| The first time of a global Marine phosphorite deposition occurred in geohistory turning period of the Late Neoproterozoic to Early Paleozoic. The rich organic phosphorite is widely distributed at Sinian and Cambrian in southern China. The phosphorite of the Niutitang Formation Lower Cambrian is characteristed by Ni, Mo, U super-enrichment and Cu, Zn, Re, Tl enrichment. As a catastrophic result of polymetallic phosphorite attracted by the scholars both at home and abroad. But the enrichment mechanism of polymetallic phosphorite is still controversial. In this paper, the detailed study of four typical profiles(Zhongnan in Guizhou province, Jinding in Guizhou province, Daping in Hunan province and Dahu in Hunan province)was carried out by the author in the following two aspects of geochemistry and mineralogy to investigate the enrichment mechanism of polymetallic phosphorite of shallow sedimentary system in the north of Guizhou province and deep water sedimentary system in the northwest of Hunan and the following results have been obtained:(1) The Niutitang Formation Lower Cambrian is mainly represented by phosphorite, carbonaceous shale, and carbonaceous slate and siliceous rock in Hunan and Guizhou provinces. Dolomite was developed in the late sinian in the north of Guizhou province. The the north-west of Hunan province was in the marginal rifting environment. Because of its high water depth deposition character, in late sinian time siliceous rocks were mainly developed, but also dolomite was developed in the shallow sea water environment in case of the change of ancient geographical environment. The polymetallic phosphorite with characteristics of U, Ni, Mo, Cu, Zn, Re, Tl enrichment in the Niutitang Formation Lower Cambrian in Hunan and Guizhou provinces. The character of δU and V/(V+Ni)-U/Th, Ni/Cr-V/Cr characteristic ratio diagram of the study area show that the ancient sedimentary environment was hypoxia in the Early Cambrian.(2) The characteristics of Fe/Ti,(Fe+Mn)/Ti, Al/(Al+Fe+Mn), U/Th, Sr/Ba and Fe/Ti-Al/(Al+Fe+Mn), Mn-Al-Fe, Cr-Zr, Ni-Co-Zn diagrams show that the polymetallic phosphorite is affected by large scale underwater volcanism and hydrothermal sedimentation.(3) The polymetallic phosphorite with the characteristics of the δCe negative anomaly and δEu positive anomaly. In La/Yb-∑REE diagrams pitch mainly falls in basalt area, The characteristics ofεNd, Nd model ages, carbon and oxygen isotopic features and δ13CPDB-δ18OSMOW diagram show that the mechanism of polymetallic phosphorite is mixture of normal sea water deposition, biological-chemical depisition and hydrothermal sedimentation, indicating the polymetallic phosphorite is resulted from the normal sea water chemical deposition and biological-chemical deposition, also affected by the hydrothermal sedimentation, as a product of the normal deposition and hydrothermal sedimentary mixed.(4)It is the first finding of micro uraninite of the Niutitang Formation Lower Cambrian in northen Guizhou province. The cubic shape of uraninite filling corrosion hole, micro-cracks and micro-pores that is represented by dissoluted and recrystallized oolite phosphorite. Micro uraninite, Gersdorffite, millerite, molybdenite and sphalerite occur in paragenesis in polymetallic phosphorite. It is great significance to recognize the genesis of natural uraninite.(5)The uranium-polymetallic phosphorite are distributed continuously in baded form, greetly changeable in 2 cm ~ 5 m, with characteristics of larger eruption, controlled by the Yangtze block margin rifting. On the basis of SEM study, the mineral composition and existing form of uranium in polymetallic phosphorite are as certained. It provices new microscopic evidences for revealing hydrothemal deposition occurred in the Yangtze block margin rifting, and providing the theoritc basis for the development, utilization and extraction technology of unconventional uranium resources. The study of mineral composition, existing form of uranium and the enrichment mechanism in polymetallic phosphorite is the development of the phosphorite metallogenic theory, is the innovative achievements in the study of phosphorite.On the basis of the study, the formation of polymetallic phosphorite in the study area can be divided into three stages:(1) The stage of synsedimentary oolitic phosphorite formation: in the lower Cambrian northwestern Hunan province Zhangjiajie region and northen Guizhou provience Zunyi region are located in margin slope and depression of platform. With the underlying currents rise, carrying a large amount of nutrients, a large number of algae and plankton were developed, and biological productivity become high. Via the important geological events(global anoxic event), with the a large number of organisms die, uranium bearing phosphorite was formed.(2) The stage of the submarine exhalation marine phosphorite of dissolution and recrystallization: After intermittent ancient hydrothermal vents, deep material upwelling through fracture occurred along the deep and large submarine volcanic eruption and intrusion activities and together with seawater forms a certain temperature of hydrothermal solution containing multiple metal elements. Via hydrothermal circulation and hydrothermal activities, synsedimentary oolitic phosphorite were be in dissolution and formed colloidal apatite and recrystallization apatite.(3) The stage of uranium polymetallic coprecipitation: Affected by hydrothermal sedimentation in the phosphorite, kerogen was pyrolysis and depolymerization. In this process the CH4, H2 S and residual carbon were product in medium-high temperature hydrothermal decarbonization. By the gas reduction mechanism, the uranium polymetallic minerals were sedimented in the solution pores and micro-cracks and micro-pores. As a result the polymetallic phosphorite wew formed in the Niutitang Formation Lower Cambrian in the north of Guizhou province and the north-west of Hunan province.
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