Bacteriogenic Textures And Bacterial Fossils In Sulfide Ores And Their Metallogenic Implication In The Giant Jinding Pb-Zn Deposit,Yunnan,China

The giant Jinding Pb-Zn deposit is the youngest sediment-hosted deposit in the world,and endowed with the largest Pb-Zn resources in China at present.The research of this thesis is based on the detailed observation of ores under reflected light microscope and revealed a variety of ore textures that may be related to bacterial processes,such as framboidalsphalerite,spherical aggregate of galena-sphalerite,and roe-shaped sphalerite,dendritic colloidal sphalerite-pyrite,metacolloidal sphalerite-pyrite,multinuclear-metacolloidal-zonal sphalerite-pyrite,botryoidal sphalerite-pyrite,and framboidal pyrite and bacterial plaque-like galena-sphalerite.Field emission scanning electron microscopy?FESEM?and energy dispersive spectrometer?EDS?were applied for further observation and analyses of these bacteriogenic textures.It is demonstrated that the nanoscale bacteria fossils are composed of nano sized sphalerite,galena,pyrite,calcite or multiple sulfide minerals,presenting as shapes of bacterial colony in the ores.Individual bacteria fossils usually exhibit shapes as spherical,botryoidalis or annularity,with a diameter of200⁵00 nm.Extracellular polymeric substances?EPS?associated with the sulfide bacteria fossils had been observed with filamentous and mucoid structures and had similar compositions with bacterial fossils.In situ sulfur isotopic composition of bacteriogenic textures of sulfides and bacteria fossils were analyzed by secondary ion microprobe analysis?SIMS?,reflecting negative?³⁴S_V-CDT-CDT values from?48.6 to?9.5 per mille,thereby indicating the abundant existence of sulfate reducing bacteria in the ore-forming process.According to the various hydraulic fractures and sand injection structures in the field and previous fluid inclusion studies,a multiple stage influx of ore-bearing hydrothermal is suggested.For an individual stage,period of the hydrothermal activity is short,while the duration of non-hydrothermal is relatively longer.During the period of hydrothermal activities,BSR may have ceased in open space proximal to the main conduits,and TSR may have taken over.Whereas,during non-hydrothermal activities,the site of mineralization may have resumed the ambient thermal conditions,and BSR is dominant across the deposit.Considering the shallow metallogenic depth,relatively lower temperature,barely visible hydrothermal alteration,presence of evaporation sulfate layers and existence of paleo-oil and gas reservoir in Jinding dome,we suggest that bacterial sulfate reduction?BSR?process is the key genetic mechanism of H₂S required by large-scale Pb-Zn sulfide mineralization in the Jinding dome.