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1.
Lead isotopic compositions of mineral separates are presented from the mineralized zones (Roby, Twilight, and High Grade zones)
of the Lac des Iles palladium deposit (approximately 2.69 Ga) and tonalitic country rocks (approximately 2.727 to 2.775 Ga)
in the Wabigoon subprovince of the western Superior Province of Canada. Plagioclase separates show Pb isotope ratios similar
to those of the late Archean depleted mantle. Sulfide minerals coexisting with plagioclase have a more radiogenic Pb isotope
composition, but very low concentrations of U (<0.2 ppb U) and Th (<0.01 ppb) compared to Pb (≫50 ppb). The isotope data are
consistent with a model involving the incorporation of radiogenic Pb from country rocks to sulfide melt near the base of the
magma chamber or along the conduit of the parental magmas. The proposed interpretation is also supported by decreasing Cu/Pd
ratios from earlier barren to late fertile gabbro intrusions in the complex. The ponding sulfide melt became enriched in platinum
group elements, as it was interacting with a large magma volume during the evolution of the Lac des Iles igneous complex. 相似文献
2.
Fractionation of sulfur isotopes and selenium was measured between coexisting pyrite and chalcopyrite and between coexisting pyrrhotite and chalcopyrite from the Besshi deposit of Kieslager-type, Central Shikoku, Japan. In all the pyrite-chalcopyrite pairs studied, 34S is enriched in pyrite relative to chalcopyrite, while selenium is enriched conversely in chalcopyrite relative to pyrite. The mean 34Spy-cp value is +0.53±0.36 per mil, and the mean value of the distribution coefficient of selenium, Dcp-py, is 2.58±0.64. In all the pyrrhotite-chalcopyrite pairs studied, the two minerals are very close to each other both in sulfur isotope and Se/S ratios. The mean 34Spo-cp value is –0.08±0.16 per mil and the mean Dcp-po value is 0.99±0.05. The results have been discussed in comparison with similar data obtained for the Hitachi deposits of Kieslager-type, Japan (Yamamoto et al. 1983). 相似文献
3.
The Northern Ultramafic Centre (NUC) of the Lac des Iles Complex, Northwest Ontario hosts several platinum group element (PGE) occurrences, including the Sutcliffe Zone, which consists of four subparallel, stratiform PGE-enriched intervals exposed within the cyclically layered eastern flank of the NUC. Field relationships, mineral paragenesis and lithogeochemistry allowed for the identification of 14 cyclic cumulate sequences of two distinct types – Cyclic unit type A (CUA) and Cyclic unit type B (CUB). CUA-type and CUB-type units are interpreted to have formed from a Si-enriched and Si-poor parent magmas, respectively. PGE-enriched intervals occur in four of the CUA-type cyclic units (CUA-5, -6, -8 and -11). PGE enriched intervals are commonly associated with websterite, olivine websterite and gabbronorite containing primary disseminated sulfide (0.2–2 vol%) which are dominated by pyrrhotite, chalcopyrite, and pentlandite with minor cubanite, and troilite. In hydrothermally altered rocks enriched in PGE, primary sulfides are locally partially replaced by secondary chalcopyrite, sphalerite, heazlewoodite, and chalcocite. Palladium occurs either in solid solution with primary pentlandite or is associated with platinum group minerals (PGM) such as Pd-plumbide, Pd-telluride, and Pt-bismuthotelluride. PGMs commonly occur within primary sulfides, at contacts between primary sulfide–silicate minerals, or in association with secondary serpentine and actinolite. Gold and silver typically occur as electrum that exhibits similar textural characteristics and mineralogical associations as the PGMs.Two different chemostratigraphic patterns of PGE, Cu and S enrichment can be recognized among the mineralized CUA cycles: The first (top-loaded) occurs near the top of CUA cycles (CUA-6, -8 and -11) in websterite and/or gabbronorite, just below the levels at which CUB magmas were emplaced. The second (middle-loaded), occurs midway through the lower cycle (CUA-5) in the olivine websterite, which is overlain by CUA-6. Within the four mineralized intervals, PGE tenors average 643 ppm Pd + Pt (in 100% sulfide), Pd/Pt and Pd/Ir ratios range from 0.9 to 3.5 and 35 to 537, respectively, and S/Se ratios range between 500 and 6000. The highest PGE tenors (4377 ppm Pd + Pt) are found in the lowermost interval in serpentinized olivine websterite and have an average Pd/Pt ratio of 3.5 and a S/Se ratio of approximately 2000.It is proposed that orthomagmatic processes of fractional crystallization and dynamic magma recharge were the dominant mineralization processes triggering sulfide-saturation and PGE concentration at the Sutcliffe Zone. Textural relationships between PGM, sulfide minerals, and primary and secondary hydrous silicates suggest that late magmatic to postcumulus hydrothermal fluid infiltration occurred locally during and after sulfide mineralization of the PGE-enriched intervals. However, these fluids had a minimal effect on the distribution of PGE in the Sutcliffe Zone. The Sutcliffe Zone shares many similarities with classic stratiform PGE deposits in terms of Pd/Pt ratio, high PGE tenors, low abundance of sulfide, and PGM assemblages. However, it is distinguished from most stratiform PGE deposits by its tectonic environment and lithostratigraphic position and by the intimate spatial association of the two parental magmas that are interpreted to have been responsible for the observed chemostratigraphy and PGE enrichment. 相似文献
4.
