| The southwest Sichuan and northeast Yunnan are important phosphate prospects in China,Phosphate ore bearing horizons are mainly located in the Lower Cambrian Maidiping Formation(Meishucun Formation)in this area.The Leibo-Yongshan area,located in the prospective area of phosphate mines in southwest Sichuan and northeast Yunnan,has become one of the ideal areas for phosphate rock research due to its unique sedimentary environment and huge mineralization potential.In recent years,the research on the characteristics and genetic mechanism of phosphate deposits related to the Leibo-Yongshan area and neighboring areas has mainly focused on the aspects of ore deposit science and sedimentation,but there is a lack of relevant studies linking the sedimentary characteristics of the Maidiping Formation with the regional tectonic setting,basin properties and sedimentary phase transition.Therefore,this paper analyzes the change characteristics of the sedimentary facies of the phosphorus bearing strata of the Maidiping Formation in the Leibo-Yongshan area and establishes the deposition model by carrying out the actual measurement of the profile and the recording of the drilling core in the study area;Especially for the rhyolite at the top of the Maidiping Formation,the petrology,geochronology and geochemistry are mainly studied,and the sedimentary age and tectonic setting of the Maidiping Formation are discussed,which provides new constraints for basin property and metallogenic age;In addition,based on the understanding of phosphate rock,sedimentary facies,volcanism and basin properties,the controlling factors and genesis of the phosphate mineralization of the Maidiping Formation are proposed,which provides new inspiration and thinking for the further development of phosphate exploration in the study area and adjacent areas.The following results were obtained:(1)The lithology and thickness of Maidiping Formation are different on the east and west sides of the study area,showing a pattern of uplift and depression.The lithology on the west side is mainly fine crystal dolomite,phosphate block rock,phosphorous siliceous dolomite and lime dolomite,with a thickness of 210 m.The lithology of the east side is mainly siliceous rock,dolomitic siliceous rock,powdery-microcrystalline limestone,etc.,with a thickness of 42.7m.(2)The rhyolite on the top of the Maidiping Formation has a porphyritic structure,and the zircon U-Pb age is 527.8 ± 2.8 Ma,belonging to the Early Cambrian.The elemental geochemical analysis results of the rhyolite sample showed that it was formed in a tensile environment within the plate.Based on the chronologic data and the regional tectonic setting,it is considered that the Maidiping Formation sedimentation have the nature of a rift basin.(3)According to the identification marks of sedimentary facies,the Maidiping Formation is divided into tidal flat subfacies and platform facies of the limited platform facies in this paper.The tidal flat subfacies developed in the west side of the study area and the platform facies developed in the east side of the study area.(4)Based on the comparative analysis of tectonic setting,basin properties and sedimentary facies,it is believed that the Maidiping Formation in the study area was deposited as a paleogeographic pattern of rift basins with uneven subsidence,syngenetic faults and alternation of uplift and depression.(5)According to the analysis of metallogenic material sources,paleostructures,sedimentary environment and other conditions,it is considered that the source of phosphorus in the Maidiping Formation is mainly a deep source,which is the result of the combined action of volcanic hydrothermal fluid,ocean currents and biology,and the shallow sea tidal flat environment further promote the regeneration and enrichment of phosphorus. |
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