| Popis: |
The Dongping gold deposit is a mesothermal lode gold deposit hosted in syenite. The ore petrography and chemistry of the tellurides from the alteration zone of the deposit have been studied in detail using optical microscopy, scanning electron microscopy, electron probe micro-beam and X-ray diffraction facilities. The tellurides, consisting mostly of calaverite, altaite, petzite tellurobismuthite and tetradymite, are hosted irregularly in pyrite fractures and voids. In the ore bodies, the species and quantity of tellurides decrease from the top downwards, accompanied with lowering of gold fineness, and the existence of tellurides exhibits a positive correlation with gold enrichment. Mineral paragenesis and chemical variations suggest that during evolution of the ore-forming fluids Te preferably incorporated with Pb to form altaite, followed in sequence by precipitation of petzite, and calaverite when Ag has been exhausted, and the residue fluids were enriched in Au, giving rise to formation of native gold. Calculation with reference of the fineness of native gold coexisting with the tellurides indicates that at 300 °C, log f (Te 2 ) varied between − 8.650 and − 7.625. Taking account of the Au–Ag–Te mineral paragenesis, it is inferred that log ƒ (Te 2 ) varies from − 9.12 to − 6.43, log ƒ (S 2 ) − 11.47 to − 8.86. In consideration of the physicochemical conditions for formation of tellurides, with comparison to some known telluride deposits, it is suggested that high log ƒ (Te 2 ) is a key factor for high fineness of native gold as well as precipitation of abundant tellurides. |
Full Text from ScienceDirect