie the sequence of basaltic and andesitic rocks. Based on the bimodal nature of volcanism, the regional geologic setting and petrochemistry of the volcanic rocks, we suggest massive sulfide mineralization in the Sargaz formed in a nascent ensialic back-arc basin. The current reserves (after ancient mining) of the Sargaz deposit are 3 Mt at 1.34% Cu, 0.38% Zn, 0.08%Pb, 0.24 g/t Au, and 7 g/t Ag. The structurally dismembered massive sulfide lens is zoned from a pyrite-rich base, to a pyrite?±?chalcopyrite-rich central part, and a sphalerite–chalcopyrite-rich upper part, with a sphalerite-rich zone lateral to the upper part. The main sulfide mineral is pyrite, with lesser chalcopyrite and sphalerite. The feeder zone, comprised of a vein stockwork consists of quartz–sulfide–sericite pesudobreccia and, in the deepest part, chlorite–quartz–pyrite pesudobreccia. Footwall hydrothermal alteration extends at least 70–80 m below the massive sulfide lens and more than a hundred meters along strike from the massive sulfide lens. Jasper and Fe–Mn bearing chert horizons lateral to the sulfide deposit represent low-temperature hydrothermal precipitates of the evolving hydrothermal system. Based on mineral textures and paragenetic relationships, the growth history of the Sargaz deposit is complex and includes: (1) early precipitation of sulfides (protore) on the seafloor as precipitation of fine-grained anhedral pyrite, sphalerite, quartz, and barite; (2) anhydrite precipitation in open spaces and mineral interstices within the sulfide mound followed by its subsequent dissolution, formation of breccia textures, and mound clasts and precipitation of coarse-grained pyrite, sphalerite, tetrahedrite–tennantite, galena and barite; (3) replacement of pre-existing sulfides by chalcopyrite precipitated at higher temperatures (zone refining); (4) continued “refining” led to the dissolution of stage 3 chalcopyrite and formation of a base-metal-depleted pyrite body in the lowermost part of the massive sulfide lens; (5) carbonate veins were emplaced into the sulfide lens, replacing stage 2 barite. The δ34S composition of the sulfides ranges from +2.8‰ to +8.5‰ (average, +5.6‰) with a general increase of δ34S ratios with depth within the massive sulfide lens and underlying stockwork zone. The heavier values indicate that some of the sulfur was derived from seawater sulfate that was ultimately thermochemically reduced in deep hydrothermal reaction zones.  相似文献   

12.
The Inkaya Cu-Pb-Zn-(Ag) mineralization, located about 20 km west of the Simav (Kütahya-Turkey), is situated in the northern part of the Menderes Massif Metamorphics. The mineralization is located along an E-W trending fault in the Cambrian Simav metamorphics consisting of quartz-muscovite schist, quartz-biotite schist, muscovite schist, biotite schist and the Ar?kayas? formation composed of marbles. Mineralized veins are 30–35 cm in width. The primary mineralization is represented by abundant galena, sphalerite, chalcopyrite, pyrite, fahlore and minor amounts of cerussite, anglesite, digenite, enargite, chalcocite, covellite, bornite, limonite, hematite and goethite with gangue quartz. Fluid inclusion studies on the quartz samples collected from the mineralized veins indicate that the temperature range of the fluids is 235°C to 340°C and the salinities are 0.7 to 4.49 wt. % NaCl equivalent. The wide range of homogenization temperatures indicates that two different fluid generations were trapped in quartz. Sulfur isotope studies of the sulfide minerals showed that all of the δ 34S values are between ?2.1 and 2.6 per mil. These values are a typical range for hydrothermal sulfide minerals that have sulfur derived from a magmatic source. Pyrite-galena and pyrite-chalcopyrite sulfur isotope fractionation is consistent with an approach to isotopic equilibrium, and calculated temperatures are 254.6 and 277.4°C for pyrite-galena and 274.7°C for pyrite-chalcopyrite. The microthermometric data and sulfur isotope thermometry indicate the existence of a hydrothermal fluid that circulated along the fault crossing the Simav metamorphics and Ar?kayas? formation. Fluid inclusion and sulfur isotope thermometry can be used in combination with ore petrographical and geological information to provide site-specific targets for meso-hypothermal metal concentrations.  相似文献   

