Geological Characteristics And Provenance Analysis Of The Tianxing Quartz Sandstone Deposit In Daguan County,Yunnan

The study area is located in the northeastern Yunnan,and the stratigraphic division belongs to the Zhaotong mic-region in the upper Yangtze sub-region in Yangtze region of South China area.The geotectonic location is located in the junction of the two global giant tectonic domains,the Tethys-Himalaya and the Pacific tectonic domains.A large number of quartz sandstone deposits have been discovered in Lianghe,Zhongming,Daguan,Kuixiang,Longjie and Yiliang of Northeast Yunnan in recent years.This paper selects the Tianxing quartz sandstone deposit as the research object,and the mineralization model of the deposit were established by the study of the stratigraphic ore-controlling conditions,diagenesis process and the genesis of the deposit.Sedimentology,petrology and geochemical methods were used to analyze the provenance of the celestial quartz sandstone,and to understand the nature,tectonic background and provenance direction of the quartz sandstone deposits in the study area.The Tianxing quartz sandstone deposit is produced in the Shuotoushan Formation.The orebody is monoclinic,and its distribution and occurrence are basically consistent with the formation of the Shuotoushan Formation.The orebody extends roughly horizontally along SE-NW direction,with a regular shapes.The morphology of the orebody produced slight folds and deformations due to the later structural compression.There are a good overall continuity and stable thickness of the deposit,with two stones,J₁ and J₂.The structure of the ore includes massive structure and layered structure.The lithofacies palaeogeography shows that there were a bay during the Middle Devonian in the study area,which provided good development conditions for quartz sandstone.The characteristics of the sediment grain size in the study area shows that the grain size of the quartz sandstone are fine and medium;the frequency curve is mainly a normal curve,which is in a symmetrical single-peak shape;the sediment transportation is mainly based on jump,and the overall percentage of jump is more than 50%.The sedimentary environment of the Shuotoushan Formation belongs to the foreshore subfacies in the coastal environment.The study area was in a coastal environment during the sedimentation stage,and the terrestrial detritus was fully washed and selected to be deposited in the foreshore zone,a thick,high-purity quartz sandstone body is formed.The pressure solution between the quartz particles and the suture structure developed between the layers show that the mineralization materials have been redistributed during the diagenesis process.The re-precipitated and recrystallized of Si O₂ around the quartz sand particles further purified the quartz sandstone.Therefore,the Si O₂ content in the Tianxing quartz sandstone orebody is extremely high.The paleocurrent analysis shows that the paleocurrent direction of the Shuotoushan Formation in the study area is mostly between 320°-345°,with an average flow direction of 329.6°.The main element analysis shows that the Si O₂ content of the Tianxing quartz sandstone deposit is extremely high,most of which are greater than 98%,and the average content is more than 95%.According to the ratios of La to Sc and Sc to Th,it can be judged that the material of quartz sandstones of the Shuotoushan Formation originated from the felsic rocks of the continental upper crust.The discriminating diagrams of main element such as Al₂O₃-Si O₂ and Fe₂O₃-Al₂O₃show that the sedimentary tectonic environment of the quartz sandstones of the Shuotoushan Formation is the passive continental margin,and the detrital material mainly comes from the mature continental quartz provenance area.The total amount of rare earth elements in the Shuotoushan Formation is relatively low,the difference between light and heavy rare earth elements is large,the light rare earth elements are enriched,and the heavy rare earth elements are seriously deficient;Eu is negative anomaly;?Ce is positive anomaly.The distribution curve of rare earth elements shows that the quartz sandstones of the Shoutoushan Formation are products accumulated in the passive continental margin tectonic environment.