Record details

Title
    Tin-polymetallic sulfide deposits in the eastern part of the Dachang tin field (South China) and the role of black shales in their origin
Statement of responsibility
    Jan Pašava, Bohdan Kříbek, Petr Dobeš, Ivan Vavřín, Karel Žák, Fan Delian, Zhang Tao, Marie-Christine Boiron
Author
    Boiron, Marie-Christine
    Delian, Fan
    Dobeš, Petr
    Kříbek, Bohdan, 1946-
    Pašava, Jan
    Tao, Zhang
    Vavřín, Ivan
    Žák, Karel, 1957-
Language
    anglicky
Source title - serial
    Mineralium Deposita
Vol./nr.
    Vol. 38, no. 1
Pages
    p. 39-66
Year
    2003
Notes
    16 obr., 4 fot., 9 tab., 2 s. bibl.
    il.
    Zkr. název ser.: Mineralium Depos. (Berlin).
Subject group
    břidlice černá
    devon
    geneze ložiska
    grafitizace
    inkluze fluidní
    izotopy C
    izotopy O
    izotopy S
    izotopy stabilní
    karbonáty
    kasiterit
    ložisko typu stratabound
    organická substance
    podmínky P-T
    rudy barevných kovů
    rudy Sn
    sulfidy
    žíla rudní
Geographical name
    Čína jižní
    Dachang (Čína jižní)
Keyword
    Black
    China
    Dachang
    Deposits
    Eastern
    Field
    Origin
    Role
    Shales
    South
    Sulfide
    Tin
    Tin-polymetallic
Abstract (in english)
   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 (91+-2 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 ŕ Kangma deposit ŕ Huile deposit. The pyrolysate of wall rocks at the Dafulou deposit is relatively enriched in asphaltenes and maltenes (55.6-72.0 per cent of the pyrolysate) comparable with pyrolysate obtained from more distal black shales (19.2-28.5 per cent). 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 per cent 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 aqueouscarbonic fluid
Contributor
    Česká geologická služba
Contributor code
    ČGS (UNM)
Source format
    U
Entered date
    31. 8. 2007
Import date
    8. 8. 2012