Geological Characteristics And Sedimentary Environment Of Panjiazhai Sedimentary Silica Deposit,Yiliang County,Yunnan Province

The stratigraphic division of the study area is Zhaotong stratigraphic community.The geotectonic location is located at the intersection of the littoral Pacific tectonic domain and Tethys Himalayan tectonic domain,and the Weining Zhaotong fold thrust belt,a class IV tectonic unit in the southwest margin of the Yangtze block.In this paper,the geological characteristics of panjiazhai sedimentary silica deposit and the sedimentary environment of ore bearing rock series in the study area are analyzed comprehensively.Through the collection of previous research data,profile survey,trenching construction,analysis of major and trace elements and rare earth elements,thin section identification and other work to analyze and explore the geological characteristics of panjiazhai sedimentary type silica deposit;while paleontological fossil observation,sedimentary structure observation,geochemical analysis?element data analysis drawing discrimination diagram?,grain size analysis and other work to analyze the sedimentary environment,Finally,combined with the analysis of geological characteristics and sedimentary environment of ore bearing rock series,the metallogenic model of sedimentary silica deposit in panjiazhai mining area is discussed.The silica deposit in this area is a typical non-metallic deposit.The ore-bearing stratum is the Middle Devonian shoutoushan formation?D₂st?,which is obviously controlled by the stratum and has a typical metallogenic exclusive stratum attribute.The ore composition is very simple,mainly composed of clastic particles and cement,and the clastic particles are mainly quartz?content>95%?,followed by rock debris and a small amount of mica;the cement is mainly argillaceous,Ferritic and siliceous.The ore structure is dominated by fine-grained sand structure,followed by medium-sized sand structure,and the ore structure is dominated by massive structure.The mineral particles are mainly quartz single crystal,the support type is particle support,the cementation type is line contact cementation,the particle separation is good,mainly in sub angular shape,with high component maturity and structural maturity.The occurrence state of the ore body is strictly controlled by the stratum,and it is monoclinic.It is distributed in the core of Yiliang Luowang compound Syncline in a large area.The spatial distribution of the ore body is generally in the direction of NE-SW,with a dip angle of 230°-330°and a dip angle of 5°-15°.The length of the ore body is about 1710m,the thickness is relatively stable,and the thickness is about 100.76-125.74m.As for the analysis of sedimentary environment,the sedimentary environment of ore bearing rock series is comprehensively and deeply analyzed through the study of petrographic characteristics,paleontological fossil characteristics,grain size analysis and the analysis of main and micro geochemical characteristics.The comprehensive analysis and research indicate that the sedimentary environment of the sandstones of shoutoushan formation?D₂st?in panjiazhai mining area should be that of barrier free coastal foreshore zone The tectonic setting of the area is passive continental margin environment.In terms of metallogenic model,the source of ore-forming materials of sedimentary type silica deposits in the mining area:the clastic particles should come from the mature continental source area of the upper Yangtze ancient land;the source of siliceous material in cement is mainly the siliceous material released by the clastic quartz particles in the sand body through pressure dissolution.Through particle size analysis,the diagram of sample particle size characteristics shows that the particle size characteristics of the five samples are nearly normal distribution,and the percentage content of jumping population is very high,but there is no traction population and suspension population,indicating that the transport medium conditions should be the impact and return of waves in coastal sedimentary environment.The ore-forming age of sedimentary silica deposit in panjiazhai mining area is basically the same as that of the strata,which should be the Middle Devonian of Late Paleozoic.The main factors controlling the sedimentary silica deposit in panjiazhai mining area are strata,lithology and lithofacies palaeogeography.The mineralization can be roughly divided into two stages:the early syngenetic stage and the late epigenetic stage.The terrigenous clastic particles are initially enriched by syngenetic mineralization,and then further enriched by epigenetic mineralization,forming a sedimentary type silica deposit with high purity and large reserves.The panjiazhai silica deposit in Yiliang County,Yunnan Province,should belong to the mechanical sedimentary beach sand deposit in the exogenetic deposit according to the genetic classification of the deposit.