Dolphin Types And Geochemical Characteristics Of Dengying Formation In Songjia Area, Songjia Area, Northeastern Yunnan Province

Upper Sinian Dengying formation dolomite is the main object of this paper. Based on the filed work about Songliang village office-Tangjia slope section, Huilong section, Erlong section and Aijiachang section, measurement, description and sampling have been done. After observation under microscope, some key samples been selected to do geochemistry analysis, X-ray diffraction, cathodoluminescence and electron microprobe. Dengying formation dolomite stratigraphic sequence, the type of dolomite, sedimentary environment and evolution process result from the study in terms of petrology and mineralogy, sedimentary and geochemical characteristics. Conlusions are as follows:Dengying formation dolomite on studying area can been divided into three members, five submembers. Upper member of Dengying formation include two submembers:upper submember is grey aplite-dolomite, which develop of chert bands and block mass and calcite network occasionally. Two Conglomerate layers are the marker bed of upper submember, second layer is the demarcation line of upper submember and lower submember. Lower submember is grey-white, white dolomite. Develop of bird-eye structure and zebra structure in the bottom. The middle member also can be separated into two submember:upper submember is maize-yellow, grey-white siliceous dolomite, richful black siliceous bands. Calcite and bitumen filled in the fissure. Pyrite, hematite and lead-zinc mineralization can been seen. Lower submember is grey fine grain containing siliceous dolomite, which is the main occurrence horizon of vein ore bodies. Lower submember is characteristic of the development of quartz and dolomite miarolitic cavity and hematite mineralization. Lower member is laminar algal dolomite include a dolomite interlayer. Algae particles full of all Dengying formation dolomite, the content various with depth.Five dolomite types in Maozu-Songliang district resulting from filed work and observation under microscope been recognized:(1) algae-lamina dolomite; (2)algae-chip dolomite; (3)algae-nuclear dolomite; (4)oolitic dolomite; (5)grain-refining dolomite. Cement of dolomite has circle layer obviously, indicate multi-stage. Cathodoluminescence features are various from different dolomite type. Luminescence from strong to weak.From geochemistry analysis, low content of Al2O3、K2O、Fe2O3、TiO2 indicate that the sedimentation of dolomite without effect of terrigenous component, whereas, V/Cr<2,Ni/Co<5, V/(V+Ni)<0.6 means the oxidizing condition of sedimentary water. U/Th>1and Sr/Ba<1indicate the dolomite sedimentation process with the participation of hydrothermal sedimentation, without terrigenous component. CaO/(Fe+CaO) is 0.980 and m far more than 500. The value indicate the sedimentation environment of Dengying formation dolomite is epicontinental sea or lagon facies.Decrease of order degree from top to down result from X-ray diffraction. The top formation of dolomite has higher order degree, however, the bottom lower. Electronic microprobe date demonstrate that the cathodoluminescence diversity of Dengying formation dolomite in studying area is controlled by Fe, Mn atom, Mn is accelerator, Fe quenching. In addition, Dengying formation dolomite experience four diagenesis process:parasyngenetic, contemporaneous, burying and supergene.