Study on complexity of groundwater systems in the karst mining areas with abundant water on the Yunnan plateau

A mining area with abundant water usually refers to the mine with a pit water inflow greater than 10,000 m³·d⁻¹. In view of the unevenness of the water-richness of karst aquifers and the poor accuracy of predicting water inflow, the definition of a mining area with abundant water should not be confined to the specific values of water inflow. Instead, it should be defined mainly based on the conditions of high water-richness, abundant recharge and pipeline flow of aquifers. According to the standard of hydrogeological terminology, a hydrogeological unit is defined as a groundwater system characterized by uniform recharge boundaries and conditions of recharge, runoff, and discharge. The groundwater systems described in this paper belong to the same object and category. The Yunnan plateau refers to the western section of the Yunnan-Guizhou Plateau, and, in a broad sense, encompasses Yunnan Province, which covers an area of 39.4×10⁴ km². The karst contiguous areas on the Yunnan plateau are mainly located in the east area of 102°E and north of the Yuanjiang river in eastern Yunnan, and the northwest and the west from Baoshan to Cangyuan. These karst contiguous areas total 11.09×10⁴ km², corresponding to the upper Yangtze massif, South China massif, Sanjiang orogenic belt and Tengchong orogenic belt, with superior mineralization conditions and abundant mineral resources. Historically, minerals in karst areas are primarily exploited above the erosion base. The mountainous terrain typically facilitates natural drainage, which has led to a lack of emphasis on and research into the complexity of groundwater systems in mining areas. With the growing economic and social demands, the exploration areas and mining areas are continually expanded, and are increasingly extending to deeper areas. Some deposits with abundant water that were previously challenging in exploitation have been developed. This shift has transformed hydrogeological conditions, evolving from simple to complex or even extremely complex scenarios. As a result, the challenges associated with mine water control have intensified, and the requirements for exploration have correspondingly increased. Therefore, it is both necessary and urgent to study the complexity of groundwater systems in karst mining areas with abundant water, enhance the research level, and strengthen measures for exploration control.

The complexity of a system encompasses the characteristics such as disorder, sudden change, detection errors, and inference errors, which arise from the pluralism, nonlinearity, and randomness of its constituent elements, organizational structures, influencing factors, and their interrelations and interactions with the environment. Based on existing research and exploration findings, the complexity of groundwater systems in karst mining areas with abundant water is mainly reflected in the intricate and variable characteristics of system boundary conditions, hydrogeological structures, properties of water-bearing media, and the effects of mining activities.

In karst areas, the geological processes of mineralization and subsequent transformation are highly intense, and the geological conditions are exceedingly complex, no matter whether the deposits are endogenous, exogenous, or metamorphic. The complexity of boundary conditions of groundwater systems in karst mining areas with abundant water is mainly manifested in the irregularity of topographic watersheds, the multistage nature of erosion datum, the diversity and invisibility of genesis–tectonic types of geological boundary, and the variability of boundary hydrodynamic properties. The complexity of groundwater system structure is mainly manifested in the diversity and variability of karst aquifers, non-soluble rock aquifers (bodies), primary and secondary structural properties and their mutual relationship. The complexity of the properties of water-bearing media is mainly manifested in karst aquifers, which are not only strongly developed but also exhibit significant variability. This variability includes the direction, scale, density, and connectivity of karst caves, conduits and fissures. The characteristics of water richness, permeability, and hydraulic connections also display prominent anisotropy. The influence of mining engineering and mining activities on groundwater systems in mining areas is huge and far-reaching. In addition, the design of mine shafts, mining pits, and development engineering often requires real-time adjustments in response to changes in ore bodies and mining technical conditions during the mining process. The disturbances and impacts of mining engineering and activities on the water environment and groundwater systems are also difficult to predict accurately. These influences have increased the complexity of groundwater systems in mining areas to varying degrees.

This paper systematically examines the complexity of groundwater systems in karst mining areas with abundant water. It provides a detail analysis of typical examples, along with a visual representation of the distinctive characteristics of these systems. This paper discusses the complexity of groundwater systems in mining areas with abundant water. It addresses the challenges encountered in hydrogeological exploration within mining areas. The discussion focuses on optimizing and adjusting the evaluation indices for the complexity of hydrogeological conditions as outlined in current specifications. Furthermore, it emphasizes the need for quantifying evaluation standards and establishing a reasonable assessment scale for the exploration control of complex hydrogeological conditions in mining areas. Besides, the paper offers recommendations for revising and improving the existing specifications.