Abstract: The study of the volcanic rocks in Luxi area of Junggar basin indicates that the carbonate minerals placing in pores has great effect on the reservoir property. The oxygen-carbon stable isotopes in them are analyzed, showing that the values of δ 13 C and δ 18 O are lighter and Z value is low, which reflect they are formed in fresh water environment. Based on the carbonate crystallization temperature they occur in three settings: the most carbonate minerals are formed in the early stage of early diagenesis, some formed in the weathered and leaching stage, a few in the hydrothermal stage. Through the relationship between the oxygen isotope and the paleo-temperature, it is deduced that the crystallization time of spacing carbonate minerals could be from Late Triassic to Early Jurassic. The source rocks reach the stage of low maturity to early high maturity. They are distributed in low swell zone adjacent to the source sag and subjected to fresh- water leaching process. In the volcanic rocks there still exists part of the pores not filled by the carbonate minerals. In period of major hydrocarbon expulsion from the source rocks, the nearer the source sag, the stronger the solution is, and there could be relatively premium volcanic reservoirs in this area.

Key words: Junggar basin, volcanic rocks, oxygen isotope, carbon isotope, sedimentary environment, pore