| The Early Cambrian Meishucun stage is an important phosphorous forming stage in China.A large number of large and medium-sized phosphate deposits developed in the Meishucun Formation or its equivalent strata in eastern Yunnan and central Sichuan,forming a large-scale Sichuan-Yunnan phosphate belt.The available data show that the study of phosphate deposits in this metallogenic belt is mainly concentrated in the Kunyang of Yunnan to Zhijin area of Guizhou province,while the study of phosphate deposits in the Sichuan area is relatively weak,and there is a dispute on the genetic understanding of the deposits.In view of this,this paper takes the Xiaogou phosphate deposit in Sichuan province as the research object,through the in-depth study of geological-geochemical characteristics and the comparative analysis of regional typical deposits,preliminarily established the metallogenic model of the deposit,and summarized the regional metallogenic rules.The study shows that the industrial ore body of Xiaogou phosphate deposit is stratified in the second member of the lower Cambrian Maidiping Formation,which is controlled by stratigraphic lithology and lithofacies paleogeography,and the phosphorus-bearing Formation has some characteristics of the uplifting current Formation.Biological fossils are developed in the ore,and the mainly mineral is fluorapatite,gangue mineral is dolomite,calcite,quartz,chalcedony,pyrite and hematite,etc.The ore is common arenaceous structure,and develops dense block structure and stripe-strip structure.Geochemical indicators such as Al,Ti,Eu,Co,Mn and 87Sr/86Sr show that the source of phosphorus is related to the enhancement of continental weathering,hydrothermal activities at the bottom of the sea,and the activities of upwelling,and the upwelling activity is likely to be the main source of phosphorus.Ce,U,Mo and other redox sensitive elements indicate the underlying water conditions of sub-oxidation during mineralization.Pauth,Baauth and other paleoproductivity indexes indicate the high paleomarine productivity conditions in the mineralization process.Based on the geological and geochemical characteristics of the deposit,it is concluded that the phosphate enrichment is affected by BSR,EPS and physical enrichment.BSR decomposes phosphate ions from organic matter.EPS provides nucleation sites for the Formation of phosphorus particles in phosphate Formation,which is conducive to the rapid precipitation of phosphorus.By physical enrichment,the semi-consolidated or consolidated phosphate ore is transformed,which is broken,scour,winnowed,transported,precipitated again,and then forms thick phosphate rock with industrial value.The phosphorus-bearing layers of Xiaogou phosphate deposit and the sections of Xiaotan,Meishucun and Gezhongwu have similar geological-geochemical characteristics,lithofacies paleogeography,uplifting ocean current,paleoproductive conditions and biological action are the key factors for phosphorus mineralization in Meishucun period. |
