A study of enrichment environment and formation mechanism of strontium mineral water in Gansu Province

Gansu Province is located at the juncture of the four major geographical areas of China, i.e., north area, south area, northwest area and the Tibetan Plateau, and is characterized by various climates, strong geo-tectonic activities, complex topography, diverse geomorphologic forms, and complex geological and hydrogeological conditions; all these factors provide favorable conditions for forming strontium mineral water. The test and analysis of the mineral water samples from 644 water spots in the whole province show the strontium content of these mineral water are mainly in the range of 0.09-1.00 mg/L, the highest value is 15.6 mg/L, and there are 411 water points where the strontium content is higher than or equal to 0.40 mg/L, and reaches the level content of drinking natural mineral water, accounting for 58.1% of all water points; therefore, strontium is one of the most common and abundant trace elements in groundwater of Gansu Province. The statistic analysis of these testing data shows the following phenomena:the hydrogeological units which are most favorable to strontium enrichment are the Quaternary groundwater in the piedmont basin of the Hexi Corridor plain area and the Cretaceous pore and gap groundwater of clastic rock in the Loess hilly area in east Gansu Province; the type of groundwater which is likely to enrich strontium element is the Mesozoic and Cenozoic detrital groundwater rather than the fractured groundwater of bedrock in metamorphic rock area. The circulation characteristics are that the basin-type groundwater system with deep circulation conditions is most favorable to strontium enrichment, while the groundwater strontium content of the local flowing system where the circulation path is short and the alternate conditions are stronger is poor. The content of strontium in groundwater depends on the strontium abundance in surrounding rocks. Strontium abundance is higher in Cretaceous and Neogene clastic rocks and Paleozoic carbonate rocks than in the other rocks, so the groundwater in the Cretaceous and Neogene clastic rocks and the carbonate karst groundwater has certain material conditions for enrichment of strontium mineral water. At the same time, strontium accumulation in groundwater is related to the geo-tectonic environment in which the groundwater is located and the characteristics of groundwater circulation and migration. The basin-type groundwater flowing system and the groundwater for deep circulation are far away from the recharge area to the discharge area, and the circulation path is long. The retention time of groundwater is long in aquifers, which is beneficial to the dissolution and enrichment of strontium in groundwater.