A number of giant magnesite deposits occur in the Early Proterozoic Dashiqiao Formation of magnesian carbonate and argillite rock sequences in the eastern Liaoning province, northeastern China. The magnesite orebody is hosted only in the third section of the Dashiqiao Formation with rock associations of dolomitic marble, magnesitic marble, magnesite and phyllite thin layer. Below the orebody is the 2nd section of the Dashiqiao Formation of mica schist. In the 1st section of the Dashiqiao Formation occurs interbedded dolomitic marble and mica schist without any magnesite orebody. The magnesite ores show lower δ18O values (5.2 to 13.8 per mil relative to V-SMOW) than the marbles (11.2 to 22.8 per mil), but both the magnesite ores and marbles have similar around zero δ13C values with variations of - 1.4 to 1.2 per mil and - 4.5 to 4.4 per mil, respectively. Gypsum strata and veins have been found associated with the magnesite ores with δ34 S values of 23.9 to 26.5 per mil (relative to V-CDT), indicating a marine facies sedimentary evaporatic origin. Magnesites display three types of shale-normalized REE patterns, with type Ⅱ similar to the host rock marbles, and type Ⅰ of middle REE enrichment and type Ⅲ of heavy REE enrichment and positive Eu anomaly, which may reflect fluiddominated features. We suggest that the magnesian carbonate rocks (Mg-rich calcite and dolomite) were precipitated from an evaporitive lagoon, whereas the magnesite ores were mainly formed by subsequent replacement of Mg-rich brine penetrated down from a brine pool. Due to the low permeability of the 2nd section of the Dashiqiao Formation, the magnesite mineralization took place only above this low-permeability layer of mica schist, i. e. , constrain in the 3rd section of the Dashiqiao Formation. The magnesite orebody has been recrystallized during late regional metamorphism and some magnesite veins may have formed during later hydrothermal event.