Identifying strontium sources of flowback fluid and groundwater pollution using 87Sr/86Sr and geochemical model in Sulige gasfield, China

Sr Isotope, Major, and Trace Element Signatures in Karst Groundwaters

“…The 87 Sr/ 86 Sr ratio of the Sr originating from silicate dissolution is higher (0.716-0.720) than that originating from calcite (0.7075-0.7080) and dolomite (0.7080-0.7100). In our case, most of the groundwater samples lay in the carbonate dissolution area, and few were in the transition area between silicates and carbonates [39]. It can be observed (Figure 8) that groundwaters with a high Sr concentration (GWR20, GWR23, and GWR24 from the APS region) and moderate 87 Sr/ 86 Sr ratios are clearly separated from the other samples and are characterized by the carbonates' dissolution, whereas in the samples with low Sr concentrations and high 87 Sr/ 86 Sr ratios (>0.7100), the Sr originates from the dissolution of both silicates and carbonates (GWR1-3 in the SCP region).…”

“…Only GWR18 and GWR19, from the APS region, were plotted in the transition area between the silicates and dolomites, indicating that the Sr concentration in these two samples was derived from the dolomite or silicate dissolution, in both years (Figure 9). There were no significant differences in the relationship between the εSr and Mg/Ca among the sampling seasons, indicating no external interference in the origin of the Sr, except for carbonate and silicate dissolutions [39].…”

“…The relationship between the strontium isotope ratios was expressed using a εSr notation (Equation ( 1)), where the 87 Sr/ 86 Sr in the sample was normalized to the globally uniform, 87 Sr/ 86 Sr, of present-day seawater (0.709169) [13,39,40].…”

“…The dissolutions of Sr-bearing minerals (silicates and carbonates), meteoric water, and, to a smaller extent, anthropogenic inputs (fertilizers and deicing salts) are the main Sr sources in groundwater [24,39,[42][43][44]. As both the SCP and APS regions are located inland, far from marine influence, in rural areas, the Sr input from human activities and atmospheric deposition is low.…”

“…In general, Ba and Sr occur in various minerals with different dissolution rates. Usually, Sr substitutes Ca and Mg, and to a lesser extent K, while Ba mainly substitutes K [39]. The Ba/Sr molar ratio was very low (<1) in the groundwater samples, in both years and seasons, except for GWR23 in January 2021, where the ratio was slightly higher (Table S3).…”