煤矿区地下水稀土元素地球化学特征:以皖北许疃矿为例

Rare Earth Elements Characteristics of Groundwater in Coalfield: A Case from Xutuan Coal Mine in Northern Anhui Province

为了解煤矿区地下水稀土元素地球化学特征,采集了许疃煤矿3个含水层水样,进行常规离子和稀土元素测试,探讨了稀土组成及元素异常特征,结果表明:许疃矿3个含水层呈碱性,pH值平均为8.7,地下水中阴离子以HCO_3^-为主,阳离子以K^++Na^+为主。Ca^(2+)和Mg^(2+)含量在灰岩水中最大,Na^++K^+浓度在煤系水中最高。地下水中稀土总量偏低(∑REE=0.023~0.251μg·L^(-1)),经后太古宙平均页岩标准化,表现为轻稀土亏损,重稀土富集,所有样品均表现为明显的Eu正异常,多数样品表现为Ce和Y负异常;这些特征受到多种因素控制,其中Ce负异常受到地下水pH值影响,而Eu异常受长石类矿物溶解的影响,Y负异常和较低的Y/Ho值与Ca^(2+)浓度密切相关,受到围岩作用的影响。这些特征及影响因素表明利用稀土元素特征进行矿井水源识别具有一定的可行性。

In order to understand the geochemical characteristics of rare earth elements（REEs） in groundwater of coalfield,the analysis of REEs and major ions were carried out for the groundwater samples collected from three aquifers in Xutuan coal mine,and the REEs characteristics and anomalies were discussed,the results showed that all the groundwater samples are alkaline,with average pH 8. 7. The HCO3-and K＋＋ Na＋ions are the mainly cation and anion in groundwater samples. The concentrations of Ca2＋and Mg2＋are the highest in groundwater samples from limestone aquifer,while the Na＋＋ K＋contents are the highest in coal bearing aquifers. Groundwater samples from three aquifers have low REEs,with the ∑REE value ranging from 0. 023 to 0. 251 μg·L-1,and groundwater samples characterized by depletion of LREEs and enriched in HREEs with PAAS normalization. All the groundwater samples presented positive Eu anomalies clearly,with mostly groundwater samples expressed Ce and Y negative anomalies. All these features were controlled by many factors,in detail,Ce negative anomalies and Eu positive anomalies were influenced by pH and dissolution of feldspar,respectively. While Y negative anomalies and lower value of Y/Ho in groundwater are controlled by the dissolution of surrounding rock,for the relationships between Y＊,Y/Ho and Ca2＋are closely. All the characteristics of REE in deep groundwater and its influence factors revealed that using rare earth elements to discriminate the water source in coal mines is feasible.