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31.
Summary Pervasive hydrothermal alteration zones in quartz-feldspar porphyry domes underly all massive sulfide lenses in the D-68 Zone Cu-Zn deposit, Noranda. Alteration pipes are mineralogically zoned and contain chloritic cores consisting of stringer sulfides, enveloped by sericitic haloes. Silicified rocks are found locally.Alteration took place at nearly constant volume. Na depletion, and K enrichment relative to the least altered rocks, are found in all alteration zones. Fe and Mg have been added to the chloritic zone and subtracted in the sericitic and silicic zones. Ca and Si are enriched mainly in the silicic zone. Al, Ti and Zr were the least mobile of the elements studied.Whole-rock 18O values vary from +5.6 to +6.2 per mil in chloritized rocks, +5.8 to + 7.3 per mil in sericitized rocks and + 7.2 to + 8.3 per mil in silicified rocks. D values for two chloritized samples are – 63 and – 70 per mil whereas in two sericitized samples they are close to –62 per mil. Quartz from the chlorite alteration zone is isotopically heavier (18O = 8.6 per mil) than that from the sericite alteration zone (18O = 6.4 per mil), suggesting equilibration with different hydrothermal fluid or different temperature of alteration. Assuming an alteration temperature of 300° + 50°C the fluid in equilibrium with quartz and chlorite had 18O and D values of about 1.5 ± 2.0 per mil and –23 ± 5 per mil, respectively. The fluid in equilibrium with quartz and sericite had 18O and D values of about –0.5 ± 2 per mil and –30 ± 5 per mil, respectively. On the basis of isotopic data, seawater was probably the major constituent of the hydrothermal fluids.
With 7 Figures 相似文献
Hydrothermale Umwandlung und Sauerstoff-Wasserstoff-Isotopengeochemie der Zone D-68 Cu-Zn Derberz Sulfidlagerstätte, Noranda District, Quebec, Canada
Zusammenfassung Hydrothermale Umwandlungszonen in porphyrischen Quarz-Feldspat Gesteinskörpern liegen unterhalb von Derberz Sulfidlinsen in der D-68 Zone Cu-Zn Lagerstätte, Noranda. Umgewandelte pipes sind mineralogisch zoniert; sie enthalten aus Sulfiden bestehende chloritische Kerne, die von sericitischen Höfen umhüllt werden. Lokal treten silicifizierte Gesteine auf.Die Umwandlung ging bei annähernd konstantem Volumen vor sich. Na-Verarmung und K-Anreicherung, bezogen auf die am wenigsten umgewandelten Gesteine, liegen in allen Umwandlungszonen vor. Fe und Mg wurden der Chloritzone zugeführt, in den Sericit- und Si-Zonen abgeführt. Ca und Si sind vor allem in der Si-Zone angereichert. Al, Ti und Zr waren von den untersuchten Elementen am wenigsten mobil.Gesamtgesteins-18O Werte variieren von +5,6 bis +6,2 in den chloritisierten Gesteinen, von +5,8 bis 7,3 in sericitisierten Gesteinen und von +7,2 bis +8,3 in den silicifizierten Gesteinen. Die D Werte für zwei chloritisierte Proben betragen –63 und –70, in zwei sericitisierten Proben liegen sie hingegen nahe bei –62. Quarz von der Chlorit-Umwandlungszone ist isotopisch schwerer (18O = 8,6) als von der Sericit-Umwandlungszone (18O = 6.4), was eine Gleichgewichtseinstellung mit verschiedenen hydrothermalen Lösungen oder eine verschiedene Umwandlungstemperatur nahelegt. Bei einer angenommenen Umwandlungstemperatur von 300 ± 50°C, hatte die im Gleichgewicht mit Quarz und Chlorit stehende Lösung 18O und D Werte von etwa 1,5 ± 2 bzw. –23 + 5. Die im Gleichgewicht mit Quarz und Sericit befindliche Lösung hatte 18O und D Werte von etwa –0,5 ± 2%o bzw. –30 ± 5. Aufgrund der Isotopendaten war wahrscheinlich Meerwasser der Hauptbestandteil der hydrothermalen Lösungen.
