METAMORPHC OVERPRINTS ON THE TALATE PB-ZN DEPOSIT IN ALTAY—EVIDENCES FROM GEOLOGY AND FLUID INCLUSIONS

The Talate Pb-Zn deposit, located on the southeast limb of the Kelan volcanic-sedimentary basin in the Altaides, occurs in the metamorphic rocks of the lower Kangbutiebao formation of lower Devonian (D₁k₁²)(Xu,1996; Wan et al., 2010). The deposit is recognized as VMS by many ore geologists (Wang et al., 1996), but metamorphic overprints of late sulfide-quartz veins can be found in the area. Deformed and metasomatic textures of ores in the Talate deposit can be seen in outcrop and under microscope. Two mineralizing periods of ore growth can be identified: 1) a primary depositional sea-floor volcanic-hydrothermal characterized by disseminated, banded and brecciaed sphalerite-galena ores; and 2) metamorphic overprints that include early foliated sulfide-quartz veins (Q1) related to synorogenic metamorphic event and late pyrite-chalcopyrite quartz veins (Q2) cutting the schist related to a younger event. Primary L-V fluid inclusions in sphalerite (Sp) of VMS ores were mostly fractured, but a few are remained, which have Th_TOT=267~334°C. Secondary L-V inclusions and H₂O-CO₂ inclusions trapped in tiny fissures can be found in Sp, which have Tm_CO2=-61.2°C and Th_CO2=10.7~11.0°C. A large number of H₂O-CO₂ inclusions and carbonic (CO₂±CH₄) inclusions exist in early foliated sulfide-quartz veins of metamorphic period. H₂O-CO₂ inclusions have Th,_TOT of 294~368°C, with salinities of 5.5%~18.3% NaCleqv. A great many H₂O-CO₂ inclusions and carbonic inclusions are also found in late pyrite-chalcopyrite quartz veins. H₂O-CO₂ inclusions have 275~331°C of Th_TOT, and 3.3%~16.5%NaCleqv of salinities. Carbonic inclusions have -61.5~-58.0°C of Tm_CO2, and have two groups of Th_CO2 (-27~-20.6°C and 28~28.7°C, respectively). The P-T trapping conditions of CO₂-rich fluids are coincided with those of late or post regional metamorphism.CO₂-rich fluids might come from phase separation or unmixing of original metamorphic fluids during orogenic process of the Altaides. Water in these fluids was used up in wall rock alteration and metasomatism of ores.

References

Wan B, Zhang LC and Xiao WJ. 2010. Ore Geology Review, 37(2): 114-126

Wang JB, Qin KZ, Wu ZL, Hu JH and Deng JN. 1998. Beijing: Geological Publishing House, 1-210(in Chinese)

Xu XC. 1996. Earth Science Frontiers, 3(3~4): 200-208