13.
Karavansalija ore zone is situated in the Serbian part of the Serbo‐Macedonian magmatic and metallogenic belt. The Cu–Au mineralization is hosted mainly by garnet–pyroxene–epidote skarns and shifts to lesser presence towards the nearby quartz–epidotized rocks and the overlying volcanic tuffs. Within the epidosites the sulfide mineralogy is represented by disseminated cobalt‐nickel sulfides from the gersdorfite‐krutovite mineral series and cobaltite, and pyrite–marcasite–chalcopyrite–base metal aggregates. The skarn sulfide mineralization is characterized by chalcopyrite, pyrite, pyrrhotite, bismuth‐phases (bismuthinite and cosalite), arsenopyrite, gersdorffite, and sphalerite. The sulfides can be observed in several types of massive aggregates, depending on the predominant sulfide phases: pyrrhotite‐chalcopyrite aggregates with lesser amount of arsenopyrite and traces of sphalerite, arsenopyrite–bismuthinite–cosalite aggregates with subordinate sphalerite and sphalerite veins with bismuthinite, pyrite and arsenopyrite. In the overlying volcanoclastics, the studied sulfide mineralization is represented mainly by arsenopyrite aggregates with subordinate amounts of pyrite and chalcopyrite. Gold is present rarely as visible aggregate of native gold and also as invisible element included in arsenopyrite. The fluid inclusion microthermometry data suggest homogenization temperature in the range of roughly 150–400°C. Salinities vary in the ranges of 0.5–8.5 wt% NaCl eq for two‐phase low density fluid inclusions and 15–41 wt% NaCl eq for two‐phase high‐salinity and three‐phase high‐salinity fluid inclusions. The broad range of salinity values and the different types of fluid inclusions co‐existing in the same crystals suggest that at least two fluids with different salinities contributed to the formation of the Cu–Au mineralization. Geothermometry, based on EPMA data of arsenopyrite co‐existing with pyrite and pyrrhotite, suggests a temperature range of 240–360°C for the formation of the arsenopyrite, which overlaps well with the data for the formation temperature obtained through fluid inclusion microthermometry. The sulfur isotope data on arsenopyrite, chalcopyrite, pyrite and marcasite from the different sulfide assemblages (ranging from 0.4‰ to +3.9‰ δ34SCDT with average of 2.29 δ34SCDT and standard deviation of 1.34 δ34SCDT) indicates a magmatic source of sulfur for all of the investigated phases. The narrow range of the data points to a common source for all of the investigated sulfides, regardless of the host rock and the paragenesis. The sulfur isotope data shows good overlap with that from nearby base‐metal deposits; therefore the Cu–Au mineralization and the emblematic base‐metal sulfide mineralization from this metallogenic belt likely share same fluid source.  相似文献   

14.
To characterize the hydrothermal processes of East Pacific rise at 9o-10oN, sulfide mineral compositions, textural, and geochemical features of chimney ores were studied using ore microscope, scanning electron microscope, X-ray diffraction analysis, and electron microprobe techniques. Results show that there are three mineral assemblages for the hydrothermal chimney ores, namely: (i) anhydrite marcasite pyrite, (ii) pyrite sphalerite chalcopyrite, and (iii) chalcopyrite bornite digenite covellite. Mineral assemblages, zonational features, and geochemical characteristics of the ore minerals indicate that ore fluid temperature changed from low to high then to low with a maximum temperature up to 400 ℃. The chimney is a typical black smoker. The initial structure of the chimney was formed by the precipitation of anhydrites, and later the sulfides began to precipitate in the inner wall.  相似文献   

15.
The Okinawa Trough is characterized by enrichment of Ag in hydrothermal precipitates; however, the distribution of this enrichment remains poorly constrained. This study presents the results of a field-emission scanning electron microscopy and electron-microprobe analysis based mineralogical and geochemical investigation of the spatial distribution of Ag within Ag-rich sulfide samples from the Okinawa Trough. The tetrahedrite, covellite, and galena in these samples contain high concentrations of Ag(average values of 1.60, 0.78, and 0.23 wt%, respectively) and also various Ag sulfosalts. Examination of the Ag budget of these samples indicates that most of the Ag is hosted by tetrahedrite followed by galena. The Ag within tetrahedrite is incorporated by substitution into the Cu site, whereas galena becomes Ag-enriched by the coupled incorporation of monovalent Ag, Tl, and Cu, and trivalent Sb and Bi into Pb lattice sites. Tetrahedrite and galena containing higher concentrations of Sb favor increased Ag substitution. Four sets of Ag host minerals are identified with distinct ore formation temperatures. Tetrahedrite and galena concentrate the majority of Ag at medium temperatures(150–300°C). Other Ag host minerals concentrate only minor or trace amounts of Ag, including massive sphalerite, chalcopyrite, and pyrite at high temperatures(300°C), colloform pyrite and sphalerite at low temperatures(150°C), and Ag-sulfosalts at even lower temperatures(100°C).  相似文献   

