Using Clustering, Geochemical Modeling, and a Decision Tree for the Hydrogeochemical Characterization of Groundwater in an In Situ Leaching Uranium Deposit in Bayan-Uul, Northern China

Abstract

Uranium extraction through the in situ leaching method stands as a pivotal approach in uranium mining. In an effort to comprehensively assess the repercussions of in situ uranium leaching on groundwater quality, this study collected 12 representative groundwater samples within the Bayan-Uul mining area. The basic statistical characteristics of the water samples showed that the concentrations of SO42− and total dissolved solids (TDS) were relatively high. Through the use of cluster analysis, the water samples were categorized into two distinct clusters. Seven samples from wells W-d, W-u, N01, W10-2, W08-1, W10-1, and W13-1, situated at a considerable distance from the mining area, were grouped together. Conversely, five samples from wells W08-2, W13-2, W01-1, W02-2, and the pumping well located in closer proximity to the mining area, formed a separate cluster. A decision tree-based machine learning approach was employed to discern the influence of various hydrochemical indicators in forming these clusters, with results indicating that SO42− exerts the most substantial influence, followed by Ca2+. The mineral saturation indices from geochemical modeling indicated that, as the distance from the mining area increased, the trend of calcium minerals changed from dissolution to precipitation; iron minerals were in a precipitation state, and the precipitation trend was gradually weakening. In light of these findings, it is clear that in situ uranium leaching significantly impacted the groundwater in the vicinity of the mining area. The prolonged consumption of groundwater sourced near the study area, or its use for animal husbandry, poses potential health risks that demand heightened attention.

A Review of In Situ Leaching (ISL) for Uranium Mining

“…Unlike open-pit and underground mining, in situ leaching does not rely on burial depth as a criterion but is based on the properties of the uranium deposit. As a mining technique conducted under the natural conditions of ore deposits, in situ leaching is well-suited for uranium deposits situated within aquifers and characterized by favorable permeability [58][59][60]. This method involves strategically arranging and drilling wells, including injection wells and production wells (or recovery wells), within the uranium deposit.…”

“…Table 1 presents the applicable conditions for these three uranium mining methods, along with their respective advantages and disadvantages. [58][59][60]62] Compared to open-pit and underground mining, in situ leaching offers distinctive advantages. By operating directly within natural ore deposits, this mining method avoids extensive surface disruption and excavation.…”

Hydrogeochemical Characteristics of the Geothermal System in the Woka-Cuona Rift Zone, Tibet

“…This intricate process involves a continuous exchange of matter and energy between infiltrating meteoric water and the subsurface environment, leading to alterations in hydrogeochemical characteristics. Hence, hydrogeochemical characteristics play a crucial role in analyzing the circulation, water-rock interaction, runoff path, and accumulation environment of groundwater [9][10][11].…”