Alireza Karimzadeh Somarin Stephen A. Kissin Donald D. Heerema Daniel J. Bihari 《Resource Geology》2009,59(2):107-120
The Archean mafic–ultramafic complex of Lac des Iles, Ontario, Canada, hosts economic platinum group elements (PGE)-Au-Cu-Ni mineralization in the Roby Zone. All lithologies in the North Roby Zone have been affected by hydrothermal alteration. The alteration products include talc (the most dominant mineral), anthophyllite, serpentine, actinolite, tremolite, chlorite, hornblende, zoisite, clinozoisite, epidote and sericite. In the altered rocks, light rare earth elements (La, Ce, Nd, Sm), Pb, Rb, Ba, Cs, S and possibly Y have been added by hydrothermal solution whereas Eu and heavy rare earth elements (Yb, Gd, Dy, Er) remained immobile. There are five types of fluid inclusions in the pegmatitic plagioclase with homogenization temperature and salinity ranging from 240°C to 445°C and 15.37 to 48.52 wt% equivalent NaCl, respectively. The δ18 O and δD of talc range form 6.2‰ to 6.9‰ and −28‰ to −48‰, respectively. δ18 O and δD water in equilibrium with talc during the hydrothermal alteration suggest a modified source for the hydrothermal solution. Microthermometry and stable isotope studies suggest that high temperature–high salinity fluid was diluted by, and mixed with, low temperature–low salinity meteoric solution. This mechanism precipitated the hydrothermal assemblage and redistributed trace elements during and after pegmatite formation in the North Ruby Zone. 相似文献
5.
U-Mo and Cu mineralization occurs in horizons as well as in veins in the Permian formations near Novoveská Huta. Ore mineralization is represented by uraninite, U-Ti oxides, coffinite, molybdenite, chalcopyrite, tennantite and pyrite. The isotopic composition of S and C displays a larger variability in the stratiform ores (34S from –32.7 to +2.7 and 13C from –27.1 to — 0.5) These data suggest mixing of meteoric solutions with fluids of volcanic origin and a complex history. There is a narrower range of 34S from –18.8 to –4.6 and 13C from –6.3 to –2.5% in quartz-carbonate veins with Cu mineralization suggesting a deep source of ore-bearing solutions. The Permian volcanics were a significant source of ore elements.Their contents of U, Mo, Cu and Y are from two to eight times higher than in sedimentary rocks. Accumulations of ore elements in the horizons were formed by the reduction and adsorption processes 240 ± 30 Ma ago according to U-Pb isotopic dating. Due to Alpine tectonism, these low-grade ores (U<0.1 wt%) were remobilized and higher-grade U-Mo ores (U>0.1 wt%) were formed 130 ± 20 Ma ago at temperatures ranging from 110 to 120° C, according to fluid inclusions. Younger veins with Cu mineralization were formed 115 ± 10 Ma according to the model age of Pb at temperatures ranging from 95 to 190°C. 相似文献
6.
Te-Se-bearing gold-silver ores from Salida in Sumatra, Indonesia, show carbonate and sulfidic diffusion bands in quartz incrustations. The sulfidic diffusion bands show a fine diffusion zoning with: 1. an earliest or inner zone with concentrations of Zn, Cu, Fe, S (sphalerite, chalcopyrite, pyrite); 2. an intermediate zone with concentrations of Pb, Au, Ag, S, Te, Se (galena and Au-Ag-tellurides in Te-bearing parageneses; galena, electrum and acanthite in Te-free parageneses); and 3. a zone of As-bearing minerals (tennantite, enargite or luzonite, arsenpolybasite) superimposed on the first two zones. In the telluride-bearing ores paragenetic relations suggest that galena, altaite, hessite, and -phase and x-phase solid solutions originally crystallized above about 120 °C; on cooling this assemblage equilibrated into one stable below 50 °C and consisting of galena, altaite, hessite, hessite-sylvanite intergrowths, and hessite-petzite aggregates. Se is concentrated in sulfides of the intermediate diffusion zones; microprobe analyses indicate up to 4.0 weight percent Se in some acanthites and up to 0.45 weight percent Se in some galenas; arsenpolybasite also contains up to 4.0 weight percent Se but only when replacing seleniferous acanthite. The concentration of Se with Pb, Au, Ag, S, Te in intermediate diffusion zones is ascribed to solution differentiation during solute diffusion. Microprobe analyses are given of hessite, sylvanite, petzite, minerals of the pearceite-polybasite group, mckinstryite, and the Fe-, Mn- and Cd-contents in sphalerites.
