甘肃省锶矿泉水的富集环境及其形成机理研究

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

甘肃省位于中国四大地理区(北方区、南方区、西北区和青藏高原区)的相接部位,气候类型多样、地质构造活动强烈、地形复杂、地貌形态多样,复杂的地质条件、多样的地理气候环境和水文地质条件,为锶矿泉水的形成提供了有利条件。通过对全省644个水点的样品检测分析,表明锶含量主要集中在0.09~1.00 mg/L,最高值达15.6 mg/L,锶含量≥0.40 mg/L、达到饮用天然矿泉水界限含量的水点共有411个,占全部水点的58.1%,锶是甘肃省地下水中普遍含有并且含量较丰的微量元素之一。经统计分析表明,在水文地质单元上,以山前盆地第四系地下水为主的河西走廊平原区和以白垩系碎屑岩孔隙裂隙水为主的陇东黄土丘陵区地下水中最有利于锶的富集;地下水类型上,以中新生界碎屑岩地下水锶最易富集,而以变质岩为主的基岩裂隙水不利于锶的富集;循环特征上,以具备深循环条件的盆地型地下水系统最有利于锶的富集,而循环路径短、交替条件较强烈的局部水流系统中地下水锶偏贫。围岩中的锶丰度,决定了地下水中锶的含量,白垩系和新近系碎屑岩、古生界碳酸盐岩中锶丰度高,决定了白垩系碎屑岩地下水、新近系碎屑岩地下水和碳酸盐岩岩溶水具备锶矿泉水富集的物质条件;同时锶在地下水中富集,还与地下水所处的构造环境和地下水循环运移特征有关,盆地型的地下水流系统和进行深循环的地下水从补给区到排泄区径流距离远,循环路径长,地下水在含水层的滞留时间长,有利于锶在地下水中的溶解和富集。

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.