Analysis on impact factors of karst development in Dao County iron and manganese mining area of Hunan

The karst development at iron-manganese mining area in Dao County, Hunan Province is mainly controlled by lithology, landform and fracture. There are many forms of karst landforms, including cave, Underground River, karren, groove, funnel, ponor and uvala, with obviously heterogeneity features. Karst is most developed, one in the 2nd-4th layer dolomitic limestone and dolomite of the Shetianqiao Group and the Xikuangshan Group of the upper Devonian system that having the highest CaO content; and another in the aquiclude junction of between marl and argillaceous limestone of the Xikuangshan Group lower members. There are 260 caves in the Shetianqiao Group, that accounting for 96.7%of the total. In plane view, the karst is the most developed in the covered karst flat area at the central and the northern parts with 54.8% of cave ratio; the next developed of karst is in the karst-hills at the eastern and southern parts with 40.4% of cave ratio. Vertically, the karst growth gets weaker with depth, 237 caves, accounting for 86.5% of the total, are uncovered by drill at 0~220 m in elevation; and 28 caves, accounting for 10.2% of the total, are uncovered by drill at -150~0 m; but no caves or corrosion below-400 m. Tectonically, fracture zone affects karst development. There are 209 caves with relatively high cave filling ratio, accounting for 76.3% of the total, along the fracture zone.