Zusammenfassung Te-Se-führende Gold-Silber Erze von Salida in Sumatra, Indonesien, zeigen karbonatische und sulfidische Diffusionsbänder in Quarzkrusten. Die sulfidischen Diffusionsbänder zeigen eine feine Zonierung mit: 1. einer ältesten, inneren Zone mit Konzentrationen von Zn, Cu, Fe, S (Zinkblende, Kupferkies, Pyrit); 2. einer intermediären Zone mit Konzentrationen von Pb, Au, Ag, S, Te, Se (Bleiglanz und Au-Ag-Telluride in Te-haltigen Paragenesen; Bleiglanz und Akanthit in Te-freien Paragenesen); und 3. einer die erstgenannten Zonen überlagernden Zone von As-haltigen Mineralen (Tennantit, Enargit oder Luzonit, Arsenpolybasit). Die paragenetischen Beziehungen der Telluride deuten auf eine ursprüngliche Kristallisation von Bleiglanz, Altait, Hessit und - und X-Phase Mischkristalle bei Temperaturen oberhalb 120 °C; bei der Abkühlung wurde diese Mineralassoziation ersetzt durch eine unterhalb 50 °C stabile Paragenese von Bleiglanz, Altait, Hessit, Hessit-Sylvanit-Verwachsungen und Hessit-Petzit Aggregaten. Selen hat sich in den Sulfiden der intermediären Diffusionszonen angereichert. Mikrosondeanalysen zeigen Se-Gehalte bis 4.0 Gew. % in Akanthit und bis 0.45 Gew. % in Bleiglanz. Arsenpolybasit kann ebenfalls bis 4.0 Gew. % Se enthalten, aber nur wenn er als Verdränger von Se-reichen Akanthiten auftritt. Die Ursache der Anreicherung von Se zusammen mit Pb, Au, Ag, S, Te in den intermediären Diffusionszonen ist in einer Art von Lösungsdifferentiation während des Diffusionsprozesses zu suchen. Mikrosondeanalysen von Au-Ag-Telluriden, Mineralen der Pearceit-Polybasit Gruppe, Mckinstryit, und den Fe-, Mn- und Cd-Gehalten der Zinkblenden werden gegeben.相似文献
7.
The recently discovered Offset Zone of the Mine Block Intrusion of the Lac des Iles Complex hosts palladium mineralization with unusually high Pd/Pt and Pd/Ir ratios in rocks that range from relatively unaltered norite to amphibolites and chlorite–actinolite–talc schist. Quantitative assessment of the effect of progressive alteration using mineral modes was done using total silicate H2O as a monitor of reaction progress (ξ = moles H2O added to form alteration minerals per 100 g of rock). Major mineral modal variations define three reaction regions: (1) ξ?=?0.00–0.03, characterized by epidote/clinozoisite formation and some amphibole; (2) ξ?=?0.03–0.23, characterized by formation of chlorite, amphibole, quartz muscovite/sericite, and calcite after plagioclase?+?pyroxene; and (3) ξ?=?0.23–0.28, characterized by the formation of talc after earlier formed amphibole. Epidote occurs as an incongruent product from the destruction of plagioclase that is itself lost as the reaction proceeds. Pyroxene is altered at about twice the rate of plagioclase, resulting in pyroxene-rich protoliths to be more altered than those relatively enriched in plagioclase. Major elements variations largely reflect variations in the plagioclase/pyroxene ratio of the protolith, but compositional trends suggest a loss of Na with reaction progress. The base metal sulfides chalcopyrite, pyrrhotite, and pentlandite show decreasing abundance with reaction progress, forming pyrite (± magnetite) as an intermediate reaction product that also is lost as the reaction proceeds. Millerite is overall low but increases slightly. A more limited data set on the platinum-group minerals suggests that platinum-group element (PGE)-arsenides increase whereas PGE-sulfides and PGE-Bi-tellurides decrease with reaction progress. Assuming ore element concentrations in the protolith were constant and similar to relatively fresh norites, Pd increases modestly, by 5 %, whereas Pt decreases by about 65 % in the most altered rocks. Similarly, Cu, Au, and S decrease by 60, 82, and 94 %, respectively, in the most altered rocks. The antithetical behavior of Pd and the fact that Pd enrichment is not seen in altered dikes suggest that the Pd originally was enriched in the more melanocratic protoliths that are most extensively altered and that Pd also was lost in part. These results are consistent with the mineralization having been a high-temperature event that predated the amphibolite/greenschist alteration. 相似文献
8.
A. R. Campbell 《Mineralium Deposita》1987,22(1):42-46
The San Cristobal tungsten-base metal deposit differs from other quartz-wolframite vein deposits in that it has a major period of base metal mineralization consisting of pyrite, chalcopyrite, sphalerite, and galena. Homogenization temperatures of primary and pseudosecondary inclusions were measured in augelite (260–400°C), quartz (230–350°C) and sphalerite (180–220°C). The 34S values of H2S in solution in equilibrium with the vein minerals range from 1.6 to 9.0 permil increasing through the paragenesis. The relatively heavy
values suggest a nonmagmatic source for the sulfur. Evaporitic sulfates are a likely source of heavy sulfur and sedimentary anhydrite is known to occur near the San Cristobal region. In contrast to San Cristobal are three similar quartz-wolframite vein deposits, Pasto Bueno, Panasqueira, and Tungsten Queen. They each have an average 34S value for sulfides of about 0 permil, suggesting a sulfur of magmatic origin. At San Cristobal an influx of sedimentary sulfur could not only account for the distinctive isotopic signature of the sulfides but also for the presence of the base metal mineralization. 相似文献
9.
