Keywords: 
• hydrothermal dolomite

Abstract: Late Carboniferous to Early Permian was an important period of tectonic changes and oceancontinent transformation in northern Xinjiang area. Several approximately eastwest intracontinental rifts occurred,such as Santanghu basin, where abundant basic, intermediate, and acidic volcanic rocks are present. Deposition of moderately deep lacustrine sediments of the Lucaogou Formation occurred during Middle Permian in Northern Xinjiang. The sediments include thick dark colored shale, tuffaceous shale, and dolomite shale, intercalated with dolomitic micritic limestone, tuff, dolomite, and volcanic rocks. They contain Turfania, bivalve, conchostracans, and ostracoda. The dolomite is composed of interlaminated ankerite,cryptocrystalline quartz and organic matter including algae, and analcime laminae as annalcite.The analcites were cenmented and replaced by ankerite. In addition, hydrothermal minerals like albite, illite, anhydrite,and pyrite are present. These hydrothermal minerals were firstly recognized in the Lucaogou,and the distribution of dolomite is consistent with that of the underlying Upper Carboniferous volcanic rocks, which occur in fractures and point sources. The networklike and branchlike fractures in volcanic rocks with a brecciated structure are filled with hydrothermal minerals indicating deposition around a hydrothermal vent. Preliminary analysis indicateds that dolomites were related to magmatism and mantle hydrothermal fluid, and formed as lacustrine eruptive hydrothermal dolomites.