16.
The Chehugou Mo–Cu deposit, located 56 km west of Chifeng, NE China, is hosted by Triassic granite porphyry. Molybdenite–chalcopyrite mineralization of the deposit mainly occurs as veinlets in stockwork ore and dissemination in breccia ore, and two ore‐bearing quartz veins crop out to the south of the granite porphyry stock. Based on crosscutting relationships and mineral paragenesis, three hydrothermal stages are identified: (i) quartz–pyrite–molybdenite ± chalcopyrite stage; (ii) pyrite–quartz ± sphalerite stage; and (iii) quartz–calcite ± pyrite ± fluorite stage. Three types of fluid inclusions in the stockwork and breccia ore are recognized: LV, two‐phase aqueous inclusions (liquid‐rich); LVS, three‐phase liquid, vapor, and salt daughter crystal inclusions; and VL, two‐phase aqueous inclusions (gas‐rich). LV and LVS fluid inclusions are recognized in vein ore. Microthermometric investigation of the three types of fluid inclusions in hydrothermal quartz from the stockwork, breccia, and vein ores shows salinities from 1.57 to 66.75 wt% NaCl equivalents, with homogenization temperatures varying from 114°C to 550°C. The temperature changed from 282–550°C, 220–318°C to 114–243°C from the first stage to the third stage. The homogenization temperatures and salinity of the LV, LVS and VL inclusions are 114–442°C and 1.57–14.25 wt% NaCl equivalent, 301–550°C and 31.01–66.75 wt% NaCl equivalent, 286–420°C and 4.65–11.1 wt% NaCl equivalent, respectively. The VL inclusions coexist with the LV and LVS, which homogenize at the similar temperature. The above evidence shows that fluid‐boiling occurred in the ore‐forming stage. δ34S values of sulfide from three type ores change from ?0.61‰ to 0.86‰. These δ34S values of sulfide are similar to δ34S values of typical magmatic sulfide sulfur (c. 0‰), suggesting that ore‐forming materials are magmatic in origin.  相似文献   

17.
Cobalt-bearing pyrite (0.5?C2.0?wt.% Co) is abnormally abundant (up to 35?vol.% of the total volume of the sulfide phase) in some eastern Pyrenean peridotite massifs, compared to pieces of subcontinental mantle studied so far for sulfides. Pyrite occurs as vermicular intergrowths inside pentlandite and/or chalcopyrite or as coarser, blocky grains in the intergranular pores of host peridotites. Those different pyrites are characterized by different platinum-group element systematics (measured by laser ablation microprobe and ICP-MS). Vermicular pyrite intergrown with pentlandite displays Os-, Ir-, Ru- and Rh-enriched chondrite normalized PGE patterns of Monosulfide solid solution (Mss). In contrast, coarse-grained intergranular (??blocky??) pyrites, are PGE-poor. Chalcophile trace elements (i.e. Zn, Pb, Ag, Au) that are not usually concentrated in mantle-derived sulfides were commonly detected. By contrast, selenium contents are generally low, yielding thus pyrite with high S/Se ratio (>105), consistent with a sedimentary sulfur source. Pyrite microtextures and chalcophile trace element contents support a process of assimilation of crustal sulfur from the metamorphosed sedimentary country rocks. These latter generated highly reactive CO2-S fluids, which were injected into structural discontinuities of the lherzolitic bodies. Sulfur has reacted at T?=?300?C550°C with pre-existing, mantle-derived, metal-rich sulfide assemblages (pentlandite-chalcopyrite). Addition of crustal sulfur did produce Mss which, on cooling, exsolved the Os-rich pyrite in addition to pentlandite. The coarse-grained pyrite types have crystallized directly from S-rich fluids.  相似文献   

18.