A sulfur isotope study of volcanogenic massive sulfide deposits of the Eastern Black Sea province,Turkey 总被引：1，自引：0，他引：1
Kuroko-type massive sulfide deposits of the Eastern Black Sea province of Turkey are related to the Upper Cretaceous felsic lavas and pyroclastic rocks, and associated with clay and carbonate alteration zones in the footwall and hangingwall lithologies. A complete upward-vertical section of a typical orebody consists of a stringer-disseminated sulfide zone composed mainly of pyrite and chalcopyrite; a massive pyrite zone; a massive yellow ore consisting mainly of chalcopyrite and pyrite; a black ore made up mainly of galena and sphalerite with minor amounts of chalcopyrite, bornite, pyrite and various sulfosalts; and a barite zone. Most of the deposits in the province are associated with gypsum in the footwall or hangingwall. The paragenetic sequence in the massive ore is pyrite, sphalerite, chalcopyrite, bornite, galena and various sulfosalts, with some overlap between the mineral phases. Massive, stringer and disseminated sulfides from eight kuroko-type VMS deposits of the Eastern Black Sea province have a
34S range of 0–7 per mil, consistent with the
34S range of felsic igneous rocks. Sulfides in the massive ore at Madenköy (4.3–6.1 per mil) differ isotopically from sulfides in the stringer zone (6.3–7.2 per mil) suggesting a slightly increased input of H2S derived from marine sulfate with time. Barite and coarse-grained gypsum have a
34S range of 17.7–21.5 per mil, a few per mil higher than the
34S value of contemporaneous seawater sulfate. The deposits may, therefore, have formed in restricted basins in which bacterial reduction of sulfate was taking place. Fine-grained, disseminated gypsum at Kutlular and Tunca has
34S values (2.6–6.1 per mil) overlapping those of ore sulfides, indicating sulfide oxidation during waning stages of hydrothermal activity. 相似文献
10.
The Baishan Mo–Re deposit is located in the eastern section of the eastern Tianshan orogenic belt, NW China. The deposit has a grade of 0.06% Mo and a high content of rhenium of 1.4 g/t. Rhenium and osmium isotopes in sulfide minerals from the Baishan deposit are used to determine the age of mineralization. Rhenium concentrations in molybdenite samples are between 74 and 250 g/g. Analysis of eight molybdenite samples yields an isochron age of 224.8±4.5 Ma (2). Pyrite samples have rhenium and osmium concentrations varying in the range 33.4–330.6 ng/g and 0.08–0.81 ng/g, respectively. Isotope data on seven pyrite samples yield an isochron age of 225±12 Ma (2) on the 187Re/188Os versus 187Os/188Os plot and an age of 233±14 Ma (2) on the 187Os versus 187Re correlation diagram. The ages of molybdenite and pyrite are consistent within the analytical errors. Combined with field observations, the data indicate that Mo–Re mineralization in the Baishan deposit is produced by a magmatic-hydrothermal event in an intracontinental extensional setting after late Paleozoic orogeny. The initial 187Os/188Os ratio of pyrite is 0.3±0.07. The 34S values of molybdenite vary from +0.5 to +3.6. Both data indicate that mineralization is derived mainly from a mantle source.Editorial handling: J. Richards 相似文献
11.
The Quesnel River gold deposit (1.2 million tonnes grading 5.22 g/t Au in three separate zones) occurs within Takla Group volcanic rocks of Upper Triassic age proximal to an alkalic stock. The deposit occurs in amphibole-augite phyric, fragmental, basaltic rocks. Alteration has produced an assemblage of epidote-chloritetremolite-calcite-quartz with lesser pyrite, chalcopyrite, pyrrhotite, sphalerite, marcasite, galena, arsenopyrite and gold.The West Zone comprises a tabular, conformable sulfide body underlain by bedded, variably altered fragmental basaltic rocks and overlain by siltstone and argillite. In the Main Zone, highest gold grades occur adjacent to a sharp discordant alteration front with barren, strongly carbonatized, pyritic basaltic lapilli-tuff. It is overlain by siltstone and argillite and bounded to the east and a depth by a west dipping reverse fault. To the west the auriferous, propylitically altered, rocks grade laterally into lower grade and barren basaltic rocks.Oxygen(18O = + 9 to + 15) and carbon (13O= -14 to –7) isotopic signatures of calcite from carbonate-altered and propylitically altered rocks are similar. However, sulfur isotopic values for pyrite are different, with gold-associated pyrite (34S = –7 to –3) distinct from pyrite in carbonate altered rocks with (34S = + 8 to + 13).The carbonization occurred before complete induration of the basaltic fragmental rocks, whereas propylitization and gold plus sulfide precipitation is clearly epigenetic. 相似文献
12.
Summary The Dumont Sill is an Archaean komatiitic intrusion, whichDuke (1986) subdivided into a mafic (MZ) and ultramafic zone (UMZ). The UMZ comprises an upper (UPZ) and a lower peridotite subzone (LPZ) consisting of olivine + chromite cumulates and a dunite subzone (DZ) between them, consisting of olivine ± sulfide cumulates.Three sulfide-rich layers in the DZ are delineated by anomalously high Ni, Cu, S and Se concentrations (Ni 0.95 wt %, Cu 0.07 wt.%, S 1.0 wt.%, Se 2.7 ppm). They also contain elevated contents of noble metals (Au 31.5 ppb, Pd 210 ppb, Pt 180 ppb, Ir 8.4 ppb, Os 6 ppb). Unmineralized samples contain 3–8 ppb Pd, 1–20 ppb Pt, 0.2–3.6 ppb Au, 0.5–6 ppb Ir, and 1–6 ppb Os.Samples belonging to the LPZ and UPZ and lying above and beneath the mineralized horizons have rather high Ir contents, generally between 2.9 to 4.4 ppb. In contrast, Ir contents of sulfide-free samples from the DZ and UPZ which lie immediately above the mineralized zones have significantly lower Ir concentrations, ranging from 0.1 to 1.5 ppb. This zone of Ir depletion coincides with a zone of Ni-depleted olivine and sulfide which crystallized just above sulfide-rich horizons in the DZ (Duke, 1986). It is suggested that Ir and Ni depletion in cumulates which lie between or above sulfide-rich zones are due to the lower Ir and Ni contents in olivine which crystallized from a silicate magma from which a sulfide liquid had already been segregated. Alternatively, if metal alloys control the distribution of Ir and Os in the DZ, the Ir depletion in the cumulates above the ore' horizons implies that crystallization of the metal phase ceased. This would be the case if, due to the segregation of sulfides, the Ir concentration in the silicate liquid falls below the solubility limit of the metal phase.The sulfide mineralization probably formed by fractional segregation of a sulfide/ oxide liquid, as the PGE concentrations in the sulfide liquid and PGE/Se, or PGE/S ratios tend to decrease from the bottom to the top in the mineralized zones.Duke (1986) proposed that sulfide saturation was caused by mixing of primitive komatiite magma with fractionated interstitial liquid, which was squeezed out of the cumulate pile. Sulfide segregation at the floor of the magma chamber is likely to have been a very localized event implying low R-factors. The small PGE-enrichment in the sulfide horizons of the Dumont Sill and the narrow zones of Ir-depletion just above the sulfide zones are consistent with the proposed process.
