| The Xiangshan uranium orefield,located in the Gan-Hang tectonic volcano rock uranium metallogenic belt,is the largest volcanic rock uranium deposit in China which has been discovered currently.As one of the seven largest integrated exploration areas of uranium ore,the orefield has good geological conditions of uranium metallogenesis.This paper is on the basis of the extant prospecting and study with the older generation of geologists in Xiangshan area.Through systematic collation and comprehensive analysis of the existing geological,geophysical,geochemical,drilling,and other aspects of the field basic materials,and from first to last throughout the activity theory.By making full use of the new theories and methods in structural geology,such as strike-slip structure,extensional tectonic,compression tectonic,thrust-nappe structure and gravitational detachment tectonics,we carried on a systematical and deeply study on structural features and uranium mineralization of Xiangshan uranium orefield in Jiangxi province.To determine the tectonic framework and divide the tectonic level of orefield fracture,and to analyze the characteristics of various faults.Combined with the regional tectonic evolution and dynamicsresearch,analysis of the causes of fault structure and the emplacement mechanism of volcano agency,and summarize the tectonic and uranium mineralization.We achieve a more rational and realistic cognition about the feature of tectonic deformation in this orefield,providing a more firm basis for exploring favorable district of uranium ore.There are several achievements in this study,which would discuss as following:1.Yongfei-Fuzhou deep fracture,the middle section of Dexing-Suichuan deep fracture,crossed the northwest of Xiangshan uranium orefield.This fracture went through three evolutionary stages,from transpressional to extension to thrust,which playing an important role in the formation of Xiangshan uranium orefield.2.There are three EW-trending fracture belts,three SN-trending fracture belts and NE-trending fractures in Xiangshan uranium orefield,which are interconnected with each other and making tessellated and diamond clathrate shape(the west of orefield).According to its distribution,geologic evolution,rock-controlled and ore-controlled features,we divided these fractures into four grades,this is first graded deep-cut basement fracture,second graded basement fracture,third graded superficial fracture and forth graded crack structure.3.The main tectonic line of basement fracture in Xiangshan uranium orefield is EW-trending,SN-trending and Ne-trending is minor,which controlled the formation and development of inherited superficial structure,the spread and location of volcanic edifice,the distribution of ore-concentration zone and ore deposit.The evolution path,rock-controlled and ore-controlled function of the three EW-trending fracture belts,which is north belt,middle belt and south belt,vary greatly from each other,and the middle belt is the best rock-controlled and ore-controlled function.4.It is evident that the superficial fracture is inherited and lasted for a long time,which is supported by the line-ring interconnected structure,mainly NE-trending fault structure.Zhou-Shi fracture,an important ore-controlled fracture,is developed on the basis of the NE-trending strike-slip tectonics in the basement,indulge inherited activities through to the cover of the basin.In different space,its degree of development,appearance and ore-controlled function are obvious differences,and the middle section is the most favorable for ore-forming,with the most developed and complex geological conditions.5.Volcanic collapse structure,as the most important volcanic structure,is intimate to the mineralization of uranium.Its degree of development,shape and ore-controlled function is distinctive in different parts of volcanic basin.The volcanic collapse structure in the west of orefield is most developed and typical,formed ruffle,bend,flexure and more complicated shapes.The more developed of ruffle and bend,the better mineralization of rocks.Accord with the NE-trending and EW-trending fracture,controlled the most uranium-enrichment ore deposit which is closely related to the volcanic collapse structure.6.Xiangshan volcanic basin was formed by the shear strike-slip to pull-apart mechanism of Yongfeng-Fuzhou deep fracture.Since the dextral strike-slip and pull-apart processes revived the EW-trending basement fracture in the middle and north region of Xiangshan,the first volcanic cycle is mainly consist of EW-trending fissure-bead-like rhyolitic dacite.Then,the violent left-lateral strike-slip and pull-apart processes recovered the SN-trending basement fracture,forming common region with the the stretch-collapsed EW-trending fracture of the first volcanic cycle,and controlling the flood of centre type volcano.This flood crystallized to be the main body of Xiangshan volcanic basin,porphyroclastic lava.7.By analyzing the tectonic stress field of Xiangshan uranium orefield,determine the direction of structural principal stress and the age of tectonic stress field,combined with the evolution of tectonic stress field and the role of uranium mineralization,that there are two main metallogenic stage,and the evolution law of faults,mechanical properties control the uranium mineralization,the multiple periods of tectonic activity with fault and the superposition of mineralization is conducive to the formation of rich and large uranium deposit.8.By summarizing the location mode of large and rich uranium ore bodies in Xiangshan uranium orefield,we concluded that the volcanic collapse basin which has coordinately tectonic evolution,dominated the location of the large and rich Xiangshan uranium orefield,the EW-trending tectonic belt controlled the ore-enrichment belt in the north and middle region of Xiangshan uranium orefield,the common region of NE-trending fracture and EW-trending fracture is the major factor on locating the ore deposit,the uranium ore bodies are directly decided by fracture and crack belt.9.In this study,we consider that metamorphism and deformation benefit the activation and transportation of uranium,including the deep-level ductile shearing deformation.Flexural slip fold offered a place for uranium enrichment.Brittle shear is significant for uranium enrichment to become an ore.Abundant uranium sources,mutil-periods tectonomagmatic activities,widespread and multi-episodes acid-alkali metasomatism are essential for the formation of large and rich uranium ore deposit.10.In the light of combining the study of structural evolution with large scale uranium mineralization,we divided each structural evolution into stages and periods,and matching each stage with ore-controlling,ore-formation and ore-conservation of uranium mineralization.Then,we synthetic analyzed the source of ore-forming material,fluid and heat,and proposed a new cognition that the mineralization mode of Xiangshan uranium orefield with a feature of coordinately tectonic evolution,which would draw a new direction for future prospecting and has great significance for exploring large and rich uranium ore deposit in Xiangshan district. |
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