Abstract:

The Qingshankou Formation in the Honggang oilfield in the southern Songliao basin contains abundant dawsonite-bearing sandstones. The results show that these sandstones are arkoses and lithic arkoses. The dominant cements are secondary quartz overgrowths, calcite, dawsonite, ankerite and clay minerals. Dawsonite, either as cements, filling inter-grain pores as radial,comb and platy collectives, or as replacement of feldspar and lithic grains with intricately trichoid and platy shapes，and alkaline feldspar replaced by dawsonite are much more than plagioclase. Besides，dawsonite filling in inter-grain pores is microlite collectives when beginning to grow，with the augment of the depth, the average granularity of radial dawsonite and comb dawsonite is bigger and bigger, and the content of platy dawsonite is increased. However, the total content of dawsonite is increased firstly, then decreased. According to the crystal characteristic, combined with the experiment about hydrothermal synthesis and stability of dawsonite, we have discussed the genesis of dawsonite. The crystal characteristic and content of dawsonite correlate with temperature, pH value and CO₂ pressure of fluid closely.

Key words: Honggang oilfield, dawsonite, crystal characteristic, genesis, Songliao basin, mineralogy