Prediction of water inflow in karst-fracture of Fushan copper mine，Shandong Province，China

Fushan copper mine is located in Fushan district, a hilly area in Yantai City, Shandong Province. Geologically, the region is composed of the lower Proterozoic Fenzishan group and Quaternary deposits, with lithology of the former mainly characterized by metamorphic rocks as marble which forms the wall rock of the mine. Karst landscapes are not fairly developed in the study region where, the major karst morphologies are corrosion fractures and pores. There are two type of aquifers, of which the fractured rock aquifer comprises mica schist intercalated with tremolite marble of the lower of Gangyu Formation and karst-fractured one consists of silicate marble and graphite marble of the upper of Jutun Formation. The ore body is mainly located in the lower of Gangyu Formation and the upper of Jutun Formation at the elevations above -450 m. In case of the large differences in lithologies, fractures development, groundwater storage and the permeability of aquifer media, the aquifer was conceptualized as a double-layered structure model, in which the parameter zones were accordingly yielded. Taking the mine dewatering with large drawdown and large discharge into account, a three-dimensional conceptual and anisotropic groundwater flow model was thus established. In this model, boundary conditions of the study area are controlled by regional faults, which can be conceptualized as confining and weak permeable boundaries. And the general head boundary was also used, so that the calculation of lateral inflow came from the change of water level to the weak permeable boundary. Meanwhile, the dewatering tunnel was generalized as drainage ditch. As a result, the total model area is 9.87 km2; and the hydrogeological conceptual model of the study area is regarded as a homogeneously anisotropic, double-deckered and 3D confined unsteady flow unity. On this basis, the numerical modelling for the groundwater seepage could be performed, which was examined and validated by using the data derived from multiple hole pumping tests and the long-term borehole observation. The drainage water inflow of the mine and normal water inflow in different years were predicted. The results showed that the drainage water inflow were 10,200 m3/d, 17,400 m3/d, 26,450 m3/d, 47,300 m3/d and 46,400 m3/d, respectively, at the -80 m, -200 m, -300 m, -400 m and -450 m levels , while normal water inflow were 7,500 m3/d, 14,060 m3/d, 28,070 m3/d, 37,200 m3/d and 41,600 m3/d, respectively. In all, it was feasible to establish the three-dimensional model of groundwater seepage in the study area according to the characteristics of karst development and groundwater flow. Meanwhile, the dewatering tunnel was generalized as drainage ditch and the general head boundary was used in the model, which make the conceptual model more reasonable.