Multiple isotope identification of hydrogeochemical processes of
aquifers in abandoned mining areas in southwest China
Abstract
The sources of the replenishment and hydrogeochemical evolution of acid
mine drainage (AMD) from abandoned mines are issues of public concern
around the world. To reveal the sources of groundwater replenishment and
the nature of the hydrogeochemical processes that control the evolution
of water quality in the multi-aquifer system of the abandoned Dashu
pyrite mine in southwest China, the main control mechanisms of
groundwater evolution are examined, based on hydrogeochemical analysis
methods in combination with environmental isotope tracing methods, which
in turn clarify the hydrogeochemical causes of groundwater pollution.
According to the hydrogeochemical and stable and unstable isotope
analyses, the diversity of groundwater hydrochemical types in the study
area reflects the complexity of the groundwater hydrogeochemical
environment, where groundwater is formed after the mixing of atmospheric
precipitation and groundwater over multiple periods. The analysis of
2H, 18O, and T is used to identify
the main sources of hydraulic connection between aquifers, groundwater,
and mine water. The results show that there are close hydraulic
connections between aquifers. Mine water and groundwater mainly come
from the groundwater in the Quaternary accumulation platform. The
results of the ion analysis and sulfur isotope tracing show that the
main ions in the groundwater are derived from mineral
dissolution/precipitation, cation exchange, pyrite oxidation, and other
water-rock interaction processes. The sulfur in the groundwater mainly
comes from the dissolution of gypsum, while the main source of sulfur in
the mine water is the oxidation of pyrite, indicating that pyrite
oxidation and cation exchange are the dominant processes in the mine
water. The key hydrogeochemical processes were simulated using the
reverse hydrogeochemical simulation method. The results show that the
mining activities changed the water levels and flow conditions,
strengthened the interaction between groundwater and aquifer lithology,
which in turn affected the accompanying hydrogeochemical processes.
After all of the mine was abandoned, it saw the cross-contamination
between the aquifer and mine water. These results provide theoretical
guidance for the identification of sources and key hydrogeochemical
processes affecting groundwater and pollutants in the abandoned Dashu
pyrite mines and similar abandoned mines with multiple aquifers, and
can, therefore, provide technical support for the preparation of source
prevention and control plans.