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451.
Tin–polymetallic sulfide deposits in the eastern part of the Dachang tin field (South China) and the role of black shales in their origin 总被引:3,自引:0,他引:3
Pašava Jan Kříbek Bohdan Dobeš Petr Vavřín Ivan Žák Karel Delian Fan Tao Zhang Boiron Marie-Christine 《Mineralium Deposita》2003,38(1):39-66
The Dafulou and Huile vein and stratabound cassiterite-sulfide deposits and sheeted ore veins at the Kangma cassiterite-sulfide deposit are located in the eastern part of the Dachang tin field. These deposits are hosted in a sedimentary sequence containing significant concentrations of organic matter in the form of Lower Devonian calcareous black shales and hornfels. These rocks together with the younger intrusion of Longxianggai granite (91DŽ Ma) actively participated in the formation of Sn-polymetallic deposits. The following three major stages have been distinguished in stratiform and vein-type orebodies at Dafulou, Huile and Kangma: stage I (cassiterite, pyrrhotite, arsenopyrite, tourmaline, carbonate), stage II - main sulfide stage (quartz, cassiterite, arsenopyrite, pyrrhotite, sphalerite, stannite, pyrite, carbonates) and stage III (native Bi, galena, electrum, sulfosalts). Stage IV (post-ore), recognized at Huile is represented by barren carbonates and zeolites. Whole rock geochemistry has revealed that at Dafulou, Bi and Cu correlate strongly with S, whereas V and Pb correlate well with Corg (organic carbon). The similar distribution patterns of selected elements in average slightly mineralized low-Ca black shales indicate a fluid composition similar for all deposits studied. Studies of graphitization of the organic matter in black shales adjacent to orebodies indicate that d(002) and FWHM (full width in half maximum)/peak height values gradually decrease in the following sequence: Dafulou deposit M Kangma deposit M Huile deposit. The pyrolysate of wall rocks at the Dafulou deposit is relatively enriched in asphaltenes and maltenes (55.6-72.0% of the pyrolysate) comparable with pyrolysate obtained from more distal black shales (19.2-28.5%). Typical GC-MS spectra of pyrolysate from distal black shales are dominated by alkanes in the n-C15 to n-C25 range, aromatic molecules being represented mostly by alkyl-naphthalenes. In contrast, only traces of aliphatic hydrocarbons in the n-C14 to n-C18 range and elemental sulfur were identified in pyrolysates from pyrrhotitized wall rocks. The earliest fluid inclusions of the studied system occur in the quartz-tourmaline-cassiterite assemblage of stage I at Dafulou. These inclusions are H2O-CO2-CH4-rich, with 10 to 20 vol% of aqueous phase. P-T conditions of the trapping of inclusions are estimated to be up to 400 °C and 1.3 to 2.0 kbar (between 5.0 and 7.5 km under lithostatic pressure). In contrast, the presence of a low density gaseous CO2-CH4 phase indicates relatively low pressures during the formation of the breccia-type quartz-calcite-cassiterite-sulfide mineralization (stage II), when P-T conditions probably reached approx. 380 to 400 °C and 0.6 kbar (up to 6 km under hydrostatic pressure). Fluid inclusion data and oxygen isotope thermometry indicate that cassiterite-sulfide ores of the main sulfide stage (stage II) formed from aqueous-carbonic fluid (CO2/CH4 =ᄺ) at temperatures of up to 390 °C at Dafulou and in a temperature range of 250 to 360 °C at Huile and 260 to 370 °C at Kangma. The '34S values of sulfides from Dafulou range mostly between -1 and -6, whereas sulfides from the Kangma and Huile deposits are characterized by more negative '34S values (between -8 and -11, and between -9 and -12, respectively). These data suggest that bacteriogenic sulfides of black shales were a dominant source of reduced sulfur for epigenetic (vein and replacement) mineralization. Oxygen isotopic compositions of five quartz-cassiterite pairs from Dafulou and Huile show a relatively narrow range of calculated oxygen isotope temperatures (250-320 °C, using the equation of Alderton 1989) and high '18Ofluid values between +8 and +10 (SMOW), which are in agreement with fluid derivation from and/or high temperature equilibration with the Longxianggai granite. The carbon and oxygen isotope composition of carbonates reflects