With 6 Figures 相似文献
Die Verteilung von Platingruppen-Elementen im Dumont Sill, Quebec und ihre Bedeutung für die Bildung von Ni-Sulfid MIneralisationen
Zusammenfassung Der Dumont Sill ist eine komatiitische Intrusion, die von Duke (1986) in eine mafische (MZ) und eine ultramafische (UMZ) Zone untergliedert wurde. Die UMZ setzt sich aus einer oberen (UPZ) und einer unteren (LPZ) peridotitischen Subzone, die aus Olivinund Chromft-Kumulaten besteht, und einer dunitischen Subzone (DZ), zwischen diese beiden eingeschaltet, zusammen. Letztere besteht aus Olivin- und Sulfid-Kumulaten.Drei sulfidreiche Lagen innerhalb der DZ sind durch anomal hohe Gehalte an Ni, Cu, S und Se (Ni 0.95 Gew. %, Cu 0.07 Gew. %, S 1.0 Gew. %, Se 2.7 ppm) charakterisiert. Erhöhte Gehalte an Edelmetallen (Au 31.5 ppb, Pd 210 ppb, Pt 180 ppb, Ir 8.4 ppb, Os 6 ppb) sind ebenfalls an diese Lagen gebunden. Unvererzte Proben enthalten < 3–8 ppb Pd, 1–20 ppb Pt, 0.2–3.6 ppb Au, 0.5–6 ppb Ir und 1–6 ppb Os.Proben aus der LPZ und UPZ und solche aus dem Hangenden und Liegenden der Mineralisationshorizonte zeigen relativ hohe Ir-Gehalte; im allgemeinen zwischen 2.9 und 4.4 ppb. Im Gegensatz dazu sind die Ir-Gehalte sulfidfreier Proben unmittelbar über vererzten Lagen deutlich erniedrigt; sie variieren zwischen 0.1–1.5 ppb. Diese an Ir verarmte Zone entspricht einer Zone nickelarmer Olivine und Sulfide, die unmittelbar oberhalb der sulfidreichen Horizonte in der DZ kristallisierten (Duke, 1986). Es wird vermutet, daß die Ir- und Ni-Abreicherung in den Kumulaten, die oberhalb und zwischen den sulfid-reichen Zonen liegen, mit den niedrigeren Ir- und Ni-Gehalten der Olivinen zusammenhängt. Die Olivine kristallisierten aus einem Silikatmagma, von dem sich bereits eine Sulfidschmelze abgeschieden hatte.Soferne metallische Verbindungen die Ir- und Os-Verteilung in der DZ kontrollieren, würde die Ir-Abreicherung in den Kumulaten oberhalb des Erzhorizontes auf ein Ende der Kristallisation einer metallischen Phase hinweisen. Dieser Fall könnte eintreten, sobald durch die Ausscheidung von Sulfiden, die Ir-Konzentration in der silikatischen Schmelze unter die Löslichkeitsgrenze der Metallphase fällt.Die Sulfidvererzung bildete sich wahrscheinlich infolge von fraktionierter kristallisation einer Sulfid/Oxidschmelze, da die PGE Konzentrationen der Sulfidschmelze, und das PGE/S Verhältnis vom Liegenden zum Hangenden hin in den mineralisierten Horizonten abnehmen. Duke (1986) schlug ein Modell vor, in dem die Sulfid-Sättigung der silikatischen Schmelze durch eine Vermischung eines komatiitischen Magmas mit einer fraktionierten, interstitialen, aus den Kumulaten ausgequetschten Schmelze erklärt wird. Die Sulfidausfällung an der Basis der Magmenkammer scheint ein lokal recht begrenztes Phänomen gewesen zu sein, die niedrige R-Faktoren bedingt. Die geringfügige PGE-Anreicherung in den Sulfidlagen des Dumont Sills und die schmale Zone der Ir-Abreicherung unmittelbar oberhalb dieser sulfidischen Zone stehen mit diesen vorgeschlagenen Prozessen im Einklang.
With 6 Figures 相似文献
13.
