[Objective]Lacustrine dolomite is an important reservoir rock type,but its genetic mechanism is rela-tively weak and late.[Methods]To study the genetic mechanism of lacustrine hydrothermal dolomite,taking the Permian Fengcheng Formation dolomite in the Mahu Sag,Junggar Basin as an example,the petrographic and geo-chemical characteristics of the Fengcheng Formation dolomite were systematically studied by means of core observa-tion and description,thin section identification,and scanning electron microscopy(SEM)analysis of rare earth ele-ment(REE)stable isotope fluid inclusions.[Results]The study shows that the dolomite of the Fengcheng Formation is mainly developed in the Second and Third members of the Fengcheng Formation,and the dolomite is formed in the typical alkali lake environment with high salinity and strong reduction and controlled by hydrothermal.It is produced in the form of dispersing type,laminated type,banded and massive size type.The deep hydrothermal intrusion pro-vided abundant ions of Mg2+,Fe2+,HCO3-,and CO32- for the lacustrine basin,which provided material basis for the formation of dolomite.Lacustrine hydrothermal dolomite has two types of genesis:one is hydrothermal-evaporative de-position.Based on the hydrothermal intrusion and intense evaporation,the high Mg/Ca ratio,PH,and salinity lake basin water provided the medium for cloud formation and formed lamellar dolomite.The other is burial-hydrothermal metasomatism.Deep heat flow rises along the fault and intruded into the formation,promoting burial dolomitization,and forming massive and banded dolomite.[Conclusion]The results are of great significance for the study of hydro-thermal dolomite in other basins in China.
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