ON MIGRATION FORM AND SEDIMENTARY ENRICHMENTS OF URANIUM IN NATURAL WATER UNDER WET CLIMATE IN SOUTH CHINA

The migration form in UO₂OH⁺-humic acid complex has been observed innatural water of the coal-bearing detrital rock-type uranium deposits of theEogene period under the wet climate in South China. The relationship betweenuranium and organic substance in natural water is discussed in this paper.We havedetermined both uranium content combined with dissolved humic acid in naturalwater from 68 to 93% and uranium content itt the form of UO₂OH⁺ combined with dissolved humic acid from 62 to 99% How much organic matters contained in water does not fully indicate how muchthey have combined with uranium，but it is neccessary to see in what form the uranium exists. Only when the form of UO₂OH⁺-ion is present, will the dissolved humic acid combine with much uranium. pH and HCO₃^-ion concentrations play an important controlling role on thetransporting form of uranium in natural water.When the concentration of HCO₃^-ion in flowing water is high，uranium is transported in the form of uranylcarbonate complexes. Only when the concentration of HCO^-₃ion is low, willuranium be transported in the form of urano-organic complexes. The transport in the form of UO₂OH⁺-humic acid complexes is carried out inthe weakly acidic (pH<7) medium in the strongly oxidizing environment(Eh:+410- +490mv).The transport in the form of uranyl carbonate complexesis carried out in the weakly alkaline (pH>7.5) mediu m in the m oderate oxidizingenvironmgnt (Eh:+370- +379mv). After natural water in the form of UO₂OH⁺-humic acid complexes flows intothe Eogene bog basin, during the peatification stage the urano-organic complexeswill be deposited tagether with peats, or will be absorbed by clay matter.Hereafter, during the diagenetic process the sediments undergo compressions,consolidations, dehydrations as well as transformations of organic matter, in whichpolymerizations and condensations into macromolecules in the dissolved humic acidgradually take place.As a result, uranium retained and fixed in organic rocks forms ore deposit.