With 7 Figures 相似文献
32.
ANNE HORMES NAKI AKÇAR PETER W. KUBIK 《Boreas: An International Journal of Quaternary Research》2011,40(4):636-649
Hormes, A., Akçar, N. & Kubik, P. W. 2011: Cosmogenic radionuclide dating indicates ice‐sheet configuration during MIS 2 on Nordaustlandet, Svalbard. Boreas, 10.1111/j.1502‐3885.2011.00215.x. ISSN 0300‐9483.0300‐9843 Glacial geological field surveys, aerial image interpretation and cosmogenic radionuclide (CRN) dating allowed us to reconstruct the ice‐sheet configuration on Nordaustlandet, the northernmost island of the European sector on the margin of the Arctic Ocean. The timing of deglaciation was investigated by determining the 26Al and 10Be ages of glacially scoured bedrock, weathered periglacial blockfields and glacial erratic boulders. Only 10Be ages were useful for our interpretations, because of unresolved analytical problems with 26Al. Fjords and lowlands on Nordaustlandet yielded Late Weichselian 10Be ages, indicating that actively erosive ice streams scoured the coastal fjord bathymetry during marine isotope stage (MIS) 2. In Murchisonfjorden, ground‐truthed air‐photograph interpretation and 10Be ages of boulders indicated a cold‐based glacier ice cover during MIS 2 on higher plateaus. 10Be ages and lithological studies of erratic boulders on higher and interior plateaus of Prins Oscars Land (>200–230 m a.s.l.) suggest that the Mid‐Weichselian glaciation (MIS 4) might have been more extensive than that during MIS 2. 相似文献
33.
The Ansil Cu–Au volcanogenic massive sulfide deposit is located within an Archean-age cauldron infill sequence that contains
the well-known Noranda base metal mining district. The deposit is unusual in that 17% of the massive pyrrhotite–chalcopyrite
orebody is replaced by semi-massive to massive magnetite. Temporally associated with the magnetite formation are several calc-silicate
mineral assemblages within the massive sulfide lens and the underlying sulfide stockwork vein system. Coarse-grained andradite–hedenbergite
and ferroactinolite–ilvaite alteration facies formed in the immediate footwall to the massive magnetite–sulfide lens, whereas
an epidote–albite–pyrite-rich mineral assemblage overprints the margins of the chlorite-rich stockwork zone. The epidote-rich
facies is in turn overprinted by a retrograde chlorite–magnetite–calcite mineral assemblage, and the andradite–hedenbergite
is overprinted first by ferroactinolite–ilvaite, followed by semi-massive to massive magnetite. The footwall sulfide- and
magnetite-rich alteration facies are truncated by a late phase of the Flavrian synvolcanic tonalite–trondhjemite complex.
Early phases of this intrusive complex are affected to varying degrees by calc-silicate-rich mineral assemblages that are
commonly confined to miarolitic cavities, pipe vesicles and veins. The vein trends parallel the orientation of synvolcanic
faults that controlled volcanism and hydrothermal fluid migration in the overlying cauldron succession. The magnetite-rich
calc-silicate alteration facies are compositionally similar to those of volcanic-hosted Ca–Fe-rich skarn systems typical of
oceanic arc terranes. Tonalite–trondhjemite phases of the Flavrian complex intruded to within 400 m of the base of the earlier-formed
Ansil deposit. The low-Al trondhjemites generated relatively oxidized, acidic, Ca–Fe-rich magmatic–hydrothermal fluids either
through interaction with convecting seawater, or by assimilation of previously altered rocks. These fluids migrated upsection
along synvolcanic faults that controlled the formation of the original volcanogenic massive sulfide deposit. This is one of
the few documented examples of intense metasomatism of a VMS orebody by magmatic–hydrothermal fluids exsolved from a relatively
primitive composite sub-seafloor intrusion.
Received: 15 April 1999 / Accepted: 20 January 2000 相似文献
34.