variable carbon sources. Stage I calcite is characterized by narrow ranges of '13C (-7.0 to -9.5 PDB) and '18O (+15.0 to +17.5 SMOW). This calcite shows ubiquitous deformation, evidenced by intense development of twins. Fluid compositions calculated at 330 °C for the Dafulou and Huile deposits and at 270-300 °C for the Kangma deposit ('18Ofluid between +10.0 and +11.5 SMOW, '13Cfluid between -5.5 and -7.5 PDB), agree with fluid derivation from and/or equilibration with the peraluminous, high-'18O Longxianggai granite and suggest a significant influence of contact metasedimentary sequences (carbon derived from decomposition and/or alteration of organic matter of calcareous black shales). The '13 C values of organic matter from the Lower to Upper Devonian host rocks at the Dafulou deposit (-24.0 and -28.0) fit with a marine origin from algae. However, organic matter adjacent to the host rock-ore contact displays a slight enrichment in 13C. The organic carbon from the Huile and Kangma deposits is even more 13C enriched (-24.6 to -23.5). The most heavy '13 C values (-16.5) were detected in hornfels sampled at the contact of the Upper Devonian sediments with the Longxianggai granite. The '13C data broadly correlate with the degree of structural ordering (degree of graphitization) of organic matter, which indicates that both variables are related to thermal overprint. 相似文献
452.
Linear Amplification of Horizontal Strong Ground Motion in Zagreb (Croatia) for a Realistic Range of Scaled Point Sources 总被引:2,自引:0,他引:2
Marijan Herak Ivan Lokmer Franco Vaccari Giuliano F. Panza 《Pure and Applied Geophysics》2004,161(5-6):1021-1040
— The linear amplification of the larger horizontal component of strong ground motion along a selected profile in the city of Zagreb is estimated by examining the synthetic waveforms corresponding to a suite of 16 realistically chosen scaled point sources. The accelerograms, computed for the average bedrock model by modal summation, are propagated through local laterally heterogeneous anelastic models by the finite-difference algorithm. The ratio of peak ground acceleration (PGA) and of the response spectra (RS), obtained by using local and bedrock models, define the PGA and RS amplification AMP(PGA) and AMP(RS), respectively. Even variations of the order of commonly observed uncertainties of only dip and rake angles of the causative fault show that both AMP(PGA) and AMP(RS) vary at some sites by more than a factor of two. It follows that, especially for strongly laterally heterogeneous structures, local effects must be determined for each of the relevant sources considering all associated uncertainties as completely as possible. Such a conclusion certainly holds for the case of the microzonation of Zagreb, where the local geology is quite complex, and the seismicity is not confined to a single seismic source zone. 相似文献
453.
Ivan Madirazza 《International Journal of Earth Sciences》1968,57(3):1034-1066
This paper deals with two salt domes, Mønsted and Sevel, located in northern Jutland, and is primarily concerned with the problem of Quaternary salt tectonics and its possible relationship to the Quaternary morphology.Geological mapping of the two areas during the summers of 1965 and 1966 included a detailed surveying by means of a theodolite of a stream valley extending over the north-eastern part of Mønsted salt dome and of two valleys in the southern part of Sevel salt dome. In the Mønsted area extensive use of aerial photographs was made.In the light of the results of the geological study, an interpretation of the available geophysical data — in the case of Mønsted both gravimetric and magnetic — is attempted.
Zusammenfassung Die Salzstöcke Mønsted und Sevel in Nordjütland werden untersucht. Es wird versucht in beiden Gebieten eine Beziehung zwischen Quartär-Morphologie und Salztektonik herzustellen.Eine geologische Kartierung der beiden Gebiete wurde im Sommer 1965 und 1966 durchgeführt. Sie umfaßt eine detaillierte Vermessung des Bachlaufes, der über den Nordostteil des Mønsted-Salzstockes fließt, so wie zweier Täler im Südteil des Sevel-Salzstockes.Die Ergebnisse der geologischen Untersuchung werden in Beziehung zu den geophysikalischen Daten — für Mønsted gravimetrische und magnetische gesetzt.
