Abstarct: The chopoghlu section is located on 90 km south-east of Zanjan city and in Soltanieh Mountains. The study is done on late Precambrian deposits includes the Bayondor Formation with a thickness of 605 m mainly composed of shale with interbedded of dolomite, and lower dolomite of Soltanieh Formation with a thickness of 100 meters. The chopoghlu section is located in the central Alborz Zone in terms of Iran's sedimentary-structural divisions. XRD results from dolomite samples in the region indicate that the most abundant mineral is dolomite, and calcite, quartz and moscovite minerals are present as minor and trace minerals in the studied rocks. Petrographic and geochemical studies (XRD and ICP-OES) of dolomites show that this section has 5 types of dolomite as follows: 1) very fine-crystalline dolomites 2) fine-crystalline dolomites 3) medium-crystalline dolomites 4) medium to coarse-crystalline dolomites and 5) dolomitic cement, which is the fine-crystalline dolomite type of most abundant in the region. Very fine-crystalline dolomite is related to primary diagenesis. Second type of the dolomite mainly formed from recrystallization of the first-type dolomite. Second type of the dolomite mainly formed from recrystallization of the first-type dolomite. Third to fifth type of dolomites is formed during last stages of diagenesis and by impact of interstitial fluids. The dolomitization mechanism for the first-type dolomite is related to Sabkha model, the second-type dolomite is related to shallow burial and finally the third to fifth-types of dolomites is related to deep burial. Geochemical studies show that lower amount of strontium in coarse crystalline dolomites compared to seawater, modern dolomites and compared to very fine crystalline dolomite indicate that the formation of these dolomites is related to increasing depth of burial. The higher amount of iron and manganese in Chopoghlu dolomites in comparison with modern dolomites and seawater indicate that the formation of these dolomites is carried out in reduction conditions and the presence of sulfate-reducing bacteria.