R. W. Talkington D. H. Watkinson P. J. Whittaker P. C. Jones 《Mineralogy and Petrology》1984,32(4):285-301
Summary Platinum-group mineral, silicate and other solid and fluid inclusions occur in disseminated and massive chromite in a variety of lithologies from ophiolitic and other mafic-ultramafic complex-types. The inclusions are small (<250 microns) and randomly distributed throughout their host. Silicate inclusions are modally more abundant than the other inclusion types. Platinum-group mineral phases are ruthenium-rich sulphides and PGE alloys are osmium-rich. Mafic silicates (olivine, pyroxenes, pargasitic-amphiboles, micas) are magnesium-, titanium-, and alkali-rich and felsic silicates are sodium-rich (albite, nepheline).The intimate association of these inclusions with chromite suggests that their origin must be considered within a chromite crystallization model. A hypothesis of origin is suggested wherein the platinum-group minerals and silicates are trapped as discrete, crystalline euhedral phases and silicate liquid during the precipitation of chromite. The similarity of physical characteristics, modal mineralogy and chemical compositions indicates that this model may be applicable to all mafic-ultramafic complex-types.
Minerale der Platin-Gruppe und andere feste Einschlüsse in Chromiten aus Ophiolit-Komplexen: Vorkommen und petrologische Bedeutung
Zusammenfassung Minerale der Platin-Gruppe, Silikate und andere feste und flüssige Einschlüsse kommen in disseminierten und massiven Chromiten in einer Vielzahl von Gesteinen in ophiolitischen und anderen mafisch-ultramafischen Komplexen vor. Die Einschlüsse sind klein (<250 microns) und unregelmäßig im Chromit verteilt. Silikat-Einschlüsse sind modal weiter verbreitet als andere Arten von Einschlüssen. Minerale der Platin-Gruppe sind durch Ruthenium-reiche Sulfide und Osmium-reiche Legierungen vertreten. Mafische Silikate (Olivin, Pyroxen, pargasitische Amphibole, Glimmer) sind Magnesium-, Titan- und Alkali-reich; felsische Silikate sind Natrium-reich (Albit, Nephelin).Die ausgeprägte Assoziation dieser Einschlüsse mit Chromit weist darauf hin, daß ihre Herkunft im Zusammenhang mit einem Kristallisations-Modell für Chromit zu sehen ist. Ein genetisches Konzept wird vorgelegt, wobei die Platin-Gruppen-Minerale als gut ausgebildete, idiomorphe kristalline Phasen, und die Silikate als Silikatschmelze während des Ausfallens des Chromites eingeschlossen werden. Die Ähnlichkeit der physikalischen Eigenschaften, der modalen mineralogischen Zusammensetzung und der chemischen Zusammensetzung weisen darauf hin, daß dieses Modell auf alle mafisch-ultramafischen Komplexe anzuwenden ist.相似文献
35.
Bending anisotropy: A mechanical constraint on the orientation of fold axes in an anisotropic medium
Bending anisotropy is the property of a layer of material whereby it bends more easily in some directions than it does in others. In macroscopically homogeneous layers, bending anisotropy results from the material itself being rheologically anisotropic in the plane of the layering.In this paper we investigate bending anisotropy in materials with orthorhombic symmetry and linear elastic or viscous behaviour. Although such models are rheologically simple, we believe they may provide a first approximation to the behaviour of some tectonites with linear and planar fabrics. Thus we predict that in rocks with strong linear fabrics, folds will form with axes nearly parallel to the linear fabrics, for a variety of different stress fields. This has important geological consequences. 相似文献
36.
This paper examines the geological implications of an analysis of constraints on the orientation of fold axes in orthotropic materials. We argue that rocks with penetrative linear and planar shape fabrics may have orthotropic (anisotropic) properties during deformation. Two forms of anisotropy (rheological and structural) could be potentially important in the control of fold axial directions. We discuss a model of deformation of rocks with linear/planar fabrics where, in a single deformation event, major fold axes need not be parallel to minor fold axes and neither need be perpendicular to the principal compressive stress direction. Geological and model examples of anistropic control on fold axial directions are given. 相似文献