Geochemical modelling and seasonal hydrogeochemical processes of the open-pit groundwater at O’Kiep, Namaqualand, South Africa

To assess dissolution, precipitation processes and saturation indices (SI) of some mineral phases, PHREEQC modelling software was used to assess these different geochemical processes and to elucidate reactive minerals of the open-pit groundwater (OPGW) in O’Kiep, Namaqualand, South Africa. Equilibrium constants were not fixed into the coding of the software PHREEQC, to accommodate equilibrium constant changes, and PHREEQC user input file manipulation. The SI of less than zero implied that the OPGW was undersaturated and that mineral dissolution was required to reach equilibrium. The data of the hydrogeochemical analysis indicated that the sources of ions into the OPGW are largely from the dissolution and leaching of mine waste and tailings including runoffs during the wet season, with the underlying fracturing of rocks, cation exchanges and other anthropogenic activities making a contribution. Additionally, climatic seasonality significantly influenced the OPGW hydrogeochemistry, indicating that the hydrological processes which control changes were dilution and mobilization of potentially toxic elements (PTEs). The data set generated showed that the OPGW chemistry was mainly influenced by evaporation, ion exchange, silicate weathering and dissolution of minerals including precipitation. Overall, this dataset details hydrogeochemical processes that are responsible for seasonal variations in the OPGW chemistry.

为评估部分矿物相的溶解、沉淀过程与饱和指数（SI），本研究采用PHREEQC建模软件，对南非纳米夸兰地区奥基普（O’Kiep）的露天矿地下水（OPGW）中的各类地球化学过程进行评估，并阐明其中的反应性矿物。为适配平衡常数的变动需求并支持PHREEQC用户输入文件的操作，该软件的编码中未固定平衡常数。当饱和指数小于0时，表明露天矿地下水处于不饱和状态，需通过矿物溶解以达到平衡状态。水文地球化学分析数据表明，露天矿地下水中的离子来源主要为矿山废料与尾矿的溶解、淋滤（含湿季径流），基底岩石裂隙作用、阳离子交换及其他人为活动亦有贡献。此外，气候季节性对露天矿地下水的水文地球化学特征具有显著影响，表明调控其化学变化的水文过程为潜在有毒元素（PTEs）的稀释与迁移活化。本次生成的数据集显示，露天矿地下水的化学组成主要受蒸发作用、离子交换、硅酸盐矿物风化以及矿物溶解与沉淀作用的影响。综上，本数据集详细阐明了驱动露天矿地下水化学特征季节性变化的水文地球化学过程。