A practical use of ³⁴S in the investigation of karst groundwater resource in North China

In view of geo-chemical background, there are three major origins for sulfate form the karst water in most karst shallow circulation system in North China, whose aquifers is Ordovician carbonate rock: (1) dissolution of gypsum in the middle of Ordovician;(2) oxidation and dissolution of the pyrite in the overlying strata of coal measures, which recharge the karst groundwater; (3) sulfate from surface water that is directly related with top soil. Many tests indicate that the 34S value in groundwater changes greatly among different sulfate radical origins. Generally, the sulfate isotope from sulfate radical in the middle of Ordovician is heaviest in the three kinds of water with a δ34S value of 20‰～ 32‰.while,the sulfate isotope from the pyrite in coal measures is lightest with a δ34S value of -10‰～ 10‰, which is mostly less than 4‰. The sulfate isotope from surface water is between the two kinds of origins mentioned above with a δ34S value of 7‰～12‰. In light of the tracing significance features, the relations between recharge and discharge and the origins of some hydro-chemical elements in some spring systems are successfully interpreted, which give powerful proof for further understanding of the hydro-geological conditions.