| The Ordos Cretaceous basin is a large scale artesian water basin which is constituted by the thick layer Cretaceous foot length Bao'an group continental facies calstic rock. The basin is division to south and north basin in terms of Baiyu Mountain. In south of Baiyu Mountain, the area is 5.5892 ten thousand km2, surface water shortage, groundwater quality complexity, and the available water resource is super shortage, that effect on the Ordos Energy Base construction. So, in order to find the high quality groundwater fountain, the groundwater hydrochemical evolution mechanism study is necessity and imminence.The paper rely on the China Geological Survy Ministry of Land and Resources survey items "Ordos basin groundwater survey", aim at the south of Ordos Cretaceous Bao'an group groundwater, according to the hydrogeochemical theory, using the mathematical statistics, cluster analysis, hydrogeochemical simulation and so on technical and custom hydrogeological analysis, the south of basin Cretaceous Bao'an group groundwater hydrochemical evolution course and rule was studied. Through these works, some main research results were obtained, as follows:1. The south of basin Luo he group and Huan he group groundwater hydrochemical type is SO4·Cl—Na mostly, the water quality is bad; but, the south of basin from eastern boundary and western south boundary to Ma lian river, the groundwater hydrochemical type is from HCO3—Ca·Mg·Na,HCO3SO4—Na,HCO3SO4Cl—Na,SO4—Na and SO4·Cl—Na present level zoning phenomenon; The Luo handong group groundwater from western north to eastern south, the hydrochemical type is from SO4·Cl,HCO3·SO4·Cl to HCO3SO4,SO4, in south boundary the hydrochemical type is HCO3.2. The denotation of groundwater hydrochemical field on the groundwater flow field in the south of basin Bao'an group was studied:Luo group and Huan he group groundwater hydrochemical zoning is anastomsis with hydrodynamic force partition, from recharge region to excretion region, the content of HCO3- in groundwater is decrease gradually, TDS and the others constant component present increase trend. The Luo handong group groundwater hydrochemical zoning is not anastomsis with hydrodynamic force partition.3. The hydrogeochemical cource in different stream path was studied using the main ion content and ion equivalent ration variation trend. The groundwater chemical compositions are effected by hydrodynamic and soluble salt cumulation. The ratio of rCa/rNa,rMg/rNa,Ca/rCl,rHCO3/rCl is higher in western south end, eastern edge and western north Liu pan Mountain, in the nature of recharge characteristic. The ratio is little in Ma lian river, Jing River, in the nature of drainage characteristic. The ratio of rNa/rCl和rSO4/rCl is more than one, which reflect the Na enrichment salinazation, and the enrichment speed of sulfate is faster than halite.4. Through analysis the hydrochemical characteristic of stream path B12→2-6-1→sample D20 and sample D30, conclude the drainage datum plane of Luo river group groundwater is between in sample D20 and sample D30. For there exist mixing in Luo handong group stream path from Yan 65 to Zhenji7-1, the groundwater hydrochemical zoning is not anastomsis with hydrodynamic force partition.5. The mass balance simulation result shows, the lixiviation is the main hydrogeochemistry in groundwater evolution. In the groundwater stream process, the gypsum, halite, plagioclase, muscovite or CO2 dissolutes differently degree and illite precipitate. The ion exchange is stronger in Luo river group and Huan river group groundwater, but in Luo handong group is weaker; The mixing is in the thin overlay region or bareness district.6. Through analysis the chemical denudation capacityof gypsum, halite, plagioclase in simulation path, the results show that lower the unit distance chemical denudation capacity is in the supply region and the higher the unit distance chemical denudation capacity is in the drainage region. The hydrochemical simulation results further certificate that the denotation of groundwater hydrochemical field on the groundwater flow field.7. The forward hydrogeochemical simulation results indicate that the influence factor of the Luo river group and Huan river group groundwater hydrochemical evolution is lixiviation and exchange. The ion exchange is weaker s in Luo handong group and the lixiviation is stronger.
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