Taking outcrop dolomites in Guangyuan Xiagou coal mine in northern Sichuan Basin as an example

this paper studies the characteristics and genesis of hydrothermal dolomite reservoir.From the bottom to the top of the outcrop cross section

the dolomitization gradually enhances;the color of rocks changes from dark to light;the lithologies change from bioclastic limestones to patchy dolostones

then to medium-and coarse-grained dolomites

and end up with the Maokou Formation marlstones.The medium-to coarse-grained dolomites occur at the top of the Qixia Formation and the bottom of the Maokou Formation

and are composed of medium-to coarse-grained subhedral or euhedral dolomites and some saddle-like dolomites.Dissolved caverns and pores are well-developed and filled with asphaltares.The δ

13

C value (PDB) and δ

18

O value (PDB) of micritic limestones are 3.23‰ and -5.03‰

respectively.The δ

13

C value (PDB) and δ

18

O value (PDB) of the dolomites are 3.29~4.14‰ and -6.07~-6.75‰ respectively.Fluids may be sourced from magmatic hydrothermal fluid

or meteoric water experiencing deep circulation.The deep hydrothermal fluids migrated up along open faults and slowed down or even stopped when arriving at the Qixia and Maokou Formations due to the sealing of marl and politic dolostones in the Wu Jiaping Formation.The stagnant thermal fluids caused dolomitization dissolution of the surrounding rocks.Therefore

it is possible that hydrothermal dolomite reservoirs occur at the top of Qixia Formation and the bottom of Maokou Formation.