Coal mining is bound to produce a large amount of mine water and may cause water environmental pollution problems. The formation and evolution mechanism of mine water quality is the theoretical basis for water pollution prevention and control in coal mining areas. Almost all the coal fields in northwest China are located in arid-semi-arid areas, with severe water shortage on the surface and fragile ecological environment, and their mine water is characterized by high TDS(Total dissolved solids), high suspension, rich in sulfate and sodium ions.In this study, we proposed the "three zones" model of mine water quality formation in mining area of northwest China according to the influence of coal mining activities, which are the initial zone,the mixed zone, and the water retention zone, and considered the third zone as the most critical area for mine water quality formation. And we selected a mine mining area in the Ordos coal-bearing basin in northwest China as the study area, and carried out indoor physical model simulation and sampling monitoring of the water retention zone. The research results shows that from the perspective of the whole life cycle of the mine, the evolution of water quality in the mine area is divided into three stages: initial-deterioration stage,balance stage and self-purification stage, and the water quality evolution mechanism is closely related to the provenance characteristics, anoxic or aerobic environment, microbial activities, etc. This study provides a new idea for mine water treatment technology with high salt and high salinity in the mining area of Northwest China and also provides theoretical support for safe and green coal mining and water ecological environmental protection in this region.

Mining area of Northwest China,Mine water; Three-zones of water quality,Evolution mechanism of water quality,Microorganism