The Felbertal scheelite deposit is the largest known strata-bound tungsten concentration. It lies in an up to 400 m thick rock pile in the lowermost part of the volcanic rock sequence, probably of the Early Paleozoic Habach Formation. Both ore fields (eastern and western) have been affected by Variscan and Alpine metamorphism and tectonism, resulting in a remobilization of the ore mineralization. This ore deposit and the neighboring rocks show a strikingly low sulfur content. The eastern field with one major orebody has very little sulfide mineralization. The western field, with 8 orebodies (K1–K8) and two remobilized vein zones (S1 and S2), reveals somewhat more minor sulfide enrichments that are mainly within and around the K1 and K2 orebodies and in some parts of the interlayered schist sequence. Sulfur isotope compositions of 90 sulfide minerals (37 pyrrhotite, 20 chalcopyrite, 19 pyrite and 11 molybdenite and/or WS2-MoS2 solid solutions and 3 Pb-Bi sulfosalts, including 7 sulfides within scheelite grains) from 60 ore and host rock samples have been determined with a standard error of less than ±0.2 per mil. All data range from –3.6 to +4.3 34S. There are small differences in the sulfur isotope values from place to place and in time from the first and second to the third generation. In the western field, the K1 orebody differs from other orebodies (K2, K4, K7) due to isotopically heavier 34S values. The three scheelite generations show differences in the 34S values of the sulfide microphases within scheelite grains, from +1.0 to +4.3 per mil for the first and the second, and from –1.8 to –3.3 per mil for the third generation. Sulfide phases within molybdoscheelites may have crystallized under the same conditions as the other coeval sulfide minerals in the same orebody. They commonly formed later than scheelite. These changes may be explained using data from Ohmoto and Rye (1979): Small changes in temperature, pH, and/or
may result in large changes in the 34S values with the precipitation of isotopically heavier sulfides under more reducing conditions. Only four samples with sulfide mineral pairs show isotopic equilibrium. All others display some disequilibrium. We suggest that the sulfides in the ores and surrounding volcanogenic host rocks formed contemporaneously from the same hydrothermal ore fluids, and that the sulfur species in these fluids may have been dominantly H2S. 相似文献
14.
The Glen Eden Mo-Sn-W deposit in north-eastern New South Wales, Australia, is an example of a leucogranite-related, low-grade, large-tonnage hydrothermal system. It occurs in the southern part of the New England Orogen and is hosted within Permian felsic volcanic rocks, intruded at depth by dykes of porphyritic microleucogranite (Glen Eden Granite). The deposit is hosted within a pipe-like quartz-rich greisen breccia body about 500 m in diameter, surrounded by a greisen zone several hundred metres across, zoning out into altered volcanic rocks. The dominant ore minerals, largely hosted as open space fillings and disseminations in quartz and quartz-rich greisen, are molybdenite, wolframite and cassiterite; they are accompanied by minor to trace amounts of muscovite, fluorite, topaz, siderite, pyrrhotite, arsenopyrite, chalcopyrite, sphalerite, bismuth, bismuthinite, joseite A, cosalite, galenobismutite, beryl, anatase and late-stage dickite and kaolinite. Two types of breccia are recognised: (1) greisenised volcanic rock fragments (quartz + muscovite), cemented by hydrothermal quartz ± K-feldspar ± ore minerals, and (2) fragments of hydrothermal quartz ± cassiterite ± wolframite enclosed in quartz ± clay. In both types of breccia and in stockwork veins, there is evidence of early precipitation of Mo-Sn-W phases, followed by Bi minerals and base metal sulfides (± fluorite, siderite).Breccia formation and associated hydrothermal alteration (greisen, potassic, argillic, propylitic) are interpreted to be related to devolatilisation of the highly fractionated Glen Eden Granite of early Triassic age (240±1 Ma based on 40Ar/39Ar geochronology of greisen muscovite) as well as to fluid mixing with meteoric waters. The breccia pipe could have formed in part by rock dissolution and collapse, as well as by explosive degassing of boiling fluids. Fluid inclusion evidence is consistent with boiling, with breccia pipe formation and mineralisation having mainly occurred at 250–350 °C from fluids with salinity of 0.4–9 wt% NaCl equivalent in the dilute types and 30–47 wt% NaCl equivalent in the hypersaline types. Stable isotopic evidence (O, D, C, S) indicates a strong magmatic contribution to the hydrothermal fluids and metals in the breccia. The 18O values of quartz decrease outward from the breccia pipe (10.6–12.3 in the pipe to 3.4–8.7 in the peripheral quartz) indicating that there has been mixing with isotopically light (high latitude) meteoric fluids, mainly after formation of the breccia pipe. 相似文献
15.
The first laser-induced 40Ar-39Ar incremental-heating mineral age data for the Timok Massif of the Banatitic Magmatic and Metallogenetic Belt (BMMB) demonstrate that the main mineralization stage at the giant Majdanpek Cu–Au(–Mo) porphyry deposit took place at 83.6–84.0±0.6 Ma (2), coinciding with the later, 83±1–89.0±0.6 Ma, stages of the first cycle of andesitic volcanism. The earliest-Campanian age for hydrothermal activity precludes an association with the later history of the BMMB, and discounts the metallogenetic role of Laramide plutonism for the dated deposits.Editorial handling: A. Cheilletz 相似文献
16.
