Abstract River water and sediments collected from the Erdenet, Gavil, and Khangal Rivers, near the Erdenet Cu–Mo mine were analyzed for their rare earth elements (REE) and yttrium (YREE) contents. Surface water samples were also collected from the tailing pond and ash pond of the mine, as well as in the seepage from the ash pond, where a part of the effluent flows into the Khangal river. The major chemical compositions of river and surface waters were found to vary slightly with water flow. The river water is Ca–HCO3-dominated in the upstream of the Erdenet and Gavil Rivers and ash pond; Ca–SO4-dominated in the tailing pond and seepage from the ash pond; and Ca–HCO3–SO4-dominated downstream of the Erdenet and Khangal Rivers. Both river and surface water exhibited a significant diatom content and the dissolved organic matter mainly comprise of fulvic acid-like materials, protein-like materials and microbial materials. The concentrations of YREE in river and surface waters ranged from 4.6 to 14.9 ng/L, whereas those of the sediments and rocks were 10–43 mg/kg and 25–34 mg/kg, respectively. Shale-normalized YREE patterns of river and surface waters, irrespective of water type, were characterized by enrichments in the middle REE (MREE) and heavy REE (HREE) relative to the light REE (LREE), exceptionally positive La anomalies, and super-chondritic Y/Ho ratios. The predominant REE species were REE(CO3)2−, REECO3+, and REESO4+ in the Ca–SO4-rich water. The HREE enrichment in both river and surface waters resulted in stronger complexation with carbonate ions and fulvic-acid like materials with increasing atomic number and preferential sorption of LREE onto sediments in neutral to slightly alkaline pH water. The YREE patterns of sediments showed MREE enrichment. Total YREE contents in the river sediments were correlated with Fe2O3, P2O5 and loss on ignition (LOI), suggesting the MREE enrichment fractionated by precipitation of authigenic MREE-enriched minerals such as phosphate, Fe (oxy)hydroxides and organic matter. With the exception of La, there were significant correlations among neighboring YREE concentrations, indicating that most YREEs were fractionated by the same geochemical processes, such as aqueous complexation and sorption onto the sediment surfaces. The concentrations of La did not correlate with those of the other YREE, suggesting that the La anomaly was probably induced by a biogenic activity such as diatom blooming and/or anthropogenic processes. Our results provide better understanding of REE behavior because of (bio)geochemical and anthropogenic contamination in terrestrial water systems.

中文翻译：

---

蒙古国额尔登特铜钼矿区河流和沉积物中稀土元素分布

摘要 对从 Erdenet 铜钼矿附近的 Erdenet、Gavil 和 Khangal 河收集的河流水和沉积物进行了稀土元素 (REE) 和钇 (YREE) 含量分析。地表水样也取自矿山的尾矿池和灰池，以及灰池的渗水，部分污水流入康嘎河。发现河流和地表水的主要化学成分随水流略有变化。Erdenet 和 Gavil 河和灰池上游的河水以 Ca-HCO3 为主；尾矿池和灰池渗出物以Ca-SO4为主；和 Ca–HCO3–SO4 在 Erdenet 和 Khangal 河下游占主导地位。河流和地表水均表现出显着的硅藻含量，溶解有机物主要由类富里酸物质、类蛋白质物质和微生物物质组成。河流和地表水中 YREE 的浓度范围为 4.6 至 14.9 ng/L，而沉积物和岩石中的 YREE 浓度分别为 10-43 mg/kg 和 25-34 mg/kg。河流和地表水的页岩归一化 YREE 模式，无论水类型如何，都具有相对于轻稀土 (LREE) 的中稀土 (MREE) 和重稀土 (HREE) 富集、异常正的 La 异常和超球粒状 Y/Ho 比率。在富含 Ca-SO4 的水中，主要的 REE 种类是 REE(CO3)2−、REECO3+ 和 REESO4+。河流和地表水中的重稀土富集导致与碳酸盐离子和富里酸类物质的更强络合，随着原子序数的增加，轻稀土优先吸附在中性至微碱性 pH 值水中的沉积物上。沉积物的YREE模式显示MREE富集。河流沉积物中的总 YREE 含量与 Fe2O3、P2O5 和烧失量 (LOI) 相关，表明 MREE 富集是由自生 MREE 富集矿物（如磷酸盐、Fe（羟基）氢氧化物和有机物）的沉淀分离的。除 La 外，相邻 YREE 浓度之间存在显着相关性，表明大多数 YREE 是通过相同的地球化学过程进行分馏的，例如水络合和吸附到沉积物表面。La 的浓度与其他 YREE 的浓度无关，表明 La 异常可能是由生物活动引起的，例如硅藻开花和/或人为过程。由于陆地水系统中的（生物）地球化学和人为污染，我们的结果提供了对 REE 行为的更好理解。