At the well-preserved Yubileynoe VMS deposit (Southern Urals), sulfide breccias and turbidites host abundant tellurides represented by hessite, coloradoite, altaite, volynskite, stützite, petzite, and calaverite, as well as phases of the intermediate tellurobismuthite → rucklidgeite solid solution. Three telluride generations were highlighted: (1) primary hydrothermal tellurides in fragments of chalcopyrite and sphalerite of chalcopyrite-rich black smoker chimneys; (2) authigenic tellurides in pseudomorphic chalcopyrite and chalcopyrite veins after fragments of colloform and granular pyrite; and (3) authigenic tellurides in pyrite nodules. Authigenic tellurides are widespread in pyrite-chalcopyrite turbidites. Primary hydrothermal and authigenic tellurides are less common in sulfide turbidites and gritstones with fragments of sphalerite-pyrite, pyrite-sphalerite paleosmoker chimneys and clasts of colloform and fine-grained seafloor hydrothermal crusts. Siliceous siltstones intercalated with sulfide turbidites contain pyrite nodules, whose peripheral parts contain inclusions of epigenetic tellurides. It is assumed that Te for authigenic tellurides originated from fragments of colloform pyrite and hydrothermal chalcopyrite of pyrite-chalcopyrite chimneys, which dissolved during the postsedimentation processes. The main Te concentrators in clastic ores include pseudomorphic chalcopyrite, which inherits high Te, Bi, Au, Ag, Co, Ni, and As contents from the substituted colloform pyrite, and varieties of granular pyrite containing microinclusions of tellurobismuthite (Bi, Te), petzite (Au, Ag, Te), altaite (Pb, Te), coloradoite, and hessite (Ag, Te).

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19.
近年来,在相山铀矿田的西部牛头山地区深部发现了铅锌矿化体,其成因机制不明.为探讨牛头山铅锌矿化体物质来源,开展了硫化物原位硫同位素分析研究.根据硫化物矿物之间的充填和包裹关系判断,铅锌矿化体金属硫化物形成的先后顺序是:黄铁矿形成最早,方铅矿和闪锌矿次之,细脉状黄铜矿形成最晚.利用LA-MC-ICP-MS技术对矿化体中几种金属硫化物分别进行了系统的原位硫同位素分析.结果显示:黄铁矿、闪锌矿、方铅矿、细脉状黄铜矿的δ34S值介于-4.8‰~+5.4‰之间,各硫化物矿物之间硫同位素未达到完全平衡分馏,利用黄铁矿δ34S值得到的矿化流体δ34SΣS值（总硫同位素组成）近似为+3.7‰,与共生矿物对（闪锌矿-方铅矿）图解法得到的闪锌矿和方铅矿沉淀时矿化流体的δ34SΣS值（+3.2‰）相近,表明形成牛头山铅锌矿化体的矿化流体δ34SΣS值大约为+3.7‰,为岩浆硫.结合前人的岩浆岩年龄数据,我们判断该铅锌矿化体金属硫化物的硫可能主要来自次火山岩相花岗斑岩岩浆热液.同一薄片中闪锌矿δ34S值高于共生的方铅矿,表明两者硫同位素基本平衡,利用共生矿物对（闪锌矿-方铅矿）硫同位素温度计计算得出平衡温度为197~476℃,与前人通过脉石矿物流体包裹体得到的铅锌矿化流体温度基本一致.相山火山盆地与相邻的北武夷黄岗山、梨子坑等产铅锌矿的火山盆地具有相似的成矿条件及成矿物质来源,使相山火山盆地具有良好的铅锌多金属找矿前景.   相似文献   

20.
The metalized quartz veins is located 5 km west of the Iraqi-Iran border in the Qandil range. The quartz veins included sulfide and oxide ore minerals which mostly occur in the form of open-space filling texture. The polymetallic mesothermal quartz veins are hosted by marble and phyllite rocks. Within these veins, multiphase, open-space filling and crustiform, bedding to massive textures with pyrite, sphalerite, galena, chalcopyrite,galena, sphalerite, tenorite, azurite, and malachite are observed. Selected samples were analyzed by using ore microscopy and electron probe micro analyzer (EPMA) and scanning electron microscope (SEM). Ore minerals show replacement textures. The paragenesis diagram was made from a careful study of polished sections and three stages have been identified including pre-stage mineralization, mineralization, and post-mineralization stages.Fluid inclusion microthermometric analysis of 15 primary inclusions of quartz veins indicated that ore mineralization at the studied area were formed by a mesothermal, low to medium density, and dilute NaCl-type fluid system. The source of the fluid is mostly metamorphic which became mixed with other fluids later. Hydrothermal fluids of the selected studied area were classified into two groups based on microthermometry study; the first group had a higher homogenization temperature (335.5 to 386.8 °C) than the second group (194.1 to 298.5 °C), with a small difference in salinity between them. Nearly each group has different complexes including chloride and sulfide complexes respectively. The results of stable sulfur isotope of the ore minerals (chalcopyrite and sphalerite) confirmed the sedimentary and/or metamorphic origin of the ore mineralization.  相似文献   

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