Tin–polymetallic sulfide deposits in the eastern part of the Dachang tin field (South China) and the role of black shales in their origin

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 C_org (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 '¹⁸O_fluid 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 ('¹⁸O_fluid between +10.0 and +11.5‰ SMOW, '¹³C_fluid 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.     

Induction vector estimates in the Polish-Czechoslovak part of the Carpathians

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Spectral analysis of geomagneticPc3 pulsations recorded at Budkov and Niemegk

Summary The dependence of the individual parameters of geomagnetic Pc3 pulsations, of their frequencies, amplitudes, phases, flattening of their polarization ellipses, the orientation of their major axis and the sense of rotation of the disturbance vector, are determined from the records made at the Budkov and Niemegk Observatories. Also their diurnal variations at both stations and the correlation of the numerical values between both stations are given.     

Theoretical seismograms for block structures

Summary In constructing theoretical seismograms for large models with block structures, approximate methods are particularly efficient. For example, in treating Earth's crust block models, the ray method with various modifications for including diffracted waves can be used. Smaller block structures, of dimensions comparable to a wavelength, are efficiently treated by direct numerical methods. In this way practically important problems of engineering seismology, seismic microzoning, etc., can be solved. The method of so-called conservative diference schemes combines effectively the advantageous features of both the standard finite element and finite difference methods. The basic properties of the method, as well as some features of the corresponding Fortran IV program LATER, are explained on a computational example. The example concerns a highly simplified evaluation of the seismic response of the earth fill. In the frequency range under study two resonance frequencies are identified. Moving along the surface of the fill, from the base to the peak, the predominant frequency decreases. Some prospects of direct numerical methods in seismology are briefly discussed in concluding section.Presented at the Workshop on Seismic waves in laterally inhomogeneous media, Liblice (Czechoslovakia), 27. 2–3. 3. 1978.     

Two-dimensional correlation of geophysical data applied to the heat flow and earth's crust thickness patterns in Czechoslovakia

Summary A simple method for the mutual correlation of various geophysical fields is proposed to disclose their prospective inherent correlations. Some problems connected with the statistical and physical confidence of the resulting maps of the correlation coefficient are mentioned. The correlation between the surface heat flow pattern and the crustal thickness on the territory of Czechoslovakia is presented as an example and briefly discussed in terms of crustal structure.     

A re-examination of Bořickýite

Summary New chemical and physical data are given for four samples labeled delvauxite and boickýite. The set includes delvauxite from the type locality at Berneau, near Visé, Belgium, and boickýite from the type localities at Leoben, Styria, Austria, and Nenaovice, Bohemia, Czechoslovakia. Chemical analyses yield an approximate chemical formula (Ca, Mg) (Fe³⁺, Al)₄(PO₄, SO₄, CO₃)₂(OH)₈·n H₂O, wheren=3–7.5. Amorphous to X-rays, except for material from Nenaovice (admixed diadochite). Delvauxite, boickýite and foucherite are probably identical.

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Eine neu-untersuchung von Boickýit

Zusammenfassung Es sind neue chemische Analysen und physikalische Eigenschaften von vier Proben, die als Delvauxit und Boickýit bezeichnet sind, angegeben. Die untersuchte Serie enthält Delvauxit aus der ursprünglichen Lokalität Berneau bei Visé (Belgien) als auch Bôrickýite von Leoben (Steiermark, Österreich) und Nenaovice (Böhmen, Tschechoslowakei). Die chemischen Analysen führen zur annähernden Formel (Ca, Mg) (Fe³⁺, Al)₄(PO₄, SO₄, CO₃)₂(OH)₈·nH₂O, won dem Werte 3 bis 7,5 gleich ist. Die untersuchten Proben sind, mit der Ausnahme der aus Nenaovice, die beigemischten Diadochit enthält, röntgenamorph. Aus der durchgeführten Untersuchung geht hervor, daß Delvauxit, Boickýit und Foucherit höchstwahrscheinlich identisch sind.

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With 3 Figures     

The preliminary heat flow map of Europe and some of its tectonic and geophysical implications

The heat flow map of Europe was derived from 2605 existing observations, which for this purpose were supplemented by numerous results of deep borehole temperatures, gradients and local heat flow patterns. In areas without data the heat flow field was extrapolated on the basis of the regional tectonic structure and the observed correlation of heat flow and the age of the last tectono-thermal event. The heat flow pattern as obtained in the map may be described by two components: (i) regional part and (ii) local part of the measured surface geothermal activity. The regional part of the heat flow field in Europe is dominated on the whole by a general north-east to south-west increase of the geothermal activity, which is an obvious consequence of the tectonic evolution, the major heat flow provinces corresponding thus to the principal tectonic units. The geothermal fine structure (local part) superimposing the former is mainly controlled by local tectonics, especially by the distribution of the deep reaching fracture zones and by the hydrogeological parameters. The correlation between the heat flow pattern and the crustal structure allows some preliminary geophysical implications: (a) areas of the increased seismicity may be connected with the zones of high horizontal temperature gradient, (b) increased surface heat flow may be generally observed in the zones of weakened crustal thickness, (c) there are considerable regional variations in the calculated temperature on the Moho-discontinuity, as well as in the upper mantle heat flow contribution.     

Heat flow in the Upper Silesian coal basin

Summary The paper presents results of heat flow measurements made in 6 deep bores in the Czechoslovakian part of the Upper Silesian coal basin. The heat flow measured was in the range from 1.74 to 1.87 cal/cm²s. The undisturbed period before the temperature measurement in the bore is discussed and results of repeated temperature measurements carried out 0.1, 1,5 and 36 days after cessation of drilling in one of the bores NP-522, are also given. Although the temperature in the bore still differs considerably from equilibrium, it is possible to determine the temperature gradient with an accuracy better than 5% as soon as 5 days after drilling was finished.