The Lewis Ponds Zn–Pb–Cu–Ag–Au deposit, located in the eastern Lachlan Fold Belt, central western New South Wales, exhibits the characteristics of both volcanic-hosted massive sulphide and carbonate-hosted replacement deposits. Two stratabound massive to disseminated sulphide zones, Main and Toms, occur in a tightly folded Upper Silurian sequence of marine felsic volcanic and sedimentary rocks. They have a combined indicated resource of 5.7 Mt grading 3.5% Zn, 2.0% Pb, 0.19% Cu, 97 g/t Ag and 1.9 g/t Au. Main Zone is hosted by a thick unit of poorly sorted mixed provenance breccia, limestone-clast breccia and quartz crystal-rich sandstone, whereas Toms Zone occurs in the overlying siltstone. Pretectonic carbonate–chalcopyrite–pyrite and quartz–pyrite stringer veins occur in the footwall porphyritic dacite, south of Toms Zone. Strongly sheared dolomite–chalcopyrite–pyrrhotite veins directly underlie the Toms massive sulphide lens. The mineralized zones consist predominantly of pyrite, sphalerite and galena. Paragenetically early framboidal, dendritic and botryoidal pyrite aggregates and tabular pyrrhotite pseudomorphs of sulphate occur throughout the breccia and sandstone beds that host Main Zone, but are rarely preserved in the annealed massive sulphide in Toms Zone. Main and Toms zones are associated with a semi-conformable hydrothermal alteration envelope, characterized by texturally destructive chlorite-, dolomite- and quartz-rich assemblages. Dolomite, chlorite, quartz, calcite and sulphides have selectively replaced breccia and sandstone beds in the Main Zone host sequence, whereas the underlying porphyritic dacite is weakly sericite altered. Vuggy and botryoidal textures resulted from partial dissolution of the dolomite-altered sedimentary rocks and unimpeded growth of base metal sulphides, carbonate and quartz into open cavities. The intense chlorite-rich alteration assemblage, underlying Toms Zone, grades outward into a weak pervasive sericite–quartz assemblage with distance from the massive sulphide lens. Limestone clasts and hydrothermal dolomite at Lewis Ponds are enriched in light carbon and oxygen isotopes. The dolomite yielded 13CVPDB values of –11 to +1 and 18OVSMOW values of 6 to 16. Liquid–vapour fluid inclusions in the dolomite have low salinities (1.4–7.7 equiv. wt% NaCl) and homogenization temperatures (166–232°C for 1,000 m water depth). Dolomitization probably involved fluid mixing or fluid–rock interactions between evolved heated seawater and the limestone-bearing facies, prior to and during mineralization. 34SVCDT values range from 2.0 to 5.0 in the massive sulphide and 3.9 to 7.4 in the footwall carbonate–chalcopyrite–pyrite stringer veins, indicating that the hydrothermal fluid may have contained mamgatic sulphur and a component of partially reduced seawater. The sulphide mineral assemblages at Lewis Ponds are consistent with moderate to strongly reduced conditions during diagenesis and mineralization. Low temperature dolomitization of limestone-bearing facies in the Main Zone host sequence created secondary porosity and provided a reactive host for fluid-rock interactions. Main Zone formed by lateral fluid flow and sub-seafloor replacement of the poorly sorted breccia and sandstone beds. Base metal sulphide deposition probably resulted from dissolution of dolomite, fluid mixing and increased fluid pH. Pyrite, sphalerite and galena precipitated from a relatively low temperature, 150–250°C hydrothermal fluid. In contrast, Toms Zone was emplaced into fine-grained sediment at or near the seafloor, above a zone of focused up-flowing hydrothermal fluids. Copper-rich assemblages were deposited in the Toms Zone footwall and massive sulphide lenses in Main and Toms zones as the hydrothermal system intensified. During the D1 deformation, fracture-controlled fluids within the Lewis Ponds fault zone and adjacent footwall volcanic succession remobilized sulphides into syntectonic quartz veins. Lewis Ponds is a rare example of a synvolcanic sub-seafloor hydrothermal system developed within fossiliferous limestone-bearing facies. The close spatial association between limestone, hydrothermal dolomite, massive sulphide and dacite provides a basis for new exploration targets elsewhere in New South Wales.Editorial handling: D. Lentz 相似文献
17.
Jan Pašava Anna Vymazalová Jan Košler Rustam I. Koneev Alexander V. Jukov Rustam A. Khalmatov 《Mineralium Deposita》2010,45(5):411-418
We studied primary ore samples from Kalmakyr, a giant Cu–Au–Mo porphyry deposit in eastern Uzbekistan. Disseminated and stockwork-type
high-grade Cu–Au–Mo mineralization showed average concentrations of 55 ppb Pd, 5.5 ppb Pt, 0.95 ppb Rh, 0.49 ppb Ir, and 4.1 ppm
Au (n = 8). This type of mineralization is characterized by the presence of pyrite, chalcopyrite, molybdenite, and gold. A peak
Pd content of 292 ppb was determined in a base-metal-rich quartz vein in granodiorite porphyry, which contains galena, sphalerite,
chalcopyrite, tetrahedrite, and gold. Palladium correlates with Cu, Ag, Se, and S. Mineralogical and laser ablation ICP-MS
study confirmed that Pd is homogeneously distributed in chalcopyrite, which contains up to 110 ppm Pd, and tetrahedrite, containing
up to 20 ppm Pd. An assessment of the Pd and Pt budget at Kalmakyr showed the potential of approximately 17 t of Pd and 1.7 t
of Pt. 相似文献
18.