Résumé Cet article traite deux dômes de sel, Mønsted et Sevel, situés au Nord du Jutland, et il s'occupe en premier lieu du problème de la tectonique du sel pendant le Quaternaire, et son éventuelle influence sur la morphologie quaternaire.L'étude géologique des deux régions, faite au cours des étés 1965 et 1966, comprenait un mesurage détaillé à l'aide d'un théodolite d'une vallée qui s étend sur la partie Nord-Est du dôme de sel à Mønsted et de deux vallées dans la partie Sud du dôme de sel à Sevel. Dans le cas de Mønsted on a fait ample usage de photographies aériennes.S'appuyant sur les résultats de l'étude géologique, l'auteur propose une interprétation des données géophysiques disponibles, qui dans le cas de Mønsted, comportent des mesurages tant gravimétriques que magnétiques.
Mø nsted Sevel . . ( Mønsted).相似文献
454.
Summary The present paper deals with a hydromagnetic dynamo model of the generation mechanism of the Earth's magnetic field. An attempt has been made at selecting a flow-velocity field in the Earth's core which would satisfy the condition 0 for regenerating the field according to [2], and which would yield a velocity field pattern on the core surface as given in the papers by Kahle et al. [9]. These conditions are satisfied by the velocityv=V
1+U
2
c
–V
2
c
and, geometrically, this velocity field is represented in space by a spiral convective motion. On the core surface two downflows and two upflows with the corresponding rotating cells may then be found. Only the axisymmetric harmonic component regeneration of the magnetic field has been considered. Adequate regeneration equations have been obtained by means of Braginski's method of quantity estimates in order of magnitude. 相似文献
455.
Vlastislav ěrvený Ivan Pšenčík Reviewer J. Vaněk 《Studia Geophysica et Geodaetica》1975,19(3):298-299
Summary Seismic rays and geometrical spreading in laterally inhomogeneous media are described by a system of ordinary differential equations of the first order. When the ray crosses an interface of the second order, certain quantities in the system change discontinuously. The initial conditions for the system at the point of intersection of the ray with the interface are presented. 相似文献
456.
457.
L.M. Willey Y.K. Kharaka T.S. Presser J.B. Rapp Ivan Barnes 《Geochimica et cosmochimica acta》1975,39(12):1707-1711
High alkalinity values found in some formation waters from Kettleman North Dome oil field are due chiefly to acetate and propionate ions, with some contribution from higher molecular weight organic acid ions. Some of these waters contain no detectable bicarbonate alkalinity. For waters such as these, high supersaturation with respect to calcite will be incorrectly indicated by thermodynamic calculations based upon carbonate concentrations inferred from traditional alkalinity measurements 相似文献
458.
Rudolf Jaffe Ivan Leal Jose Alvarado Piero Gardinali Jos Sericano 《Marine pollution bulletin》1995,30(12):820-825
Bivalve samples were collected at seven sampling stations located between the town of Machurucuto and the Bay of Higuerote, Venezuela, covering approximately 70 km of coastline. Samples were collected both east and west of the Tuy River mouth, which has a plume known to move in a north-westerly direction. Petroleum hydrocarbons, both aliphatic (n-alkanes and UCM) and polyaromatic (PAHs), were detected and quantified in the samples. These hydrocarbons were found to be primarily derived from fossil fuels. Halogenated organics consisted mostly of polychlorinated biphenyls (PCBs) and some chlorinated pesticides, primarily of the DDT group. Heavy metals such as Pb, Cu, Ni, Zn, Cr and Cd were analysed in the samples. The results clearly show the influence of the Tuy River plume on the water quality of the coastal zone, particularly that located west of the river mouth. One sampling station, located just east of the river mouth, also showed significant influence from the river plume. 相似文献
459.
Ivan Gams Dr. 《GeoJournal》1991,24(4):331-340
The territory of the youngest European state is crossed by strategically important passes, the lowest in the entire Alps, leading from the Danubian basin to the Mediterranean (Italy). Thus, the Slovenes had been under cultural, civilization and political domination of centers from these two parts of Europe all until 1918. Because the mountanous land forms, dissected also by valleys and basins, were prone to processes of diffucion rather than fusion, the Slovenians became a national and political subject of their own as late as 19th C. From 1918 to 1990 they were joined with Yugoslavia, a SE European state, and learnt to their cost all the differences between the cultures of W and Central Europe on the one hand, and SE and E Europe and the Near East on the other. Hence the plebiscite decision by the nation for an independent state. 相似文献
460.