The elements and hydrogen and oxygen isotope geochemistry analysis of oilfield water in the Tertiary in western Qaidam basin shows high salinity and abundant ions of potassium

boron and lithium of industrial mining grade.The analysis also reveals a hydrogen isotope value distribution of 75.61‰ to 13.35‰ and an oxygen isotope value distribution between -7.68‰ and 10.58‰.Combining these results with chemical analysis of the water

we concluded that the water was of typical terrestrial origin and was sourced from meteoric water

which seeped down along deep faults and was in-fluenced by deep-sourced magmatic fluids during its "deep circulation".The high salinity of the water may be caused by dissolution of saline minerals and their concentration through evaporation.Potassium

boron and lithium are mostly controlled by deep-sourced fluids and ions like Ca

2+

and HCO

3

-

are mainly sourced from dissolution of carbonate minerals.High concentration of calcium ion and low concentration of bicarbonate radical are thought to be linked to replacement of calcite by dolomite and dissolution of calcite.The formation of CaCl

2

type water is therefore inferred as the result of an adequate water-rock reaction and the participation of deep-sourced fluids.It is preliminarily inferred that the Tertiary in Nanyishan area of the basin may be a potential target for exploration of potassium.