Philip M. Scotney Stephen Roberts Richard J. Herrington Adrian J. Boyce Ray Burgess 《Mineralium Deposita》2005,40(1):76-99
Wetar Island is composed of Neogene volcanic rocks and minor oceanic sediments and forms part of the Inner Banda Arc. The island preserves precious metal-rich volcanogenic massive sulfide and barite deposits, which produced approximately 17 metric tonnes of gold. The polymetallic massive sulfides are dominantly pyrite (locally arsenian), with minor chalcopyrite which are cut by late fractures infilled with covellite, chalcocite, tennantite–tetrahedrite, enargite, bornite and Fe-poor sphalerite. Barite orebodies are developed on the flanks and locally overly the massive sulfides. These orebodies comprise friable barite and minor sulfides, cemented by a series of complex arsenates, oxides, hydroxides and sulfate, with gold present as <10 m free grains. Linear and pipe-like structures comprising barite and iron-oxides beneath the barite deposits are interpreted as feeder structures to the barite mineralization. Hydrothermal alteration around the orebodies is zoned and dominated by illite–kaolinite–smectite assemblages; however, local alunite and pyrophyllite are indicative of late acidic, oxidizing hydrothermal fluids proximal to mineralization. Altered footwall volcanic rocks give an illite K–Ar age of 4.7±0.16 Ma and a 40Ar/39Ar age of 4.93±0.21 Ma. Fluid inclusion data suggest that hydrothermal fluid temperatures were around 250–270°C, showed no evidence of boiling, with a mean salinity of 3.2 wt% equivalent NaCl. The 34S composition of sulfides ranges between +3.3 and +11.7 and suggests a significant contribution of sulfur from the underlying volcanic edifice. The 34S barite data vary between +22.4 and +31.0, close to Miocene seawater sulfate. Whole rock 87Sr/86Sr analyses of unaltered volcanic rocks (0.70748–0.71106) reflect contributions from subducted continental material in their source region. The 87Sr/86Sr barite data (0.7076–0.7088) indicate a dominant Miocene seawater component to the hydrothermal system. The mineral deposits formed on the flanks of a volcanic edifice at depths of ~2 km. Spectacular sulfide mounds showing talus textures are localized onto faults, which provided the main pathways for high-temperature hydrothermal fluids and the development of associated stockworks. The orebodies were covered and preserved by post-mineralization chert, gypsum, Globigerina-bearing limestone, lahars, subaqueous debris flows and pyroclastics rocks. 相似文献
19.
V. Gallagher M. Feely H. Högelsberger G. R. T. Jenkin A. E. Fallick 《Mineralium Deposita》1992,27(4):314-325
Mo mineralization within the Galway Granite at Mace Head and Murvey, Connemara, western Ireland, has many features of classic porphyry Mo deposits including a chemically evolved I-type granite host, associated K- and Si-rich alteration, quartz vein(Mace Head) and granite-hosted (Murvey) molybdenite, chalcopyrite, pyrite and magnetite mineralization and a gangue assemblage which includes quartz, muscovite and K-feldspar. Most fluid inclusions in quartz veins homogenize in the range 100–350°C and have a salinity of 1–13 eq. wt.% NaCl. They display Th-salinity covariation consistent with a hypothesis of dilution of magmatic water by influx of meteoric water. CO2-bearing inclusions in an intensely mineralized vein at Mace Head provide an estimated minimum trapping temperature and pressure for the mineralizing fluid of 355°C and 1.2 kb and are interpreted to represent a H2O-CO2 fluid, weakly enriched in Mo, produced in a magma chamber by decompression-activated unmixing from a dense Mo-bearing NaCl-H2O-CO2 fluid. 34S values of most sulphides range from c. 0 at Murvey to 3–4 at Mace Head and are consistent with a magmatic origin. Most quartz vein samples have 18O of 9–10.3 and were precipitated from a hydrothermal fluid with 18O of 4.6–6.7. Some have 18O of 6–7 and reflect introduction of meteoric water along vein margins. Quartz-muscovite oxygen isotope geothermometry combined with fluid inclusion data indicate precipitation of mineralized veins in the temperature range 360–450°C and between 1 and 2 kb. Whole rock granite samples display a clear 18O-D trend towards the composition of Connemara meteoric waters. The mineralization is interpreted as having been produced by highlyfractionated granite magma; meteoric water interaction postdates the main mineralizing event. The differences between the Mace Head and Murvey mineralizations reflect trapping of migrating mineralizing fluid in structural traps at Mace Head and precipitation of mineralization in the granite itself at Murvey. 相似文献
20.
Further support for the view that mineralization at Mount Isa comprises two separate events is provided by 34S/32S measurement. Isotopic exchange between sulphides in lead-zinc-silver ores appears to have been promoted locally during metamorphism, whereas isotopic disequilibrium persists in the copper ores. These isotopic data are explained by a model in which sedimentary deposition of lead, zinc and silver was succeeded by the post-metamorphic emplacement of copper. Past biological activity is inferred from the occurrence of low concentrations of organic carbon with 13C values ranging from –21 to –26 PDB. Carbonate contents, expressed as carbon, vary from <0.1% to 10.9%. The 13C and 18O values for the carbonates are relatively constant at –4.4±1.1 and –17.6±1.1 PDB respectively. These values are interpreted as reflecting isotopic changes induced in original marine carbonates by isotopic exchange during lower greenschist metamorphism. 相似文献