Ili Basin, Southern Margin Of Its Gul Uranium Deposits Formation Research

Based on theories of sandstone-hosted uranium deposit, the present thesis makesa systematic dissection to Mengqiguer uranium deposit at the southern margin of Yilibasin.Firstly,the regional geologic bacground, metallogenic geo-environment,zonationand characteristics of interlayer oxidized zone and characteristics of mineralization ofthis deposit are analysed and discussed in detail. Then the thesis takes orecomposition, characteristics of clay minerals and its relation to uraniummineralization, geochenmistry of mineral deposit, U-Pb isotopes and uraniummetallogenetic epoch as the focus key points of the study.Based on all above discussion, the thesis puts forward that the different interlayeroxidation subzones show different alteration characteristics and the U-precipitationzone belongs to intermediately to weakly acidic reduction-oxidation transitionalenvironment. The geochenmical characteristics of macroelements,microelments andrare earth elements indicate certain change rule in different interlayer oxidationsubzones. Organic matter and microorganism exert important effection onprecipitation and enrichment of uranium. The S-isotopes characteristics prove that thisdeposit is of obvious biogenetic origin. Also sulphides have important effection onreduction and precipitation of uranium. Clay menerals at this deposit has influencecharacteristics distinct from those of deposits at the southern margin of Yili basin. Theclay meneral’s effections on the uranium precipitation and enrichment not only reflecton mechanical adsorption, but also on porosity and permeability of sandstone.By the determination of pitchblende, U-Pb isotopes age and contain with thereground construct merge with structural evolution of this region,the anthor pointsout at this deposit three phase minerralizations exist. The fiest phase is a weakmineralization and happened before12Ma; the seconed took place during12-4Ma,being the main mineralization; and the last phase lasts from2Ma to present.Based on the discussion of this typical deposit, this paper finalize a systematic analysis regarding the U-source, the mechanism of uranium precipitation andenrichment. The final formation of this deposit is oringinated from longtermgeological evolution, which can be divided into4phases. And then the genetic modelof this deposit has been established.